Pilot’s Handbook of 

Aeronautical Knowledge 

U.S. Department of Transportation 

FEDERAL AVIATION ADMINISTRATION 

Flight Standards Service 

2016 
ii 
iii 

The Pilot’s Handbook of Aeronautical Knowledge provides basic knowledge that is essential for pilots. This handbook 

introduces pilots to the broad spectrum of knowledge that will be needed as they progress in their pilot training. Except for 

the Code of Federal Regulations pertinent to civil aviation, most of the knowledge areas applicable to pilot certification are 

presented. This handbook is useful to beginning pilots, as well as those pursuing more advanced pilot certificates. 

Occasionally the word “must” or similar language is used where the desired action is deemed critical. The use of such language 

is not intended to add to, interpret, or relieve a duty imposed by Title 14 of the Code of Federal Regulations (14 CFR). 

It is essential for persons using this handbook to become familiar with and apply the pertinent parts of 14 CFR and the 

Aeronautical Information Manual (AIM). The AIM is available online at www.faa.gov. The current Flight Standards 

Service airman training and testing material and learning statements for all airman certificates and ratings can be obtained 

from www.faa.gov. 

This handbook supersedes FAA-H-8083-25A, Pilot’s Handbook of Aeronautical Knowledge, dated 2008. 

This handbook is available for download, in PDF format, from www.faa.gov. 

This handbook is published by the United States Department of Transportation, Federal Aviation Administration, Airman 

Testing Standards Branch, AFS-630, P.O. Box 25082, Oklahoma City, OK 73125. 

Comments regarding this publication should be sent, in email form, to the following address: 

AFS630comments@faa.gov 

John S. Duncan 

Director, Flight Standards Service 

Preface 
iv 
 

v 

The Pilot’s Handbook of Aeronautical Knowledge was produced by the Federal Aviation Administration (FAA) with the 

assistance of Safety Research Corporation of America. The FAA wishes to acknowledge the following contributors: 

Mrs. Nancy A. Wright for providing imagery of a de Haviland DH-4 inaugural air mail flight (Chapter 1) 

The Raab Collection, Philadelphia, Pennsylvania, for images of the first pilot license (Chapter 1) 

Sandy Kenyon and Rod Magner (magicair.com) for photo of 1929 TravelAir 4000 (Chapter 1) 

Dr. Pat Veillette for information used on decision-making (Chapter 2) 

Adventure Seaplanes for photos of a ski and float training plane (Chapter 3) 

Jack Davis, Stearman Restorers Asociation, for photo of a 1941 PT-17 Army Air Corps trainer (Chapter 3) 

Michael J. Hoke, Abaris Training Resources, Inc., for images and information about composite aircraft (Chapter 3) 

Colin Cutler, Boldmethod, for images and content on the topic of ground effect (Chapter 5) 

Mark R. Korin, Alpha Systems, for images of AOA disaplys (Chapter 5) 

M. van Leeuwen (www.zap16.com) for image of Piaggio P-180 (Chapter 6) 

Greg Richter, Blue Mountain Avionics, for autopilot information and imagery (Chapter 6) 

Mountain High E&S Company for various images provided regarding oxygen systems (Chapter 7) 

Jeff Callahan, Aerox, for image of MSK-AS Silicone Mask without Microphone (Chapter 7) 

Nonin Medical, Inc. for image of Onyx pulse oximeter (Chapter 7) 

Pilotfriend.com for photo of a TKS Weeping Wing (Chapter 7) 

Chelton Flight Systems for image of FlightLogic (Chapter 8) 

Avidyne Corporation for image of the Entegra (Chapter 8) 

Teledyne Controls for image of an air data computer (Chapter 8) 

Watson Industries, Inc. (www.watson-gyro.com) for image of Attitude and Heading Reference system (Chapter 8) 

Engineering Arresting Systems Corporation (www.esco.zodiacaerospace.com) for EMAS imagery and EMASMAX 

technical digrams (Chapter 14) 

Caasey Rose and Jose Roggeveen (burningholesinthesky.wordpress.com) for flight checklist image (Chapter 14) 

Tim Murnahan for images of EMAS at Yeager Airport, Charleston, West Virginia, and EMAS arrested 

aircraft (Chapter 14) 

Cessna Aircraft Company, Columbia Aircraft Manufacturing Corporation, Eclipse Aviation Corporation, Garmin Ltd., 

The Boeing Company for images provided and used throughout the Handbook. 

Additional appreciation is extended to the Aircraft Owners and Pilots Association (AOPA), the AOPA Air Safety Foundation, 

the General Aviation Manufacturers Association (GAMA), and the National Business Aviation Association (NBAA) for 

their technical support and input. 

Disclaimer: Information in Chapter 14 pertaining to Runway Incursion Avoidance was created using FAA orders, documents, 

and Advisory Circulars that were current at the date of publication. Users should not assume that all references are current 

and should check often for reference updates. 

Acknowledgments 
vi 
Table of Contents 

Preface....................................................................iii
 

Acknowledgments..................................................v
 

Table of Contents .................................................vii
 

Chapter 1
 

Introduction To Flying.........................................1-1
 

Introduction....................................................................1-1
 

History of Flight.............................................................1-2
 

History of the Federal Aviation Administration (FAA) 1-3
 

Transcontinental Air Mail Route................................1-4
 

Federal Certification of Pilots and Mechanics...........1-4
 

The Federal Aviation Act of 1958..............................1-6
 

Department of Transportation (DOT) ........................1-6
 

ATC Automation........................................................1-6
 

The Professional Air Traffic Controllers
 

Organization (PATCO) Strike....................................1-6
 

The Airline Deregulation Act of 1978 .......................1-7
 

The Role of the FAA......................................................1-7
 

The Code of Federal Regulations (CFR)....................1-7
 

Primary Locations of the FAA...................................1-8
 

Field Offices ...........................................................1-8
 

Aviation Safety Inspector (ASI) ................................1-9
 

FAA Safety Team (FAASTeam)................................1-9
 

Obtaining Assistance from the FAA ..........................1-9
 

Aeronautical Information Manual (AIM)...............1-9
 

Handbooks ............................................................1-10
 

Advisory Circulars (ACs).....................................1-10
 

Flight Publications................................................1-11
 

Pilot and Aeronautical Information .........................1-12
 

Notices to Airmen (NOTAMs) ............................1-12
 

Safety Program Airmen Notification System
 

(SPANS) ...............................................................1-14
 

Aircraft Classifications and Ultralight Vehicles..........1-14
 

Pilot Certifications .......................................................1-16
 

Privileges: .............................................................1-16
 

Limitations:...........................................................1-17
 

Recreational Pilot .....................................................1-17
 

Privileges: .............................................................1-17
 

Limitations:...........................................................1-17
 

Private Pilot ..............................................................1-17
 

Commercial Pilot......................................................1-18
 

Airline Transport Pilot..............................................1-18
 

Selecting a Flight School ............................................1-18
 

How To Find a Reputable Flight Program ...............1-19
 

How To Choose a Certificated Flight
 

Instructor (CFI).........................................................1-19
 

The Student Pilot .........................................................1-20
 

Basic Requirements..................................................1-20
 

Medical Certification Requirements.....................1-20
 

Becoming a Pilot..........................................................1-21
 

Knowledge and Skill Tests ..........................................1-21
 

Knowledge Tests ......................................................1-21
 

When To Take the Knowledge Test .....................1-22
 

Practical Test ............................................................1-22
 

When To Take the Practical Test..........................1-23
 

Who Administers the FAA Practical Tests?.........1-23
 

Role of the Certificated Flight Instructor .................1-23
 

Role of the Designated Pilot Examiner ...................1-24
 

Chapter Summary .......................................................1-24
 

Chapter 2
 

Aeronautical Decision-Making ...........................2-1
 

Introduction....................................................................2-1
 

History of ADM.............................................................2-2
 

Risk Management ..........................................................2-3
 

Crew Resource Management (CRM) and SinglePilot Resource Management ..........................................2-4
 

Hazard and Risk.............................................................2-4
 

Hazardous Attitudes and Antidotes............................2-5
 

Risk.............................................................................2-6
 

Assessing Risk........................................................2-6
 

Mitigating Risk .......................................................2-8
 

The PAVE Checklist .................................................2-8
 

P = Pilot in Command (PIC) ..................................2-8
 

A = Aircraft ............................................................2-8
 

V = EnVironment ...................................................2-9
 

E = External Pressures............................................2-9
 

Human Factors.............................................................2-10
 

vii 
 

Human Behavior ..........................................................2-11
 

The Decision-Making Process .....................................2-12
 

Single-Pilot Resource Management (SRM) ...........2-13
 

The 5 Ps Check ........................................................2-13
 

The Plan ...............................................................2-14
 

The Plane .............................................................2-14
 

The Pilot ...............................................................2-14
 

The Passengers .....................................................2-14
 

The Programming ................................................2-15
 

Perceive, Process, Perform (3P) Model....................2-15
 

PAVE Checklist: Identify Hazards and
 

Personal Minimums..............................................2-15
 

CARE Checklist: Review Hazards and
 

Evaluate Risks ......................................................2-16
 

TEAM Checklist: Choose and Implement
 

Risk Controls ........................................................2-16
 

The DECIDE Model.............................................2-18
 

Detect (the Problem).............................................2-20
 

Estimate (the Need To React)...............................2-20
 

Choose (a Course of Action) ................................2-20
 

Identify (Solutions)...............................................2-20
 

Do (the Necessary Actions)..................................2-20
 

Evaluate (the Effect of the Action) ......................2-20
 

Decision-Making in a Dynamic Environment ............2-21
 

Automatic Decision-Making ...................................2-21
 

Operational Pitfalls ...............................................2-21
 

Stress Management...................................................2-21
 

Use of Resources......................................................2-21
 

Internal Resources ................................................2-23
 

External Resources ...............................................2-23
 

Situational Awareness..................................................2-24
 

Obstacles to Maintaining Situational Awareness.....2-24
 

Workload Management ........................................2-24
 

Managing Risks ....................................................2-25
 

Automation ..................................................................2-25
 

Results of the Study..................................................2-27
 

Equipment Use .........................................................2-27
 

Autopilot Systems.................................................2-27
 

Familiarity.............................................................2-27
 

Respect for Onboard Systems...............................2-29
 

Getting Beyond Rote Workmanship.....................2-29
 

Understand the Platform ......................................2-29
 

Managing Aircraft Automation ...............................2-29
 

Information Management .....................................2-30
 

Enhanced Situational Awareness .............................2-30
 

Automation Management.........................................2-31
 

Risk Management.....................................................2-31
 

Chapter Summary .......................................................2-32
 

Chapter 3
 

Aircraft Construction ..........................................3-1
 

Introduction....................................................................3-1
 

Aircraft Design, Certification, and Airworthiness.........3-2
 

A Note About Light Sport Aircraft ............................3-2
 

Lift and Basic Aerodynamics.........................................3-2
 

Major Components.........................................................3-3
 

Fuselage......................................................................3-3
 

Wings .........................................................................3-3
 

Empennage .................................................................3-6
 

Landing Gear..............................................................3-7
 

The Powerplant...........................................................3-7
 

Subcomponents..............................................................3-8
 

Types of Aircraft Construction ......................................3-8
 

Truss Structure ...........................................................3-8
 

Semimonocoque .........................................................3-9
 

Composite Construction.............................................3-9
 

History ....................................................................3-9
 

Advantages of Composites ...................................3-10
 

Disadvantages of Composites...............................3-10
 

Fluid Spills on Composites...................................3-11
 

Lightning Strike Protection...................................3-11
 

The Future of Composites ....................................3-12
 

Instrumentation: Moving into the Future ....................3-12
 

Control Instruments .................................................3-13
 

Navigation Instruments ...........................................3-13
 

Global Positioning System (GPS)................................3-13
 

Chapter Summary ........................................................3-13
 

Chapter 4
 

Principles of Flight ..............................................4-1
 

Introduction....................................................................4-1
 

Structure of the Atmosphere ..........................................4-1
 

Air is a Fluid ..............................................................4-2
 

Viscosity .................................................................4-2
 

Friction....................................................................4-2
 

Pressure...................................................................4-3
 

Atmospheric Pressure.................................................4-3
 

Pressure Altitude ........................................................4-4
 

Density Altitude .........................................................4-4
 

Effect of Pressure on Density .................................4-4
 

Effect of Temperature on Density ..........................4-4
 

Effect of Humidity (Moisture) on Density .............4-5
 

Theories in the Production of Lift..................................4-5
 

Newton’s Basic Laws of Motion................................4-5
 

Bernoulli’s Principle of Differential Pressure............4-6
 

Airfoil Design ................................................................4-6
 

Low Pressure Above ..................................................4-7
 

High Pressure Below..................................................4-8
 

viii 
Pressure Distribution ..................................................4-8
 

Airfoil Behavior .........................................................4-8
 

A Third Dimension ........................................................4-9
 

Chapter Summary ..........................................................4-9
 

Chapter 5
 

Aerodynamics of Flight.......................................5-1
 

Forces Acting on the Aircraft ........................................5-1
 

Thrust .........................................................................5-2
 

Lift..............................................................................5-3
 

Lift/Drag Ratio........................................................5-5
 

Drag............................................................................5-6
 

Parasite Drag...........................................................5-6
 

Induced Drag ..........................................................5-7
 

Weight ........................................................................5-8
 

Wingtip Vortices............................................................5-8
 

Formation of Vortices ................................................5-8
 

Avoiding Wake Turbulence .......................................5-9
 

Ground Effect...............................................................5-11
 

Axes of an Aircraft.......................................................5-12
 

Moment and Moment Arm ..........................................5-13
 

Aircraft Design Characteristics ...................................5-14
 

Stability ....................................................................5-14
 

Static Stability.......................................................5-14
 

Dynamic Stability .................................................5-14
 

Longitudinal Stability (Pitching) ..........................5-15
 

Lateral Stability (Rolling).....................................5-17
 

Directional Stability (Yawing) .............................5-19
 

Free Directional Oscillations (Dutch Roll) ..............5-20
 

Spiral Instability .......................................................5-20
 

Effect of Wing Planform .............................................5-20
 

Aerodynamic Forces in Flight Maneuvers...................5-22
 

Forces in Turns.........................................................5-22
 

Forces in Climbs.......................................................5-23
 

Forces in Descents....................................................5-24
 

Stalls ............................................................................5-25
 

Angle of Attack Indicators...........................................5-26
 

Basic Propeller Principles............................................5-28
 

Torque and P-Factor.................................................5-30
 

Torque Reaction .......................................................5-31
 

Corkscrew Effect......................................................5-31
 

Gyroscopic Action....................................................5-31
 

Asymmetric Loading (P-Factor) ..............................5-32
 

Load Factors.................................................................5-33
 

Load Factors in Aircraft Design...............................5-33
 

Load Factors in Steep Turns.....................................5-34
 

Load Factors and Stalling Speeds ............................5-34
 

Load Factors and Flight Maneuvers.........................5-36
 

Vg Diagram ..............................................................5-37
 

Rate of Turn..............................................................5-38
 

Radius of Turn..........................................................5-39
 

Weight and Balance .....................................................5-40
 

Effect of Weight on Flight Performance ..................5-42
 

Effect of Weight on Aircraft Structure.....................5-42
 

Effect of Weight on Stability and Controllability ....5-42
 

Effect of Load Distribution ......................................5-43
 

High Speed Flight ........................................................5-44
 

Subsonic Versus Supersonic Flow ...........................5-44
 

Speed Ranges ...........................................................5-44
 

Mach Number Versus Airspeed ...............................5-45
 

Boundary Layer........................................................5-46
 

Laminar Boundary Layer Flow ............................5-46
 

Turbulent Boundary Layer Flow ..........................5-46
 

Boundary Layer Separation ..................................5-46
 

Shock Waves ............................................................5-46
 

Sweepback................................................................5-48
 

Mach Buffet Boundaries ..........................................5-49
 

High Speed Flight Controls......................................5-49
 

Chapter Summary ........................................................5-51
 

Chapter 6
 

Flight Controls.....................................................6-1
 

Introduction....................................................................6-1
 

Flight Control Systems .................................................6-2
 

Flight Controls............................................................6-2
 

Primary Flight Controls..............................................6-2
 

Elevator...................................................................6-5
 

T-Tail ......................................................................6-6
 

Stabilator.................................................................6-7
 

Canard.....................................................................6-7
 

Rudder.....................................................................6-8
 

V-Tail......................................................................6-8
 

Secondary Flight Controls..........................................6-8
 

Flaps........................................................................6-8
 

Leading Edge Devices............................................6-9
 

Spoilers .................................................................6-10
 

Trim Tabs..............................................................6-10
 

Balance Tabs.........................................................6-11
 

Servo Tabs ............................................................6-11
 

Antiservo Tabs......................................................6-11
 

Ground Adjustable Tabs.......................................6-11
 

Adjustable Stabilizer.............................................6-12
 

Autopilot ......................................................................6-12
 

Chapter Summary ........................................................6-12
 

Chapter 7
 

Aircraft Systems..................................................7-1
 

Introduction....................................................................7-1
 

Powerplant .....................................................................7-1
 

Reciprocating Engines................................................7-2
 

Propeller .....................................................................7-4
 

ix 
Fixed-Pitch Propeller..............................................7-5
 

Adjustable-Pitch Propeller......................................7-6
 

Propeller Overspeed in Piston Engine Aircraft ......7-7
 

Induction Systems......................................................7-7
 

Carburetor Systems....................................................7-8
 

Mixture Control ......................................................7-9
 

Carburetor Icing......................................................7-9
 

Carburetor Heat ....................................................7-10
 

Carburetor Air Temperature Gauge......................7-11
 

Outside Air Temperature Gauge ..............................7-11
 

Fuel Injection Systems .............................................7-11
 

Superchargers and Turbosuperchargers.......................7-12
 

Superchargers...........................................................7-12
 

Turbosuperchargers..................................................7-13
 

System Operation..................................................7-14
 

High Altitude Performance...................................7-14
 

Ignition System ............................................................7-15
 

Oil Systems ..................................................................7-16
 

Engine Cooling Systems..............................................7-17
 

Exhaust Systems ..........................................................7-18
 

Starting System ............................................................7-18
 

Combustion..................................................................7-18
 

Full Authority Digital Engine Control (FADEC) ........7-20
 

Turbine Engines...........................................................7-20
 

Types of Turbine Engines ........................................7-20
 

Turbojet.................................................................7-20
 

Turboprop .............................................................7-21
 

Turbofan ...............................................................7-21
 

Turboshaft.............................................................7-21
 

Turbine Engine Instruments .....................................7-22
 

Engine Pressure Ratio (EPR) ...............................7-22
 

Exhaust Gas Temperature (EGT) ........................7-22
 

Torquemeter..........................................................7-22
 

N1 Indicator...........................................................7-23
 

N2 Indicator...........................................................7-23
 

Turbine Engine Operational Considerations ............7-23
 

Engine Temperature Limitations ..........................7-23
 

Thrust Variations ..................................................7-23
 

Foreign Object Damage (FOD) ............................7-23
 

Turbine Engine Hot/Hung Start............................7-23
 

Compressor Stalls .................................................7-23
 

Flameout ...............................................................7-24
 

Performance Comparison.........................................7-24
 

Airframe Systems ........................................................7-25
 

Fuel Systems ................................................................7-25
 

Gravity-Feed System ...............................................7-25
 

Fuel-Pump System ...................................................7-25
 

Fuel Primer...............................................................7-25
 

Fuel Tanks................................................................7-25
 

Fuel Gauges..............................................................7-26
 

Fuel Selectors ...........................................................7-26
 

Fuel Strainers, Sumps, and Drains ...........................7-27
 

Fuel Grades...............................................................7-27
 

Fuel Contamination ..................................................7-27
 

Fuel System Icing.....................................................7-28
 

Prevention Procedures ..........................................7-28
 

Refueling Procedures...................................................7-29
 

Heating System ............................................................7-29
 

Fuel Fired Heaters ....................................................7-29
 

Exhaust Heating Systems.........................................7-29
 

Combustion Heater Systems ....................................7-29
 

Bleed Air Heating Systems ......................................7-30
 

Electrical System .........................................................7-30
 

Hydraulic Systems .......................................................7-31
 

Landing Gear............................................................7-33
 

Tricycle Landing Gear..........................................7-33
 

Tailwheel Landing Gear .......................................7-33
 

Fixed and Retractable Landing Gear ....................7-34
 

Brakes.......................................................................7-34
 

Pressurized Aircraft .....................................................7-34
 

Oxygen Systems...........................................................7-37
 

Oxygen Masks..........................................................7-38
 

Cannula.....................................................................7-38
 

Pressure-Demand Oxygen Systems..........................7-38
 

Continuous-Flow Oxygen System ...........................7-38
 

Electrical Pulse-Demand Oxygen System................7-38
 

Pulse Oximeters........................................................7-39
 

Servicing of Oxygen Systems ..................................7-39
 

Anti-Ice and Deice Systems.........................................7-40
 

Airfoil Anti-Ice and Deice .......................................7-40
 

Windscreen Anti-Ice.................................................7-41
 

Propeller Anti-Ice.....................................................7-41
 

Other Anti-Ice and Deice Systems ...........................7-41
 

Chapter Summary ........................................................7-41
 

Chapter 8
 

Flight Instruments ...............................................8-1
 

Introduction....................................................................8-1
 

Pitot-Static Flight Instruments.......................................8-1
 

Impact Pressure Chamber and Lines..........................8-2
 

Static Pressure Chamber and Lines............................8-2
 

Altimeter.....................................................................8-3
 

Principle of Operation.............................................8-3
 

Effect of Nonstandard Pressure and Temperature ..8-4
 

Setting the Altimeter...............................................8-5
 

Altimeter Operation................................................8-6
 

Types of Altitude ....................................................8-6
 

Instrument Check....................................................8-7
 

Vertical Speed Indicator (VSI)...................................8-7
 

x 
Principle of Operation.............................................8-7
 

Instrument Check....................................................8-8
 

Airspeed Indicator (ASI)............................................8-8
 

Airspeed Indicator Markings..................................8-9
 

Other Airspeed Limitations ....................................8-9
 

Instrument Check..................................................8-10
 

Blockage of the Pitot-Static System.........................8-10
 

Blocked Pitot System............................................8-10
 

Blocked Static System ..........................................8-11
 

Electronic Flight Display (EFD)..................................8-12
 

Airspeed Tape...........................................................8-12
 

Attitude Indicator .....................................................8-13
 

Altimeter...................................................................8-13
 

Vertical Speed Indicator (VSI).................................8-13
 

Heading Indicator.....................................................8-13
 

Turn Indicator...........................................................8-13
 

Tachometer...............................................................8-13
 

Slip/Skid Indicator....................................................8-13
 

Turn Rate Indicator ..................................................8-13
 

Air Data Computer (ADC).......................................8-14
 

Trend Vectors...........................................................8-14
 

Gyroscopic Flight Instruments.....................................8-15
 

Gyroscopic Principles...............................................8-15
 

Rigidity in Space...................................................8-15
 

Precession .............................................................8-15
 

Sources of Power......................................................8-16
 

Turn Indicators .........................................................8-16
 

Turn-and-Slip Indicator ........................................8-16
 

Turn Coordinator ..................................................8-17
 

Inclinometer..............................................................8-18
 

Yaw String............................................................8-18
 

Instrument Check..................................................8-18
 

Attitude Indicator .....................................................8-18
 

Heading Indicator.....................................................8-19
 

Attitude and Heading Reference System (AHRS) ...8-20
 

The Flux Gate Compass System ..............................8-20
 

Remote Indicating Compass.....................................8-21
 

Instrument Check..................................................8-22
 

Angle of Attack Indicators...........................................8-22
 

Compass Systems.........................................................8-23
 

Magnetic Compass ...................................................8-23
 

Magnetic Compass Induced Errors.......................8-24
 

The Vertical Card Magnetic Compass .....................8-27
 

Lags or Leads........................................................8-27
 

Eddy Current Damping.........................................8-27
 

Outside Air Temperature (OAT) Gauge ......................8-28
 

Chapter Summary ........................................................8-28
 

Chapter 9
 

Flight Manuals and Other Documents...............9-1
 

Introduction....................................................................9-1
 

Preliminary Pages.......................................................9-2
 

General (Section 1).....................................................9-2
 

Limitations (Section 2)...............................................9-2
 

Airspeed..................................................................9-2
 

Powerplant ..............................................................9-3
 

Weight and Loading Distribution ...........................9-3
 

Flight Limits ...........................................................9-4
 

Placards...................................................................9-4
 

Emergency Procedures (Section 3) ............................9-4
 

Normal Procedures (Section 4) ..................................9-4
 

Performance (Section 5).............................................9-4
 

Weight and Balance/Equipment List (Section 6).......9-4
 

Systems Description (Section 7) ................................9-4
 

Handling, Service, and Maintenance (Section 8).......9-5
 

Supplements (Section 9).............................................9-5
 

Safety Tips (Section 10).............................................9-6
 

Aircraft Documents........................................................9-6
 

Certificate of Aircraft Registration.............................9-6
 

Airworthiness Certificate ...........................................9-7
 

Aircraft Maintenance..................................................9-8
 

Aircraft Inspections........................................................9-8
 

Annual Inspection.......................................................9-8
 

100-Hour Inspection...................................................9-8
 

Other Inspection Programs.........................................9-9
 

Altimeter System Inspection ..................................9-9
 

Transponder Inspection ..........................................9-9
 

Emergency Locator Transmitter.............................9-9
 

Preflight Inspections...............................................9-9
 

Minimum Equipment Lists (MEL) and Operations
 

With Inoperative Equipment .........................................9-9
 

Preventive Maintenance...............................................9-10
 

Maintenance Entries .............................................9-10
 

Examples of Preventive Maintenance ..................9-10
 

Repairs and Alterations ............................................9-12
 

Special Flight Permits ..............................................9-12
 

Airworthiness Directives (ADs) ..................................9-12
 

Aircraft Owner/Operator Responsibilities ...................9-13
 

Chapter Summary ........................................................9-13
 

Chapter 10
 

Weight and Balance ..........................................10-1
 

Introduction..................................................................10-1
 

Weight Control.............................................................10-1
 

Effects of Weight......................................................10-2
 

Weight Changes .......................................................10-2
 

xi 
Balance, Stability, and Center of Gravity ....................10-2
 

Effects of Adverse Balance ......................................10-3
 

Stability.................................................................10-3
 

Control ..................................................................10-3
 

Management of Weight and Balance Control ..........10-4
 

Terms and Definitions..............................................10-4
 

Principles of Weight and Balance Computations.....10-5
 

Weight and Balance Restrictions .............................10-6
 

Determining Loaded Weight and CG ..........................10-7
 

Computational Method.............................................10-7
 

Graph Method...........................................................10-7
 

Table Method ...........................................................10-9
 

Computations With a Negative Arm......................10-10
 

Computations With Zero Fuel Weight...................10-10
 

Shifting, Adding, and Removing Weight...............10-10
 

Weight Shifting...................................................10-10
 

Weight Addition or Removal..............................10-11
 

Chapter Summary ......................................................10-11
 

Chapter 11
 

Aircraft Performance.........................................11-1
 

Introduction..................................................................11-1
 

Importance of Performance Data .................................11-1
 

Structure of the Atmosphere ........................................11-2
 

Atmospheric Pressure ..................................................11-2
 

Pressure Altitude..........................................................11-3
 

Density Altitude ...........................................................11-3
 

Effects of Pressure on Density .................................11-4
 

Effects of Temperature on Density ..........................11-5
 

Effects of Humidity (Moisture) on Density .............11-5
 

Performance .................................................................11-5
 

Straight-and-Level Flight .........................................11-5
 

Climb Performance...................................................11-6
 

Angle of Climb (AOC) .........................................11-7
 

Rate of Climb (ROC)............................................11-7
 

Climb Performance Factors ..................................11-8
 

Range Performance ..................................................11-9
 

Region of Reversed Command...............................11-11
 

Takeoff and Landing Performance.........................11-12
 

Runway Surface and Gradient................................11-12
 

Water on the Runway and Dynamic
 

Hydroplaning..........................................................11-13
 

Takeoff Performance..............................................11-14
 

Landing Performance .............................................11-16
 

Performance Speeds...................................................11-18
 

Performance Charts....................................................11-19
 

Interpolation ...........................................................11-20
 

Density Altitude Charts..........................................11-20
 

Takeoff Charts........................................................11-20
 

Climb and Cruise Charts ........................................11-21
 

Crosswind and Headwind Component Chart.........11-25
 

Landing Charts .......................................................11-26
 

Stall Speed Performance Charts.............................11-27
 

Transport Category Aircraft Performance .................11-28
 

Air Carrier Obstacle Clearance Requirements...........11-28
 

Chapter Summary ......................................................11-28
 

Chapter 12
 

Weather Theory .................................................12-1
 

Introduction..................................................................12-1
 

Atmosphere ..................................................................12-2
 

Composition of the Atmosphere...............................12-2
 

Atmospheric Circulation ..........................................12-3
 

Atmospheric Pressure...............................................12-3
 

Coriolis Force...............................................................12-3
 

Measurement of Atmosphere Pressure ........................12-4
 

Altitude and Atmospheric Pressure .............................12-5
 

Altitude and Flight .......................................................12-6
 

Altitude and the Human Body .....................................12-6
 

Wind and Currents .......................................................12-7
 

Wind Patterns ...........................................................12-7
 

Convective Currents.................................................12-7
 

Effect of Obstructions on Wind................................12-8
 

Low-Level Wind Shear ..........................................12-11
 

Wind and Pressure Representation on Surface
 

Weather Maps.........................................................12-12
 

Atmospheric Stability ................................................12-12
 

Inversion.................................................................12-13
 

Moisture and Temperature .....................................12-13
 

Relative Humidity ..................................................12-13
 

Temperature/Dew Point Relationship ....................12-13
 

Methods by Which Air Reaches the Saturation
 

Point .......................................................................12-14
 

Dew and Frost ........................................................12-15
 

Fog..........................................................................12-15
 

Clouds.....................................................................12-15
 

Ceiling ....................................................................12-17
 

Visibility.................................................................12-17
 

Precipitation............................................................12-17
 

Air Masses .................................................................12-17
 

Fronts .........................................................................12-18
 

Warm Front ............................................................12-18
 

Flight Toward an Approaching Warm Front......12-19
 

Cold Front ..............................................................12-20
 

Fast-Moving Cold Front .....................................12-20
 

Flight Toward an Approaching Cold Front ........12-20
 

Comparison of Cold and Warm Fronts ..................12-20
 

Wind Shifts.............................................................12-21
 

Stationary Front......................................................12-21
 

Occluded Front.......................................................12-21
 

Thunderstorms........................................................12-22
 

Hazards ..............................................................12-23
 

xii 
Squall Line .........................................................12-23
 

Tornadoes ..........................................................12-23
 

Turbulence .........................................................12-24
 

Icing ...................................................................12-24
 

Hail ....................................................................12-25
 

Ceiling and Visibility .........................................12-25
 

Effect on Altimeters ...........................................12-25
 

Lightning.............................................................12-25
 

Engine Water Ingestion .....................................12-25
 

Chapter Summary ......................................................12-25
 

Chapter 13
 

Aviation Weather Services ...............................13-1
 

Introduction..................................................................13-1
 

Observations ................................................................13-2
 

Surface Aviation Weather Observations ..................13-2
 

Air Route Traffic Control Center (ARTCC) ........13-2
 

Upper Air Observations............................................13-2
 

Radar Observations ..................................................13-3
 

Satellite.....................................................................13-4
 

Service Outlets.............................................................13-4
 

Flight Service Station (FSS).....................................13-4
 

Telephone Information Briefing Service (TIBS) .....13-4
 

Hazardous Inflight Weather Advisory
 

Service (HIWAS) .....................................................13-4
 

Transcribed Weather Broadcast (TWEB)
 

(Alaska Only) ..........................................................13-4
 

Weather Briefings ........................................................13-5
 

Standard Briefing .....................................................13-5
 

Abbreviated Briefing................................................13-5
 

Outlook Briefing ......................................................13-5
 

Aviation Weather Reports............................................13-5
 

Aviation Routine Weather Report (METAR) ..........13-6
 

Pilot Weather Reports (PIREPs) ..............................13-8
 

Aviation Forecasts....................................................13-9
 

Terminal Aerodrome Forecasts (TAF).....................13-9
 

Area Forecasts (FA) ...............................................13-10
 

Inflight Weather Advisories...................................13-11
 

AIRMET.............................................................13-11
 

SIGMET .............................................................13-12
 

Convective Significant Meteorological
 

Information (WST).............................................13-12
 

Winds and Temperature Aloft Forecast (FB).........13-13
 

Weather Charts...........................................................13-13
 

Surface Analysis Chart...........................................13-13
 

Weather Depiction Chart........................................13-15
 

Significant Weather Prognostic Charts..................13-15
 

ATC Radar Weather Displays ..................................13-16
 

Weather Avoidance Assistance..............................13-18
 

Electronic Flight Displays (EFD) /Multi-Function
 

Display (MFD) Weather ...........................................13-18
 

Weather Products Age and Expiration ...................13-18
 

What Can Pilots Do? ..........................................13-19
 

NEXRAD Abnormalities....................................13-21
 

NEXRAD Limitations........................................13-21
 

AIRMET/SIGMET Display ...................................13-21
 

Graphical METARs................................................13-21
 

Data Link Weather .................................................13-21
 

Data Link Weather Products ..................................13-23
 

Flight Information Service- Broadcast (FIS-B)..13-23
 

Pilot Responsibility....................................................13-24
 

Chapter Summary ......................................................13-24
 

Chapter 14
 

Airport Operations.............................................14-1
 

Introduction..................................................................14-1
 

Airport Categories........................................................14-1
 

Types of Airports......................................................14-2
 

Towered Airport ...................................................14-2
 

Nontowered Airport..............................................14-2
 

Sources for Airport Data..............................................14-3
 

Aeronautical Charts..................................................14-3
 

Chart Supplement U.S. (formerly Airport/Facility 

Directory) .................................................................14-3
 

Notices to Airmen (NOTAM) ..................................14-4
 

Automated Terminal Information Service (ATIS)...14-5
 

Airport Markings and Signs.........................................14-5
 

Runway Markings and Signs....................................14-5
 

Relocated Runway Threshold...............................14-5
 

Displaced Threshold .............................................14-5
 

Runway Safety Area ............................................14-6
 

Runway Safety Area Boundary Sign....................14-6
 

Runway Holding Position Sign ............................14-6
 

Runway Holding Position Marking......................14-8
 

Runway Distance Remaining Signs......................14-8
 

Runway Designation Marking..............................14-8
 

Land and Hold Short Operations (LAHSO).......14-10
 

Taxiway Markings and Signs.................................14-11
 

Enhanced Taxiway Centerline Markings............14-12
 

Destination Signs................................................14-12
 

Holding Position Signs and Markings for an
 

Instrument Landing System (ILS) Critical Area ..14-12
 

Holding Position Markings for Taxiway/Taxiway 

Intersections........................................................14-14
 

Marking and Lighting of Permanently Closed 

Runways and Taxiways......................................14-14
 

Temporarily Closed Runways and Taxiways.....14-15
 

Other Markings.......................................................14-15
 

Airport Signs ..........................................................14-15
 

Airport Lighting.........................................................14-16
 

Airport Beacon .......................................................14-16
 

xiii 
Approach Light Systems........................................14-16
 

Visual Glideslope Indicators..................................14-16
 

Visual Approach Slope Indicator (VASI)...........14-16
 

Other Glidepath Systems....................................14-16
 

Runway Lighting....................................................14-17
 

Runway End Identifier Lights (REIL)................14-17
 

Runway Edge Lights...........................................14-17
 

In-Runway Lighting............................................14-18
 

Control of Airport Lighting....................................14-18
 

Taxiway Lights.......................................................14-19
 

Omnidirectional .................................................14-19
 

Clearance Bar Lights ..........................................14-19
 

Runway Guard Lights.........................................14-19
 

Stop Bar Lights...................................................14-19
 

Obstruction Lights..................................................14-19
 

New Lighting Technologies...................................14-19
 

Wind Direction Indicators..........................................14-20
 

Traffic Patterns ..........................................................14-20
 

Example: Key to Traffic Pattern Operations—
 

Single Runway .......................................................14-21
 

Example: Key to Traffic Pattern Operations—
 

Parallel Runways....................................................14-21
 

Radio Communications..............................................14-22
 

Radio License.........................................................14-22
 

Radio Equipment....................................................14-22
 

Using Proper Radio Procedures ............................14-22
 

Lost Communication Procedures...........................14-23
 

Air Traffic Control (ATC) Services...........................14-24
 

Primary Radar.........................................................14-24
 

ATC Radar Beacon System (ATCRBS) ................14-24
 

Transponder............................................................14-25
 

Automatic Dependent Surveillance–
 

Broadcast (ADS-B) ................................................14-26
 

Radar Traffic Advisories........................................14-26
 

Wake Turbulence .......................................................14-26
 

Vortex Generation ..................................................14-26
 

Terminal Area ....................................................14-27
 

En Route .............................................................14-27
 

Vortex Behavior.....................................................14-27
 

Vortex Avoidance Procedures................................14-28
 

Collision Avoidance...................................................14-28
 

Clearing Procedures ...............................................14-28
 

Pilot Deviations (PDs)............................................14-30
 

Runway Incursion Avoidance ................................14-30
 

Causal Factors of Runway Incursions....................14-31
 

Runway Confusion.................................................14-31
 

Causal Factors of Runway Confusion ................14-31
 

ATC Instructions....................................................14-32
 

ATC Instructions—“Hold Short” ......................14-32
 

ATC Instructions—Explicit Runway Crossing.... 14-33
 

ATC Instructions—“Line Up and Wait”
 

(LUAW)..............................................................14-33
 

ATC Instructions—“Runway Shortened” ..........14-34
 

Pre-Landing, Landing, and After-Landing.............14-34
 

Engineered Materials Arresting Systems (EMAS)....14-35
 

Incidents .................................................................14-35
 

EMAS Installations and Information .....................14-35
 

Pilot Considerations ...............................................14-36
 

Chapter Summary ......................................................14-37
 

Chapter 15
 

Airspace .............................................................15-1
 

Introduction..................................................................15-1
 

Controlled Airspace .....................................................15-2
 

Class A Airspace ......................................................15-2
 

Class B Airspace ......................................................15-2
 

Class C Airspace ......................................................15-2
 

Class D Airspace ......................................................15-2
 

Class E Airspace.......................................................15-2
 

Uncontrolled Airspace .................................................15-3
 

Class G Airspace ......................................................15-3
 

Special Use Airspace ...................................................15-3
 

Prohibited Areas.......................................................15-3
 

Restricted Areas .......................................................15-3
 

Warning Areas..........................................................15-4
 

Military Operation Areas (MOAs)...........................15-4
 

Alert Areas ...............................................................15-4
 

Controlled Firing Areas (CFAs)...............................15-4
 

Other Airspace Areas...................................................15-4
 

Local Airport Advisory (LAA) ................................15-6
 

Military Training Routes (MTRs)............................15-6
 

Temporary Flight Restrictions (TFR).......................15-6
 

Published VFR Routes .............................................15-6
 

Terminal Radar Service Areas (TRSAs)..................15-7
 

National Security Areas (NSAs) ..............................15-7
 

Air Traffic Control and the National Airspace System..15-7
 

Coordinating the Use of Airspace ............................15-7
 

Operating in the Various Types of Airspace............15-7
 

Basic VFR Weather Minimums............................15-7
 

Operating Rules and Pilot/Equipment
 

Requirements ........................................................15-8
 

Ultralight Vehicles..............................................15-11
 

Unmanned Free Balloons ...................................15-11
 

Unmanned Aircraft Systems...............................15-11
 

Parachute Jumps .................................................15-11
 

Chapter Summary ......................................................15-11
 

xiv 
Chapter 16
 

Navigation ..........................................................16-1
 

Introduction..................................................................16-1
 

Aeronautical Charts .....................................................16-2
 

Sectional Charts........................................................16-2
 

VFR Terminal Area Charts ......................................16-2
 

World Aeronautical Charts.......................................16-2
 

Latitude and Longitude (Meridians and Parallels).......16-3
 

Time Zones...............................................................16-3
 

Measurement of Direction........................................16-5
 

Variation...................................................................16-6
 

Magnetic Variation ...............................................16-7
 

Magnetic Deviation ..............................................16-7
 

Deviation ..................................................................16-8
 

Effect of Wind..............................................................16-8
 

Basic Calculations......................................................16-11
 

Converting Minutes to Equivalent Hours...............16-11
 

Time T = D/GS...................................................16-11
 

Distance D = GS X T..........................................16-11
 

GS GS = D/T ......................................................16-11
 

Converting Knots to Miles Per Hour......................16-11
 

Fuel Consumption ..................................................16-11
 

Flight Computers....................................................16-12
 

Plotter .....................................................................16-12
 

Pilotage ......................................................................16-12
 

Dead Reckoning.........................................................16-13
 

Wind Triangle or Vector Analysis.........................16-13
 

Step 1 ..................................................................16-14
 

Step 2 ..................................................................16-15
 

Step 3 ..................................................................16-15
 

Step 4 ..................................................................16-15
 

Flight Planning...........................................................16-17
 

Assembling Necessary Material.............................16-17
 

Weather Check .......................................................16-17
 

Use of Chart Supplement U.S. (formerly
 

Airport/Facility Directory).....................................16-17
 

Airplane Flight Manual or Pilot’s Operating
 

Handbook (AFM/POH)..........................................16-17
 

Charting the Course ...................................................16-18
 

Steps in Charting the Course..................................16-18
 

Filing a VFR Flight Plan............................................16-21
 

Ground-Based Navigation .........................................16-22
 

Very High Frequency (VHF) Omnidirectional
 

Range (VOR)..........................................................16-22
 

Using the VOR ...................................................16-23
 

Course Deviation Indicator (CDI)..........................16-23
 

Horizontal Situation Indicator................................16-24
 

Radio Magnetic Indicator (RMI)............................16-24
 

Tracking With VOR...............................................16-25
 

Tips on Using the VOR..........................................16-26
 

Time and Distance Check From a Station Using
 

a RMI......................................................................16-26
 

Time and Distance Check From a Station Using
 

a CDI ......................................................................16-27
 

Course Intercept ....................................................16-27
 

Rate of Intercept .................................................16-27
 

Angle of Intercept ..............................................16-27
 

Distance Measuring Equipment (DME).................16-27
 

VOR/DME RNAV .................................................16-28
 

Automatic Direction Finder (ADF)........................16-29
 

Global Positioning System.....................................16-30
 

Selective Availability..........................................16-31
 

VFR Use of GPS ................................................16-32
 

RAIM Capability ................................................16-32
 

Tips for Using GPS for VFR Operations...............16-33
 

VFR Waypoints .....................................................16-33
 

Lost Procedures..........................................................16-34
 

Flight Diversion .........................................................16-34
 

Chapter Summary ......................................................16-35
 

Chapter 17
 

Aeromedical Factors.........................................17-1
 

Introduction..................................................................17-1
 

Obtaining a Medical Certificate...................................17-2
 

Health and Physiological Factors Affecting Pilot 

Performance .................................................................17-3
 

Hypoxia ....................................................................17-3
 

Hypoxic Hypoxia..................................................17-3
 

Hypemic Hypoxia.................................................17-3
 

Stagnant Hypoxia..................................................17-3
 

Histotoxic Hypoxia...............................................17-4
 

Symptoms of Hypoxia..............................................17-4
 

Treatment of Hypoxia...........................................17-4
 

Hyperventilation.......................................................17-4
 

Middle Ear and Sinus Problems ...............................17-5
 

Spatial Disorientation and Illusions .........................17-6
 

Vestibular Illusions...............................................17-7
 

Visual Illusions .....................................................17-8
 

Postural Considerations............................................17-8
 

Demonstration of Spatial Disorientation..................17-8
 

Climbing While Accelerating...............................17-9
 

Climbing While Turning.......................................17-9
 

Diving While Turning...........................................17-9
 

Tilting to Right or Left .........................................17-9
 

Reversal of Motion ...............................................17-9
 

Diving or Rolling Beyond the Vertical Plane.......17-9
 

Coping with Spatial Disorientation ..........................17-9
 

Optical Illusions .....................................................17-10
 

Runway Width Illusion.......................................17-10
 

xv 
Runway and Terrain Slopes Illusion...................17-10
 

Featureless Terrain Illusion ................................17-10
 

Water Refraction.................................................17-10
 

Haze ....................................................................17-10
 

Fog ......................................................................17-10
 

Ground Lighting Illusions...................................17-10
 

How To Prevent Landing Errors Due to
 

Optical Illusions .....................................................17-10
 

Motion Sickness.....................................................17-12
 

Carbon Monoxide (CO) Poisoning ........................17-12
 

Stress ......................................................................17-12
 

Fatigue....................................................................17-13
 

Exposure to Chemicals...........................................17-13
 

Hydraulic Fluid...................................................17-13
 

Engine Oil...........................................................17-14
 

Fuel .....................................................................17-14
 

Dehydration and Heatstroke...................................17-14
 

Alcohol ...................................................................17-15
 

Drugs ......................................................................17-16
 

Altitude-Induced Decompression Sickness (DCS).. 17-18
 

DCS After Scuba Diving ....................................17-18
 

Vision in Flight ..........................................................17-19
 

Vision Types ..........................................................17-20
 

Photopic Vision ..................................................17-20
 

Mesopic Vision...................................................17-21
 

Scotopic Vision...................................................17-21
 

Central Blind Spot..................................................17-21
 

Empty-Field Myopia ..............................................17-22
 

Night Vision ...........................................................17-22
 

Night Blind Spot.................................................17-22
 

Dark Adaptation..................................................17-23
 

Scanning Techniques .........................................17-23
 

Night Vision Protection ......................................17-23
 

Self-Imposed Stress ...........................................17-25
 

Distance Estimation and Depth Perception .......17-25
 

Binocular Cues....................................................17-26
 

Night Vision Illusions ............................................17-26
 

Autokinesis .........................................................17-26
 

False Horizon......................................................17-26
 

Reversible Perspective Illusion...........................17-26
 

Size-Distance Illusion.........................................17-27
 

Fascination (Fixation).........................................17-27
 

Flicker Vertigo....................................................17-27
 

Night Landing Illusions..........................................17-27
 

Enhanced Night Vision Systems............................17-27
 

Synthetic Vision System.....................................17-28
 

Enhanced Flight Vision System..........................17-28
 

Chapter Summary ......................................................17-29
 

Appendix A
 

Performance Data for Cessna Model 172R
 

and Challenger 605.............................................A-1
 

Appendix B
 

Acronyms, Abbreviations, and NOTAM 

Contractions .......................................................B-1
 

Appendix C
 

Airport Signs and Markings...............................C-1
 

Glossary ..............................................................G-1
 

Index ......................................................................I-1
 

xvi 
1-1 

Introduction 

The Pilot’s Handbook of Aeronautical Knowledge provides 

basic knowledge for the student pilot learning to fly, as well 

as pilots seeking advanced pilot certification. For detailed 

information on a variety of specialized flight topics, see 

specific Federal Aviation Administration (FAA) handbooks 

and Advisory Circulars (ACs). 

This chapter offers a brief history of flight, introduces the 

history and role of the FAA in civil aviation, FAA regulations 

and standards, government references and publications, 

eligibility for pilot certificates, available routes to flight 

instruction, the role of the Certificated Flight Instructor (CFI) 

and Designated Pilot Examiner (DPE) in flight training, 

Practical Test Standards (PTS), and new, industry-developed 

Airman Certification Standards (ACS) framework that will 

eventually replace the PTS. 

Introduction 

To Flying 

Chapter 1 
History of Flight 

From prehistoric times, humans have watched the flight of 

birds, and longed to imitate them, but lacked the power to do 

so. Logic dictated that if the small muscles of birds can lift 

them into the air and sustain them, then the larger muscles 

of humans should be able to duplicate the feat. No one knew 

about the intricate mesh of muscles, sinew, heart, breathing 

system, and devices not unlike wing flaps, variable-camber 

and spoilers of the modern airplane that enabled a bird to 

fly. Still, thousands of years and countless lives were lost in 

attempts to fly like birds. 

The identity of the first “bird-men” who fitted themselves 

with wings and leapt off of cliffs in an effort to fly are lost in 

time, but each failure gave those who wished to fly questions 

that needed to be answered. Where had the wing flappers 

gone wrong? Philosophers, scientists, and inventors offered 

solutions, but no one could add wings to the human body 

and soar like a bird. During the 1500s, Leonardo da Vinci 

filled pages of his notebooks with sketches of proposed 

flying machines, but most of his ideas were flawed because 

he clung to the idea of birdlike wings. [Figure 1-1] By 

1655, mathematician, physicist, and inventor Robert Hooke 

concluded that the human body does not possess the strength 

to power artificial wings. He believed human flight would 

require some form of artificial propulsion. 

The quest for human flight led some practitioners in another 

direction. In 1783, the first manned hot air balloon, crafted 

by Joseph and Etienne Montgolfier, flew for 23 minutes. 

Ten days later, Professor Jacques Charles flew the first gas 

balloon. A madness for balloon flight captivated the public’s 

imagination and for a time flying enthusiasts turned their 

expertise to the promise of lighter-than-air flight. But for 

all its majesty in the air, the balloon was little more than a 

billowing heap of cloth capable of no more than a one-way, 

downwind journey. 

Balloons solved the problem of lift, but that was only one of 

the problems of human flight. The ability to control speed and 

direction eluded balloonists. The solution to that problem lay 

in a child’s toy familiar to the East for 2,000 years, but not 

introduced to the West until the 13th century—the kite. The 

kites used by the Chinese for aerial observation, to test winds 

for sailing, as a signaling device, and as a toy, held many of 

the answers to lifting a heavier-than-air device into the air. 

One of the men who believed the study of kites unlocked 

the secrets of winged flight was Sir George Cayley. Born 

in England 10 years before the Mongolfier balloon flight, 

Cayley spent his 84 years seeking to develop a heavier-thanair vehicle supported by kite-shaped wings. [Figure 1-2] The 

“Father of Aerial Navigation,” Cayley discovered the basic 

principles on which the modern science of aeronautics is 

founded; built what is recognized as the first successful flying 

model; and tested the first full-size man-carrying airplane. 

Figure 1-2. Glider from 1852 by Sir George Cayley, British aviator 

Figure 1-1. Leonardo da Vinci’s ornithopter wings. (1773–1857).

1-2 
For the half-century after Cayley’s death, countless scientists, 

flying enthusiasts, and inventors worked toward building 

a powered flying machine. Men, such as William Samuel 

Henson, who designed a huge monoplane that was propelled 

by a steam engine housed inside the fuselage, and Otto 

Lilienthal, who proved human flight in aircraft heavier than 

air was practical, worked toward the dream of powered flight. 

A dream turned into reality by Wilbur and Orville Wright at 

Kitty Hawk, North Carolina, on December 17, 1903. 

The bicycle-building Wright brothers of Dayton, Ohio, had 

experimented for 4 years with kites, their own homemade 

wind tunnel, and different engines to power their biplane. One 

of their great achievements in flight was proving the value of 

the scientific, rather than a build-it-and-see approach. Their 

biplane, The Flyer, combined inspired design and engineering 

with superior craftsmanship. [Figure 1-3] By the afternoon 

of December 17th, the Wright brothers had flown a total of 

98 seconds on four flights. The age of flight had arrived. 

History of the Federal Aviation

Administration (FAA) 

During the early years of manned flight, aviation was a 

free for all because no government body was in place to 

establish policies or regulate and enforce safety standards. 

Individuals were free to conduct flights and operate aircraft 

with no government oversight. Most of the early flights were 

conducted for sport. Aviation was expensive and became the 

playground of the wealthy. Since these early airplanes were 

small, many people doubted their commercial value. One 

group of individuals believed otherwise and they became 

the genesis for modern airline travel. 

P. E. Fansler, a Florida businessman living in St. Petersburg, 

approached Tom Benoist of the Benoist Aircraft Company 

in St. Louis, Missouri, about starting a flight route from St. 

Petersburg across the waterway to Tampa. Benoist suggested 

using his “Safety First” airboat and the two men signed an 

agreement for what would become the first scheduled airline 

in the United States. The first aircraft was delivered to St. 

Petersburg and made the first test flight on December 31, 

1913. [Figure 1-4] 

A public auction decided who would win the honor of 

becoming the first paying airline customer. The former 

mayor of St. Petersburg, A. C. Pheil, made the winning bid 

of $400.00, which secured his place in history as the first 

paying airline passenger. 

On January 1, 1914, the first scheduled airline flight was 

conducted. The flight length was 21 miles and lasted 23 

minutes due to a headwind. The return trip took 20 minutes. 

The line, which was subsidized by Florida businessmen, 

continued for 4 months and offered regular passage for $5.00 

per person or $5.00 per 100 pounds of cargo. Shortly after the 

opening of the line, Benoist added a new airboat that afforded 

more protection from spray during takeoff and landing. 

The routes were also extended to Manatee, Bradenton, and 

Sarasota giving further credence to the idea of a profitable 

commercial airline. 

The St. Petersburg-Tampa Airboat Line continued throughout 

the winter months with flights finally being suspended when 

the winter tourist industry began to dry up. The airline 

operated for only 4 months, but 1,205 passengers were 

carried without injury. This experiment proved commercial 

passenger airline travel was viable. 

The advent of World War I offered the airplane a chance 

to demonstrate its varied capabilities. It began the war as a 

reconnaissance platform, but by 1918, airplanes were being 

Figure 1-4. Benoist airboat. 

Figure 1-3. First flight by the Wright brothers. 

1-3 
 

mass produced to serve as fighters, bombers, trainers, as well 

as reconnaissance platforms. 

Aviation advocates continued to look for ways to use 

airplanes. Airmail service was a popular idea, but the 

war prevented the Postal Service from having access to 

airplanes. The War Department and Postal Service reached an 

agreement in 1918. The Army would use the mail service to 

train its pilots in flying cross-country. The first airmail flight 

was conducted on May 15, 1918, between New York and 

Washington, DC. The flight was not considered spectacular; 

the pilot became lost and landed at the wrong airfield. In 

August of 1918, the United States Postal Service took control 

of the airmail routes and brought the existing Army airmail 

pilots and their planes into the program as postal employees. 

Transcontinental Air Mail Route 

Airmail routes continued to expand until the Transcontinental 

Mail Route was inaugurated. [Figure 1-5] This route spanned 

from San Francisco to New York for a total distance of 2,612 

miles with 13 intermediate stops along the way. [Figure 1-6] 

On May 20, 1926, Congress passed the Air Commerce Act, 

which served as the cornerstone for aviation within the 

United States. This legislation was supported by leaders in 

the aviation industry who felt that the airplane could not 

reach its full potential without assistance from the Federal 

Government in improving safety. 

The Air Commerce Act charged the Secretary of Commerce 

with fostering air commerce, issuing and enforcing air traffic 

rules, licensing pilots, certificating aircraft, establishing 

airways, and operating and maintaining aids to air navigation. 

The Department of Commerce created a new Aeronautics 

Branch whose primary mission was to provide oversight for the 

aviation industry. In addition, the Aeronautics Branch took over 

the construction and operation of the nation’s system of lighted 

airways. The Postal Service, as part of the Transcontinental 

Air Mail Route system, had initiated this system. The 

Figure 1-5. The de Haviland DH-4 on the New York to San 

Francisco inaugural route in 1921. 

15 

14 

13 

12 11 10 

9 8 7 6 5 4 3 2 1 

11 Rock Springs 12 Salt Lake City 13 Elko 14 Reno 15 San Francisco 1 New York 2 Bellefonte 3 Cleveland 4 Bryan 5 Chicago 6 Iowa City 7 Omaha 8 North Platte 9 Cheyenne 10 Rawlins 

Figure 1-6. The transcontinental airmail route ran from New York 

to San Francisco. 

Department of Commerce made significant advances in 

aviation communications, including the introduction of radio 

beacons as an effective means of navigation. 

Built at intervals of approximately 10 miles apart, the 

standard beacon tower was 51 feet high, and was topped 

with a powerful rotating light. Below the rotating light, two 

course lights pointed forward and back along the airway. The 

course lights flashed a code to identify the beacon’s number. 

The tower usually stood in the center of a concrete arrow 

70 feet long. A generator shed, where required, stood at the 

“feather” end of the arrow. [Figure 1-7] 

Federal Certification of Pilots and Mechanics 

The Aeronautics Branch of the Department of Commerce 

began pilot certification with the first license issued on April 

6, 1927. The recipient was the Chief of the Aeronautics 

Branch, William P. MacCracken, Jr. [Figure 1-8] (Orville 

Wright, who was no longer an active flier, had declined the 

honor.) MacCracken’s license was the first issued to a pilot 

by a civilian agency of the Federal Government. Some 3 

months later, the Aeronautics Branch issued the first Federal 

aircraft mechanic license. 

Equally important for safety was the establishment of a 

system of certification for aircraft. On March 29, 1927, 

the Aeronautics Branch issued the first airworthiness 

type certificate to the Buhl Airster CA-3, a three-place 

open biplane. 

In 1934, to recognize the tremendous strides made in aviation 

and to display the enhanced status within the department, 

the Aeronautics Branch was renamed the Bureau of Air 

Commerce. [Figure 1-9] Within this time frame, the Bureau 

of Air Commerce brought together a group of airlines 

1-4 
Figure 1-8. Standard airway beacon installation.

 

D-KC 

Figure 1-7. A standard airway beacon tower. 

Figure 1-8. The first pilot license was issued to William P. 

MacCracken, Jr. 

Figure 1-9. The third head of the Aeronautics Branch, Eugene 

L. Vidal, is flanked by President Franklin D. Roosevelt (left) and 

Secretary of Agriculture Henry A. Wallace (right). The photograph 

was taken in 1933. During Vidal’s tenure, the Aeronautics Branch 

was renamed the Bureau of Air Commerce on July 1, 1934. The 

new name more accurately reflected the status of the organization 

within the Department of Commerce. 

and encouraged them to form the first three Air Traffic 

Control (ATC) facilities along the established air routes. 

Then in 1936, the Bureau of Air Commerce took over the 

responsibilities of operating the centers and continued to 

advance the ATC facilities. ATC has come a long way from 

the early controllers using maps, chalkboards, and performing 

mental math calculations in order to separate aircraft along 

flight routes. 

The Civil Aeronautics Act of 1938 

In 1938, the Civil Aeronautics Act transferred the civil 

aviation responsibilities to a newly created, independent 

body, named the Civil Aeronautics Authority (CAA). This 

Act empowered the CAA to regulate airfares and establish 

new routes for the airlines to service. 

President Franklin Roosevelt split the CAA into two 

agencies—the Civil Aeronautics Administration (CAA) 

and the Civil Aeronautics Board (CAB). Both agencies 

were still part of the Department of Commerce but the CAB 

functioned independently of the Secretary of Commerce. 

The role of the CAA was to facilitate ATC, certification of 

airmen and aircraft, rule enforcement, and the development 

of new airways. The CAB was charged with rule making to 

enhance safety, accident investigation, and the economic 

regulation of the airlines. Then in 1946, Congress gave the 

CAA the responsibility of administering the Federal Aid 

1-5 
 

 

Airport Program. This program was designed to promote 

the establishment of civil airports throughout the country. 

The Federal Aviation Act of 1958 

By mid-century, air traffic had increased and jet aircraft had 

been introduced into the civil aviation arena. A series of 

mid-air collisions underlined the need for more regulation 

of the aviation industry. Aircraft were not only increasing in 

numbers, but were now streaking across the skies at much 

higher speeds. The Federal Aviation Act of 1958 established 

a new independent body that assumed the roles of the CAA 

and transferred the rule making authority of the CAB to the 

newly created Federal Aviation Agency (FAA). In addition, 

the FAA was given complete control of the common civilmilitary system of air navigation and ATC. The man who 

was given the honor of being the first Administrator of the 

FAA was former Air Force General Elwood Richard “Pete” 

Quesada. He served as the administrator from 1959–1961. 

[Figure 1-10] 

Department of Transportation (DOT) 

On October 15, 1966, Congress established the Department 

of Transportation (DOT), which was given oversight of the 

transportation industry within the United States. The result 

was a combination of both air and surface transportation. Its 

mission was and is to serve the United States by ensuring a 

fast, safe, efficient, accessible, and convenient transportation 

system meeting vital national interests and enhancing the 

quality of life of the American people, then, now, and into 

Figure 1-10. First Administrator of the FAA was General Elwood 

Richard “Pete” Quesada, 1959–1961. 

the future. The DOT began operation on April 1, 1967. At 

this same time, the Federal Aviation Agency was renamed 

to the Federal Aviation Administration (FAA). 

The role of the CAB was assumed by the newly created 

National Transportation Safety Board (NTSB), which was 

charged with the investigation of all transportation accidents 

within the United States. 

As aviation continued to grow, the FAA took on additional 

duties and responsibilities. With the highjacking epidemic 

of the 1960s, the FAA was responsible for increasing the 

security duties of aviation both on the ground and in the air. 

After September 11, 2001, the duties were transferred to 

a newly created body called the Department of Homeland 

Security (DHS). 

With numerous aircraft flying in and out of larger cities, the 

FAA began to concentrate on the environmental aspect of 

aviation by establishing and regulating the noise standards 

of aircraft. Additionally, in the 1960s and 1970s, the FAA 

began to regulate high altitude (over 500 feet) kite and balloon 

flying. In 1970, more duties were assumed by the FAA in the 

addition of a new federal airport aid program and increased 

responsibility for airport safety. 

ATC Automation 

By the mid-1970s, the FAA had achieved a semi-automated 

ATC system based on a marriage of radar and computer 

technology. By automating certain routine tasks, the system 

allowed controllers to concentrate more efficiently on the 

vital task of providing aircraft separation. Data appearing 

directly on the controllers’ scopes provided the identity, 

altitude, and groundspeed of aircraft carrying radar beacons. 

Despite its effectiveness, this system required enhancement 

to keep pace with the increased air traffic of the late 1970s. 

The increase was due in part to the competitive environment 

created by the Airline Deregulation Act of 1978. This law 

phased out CAB’s economic regulation of the airlines, and 

CAB ceased to exist at the end of 1984. 

To meet the challenge of traffic growth, the FAA unveiled 

the National Airspace System (NAS) Plan in January 

1982. The new plan called for more advanced systems 

for en route and terminal ATC, modernized flight service 

stations, and improvements in ground-to-air surveillance 

and communication. 

The Professional Air Traffic Controllers 

Organization (PATCO) Strike 

While preparing the NAS Plan, the FAA faced a strike 

by key members of its workforce. An earlier period of 

discord between management and the Professional Air 

1-6 
 

Traffic Controllers Organization (PATCO) culminated in a 

1970 “sickout” by 3,000 controllers. Although controllers 

subsequently gained additional wage and retirement 

benefits, another period of tension led to an illegal strike in 

August 1981. The government dismissed over 11,000 strike 

participants and decertified PATCO. By the spring of 1984, 

the FAA ended the last of the special restrictions imposed to 

keep the airspace system operating safely during the strike. 

The Airline Deregulation Act of 1978 

Until 1978, the CAB regulated many areas of commercial 

aviation such as fares, routes, and schedules. The Airline 

Deregulation Act of 1978, however, removed many of 

these controls, thus changing the face of civil aviation in the 

United States. After deregulation, unfettered free competition 

ushered in a new era in passenger air travel. 

The CAB had three main functions: to award routes to 

airlines, to limit the entry of air carriers into new markets, 

and to regulate fares for passengers. Much of the established 

practices of commercial passenger travel within the United 

States went back to the policies of Walter Folger Brown, the 

United States Postmaster General during the administration 

of President Herbert Hoover. Brown had changed the mail 

payments system to encourage the manufacture of passenger 

aircraft instead of mail-carrying aircraft. His influence 

was crucial in awarding contracts and helped create four 

major domestic airlines: United, American, Eastern, and 

Transcontinental and Western Air (TWA). Similarly, 

Brown had also helped give Pan American a monopoly on 

international routes. 

The push to deregulate, or at least to reform the existing laws 

governing passenger carriers, was accelerated by President 

Jimmy Carter, who appointed economist and former 

professor Alfred Kahn, a vocal supporter of deregulation, to 

head the CAB. A second force to deregulate emerged from 

abroad. In 1977, Freddie Laker, a British entrepreneur who 

owned Laker Airways, created the Skytrain service, which 

offered extraordinarily cheap fares for transatlantic flights. 

Laker’s offerings coincided with a boom in low-cost domestic 

flights as the CAB eased some limitations on charter flights 

(i.e., flights offered by companies that do not actually own 

planes but leased them from the major airlines). The big air 

carriers responded by proposing their own lower fares. For 

example, American Airlines, the country’s second largest 

airline, obtained CAB approval for “SuperSaver” tickets. 

All of these events proved to be favorable for large-scale 

deregulation. In November 1977, Congress formally 

deregulated air cargo. In late 1978, Congress passed the 

Airline Deregulation Act of 1978, legislation that had been 

principally authored by Senators Edward Kennedy and 

Howard Cannon. [Figure 1-11] There was stiff opposition to 

the bill—from the major airlines who feared free competition, 

from labor unions who feared non-union employees, and 

from safety advocates who feared that safety would be 

sacrificed. Public support was, however, strong enough to 

pass the act. The act appeased the major airlines by offering 

generous subsidies and pleased workers by offering high 

unemployment benefits if they lost their jobs as a result. The 

most important effect of the act, whose laws were slowly 

phased in, was on the passenger market. For the first time 

in 40 years, airlines could enter the market or (from 1981) 

expand their routes as they saw fit. Airlines (from 1982) 

also had full freedom to set their fares. In 1984, the CAB 

was finally abolished since its primary duty of regulating the 

airline industry was no longer necessary. 

The Role of the FAA 

The Code of Federal Regulations (CFR) 

The FAA is empowered by regulations to promote aviation 

safety and establish safety standards for civil aviation. The 

FAA achieves these objectives under the Code of Federal 

Regulations (CFR), which is the codification of the general 

and permanent rules published by the executive departments 

and agencies of the United States Government. The 

regulations are divided into 50 different codes, called Titles, 

that represent broad areas subject to Federal regulation. 

FAA regulations are listed under Title 14, “Aeronautics and 

Space,” which encompasses all aspects of civil aviation from 

how to earn a pilot’s certificate to maintenance of an aircraft. 

Title 14 CFR Chapter 1, Federal Aviation Administration, 

is broken down into subchapters A through N as illustrated 

in Figure 1-12. 

For the pilot, certain parts of 14 CFR are more relevant 

than others. During flight training, it is helpful for the pilot 

to become familiar with the parts and subparts that relate 

Figure 1-11. President Jimmy Carter signs the Airline Deregulation 

Act in late 1978. 

1-7 
 

Code of Federal Regulations 

Title Volume Chapter Subchapters 

Title 14 

Aeronautics 

and Space 

1 I A 

B 

C 

Definitions and Abbreviations 

Procedural Rules 

Aircraft 

2 D 

E 

F 

Airmen 

Airspace 

Air Traffic and General Rules 

3 G 

H 

I 

J 

K 

L–M 

N 

Air Carriers and Operators for Compensation or Hire: Certification and 

Operations 

Schools and Other Certified Agencies 

Airports 

Navigational Facilities 

Administrative Regulations 

Reserved 

War Risk Insurance 

4 II 

III 

A 

B 

C 

D 

E 

F 

Economic Regulations 

Procedural Regulations 

Reserved 

Special Regulations 

Organization 

Policy Statements 

A 

B 

C 

General 

Procedure 

Licensing 

5 V 

VI A 

B 

Office of Management and Budget 

Air Transportation Stabilization Board 

 

Figure 1-12. Overview of 14 CFR, available online free from the FAA and for purchase through commercial sources. 

to flight training and pilot certification. For instance, 14 

CFR part 61 pertains to the certification of pilots, flight 

instructors, and ground instructors. It also defines the 

eligibility, aeronautical knowledge, and flight proficiency, 

as well as training and testing requirements for each type of 

pilot certificate issued. 14 CFR part 91 provides guidance in 

the areas of general flight rules, visual flight rules (VFR), and 

instrument flight rules (IFR), while 14 CFR part 43 covers 

aircraft maintenance, preventive maintenance, rebuilding, 

and alterations. 

Primary Locations of the FAA 

The FAA headquarters are in Washington, DC, and there are 

nine regional offices strategically located across the United 

States. The agency’s two largest field facilities are the Mike 

Monroney Aeronautical Center (MMAC) in Oklahoma 

City, Oklahoma, and the William J. Hughes Technical 

Center (WJHTC) in Atlantic City, New Jersey. Home to 

FAA training and logistics services, the MMAC provides 

a number of aviation safety-related and business support 

services. The WJHTC is the premier aviation research and 

development and test and evaluation facility in the country. 

The center’s programs include testing and evaluation in ATC, 

communication, navigation, airports, aircraft safety, and 

security. Furthermore, the WJHTC is active in long-range 

development of innovative aviation systems and concepts, 

development of new ATC equipment and software, and 

modification of existing systems and procedures. 

Field Offices 

Flight Standards Service 

Within the FAA, the Flight Standards Service promotes safe 

air transportation by setting the standards for certification 

and oversight of airmen, air operators, air agencies, and 

designees. It also promotes safety of flight of civil aircraft 

and air commerce by: 

•	 Accomplishing certification, inspection, surveillance, 

investigation, and enforcement. 

•	 Setting regulations and standards. 

•	 Managing the system for registration of civil aircraft 

and all airmen records. 

The focus of interaction between Flight Standards Service 

and the aviation community/general public is the Flight 

Standards District Office (FSDO). 

1-8 
 

Flight Standards District Office (FSDO) 

The FAA has approximately 80 FSDOs. [Figure 1-13] These 

offices provide information and services for the aviation 

community. FSDO phone numbers are listed in the telephone 

directory under Government Offices, DOT, FAA. Another 

convenient method of finding a local office is to use the 

FSDO locator available at: www.faa.gov/about/office_org/ 

field_offices/fsdo. 

In addition to accident investigation and the enforcement of 

aviation regulations, the FSDO is also responsible for the 

certification and surveillance of air carriers, air operators, 

flight schools/training centers, and airmen including pilots 

and flight instructors. Each FSDO is staffed by Aviation 

Safety Inspectors (ASIs) who play a key role in making the 

nation’s aviation system safe. 

Aviation Safety Inspector (ASI) 

The ASIs administer and enforce safety regulations and 

standards for the production, operation, maintenance, and/ 

or modification of aircraft used in civil aviation. They also 

specialize in conducting inspections of various aspects of the 

aviation system, such as aircraft and parts manufacturing, 

aircraft operation, aircraft airworthiness, and cabin safety. 

ASIs must complete a training program at the FAA Academy 

in Oklahoma City, Oklahoma, which includes airman 

evaluation and pilot testing techniques and procedures. ASIs 

also receive extensive on-the-job training and recurrent 

training on a regular basis. The FAA has approximately 

3,700 inspectors located in its FSDO offices. All questions 

concerning pilot certification (and/or requests for other 

aviation information or services) should be directed to the 

local FSDO. 

FAA Safety Team (FAASTeam) 

The FAA is dedicated to improving the safety of United 

States civilian aviation by conveying safety principles and 

practices through training, outreach, and education. The FAA 

Figure 1-13. Atlanta Flight Standards District Office (FSDO). 

Safety Team (FAASTeam) exemplifies this commitment. 

The FAASTeam has replaced the Aviation Safety Program 

(ASP), whose education of airmen on all types of safety 

subjects successfully reduced accidents. Its success led to 

its demise because the easy-to-fix accident causes have been 

addressed. To take aviation safety one step further, Flight 

Standards Service created the FAASTeam, which is devoted 

to reducing aircraft accidents by using a coordinated effort 

to focus resources on elusive accident causes. 

Each of the FAA’s nine regions has a Regional FAASTeam 

Office dedicated to this new safety program and managed by 

the Regional FAASTeam Manager (RFM). The FAASTeam 

is “teaming” up with individuals and the aviation industry 

to create a unified effort against accidents and tip the safety 

culture in the right direction. To learn more about this effort 

to improve aviation safety, to take a course at their online 

learning center, or to join the FAASTeam, visit their website 

at www.faasafety.gov. 

Obtaining Assistance from the FAA 

Information can be obtained from the FAA by phone, 

Internet/e-mail, or mail. To talk to the FAA toll-free 24 

hours a day, call 1-866-TELL-FAA (1-866-835-5322). To 

visit the FAA’s website, go to www.faa.gov. Individuals can 

also e-mail an FAA representative at a local FSDO office by 

accessing the staff e-mail address available via the “Contact 

FAA” link at the bottom of the FAA home page. Letters can 

be sent to: 

Federal Aviation Administration 

800 Independence Ave, SW 

Washington, DC 20591 

FAA Reference Material 

The FAA provides a variety of important reference material 

for the student, as well as the advanced civil aviation pilot. 

In addition to the regulations provided online by the FAA, 

several other publications are available to the user. Almost 

all reference material is available online at www.faa.gov in 

downloadable format. Commercial aviation publishers also 

provide published and online reference material to further 

aid the aviation pilot. 

Aeronautical Information Manual (AIM) 

The Aeronautical Information Manual (AIM) is the official 

guide to basic flight information and ATC procedures for the 

aviation community flying in the NAS of the United States. 

[Figure 1-14] An international version, containing parallel 

information as well as specific information on international 

airports, is also available. The AIM also contains information 

of interest to pilots, such as health and medical facts, flight 

1-9 
 

 

 

 

Figure 1-14. Aeronautical Information Manual. 

safety, a pilot/controller glossary of terms used in the 

system, and information on safety, accidents, and reporting 

of hazards. This manual is offered for sale on a subscription 

basis or is available online at: http://bookstore.gpo.gov. 

Order forms are provided at the beginning of the manual or 

online and should be sent to the Superintendent of Documents, 

United States Government Printing Office (GPO). The AIM 

is complemented by other operational publications that are 

available via separate subscriptions or online. 

Handbooks 

Handbooks are developed to provide specific information 

about a particular topic that enhances training or understanding. 

The FAA publishes a variety of handbooks that generally fall 

into three categories: aircraft, aviation, and examiners and 

inspectors. [Figure 1-15] These handbooks can be purchased 

from the Superintendent of Documents or downloaded at www. 

faa.gov/regulations_policies. Aviation handbooks are also 

published by various commercial aviation companies. Aircraft 

flight manuals commonly called Pilot Operating Handbooks 

(POH) are documents developed by the airplane manufacturer, 

approved by the FAA, and are specific to a particular make 

and model aircraft by serial number. This subject is covered 

in greater detail in Chapter 8, “Flight Manuals and Other 

Documents,” of this handbook. [Figure 1-16] 

Advisory Circulars (ACs) 

An AC is an informational document that the FAA wants to 

distribute to the aviation community. This can be in the form 

The Aeronautical Information Manual is designed to provide 

the aviation community with basic flight information and 

ATC procedures for use in the NAS of the United States. It 

also contains the fundamentals required in order to fly in the 

United States NAS, including items of interest to pilots 

concerning health/medical facts, factors affecting flight 

safety, etc. 

Aeronautical Information Manual (AIM) 

The Aircraft Flying Handbooks are designed as technical 

manuals to introduce basic pilot skills and knowledge that 

are essential for piloting aircraft. They provide information 

on transition to other aircraft and the operation of various 

aircraft systems. 

Aircraft Flying Handbooks (by category) 

The Aviation Instructor’s Handbook provides the foundation 

for beginning instructors to understand and apply the 

fundamentals of instructing. This handbook also provides 

aviation instructors with up-to-date information on learning 

and teaching, and how to relate this information to the task 

of conveying aeronautical knowledge and skills to students. 

Experienced aviation instructors also find the new and 

updated information useful for improving their effectiveness 

in training activities. 

Aviation Instructor’s Handbook 

The Instrument Flying Handbook is designed for use by 

instrument flight instructors and pilots preparing for 

instrument rating tests. Instructors find this handbook a 

valuable training aid as it includes basic reference material 

for knowledge testing and instrument flight training. 

Instrument Flying Handbook 

The Instrument Procedures Handbook is designed as a 

technical reference for professional pilots who operate 

under IFR in the NAS and expands on information contained 

in the Instrument Flying Handbook. 

Instrument Procedures Handbook 

Figure 1-15. A sample of handbooks available to the public. Most 

can be downloaded free of charge from the FAA website. 

of a text book used in a classroom or a one page document. 

Some ACs are free while others cost money. They are to 

be used for information only and are not regulations. The 

FAA website www.faa.gov/regulations_policies/advisory_ 

circulars/ provides a database that is a searchable repository 

of all aviation safety ACs. All ACs, current and historical, 

are provided and can be viewed as a portable document 

format (PDF) copy. 

ACs provide a single, uniform, agency-wide system that the 

FAA uses to deliver advisory material to FAA customers, 

industry, the aviation community, and the public. An AC 

may be needed to: 

•	 Provide an acceptable, clearly understood method for 

complying with a regulation 

1-10 
Figure 1-16. Pilot Operating Handbooks from manufacturers. 

•	 Standardize implementation of a regulation or 

harmonize implementation for the international 

aviation community 

•	 Resolve a general misunderstanding of a regulation 

•	 Respond to a request from some government entity, 

such as General Accounting Office, NTSB, or the 

Office of the Inspector General 

•	 Help the industry and FAA effectively implement a 

regulation 

•	 Explain requirements and limits of an FAA grant 

program 

•	 Expand on standards needed to promote aviation 

safety, including the safe operation of airports 

There are three parts to an AC number, as in 25-42C. The 

first part of the number identifies the subject matter area 

of the AC and corresponds to the appropriate 14 CFR part. 

For example, an AC on “Certification: Pilots and Flight and 

Ground Instructors” is numbered as AC 61-65E. Since ACs 

are numbered sequentially within each subject area, the 

second part of the number beginning with the dash identifies 

this sequence. The third part of the number is a letter assigned 

by the originating office and shows the revision sequence if 

an AC is revised. The first version of an AC does not have 

a revision letter. In Figure 1-17, this is the fifth revision, as 

designated by the “E.” 

Flight Publications 

The FAA, in concert with other government agencies, 

orchestrates the publication and changes to publications 

that are key to safe flight. Figure 1-18 illustrates some 

publications a pilot may use. 

Figure 1-17. Example of an Advisory Circular in its fifth revision. 

1-11 
• • • • • • • • • • • • • • • •

NEVADA 245

ALAMO LANDING FL(L92 D ) 2 W UTC 8( 7DT) N37°21.75 W115°11.67 LAS VEGAS

3719 NOTAM FILE RNO
 

RWY 14–325000X12 : 0 (DIRT)
 

RWY 14:Brush. RWY 32:Berm.
 

RWY 15–332500X7 : 0 (DIRT)
 

RWY 15:Berm. RWY 33:Berm.
 

AIRPORT REMARKSUnattended : . Uncontrolled vehicle access. No line of sight between rwy ends. Rwys 15–33 and Rwy

14–32 livestock in vicinity of rwys.

COMMUNICATIONS: CTA122. F 9

AUSTIN (TMT) 4 SW UTC 8( 7DT) N39°28.08 W117°11.72 LAS VEGAS

5735 B NOTAM FILE RNO H–3C, L–9B

RWY 18–36H6000X7 : 5 (ASPH) S–30 MIRL

RWY 18:REIL. PAPI(P2L)—GA 3.0 ° TCH 40 . RWY 36:REIL. PAPI(P2L)—GA 3.0 ° TCH 40 . Fence.
 

AIRPORT REMARKSUnattended : . Military acft opr in vicinity of arpt. ACTIVATE MIRL Rwy 18–36, PAPI Rwys 18 and 36,

REIL Rwy 18 and 36—CTAF.

WEATHER DATA SOURCES AWOS–3P : T 132.925 (775) 964–1144.

COMMUNICATIONS: CTA122. F 9

RADIO AIDS TO NAVIGATION NOTA: M FILE RNO.
 

MINA (H) VORTA115. C 1	 MVA Chan 98 N38 °33.92
 W118°01.97 019° 66.7 NM to fld. 7860/17E.

HIWAS.

BATTLE MOUNTAIN(BAM) 3 SE UTC 8( 7DT) N40°35.94 W116°52.46 SALT LAKE CITY

4536 B S4 FUEL 100LL, JET A NOTAM FILE RNO H–3C, L–9B, 11B

RWY 12–30H7302X15 : 0 (ASPH) S–30, D–104, 2S–132 MIRL IAP

RWY 03–21H7299X15 : 0 (ASPH) S–30, D–125, 2S–159 MIRL

RWY 03:VASI(V2R)—GA 3.0 ° TCH 26 .

RWY 21:PAPI(P4L)—GA 3.0 ° TCH 45 .

AIRPORT REMARKSAttende : d Oct–May 1500–0100Z ‡, Jun–Sep
 

1500–0200Z‡. After hrs call 775–635–2245. ACTIVATE MIRL Rwy
 

03–21 and Rwy 12–30, and perimeter lgts H1—CTAF.
 

WEATHER DATA SOURCES AWOS– : 3 119.45 (775) 635–8419.

COMMUNICATIONS: CTAF/UNICO 122.M8
 

MT LEWIS RCO122.65 (RENO RADIO)
 

SALT LAKE CENTER APP/DEP CO132.2 N 5

RADIO AIDS TO NAVIGATION NOTA: M FILE RNO.

(H) VORTACW112.2 BAM Chan 59 N40 °34.15
 

W116°55.34
 033° 2.8 NM to fld. 4536/18E.

VORTAC unusable:
 

050°–060° byd 30 NM blo 12,000
 

115°–165° byd 15 NM blo 12,000
 

255°–290° byd 15 NM blo 12,000
 

DME unusable 246 °–255° byd 34 NM blo 14,000

HELIPAD H1H60X6 : 0 (CONC)

HELIPAD H2H60X6 : 0 (CONC)

HELIPORT REMARKSRw: y H1 perimeter lights. ACTIVATE MIRL Rwy 03–21 and Rwy 12–30, and perimeter lgts

H1—CTAF.

, 

Figure 1-18. From left to right, a sectional VFR chart, IFR chart, and chart supplement U.S. (formerly Airport/Facility Directory) with 

a sample of a page from the supplement. 

Pilot and Aeronautical Information 

Notices to Airmen (NOTAMs) 

Notices to Airmen, or NOTAMs, are time-critical aeronautical 

information either temporary in nature or not sufficiently 

known in advance to permit publication on aeronautical 

charts or in other operational publications. The information 

receives immediate dissemination via the National Notice to 

Airmen (NOTAM) System. NOTAMs contain current notices 

to airmen that are considered essential to the safety of flight, 

as well as supplemental data affecting other operational 

publications. There are many different reasons that NOTAMs 

are issued. Following are some of those reasons: 

•	 Hazards, such as air shows, parachute jumps, kite 

flying, and rocket launches 

•	 Flights by important people such as heads of state 

•	 Closed runways 

•	 Inoperable radio navigational aids 

•	 Military exercises with resulting airspace restrictions 

•	 Inoperable lights on tall obstructions 

•	 Temporary erection of obstacles near airfields 

•	 Passage of flocks of birds through airspace (a NOTAM 

in this category is known as a BIRDTAM) 

•	 Notifications of runway/taxiway/apron status with 

respect to snow, ice, and standing water (a SNOWTAM) 

•	 Notification of an operationally significant change in 

volcanic ash or other dust contamination (an ASHTAM) 

•	 Software code risk announcements with associated 

patches to reduce specific vulnerabilities 

NOTAM information is generally classified into four 

categories: NOTAM (D) or NOTAMs that receive distant 

dissemination, distant and Flight Data Center (FDC) 

NOTAMs, Pointer NOTAMs, and Military NOTAMs 

pertaining to military airports or NAVAIDs that are part of the 

NAS. NOTAMs are available through Flight Service Station 

(FSS), Direct User Access Terminal Service (DUATS), 

private vendors, and many online websites. 

NOTAM (D) Information 

NOTAM (D) information is disseminated for all navigational 

facilities that are part of the NAS, and all public use airports, 

seaplane bases, and heliports listed in the Chart Supplement 

U.S. (formerly Airport/Facility Directory). NOTAM (D) 

information now includes such data as taxiway closures, 

personnel and equipment near or crossing runways, and 

airport lighting aids that do not affect instrument approach 

criteria, such as visual approach slope indicator (VASI). 

All D NOTAMs are required to have one of the following 

keywords as the first part of the text: RWY, TWY, RAMP, 

APRON, AD, OBST, NAV, COM, SVC, AIRSPACE, (U), 

or (O). [Figure 1-19] 

1-12 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

FDC NOTAMs 

FDC NOTAMs are issued by the National Flight Data 

Center and contain information that is regulatory in nature 

pertaining to flight including, but not limited to, changes 

to charts, procedures, and airspace usage. FDC NOTAMs 

refer to information that is regulatory in nature and includes 

the following: 

•	 Interim IFR flight procedures: 

1.	 Airway structure changes 

2.	 Instrument approach procedure changes (excludes 

Departure Procedures (DPs) and Standard 

Terminal Arrivals (STARs) 

3.	 Airspace changes in general 

4.	 Special instrument approach procedure changes 

•	 Temporary flight restrictions (discussed in Chapter 15): 

1.	 Disaster areas 

2.	 Special events generating a high degree of interest 

3.	 Hijacking 

•	 Flight restrictions in the proximity of the President 

and other parties 

•	 14 CFR part 139 certificated airport condition changes 

•	 Snow conditions affecting glide slope operation 

•	 Air defense emergencies 

•	 Emergency flight rules 

•	 Substitute airway routes 

•	 Special data 

•	 U.S. Government charting corrections 

•	 Laser activity 

NOTAM Composition 

NOTAMs contain the elements below from left to right in 

the following order: 

•	 An exclamation point (!) 

•	 Accountability Location (the identifier of the 

accountability location) 

Keyword Example Meaning 

RWY RWY 3/21 CLSD 

TWY TWY F LGTS OTS 

RAMP RAMP TERMINAL EAST SIDE 

CONSTRUCTION 

APRON APRON SW TWY C NEAR 

HANGARS CLSD 

AD AD ABN OTS 

OBST OBST TOWER 283 (245 AGL) 2.2 

S LGTS OTS (ASR 1065881) TIL 

0707272300 

NAV NAV VOR OTS 

COM COM ATIS OTS 

SVC SVC TWR 1215-0330 

MON -FRI/1430-2300 SAT/1600-0100 

SUN TIL 0707300100 

SVC FUEL UNAVBL TIL 0707291600 

SVC CUSTOMS UNAVBL TIL 0708150800 

AIRSPACE AIRSPACE AIRSHOW ACFT 

5000/BLW 5 NMR AIRPORT 

AVOIDANCE ADZD WEF 

0707152000-0707152200 

U ORT 6K8 (U) RWY ABANDONED VEHICLE 

O LOZ LOZ (O) CONTROLLED BURN OF 

HOUSE 8 NE APCH END RWY 23 WEF 

0710211300-0710211700 

Runways 3 and 21 are closed to aircraft. 

Taxiway F lights are out of service. 

The ramp in front of the east side of the terminal has ongoing 

construction. 

The apron near the southwest taxiway C in front of the hangars 

is closed. 

Aerodromes: The airport beacon is out of service. 

Obstruction: The lights are out of service on a tower that is 283 feet 

above mean sea level (MSL) or 245 feet above ground level (AGL) 

2.2 statute miles south of the field. The FCC antenna structure 

registration (ASR) number is 1065881. The lights will be returned to 

service 2300 UTC (Coordinated Universal Time) on July 27, 2007. 

Navigation: The VOR located on this airport is out of service. 

Communications: The Automatic Terminal information Service 

(ATIS) is out of service. 

Service: The control tower has new operating hours, 1215-0330 

UTC Monday Thru Friday. 1430-2300 UTC on Saturday and 

1600-0100 UTC on Sunday until 0100 on July 30, 2007. 

Service: All fuel for this airport is unavailable until July 29, 2007, 

at 1600 UTC. 

Service: United States Customs service for this airport will not be 

available until August 15, 2007, at 0800 UTC. 

Airspace. There is an airshow being held at this airport with aircraft 

flying 5,000 feet and below within a 5 nautical mile radius. 

Avoidance is advised from 2000 UTC on July 15, 2007, until 2200 

on July 15, 2007. 

Unverified aeronautical information. 

Other aeronautical information received from any authorized source 

that may be beneficial to aircraft operations and does not meet 

defined NOTAM criteria. 

Figure 1-19. NOTAM (D) Information. 

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•	 Affected Location (the identifier of the affected facility 

or location) 

•	 KEYWORD (one of the following: RWY, TWY, 

RAMP, APRON, AD, COM, NAV, SVC, OBST, 

AIRSPACE, (U) and (O)) 

•	 Surface Identification (optional—this shall be the 

runway identification for runway related NOTAMs, 

the taxiway identification for taxiway-related 

NOTAMs, or the ramp/apron identification for ramp/ 

apron-related NOTAMs) 

•	 Condition (the condition being reported) 

•	 Time (identifies the effective time(s) of the NOTAM 

condition) 

Altitude and height are in feet mean sea level (MSL) up to 

17,999; e.g., 275, 1225 (feet and MSL is not written), and in 

flight levels (FL) for 18,000 and above; e.g., FL180, FL550. 

When MSL is not known, above ground level (AGL) will be 

written (304 AGL). 

When time is expressed in a NOTAM, the day begins at 0000 

and ends at 2359. Times used in the NOTAM system are 

universal time coordinated (UTC) and shall be stated in 10 

digits (year, month, day, hour, and minute). The following 

are two examples of how the time would be presented: 

!DCA LDN NAV VOR OTS WEF 

0708051600-0708052359 

!DCA LDN NAV VOR OTS WEF 

0709050000-0709050400 

NOTAM Dissemination and Availability 

The system for disseminating aeronautical information is 

made up of two subsystems: the Airmen's Information System 

(AIS) and the NOTAM System. The AIS consists of charts and 

publications and is disseminated by the following methods: 

Aeronautical charts depicting permanent baseline data: 

•	 IFR Charts—EnrouteHighAltitudeConterminousU.S., 

Enroute Low Altitude Conterminous U.S., Alaska 

Charts, and Pacific Charts 

•	 U.S. Terminal Procedures—Departure Procedures 

(DPs), Standard Terminal Arrivals (STARs) and 

Standard Instrument Approach Procedures (SIAPs) 

•	 VFR Charts—Sectional Aeronautical Charts, Terminal 

Area Charts (TAC), and World Aeronautical Charts 

(WAC) 

Flight information publications outlining baseline data: 

•	 Notices to Airmen (NTAP)—Published by System 

Operations Services, System Operations and Safety, 

Publications, every 28 days) 

•	 Chart Supplement U.S. (formerly Airport/Facility 

Directory) 

•	 Pacific Chart Supplement 

•	 Alaska Supplement 

•	 Alaska Terminal 

•	 Aeronautical Information Manual (AIM) 

NOTAMs are available in printed form through subscription 

from the Superintendent of Documents, from an FSS, or 

online at PilotWeb (www.pilotweb.nas.faa.gov), which 

provides access to current NOTAM information. Local 

airport NOTAMs can be obtained online from various 

websites. Some examples are www.fltplan.com and www. 

aopa.org/whatsnew/notams.html. Most sites require a free 

registration and acceptance of terms but offer pilots updated 

NOTAMs and TFRs. 

Safety Program Airmen Notification System (SPANS) 

In 2004, the FAA launched the Safety Program Airmen 

Notification System (SPANS), an online event notification 

system that provides timely and easy-to-assess seminar 

and event information notification for airmen. The SPANS 

system is taking the place of the current paper-based mail 

system. This provides better service to airmen while reducing 

costs for the FAA. Anyone can search the SPANS system 

and register for events. To read more about SPANS, visit 

www.faasafety.gov/spans. 

Aircraft Classifications and Ultralight

Vehicles 

The FAA uses various ways to classify or group machines 

operated or flown in the air. The most general grouping uses 

the term aircraft. This term is in 14 CFR 1.1 and means a 

device that is used or intended to be used for flight in the air. 

Ultralight vehicle is another general term the FAA uses. 

This term is defined in 14 CFR 103. As the term implies, 

powered ultralight vehicles must weigh less than 254 pounds 

empty weight and unpowered ultralight vehicles must 

weigh less than 155 pounds. Rules for ultralight vehicles 

are significantly different from rules for aircraft; ultralight 

vehicle certification, registration, and operation rules are also 

contained in 14 CFR 103. 

1-14 
 

 

 

 

 

The FAA differentiates aircraft by their characteristics and center of gravity with respect to the wing. Flight control 

physical properties. Key groupings defined in 14 CFR 1.1 of the aircraft depends on the wing's ability to flexibly 

include: deform rather than the use of control surfaces. 

•	 Airplane—an engine-driven fixed-wing aircraft 

heavier than air, that is supported in flight by the 

dynamic reaction of the air against its wings. 

•	 Glider—a heavier-than-air aircraft, that is supported 

in flight by the dynamic reaction of the air against its 

lifting surfaces and whose free flight does not depend 

principally on an engine. 

•	 Lighter-than-air aircraft—an aircraft that can rise and 

remain suspended by using contained gas weighing 

less than the air that is displaced by the gas. 

- Airship—an engine-driven lighter-than-air 

aircraft that can be steered. 

- Balloon—a lighter-than-air aircraft that is not 

engine driven, and that sustains flight through the 

use of either gas buoyancy or an airborne heater. 

•	 Powered-lift—a heavier-than-air aircraft capable of 

vertical takeoff, vertical landing, and low speed flight 

that depends principally on engine-driven lift devices 

or engine thrust for lift during these flight regimes and 

on nonrotating airfoil(s) for lift during horizontal flight. 

•	 Powered parachute—a powered aircraft comprised of 

a flexible or semi-rigid wing connected to a fuselage 

so that the wing is not in position for flight until 

the aircraft is in motion. The fuselage of a powered 

parachute contains the aircraft engine, a seat for each 

occupant and Is attached to the aircraft's landing gear. 

•	 Rocket—an aircraft propelled by ejected expanding 

gases generated in the engine from self-contained 

propellants and not dependent on the intake of outside 

substances. It includes any part which becomes 

separated during the operation. 

•	 Rotorcraft—a heavier-than-air aircraft that depends 

principally for its support in flight on the lift generated 

by one or more rotors. 

- Gyroplane—a rotorcraft whose rotors are not 

engine-driven, except for Initial starting, but 

are made to rotate by action of the air when 

the rotorcraft Is moving; and whose means of 

propulsion, consisting usually of conventional 

propellers, is Independent of the rotor system. 

- Helicopter—a rotorcraft that, for its horizontal 

motion, depends principally on its engine-driven 

rotors. 

•	 Weight-shift-control—a powered aircraft with a framed 

pivoting wing and a fuselage controllable only in pitch 

and roll by the pilot's ability to change the aircraft’s 

Size and weight are other methods used in 14 CFR 1.1 to 

group aircraft: 

•	 Large aircraft—an aircraft of more than 12,500 

pounds, maximum certificated takeoff weight. 

•	 Light-sport aircraft (LSA)—an aircraft, other than 

a helicopter or powered-lift that, since its original 

certification, has continued to meet the definition in 

14 CFR 1.1. (LSA can include airplanes, airships, 

balloons, gliders, gyro planes, powered parachutes, 

and weight-shift-control.) 

•	 Small Aircraft—aircraft of 12,500 pounds or less, 

maximum certificated takeoff weight. 

We also use broad classifications of aircraft with respect to 

the certification of airmen or with respect to the certification 

of the aircraft themselves. See the next section, Pilot 

Certifications, and Chapter 3, for further discussion of 

certification. These definitions are in 14 CFR 1.1: 

•	 Category 

1. As used with respect to the certification, ratings, 

privileges, and limitations of airmen, means a 

broad classification of aircraft. Examples include: 

airplane; rotorcraft; glider; and lighter-than-air; 

and 

2.	 As used with respect to the certification of 

aircraft, means a grouping of aircraft based upon 

intended use or operating limitations. Examples 

include: transport, normal, utility, acrobatic, 

limited, restricted, and provisional. 

• Class 

1. As used with respect to the certification, ratings, 

privileges, and limitations of airmen, means a 

classification of aircraft within a category having 

similar operating characteristics. Examples 

Include: single engine; multiengine; land; water; 

gyroplane, helicopter, airship, and free balloon; 

and 

2.	 As used with respect to the certification of 

aircraft, means a broad grouping of aircraft having 

similar characteristics of propulsion, flight, or 

landing. Examples include: airplane, rotorcraft, 

gilder, balloon, landplane, and seaplane. 

•	 Type 

1. As used with respect to the certification, ratings, 

privileges, and limitations of airmen, means 

1-15 
 

 

a specific make and basic model of aircraft, 

Including modifications thereto that do not 

change its handling or flight characteristics. 

Examples include: 737-700, G-IV, and 1900; and 

2.	 As used with respect to the certification of 

aircraft, means those aircraft which are similar 

in design. Examples include: 737-700 and 737­

700C; G-IV and G-IV-X; and 1900 and 1900C. 

This system of definitions allows the FAA to group and 

regulate aircraft to provide for their safe operation. 

Pilot Certifications 

The type of intended flying influences what type of pilot’s 

certificate is required. Eligibility, training, experience, 

and testing requirements differ depending on the type of 

certificates sought. [Figure 1-20] Each type of pilot’s 

certificate has privileges and limitations that are inherent 

within the certificate itself. However, other privileges and 

limitations may be applicable based on the aircraft type, 

operation being conducted, and the type of certificate. 

For example, a certain certificate may have privileges and 

limitations under 14 CFR part 61 and part 91. 

Figure 1-20. Front side (top) and back side (bottom) of an airman 

certificate issued by the FAA. 

•	 Privileges—define where and when the pilot may fly, 

with whom they may fly, the purpose of the flight, and 

the type of aircraft they are allowed to fly. 

•	 Limitations—the FAA may impose limitations on a 

pilot certificate if, during training or the practical test, 

the pilot does not demonstrate all skills necessary to 

exercise all privileges of a privilege level, category, 

class, or type rating. 

Endorsements, a form of authorization, are written to establish 

that the certificate holder has received training in specific skill 

areas. Endorsements are written and signed by an authorized 

individual, usually a certificated flight instructor (CFI), and 

are based on aircraft classification. [Figure 1-21] 

Sport Pilot 

To become a sport pilot, the student pilot is required to have 

flown, at a minimum, the following hours depending upon 

the aircraft: 

•	 Airplane: 20 hours 

•	 Powered Parachute: 12 hours 

•	 Weight-Shift Control (Trikes): 20 hours 

•	 Glider: 10 hours 

•	 Rotorcraft (gyroplane only): 20 hours 

•	 Lighter-Than-Air: 20 hours (airship) or 7 hours 

(balloon) 

To earn a Sport Pilot Certificate, one must: 

•	 Be at least 16 years old to become a student sport pilot 

(14 years old for gliders or balloons) 

•	 Be at least 17 years old to test for a sport pilot 

certificate (16 years old for gliders or balloons) 

•	 Be able to read, write, and understand the English 

language 

•	 Hold a current and valid driver’s license as evidence 

of medical eligibility 

When operating as a sport pilot, some of the following 

privileges and limitations may apply. 

Privileges: 

•	 Operate as pilot in command (PIC) of a light-sport 

aircraft 

•	 Carry a passenger and share expenses (fuel, oil, airport 

expenses, and aircraft rental) 

•	 Fly during the daytime using VFR, a minimum of 

3 statute miles visibility and visual contact with the 

ground are required 

1-16 
Recreational pilot to conduct solo flights for the purpose of obtaining an additional certificate or rating while under 

the supervision of an authorized flight instructor: section 61.101(i). 

I certify that (First name, MI, Last name) has received the required training of section 61.87 in a (make and model 

aircraft). I have determined he/she is prepared to conduct a solo flight on (date) under the following conditions: (List 

all conditions which require endorsement, e.g., flight which requires communication with air traffic control, flight in an 

aircraft for which the pilot does not hold a category/class rating, etc.). 

Figure 1-21. Example endorsement for a recreational pilot to conduct solo flights for the purpose of determining an additional certificate 

or rating. 

Limitations: As a recreational pilot, cross-country flight is limited to a 50 

NM range from the departure airport but is permitted with •	 Prohibited from flying in Class A airspace additional training per 14 CFR part 61, section 61.101(c). 

•	 Prohibited from flying in Class B, C, or D airspace Additionally, recreational pilots are restricted from flying 

until you receive training and a logbook endorsement at night and flying in airspace where communications with 

from an instructor ATC are required. 

•	 No flights outside the United States without prior The minimum aeronautical experience requirements for a permission from the foreign aviation authority recreational pilot license involve: •	 May not tow any object •	 30 hours of flight time including at least: •	 No flights while carrying a passenger or property for •	 15 hours of dual instruction compensation or hire 

•	 2 hours of en route training •	 Prohibited from flying in furtherance of a business 

•	 3 hours in preparation for the practical test 

The sport pilot certificate does not list aircraft category •	 3 hours of solo flight and class ratings. After successfully passing the practical 

test for a sport pilot certificate, regardless of the light-sport When operating as a recreational pilot, some of the following aircraft privileges you seek, the FAA will issue you a sport privileges and limitations may apply. pilot certificate without any category and class ratings. The 

Instructor will provide you with the appropriate logbook 

endorsement for the category and class of aircraft in which Privileges: 

you are authorized to act as pilot in command. •	 Carry no more than one passenger; 

•	 Not pay less than the pro rata share of the operating Recreational Pilot 

expenses of a flight with a passenger, provided the To become a recreational pilot, one must: expenses involve only fuel, oil, airport expenses, or 

•	 Be at least 17 years old aircraft rental fees 

•	 Be able to read, write, speak, and understand the 

English language Limitations: 

•	 Pass the required knowledge test •	 A recreational pilot may not act as PIC of an aircraft 

that is certificated for more than four occupants or has •	 Meet the aeronautical experience requirements in more than one powerplant. either a single-engine airplane, a helicopter, or a 

gyroplane. Private Pilot •	 Obtain a logbook endorsement from an instructor A private pilot is one who flies for pleasure or personal 

•	 Pass the required practical test business without accepting compensation for flying except 

in some very limited, specific circumstances. The Private •	 Obtain a third-class medical certificate issued under 

Pilot Certificate is the certificate held by the majority of 14 CFR part 67 

1-17 
active pilots. It allows command of any aircraft (subject 

to appropriate ratings) for any noncommercial purpose 

and gives almost unlimited authority to fly under VFR. 

Passengers may be carried and flight in furtherance of a 

business is permitted; however, a private pilot may not be 

compensated in any way for services as a pilot, although 

passengers can pay a pro rata share of flight expenses, such 

as fuel or rental costs. If training under 14 CFR part 61, 

experience requirements include at least 40 hours of piloting 

time, including 20 hours of flight with an instructor and 10 

hours of solo flight. [Figure 1-22] 

Commercial Pilot 

A commercial pilot may be compensated for flying. Training 

for the certificate focuses on a better understanding of 

aircraft systems and a higher standard of airmanship. The 

Commercial Pilot Certificate itself does not allow a pilot 

to fly in instrument meteorological conditions (IMC), and 

commercial pilots without an instrument rating are restricted 

to daytime flight within 50 NM when flying for hire. 

A commercial airplane pilot must be able to operate 

a complex airplane, as a specific number of hours of 

complex (or turbine-powered) aircraft time are among 

the prerequisites, and at least a portion of the practical 

examination is performed in a complex aircraft. A complex 

aircraft must have retractable landing gear, movable flaps, 

and a controllable-pitch propeller. See 14 CFR part 61, 

section 61.31(e) for additional information. [Figure 1-23] 

Airline Transport Pilot 

The airline transport pilot (ATP) is tested to the highest level 

of piloting ability. The ATP certificate is a prerequisite for 

serving as a PIC and second in command (SIC) of scheduled 

airline operations. It is also a prerequisite for serving as a PIC 

in select charter and fractional operations. The minimum pilot 

experience is 1,500 hours of flight time. In addition, the pilot 

must be at least 23 years of age, be able to read, write, speak, 

Figure 1-23. A complex aircraft. 

and understand the English language, and be “of good moral 

standing.” A pilot may obtain an ATP certificate with restricted 

privileges enabling him/her to serve as an SIC in scheduled 

airline operations. The minimum pilot experience is reduced 

based upon specific academic and flight training experience. 

The minimum age to be eligible is 21 years. [Figure 1-24] 

Selecting a Flight School 

Selecting a flight school is an important consideration in 

the flight training process. FAA-approved training centers, 

FAA-approved pilot schools, noncertificated flying schools, 

and independent flight instructors conduct flight training in 

the United States. All flight training is conducted under the 

auspices of the FAA following the regulations outlined in 

14 CFR parts 142, 141, or 61. Training centers, also referred 

to as flight academies, operate under 14 CFR part 142 and 

are certificated by the FAA. Application for certification 

is voluntary and the training center must meet stringent 

requirements for personnel, equipment, maintenance, 

facilities, and must teach a curriculum approved by the 

FAA. Training centers typically utilize a number of flight 

simulation training devices as part of its curricula. Flight 

training conducted at a training center is primarily done 

under contract to airlines and other commercial operators 

in transport or turbine aircraft, however many also provide 

Figure 1-22. A typical aircraft a private pilot might fly. Figure 1-24. Type of aircraft flown by an airline transport pilot. 

1-18 
flight training for the private pilot certificate, commercial 

pilot certificate, instrument rating, and ATP certificate. 

Flight schools operating under 14 CFR part 141 are 

certificated by the FAA. Application for certification is 

voluntary and the school must meet stringent requirements 

for personnel, equipment, maintenance, facilities, and must 

teach an established curriculum, which includes a training 

course outline (TCO) approved by the FAA. The certificated 

schools may qualify for a ground school rating and a flight 

school rating. In addition, the school may be authorized 

to give its graduates practical (flight) tests and knowledge 

(computer administered written) tests. The FAA Pilot School 

Search database located at http://av-info.faa.gov/PilotSchool. 

asp, lists certificated ground and flight schools and the pilot 

training courses each school offers. 

Enrollment in a 14 CFR part 141 flight school ensures 

quality, continuity, and offers a structured approach to flight 

training because these facilities must document the training 

curriculum and have their flight courses approved by the 

FAA. These strictures allow 14 CFR part 141 schools to 

complete certificates and ratings in fewer flight hours, which 

can mean a savings on the cost of flight training for the 

student pilot. For example, the minimum requirement for a 

Private Pilot Certificate is 35 hours in a part 141-certificated 

school and 40 hours in a part 61-certificated school. (This 

difference may be insignificant for a Private Pilot Certificate 

because the national average indicates most pilots require 60 

to 75 hours of flight training.) 

Many excellent flight schools find it impractical to qualify 

for the FAA part 141 certificates and are referred to as part 

61 schools. 14 CFR part 61 outlines certificate and rating 

requirements for pilot certification through noncertificated 

schools and individual flight instructors. It also states what 

knowledge-based training must be covered and how much 

flight experience is required for each certificate and rating. 

Flight schools and flight instructors who train must adhere 

to the statutory requirements and train pilots to the standards 

found in 14 CFR part 61. 

One advantage of flight training under 14 CFR part 61 is its 

flexibility. Flight lessons can be tailored to the individual 

student, because 14 CFR part 61 dictates the required 

minimum flight experience and knowledge-based training 

necessary to gain a specific pilot’s license, but it does not 

stipulate how the training is to be organized. This flexibility 

can also be a disadvantage because a flight instructor who 

fails to organize the flight training can cost a student pilot 

time and expense through repetitious training. One way for 

a student pilot to avoid this problem is to ensure the flight 

instructor has a well-documented training syllabus. 

How To Find a Reputable Flight Program 

To obtain information about pilot training, contact the local 

FSDO, which maintains a current file on all schools within its 

district. The choice of a flight school depends on what type of 

certificate is sought, and whether an individual wishes to fly 

as a sport pilot or wishes to pursue a career as a professional 

pilot. Another consideration is the amount of time that can 

be devoted to training. Ground and flight training should 

be obtained as regularly and frequently as possible because 

this assures maximum retention of instruction and the 

achievement of requisite proficiency. 

Do not make the determination based on financial concerns 

alone, because the quality of training is very important. 

Prior to making a final decision, visit the schools under 

consideration and talk with management, instructors, and 

students. Request a personal tour of the flight school facility. 

Be inquisitive and proactive when searching for a flight 

school, do some homework, and develop a checklist of 

questions by talking to pilots and reading articles in flight 

magazines. The checklist should include questions about 

aircraft reliability and maintenance practices, and questions 

for current students such as whether or not there is a safe, 

clean aircraft available when they are scheduled to fly. 

Questions for the training facility should be aimed at 

determining if the instruction fits available personal time. 

What are the school’s operating hours? Does the facility have 

dedicated classrooms available for ground training required 

by the FAA? Is there an area available for preflight briefings, 

postflight debriefings, and critiques? Are these rooms private 

in nature in order to provide a nonthreatening environment 

in which the instructor can explain the content and outcome 

of the flight without making the student feel self-conscious? 

Examine the facility before committing to any flight training. 

Evaluate the answers on the checklist, and then take time to 

think things over before making a decision. This proactive 

approach to choosing a flight school will ensure a student 

pilot contracts with a flight school or flight instructor best 

suited to their individual needs. 

How To Choose a Certificated Flight Instructor (CFI) 

Whether an individual chooses to train under 14 CFR part 

141 or part 61, the key to an effective flight program is the 

quality of the ground and flight training received from the 

CFI. The flight instructor assumes total responsibility for 

training an individual to meet the standards required for 

certification within an ever-changing operating environment. 

A CFI should possess an understanding of the learning 

process, knowledge of the fundamentals of teaching, and 

1-19 
 

 

the ability to communicate effectively with the student pilot. 

During the certification process, a flight instructor applicant 

is tested on the practical application of these skills in specific 

teaching situations. The flight instructor is crucial to the 

scenario-based training program endorsed by the FAA. He 

or she is trained to function in the learning environment as an 

advisor and guide for the learner. The duties, responsibilities, 

and authority of the CFI include the following: 

•	 Orient the student to the scenario-based training 

system 

•	 Help the student become a confident planner and 

inflight manager of each flight and a critical evaluator 

of their own performance 

•	 Help the student understand the knowledge 

requirements present in real world applications 

•	 Diagnose learning difficulties and help the student 

overcome them 

•	 Evaluate student progress and maintain appropriate 

records 

•	 Provide continuous review of student learning 

Should a student pilot find the selected CFI is not training in 

a manner conducive for learning, or the student and CFI do 

not have compatible schedules, the student pilot should find 

another CFI. Choosing the right CFI is important because the 

quality of instruction and the knowledge and skills acquired 

from their flight instructor affect a student pilot’s entire 

flying career. 

The Student Pilot 

The first step in becoming a pilot is to select a type of aircraft. 

FAA rules for obtaining a pilot’s certificate differ depending 

on the type of aircraft flown. Individuals can choose among 

airplanes, gyroplanes, weight-shift, helicopters, powered 

parachutes, gliders, balloons, or airships. A pilot does not 

need a certificate to fly ultralight vehicles. 

Basic Requirements 

A student pilot is one who is being trained by an instructor 

pilot for his or her first full certificate, and is permitted 

to fly alone (solo) under specific, limited circumstances. 

Before a student pilot may be endorsed to fly solo, that 

student must have a Student Pilot Certificate. There are 

multiple ways that an aspiring pilot can obtain their Student 

Pilot Certificate. The application may be processed by an 

FAA inspector or technician, an FAA-Designated Pilot 

Examiner, a Certified Flight Instructor (CFI), or an Airman 

Certification Representative (ACR). If the application is 

completed electronically, the authorized person will submit 

the application to the FAA’s Airman Certification Branch 

(AFS-760) in Oklahoma City, OK, via the Integrated 

Airman Certification and Rating Application (IACRA). If 

the application is completed on paper, it must be sent to 

the local Flight Standards District Office (FSDO), who will 

forward it to AFS-760. Once the application is processed, the 

applicant will receive the Student Pilot Certificate by mail at 

the address provided on the application. 

The aforementioned process will become effective on April 

1, 2016. The new certificate will be printed on a plastic card, 

which will replace the paper certificate that was issued in the 

past. The plastic card certificate will not have an expiration 

date. Paper certificates issued prior to the new process will 

still expire according to the date on the certificate; however, 

under the new process, paper certificates cannot be renewed. 

Once the paper certificate expires, the Student Pilot must 

submit a new application under the new process. Another 

significant change in the new process is that flight instructors 

will now make endorsements for solo privileges in the 

Student Pilot’s logbook, instead of endorsing the Student 

Pilot Certificate. 

To be eligible for a Student Pilot Certificate, the applicant 

must: 

•	 Be at least 16 years of age (14 years of age to pilot a 

glider or balloon). 

•	 Be able to read, speak, write, and understand the 

English language. 

Medical Certification Requirements 

The second step in becoming a pilot is to obtain a medical 

certificate (if the choice of aircraft is an airplane, helicopter, 

gyroplane, or an airship). (The FAA suggests the individual 

get a medical certificate before beginning flight training to 

avoid the expense of flight training that cannot be continued 

due to a medical condition.) Balloon or glider pilots do not 

need a medical certificate, but do need to write a statement 

certifying that no medical defect exists that would prevent 

them from piloting a balloon or glider. The new sport pilot 

category does not require a medical examination; a driver’s 

license can be used as proof of medical competence. 

Applicants who fail to meet certain requirements or who 

have physical disabilities which might limit, but not 

prevent, their acting as pilots, should contact the nearest 

FAA office. Anyone requesting an FAA Medical Clearance, 

Medical Certificate, or Student Pilot Medical Certificate can 

electronically complete an application through the FAA’s 

MedXPress system available at https://medxpress.faa.gov/. 

A medical certificate is obtained by passing a physical 

examination administered by a doctor who is an FAAauthorized AME. There are approximately 6,000 

FAA-authorized AMEs in the nation. To find an AME near 

1-20 
you, go to the FAA’s AME locator at www.faa.gov/pilots/ 

amelocator/. Medical certificates are designated as first class, 

second class, or third class. Generally, first class is designed 

for the airline transport pilot; second class for the commercial 

pilot; and third class for the student, recreational, and private 

pilot. A Student Pilot Certificate can be processed by an FAA 

inspector or technician, an FAA Designated pilot examiner 

(DPE), an Airman Certification Representative (ACR), or a 

Certified Flight Instructor (CFI). This certificate allows an 

individual who is being trained by a flight instructor to fly 

alone (solo) under specific, limited circumstances and must 

be carried with the student pilot while exercising solo flight 

privileges. The Student Pilot Certificate is only required 

when exercising solo flight privileges. The new plastic 

student certificate does not have an expiration date. For 

airmen who were issued a paper certificate, that certificate 

will remain valid until its expiration date. A paper certificate 

cannot be renewed. When the paper certificate expires, a new 

application must be completed via the IACRA system, and 

a new plastic certificate will be issued. 

Student Pilot Solo Requirements 

Once a student has accrued sufficient training and experience, 

a CFI can endorse the student’s logbook to authorize limited 

solo flight in a specific type (make and model) of aircraft. 

A student pilot may not carry passengers, fly in furtherance 

of a business, or operate an aircraft outside of the various 

endorsements provided by the flight instructor. There is no 

minimum aeronautical knowledge or experience requirement 

for the issuance of a Student Pilot Certificate, however, the 

applicant must be at least 16 years of age (14 years of age for 

a pilot for glider or balloon), and they must be able to read, 

speak, write and understand the English language. There are, 

however, minimum aeronautical knowledge and experience 

requirements for student pilots to solo. 

Becoming a Pilot 

The course of instruction a student pilot follows depends on 

the type of certificate sought. It should include the ground and 

flight training necessary to acquire the knowledge and skills 

required to safely and efficiently function as a certificated 

pilot in the selected category and class of aircraft. The 

specific knowledge and skill areas for each category and 

class of aircraft are outlined in 14 CFR part 61. Eligibility, 

aeronautical knowledge, proficiency, and aeronautical 

requirements can be found in 14 CFR part 61. 

•	 Recreational Pilot, see subpart D 

•	 Private Pilot, see subpart E 

•	 Sport Pilot, see subpart J 

The knowledge-based portion of training is obtained through 

FAA handbooks such as this one, textbooks, and other sources 

of training and testing materials which are available in print 

form from the Superintendent of Documents, GPO, and 

online at the Regulatory Support Division: www.faa.gov/ 

about/office_org/headquarters_offices/avs/offices/afs/afs600. 

The CFI may also use commercial publications as a source 

of study materials, especially for aircraft categories where 

government materials are limited. A student pilot should 

follow the flight instructor’s advice on what and when to 

study. Planning a definite study program and following it as 

closely as possible will help in scoring well on the knowledge 

test. Haphazard or disorganized study habits usually result 

in an unsatisfactory score. 

In addition to learning aeronautical knowledge, such as the 

principles of flight, a student pilot is also required to gain 

skill in flight maneuvers. The selected category and class of 

aircraft determines the type of flight skills and number of 

flight hours to be obtained. There are four steps involved in 

learning a flight maneuver: 

•	 The CFI introduces and demonstrates flight maneuver 

to the student. 

•	 The CFI talks the student pilot through the maneuver. 

•	 The student pilot practices the maneuver under CFI 

supervision. 

•	 The CFI authorizes the student pilot to practice the 

maneuver solo. 

Once the student pilot has shown proficiency in the required 

knowledge areas, flight maneuvers, and accrued the required 

amount of flight hours, the CFI endorses the student pilot 

logbook, which allows the student pilot to take the written 

and practical tests for pilot certification. 

Knowledge and Skill Tests 

Knowledge Tests 

The knowledge test is the computer portion of the tests taken 

to obtain pilot certification. The test contains questions of 

the objective, multiple-choice type. This testing method 

conserves the applicant's time, eliminates any element of 

individual judgment in determining grades, and saves time 

in scoring. 

FAA Airman Knowledge Test Guides for every type of pilot 

certificate address most questions you may have regarding 

the knowledge test process. The guides are available online (free of charge) at http://www.faa.gov/training_testing/ 

testing/test_guides/. 

1-21 
When To Take the Knowledge Test 

The knowledge test is more meaningful to the applicant 

and more likely to result in a satisfactory grade if it is taken 

after beginning the flight portion of the training. Therefore, 

the FAA recommends the knowledge test be taken after the 

student pilot has completed a solo cross-country flight. The 

operational knowledge gained by this experience can be used 

to the student’s advantage in the knowledge test. The student 

pilot’s CFI is the best person to determine when the applicant 

is ready to take the knowledge test. 

Practical Test 

The FAA has developed PTS for FAA pilot certificates 

and associated ratings. [Figure 1-25] In 2015, the FAA 

began transitioning to the ACS approach. The ACS is 

essentially an “enhanced” version of the PTS. It adds taskspecific knowledge and risk management elements to each 

PTS Area of Operation and Task. The result is a holistic, 

integrated presentation of specific knowledge, skills, and 

risk management elements and performance metrics for each 

Area of Operation and Task The ACS evaluation program 

will eventually replace the PTS program for evaluating and 

certifying pilots. 

The practical tests are administered by FAA ASIs and DPEs. 

Title 14 CFR part 61 specifies the areas of operation in which 

knowledge and skill must be demonstrated by the applicant. 

Since the FAA requires all practical tests be conducted in 

accordance with the appropriate PTS and the policies set forth 

in the Introduction section of the PTS book. The pilot applicant 

should become familiar with this book during training. 

The PTS book is a testing document and not intended to be 

a training syllabus. An appropriately-rated flight instructor 

is responsible for training the pilot applicant to acceptable 

standards in all subject matter areas, procedures, and 

maneuvers. Descriptions of tasks and information on how to 

perform maneuvers and procedures are contained in reference 

and teaching documents such as this handbook. A list of 

reference documents is contained in the Introduction section 

of each PTS book. Copies may obtained by: 

•	 Downloading from the FAA website at www.faa.gov 

•	 Purchasing print copies from the GPO, Pittsburgh, 

Pennsylvania, or via their official online bookstore 

at www.access.gpo.gov 

The flight proficiency maneuvers listed in 14 CFR part 61 

are the standard skill requirements for certification. They 

are outlined in the PTS as “areas of operation.” These are 

phases of the practical test arranged in a logical sequence 

within the standard. They begin with preflight preparation 

and end with postflight procedures. Each area of operation 

FAA-S-8081-12C

FAA-S-8081-14B

FAA-S-8081-8B

Figure 1-25. Examples of Practical Test Standards. 

1-22 
contains “tasks,” which are comprised of knowledge areas, or GPO bookstores. Most airport fixed-base operators and flight 

flight procedures, and/or flight maneuvers appropriate to the schools carry a variety of government publications and charts, 

area of operation. The candidate is required to demonstrate as well as commercially published materials. 

knowledge and proficiency in all tasks for the original 

issuance of all pilot certificates. Who Administers the FAA Practical Tests? 

Due to the varied responsibilities of the FSDOs, practical tests 

When To Take the Practical Test are usually given by DPEs. An applicant should schedule the 

14 CFR part 61 establishes the ground school and flight practical test by appointment to avoid conflicts and wasted 

experience requirements for the type of certification and time. A list of examiner names can be obtained from the local 

aircraft selected. However, the CFI best determines when an FSDO. Since a DPE serves without pay from the government 

applicant is qualified for the practical test. A practice practical for conducting practical tests and processing the necessary 

test is an important step in the flight training process. reports, the examiner is allowed to charge a reasonable fee. 

There is no charge for the practical test when conducted by 

The applicant will be asked to present the following an FAA inspector. 

documentation: 

Role of the Certificated Flight Instructor •	 FAA Form 8710-1 (8710.11 for sport pilot applicants), To become a CFI, a pilot must meet the provisions of 14 CFR Application for an Airman Certificate and/or Rating, part 61. The FAA places full responsibility for student flight with the flight instructor’s recommendation training on the shoulders of the CFI, who is the cornerstone •	 An Airman Knowledge Test Report with a of aviation safety. It is the job of the flight instructor to train satisfactory grade the student pilot in all the knowledge areas and teach the 

•	 A medical certificate (not required for glider or skills necessary for the student pilot to operate safely and 

balloon), a Student Pilot Certificate, and a pilot competently as a certificated pilot in the NAS. The training 

logbook endorsed by a flight instructor for solo, solo includes airmanship skills, pilot judgment and decisioncross-country (airplane and rotorcraft), and for the making, and good operating practices. 

make and model aircraft to be used for the practical 

test (driver’s license or medical certificate for sport A pilot training program depends on the quality of the 

pilot applicants) ground and flight instruction the student pilot receives. The 

flight instructor must possess a thorough understanding of •	 The pilot log book records the learning process, knowledge of the fundamentals of •	 A graduation certificate from an FAA-approved school teaching, and the ability to communicate effectively with the 

(if applicable) student pilot. Use of a structured training program and formal 

course syllabus is crucial for effective and comprehensive 

The applicant must provide an airworthy aircraft with flight training. It should be clear to the student in advance of 

equipment relevant to the areas of operation required for every lesson what the course of training will involve and the 

the practical test. He or she will also be asked to produce criteria for successful completion. This should include the 

and explain the: flight instructor briefing and debriefing the student before and 

•	 Aircraft’s registration certificate after every lesson. Additionally, scenario-based training has 

become the preferred method of flight instruction today. This •	 Aircraft’s airworthiness certificate involves presenting the student with realistic flight scenarios 

•	 Aircraft’s operating limitations or FAA-approved and recommended actions for mitigating risk. 

aircraft flight manual (if required) 

•	 Aircraft equipment list Insistence on correct techniques and procedures from the 

beginning of training by the flight instructor ensures that the •	 Required weight and balance data student pilot develops proper flying habits. Any deficiencies 

•	 Maintenance records in the maneuvers or techniques must immediately be 

emphasized and corrected. A flight instructor serves as a role •	 Applicable airworthiness directives (ADs) 

model for the student pilot who observes the flying habits of 

his or her flight instructor during flight instruction, as well For a detailed explanation of the required pilot maneuvers and 

as when the instructor conducts other pilot operations. Thus, performance standards, refer to the PTS pertaining to the type 

the flight instructor becomes a model of flying proficiency of certification and aircraft selected. These standards may be 

for the student who, consciously or unconsciously, attempts downloaded free of charge from the FAA at www.faa.gov. They 

may also be purchased from the Superintendent of Documents to imitate the instructor. For this reason, a flight instructor 

1-23 
should observe recognized safety practices, as well as 

regulations during all flight operations. 

The student pilot who enrolls in a pilot training program 

commits considerable time, effort, and expense to achieve a 

pilot certificate. Students often judge the effectiveness of the 

flight instructor and the success of the pilot training program 

based on their ability to pass the requisite FAA practical 

test. A competent flight instructor stresses to the student that 

practical tests are a sampling of pilot ability compressed into 

a short period of time. The goal of a flight instructor is to 

train the “total” pilot. 

Role of the Designated Pilot Examiner 

The Designated Pilot Examiner (DPE) plays an important 

role in the FAA’s mission of promoting aviation safety 

by administering FAA practical tests for pilot and Flight 

Instructor Certificates and associated ratings. Although 

administering these tests is a responsibility of the ASI, the 

FAA’s highest priority is making air travel safer by inspecting 

aircraft that fly in the United States. To satisfy the need for 

pilot testing and certification services, the FAA delegates 

certain responsibilities to private individuals who are not 

FAA employees. 

Appointed in accordance with 14 CFR part 183, section 

183.23, a DPE is an individual who meets the qualification 

requirements of the Pilot Examiner’s Handbook, FAA Order 

8710.3, and who: 

•	 Is technically qualified 

•	 Holds all pertinent category, class, and type ratings 

for each aircraft related to their designation 

•	 Meets requirements of 14 CFR part 61, sections 61.56, 

61.57, and 61.58, as appropriate 

•	 Is current and qualified to act as PIC of each aircraft 

for which he or she is authorized 

•	 Maintains at least a Third-Class Medical Certificate, 

if required 

•	 Maintains a current Flight Instructor Certificate, if 

required 

Designated to perform specific pilot certification tasks 

on behalf of the FAA, a DPE may charge a reasonable 

fee. Generally, a DPE’s authority is limited to accepting 

applications and conducting practical tests leading to the 

issuance of specific pilot certificates and/or ratings. The 

majority of FAA practical tests at the private and commercial 

pilot levels are administered by DPEs. 

DPE candidates must have good industry reputations for 

professionalism, integrity, a demonstrated willingness to 

serve the public, and must adhere to FAA policies and 

procedures in certification matters. The FAA expects the 

DPE to administer practical tests with the same degree of 

professionalism, using the same methods, procedures, and 

standards as an FAA ASI. 

Chapter Summary 

The FAA has entered the second century of civil aviation as a 

robust government organization and is taking full advantage of 

technology, such as Global Positioning System (GPS) satellite 

technology to enhance the safety of civil aviation. The Internet 

has also become an important tool in promoting aviation safety 

and providing around-the-clock resources for the aviation 

community. Handbooks, regulations, standards, references, 

and online courses are now available at www.faa.gov. 

In keeping with the FAA’s belief that safety is a learned 

behavior, the FAA offers many courses and seminars to 

enhance air safety. The FAA puts the burden of instilling safe 

flying habits on the flight instructor, who should follow basic 

flight safety practices and procedures in every flight operation 

he or she undertakes with a student pilot. Operational safety 

practices include, but are not limited to, collision avoidance 

procedures consisting of proper scanning techniques, use of 

checklists, runway incursion avoidance, positive transfer of 

controls, and workload management. These safety practices 

are discussed more fully within this handbook. Safe flight also 

depends on Scenario-Based Training (SBT) that teaches the 

student pilot how to respond in different flight situations. The 

FAA has incorporated these techniques along with decisionmaking methods, such as aeronautical decision-making 

(ADM), risk management, and crew resource management 

(CRM), which are covered more completely in Chapter 2, 

Aeronautical Decision-Making. 

1-24 
2-1 

Introduction 

Aeronautical decision-making (ADM) is decision-making 

in a unique environment—aviation. It is a systematic 

approach to the mental process used by pilots to consistently 

determine the best course of action in response to a given set 

of circumstances. It is what a pilot intends to do based on the 

latest information he or she has. 

Aeronautical 

Decision-Making 

Chapter 2 
The importance of learning and understanding effective 

ADM skills cannot be overemphasized. While progress is 

continually being made in the advancement of pilot training 

methods, aircraft equipment and systems, and services 

for pilots, accidents still occur. Despite all the changes in 

technology to improve flight safety, one factor remains the 

same: the human factor which leads to errors. It is estimated 

that approximately 80 percent of all aviation accidents are 

related to human factors and the vast majority of these 

accidents occur during landing (24.1 percent) and takeoff 

(23.4 percent). [Figure 2-1] 

ADM is a systematic approach to risk assessment and stress 

management. To understand ADM is to also understand 

how personal attitudes can influence decision-making and 

how those attitudes can be modified to enhance safety in the 

flight deck. It is important to understand the factors that cause 

humans to make decisions and how the decision-making 

process not only works, but can be improved. 

This chapter focuses on helping the pilot improve his or 

her ADM skills with the goal of mitigating the risk factors 

associated with flight. Advisory Circular (AC) 60-22, 

“Aeronautical Decision-Making,” provides background 

references, definitions, and other pertinent information about 

ADM training in the general aviation (GA) environment. 

[Figure 2-2] 

History of ADM 

For over 25 years, the importance of good pilot judgment, or 

aeronautical decision-making (ADM), has been recognized 

as critical to the safe operation of aircraft, as well as accident 

avoidance. The airline industry, motivated by the need to 

reduce accidents caused by human factors, developed the first 

training programs based on improving ADM. Crew resource 

management (CRM) training for flight crews is focused on 

the effective use of all available resources: human resources, 

hardware, and information supporting ADM to facilitate crew 

cooperation and improve decision-making. The goal of all 

flight crews is good ADM and the use of CRM is one way 

to make good decisions. 

Research in this area prompted the Federal Aviation 

Administration (FAA) to produce training directed at 

improving the decision-making of pilots and led to current 

FAA regulations that require that decision-making be taught 

as part of the pilot training curriculum. ADM research, 

development, and testing culminated in 1987 with the 

publication of six manuals oriented to the decision-making 

needs of variously rated pilots. These manuals provided 

multifaceted materials designed to reduce the number 

of decision-related accidents. The effectiveness of these 

materials was validated in independent studies where student 

pilots received such training in conjunction with the standard 

flying curriculum. When tested, the pilots who had received 

ADM-training made fewer in-flight errors than those who had 

Figure 2-1. The percentage of aviation accidents as they relate to the different phases of flight. Note that the greatest percentage of 

accidents take place during a minor percentage of the total flight. 

Flight Time 

2% 

Flight Time 

83% 

Flight Time 

15% 

Preflights/ 

Taxi 

Takeoff/ 

Initial Climb Climb Cruise Descent Maneuvering Approach Landing Other 

3.5% 3.3%

23.4% 

15.7% 

2.6% 

13% 

9.7% 

24.1% 

4.7% 

Percentage of General Aviation Accidents 

2-2 
 

 

Figure 2-2. Advisory Circular (AC) 60-22, “Aeronautical Decision Making,” carries a wealth of information for the pilot to learn. 

not received ADM training. The differences were statistically 

significant and ranged from about 10 to 50 percent fewer 

judgment errors. In the operational environment, an operator 

flying about 400,000 hours annually demonstrated a 54 

percent reduction in accident rate after using these materials 

for recurrency training. 

Contrary to popular opinion, good judgment can be taught. 

Tradition held that good judgment was a natural by-product 

of experience, but as pilots continued to log accident-free 

flight hours, a corresponding increase of good judgment 

was assumed. Building upon the foundation of conventional 

decision-making, ADM enhances the process to decrease the 

probability of human error and increase the probability of a 

safe flight. ADM provides a structured, systematic approach 

to analyzing changes that occur during a flight and how these 

changes might affect the safe outcome of a flight. The ADM 

process addresses all aspects of decision-making in the flight 

deck and identifies the steps involved in good decision-making. 

Steps for good decision-making are: 

1. Identifying personal attitudes hazardous to safe flight 

2. Learning behavior modification techniques 

3. Learning how to recognize and cope with stress 

4. Developing risk assessment skills 

5. Using all resources 

6. Evaluating the effectiveness of one’s ADM skills 

Risk Management 

The goal of risk management is to proactively identify 

safety-related hazards and mitigate the associated risks. Risk 

management is an important component of ADM. When a 

pilot follows good decision-making practices, the inherent risk 

in a flight is reduced or even eliminated. The ability to make 

good decisions is based upon direct or indirect experience 

and education. The formal risk management decision-making 

process involves six steps as shown in Figure 2-3. 

Consider automotive seat belt use. In just two decades, seat 

belt use has become the norm, placing those who do not 

wear seat belts outside the norm, but this group may learn to 

wear a seat belt by either direct or indirect experience. For 

example, a driver learns through direct experience about the 

value of wearing a seat belt when he or she is involved in a car 

accident that leads to a personal injury. An indirect learning 

experience occurs when a loved one is injured during a car 

accident because he or she failed to wear a seat belt. 

As you work through the ADM cycle, it is important to 

remember the four fundamental principles of risk management. 

2-3 
 

 

Identify 

Hazards 

Assess 

Risks 

Analyze 

Controls 

Make Control 

Decisions 

Monitor 

Results 

Use 

Controls 

START 

RISK 

MANAGEMENT 

PROCESS 

Figure 2-3. Risk management decision-making process. 

1.	 Accept no unnecessary risk. Flying is not possible 

without risk, but unnecessary risk comes without a 

corresponding return. If you are flying a new airplane 

for the first time, you might determine that the risk 

of making that flight in low visibility conditions is 

unnecessary. 

2.	 Make risk decisions at the appropriate level. Risk 

decisions should be made by the person who can 

develop and implement risk controls. Remember 

that you are pilot-in-command, so never let anyone 

else—not ATC and not your passengers—make risk 

decisions for you. 

3. Accept risk when benefits outweigh dangers (costs). 

In any flying activity, it is necessary to accept some 

degree of risk. A day with good weather, for example, 

is a much better time to fly an unfamiliar airplane for 

the first time than a day with low IFR conditions. 

4. Integrate risk management into planning at all levels. 

Because risk is an unavoidable part of every flight, 

safety requires the use of appropriate and effective risk 

management not just in the preflight planning stage, 

but in all stages of the flight. 

While poor decision-making in everyday life does not always 

lead to tragedy, the margin for error in aviation is thin. Since 

ADM enhances management of an aeronautical environment, 

all pilots should become familiar with and employ ADM. 

Crew Resource Management (CRM) and

Single-Pilot Resource Management 

While CRM focuses on pilots operating in crew environments, 

many of the concepts apply to single-pilot operations. Many 

CRM principles have been successfully applied to single-pilot 

aircraft and led to the development of Single-Pilot Resource 

Management (SRM). SRM is defined as the art and science 

of managing all the resources (both on-board the aircraft 

and from outside sources) available to a single pilot (prior 

to and during flight) to ensure the successful outcome of the 

flight. SRM includes the concepts of ADM, risk management 

(RM), task management (TM), automation management 

(AM), controlled flight into terrain (CFIT) awareness, and 

situational awareness (SA). SRM training helps the pilot 

maintain situational awareness by managing the automation 

and associated aircraft control and navigation tasks. This 

enables the pilot to accurately assess and manage risk and 

make accurate and timely decisions. 

SRM is all about helping pilots learn how to gather 

information, analyze it, and make decisions. Although the 

flight is coordinated by a single person and not an onboard 

flight crew, the use of available resources such as auto-pilot 

and air traffic control (ATC) replicates the principles of CRM. 

Hazard and Risk 

Two defining elements of ADM are hazard and risk. Hazard 

is a real or perceived condition, event, or circumstance that a 

pilot encounters. When faced with a hazard, the pilot makes 

an assessment of that hazard based upon various factors. The 

pilot assigns a value to the potential impact of the hazard, 

which qualifies the pilot’s assessment of the hazard—risk. 

Therefore, risk is an assessment of the single or cumulative 

hazard facing a pilot; however, different pilots see hazards 

differently. For example, the pilot arrives to preflight and 

discovers a small, blunt type nick in the leading edge at the 

middle of the aircraft’s prop. Since the aircraft is parked on 

the tarmac, the nick was probably caused by another aircraft’s 

prop wash blowing some type of debris into the propeller. 

The nick is the hazard (a present condition). The risk is prop 

fracture if the engine is operated with damage to a prop blade. 

The seasoned pilot may see the nick as a low risk. He 

realizes this type of nick diffuses stress over a large area, is 

located in the strongest portion of the propeller, and based 

on experience; he does not expect it to propagate a crack that 

can lead to high risk problems. He does not cancel his flight. 

2-4 
 

The inexperienced pilot may see the nick as a high risk factor 

because he is unsure of the affect the nick will have on the 

operation of the prop, and he has been told that damage to 

a prop could cause a catastrophic failure. This assessment 

leads him to cancel his flight. 

Therefore, elements or factors affecting individuals are 

different and profoundly impact decision-making. These 

are called human factors and can transcend education, 

experience, health, physiological aspects, etc. 

Another example of risk assessment was the flight of a 

Beechcraft King Air equipped with deicing and anti-icing. 

The pilot deliberately flew into moderate to severe icing 

conditions while ducking under cloud cover. A prudent pilot 

would assess the risk as high and beyond the capabilities of 

the aircraft, yet this pilot did the opposite. Why did the pilot 

take this action? 

Past experience prompted the action. The pilot had 

successfully flown into these conditions repeatedly although 

the icing conditions were previously forecast 2,000 feet above 

the surface. This time, the conditions were forecast from the 

surface. Since the pilot was in a hurry and failed to factor 

in the difference between the forecast altitudes, he assigned 

a low risk to the hazard and took a chance. He and the 

passengers died from a poor risk assessment of the situation. 

Hazardous Attitudes and Antidotes 

Being fit to fly depends on more than just a pilot’s physical 

condition and recent experience. For example, attitude 

affects the quality of decisions. Attitude is a motivational 

predisposition to respond to people, situations, or events in a 

given manner. Studies have identified five hazardous attitudes 

that can interfere with the ability to make sound decisions 

and exercise authority properly: anti-authority, impulsivity, 

invulnerability, macho, and resignation. [Figure 2-4] 

Hazardous attitudes contribute to poor pilot judgment but 

can be effectively counteracted by redirecting the hazardous 

attitude so that correct action can be taken. Recognition of 

hazardous thoughts is the first step toward neutralizing them. 

After recognizing a thought as hazardous, the pilot should 

label it as hazardous, then state the corresponding antidote. 

Antidotes should be memorized for each of the hazardous 

attitudes so they automatically come to mind when needed. 

The Five Hazardous Attitudes Antidote 

Anti-authority: “Don’t tell me.” 

This attitude is found in people who do not like anyone telling them what to do. In a 

sense, they are saying, “No one can tell me what to do.” They may be resentful of 

having someone tell them what to do or may regard rules, regulations, and procedures 

as silly or unnecessary. However, it is always your prerogative to question authority 

if you feel it is in error. 

Impulsivity: “Do it quickly.” 

This is the attitude of people who frequently feel the need to do something, anything, 

immediately. They do not stop to think about what they are about to do, they do not 

select the best alternative, and they do the first thing that comes to mind. 

Invulnerability: “It won’t happen to me.” 

Many people falsely believe that accidents happen to others, but never to them. They 

know accidents can happen, and they know that anyone can be affected. However, 

they never really feel or believe that they will be personally involved. Pilots who think 

this way are more likely to take chances and increase risk. 

Macho: “I can do it.” 

Pilots who are always trying to prove that they are better than anyone else think, “I can 

do it—I'll show them.” Pilots with this type of attitude will try to prove themselves by 

taking risks in order to impress others. While this pattern is thought to be a male 

characteristic, women are equally susceptible. 

Resignation: “What’s the use?” 

Pilots who think, “What’s the use?” do not see themselves as being able to make a 

great deal of difference in what happens to them. When things go well, the pilot is apt 

to think that it is good luck. When things go badly, the pilot may feel that someone is 

out to get them or attribute it to bad luck. The pilot will leave the action to others, for 

better or worse. Sometimes, such pilots will even go along with unreasonable requests 

just to be a "nice guy." 

Follow the rules. They are usually right. 

Not so fast. Think first. 

It could happen to me. 

Taking chances is foolish. 

I’m not helpless. I can make a difference. 

Figure 2-4. The five hazardous attitudes identified through past and contemporary study. 

2-5 
 

 

Risk 

During each flight, the single pilot makes many decisions 

under hazardous conditions. To fly safely, the pilot needs 

to assess the degree of risk and determine the best course of 

action to mitigate the risk. 

Assessing Risk 

For the single pilot, assessing risk is not as simple as it sounds. 

For example, the pilot acts as his or her own quality control 

in making decisions. If a fatigued pilot who has flown 16 

hours is asked if he or she is too tired to continue flying, the 

answer may be “no.” Most pilots are goal oriented and when 

asked to accept a flight, there is a tendency to deny personal 

limitations while adding weight to issues not germane to the 

mission. For example, pilots of helicopter emergency services 

(EMS) have been known (more than other groups) to make 

flight decisions that add significant weight to the patient’s 

welfare. These pilots add weight to intangible factors (the 

patient in this case) and fail to appropriately quantify actual 

hazards, such as fatigue or weather, when making flight 

decisions. The single pilot who has no other crew member 

for consultation must wrestle with the intangible factors that 

draw one into a hazardous position. Therefore, he or she has 

a greater vulnerability than a full crew. 

Examining National Transportation Safety Board (NTSB) 

reports and other accident research can help a pilot learn to 

assess risk more effectively. For example, the accident rate 

during night visual flight rules (VFR) decreases by nearly 

50 percent once a pilot obtains 100 hours and continues to 

decrease until the 1,000 hour level. The data suggest that for 

the first 500 hours, pilots flying VFR at night might want to 

establish higher personal limitations than are required by the 

regulations and, if applicable, apply instrument flying skills 

in this environment. 

Several risk assessment models are available to assist in the 

process of assessing risk. The models, all taking slightly 

different approaches, seek a common goal of assessing risk 

in an objective manner. The most basic tool is the risk matrix. 

[Figure 2-5] It assesses two items: the likelihood of an event 

occurring and the consequence of that event. 

Likelihood of an Event 

Likelihood is nothing more than taking a situation and 

determining the probability of its occurrence. It is rated as 

probable, occasional, remote, or improbable. For example, a 

pilot is flying from point A to point B (50 miles) in marginal 

visual flight rules (MVFR) conditions. The likelihood of 

encountering potential instrument meteorological conditions 

(IMC) is the first question the pilot needs to answer. The 

experiences of other pilots, coupled with the forecast, might 

Figure 2-5. This risk matrix can be used for almost any operation 

by assigning likelihood and consequence. In the case presented, 

the pilot assigned a likelihood of occasional and the severity as 

catastrophic. As one can see, this falls in the high risk area. 

Catastrophic Critical Marginal Negligible 

Improbable 

Remote 

Occasional 

Probable 

Risk Assessment Matrix

 Likelihood 

Severity 

Serious Medium Low

Serious 

High High Serious

High 

cause the pilot to assign “occasional” to determine the 

probability of encountering IMC. 

The following are guidelines for making assignments. 

• Probable—an event will occur several times

• Occasional—an event will probably occur sometime

• Remote—an event is unlikely to occur, but is possible 

• Improbable—an event is highly unlikely to occur

Severity of an Event 

The next element is the severity or consequence of a pilot’s 

action(s). It can relate to injury and/or damage. If the 

individual in the example above is not an instrument rated 

pilot, what are the consequences of him or her encountering 

inadvertent IMC conditions? In this case, because the pilot 

is not IFR rated, the consequences are catastrophic. The 

following are guidelines for this assignment. 

• Catastrophic—results in fatalities, total loss

• Critical—severe injury, major damage

• Marginal—minor injury, minor damage

• Negligible—less than minor injury, less than minor

system damage

Simply connecting the two factors as shown in Figure 2-5 

indicates the risk is high and the pilot must either not fly or 

fly only after finding ways to mitigate, eliminate, or control 

the risk. 

Although the matrix in Figure 2-5 provides a general viewpoint 

of a generic situation, a more comprehensive program can be 

made that is tailored to a pilot’s flying. [Figure 2-6] This 

program includes a wide array of aviation-related activities 

specific to the pilot and assesses health, fatigue, weather, 

2-6 
 

 

 

 

RISK ASSESSMENT 

Column total 

Column total 

SLEEP 

1. Did not sleep well or less than 8 hours 

2. Slept well 

2 

0 

HOW DO YOU FEEL? 

1. Have a cold or ill 

2. Feel great 

3. Feel a bit off 

4 

0 

2 

WEATHER AT TERMINATION 

1. Greater than 5 miles visibility and 3,000 feet 

ceilings 

2. At least 3 miles visibility and 1,000 feet ceilings, 

but less than 3,000 feet ceilings and 5 miles 

visibility 

3. IMC conditions 

1 

3 

4 

HOW IS THE DAY GOING? 

1. Seems like one thing after another (late, 

making errors, out of step) 

2. Great day 

3 

0 

IS THE FLIGHT 

1. Day? 

2. Night? 

1 

3 

PLANNING 

1. Rush to get off ground 

2. No hurry 

3. Used charts and computer to assist 

4. Used computer program for all planning Yes 

No 

5. Did you verify weight and balance? Yes 

No 

6. Did you evaluate performance? Yes 

No 

7. Do you brief your passangers on the Yes 

ground and in flight? No 

3 

1 

0 

3 

0 

0 

3 

0 

3 

0 

2 

Pilot’s Name Flight From To 

TOTAL SCORE 

0 Not complex flight 10 Exercise caution 20 Area of concern 30

Endangerment

Low risk

 Figure 2-6. Example of a more comprehensive risk assessment program. 

2-7 
 

 

capabilities, etc. The scores are added and the overall score 

falls into various ranges, with the range representative of 

actions that a pilot imposes upon himself or herself. 

Mitigating Risk 

Risk assessment is only part of the equation. After 

determining the level of risk, the pilot needs to mitigate the 

risk. For example, the pilot flying from point A to point B (50 

miles) in MVFR conditions has several ways to reduce risk: 

• Wait for the weather to improve to good visual flight 

rules (VFR) conditions. 

• Take an instrument-rated pilot. 

• Delay the flight. 

• Cancel the flight. 

• Drive. 

One of the best ways single pilots can mitigate risk is to use 

the IMSAFE checklist to determine physical and mental 

readiness for flying: 

1. Illness—Am I sick? Illness is an obvious pilot risk. 

2. Medication—Am I taking any medicines that might 

affect my judgment or make me drowsy? 

3. Stress—Am I under psychological pressure from the 

job? Do I have money, health, or family problems? 

Stress causes concentration and performance problems. 

While the regulations list medical conditions that 

require grounding, stress is not among them. The pilot 

should consider the effects of stress on performance. 

4.	 Alcohol—Have I been drinking within 8 hours? 

Within 24 hours? As little as one ounce of liquor, one 

bottle of beer, or four ounces of wine can impair flying 

skills. Alcohol also renders a pilot more susceptible 

to disorientation and hypoxia. 

5.	 Fatigue—Am I tired and not adequately rested? 

Fatigue continues to be one of the most insidious 

hazards to flight safety, as it may not be apparent to 

a pilot until serious errors are made. 

6. Emotion—Am I emotionally upset? 

The PAVE Checklist 

Another way to mitigate risk is to perceive hazards. By 

incorporating the PAVE checklist into preflight planning, 

the pilot divides the risks of flight into four categories: Pilotin-command (PIC), Aircraft, enVironment, and External 

pressures (PAVE) which form part of a pilot’s decisionmaking process. 

With the PAVE checklist, pilots have a simple way to 

remember each category to examine for risk prior to each flight. 

Once a pilot identifies the risks of a flight, he or she needs 

to decide whether the risk, or combination of risks, can be 

managed safely and successfully. If not, make the decision to 

cancel the flight. If the pilot decides to continue with the flight, 

he or she should develop strategies to mitigate the risks. One 

way a pilot can control the risks is to set personal minimums 

for items in each risk category. These are limits unique to that 

individual pilot’s current level of experience and proficiency. 

For example, the aircraft may have a maximum crosswind 

component of 15 knots listed in the aircraft flight manual 

(AFM), and the pilot has experience with 10 knots of direct 

crosswind. It could be unsafe to exceed a 10 knot crosswind 

component without additional training. Therefore, the 10 knot 

crosswind experience level is that pilot’s personal limitation 

until additional training with a certificated flight instructor 

(CFI) provides the pilot with additional experience for flying 

in crosswinds that exceed 10 knots. 

One of the most important concepts that safe pilots 

understand is the difference between what is “legal” in terms 

of the regulations, and what is “smart” or “safe” in terms of 

pilot experience and proficiency. 

P = Pilot in Command (PIC) 

The pilot is one of the risk factors in a flight. The pilot must 

ask, “Am I ready for this trip?” in terms of experience, 

recency, currency, physical, and emotional condition. The 

IMSAFE checklist provides the answers. 

A = Aircraft 

What limitations will the aircraft impose upon the trip? Ask 

the following questions: 

• Is this the right aircraft for the flight? 

•	 Am I familiar with and current in this aircraft? Aircraft 

performance figures and the AFM are based on a brand 

new aircraft flown by a professional test pilot. Keep 

that in mind while assessing personal and aircraft 

performance. 

• Is this aircraft equipped for the flight? Instruments? 

Lights? Navigation and communication equipment 

adequate? 

• Can this aircraft use the runways available for the trip 

with an adequate margin of safety under the conditions 

to be flown? 

• Can this aircraft carry the planned load? 

•	 Can this aircraft operate at the altitudes needed for the 

trip? 

•	 Does this aircraft have sufficient fuel capacity, with 

reserves, for trip legs planned? 

2-8 
 

 

 

 

 

 

 

 

•	 Does the fuel quantity delivered match the fuel 

quantity ordered? 

V = EnVironment 

Weather 

Weather is a major environmental consideration. Earlier it was 

suggested pilots set their own personal minimums, especially 

when it comes to weather. As pilots evaluate the weather for 

a particular flight, they should consider the following: 

•	 What is the current ceiling and visibility? In 

mountainous terrain, consider having higher 

minimums for ceiling and visibility, particularly if 

the terrain is unfamiliar. 

•	 Consider the possibility that the weather may be 

different than forecast. Have alternative plans and 

be ready and willing to divert, should an unexpected 

change occur. 

• Consider the winds at the airports being used and the 

strength of the crosswind component. 

•	 If flying in mountainous terrain, consider whether 

there are strong winds aloft. Strong winds in 

mountainous terrain can cause severe turbulence and 

downdrafts and be very hazardous for aircraft even 

when there is no other significant weather. 

• Are there any thunderstorms present or forecast? 

•	 If there are clouds, is there any icing, current or 

forecast? What is the temperature/dew point spread 

and the current temperature at altitude? Can descent 

be made safely all along the route? 

•	 If icing conditions are encountered, is the pilot 

experienced at operating the aircraft’s deicing or 

anti-icing equipment? Is this equipment in good 

condition and functional? For what icing conditions 

is the aircraft rated, if any? 

Terrain 

Evaluation of terrain is another important component of 

analyzing the flight environment. 

•	 To avoid terrain and obstacles, especially at night or 

in low visibility, determine safe altitudes in advance 

by using the altitudes shown on VFR and IFR charts 

during preflight planning. 

•	 Use maximum elevation figures (MEFs) and other 

easily obtainable data to minimize chances of an 

inflight collision with terrain or obstacles. 

Airport 

•	 What lights are available at the destination and 

alternate airports? VASI/PAPI or ILS glideslope 

guidance? Is the terminal airport equipped with them? 

Are they working? Will the pilot need to use the radio 

to activate the airport lights? 

•	 Check the Notices to Airmen (NOTAM) for closed 

runways or airports. Look for runway or beacon lights 

out, nearby towers, etc. 

•	 Choose the flight route wisely. An engine failure gives 

the nearby airports supreme importance. 

•	 Are there shorter or obstructed fields at the destination 

and/or alternate airports? 

Airspace 

•	 If the trip is over remote areas, is there appropriate 

clothing, water, and survival gear onboard in the event 

of a forced landing? 

• If the trip includes flying over water or unpopulated 

areas with the chance of losing visual reference to the 

horizon, the pilot must be prepared to fly IFR. 

•	 Check the airspace and any temporary flight restriction 

(TFRs) along the route of flight. 

Nighttime 

Night flying requires special consideration. 

•	 If the trip includes flying at night over water or 

unpopulated areas with the chance of losing visual 

reference to the horizon, the pilot must be prepared 

to fly IFR. 

•	 Will the flight conditions allow a safe emergency 

landing at night? 

•	 Perform preflight check of all aircraft lights, interior 

and exterior, for a night flight. Carry at least two 

flashlights—one for exterior preflight and a smaller 

one that can be dimmed and kept nearby. 

E = External Pressures 

External pressures are influences external to the flight that 

create a sense of pressure to complete a flight—often at the 

expense of safety. Factors that can be external pressures 

include the following: 

• Someone waiting at the airport for the flight’s arrival 

• A passenger the pilot does not want to disappoint 

• The desire to demonstrate pilot qualifications 

•	 The desire to impress someone (Probably the two most 

dangerous words in aviation are “Watch this!”) 

• The desire to satisfy a specific personal goal (“gethome-itis,” “get-there-itis,” and “let’s-go-itis”) 

•	 The pilot’s general goal-completion orientation 

2-9 
•	 Emotional pressure associated with acknowledging 

that skill and experience levels may be lower than a 

pilot would like them to be. Pride can be a powerful 

external factor! 

Managing External Pressures 

Management of external pressure is the single most important 

key to risk management because it is the one risk factor 

category that can cause a pilot to ignore all the other risk 

factors. External pressures put time-related pressure on the 

pilot and figure into a majority of accidents. 

The use of personal standard operating procedures (SOPs) is 

one way to manage external pressures. The goal is to supply a 

release for the external pressures of a flight. These procedures 

include but are not limited to: 

•	 Allow time on a trip for an extra fuel stop or to make 

an unexpected landing because of weather. 

•	 Have alternate plans for a late arrival or make backup 

airline reservations for must-be-there trips. 

• For really important trips, plan to leave early enough 

so that there would still be time to drive to the 

destination, if necessary. 

Pilot 

A pilot must continually make decisions about competency, 

condition of health, mental and emotional state, level of fatigue, 

and many other variables. For example, a pilot may be called 

early in the morning to make a long flight. If a pilot has had only 

a few hours of sleep and is concerned that the congestion 

being experienced could be the onset of a cold, it would be 

prudent to consider if the flight could be accomplished safely. 

A pilot had only 4 hours of sleep the night before being asked 

by the boss to fly to a meeting in a city 750 miles away. The 

reported weather was marginal and not expected to improve. 

After assessing fitness as a pilot, it was decided that it would 

not be wise to make the flight. The boss was initially unhappy, 

but later convinced by the pilot that the risks involved were 

unacceptable. 

Environment 

This encompasses many elements not pilot or airplane related. 

It can include such factors as weather, air traffic control, 

navigational aids (NAVAIDS), terrain, takeoff and landing 

areas, and surrounding obstacles. Weather is one element that 

can change drastically over time and distance. 

A pilot was landing a small airplane just after a heavy jet had 

departed a parallel runway. The pilot assumed that wake 

turbulence would not be a problem since landings had been 

performed under similar circumstances. Due to a combination 

of prevailing winds and wake turbulence from the heavy jet 

drifting across the landing runway, the airplane made a hard 

landing. The pilot made an error when assessing the flight 

environment. 

Figure 2-7. The PAVE checklist. 

•	 Advise those who are waiting at the destination that 

the arrival may be delayed. Know how to notify them 

when delays are encountered. 

•	 Manage passengers’ expectations. Make sure 

passengers know that they might not arrive on a firm 

schedule, and if they must arrive by a certain time, 

they should make alternative plans. 

• Eliminate pressure to return home, even on a casual 

day flight, by carrying a small overnight kit containing 

prescriptions, contact lens solutions, toiletries, or other 

necessities on every flight. 

The key to managing external pressure is to be ready for 

and accept delays. Remember that people get delayed when 

traveling on airlines, driving a car, or taking a bus. The pilot’s 

goal is to manage risk, not create hazards. [Figure 2-7] 

Human Factors 

Why are human conditions, such as fatigue, complacency 

and stress, so important in aviation? These conditions, along 

with many others, are called human factors. Human factors 

directly cause or contribute to many aviation accidents and 

Aircraft 

A pilot will frequently base decisions on the evaluations of the 

aircraft, such as performance, equipment, or airworthiness.
 

During a preflight, a pilot noticed a small amount of oil dripping 

from the bottom of the cowling. Although the quantity of oil 

seemed insignificant at the time, the pilot decided to delay the 

takeoff and have a mechanic check the source of the oil. 

The pilot’s good judgment was confirmed when the mechanic 

found that one of the oil cooler hose fittings was loose. 

External pressures 

The interaction between the pilot, airplane, and the environment 

is greatly influenced by the purpose of each flight operation. 

The pilot must evaluate the three previous areas to decide on 

the desirability of undertaking or continuing the flight as planned. 

It is worth asking why the flight is being made, how critical is it to 

maintain the schedule, and is the trip worth the risks? 

On a ferry flight to deliver an airplane from the factory, in 

marginal weather conditions, the pilot calculated the 

groundspeed and determined that the airplane would arrive at 

the destination with only 10 minutes of fuel remaining. The pilot 

was determined to keep on schedule by trying to “stretch” the 

fuel supply instead of landing to refuel. After landing with low 

fuel state, the pilot realized that this could have easily resulted 

in an emergency landing in deteriorating weather conditions. 

This was a chance that was not worth taking to keep the 

planned schedule. 

2-10 
 

have been documented as a primary contributor to more than 

70 percent of aircraft accidents. 

Typically, human factor incidents/accidents are associated 

with flight operations but recently have also become a major 

concern in aviation maintenance and air traffic management 

as well. [Figure 2-8] Over the past several years, the FAA has 

made the study and research of human factors a top priority 

by working closely with engineers, pilots, mechanics, and 

ATC to apply the latest knowledge about human factors in 

an effort to help operators and maintainers improve safety 

and efficiency in their daily operations. 

Human factors science, or human factors technologies, 

is a multidisciplinary field incorporating contributions 

from psychology, engineering, industrial design, statistics, 

operations research, and anthropometry. It is a term that 

covers the science of understanding the properties of 

human capability, the application of this understanding to 

the design, development and deployment of systems and 

services, and the art of ensuring successful application of 

human factor principles into all aspects of aviation to include 

pilots, ATC, and aviation maintenance. Human factors is 

often considered synonymous with CRM or maintenance 

resource management (MRM) but is really much broader in 

both its knowledge base and scope. Human factors involves 

gathering research specific to certain situations (i.e., flight, 

maintenance, stress levels, knowledge) about human abilities, 

limitations, and other characteristics and applying it to tool 

design, machines, systems, tasks, jobs, and environments 

to produce safe, comfortable, and effective human use. The 

entire aviation community benefits greatly from human 

factors research and development as it helps better understand 

how humans can most safely and efficiently perform their 

jobs and improve the tools and systems in which they interact. 

Human Behavior 

Studies of human behavior have tried to determine an 

individual’s predisposition to taking risks and the level of 

an individual’s involvement in accidents. In 1951, a study 

regarding injury-prone children was published by Elizabeth 

Mechem Fuller and Helen B. Baune, of the University of 

Minnesota. The study was comprised of two separate groups 

of second grade students. Fifty-five students were considered 

accident repeaters and 48 students had no accidents. Both 

groups were from the same school of 600 and their family 

demographics were similar. 

The accident-free group showed a superior knowledge 

of safety, was considered industrious and cooperative 

Figure 2-8. Human factors effects pilots, aviation maintenance technicians (AMTs) and air traffic control (ATC). 

2-11 
with others, but were not considered physically inclined. 

The accident-repeater group had better gymnastic skills, 

was considered aggressive and impulsive, demonstrated 

rebellious behavior when under stress, were poor losers, and 

liked to be the center of attention. One interpretation of this 

data—an adult predisposition to injury stems from childhood 

behavior and environment—leads to the conclusion that 

any pilot group should be comprised only of pilots who are 

safety-conscious, industrious, and cooperative. 

Clearly, this is not only an inaccurate inference, it is 

impossible. Pilots are drawn from the general population and 

exhibit all types of personality traits. Thus, it is important that 

good decision-making skills be taught to all pilots. 

Historically, the term “pilot error” has been used to describe 

an accident in which an action or decision made by the 

pilot was the cause or a contributing factor that led to the 

accident. This definition also includes the pilot’s failure 

to make a correct decision or take proper action. From a 

broader perspective, the phrase “human factors related” more 

aptly describes these accidents. A single decision or event 

does not lead to an accident, but a series of events and the 

resultant decisions together form a chain of events leading 

to an outcome. 

In his article “Accident-Prone Pilots,” Dr. Patrick R. Veillette 

uses the history of “Captain Everyman” to demonstrate how 

aircraft accidents are caused more by a chain of poor choices 

rather than one single poor choice. In the case of Captain 

Everyman, after a gear-up landing accident, he became 

involved in another accident while taxiing a Beech 58P Baron 

out of the ramp. Interrupted by a radio call from the dispatcher, 

Everyman neglected to complete the fuel cross-feed check 

before taking off. Everyman, who was flying solo, left the 

right-fuel selector in the cross-feed position. Once aloft and 

cruising, he noticed a right roll tendency and corrected with 

aileron trim. He did not realize that both engines were feeding 

off the left wing’s tank, making the wing lighter. 

After two hours of flight, the right engine quit when 

Everyman was flying along a deep canyon gorge. While he 

was trying to troubleshoot the cause of the right engine’s 

failure, the left engine quit. Everyman landed the aircraft on 

a river sand bar but it sank into ten feet of water. 

Several years later Everyman flew a de Havilland Twin 

Otter to deliver supplies to a remote location. When he 

returned to home base and landed, the aircraft veered sharply 

to the left, departed the runway, and ran into a marsh 375 

feet from the runway. The airframe and engines sustained 

considerable damage. Upon inspecting the wreck, accident 

investigators found the nose wheel steering tiller in the fully 

deflected position. Both the after takeoff and before landing 

checklists require the tiller to be placed in the neutral position. 

Everyman had overlooked this item. 

Now, is Everyman accident prone or just unlucky? Skipping 

details on a checklist appears to be a common theme in the 

preceding accidents. While most pilots have made similar 

mistakes, these errors were probably caught prior to a mishap 

due to extra margin, good warning systems, a sharp copilot, 

or just good luck. What makes a pilot less prone to accidents? 

The successful pilot possesses the ability to concentrate, 

manage workloads, and monitor and perform several 

simultaneous tasks. Some of the latest psychological 

screenings used in aviation test applicants for their ability 

to multitask, measuring both accuracy, as well as the 

individual’s ability to focus attention on several subjects 

simultaneously. The FAA oversaw an extensive research 

study on the similarities and dissimilarities of accident-free 

pilots and those who were not. The project surveyed over 

4,000 pilots, half of whom had “clean” records while the 

other half had been involved in an accident. 

Five traits were discovered in pilots prone to having 

accidents. These pilots: 

•	 Have disdain toward rules 

•	 Have very high correlation between accidents on their 

flying records and safety violations on their driving 

records 

•	 Frequently fall into the “thrill and adventure seeking” 

personality category 

•	 Are impulsive rather than methodical and disciplined, 

both in their information gathering and in the speed 

and selection of actions to be taken 

•	 Have a disregard for or tend to under utilize outside 

sources of information, including copilots, flight 

attendants, flight service personnel, flight instructors, 

and ATC 

The Decision-Making Process 

An understanding of the decision-making process provides 

the pilot with a foundation for developing ADM and SRM 

skills. While some situations, such as engine failure, require an 

immediate pilot response using established procedures, there is 

usually time during a flight to analyze any changes that occur, 

gather information, and assess risks before reaching a decision. 

Risk management and risk intervention is much more than the 

simple definitions of the terms might suggest. Risk management 

and risk intervention are decision-making processes designed 

to systematically identify hazards, assess the degree of risk, and 

2-12 
determine the best course of action. These processes involve 

the identification of hazards, followed by assessments of the 

risks, analysis of the controls, making control decisions, using 

the controls, and monitoring the results. 

The steps leading to this decision constitute a decisionmaking process. Three models of a structured framework 

for problem-solving and decision-making are the 5P, the 3P 

using PAVE, CARE and TEAM, and the DECIDE models. 

They provide assistance in organizing the decision process. 

All these models have been identified as helpful to the single 

pilot in organizing critical decisions. 

Single-Pilot Resource Management (SRM) 

Single-Pilot Resource Management (SRM) is about how to 

gather information, analyze it, and make decisions. Learning 

how to identify problems, analyze the information, and make 

informed and timely decisions is not as straightforward as the 

training involved in learning specific maneuvers. Learning 

how to judge a situation and “how to think” in the endless 

variety of situations encountered while flying out in the “real 

world” is more difficult. 

There is no one right answer in ADM, rather each pilot is 

expected to analyze each situation in light of experience 

level, personal minimums, and current physical and mental 

readiness level, and make his or her own decision. 

The 5 Ps Check 

SRM sounds good on paper, but it requires a way for pilots 

to understand and use it in their daily flights. One practical 

application is called the “Five Ps (5 Ps).” [Figure 2-9] The 

5 Ps consist of “the Plan, the Plane, the Pilot, the Passengers, 

and the Programming.” Each of these areas consists of a set 

of challenges and opportunities that every pilot encounters. 

Each challenge and opportunity can substantially increase or 

decrease the risk of successfully completing the flight based 

on the pilot’s ability to make informed and timely decisions. 

The 5 Ps are used to evaluate the pilot’s current situation at 

key decision points during the flight or when an emergency 

Figure 2-9. The Five Ps checklist. 

THE PLAN THE PLANE THE PILOT 

THE 

PASSENGERS 

THE 

PROGRAMMING 

The SRM Five “Ps” Check 

arises. These decision points include preflight, pretakeoff, 

hourly or at the midpoint of the flight, pre-descent, and just 

prior to the final approach fix or for VFR operations, just 

prior to entering the traffic pattern. 

The 5 Ps are based on the idea that pilots have essentially 

five variables that impact his or her environment and forcing 

him or her to make a single critical decision, or several less 

critical decisions, that when added together can create a 

critical outcome. These variables are the Plan, the Plane, the 

Pilot, the Passengers, and the Programming. This concept 

stems from the belief that current decision-making models 

tended to be reactionary in nature. A change has to occur 

and be detected to drive a risk management decision by the 

pilot. For instance, many pilots complete risk management 

sheets prior to takeoff. These form a catalog of risks 

that may be encountered that day. Each of these risks is 

assigned a numerical value. If the total of these numerical 

values exceeds a predetermined level, the flight is altered or 

cancelled. Informal research shows that while these are useful 

documents for teaching risk factors, they are almost never 

used outside of formal training programs. The 5P concept is 

an attempt to take the information contained in those sheets 

and in the other available models and use it. 

The 5P concept relies on the pilot to adopt a “scheduled” 

review of the critical variables at points in the flight where 

decisions are most likely to be effective. For instance, the 

easiest point to cancel a flight due to bad weather is before the 

pilot and passengers walk out the door and load the aircraft. 

So the first decision point is preflight in the flight planning 

room, where all the information is readily available to make 

a sound decision, and where communication and Fixed 

Base Operator (FBO) services are readily available to make 

alternate travel plans. 

The second easiest point in the flight to make a critical safety 

decision is just prior to takeoff. Few pilots have ever had 

to make an “emergency takeoff.” While the point of the 5P 

check is to help the pilot fly, the correct application of the 5 

P before takeoff is to assist in making a reasoned go/no-go 

decision based on all the information available. That decision 

will usually be to “go,” with certain restrictions and changes, 

but may also be a “no-go.” The key idea is that these two 

points in the process of flying are critical go/no-go points on 

each and every flight. 

The third place to review the 5 Ps is at the midpoint of the 

flight. Often, pilots may wait until the Automated Terminal 

information Service (ATIS) is in range to check weather, yet, 

at this point in the flight, many good options have already 

passed behind the aircraft and pilot. Additionally, fatigue 

2-13 
 

 

and low-altitude hypoxia serve to rob the pilot of much of 

his or her energy by the end of a long and tiring flight day. 

This leads to a transition from a decision-making mode to an 

acceptance mode on the part of the pilot. If the flight is longer 

than 2 hours, the 5 P check should be conducted hourly. 

The last two decision points are just prior to descent into the 

terminal area and just prior to the final approach fix, or if 

VFR, just prior to entering the traffic pattern as preparations 

for landing commence. Most pilots execute approaches with 

the expectation that they will land out of the approach every 

time. A healthier approach requires the pilot to assume that 

changing conditions (the 5 Ps again) will cause the pilot to 

divert or execute the missed approach on every approach. 

This keeps the pilot alert to all manner of conditions that 

may increase risk and threaten the safe conduct of the flight. 

Diverting from cruise altitude saves fuel, allows unhurried 

use of the autopilot and is less reactive in nature. Diverting 

from the final approach fix, while more difficult, still allows 

the pilot to plan and coordinate better, rather than executing 

a futile missed approach. Let’s look at a detailed discussion 

of each of the Five Ps. 

The Plan 

The “Plan” can also be called the mission or the task. It 

contains the basic elements of cross-country planning, 

weather, route, fuel, publications currency, etc. The “Plan” 

should be reviewed and updated several times during the 

course of the flight. A delayed takeoff due to maintenance, 

fast moving weather, and a short notice TFR may all radically 

alter the plan. The “plan” is not only about the flight plan, 

but also all the events that surround the flight and allow the 

pilot to accomplish the mission. The plan is always being 

updated and modified and is especially responsive to changes 

in the other four remaining Ps. If for no other reason, the 5 P 

check reminds the pilot that the day’s flight plan is real life 

and subject to change at any time. 

Obviously, weather is a huge part of any plan. The addition 

of datalink weather information gives the advanced avionics 

pilot a real advantage in inclement weather, but only if the 

pilot is trained to retrieve and evaluate the weather in real 

time without sacrificing situational awareness. And of course, 

weather information should drive a decision, even if that 

decision is to continue on the current plan. Pilots of aircraft 

without datalink weather should get updated weather in flight 

through an FSS and/or Flight Watch. 

The Plane 

Both the “plan” and the “plane” are fairly familiar to most 

pilots. The “plane” consists of the usual array of mechanical 

and cosmetic issues that every aircraft pilot, owner, or 

operator can identify. With the advent of advanced avionics, 

the “plane” has expanded to include database currency, 

automation status, and emergency backup systems that were 

unknown a few years ago. Much has been written about 

single pilot IFR flight, both with and without an autopilot. 

While this is a personal decision, it is just that—a decision. 

Low IFR in a non-autopilot equipped aircraft may depend 

on several of the other Ps to be discussed. Pilot proficiency, 

currency, and fatigue are among them. 

The Pilot 

Flying, especially when business transportation is involved, 

can expose a pilot to risks such as high altitudes, long trips 

requiring significant endurance, and challenging weather. 

Advanced avionics, when installed, can expose a pilot to high 

stresses because of the inherent additional capabilities which 

are available. When dealing with pilot risk, it is always best 

to consult the “IMSAFE” checklist (see page 2-6). 

The combination of late nights, pilot fatigue, and the effects 

of sustained flight above 5,000 feet may cause pilots to 

become less discerning, less critical of information, less 

decisive, and more compliant and accepting. Just as the most 

critical portion of the flight approaches (for instance a night 

instrument approach, in the weather, after a 4-hour flight), 

the pilot’s guard is down the most. The 5 P process helps a 

pilot recognize the physiological challenges that they may 

face towards the end of the flight prior to takeoff and allows 

them to update personal conditions as the flight progresses. 

Once risks are identified, the pilot is in a better place to 

make alternate plans that lessen the effect of these factors 

and provide a safer solution. 

The Passengers 

One of the key differences between CRM and SRM is the 

way passengers interact with the pilot. The pilot of a highly 

capable single-engine aircraft maintains a much more personal 

relationship with the passengers as he/she is positioned within 

an arm’s reach of them throughout the flight. 

The necessity of the passengers to make airline connections 

or important business meetings in a timely manner enters 

into this pilot’s decision-making loop. Consider a flight 

to Dulles Airport in which and the passengers, both close 

friends and business partners, need to get to Washington, 

D.C. for an important meeting. The weather is VFR all the 

way to southern Virginia, then turns to low IFR as the pilot 

approaches Dulles. A pilot employing the 5 P approach 

might consider reserving a rental car at an airport in northern 

North Carolina or southern Virginia to coincide with a 

refueling stop. Thus, the passengers have a way to get to 

Washington, and the pilot has an out to avoid being pressured 

into continuing the flight if the conditions do not improve. 

2-14 
 

Passengers can also be pilots. If no one is designated as pilot 

in command (PIC) and unplanned circumstances arise, the 

decision-making styles of several self-confident pilots may 

come into conflict. 

Pilots also need to understand that non-pilots may not 

understand the level of risk involved in flight. There is an 

element of risk in every flight. That is why SRM calls it risk 

management, not risk elimination. While a pilot may feel 

comfortable with the risk present in a night IFR flight, the 

passengers may not. A pilot employing SRM should ensure 

the passengers are involved in the decision-making and given 

tasks and duties to keep them busy and involved. If, upon a 

factual description of the risks present, the passengers decide 

to buy an airline ticket or rent a car, then a good decision has 

generally been made. This discussion also allows the pilot 

to move past what he or she thinks the passengers want to 

do and find out what they actually want to do. This removes 

self-induced pressure from the pilot. 

The Programming 

The advanced avionics aircraft adds an entirely new 

dimension to the way GA aircraft are flown. The electronic 

instrument displays, GPS, and autopilot reduce pilot 

workload and increase pilot situational awareness. While 

programming and operation of these devices are fairly 

simple and straightforward, unlike the analog instruments 

they replace, they tend to capture the pilot’s attention and 

hold it for long periods of time. To avoid this phenomenon, 

the pilot should plan in advance when and where the 

programming for approaches, route changes, and airport 

information gathering should be accomplished, as well as 

times it should not. Pilot familiarity with the equipment, the 

route, the local ATC environment, and personal capabilities 

vis-à-vis the automation should drive when, where, and how 

the automation is programmed and used. 

The pilot should also consider what his or her capabilities 

are in response to last minute changes of the approach (and 

the reprogramming required) and ability to make large-scale 

changes (a reroute for instance) while hand flying the aircraft. 

Since formats are not standardized, simply moving from one 

manufacturer’s equipment to another should give the pilot 

pause and require more conservative planning and decisions. 

The SRM process is simple. At least five times before 

and during the flight, the pilot should review and consider 

the “Plan, the Plane, the Pilot, the Passengers, and the 

Programming” and make the appropriate decision required 

by the current situation. It is often said that failure to make 

a decision is a decision. Under SRM and the 5 Ps, even the 

decision to make no changes to the current plan is made 

through a careful consideration of all the risk factors present. 

Perceive, Process, Perform (3P) Model 

The Perceive, Process, Perform (3P) model for ADM offers 

a simple, practical, and systematic approach that can be used 

during all phases of flight. To use it, the pilot will: 

• Perceive the given set of circumstances for a flight 

• Process by evaluating their impact on flight safety 

• Perform by implementing the best course of action 

Use the Perceive, Process, Perform, and Evaluate method as 

a continuous model for every aeronautical decision that you 

make. Although human beings will inevitably make mistakes, 

anything that you can do to recognize and minimize potential 

threats to your safety will make you a better pilot. 

Depending upon the nature of the activity and the time 

available, risk management processing can take place in 

any of three timeframes. [Figure 2-10] Most flight training 

activities take place in the “time-critical” timeframe for 

risk management. The six steps of risk management can be 

combined into an easy-to-remember 3P model for practical 

risk management: Perceive, Process, Perform with the PAVE, 

CARE and TEAM checklists. Pilots can help perceive 

hazards by using the PAVE checklist of: Pilot, Aircraft, 

enVironment, and External pressures. They can process 

hazards by using the CARE checklist of: Consequences, 

Alternatives, Reality, External factors. Finally, pilots can 

perform risk management by using the TEAM choice list 

of: Transfer, Eliminate, Accept, or Mitigate. 

PAVE Checklist: Identify Hazards and Personal 

Minimums 

In the first step, the goal is to develop situational awareness 

by perceiving hazards, which are present events, objects, or 

circumstances that could contribute to an undesired future 

event. In this step, the pilot will systematically identify and 

Strategic Deliberate Time-Critical 

Purpose

Used in a complex operation (e.g., 

introduction of new equipment); involves 

research, use of analysis tools, formal 

testing, or long term tracking of risks. 

Uses experience and brainstorming to identify 

hazards, assess risks, and develop controls 

for planning operations, review of standard 

operating or training procedures, etc. 

“On the fly” mental or verbal review using 

the basic risk management process 

during the execution phase of an activity. 

Figure 2-10. Risk management processing can take place in any of three timeframes. 

2-15 
 

list hazards associated with all aspects of the flight: Pilot, 

Aircraft, enVironment, and External pressures, which makes 

up the PAVE checklist. [Figure 2-11] For each element, 

ask “what could hurt me, my passengers, or my aircraft?” 

All four elements combine and interact to create a unique 

situation for any flight. Pay special attention to the pilotaircraft combination, and consider whether the combined 

“pilot-aircraft team” is capable of the mission you want to fly. 

For example, you may be a very experienced and proficient 

pilot, but your weather flying ability is still limited if you 

are flying a 1970s-model aircraft with no weather avoidance 

gear. On the other hand, you may have a new technically 

advanced aircraft with moving map GPS, weather datalink, 

and autopilot—but if you do not have much weather flying 

experience or practice in using this kind of equipment, you 

cannot rely on the airplane’s capability to compensate for 

your own lack of experience. 

CARE Checklist: Review Hazards and Evaluate Risks 

In the second step, the goal is to process this information to 

determine whether the identified hazards constitute risk, which 

is defined as the future impact of a hazard that is not controlled 

or eliminated. The degree of risk posed by a given hazard 

can be measured in terms of exposure (number of people or 

resources affected), severity (extent of possible loss), and 

probability (the likelihood that a hazard will cause a loss). The 

goal is to evaluate their impact on the safety of your flight, 

and consider “why must I CARE about these circumstances?” 

For each hazard that you perceived in step one, process by 

using the CARE checklist of: Consequences, Alternatives, 

Reality, External factors. [Figure 2-12] For example, let's 

evaluate a night flight to attend a business meeting: 

Consequences—departing after a full workday creates 

fatigue and pressure 

Alternatives—delay until morning; reschedule 

meeting; drive 

Reality —dangers and distractions of fatigue could 

lead to an accident 

External pressures—business meeting at destination 

might influence me 

A good rule of thumb for the processing phase: if you find 

yourself saying that it will “probably” be okay, it is definitely 

time for a solid reality check. If you are worried about missing 

a meeting, be realistic about how that pressure will affect 

not just your initial go/no-go decision, but also your inflight 

decisions to continue the flight or divert. 

TEAM Checklist: Choose and Implement Risk 

Controls 

Once you have perceived a hazard (step one) and processed 

its impact on flight safety (step two), it is time to move to the 

third step, perform. Perform risk management by using the 

TEAM checklist of: Transfer, Eliminate, Accept, Mitigate 

to deal with each factor. [Figure 2-13] 

Transfer—Should this risk decision be transferred to 

someone else (e.g., do you need to consult the chief 

flight instructor?) 

Eliminate—Is there a way to eliminate the hazard? 

Accept—Do the benefits of accepting risk outweigh 

the costs? 

Mitigate—What can you do to mitigate the risk? 

The goal is to perform by taking action to eliminate hazards 

or mitigate risk, and then continuously evaluate the outcome 

of this action. With the example of low ceilings at destination, 

for instance, the pilot can perform good ADM by selecting 

a suitable alternate, knowing where to find good weather, 

Pilots can perceive hazards by using the PAVE checklist: EnVironment 

Departure and destination airports have long runways. 

Weather is the main hazard. Although it is VFR, it is a typical 

summer day in the Mid-Atlantic region: hot (near 90 °F) hazy

Pilot (visibility 7 miles), and humid with a density altitude of 2,500 

Gayle is a healthy and well-rested private pilot with feet. Weather at the destination airport (located in the 

approximately 300 hours total flight time. Hazards include her mountains) is still IMC but forecast to improve to visual 

lack of overall and cross-country experience and the fact that meteorological conditions (VMC) prior to her arrival. En route 

she has not flown at all in 2 months. weather is VMC, but there is an AIRMET Sierra for pockets of 

IMC over mountain ridges along the proposed route of flight. 

Aircraft 

Although it does not have a panel-mount GPS or weather 

avoidance gear, the aircraft—a C182 Skylane with long-range
 

fuel tanks—is in good mechanical condition with no inoperative 

equipment. The instrument panel is a standard “six-pack.”
 

External pressures 

Gayle is making the trip to spend a weekend with relatives she 

does not see very often. Her family is very excited and has 

made a number of plans for the visit. 

Figure 2-11. A real-world example of how the 3P model guides decisions on a cross-country trip using the PAVE checklist. 

2-16 
Pilots can perceive hazards by using the CARE checklist: 

• Consequences: Gayle’s inexperience and lack of recent 

flight time create some risks for an accident, primarily because 

she plans to travel over mountains on a hazy day and land 

at an unfamiliar mountain airport that is still in IMC 

conditions. 

• Alternatives: Gayle might mitigate the pilot-related risk by 

hiring a CFI to accompany her and provide dual crosscountry instruction. An added benefit is the opportunity to 

broaden her flying experience in safe conditions. 

• Reality: Accepting the reality that limited experience can 

create additional risks is a key part of sound risk management 

and mitigation. 

• External Factors: Like many pilots, Gayle must contend with 

the emotional pressure associated with acknowledging that 

her skill and experience levels may be lower than she would 

like them to be. Pride can be a powerful external factor! 

Pilot 

Environment 

• Consequences: For a pilot whose experience consists 

mostly of local flights in good VMC, launching a long crosscountry flight over mountainous terrain in hazy conditions 

could lead to pilot disorientation and increase the risk of an 

accident. 

• Alternatives: Options include postponing the trip until the 

visibility improves, or modifying the route to avoid extended 

periods of time over the mountains. 

• Reality: Hazy conditions and mountainous terrain clearly 

create risks for an inexperienced VFR-only pilot. 

• External Factors: Few pilots are immune to the pressure of 

“get-there-itis,” which can sometimes induce a decision to 

launch or continue in less than ideal weather conditions. 

Aircraft 

• Consequences: This area presents low risk because the 

aircraft is in excellent mechanical condition and Gayle is 

familiar with its avionics. 

• Alternatives: Had there been a problem with her aircraft, 

Gayle might have considered renting another plane from her 

flight school. Bear in mind, however, that alternatives 

sometimes create new hazards. In this instance, there may 

be hazards associated with flying an unfamiliar aircraft with 

different avionics. 

• Reality: It is important to recognize the reality of an aircraft’s 

mechanical condition. If you find a maintenance discrepancy 

and then find yourself saying that it is “probably” okay to fly 

with it anyway, you need to revisit the consequences part of 

this checklist. 

• External Factors: Pilot decision-making can sometimes be 

influenced by the external pressure of needing to return the 

airplane to the FBO by a certain date and time. Because 

Gayle owns the airplane, there was no such pressure in this 

case. 

External pressures 

• Consequences: Any number of factors can create the risk of 

emotional pressure from a “get-there” mentality. In Gayle’s 

case, the consequences of her strong desire to visit family, 

her family’s expectations, and personal pride could induce 

her to accept unnecessary risks. 

• Alternatives: Gayle clearly needs to develop a mitigating 

strategy for each of the external factors associated with this 

trip. 

• Reality: Pilots sometimes tend to discount or ignore the 

potential impact of these external factors. Gayle’s open 

acknowledgement of these factors (e.g., “I might be 

pressured into pressing on so my mother won’t have to 

worry about our late arrival.”) is a critical element of effective 

risk management. 

• External Factors: (see above) 

 

 

 

Figure 2-12. A real-world examples of how the 3P model guides decisions on a cross-country trip using the CARE checklist. 

and carrying sufficient fuel to reach it. This course of action 

would mitigate the risk. The pilot also has the option to 

eliminate it entirely by waiting for better weather. 

Once the pilot has completed the 3P decision process and 

selected a course of action, the process begins anew because 

now the set of circumstances brought about by the course of 

action requires analysis. The decision-making process is a 

continuous loop of perceiving, processing, and performing. 

With practice and consistent use, running through the 3P 

cycle can become a habit that is as smooth, continuous, and 

automatic as a well-honed instrument scan. This basic set 

of practical risk management tools can be used to improve 

risk management. 

Your mental willingness to follow through on safe decisions, 

especially those that require delay or diversion is critical. You 

can bulk up your mental muscles by: 

•	 Using personal minimums checklist to make some 

decisions in advance of the flight. To develop a good 

personal minimums checklist, you need to assess your 

abilities and capabilities in a non-flying environment, 

when there is no pressure to make a specific trip. Once 

developed, a personal minimums checklist will give 

you a clear and concise reference point for making 

your go/no-go or continue/discontinue decisions. 

•	 In addition to having personal minimums, some pilots 

also like to use a preflight risk assessment checklist to 

help with the ADM and risk management processes. 

This kind of form assigns numbers to certain risks 

and situations, which can make it easier to see when 

a particular flight involves a higher level of risk 

•	 Develop a list of good alternatives during your 

processing phase. In marginal weather, for instance, 

you might mitigate the risk by identifying a reasonable 

2-17 
 

Pilots can perform risk management by using the TEAM checklist: 

To manage the risk associated with her inexperience and lack 

of recent flight time, Gayle can: 

• Transfer the risk entirely by having another pilot act as PIC. 

• Eliminate the risk by canceling the trip. 

• Accept the risk and fly anyway. 

• Mitigate the risk by flying with another pilot. 

Gayle chooses to mitigate the major risk by hiring a CFI to 

accompany her and provide dual cross-country instruction. 

An added benefit is the opportunity to broaden her flying 

experience. 

Pilot 

Environment 

To manage the risk associated with hazy conditions and 

mountainous terrain, Gayle can: 

• Transfer the risk of VFR in these conditions by asking an 

instrument-rated pilot to fly the trip under IFR. 

• Eliminate the risk by canceling the trip. 

• Accept the risk. 

• Mitigate the risk by careful preflight planning, filing a VFR 

flight plan, requesting VFR flight following, and using 

resources such as Flight Watch. 

Detailed preflight planning must be a vital part of Gayle’s 

weather risk mitigation strategy. The most direct route would 

put her over mountains for most of the trip. Because of the 

thick haze and pockets of IMC over mountains, Gayle might 

mitigate the risk by modifying the route to fly over valleys. This 

change will add 30 minutes to her estimated time of arrival 

(ETA), but the extra time is a small price to pay for avoiding 

possible IMC over mountains. Because her destination airport 

is IMC at the time of departure, Gayle needs to establish that 

VFR conditions exist at other airports within easy driving 

distance of her original destination. In addition, Gayle should 

review basic information (e.g., traffic pattern altitude, runway 

layout, frequencies) for these alternate airports. To further 

mitigate risk and practice good cockpit resource management, 

Gayle should file a VFR flight plan, use VFR flight following, 

and call Flight Watch to get weather updates en route. Finally, 

basic functions on her handheld GPS should also be practiced. 

Aircraft 

To manage risk associated with any doubts about the aircraft’s 

mechanical condition, Gayle can: 

• Transfer the risk by using a different airplane. 

• Eliminate the risk by canceling the trip. 

• Accept the risk. 

• Mitigate the remaining (residual) risk through review of 

aircraft performance and careful preflight inspection. 

Since she finds no problems with the aircraft’s mechanical 

condition, Gayle chooses to mitigate any remaining risk 

through careful preflight inspection of the aircraft. 

External pressures 

To mitigate the risk of emotional pressure from family 

expectations that can drive a “get-there” mentality, Gayle can: 

• Transfer the risk by having her co-pilot act as PIC and make 

the continue/divert decision. 

• Eliminate the risk by canceling the trip. 

• Accept the risk. 

• Mitigate the risk by managing family expectations and 

making alternative arrangements in the event of diversion to 

another airport. 

Gayle and her co-pilot choose to address this risk by agreeing 

that each pilot has a veto on continuing the flight, and that they 

will divert if either becomes uncomfortable with flight conditions. 

Because the destination airport is still IMC at the time of 

departure, Gayle establishes a specific point in the trip—an en 

route VORTAC located between the destination airport and the 

two alternates—as the logical place for her “final” continue/ 

divert decision. Rather than give her family a specific ETA that 

might make Gayle feel pressured to meet the schedule, she 

manages her family’s expectations by advising them that she 

will call when she arrives. 

Figure 2-13. A real-world example of how the 3P model guides decisions on a cross-country trip using the TEAM checklist. 

alternative airport for every 25–30 nautical mile 

segment of your route. 

• Preflight your passengers by preparing them for the 

possibility of delay and diversion, and involve them 

in your evaluation process. 

•	 Another important tool—overlooked by many pilots— 

is a good post-flight analysis. When you have safely 

secured the airplane, take the time to review and 

analyze the flight as objectively as you can. Mistakes 

and judgment errors are inevitable; the most important 

thing is for you to recognize, analyze, and learn from 

them before your next flight. 

The DECIDE Model 

Using the acronym “DECIDE,” the six-step process DECIDE 

Model is another continuous loop process that provides the 

pilot with a logical way of making decisions. [Figure 2-14] 

DECIDE means to Detect, Estimate, Choose a course of 

action, Identify solutions, Do the necessary actions, and 

Evaluate the effects of the actions. 

First, consider a recent accident involving a Piper Apache (PA23). The aircraft was substantially damaged during impact 

with terrain at a local airport in Alabama. The certificated 

airline transport pilot (ATP) received minor injuries and the 

certificated private pilot was not injured. The private pilot 

2-18 
2-19

1. Detect. The decision maker detects the fact that change has occurred.

2. Estimate. The decision maker estimates the need to counter or react to the change.

6. Evaluate. The decision maker evaluates the effect(s) of his/her action countering the change.

5. Do. The decision maker takes the necessary action.

4. Identify. The decision maker identifies actions which could successfully control the change.

3. Choose. The decision maker chooses a desirable outcome (in terms of success) for the flight.

The DECIDE model

Aeronautical Decision-Making

A. Analytical B. Automatic/Naturalistic

Evaluation of event

Outcome desired

What is best action to do

Effect of decision

Detection

Situation

Pilot Aircraft Enviroment External factors

• Risk or hazard

• Potential outcomes

• Capabilities of pilot

• Aircraft capabilities

• Outside factors

Solutions to get you there

Solution 1

Solution 2

Solution 3

Solution 4

Problem remains

Done

Evaluation of event

Outcome desired

Take action

Detection

Pilot Aircraft Enviroment External factors

• Risk to flight

• Pilot training

• Pilot experience

Successful

Figure 2-14. The DECIDE model has been recognized worldwide. Its application is illustrated in column A while automatic/naturalistic 

decision-making is shown in column B.

was receiving a checkride from the ATP (who was also a 

designated examiner) for a commercial pilot certificate with 

a multi-engine rating. After performing airwork at altitude, 

they returned to the airport and the private pilot performed a 

single-engine approach to a full stop landing. He then taxied 

back for takeoff, performed a short field takeoff, and then 

joined the traffic pattern to return for another landing. During 

the approach for the second landing, the ATP simulated a right 

engine failure by reducing power on the right engine to zero 

thrust. This caused the aircraft to yaw right. 

The procedure to identify the failed engine is a two-step 

process. First, adjust the power to the maximum controllable 

level on both engines. Because the left engine is the only 

engine delivering thrust, the yaw increases to the right, which 

necessitates application of additional left rudder application. 
 

The failed engine is the side that requires no rudder pressure, 

in this case the right engine. Second, having identified the 

failed right engine, the procedure is to feather the right engine 

and adjust power to maintain descent angle to a landing. 

However, in this case the pilot feathered the left engine because 

he assumed the engine failure was a left engine failure. During 

twin-engine training, the left engine out is emphasized more 

than the right engine because the left engine on most light 

twins is the critical engine. This is due to multiengine airplanes 

being subject to P-factor, as are single-engine airplanes. 

The descending propeller blade of each engine will produce 

greater thrust than the ascending blade when the airplane is 

operated under power and at positive angles of attack. The 

descending propeller blade of the right engine is also a greater 

distance from the center of gravity, and therefore has a longer 

moment arm than the descending propeller blade of the left 

engine. As a result, failure of the left engine will result in the 

most asymmetrical thrust (adverse yaw) because the right 

engine will be providing the remaining thrust. Many twins are 

designed with a counter-rotating right engine. With this design, 

the degree of asymmetrical thrust is the same with either engine 

inoperative. Neither engine is more critical than the other. 

Since the pilot never executed the first step of identifying 

which engine failed, he feathered the left engine and set the 

right engine at zero thrust. This essentially restricted the 

aircraft to a controlled glide. Upon realizing that he was 

not going to make the runway, the pilot increased power to 

both engines causing an enormous yaw to the left (the left 

propeller was feathered) whereupon the aircraft started to turn 

left. In desperation, the instructor closed both throttles and 

the aircraft hit the ground and was substantially damaged. 

This case is interesting because it highlights two particular 

issues. First, taking action without forethought can be just 

as dangerous as taking no action at all. In this case, the 

pilot’s actions were incorrect; yet, there was sufficient 

time to take the necessary steps to analyze the simulated 

emergency. The second and more subtle issue is that decisions 

made under pressure are sometimes executed based upon 

limited experience and the actions taken may be incorrect, 

incomplete, or insufficient to handle the situation. 

Detect (the Problem) 

Problem detection is the first step in the decision-making 

process. It begins with recognizing a change occurred or an 

expected change did not occur. A problem is perceived first 

by the senses and then it is distinguished through insight 

and experience. These same abilities, as well as an objective 

analysis of all available information, are used to determine 

the nature and severity of the problem. One critical error 

made during the decision-making process is incorrectly 

detecting the problem. In the previous example, the change 

that occurred was a yaw. 

Estimate (the Need To React) 

In the engine-out example, the aircraft yawed right, the pilot 

was on final approach, and the problem warranted a prompt 

solution. In many cases, overreaction and fixation excludes 

a safe outcome. For example, what if the cabin door of a 

Mooney suddenly opened in flight while the aircraft climbed 

through 1,500 feet on a clear sunny day? The sudden opening 

would be alarming, but the perceived hazard the open door 

presents is quickly and effectively assessed as minor. In 

fact, the door’s opening would not impact safe flight and 

can almost be disregarded. Most likely, a pilot would return 

to the airport to secure the door after landing. 

The pilot flying on a clear day faced with this minor problem 

may rank the open cabin door as a low risk. What about 

the pilot on an IFR climb out in IMC conditions with light 

intermittent turbulence in rain who is receiving an amended 

clearance from ATC? The open cabin door now becomes 

a higher risk factor. The problem has not changed, but the 

perception of risk a pilot assigns it changes because of the 

multitude of ongoing tasks and the environment. Experience, 

discipline, awareness, and knowledge influences how a pilot 

ranks a problem. 

Choose (a Course of Action) 

After the problem has been identified and its impact 

estimated, the pilot must determine the desirable outcome 

and choose a course of action. In the case of the multiengine 

pilot given the simulated failed engine, the desired objective 

is to safely land the airplane. 

Identify (Solutions) 

The pilot formulates a plan that will take him or her to the 

objective. Sometimes, there may be only one course of action 

available. In the case of the engine failure already at 500 

feet or below, the pilot solves the problem by identifying 

one or more solutions that lead to a successful outcome. It is 

important for the pilot not to become fixated on the process 

to the exclusion of making a decision. 

Do (the Necessary Actions) 

Once pathways to resolution are identified, the pilot selects the 

most suitable one for the situation. The multiengine pilot given 

the simulated failed engine must now safely land the aircraft. 

Evaluate (the Effect of the Action) 

Finally, after implementing a solution, evaluate the decision 

to see if it was correct. If the action taken does not provide 

the desired results, the process may have to be repeated. 

2-20 
 

Decision-Making in a Dynamic Environment 

A solid approach to decision-making is through the use of 

analytical models, such as the 5 Ps, 3P, and DECIDE. Good 

decisions result when pilots gather all available information, 

review it, analyze the options, rate the options, select a course 

of action, and evaluate that course of action for correctness. 

In some situations, there is not always time to make decisions 

based on analytical decision-making skills. A good example 

is a quarterback whose actions are based upon a highly fluid 

and changing situation. He intends to execute a plan, but new 

circumstances dictate decision-making on the fly. This type 

of decision-making is called automatic decision-making or 

naturalized decision-making. [Figure 2-14B] 

Automatic Decision-Making 

In an emergency situation, a pilot might not survive if he or 

she rigorously applies analytical models to every decision 

made as there is not enough time to go through all the options. 

Under these circumstances he or she should attempt to find 

the best possible solution to every problem. 

For the past several decades, research into how people 

actually make decisions has revealed that when pressed for 

time, experts faced with a task loaded with uncertainty first 

assess whether the situation strikes them as familiar. Rather 

than comparing the pros and cons of different approaches, 

they quickly imagine how one or a few possible courses of 

action in such situations will play out. Experts take the first 

workable option they can find. While it may not be the best of 

all possible choices, it often yields remarkably good results. 

The terms “naturalistic” and “automatic decision-making” 

have been coined to describe this type of decision-making. 

The ability to make automatic decisions holds true for a 

range of experts from firefighters to chess players. It appears 

the expert’s ability hinges on the recognition of patterns and 

consistencies that clarify options in complex situations. Experts 

appear to make provisional sense of a situation, without 

actually reaching a decision, by launching experience-based 

actions that in turn trigger creative revisions. 

This is a reflexive type of decision-making anchored in 

training and experience and is most often used in times of 

emergencies when there is no time to practice analytical 

decision-making. Naturalistic or automatic decision-making 

improves with training and experience, and a pilot will find 

himself or herself using a combination of decision-making 

tools that correlate with individual experience and training. 

Operational Pitfalls 

Although more experienced pilots are likely to make more 

automatic decisions, there are tendencies or operational 

pitfalls that come with the development of pilot experience. 

These are classic behavioral traps into which pilots have 

been known to fall. More experienced pilots, as a rule, try 

to complete a flight as planned, please passengers, and meet 

schedules. The desire to meet these goals can have an adverse 

effect on safety and contribute to an unrealistic assessment 

of piloting skills. All experienced pilots have fallen prey to, 

or have been tempted by, one or more of these tendencies in 

their flying careers. These dangerous tendencies or behavior 

patterns, which must be identified and eliminated, include 

the operational pitfalls shown in Figure 2-15. 

Stress Management 

Everyone is stressed to some degree almost all of the time. A 

certain amount of stress is good since it keeps a person alert 

and prevents complacency. Effects of stress are cumulative 

and, if the pilot does not cope with them in an appropriate 

way, they can eventually add up to an intolerable burden. 

Performance generally increases with the onset of stress, 

peaks, and then begins to fall off rapidly as stress levels 

exceed a person’s ability to cope. The ability to make 

effective decisions during flight can be impaired by stress. 

There are two categories of stress—acute and chronic. These 

are both explained in Chapter 17, “Aeromedical Factors.” 

Factors referred to as stressors can increase a pilot’s risk of 

error in the flight deck. [Figure 2-16] Remember the cabin 

door that suddenly opened in flight on the Mooney climbing 

through 1,500 feet on a clear sunny day? It may startle the 

pilot, but the stress would wane when it became apparent 

the situation was not a serious hazard. Yet, if the cabin door 

opened in IMC conditions, the stress level makes significant 

impact on the pilot’s ability to cope with simple tasks. The 

key to stress management is to stop, think, and analyze before 

jumping to a conclusion. There is usually time to think before 

drawing unnecessary conclusions. 

There are several techniques to help manage the accumulation 

of life stresses and prevent stress overload. For example, to 

help reduce stress levels, set aside time for relaxation each 

day or maintain a program of physical fitness. To prevent 

stress overload, learn to manage time more effectively to 

avoid pressures imposed by getting behind schedule and not 

meeting deadlines. 

Use of Resources 

To make informed decisions during flight operations, a pilot 

must also become aware of the resources found inside and 

outside the flight deck. Since useful tools and sources of 

information may not always be readily apparent, learning 

to recognize these resources is an essential part of ADM 

training. Resources must not only be identified, but a pilot 

must also develop the skills to evaluate whether there is 

2-21 
Operational pitfalls 

Peer pressure 

Poor decision-making may be based upon an emotional response to peers, rather than evaluating a situation objectively. 

Mindset 

A pilot displays mind set through an inability to recognize and cope with changes in a given situation. 

Get-there-itis 

This disposition impairs pilot judgment through a fixation on the original goal or destination, combined with a disregard for any 

alternative course of action. 

Duck-under syndrome 

A pilot may be tempted to make it into an airport by descending below minimums during an approach. There may be a belief that 

there is a built-in margin of error in every approach procedure, or a pilot may want to admit that the landing cannot be completed 

and a missed approach must be initiated. 

Scud running 

This occurs when a pilot tries to maintain visual contact with the terrain at low altitudes while instrument conditions exist. 

Continuing visual flight rules (VFR) into instrument conditions 

Spatial disorientation or collision with ground/obstacles may occur when a pilot continues VFR into instrument conditions. This can 

be even more dangerous if the pilot is not instrument rated or current. 

Getting behind the aircraft 

This pitfall can be caused by allowing events or the situation to control pilot actions. A constant state of surprise at what happens 

next may be exhibited when the pilot is getting behind the aircraft. 

Loss of positional or situational awareness 

In extreme cases, when a pilot gets behind the aircraft, a loss of positional or situational awareness may result. The pilot may not 

know the aircraft’s geographical location or may be unable to recognize deteriorating circumstances. 

Operating without adequate fuel reserves 

Ignoring minimum fuel reserve requirements is generally the result of overconfidence, lack of flight planning, or disregarding 

applicable regulations. 

Descent below the minimum en route altitude 

The duck-under syndrome, as mentioned above, can also occur during the en route portion of an IFR flight. 

Flying outside the envelope 

The assumed high performance capability of a particular aircraft may cause a mistaken belief that it can meet the demands 

imposed by a pilot’s overestimated flying skills. 

Neglect of flight planning, preflight inspections, and checklists 

A pilot may rely on short- and long-term memory, regular flying skills, and familiar routes instead of established procedures and 

published checklists. This can be particularly true of experienced pilots. 

Operational Pitfalls 

Figure 2-15. Typical operational pitfalls requiring pilot awareness. 

Stressors 

Environmental 

Conditions associated with the environment, such as temperature and humidity extremes, noise, vibration, and lack of oxygen. 

Physiological stress 

Physical conditions, such as fatigue, lack of physical fitness, sleep loss, missed meals (leading to low blood sugar levels), and 

illness. 

Psychological stress 

Social or emotional factors, such as a death in the family, a divorce, a sick child, or a demotion at work. This type of stress may 

also be related to mental workload, such as analyzing a problem, navigating an aircraft, or making decisions. 

Figure 2-16. System stressors. Environmental, physiological, and psychological stress are factors that affect decision-making skills. 

These stressors have a profound impact especially during periods of high workload. 

2-22 
 

 

time to use a particular resource and the impact its use will 

have upon the safety of flight. For example, the assistance 

of ATC may be very useful if a pilot becomes lost, but in 

an emergency situation, there may be no time available to 

contact ATC. 

Internal Resources 

One of the most underutilized resources may be the 

person in the right seat, even if the passenger has no flying 

experience. When appropriate, the PIC can ask passengers 

to assist with certain tasks, such as watching for traffic or 

reading checklist items. The following are some other ways 

a passenger can assist: 

•	 Provide information in an irregular situation, 

especially if familiar with flying. A strange smell or 

sound may alert a passenger to a potential problem. 

• Confirm after the pilot that the landing gear is down. 

• Learn to look at the altimeter for a given altitude in a 

descent. 

• Listen to logic or lack of logic. 

Also, the process of a verbal briefing (which can happen 

whether or not passengers are aboard) can help the PIC in 

the decision-making process. For example, assume a pilot 

provides a lone passenger a briefing of the forecast landing 

weather before departure. When the Automatic Terminal 

Information Service (ATIS) is picked up, the weather 

has significantly changed. The discussion of this forecast 

change can lead the pilot to reexamine his or her activities 

and decision-making. [Figure 2-17] Other valuable internal 

resources include ingenuity, aviation knowledge, and flying 

skill. Pilots can increase flight deck resources by improving 

these characteristics. 

When flying alone, another internal resource is verbal 

communication. It has been established that verbal 

communication reinforces an activity; touching an object 

while communicating further enhances the probability an 

activity has been accomplished. For this reason, many solo 

pilots read the checklist out loud; when they reach critical 

items, they touch the switch or control. For example, to 

ascertain the landing gear is down, the pilot can read the 

checklist. But, if he or she touches the gear handle during the 

process, a safe extension of the landing gear is confirmed. 

It is necessary for a pilot to have a thorough understanding 

of all the equipment and systems in the aircraft being flown. 

Lack of knowledge, such as knowing if the oil pressure 

gauge is direct reading or uses a sensor, is the difference 

between making a wise decision or poor one that leads to 

a tragic error. 

Figure 2-17. When possible, have a passenger reconfirm that critical 

tasks are completed. 

Checklists are essential flight deck internal resources. They 

are used to verify the aircraft instruments and systems are 

checked, set, and operating properly, as well as ensuring 

the proper procedures are performed if there is a system 

malfunction or in-flight emergency. Students reluctant to 

use checklists can be reminded that pilots at all levels of 

experience refer to checklists, and that the more advanced the 

aircraft is, the more crucial checklists become. In addition, the 

pilot’s operating handbook (POH) is required to be carried on 

board the aircraft and is essential for accurate flight planning 

and resolving in-flight equipment malfunctions. However, 

the most valuable resource a pilot has is the ability to manage 

workload whether alone or with others. 

External Resources 

ATC and flight service specialists are the best external 

resources during flight. In order to promote the safe, orderly 

flow of air traffic around airports and, along flight routes, the 

ATC provides pilots with traffic advisories, radar vectors, 

and assistance in emergency situations. Although it is the 

PIC’s responsibility to make the flight as safe as possible, 

a pilot with a problem can request assistance from ATC. 

[Figure 2-18] For example, if a pilot needs to level off, be 

Figure 2-18. Controllers work to make flights as safe as possible. 

2-23 
 

given a vector, or decrease speed, ATC assists and becomes 

integrated as part of the crew. The services provided by ATC 

can not only decrease pilot workload, but also help pilots 

make informed in-flight decisions. 

The Flight Service Stations (FSSs) are air traffic facilities 

that provide pilot briefing, en route communications, VFR 

search and rescue services, assist lost aircraft and aircraft 

in emergency situations, relay ATC clearances, originate 

Notices to Airmen (NOTAM), broadcast aviation weather 

and National Airspace System (NAS) information, receive 

and process IFR flight plans, and monitor navigational aids 

(NAVAIDs). In addition, at selected locations, FSSs provide 

En Route Flight Advisory Service (Flight Watch), issue 

airport advisories, and advise Customs and Immigration of 

transborder flights. Selected FSSs in Alaska also provide 

TWEB recordings and take weather observations. 

Situational Awareness 

Situational awareness is the accurate perception and 

understanding of all the factors and conditions within 

the five fundamental risk elements (flight, pilot, aircraft, 

environment, and type of operation that comprise any given 

aviation situation) that affect safety before, during, and after 

the flight. Monitoring radio communications for traffic, 

weather discussion, and ATC communication can enhance 

situational awareness by helping the pilot develop a mental 

picture of what is happening. 

Maintaining situational awareness requires an understanding 

of the relative significance of all flight related factors and their 

future impact on the flight. When a pilot understands what is 

going on and has an overview of the total operation, he or she 

is not fixated on one perceived significant factor. Not only 

is it important for a pilot to know the aircraft’s geographical 

location, it is also important he or she understand what is 

happening. For instance, while flying above Richmond, 

Virginia, toward Dulles Airport or Leesburg, the pilot 

should know why he or she is being vectored and be able to 

anticipate spatial location. A pilot who is simply making turns 

without understanding why has added an additional burden 

to his or her management in the event of an emergency. To 

maintain situational awareness, all of the skills involved in 

ADM are used. 

Obstacles to Maintaining Situational Awareness 

Fatigue, stress, and work overload can cause a pilot to fixate 

on a single perceived important item and reduce an overall 

situational awareness of the flight. A contributing factor 

in many accidents is a distraction that diverts the pilot’s 

attention from monitoring the instruments or scanning 

outside the aircraft. Many flight deck distractions begin as a 

minor problem, such as a gauge that is not reading correctly, 

but result in accidents as the pilot diverts attention to the 

perceived problem and neglects proper control of the aircraft. 

Workload Management 

Effective workload management ensures essential operations 

are accomplished by planning, prioritizing, and sequencing 

tasks to avoid work overload. [Figure 2-19] As experience 

is gained, a pilot learns to recognize future workload 

requirements and can prepare for high workload periods 

during times of low workload. Reviewing the appropriate 

chart and setting radio frequencies well in advance of when 

they are needed helps reduce workload as the flight nears the 

airport. In addition, a pilot should listen to ATIS, Automated 

Surface Observing System (ASOS), or Automated Weather 

Observing System (AWOS), if available, and then monitor 

the tower frequency or Common Traffic Advisory Frequency 

(CTAF) to get a good idea of what traffic conditions to 

expect. Checklists should be performed well in advance so 

there is time to focus on traffic and ATC instructions. These 

procedures are especially important prior to entering a highdensity traffic area, such as Class B airspace. 

Recognizing a work overload situation is also an important 

component of managing workload. The first effect of 

high workload is that the pilot may be working harder but 

accomplishing less. As workload increases, attention cannot 

be devoted to several tasks at one time, and the pilot may 

begin to focus on one item. When a pilot becomes task 

saturated, there is no awareness of input from various sources, 

so decisions may be made on incomplete information and the 

possibility of error increases. [Figure 2-20] 

When a work overload situation exists, a pilot needs to stop, 

think, slow down, and prioritize. It is important to understand 

how to decrease workload. For example, in the case of the 

cabin door that opened in VFR flight, the impact on workload 

should be insignificant. If the cabin door opens under 

IFR different conditions, its impact on workload changes. 

Therefore, placing a situation in the proper perspective, 

Figure 2-19. Balancing workloads can be a difficult task. 

2-24 
remaining calm, and thinking rationally are key elements in •	 In addition to the SAFETY list, discuss with 

reducing stress and increasing the capacity to fly safely. This passengers whether or not smoking is permitted, flight 

ability depends upon experience, discipline, and training. route altitudes, time en route, destination, weather 

during flight, expected weather at the destination, 

Managing Risks controls and what they do, and the general capabilities 

The ability to manage risks begins with preparation. Here and limitations of the aircraft. 

are some things a pilot can do to manage risks: •	 Use a sterile flight deck (one that is completely silent 

•	 Assess the flight’s risk based upon experience. Use with no pilot communication with passengers or by 

some form of risk assessment. For example, if the passengers) from the time of departure to the first 

weather is marginal and the pilot has little IMC intermediate altitude and clearance from the local 

training, it is probably a good idea to cancel the flight. airspace. 

•	 Brief passengers using the SAFETY list: •	 Use a sterile flight deck during arrival from the first 

radar vector for approach or descent for the approach. S	 Seat belts fastened for taxi, takeoff, landing •	 Keep the passengers informed during times when the Shoulder harness fastened for takeoff, landing workload is low. 

Seat position adjusted and locked in place •	 Consider using the passenger in the right seat for 

A	 Air vents (location and operation) simple tasks, such as holding the chart. This relieves 

All environmental controls (discussed) the pilot of a task. 

Action in case of any passenger discomfort Automation 

F	 Fire extinguisher (location and operation) In the GA community, an automated aircraft is generally 

E	 Exit doors (how to secure; how to open) comprised of an integrated advanced avionics system 

Emergency evacuation plan consisting of a primary flight display (PFD), a multifunction 

flight display (MFD) including an instrument-certified global Emergency/survival kit (location and contents) positioning system (GPS) with traffic and terrain graphics, 

T	 Traffic (scanning, spotting, notifying pilot) and a fully integrated autopilot. This type of aircraft is 

Talking, (“sterile flight deck” expectations) commonly known as a technically advanced aircraft (TAA). 

In a TAA aircraft, there are typically two display (computer) Y Your questions? (Speak up!) screens: PFD (left display screen) and MFD. 

Figure 2-20. The pilot has a certain capacity of doing work and handling tasks. However, there is a point where the tasking exceeds the 

pilot’s capability. When this happens, tasks are either not performed properly or some are not performed at all. 

Preflight 

Takeoff 

Cruise 

Approach & landing 

Time 

Task load 

High 

Low Pilot capabilities 

Task requirements 

2-25 
Automation is the single most important advance in aviation 

technologies. Electronic flight displays (EFDs) have made 

vast improvements in how information is displayed and 

what information is available to the pilot. Pilots can access 

electronic databases that contain all of the information 

traditionally contained in multiple handbooks, reducing 

clutter in the flight deck. [Figure 2-21] 

MFDs are capable of displaying moving maps that mirror 

sectional charts. These detailed displays depict all airspace, 

including Temporary Flight Restrictions (TFRs). MFDs are 

so descriptive that many pilots fall into the trap of relying 

solely on the moving maps for navigation. Pilots also draw 

upon the database to familiarize themselves with departure 

and destination airport information. 

More pilots now rely on electronic databases for flight 

planning and use automated flight planning tools rather 

than planning the flight by the traditional methods of laying 

out charts, drawing the course, identifying navigation 

points (assuming a VFR flight), and using the POH to 

figure out the weight and balance and performance charts. 

Whichever method a pilot chooses to plan a flight, it is 

Figure 2-21. Electronic flight instrumentation comes in many 

systems and provides a myriad of information to the pilot. 

important to remember to check and confirm calculations. 

Always remember that it is up to the pilot to maintain basic 

airmanship skills and use those skills often to maintain 

proficiency in all tasks. 

Although automation has made flying safer, automated 

systems can make some errors more evident and sometimes 

hide other errors or make them less evident. There are 

concerns about the effect of automation on pilots. In a study 

published in 1995, the British Airline Pilots Association 

officially voiced its concern that “Airline pilots increasingly 

lack ‘basic flying skills’ as a result of reliance on automation.” 

This reliance on automation translates into a lack of basic flying 

skills that may affect the pilot’s ability to cope with an in-flight 

emergency, such as sudden mechanical failure. The worry that 

pilots are becoming too reliant on automated systems and are 

not being encouraged or trained to fly manually has grown 

with the increase in the number of MFD flight decks. 

As automated flight decks began entering everyday line 

operations, instructors and check airmen grew concerned 

about some of the unanticipated side effects. Despite the 

promise of reducing human mistakes, the flight managers 

reported the automation actually created much larger errors 

at times. In the terminal environment, the workload in an 

automated flight deck actually seemed higher than in the older 

analog flight decks. At other times, the automation seemed 

to lull the flight crews into complacency. Over time, concern 

surfaced that the manual flying skills of the automated flight 

crews deteriorated due to over-reliance on computers. The 

flight crew managers said they worried that pilots would 

have less “stick-and-rudder” proficiency when those skills 

were needed to manually resume direct control of the aircraft. 

A major study was conducted to evaluate the performance 

of two groups of pilots. The control group was composed of 

pilots who flew an older version of a common twin-jet airliner 

equipped with analog instrumentation and the experimental 

group was composed of pilots who flew the same aircraft, 

but newer models equipped with an electronic flight 

instrument system (EFIS) and a flight management system 

(FMS). The pilots were evaluated in maintaining aircraft 

parameters, such as heading, altitude, airspeed, glideslope, 

and localizer deviations, as well as pilot control inputs. These 

were recorded during a variety of normal, abnormal, and 

emergency maneuvers during 4 hours of simulator sessions. 

2-26 
 

 

Results of the Study 

When pilots who had flown EFIS for several years were 

required to fly various maneuvers manually, the aircraft 

parameters and flight control inputs clearly showed some 

erosion of flying skills. During normal maneuvers, such as 

turns to headings without a flight director, the EFIS group 

exhibited somewhat greater deviations than the analog group. 

Most of the time, the deviations were within the practical test 

standards (PTS), but the pilots definitely did not keep on the 

localizer and glideslope as smoothly as the analog group. 

The differences in hand-flying skills between the two groups 

became more significant during abnormal maneuvers, such as 

accelerated descent profiles known as “slam-dunks.” When 

given close crossing restrictions, the analog crews were more 

adept at the mental math and usually maneuvered the aircraft 

in a smoother manner to make the restriction. On the other 

hand, the EFIS crews tended to go “heads down” and tried 

to solve the crossing restriction on the FMS. [Figure 2-22] 

Another situation used in the simulator experiment reflected 

real world changes in approach that are common and can 

be assigned on short notice. Once again, the analog crews 

transitioned more easily to the parallel runway’s localizer, 

whereas the EFIS crews had a much more difficult time with 

the pilot going head down for a significant amount of time 

trying to program the new approach into the FMS. 

While a pilot’s lack of familiarity with the EFIS is often 

an issue, the approach would have been made easier by 

disengaging the automated system and manually flying the 

approach. At the time of this study, the general guidelines 

in the industry were to let the automated system do as much 

of the flying as possible. That view has since changed and 

it is recommended that pilots use their best judgment when 

choosing which level of automation will most efficiently do 

the task considering the workload and situational awareness. 

Emergency maneuvers clearly broadened the difference in 

manual flying skills between the two groups. In general, the 

analog pilots tended to fly raw data, so when they were given 

an emergency, such as an engine failure, and were instructed 

to fly the maneuver without a flight director, they performed 

it expertly. By contrast, SOP for EFIS operations at the time 

was to use the flight director. When EFIS crews had their flight 

directors disabled, their eye scan again began a more erratic 

searching pattern and their manual flying subsequently suffered. 

Those who reviewed the data saw that the EFIS pilots who 

better managed the automation also had better flying skills. 

While the data did not reveal whether those skills preceded 

or followed automation, it did indicate that automation 

management needed to be improved. Recommended “best 

practices” and procedures have remedied some of the earlier 

problems with automation. 

Pilots must maintain their flight skills and ability to maneuver 

aircraft manually within the standards set forth in the PTS. It 

is recommended that pilots of automated aircraft occasionally 

disengage the automation and manually fly the aircraft to 

maintain stick-and-rudder proficiency. It is imperative that 

the pilots understand that the EFD adds to the overall quality 

of the flight experience, but it can also lead to catastrophe if 

not utilized properly. At no time is the moving map meant to 

substitute for a VFR sectional or low altitude en route chart. 

Equipment Use 

Autopilot Systems 

In a single-pilot environment, an autopilot system can greatly 

reduce workload. [Figure 2-23] As a result, the pilot is free 

to focus his or her attention on other flight deck duties. This 

can improve situational awareness and reduce the possibility 

of a CFIT accident. While the addition of an autopilot may 

certainly be considered a risk control measure, the real 

challenge comes in determining the impact of an inoperative 

unit. If the autopilot is known to be inoperative prior to 

departure, this may factor into the evaluation of other risks. 

For example, the pilot may be planning for a VHF 

omnidirectional range (VOR) approach down to minimums 

on a dark night into an unfamiliar airport. In such a case, the 

pilot may have been relying heavily on a functioning autopilot 

capable of flying a coupled approach. This would free the 

pilot to monitor aircraft performance. A malfunctioning 

autopilot could be the single factor that takes this from a 

medium to a serious risk. At this point, an alternative needs 

to be considered. On the other hand, if the autopilot were to 

fail at a critical (high workload) portion of this same flight, 

the pilot must be prepared to take action. Instead of simply 

being an inconvenience, this could quickly turn into an 

emergency if not properly handled. The best way to ensure 

a pilot is prepared for such an event is to carefully study the 

issue prior to departure and determine well in advance how 

an autopilot failure is to be handled. 

Familiarity 

As previously discussed, pilot familiarity with all equipment 

is critical in optimizing both safety and efficiency. If a pilot is 

unfamiliar with any aircraft systems, this will add to workload 

and may contribute to a loss of situational awareness. This 

level of proficiency is critical and should be looked upon as 

a requirement, not unlike carrying an adequate supply of fuel. 

As a result, pilots should not look upon unfamiliarity with the 

aircraft and its systems as a risk control measure, but instead as 

a hazard with high risk potential. Discipline is key to success. 

2-27 
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Figure 2-22. Two similar flight decks equipped with the same information two different ways, analog and digital. What are they indicating? 

Chances are that the analog pilot will review the top display before the bottom display. Conversely, the digitally trained pilot will review 

the instrument panel on the bottom first.
 

 

Figure 2-23. An example of an autopilot system. 

Respect for Onboard Systems 

Automation can assist the pilot in many ways, but a 

thorough understanding of the system(s) in use is essential 

to gaining the benefits it can offer. Understanding leads 

to respect, which is achieved through discipline and the 

mastery of the onboard systems. It is important to fly the 

aircraft using minimal information from the primary flight 

display (PFD). This includes turns, climbs, descents, and 

being able to fly approaches. 

Reinforcement of Onboard Suites 

The use of an EFD may not seem intuitive, but competency 

becomes better with understanding and practice. Computerbased software and incremental training help the pilot become 

comfortable with the onboard suites. Then the pilot needs 

to practice what was learned in order to gain experience. 

Reinforcement not only yields dividends in the use of 

automation, it also reduces workload significantly. 

Getting Beyond Rote Workmanship 

The key to working effectively with automation is getting 

beyond the sequential process of executing an action. If a 

pilot has to analyze what key to push next, or always uses 

the same sequence of keystrokes when others are available, 

he or she may be trapped in a rote process. This mechanical 

process indicates a shallow understanding of the system. 

Again, the desire is to become competent and know what to 

do without having to think about, “what keystroke is next.” 

Operating the system with competency and comprehension 

benefits a pilot when situations become more diverse and 

tasks increase. 

Understand the Platform 

Contrary to popular belief, flight in aircraft equipped with 

different electronic management suites requires the same 

attention as aircraft equipped with analog instrumentation 

and a conventional suite of avionics. The pilot should review 

and understand the different ways in which EFD are used in 

a particular aircraft. [Figure 2-24] 

The following are two simple rules for use of an EFD: 

• Be able to fly the aircraft to the standards in the PTS. 

Although this may seem insignificant, knowing how to 

fly the aircraft to a standard makes a pilot’s airmanship 

smoother and allows him or her more time to attend 

to the system instead of managing multiple tasks. 

•	 Read and understand the installed electronic flight 

systems manuals to include the use of the autopilot 

and the other onboard electronic management tools. 

Managing Aircraft Automation 

Before any pilot can master aircraft automation, he or she 

must first know how to fly the aircraft. Maneuvers training 

remains an important component of flight training because 

almost 40 percent of all GA accidents take place in the 

Figure 2-24. Examples of different platforms. Top to bottom are the 

Beechcraft Baron G58, Cirrus SR22, and Cirrus Entega. 

2-29 
 

landing phase, one realm of flight that still does not involve 

programming a computer to execute. Another 15 percent 

of all GA accidents occurs during takeoff and initial climb. 

An advanced avionics safety issue identified by the FAA 

concerns pilots who apparently develop an unwarranted 

over-reliance in their avionics and the aircraft, believing 

that the equipment will compensate for pilot shortcomings. 

Related to the over-reliance is the role of ADM, which is 

probably the most significant factor in the GA accident record 

of high performance aircraft used for cross-country flight. 

The FAA advanced avionics aircraft safety study found that 

poor decision-making seems to afflict new advanced avionics 

pilots at a rate higher than that of GA as a whole. The review 

of advanced avionics accidents cited in this study shows the 

majority are not caused by something directly related to the 

aircraft, but by the pilot’s lack of experience and a chain of 

poor decisions. One consistent theme in many of the fatal 

accidents is continued VFR flight into IMC. 

Thus, pilot skills for normal and emergency operations hinge 

not only on mechanical manipulation of the stick and rudder, 

but also include the mental mastery of the EFD. Three key 

flight management skills are needed to fly the advanced 

avionics safely: information, automation, and risk. 

Information Management 

For the newly transitioning pilot, the PFD, MFD, and GPS/ 

VHF navigator screens seem to offer too much information 

presented in colorful menus and submenus. In fact, the pilot 

may be drowning in information but unable to find a specific 

piece of information. It might be helpful to remember these 

systems are similar to computers that store some folders on 

a desktop and some within a hierarchy. 

The first critical information management skill for flying with 

advanced avionics is to understand the system at a conceptual 

level. Remembering how the system is organized helps the 

pilot manage the available information. It is important to 

understanding that learning knob-and-dial procedures is not 

enough. Learning more about how advanced avionics systems 

work leads to better memory for procedures and allows pilots 

to solve problems they have not seen before. 

There are also limits to understanding. It is generally impossible 

to understand all of the behaviors of a complex avionics 

system. Knowing to expect surprises and to continually learn 

new things is more effective than attempting to memorize 

mechanical manipulation of the knobs. Simulation software 

and books on the specific system used are of great value. 

The second critical information management skill is stop, 

look, and read. Pilots new to advanced avionics often become 

fixated on the knobs and try to memorize each and every 

sequence of button pushes, pulls, and turns. A far better 

strategy for accessing and managing the information available 

in advanced avionics computers is to stop, look, and read. 

Reading before pushing, pulling, or twisting can often save 

a pilot some trouble. 

Once behind the display screens on an advanced avionics 

aircraft, the pilot’s goal is to meter, manage, and prioritize 

the information flow to accomplish specific tasks. 

Certificated flight instructors (CFIs), as well as pilots 

transitioning to advanced avionics, will find it helpful to 

corral the information flow. This is possible through such 

tactics as configuring the aspects of the PFD and MFD 

screens according to personal preferences. For example, 

most systems offer map orientation options that include 

“north up,” “track up,” “DTK” (desired track up), and 

“heading up.” Another tactic is to decide, when possible, 

how much (or how little) information to display. Pilots can 

also tailor the information displayed to suit the needs of a 

specific flight. 

Information flow can also be managed for a specific 

operation. The pilot has the ability to prioritize information 

for a timely display of exactly the information needed for any 

given flight operation. Examples of managing information 

display for a specific operation include: 

•	 Program map scale settings for en route versus 

terminal area operation. 

• Utilize the terrain awareness page on the MFD for a 

night or IMC flight in or near the mountains. 

• Use the nearest airports inset on the PFD at night or 

over inhospitable terrain. 

• Program the weather datalink set to show echoes and 

METAR status flags. 

Enhanced Situational Awareness 

An advanced avionics aircraft offers increased safety with 

enhanced situational awareness. Although aircraft flight 

manuals (AFM) explicitly prohibit using the moving map, 

topography, terrain awareness, traffic, and weather datalink 

displays as the primary data source, these tools nonetheless 

give the pilot unprecedented information for enhanced 

situational awareness. Without a well-planned information 

management strategy, these tools also make it easy for an 

unwary pilot to slide into the complacent role of passenger 

in command. 

Consider the pilot whose navigational information 

management strategy consists solely of following the 

magenta line on the moving map. He or she can easily fly 

into geographic or regulatory disaster, if the straight-line GPS 

2-30 
 

 

 

 

course goes through high terrain or prohibited airspace, or if 

the moving map display fails. 

A good strategy for maintaining situational awareness 

information management should include practices that help 

ensure that awareness is enhanced, not diminished, by the use 

of automation. Two basic procedures are to always doublecheck the system and verbal callouts. At a minimum, ensure 

the presentation makes sense. Was the correct destination fed 

into the navigation system? Callouts—even for single-pilot 

operations—are an excellent way to maintain situational 

awareness, as well as manage information. 

Other ways to maintain situational awareness include: 

•	 Perform verification check of all programming. Before 

departure, check all information programmed while 

on the ground. 

• Check the flight routing. Before departure, ensure all 

routing matches the planned flight route. Enter the 

planned route and legs, to include headings and leg 

length, on a paper log. Use this log to evaluate what 

has been programmed. If the two do not match, do not 

assume the computer data is correct, double check the 

computer entry. 

•	 Verify waypoints. 

• Make use of all onboard navigation equipment. For 

example, use VOR to back up GPS and vice versa. 

•	 Match the use of the automated system with pilot 

proficiency. Stay within personal limitations. 

•	 Plan a realistic flight route to maintain situational 

awareness. For example, although the onboard 

equipment allows a direct flight from Denver, 

Colorado, to Destin, Florida, the likelihood of 

rerouting around Eglin Air Force Base’s airspace is 

high. 

•	 Be ready to verify computer data entries. For example, 

incorrect keystrokes could lead to loss of situational 

awareness because the pilot may not recognize errors 

made during a high workload period. 

Automation Management 

Advanced avionics offer multiple levels of automation, from 

strictly manual flight to highly automated flight. No one level 

of automation is appropriate for all flight situations, but in 

order to avoid potentially dangerous distractions when flying 

with advanced avionics, the pilot must know how to manage 

the course deviation indicator (CDI), the navigation source, 

and the autopilot. It is important for a pilot to know the 

peculiarities of the particular automated system being used. 

This ensures the pilot knows what to expect, how to monitor 

for proper operation, and promptly take appropriate action if 

the system does not perform as expected. 

For example, at the most basic level, managing the autopilot 

means knowing at all times which modes are engaged 

and which modes are armed to engage. The pilot needs to 

verify that armed functions (e.g., navigation tracking or 

altitude capture) engage at the appropriate time. Automation 

management is another good place to practice the callout 

technique, especially after arming the system to make a 

change in course or altitude. 

In advanced avionics aircraft, proper automation management 

also requires a thorough understanding of how the autopilot 

interacts with the other systems. For example, with some 

autopilots, changing the navigation source on the e-HSI from 

GPS to LOC or VOR while the autopilot is engaged in NAV 

(course tracking mode) causes the autopilot’s NAV mode to 

disengage. The autopilot’s lateral control will default to ROL 

(wing level) until the pilot takes action to reengage the NAV 

mode to track the desired navigation source. 

Risk Management 

Risk management is the last of the three flight management 

skills needed for mastery of the glass flight deck aircraft. The 

enhanced situational awareness and automation capabilities 

offered by a glass flight deck airplane vastly expand its safety 

and utility, especially for personal transportation use. At the 

same time, there is some risk that lighter workloads could 

lead to complacency. 

Humans are characteristically poor monitors of automated 

systems. When asked to passively monitor an automated 

system for faults, abnormalities, or other infrequent events, 

humans perform poorly. The more reliable the system, the 

poorer the human performance. For example, the pilot only 

monitors a backup alert system, rather than the situation 

that the alert system is designed to safeguard. It is a paradox 

of automation that technically advanced avionics can both 

increase and decrease pilot awareness. 

It is important to remember that EFDs do not replace basic 

flight knowledge and skills. They are a tool for improving 

flight safety. Risk increases when the pilot believes the gadgets 

compensate for lack of skill and knowledge. It is especially 

important to recognize there are limits to what the electronic 

systems in any light GA aircraft can do. Being PIC requires 

sound ADM, which sometimes means saying “no” to a flight. 

Risk is also increased when the pilot fails to monitor the 

systems. By failing to monitor the systems and failing to 

check the results of the processes, the pilot becomes detached 

2-31 
 

from the aircraft operation and slides into the complacent role 

of passenger in command. Complacency led to tragedy in a 

1999 aircraft accident. 

In Colombia, a multi-engine aircraft crewed with two pilots 

struck the face of the Andes Mountains. Examination of 

their FMS revealed they entered a waypoint into the FMS 

incorrectly by one degree resulting in a flight path taking 

them to a point 60 NM off their intended course. The pilots 

were equipped with the proper charts, their route was posted 

on the charts, and they had a paper navigation log indicating 

the direction of each leg. They had all the tools to manage 

and monitor their flight, but instead allowed the automation 

to fly and manage itself. The system did exactly what it was 

programmed to do; it flew on a programmed course into a 

mountain resulting in multiple deaths. The pilots simply failed 

to manage the system and inherently created their own hazard. 

Although this hazard was self-induced, what is notable is the 

risk the pilots created through their own inattention. By failing 

to evaluate each turn made at the direction of automation, the 

pilots maximized risk instead of minimizing it. In this case, a 

totally avoidable accident become a tragedy through simple 

pilot error and complacency. 

For the GA pilot transitioning to automated systems, it is 

helpful to note that all human activity involving technical 

devices entails some element of risk. Knowledge, experience, 

and mission requirements tilt the odds in favor of safe and 

successful flights. The advanced avionics aircraft offers 

many new capabilities and simplifies the basic flying tasks, 

but only if the pilot is properly trained and all the equipment 

is working as advertised. 

Chapter Summary 

This chapter focused on helping the pilot improve his or 

her ADM skills with the goal of mitigating the risk factors 

associated with flight in both classic and automated aircraft. 

In the end, the discussion is not so much about aircraft, but 

about the people who fly them. 

2-32
 
 

3-1 

Introduction 

An aircraft is a device that is used, or intended to be used, for 

flight according to the current Title 14 of the Code of Federal 

Regulations (14 CFR) part 1, Definitions and Abbreviations. 

Categories of aircraft for certification of airmen include 

airplane, rotorcraft, glider, lighter-than-air, powered-lift, 

powered parachute, and weight-shift control aircraft. Title 

14 CFR part 1 also defines airplane as an engine-driven, 

fixed-wing aircraft that is supported in flight by the dynamic 

reaction of air against its wings. Another term, not yet 

codified in 14 CFR part 1, is advanced avionics aircraft, 

which refers to an aircraft that contains a global positioning 

system (GPS) navigation system with a moving map display, 

in conjunction with another system, such as an autopilot. 

This chapter provides a brief introduction to the structure 

of aircraft and uses an airplane for most illustrations. Light 

Sport Aircraft (LSA), such as weight-shift control aircraft, 

balloon, glider, powered parachute, and gyroplane, have their 

own handbooks to include detailed information regarding 

aerodynamics and control. 

Aircraft 

Construction 

Chapter 3 
 

 

Aircraft Design, Certification, and

Airworthiness 

The FAA certifies three types of aviation products: aircraft, 

aircraft engines, and propellers. Each of these products 

has been designed to a set of airworthiness standards. 

These standards are parts of Title 14 of the Code of 

Federal Regulations (14 CFR), published by the FAA. The 

airworthiness standards were developed to help ensure that 

aviation products are designed with no unsafe features. 

Different airworthiness standards apply to the different 

categories of aviation products as follows: 

• Normal, Utility, Acrobatic, and Commuter Category 

Airplanes- 14 CFR part 23 

• Transport Category Airplanes—14 CFR part 25 

• Normal Category—14 CFR part 27 

• Transport Category Rotorcraft—14 CFR part 29 

• Manned Free Balloons—14 CFR part 31 

• Aircraft Engines—14 CFR part 33 

• Propellers—14 CFR part 35 

Some aircraft are considered “special classes” of aircraft and 

do not have their own airworthiness standards, such as gliders 

and powered lift. The airworthiness standards used for these 

aircraft are a combination of requirements in 14 CFR parts 

23, 25, 27, and 29 that the FAA and the designer have agreed 

are appropriate for the proposed aircraft. 

The FAA issues a Type Certificate (TC) for the product 

when they are satisfied it complies with the applicable 

airworthiness standards. When the TC is issued, a Type 

Certificate Data Sheet (TCDS) is generated that specifies 

the important design and operational characteristics of the 

aircraft, aircraft engine, or propeller. The TCDS defines the 

product and are available to the public from the FAA website 

at www.faa.gov. 

A Note About Light Sport Aircraft 

Light sport aircraft are not designed according to FAA 

airworthiness standards. Instead, they are designed to a 

consensus of standards agreed upon in the aviation industry. 

The FAA has agreed the consensus of standards is acceptable 

as the design criteria for these aircraft. Light sport aircraft do 

not necessarily have individually type certificated engines 

and propellers. Instead, a TC is issued to the aircraft as a 

whole. It includes the airframe, engine, and propeller. 

Aircraft, aircraft engines, and propellers can be manufactured 

one at a time from the design drawings, or through an FAA 

approved manufacturing process, depending on the size and 

capabilities of the manufacturer. During the manufacturing 

process, each part is inspected to ensure that it has been built 

exactly according to the approved design. This inspection is 

called a conformity inspection. 

When the aircraft is complete, with the airframe, engine, and 

propeller, it is inspected and the FAA issues an airworthiness 

certificate for the aircraft. Having an airworthiness 

certificate means the complete aircraft meets the design and 

manufacturing standards, and is in a condition for safe flight. 

This airworthiness certificate must be carried in the aircraft 

during all flight operations. The airworthiness certificate 

remains valid as long as the required maintenance and 

inspections are kept up to date for the aircraft. 

Airworthiness certificates are classified as either “Standard” 

or “Special.” Standard airworthiness certificates are white, 

and are issued for normal, utility, acrobatic, commuter, or 

transport category aircraft. They are also issued for manned 

free balloons and aircraft designated as “Special Class.” 

Special airworthiness certificates are pink, and are issued 

for primary, restricted, and limited category aircraft, and 

light sport aircraft. They are also issued as provisional 

airworthiness certificates, special flight permits (ferry 

permits), and for experimental aircraft. 

More information on airworthiness certificates can be found 

in Chapter 9, in 14 CFR parts 175-225, and also on the FAA 

website at www.faa.gov. 

Lift and Basic Aerodynamics 

In order to understand the operation of the major components 

and subcomponents of an aircraft, it is important to 

understand basic aerodynamic concepts. This chapter briefly 

introduces aerodynamics; a more detailed explanation can be 

found in Chapter 5, Aerodynamics of Flight. 

Four forces act upon an aircraft in relation to straight-andlevel, unaccelerated flight. These forces are thrust, lift, 

weight, and drag. [Figure 3-1] 

Thrust is the forward force produced by the powerplant/ 

propeller. It opposes or overcomes the force of drag. As a 

general rule, it is said to act parallel to the longitudinal axis. 

This is not always the case as explained later. 

Drag is a rearward, retarding force and is caused by disruption 

of airflow by the wing, fuselage, and other protruding objects. 

Drag opposes thrust and acts rearward parallel to the relative 

wind. 

3-2 
 

Lift Weight 

Drag 

Thrust 

Figure 3-1. The four forces. 

Weight is the combined load of the aircraft itself, the crew, 

the fuel, and the cargo or baggage. Weight pulls the aircraft 

downward because of the force of gravity. It opposes lift 

and acts vertically downward through the aircraft’s center 

of gravity (CG). 

Lift opposes the downward force of weight, is produced by 

the dynamic effect of the air acting on the wing, and acts 

perpendicular to the flight path through the wing’s center 

of lift (CL). 

An aircraft moves in three dimensions and is controlled by 

moving it about one or more of its axes. The longitudinal, 

or roll, axis extends through the aircraft from nose to tail, 

with the line passing through the CG. The lateral or pitch 

axis extends across the aircraft on a line through the wing 

tips, again passing through the CG. The vertical, or yaw, axis 

passes through the aircraft vertically, intersecting the CG. All 

control movements cause the aircraft to move around one or 

more of these axes and allows for the control of the aircraft 

in flight. [Figure 3-2] 

One of the most significant components of aircraft design is 

CG. It is the specific point where the mass or weight of an 

aircraft may be said to center; that is, a point around which, 

if the aircraft could be suspended or balanced, the aircraft 

would remain relatively level. The position of the CG of 

an aircraft determines the stability of the aircraft in flight. 

As the CG moves rearward (towards the tail), the aircraft 

becomes more and more dynamically unstable. In aircraft 

with fuel tanks situated in front of the CG, it is important 

that the CG is set with the fuel tank empty. Otherwise, as the 

fuel is used, the aircraft becomes unstable. [Figure 3-3] The 

CG is computed during initial design and construction and 

is further affected by the installation of onboard equipment, 

aircraft loading, and other factors. 

Major Components 

Although airplanes are designed for a variety of purposes, most 

of them have the same major components. [Figure 3-4] The 

overall characteristics are largely determined by the original 

design objectives. Most airplane structures include a fuselage, 

wings, an empennage, landing gear, and a powerplant. 

Fuselage 

The fuselage is the central body of an airplane and is designed 

to accommodate the crew, passengers, and cargo. It also 

provides the structural connection for the wings and tail 

assembly. Older types of aircraft design utilized an open truss 

structure constructed of wood, steel, or aluminum tubing. 

[Figure 3-5] The most popular types of fuselage structures 

used in today’s aircraft are the monocoque (French for 

“single shell”) and semimonocoque. These structure types 

are discussed in more detail under aircraft construction later 

in the chapter. 

Wings 

The wings are airfoils attached to each side of the fuselage 

and are the main lifting surfaces that support the airplane in 

Pitching Rolling Yawing

Lateral axis Longitudinal axis Vertical axis 

Figure 3-2. Illustrates the pitch, roll, and yaw motion of the aircraft along the lateral, longitudinal, and vertical axes, respectively. 

3-3 
independent of airspeed 

Nose-down force 

dependent upon airspeed

Nose-up force 

Fixed

Variable 

Vertical forces acting on an airplane in flight. 

CG 

CL Lift 

CG too far aft 

nose-down force 

Insufficient elevator 

If the CG is too far aft, there might not be enough elevator nose-down 

force at the low stall airspeed to get the nose down for recovery. Lift 

CG 

CL 

CG too far forward nose-up force 

Insufficient elevator 

If the CG is too far forward, there will not be enough elevator 

nose-up force to flare the airplane for landing. 

CG 

Lift 

CL 

Figure 3-3. Center of gravity (CG). 

Empennage 

Powerplant 

Fuselage 

Wing 

Landing gear 

Figure 3-4. Airplane components. 

Bulkhead Stringers 

Longerons 

Struts 

Longerons 

Figure 3-5. Truss-type fuselage structure. 

flight. There are numerous wing designs, sizes, and shapes 

used by the various manufacturers. Each fulfills a certain need 

with respect to the expected performance for the particular 

airplane. How the wing produces lift is explained in Chapter 

5, Aerodynamics of Flight. 

Wings may be attached at the top, middle, or lower portion 

of the fuselage. These designs are referred to as high-, mid-, 

and low-wing, respectively. The number of wings can also 

vary. Airplanes with a single set of wings are referred to as 

monoplanes, while those with two sets are called biplanes. 

[Figure 3-6] 

Many high-wing airplanes have external braces, or wing 

struts that transmit the flight and landing loads through the 

struts to the main fuselage structure. Since the wing struts 

are usually attached approximately halfway out on the wing, 

this type of wing structure is called semi-cantilever. A few 

high-wing and most low-wing airplanes have a full cantilever 

wing designed to carry the loads without external struts. 

The principal structural parts of the wing are spars, ribs, 

and stringers. [Figure 3-7] These are reinforced by trusses, 

I-beams, tubing, or other devices, including the skin. The 

wing ribs determine the shape and thickness of the wing 

(airfoil). In most modern airplanes, the fuel tanks are either 

an integral part of the wing’s structure or consist of flexible 

containers mounted inside of the wing. 

3-4 
Figure 3-6. Monoplane (left) and biplane (right). 

Attached to the rear, or trailing edges, of the wings are two 

types of control surfaces referred to as ailerons and flaps. 

Ailerons extend from about the midpoint of each wing 

outward toward the tip, and move in opposite directions to 

create aerodynamic forces that cause the airplane to roll. 

Flaps extend outward from the fuselage to near the midpoint 

of each wing. The flaps are normally flush with the wing’s 

surface during cruising flight. When extended, the flaps move 

simultaneously downward to increase the lifting force of the 

wing for takeoffs and landings. [Figure 3-8] 

Alternate Types of Wings 

Alternate types of wings are often found on aircraft. The 

shape and design of a wing is dependent upon the type of 

operation for which an aircraft is intended and is tailored 

to specific types of flying. These design variations are 

discussed in Chapter 5, Aerodynamics of Flight, which 

provides information on the effect controls have on lifting 

surfaces from traditional wings to wings that use both flexing 

(due to billowing) and shifting (through the change of the 

aircraft’s CG). For example, the wing of the weight-shift 

control aircraft is highly swept in an effort to reduce drag 

and allow for the shifting of weight to provide controlled 

flight. [Figure 3-9] Handbooks specific to most categories 

of aircraft are available for the interested pilot and can be 

found on the Federal Aviation Administration (FAA) website 

at www.faa.gov. 

Aileron 

Fuel tank 

Wing tip 

Wing flap 

Ribs 

Stringers 

Spar 

Skin 

Figure 3-7. Wing components. 

3-5 
 

Plain flap 

Basic section 

Split flap 

Slotted flap 

Fowler flap 

Slotted Fowler flap 

Figure 3-8. Types of flaps. 

Empennage 

The empennage includes the entire tail group and consists 

of fixed surfaces, such as the vertical stabilizer and the 

horizontal stabilizer. The movable surfaces include the 

rudder, the elevator, and one or more trim tabs. [Figure 3-10] 

The rudder is attached to the back of the vertical stabilizer. 

During flight, it is used to move the airplane’s nose left 

and right. The elevator, which is attached to the back of the 

horizontal stabilizer, is used to move the nose of the airplane 

up and down during flight. Trim tabs are small, movable 

Figure 3-9. Weight-shift control aircraft use the shifting of weight 

for control. 

portions of the trailing edge of the control surface. These 

movable trim tabs, which are controlled from the flight deck, 

reduce control pressures. Trim tabs may be installed on the 

ailerons, the rudder, and/or the elevator. 

A second type of empennage design does not require an 

elevator. Instead, it incorporates a one-piece horizontal 

stabilizer that pivots from a central hinge point. This type of 

design is called a stabilator and is moved using the control 

wheel, just as the elevator is moved. For example, when a 

pilot pulls back on the control wheel, the stabilator pivots so 

the trailing edge moves up. This increases the aerodynamic 

tail load and causes the nose of the airplane to move up. 

Stabilators have an antiservo tab extending across their 

trailing edge. [Figure 3-11] 

The antiservo tab moves in the same direction as the trailing 

edge of the stabilator and helps make the stabilator less 

sensitive. The antiservo tab also functions as a trim tab to 

relieve control pressures and helps maintain the stabilator in 

the desired position. 

Horizontal stabilizer 

Rudder 

Elevator 

Vertical stabilizer 

Trim tabs 

Figure 3-10. Empennage components. 

3-6 
Antiservo tab 

Stabilator pivot point 

Figure 3-11. Stabilator components. 

Landing Gear 

The landing gear is the principal support of the airplane when 

parked, taxiing, taking off, or landing. The most common type 

of landing gear consists of wheels, but airplanes can also be 

equipped with floats for water operations or skis for landing 

on snow. [Figure 3-12] 

Wheeled landing gear consists of three wheels—two main 

wheels and a third wheel positioned either at the front or rear 

of the airplane. Landing gear with a rear mounted wheel is 

called conventional landing gear. 

Airplanes with conventional landing gear are sometimes 

referred to as tailwheel airplanes. When the third wheel is 

located on the nose, it is called a nosewheel, and the design 

is referred to as a tricycle gear. A steerable nosewheel or 

tailwheel permits the airplane to be controlled throughout all 

operations while on the ground. Most aircraft are steered by 

moving the rudder pedals, whether nosewheel or tailwheel. 

Additionally, some aircraft are steered by differential braking. 

The Powerplant 

The powerplant usually includes both the engine and the 

propeller. The primary function of the engine is to provide 

the power to turn the propeller. It also generates electrical 

power, provides a vacuum source for some flight instruments, 

and in most single-engine airplanes, provides a source of 

heat for the pilot and passengers. [Figure 3-13] The engine 

is covered by a cowling, or a nacelle, which are both types 

of covered housing. The purpose of the cowling or nacelle 

is to streamline the flow of air around the engine and to help 

cool the engine by ducting air around the cylinders. 

The propeller, mounted on the front of the engine, translates 

the rotating force of the engine into thrust, a forward acting 

force that helps move the airplane through the air. A propeller 

Figure 3-12. Types of landing gear: floats (top), skis (middle), and 

wheels (bottom). 

is a rotating airfoil that produces thrust through aerodynamic 

action. A high-pressure area is formed at the back of the 

propeller’s airfoil, and low pressure is produced at the face of 

the propeller, similar to the way lift is generated by an airfoil 

used as a lifting surface or wing. This pressure differential 

develops thrust from the propeller, which in turn pulls the 

airplane forward. Engines may be turned around to be pushers 

with the propeller at the rear. 

There are two significant factors involved in the design 

of a propeller that impact its effectiveness. The angle of a 

3-7 
Engine 

Cowling 

Propeller 

Figure 3-13. Engine compartment. 

propeller blade, as measured against the hub of the propeller, 

keeps the angle of attack (AOA) (See definition in Glossary) 

relatively constant along the span of the propeller blade, 

reducing or eliminating the possibility of a stall. The amount 

of lift being produced by the propeller is directly related to 

the AOA, which is the angle at which the relative wind meets 

the blade. The AOA continuously changes during the flight 

depending upon the direction of the aircraft. 

The pitch is defined as the distance a propeller would travel in 

one revolution if it were turning in a solid. These two factors 

combine to allow a measurement of the propeller’s efficiency. 

Propellers are usually matched to a specific aircraft/ 

powerplant combination to achieve the best efficiency at a 

particular power setting, and they pull or push depending on 

how the engine is mounted. 

Subcomponents 

The subcomponents of an airplane include the airframe, 

electrical system, flight controls, and brakes. 

The airframe is the basic structure of an aircraft and is 

designed to withstand all aerodynamic forces, as well as the 

stresses imposed by the weight of the fuel, crew, and payload. 

The primary function of an aircraft electrical system is to 

generate, regulate, and distribute electrical power throughout 

the aircraft. There are several different power sources on 

aircraft to power the aircraft electrical systems. These 

power sources include: engine-driven alternating current 

(AC) generators, auxiliary power units (APUs), and external 

power. The aircraft’s electrical power system is used to 

operate the flight instruments, essential systems, such as 

anti-icing, and passenger services, such as cabin lighting. 

The flight controls are the devices and systems that govern 

the attitude of an aircraft and, as a result, the flight path 

followed by the aircraft. In the case of many conventional 

airplanes, the primary flight controls utilize hinged, trailingedge surfaces called elevators for pitch, ailerons for roll, and 

the rudder for yaw. These surfaces are operated by the pilot 

in the flight deck or by an automatic pilot. 

In the case of most modern airplanes, airplane brakes consist 

of multiple pads (called caliper pads) that are hydraulically 

squeezed toward each other with a rotating disk (called a 

rotor) between them. The pads place pressure on the rotor 

which is turning with the wheels. As a result of the increased 

friction on the rotor, the wheels inherently slow down and 

stop turning. The disks and brake pads are made either from 

steel, like those in a car, or from a carbon material that weighs 

less and can absorb more energy. Because airplane brakes are 

used principally during landings and must absorb enormous 

amounts of energy, their life is measured in landings rather 

than miles. 

Types of Aircraft Construction 

The construction of aircraft fuselages evolved from the early 

wood truss structural arrangements to monocoque shell 

structures to the current semimonocoque shell structures. 

Truss Structure 

The main drawback of truss structure is its lack of a 

streamlined shape. In this construction method, lengths of 

tubing, called longerons, are welded in place to form a wellbraced framework. Vertical and horizontal struts are welded 

to the longerons and give the structure a square or rectangular 

shape when viewed from the end. Additional struts are needed 

to resist stress that can come from any direction. Stringers 

and bulkheads, or formers, are added to shape the fuselage 

and support the covering. 

As technology progressed, aircraft designers began to enclose 

the truss members to streamline the airplane and improve 

performance. This was originally accomplished with cloth 

fabric, which eventually gave way to lightweight metals such 

as aluminum. In some cases, the outside skin can support all 

or a major portion of the flight loads. Most modern aircraft 

use a form of this stressed skin structure known as monocoque 

or semimonocoque construction. [Figure 3-14] 

Monocoque 

Monocoque construction uses stressed skin to support almost 

all loads much like an aluminum beverage can. Although 

very strong, monocoque construction is not highly tolerant 

3-8 
Semimonocoque 

Monocoque 

Bulkhead 

Stringers 

Stressed skin 

Formers 

Skin 

Bulkhead 

Formers 

Figure 3-14. Semimonocoque and monocoque fuselage design. 

to deformation of the surface. For example, an aluminum 

beverage can supports considerable forces at the ends of 

the can, but if the side of the can is deformed slightly while 

supporting a load, it collapses easily. 

Because most twisting and bending stresses are carried by 

the external skin rather than by an open framework, the need 

for internal bracing was eliminated or reduced, saving weight 

and maximizing space. One of the notable and innovative 

methods for using monocoque construction was employed by 

Jack Northrop. In 1918, he devised a new way to construct 

a monocoque fuselage used for the Lockheed S-1 Racer. 

The technique utilized two molded plywood half-shells that 

were glued together around wooden hoops or stringers. To 

construct the half shells, rather than gluing many strips of 

plywood over a form, three large sets of spruce strips were 

soaked with glue and laid in a semi-circular concrete mold 

that looked like a bathtub. Then, under a tightly clamped 

lid, a rubber balloon was inflated in the cavity to press 

the plywood against the mold. Twenty-four hours later, 

the smooth half-shell was ready to be joined to another to 

create the fuselage. The two halves were each less than a 

quarter inch thick. Although employed in the early aviation 

period, monocoque construction would not reemerge for 

several decades due to the complexities involved. Every 

day examples of monocoque construction can be found in 

automobile manufacturing where the unibody is considered 

standard in manufacturing. 

Semimonocoque 

Semimonocoque construction, partial or one-half, uses a 

substructure to which the airplane’s skin is attached. The 

substructure, which consists of bulkheads and/or formers 

of various sizes and stringers, reinforces the stressed skin 

by taking some of the bending stress from the fuselage. The 

main section of the fuselage also includes wing attachment 

points and a firewall. On single-engine airplanes, the engine 

is usually attached to the front of the fuselage. There is a 

fireproof partition between the rear of the engine and the 

flight deck or cabin to protect the pilot and passengers from 

accidental engine fires. This partition is called a firewall and 

is usually made of heat-resistant material such as stainless 

steel. However, a new emerging process of construction is 

the integration of composites or aircraft made entirely of 

composites. 

Composite Construction 

History 

The use of composites in aircraft construction can be dated 

to World War II aircraft when soft fiberglass insulation was 

used in B-29 fuselages. By the late 1950s, European high 

performance sailplane manufacturers were using fiberglass 

as primary structures. In 1965, the FAA type certified the 

first all-fiberglass aircraft in the normal category, a Swiss 

sailplane called a Diamant HBV. Four years later, the FAA 

certified a four-seat, single-engine Windecker Eagle in the 

normal category. By 2005, over 35 percent of new aircraft 

were constructed of composite materials. 

Composite is a broad term and can mean materials such as 

fiberglass, carbon fiber cloth, KevlarTM cloth, and mixtures 

of all of the above. Composite construction offers two 

advantages: extremely smooth skins and the ability to easily 

form complex curved or streamlined structures. [Figure 3-15] 

Composite Materials in Aircraft 

Composite materials are fiber-reinforced matrix systems. 

The matrix is the “glue” used to hold the fibers together 

and, when cured, gives the part its shape, but the fibers carry 

most of the load. There are many different types of fibers 

and matrix systems. 

In aircraft, the most common matrix is epoxy resin, which is 

a type of thermosetting plastic. Compared to other choices 

such as polyester resin, epoxy is stronger and has good hightemperature properties. There are many different types of 

epoxies available with a wide range of structural properties, 

cure times and temperatures, and costs. 

3-9 
Figure 3-15. Composite aircraft. 

The most common reinforcing fibers used in aircraft 

construction are fiberglass and carbon fiber. Fiberglass 

has good tensile and compressive strength, good impact 

resistance, is easy to work with, and is relatively inexpensive 

and readily available. Its main disadvantage is that it is 

somewhat heavy, and it is difficult to make a fiberglass loadcarrying structure lighter than a well designed equivalent 

aluminum structure. 

Carbon fiber is generally stronger in tensile and compressive 

strength than fiberglass and has much higher bending 

stiffness. It is also considerably lighter than fiberglass. 

However, it is relatively poor in impact resistance; the fibers 

are brittle and tend to shatter under sharp impact. This can 

be greatly improved with a “toughened” epoxy resin system, 

as used in the Boeing 787 horizontal and vertical stabilizers. 

Carbon fiber is more expensive than fiberglass, but the price 

has dropped due to innovations driven by the B-2 program 

in the 1980s and Boeing 777 work in the 1990s. Very welldesigned carbon fiber structures can be significantly lighter 

than an equivalent aluminum structure, sometimes by 30 

percent or so. 

Advantages of Composites 

Composite construction offers several advantages over 

metal, wood, or fabric, with its lighter weight being the most 

frequently cited. Lighter weight is not always automatic. It 

must be remembered that building an aircraft structure out of 

composites does not guarantee it will be lighter; it depends 

on the structure, as well as the type of composite being used. 

A more important advantage is that a very smooth, compound 

curved, aerodynamic structure made from composites 

reduces drag. This is the main reason sailplane designers 

switched from metal and wood to composites in the 1960s. 

In aircraft, the use of composites reduces drag for the Cirrus 

and Columbia line of production aircraft, leading to their high 

performance despite their fixed landing gear. Composites also 

help mask the radar signature of “stealth” aircraft designs, 

such as the B-2 and the F-22. Today, composites can be 

found in aircraft as varied as gliders to most new helicopters. 

Lack of corrosion is a third advantage of composites. Boeing 

is designing the 787, with its all-composite fuselage, to have 

both a higher pressure differential and higher humidity in 

the cabin than previous airliners. Engineers are no longer as 

concerned about corrosion from moisture condensation on the 

hidden areas of the fuselage skins, such as behind insulation 

blankets. This should lead to lower long-term maintenance 

costs for the airlines. 

Another advantage of composites is their good performance 

in a flexing environment, such as in helicopter rotor blades. 

Composites do not suffer from metal fatigue and crack growth 

as do metals. While it takes careful engineering, composite 

rotor blades can have considerably higher design lives than 

metal blades, and most new large helicopter designs have all 

composite blades, and in many cases, composite rotor hubs. 

Disadvantages of Composites 

Composite construction comes with its own set of 

disadvantages, the most important of which is the lack of 

visual proof of damage. Composites respond differently from 

other structural materials to impact, and there is often no 

obvious sign of damage. For example, if a car backs into an 

aluminum fuselage, it might dent the fuselage. If the fuselage 

is not dented, there is no damage. If the fuselage is dented, 

the damage is visible and repairs are made. 

In a composite structure, a low energy impact, such as a 

bump or a tool drop, may not leave any visible sign of the 

impact on the surface. Underneath the impact site there may 

be extensive delaminations, spreading in a cone-shaped area 

from the impact location. The damage on the backside of 

the structure can be significant and extensive, but it may be 

hidden from view. Anytime one has reason to think there 

may have been an impact, even a minor one, it is best to 

get an inspector familiar with composites to examine the 

structure to determine underlying damage. The appearance 

of “whitish” areas in a fiberglass structure is a good tip-off 

that delaminations of fiber fracture has occurred. 

A medium energy impact (perhaps the car backing into the 

structure) results in local crushing of the surface, which 

should be visible to the eye. The damaged area is larger than 

the visible crushed area and will need to be repaired. A high 

energy impact, such as a bird strike or hail while in flight, 

results in a puncture and a severely damaged structure. In 

3-10 
medium and high energy impacts, the damage is visible to the 

eye, but low energy impact is difficult to detect. [Figure 3-16] 

If an impact results in delaminations, crushing of the surface, 

or a puncture, then a repair is mandatory. While waiting 

for the repair, the damaged area should be covered and 

protected from rain. Many composite parts are composed 

of thin skins over a honeycomb core, creating a “sandwich” 

structure. While excellent for structural stiffness reasons, 

such a structure is an easy target for water ingress (entering), 

leading to further problems later. A piece of “speed tape” 

over the puncture is a good way to protect it from water, but 

it is not a structural repair. The use of a paste filler to cover 

up the damage, while acceptable for cosmetic purposes, is 

not a structural repair, either. 

0 

0 

+45 

-45 

0 

90 

90 

0 

-45 

+45 

0 

0 

0 

0 

+45 

-45 

0 

90 

90 

0 

-45 

+45 

0 

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Pyramid pattern matrix crack from impact 

Low Energy Impact 

0 

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0 

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Delaminations Back side fiber fracture 

Local fiber/matrix crushing 

Medium Energy Impact 

0 

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Delaminations 

High Energy Impact 

Through 

penetration 

small damage 

zone 

Loose 

fiber ends 

Figure 3-16. Impact energy affects the visibility, as well as the 

severity, of damage in composite structures. High and medium 

energy impacts, while severe, are easy to detect. Low energy impacts 

can easily cause hidden damage. 

The potential for heat damage to the resin is another 

disadvantage of using composites. While “too hot” depends 

on the particular resin system chosen, many epoxies begin 

to weaken over 150 °F. White paint on composites is often 

used to minimize this issue. For example, the bottom of 

a wing that is painted black facing a black asphalt ramp 

on a hot, sunny day can get as hot as 220 °F. The same 

structure, painted white, rarely exceeds 140 °F. As a result, 

composite aircraft often have specific recommendations 

on allowable paint colors. If the aircraft is repainted, these 

recommendations must be followed. Heat damage can also 

occur due to a fire. Even a quickly extinguished small brake 

fire can damage bottom wing skins, composite landing gear 

legs, or wheel pants. 

Also, chemical paint strippers are very harmful to composites 

and must not be used on them. If paint needs to be removed 

from composites, only mechanical methods are allowed, such 

as gentle grit blasting or sanding. Many expensive composite 

parts have been ruined by the use of paint stripper and such 

damage is generally not repairable. 

Fluid Spills on Composites 

Some owners are concerned about fuel, oil, or hydraulic fluid 

spills on composite surfaces. These are generally not a problem 

with modern composites using epoxy resin. Usually, if the 

spill does not attack the paint, it will not hurt the underlying 

composite. Some aircraft use fiberglass fuel tanks, for example, 

in which the fuel rides directly against the composite surface 

with no sealant being used. If the fiberglass structure is made 

with some of the more inexpensive types of polyester resin, 

there can be a problem when using auto gas with ethanol 

blended into the mixture. The more expensive types of 

polyester resin, as well as epoxy resin, can be used with auto 

gas, as well as 100 octane aviation gas (avgas) and jet fuel. 

Lightning Strike Protection 

Lightning strike protection is an important consideration in 

aircraft design. When an aircraft is hit by lightning, a very 

large amount of energy is delivered to the structure. Whether 

flying a light general aviation (GA) aircraft or a large airliner, 

the basic principle of lightning strike protection is the same. 

For any size aircraft, the energy from the strike must be spread 

over a large surface area to lower the amps per square inch 

to a harmless level. 

If lightning strikes an aluminum airplane, the electrical 

energy naturally conducts easily through the aluminum 

structure. The challenge is to keep the energy out of avionics, 

fuel systems, etc., until it can be safely conducted overboard. 

The outer skin of the aircraft is the path of least resistance. 

3-11 
 

 

In a composite aircraft, fiberglass is an excellent electrical 

insulator, while carbon fiber conducts electricity, but not 

as easily as aluminum. Therefore, additional electrical 

conductivity needs to be added to the outside layer of 

composite skin. This is done typically with fine metal meshes 

bonded to the skin surfaces. Aluminum and copper mesh 

are the two most common types, with aluminum used on 

fiberglass and copper on carbon fiber. Any structural repairs 

on lightning-strike protected areas must also include the mesh 

as well as the underlying structure. 

For composite aircraft with internal radio antennas, there 

must be “windows” in the lightning strike mesh in the area 

of the antenna. Internal radio antennas may be found in 

fiberglass composites because fiberglass is transparent to 

radio frequencies, where carbon fiber is not. 

The Future of Composites 

In the decades since World War II, composites have earned 

an important role in aircraft structure design. Their design 

flexibility and corrosion resistance, as well as the high 

strength-to-weight ratios possible, will undoubtedly continue 

to lead to more innovative aircraft designs in the future. 

From the Cirrus SR-20 to the Boeing 787, it is obvious that 

composites have found a home in aircraft construction and 

are here to stay. [Figure 3-17] 

Instrumentation: Moving into the Future 

Until recently, most GA aircraft were equipped with 

individual instruments utilized collectively to safely operate 

and maneuver the aircraft. With the release of the electronic 

flight display (EFD) system, conventional instruments have 

been replaced by multiple liquid crystal display (LCD) 

screens. The first screen is installed in front of the pilot 

position and is referred to as the primary flight display (PFD). 

The second screen, positioned approximately in the center 

of the instrument panel, is referred to as the multi-function 

display (MFD). These two screens de-clutter instrument 

panels while increasing safety. This has been accomplished 

through the utilization of solid state instruments that have 

a failure rate far less than those of conventional analog 

instrumentation. [Figure 3-18] 

With today’s improvements in avionics and the introduction 

of EFDs, pilots at any level of experience need an astute 

knowledge of the onboard flight control systems, as well as 

an understanding of how automation melds with aeronautical 

decision-making (ADM). These subjects are covered in detail 

in Chapter 2, Aeronautical Decision-Making. 

Whether an aircraft has analog or digital (glass) instruments, 

the instrumentation falls into three different categories: 

performance, control, and navigation. 

Figure 3-17. Composite materials in aircraft, such as Columbia 350 

(top), Boeing 787 (middle), and a Coast Guard HH-65 (bottom). 

Performance Instruments 

The performance instruments indicate the aircraft’s actual 

performance. Performance is determined by reference to the 

altimeter, airspeed or vertical speed indicator (VSI), heading 

indicator, and turn-and-slip indicator. The performance 

instruments directly reflect the performance the aircraft 

is achieving. The speed of the aircraft can be referenced 

on the airspeed indicator. The altitude can be referenced 

on the altimeter. The aircraft’s climb performance can be 

determined by referencing the VSI. Other performance 

instruments available are the heading indicator, angle of 

attack indicator, and the slip-skid indicator. [Figure 3-19] 

3-12 
 

Figure 3-18. Analog display (top) and digital display (bottom) from 

a Cessna 172. 

Control Instruments 

The control instruments display immediate attitude and power 

changes and are calibrated to permit adjustments in precise 

increments. [Figure 3-20] The instrument for attitude display 

is the attitude indicator. The control instruments do not 

indicate aircraft speed or altitude. In order to determine these 

variables and others, a pilot must reference the performance 

instruments. 

Navigation Instruments 

The navigation instruments indicate the position of the 

aircraft in relation to a selected navigation facility or fix. 

This group of instruments includes various types of course 

indicators, range indicators, glideslope indicators, and 

bearing pointers. Newer aircraft with more technologically 

advanced instrumentation provide blended information, 

giving the pilot more accurate positional information. 

Navigation instruments are comprised of indicators that 

display GPS, very high frequency (VHF) omni-directional 

radio range (VOR), nondirectional beacon (NDB), 

and instrument landing system (ILS) information. The 

instruments indicate the position of the aircraft relative to a 

selected navigation facility or fix. They also provide pilotage 

information so the aircraft can be maneuvered to keep it on 

a predetermined path. The pilotage information can be in 

either two or three dimensions relative to the ground-based or 

space-based navigation information. [Figures 3-21 and 3-22] 

Global Positioning System (GPS) 

GPS is a satellite-based navigation system composed of a 

network of satellites placed into orbit by the United States 

Department of Defense (DOD). GPS was originally intended 

for military applications, but in the 1980s the government 

made the system available for civilian use. GPS works in 

all weather conditions, anywhere in the world, 24 hours a 

day. A GPS receiver must be locked onto the signal of at 

least three satellites to calculate a two-dimensional position 

(latitude and longitude) and track movement. With four or 

more satellites in view, the receiver can determine the user’s 

three-dimensional position (latitude, longitude, and altitude). 

Other satellites must also be in view to offset signal loss 

and signal ambiguity. The use of the GPS is discussed in 

more detail in Chapter 17, Navigation. Additionally, GPS is 

discussed in the Aeronautical Information Manual (AIM). 

Chapter Summary 

This chapter provides an overview of aircraft structures. 

A more in-depth understanding of aircraft structures and 

controls can be gained through the use of flight simulation 

software or interactive programs available online through 

aviation organizations, such as the Aircraft Owners and Pilots 

Association (AOPA). Pilots are also encouraged to subscribe 

to or review the various aviation periodicals that contain 

valuable flying information. As discussed in Chapter 1, the 

National Aeronautics and Space Administration (NASA) and 

the FAA also offer free information for pilots. 

3-13 
3600

3500

3400

3300

3200

3100

Airspeed indicator Attitude indicator Altimeter indicator 

Turn coordinator Heading indicator Vertical speed indicator 

NAV1 108.00 113.00 WPT _ _ _ _ _ _ DIS _ _ ._ NM DTK _ _ _Slip/Skid indicator °T TRK 360°T 134.000 118.000 COM1 

NAV2 108.00 110.60 123.800 118.000 COM2 

Airspeed tape indicator 4000 4300 130
 2
 

4200 Vertical speed and 120
 Altimeter and tape indicator altitude trend tape 4100 1
 

110
 500
 1
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100
 4000 4000
 

9
 20
 

90 3900 
 1
 

80
 3800
 Turn rate trend vector

270° 2

4300 270° 

70
 TAS 100KT 

Heading bug 

VOR 1 Course arrow 

Turn rate indicator 

XPDR 5537 IDNT LCL23:00:34 

ALERTS

Figure 3-19. Performance instruments. 

3-14 
3-15

Figure 3-20. Control instruments.

XPDR 5537 IDNT LCL23:00:34

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VOR 1 

270°

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TAS 100KT

ALERTS

NAV1 108.00 113.00 NAV2 108.00 110.60134.000 118.000 COM1

123.800 118.000 COM2

WPT _ _ _ _ _ _ DIS _ _ ._ NM DTK _ _ _° TRK 360°

Tachometer

Manifold pressure gauge

2300

23.0

Attitude indicator
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O B S 

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W 

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21 

15 12 

30 

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TO 

30 

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2I 24

I5 

I2 

6 3 

2

30 33 

24 

2I

I2 I5 

3 6 

O B S 

N 

E 

S 

W 

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30 

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TO 

1

160° 

3 

33 

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15 12 

30

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30 

6 

N 

E 

S 

W 

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33 

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12 15 

30 

6 

25 

Glideslope 

A 2

The aircraft illustrated is heading 

020°, but the course is to the left. 

020° HDG 360° CRS 340° 

VOR 1 

1

Present position, inbound on

160° radial. 

340° N 

GS 

HDG 360° CRS 340° NAV 

W

E 

OBS S 

View is from the pilot’s 

perspective, and the 

movable card is reset 

after each turn. 

Figure 3-21. A comparison of navigation information as depicted on both analog and digital displays. 

Fly down Fly up
 

Glideslope needle indicates “fly Glideslope needle indicates “fly up” to intercept glideslope 

down” to intercept glideslope 

TO 

TO 2 0 

2 0 I 0

I 0 

I0 I0 

I0 I0 20 20 FR 20 20 FR NAV 1 

NAV 1 

OBS 

OBS 

Figure 3-22. Analog and digital indications for glideslope interception. 

3-16 
 

4-1 

Introduction 

This chapter examines the fundamental physical laws 

governing the forces acting on an aircraft in flight, and 

what effect these natural laws and forces have on the 

performance characteristics of aircraft. To control an aircraft, 

be it an airplane, helicopter, glider, or balloon, the pilot 

must understand the principles involved and learn to use or 

counteract these natural forces. 

Structure of the Atmosphere 

The atmosphere is an envelope of air that surrounds the Earth 

and rests upon its surface. It is as much a part of the Earth as 

the seas or the land, but air differs from land and water as it is 

a mixture of gases. It has mass, weight, and indefinite shape. 

The atmosphere is composed of 78 percent nitrogen, 21 

percent oxygen, and 1 percent other gases, such as argon 

or helium. Some of these elements are heavier than others. 

The heavier elements, such as oxygen, settle to the surface 

of the Earth, while the lighter elements are lifted up to the 

region of higher altitude. Most of the atmosphere’s oxygen 

is contained below 35,000 feet altitude. 

Principles of

Flight 

Chapter 4 
Air is a Fluid 

When most people hear the word “fluid,” they usually think 

of liquid. However, gasses, like air, are also fluids. Fluids 

take on the shape of their containers. Fluids generally do not 

resist deformation when even the smallest stress is applied, 

or they resist it only slightly. We call this slight resistance 

viscosity. Fluids also have the ability to flow. Just as a liquid 

flows and fills a container, air will expand to fill the available 

volume of its container. Both liquids and gasses display these 

unique fluid properties, even though they differ greatly in 

density. Understanding the fluid properties of air is essential 

to understanding the principles of flight. 

Viscosity 

Viscosity is the property of a fluid that causes it to resist 

flowing. The way individual molecules of the fluid tend to 

adhere, or stick, to each other determines how much a fluid 

resists flow. High-viscosity fluids are “thick” and resist flow; 

low-viscosity fluids are “thin” and flow easily. Air has a low 

viscosity and flows easily. 

Using two liquids as an example, similar amounts of oil and 

water poured down two identical ramps will flow at different 

rates due to their different viscosity. The water seems to flow 

freely while the oil flows much more slowly. 

As another example, different types of similar liquids will 

display different behaviors because of different viscosities. 

Grease is very viscous. Given time, grease will flow, even 

though the flow rate will be slow. Motor oil is less viscous 

than grease and flows much more easily, but it is more viscous 

and flows more slowly than gasoline. 

All fluids are viscous and have a resistance to flow, whether 

or not we observe this resistance. We cannot easily observe 

the viscosity of air. However, since air is a fluid and has 

viscosity properties, it resists flow around any object to 

some extent. 

Friction 

Another factor at work when a fluid flows over or around 

an object is called friction. Friction is the resistance that one 

surface or object encounters when moving over another. 

Friction exists between any two materials that contact each 

other. 

The effects of friction can be demonstrated using a similar 

example as before. If identical fluids are poured down two 

identical ramps, they flow in the same manner and at the 

same speed. If the surface of one ramp is rough, and the other 

smooth, the flow down the two ramps differs significantly. 

The rough surface ramp impedes the flow of the fluid due 

to resistance from the surface (friction). It is important to 

remember that all surfaces, no matter how smooth they 

appear, are not smooth on a microscopic level and impede 

the flow of a fluid. 

The surface of a wing, like any other surface, has a certain 

roughness at the microscopic level. The surface roughness 

causes resistance and slows the velocity of the air flowing 

over the wing. [Figure 4-1] 

Molecules of air pass over the surface of the wing and actually 

adhere (stick, or cling) to the surface because of friction. Air 

molecules near the surface of the wing resist motion and have 

a relative velocity near zero. The roughness of the surface 

impedes their motion. The layer of molecules that adhere to 

the wing surface is referred to as the boundary layer. 

Leading edge of wing under 1,500x magnification 

Figure 4-1. Microscopic surface of a wing. 

4-2 
 

Once the boundary layer of the air adheres to the wing by 

friction, further resistance to the airflow is caused by the 

viscosity, the tendency of the air to stick to itself. When 

these two forces act together to resist airflow over a wing, 

it is called drag. 

Pressure 

Pressure is the force applied in a perpendicular direction to the 

surface of an object. Often, pressure is measured in pounds of 

force exerted per square inch of an object, or PSI. An object 

completely immersed in a fluid will feel pressure uniformly 

around the entire surface of the object. If the pressure on one 

surface of the object becomes less than the pressure exerted 

on the other surfaces, the object will move in the direction 

of the lower pressure. 

Atmospheric Pressure 

Although there are various kinds of pressure, pilots are 

mainly concerned with atmospheric pressure. It is one of 

the basic factors in weather changes, helps to lift an aircraft, 

and actuates some of the important flight instruments. These 

instruments are the altimeter, airspeed indicator, vertical 

speed indicator, and manifold pressure gauge. 

Air is very light, but it has mass and is affected by the 

attraction of gravity. Therefore, like any other substance, 

it has weight, and because of its weight, it has force. Since 

air is a fluid substance, this force is exerted equally in all 

directions. Its effect on bodies within the air is called pressure. 

Under standard conditions at sea level, the average pressure 

exerted by the weight of the atmosphere is approximately 

14.70 pounds per square inch (psi) of surface, or 1,013.2 

millibars (mb). The thickness of the atmosphere is limited; 

therefore, the higher the altitude, the less air there is above. 

For this reason, the weight of the atmosphere at 18,000 feet 

is one-half what it is at sea level. 

The pressure of the atmosphere varies with time and location. 

Due to the changing atmospheric pressure, a standard 

reference was developed. The standard atmosphere at sea 

level is a surface temperature of 59 °F or 15 °C and a surface 

pressure of 29.92 inches of mercury ("Hg) or 1,013.2 mb. 

[Figure 4-2] 

A standard temperature lapse rate is when the temperature 

decreases at the rate of approximately 3.5 °F or 2 °C per 

thousand feet up to 36,000 feet, which is approximately –65 

°F or –55 °C. Above this point, the temperature is considered 

constant up to 80,000 feet. A standard pressure lapse rate is 

when pressure decreases at a rate of approximately 1 "Hg 

per 1,000 feet of altitude gain to 10,000 feet. [Figure 4-3] 

The International Civil Aviation Organization (ICAO) has 

established this as a worldwide standard, and it is often 

30 

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Inches of 

Mercury Millibars 

1016 

847 

677 

508 

339

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 0 

29.92 

Standard 

Sea Level 

Pressure 

Hg 1013 

Standard 

Sea Level 

Pressure 

mb 

Atmospheric Pressure 

Figure 4-2. Standard sea level pressure. 

Altitude (ft) Pressure (Hg) 

Temperature 

(°C) (°F) 

Standard Atmosphere 

0 

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-5.2 

-8.8 

-12.3 

Figure 4-3. Properties of standard atmosphere. 

referred to as International Standard Atmosphere (ISA) or 

ICAO Standard Atmosphere. Any temperature or pressure 

that differs from the standard lapse rates is considered 

nonstandard temperature and pressure. 

4-3 
 

 

Since aircraft performance is compared and evaluated with 

respect to the standard atmosphere, all aircraft instruments are 

calibrated for the standard atmosphere. In order to properly 

account for the nonstandard atmosphere, certain related terms 

must be defined. 

Pressure Altitude 

Pressure altitude is the height above a standard datum plane 

(SDP), which is a theoretical level where the weight of the 

atmosphere is 29.92 "Hg (1,013.2 mb) as measured by a 

barometer. An altimeter is essentially a sensitive barometer 

calibrated to indicate altitude in the standard atmosphere. If 

the altimeter is set for 29.92 "Hg SDP, the altitude indicated 

is the pressure altitude. As atmospheric pressure changes, the 

SDP may be below, at, or above sea level. Pressure altitude 

is important as a basis for determining airplane performance, 

as well as for assigning flight levels to airplanes operating at 

or above 18,000 feet. 

The pressure altitude can be determined by one of the 

following methods: 

1. Setting the barometric scale of the altimeter to 29.92

and reading the indicated altitude

2. Applying a correction factor to the indicated altitude

according to the reported altimeter setting

Density Altitude 

SDP is a theoretical pressure altitude, but aircraft operate in a 

nonstandard atmosphere and the term density altitude is used 

for correlating aerodynamic performance in the nonstandard 

atmosphere. Density altitude is the vertical distance above sea 

level in the standard atmosphere at which a given density is 

to be found. The density of air has significant effects on the 

aircraft’s performance because as air becomes less dense, 

it reduces: 

• Power because the engine takes in less air

• Thrust because a propeller is less efficient in thin air

• Lift because the thin air exerts less force on the airfoils 

Density altitude is pressure altitude corrected for nonstandard 

temperature. As the density of the air increases (lower 

density altitude), aircraft performance increases; conversely 

as air density decreases (higher density altitude), aircraft 

performance decreases. A decrease in air density means 

a high density altitude; an increase in air density means a 

lower density altitude. Density altitude is used in calculating 

aircraft performance because under standard atmospheric 

conditions, air at each level in the atmosphere not only has 

a specific density, its pressure altitude and density altitude 

identify the same level. 

The computation of density altitude involves consideration 

of pressure (pressure altitude) and temperature. Since aircraft 

performance data at any level is based upon air density under 

standard day conditions, such performance data apply to 

air density levels that may not be identical with altimeter 

indications. Under conditions higher or lower than standard, 

these levels cannot be determined directly from the altimeter. 

Density altitude is determined by first finding pressure 

altitude, and then correcting this altitude for nonstandard 

temperature variations. Since density varies directly with 

pressure and inversely with temperature, a given pressure 

altitude may exist for a wide range of temperatures by 

allowing the density to vary. However, a known density 

occurs for any one temperature and pressure altitude. The 

density of the air has a pronounced effect on aircraft and 

engine performance. Regardless of the actual altitude of the 

aircraft, it will perform as though it were operating at an 

altitude equal to the existing density altitude. 

Air density is affected by changes in altitude, temperature, 

and humidity. High density altitude refers to thin air, while 

low density altitude refers to dense air. The conditions that 

result in a high density altitude are high elevations, low 

atmospheric pressures, high temperatures, high humidity, or 

some combination of these factors. Lower elevations, high 

atmospheric pressure, low temperatures, and low humidity 

are more indicative of low density altitude. 

Effect of Pressure on Density 

Since air is a gas, it can be compressed or expanded. When 

air is compressed, a greater amount of air can occupy a given 

volume. Conversely, when pressure on a given volume of air 

is decreased, the air expands and occupies a greater space. 

At a lower pressure, the original column of air contains a 

smaller mass of air. The density is decreased because density 

is directly proportional to pressure. If the pressure is doubled, 

the density is doubled; if the pressure is lowered, the density is 

lowered. This statement is true only at a constant temperature. 

Effect of Temperature on Density 

Increasing the temperature of a substance decreases its 

density. Conversely, decreasing the temperature increases 

the density. Thus, the density of air varies inversely with 

temperature. This statement is true only at a constant pressure. 

In the atmosphere, both temperature and pressure decrease 

with altitude and have conflicting effects upon density. 

However, a fairly rapid drop in pressure as altitude increases 

usually has a dominating effect. Hence, pilots can expect the 

density to decrease with altitude. 

4-4 
Effect of Humidity (Moisture) on Density 

The preceding paragraphs refer to air that is perfectly dry. In 

reality, it is never completely dry. The small amount of water 

vapor suspended in the atmosphere may be almost negligible 

under certain conditions, but in other conditions humidity 

may become an important factor in the performance of an 

aircraft. Water vapor is lighter than air; consequently, moist 

air is lighter than dry air. Therefore, as the water content 

of the air increases, the air becomes less dense, increasing 

density altitude and decreasing performance. It is lightest or 

least dense when, in a given set of conditions, it contains the 

maximum amount of water vapor. 

Humidity, also called relative humidity, refers to the amount 

of water vapor contained in the atmosphere and is expressed 

as a percentage of the maximum amount of water vapor the 

air can hold. This amount varies with temperature. Warm air 

holds more water vapor, while cold air holds less. Perfectly 

dry air that contains no water vapor has a relative humidity 

of zero percent, while saturated air, which cannot hold any 

more water vapor, has a relative humidity of 100 percent. 

Humidity alone is usually not considered an important factor 

in calculating density altitude and aircraft performance, but 

it is a contributing factor. 

As temperature increases, the air can hold greater amounts 

of water vapor. When comparing two separate air masses, 

the first warm and moist (both qualities tending to lighten 

the air) and the second cold and dry (both qualities making 

it heavier), the first must be less dense than the second. 

Pressure, temperature, and humidity have a great influence 

on aircraft performance because of their effect upon density. 

There are no rules of thumb that can be easily applied, but 

the affect of humidity can be determined using several online 

formulas. In the first example, the pressure is needed at the 

altitude for which density altitude is being sought. Using 

Figure 4-2, select the barometric pressure closest to the 

associated altitude. As an example, the pressure at 8,000 feet 

is 22.22 "Hg. Using the National Oceanic and Atmospheric 

Administration (NOAA) website (www.srh.noaa.gov/ 

epz/?n=wxcalc_densityaltitude) for density altitude, enter 

the 22.22 for 8,000 feet in the station pressure window. Enter 

a temperature of 80° and a dew point of 75°. The result is a 

density altitude of 11,564 feet. With no humidity, the density 

altitude would be almost 500 feet lower. 

Another website (www.wahiduddin.net/calc/density_ 

altitude.htm) provides a more straight forward method of 

determining the effects of humidity on density altitude 

without using additional interpretive charts. In any case, the 

effects of humidity on density altitude include a decrease in 

overall performance in high humidity conditions. 

Theories in the Production of Lift 

In order to achieve flight in a machine that is heavier than air, 

there are several obstacles we must overcome. One of those 

obstacles, discussed previously, is the resistance to movement 

called drag. The most challenging obstacle to overcome in 

aviation, however, is the force of gravity. A wing moving 

through air generates the force called lift, also previously 

discussed. Lift from the wing that is greater than the force of 

gravity, directed opposite to the direction of gravity, enables 

an aircraft to fly. Generating this force called lift is based on 

some important principles, Newton's basic laws of motion, 

and Bernoulli's principle of differential pressure. 

Newton’s Basic Laws of Motion 

The formulation of lift has historically been an adaptation 

over the past few centuries of basic physical laws. These 

laws, although seemingly applicable to all aspects of lift, 

do not explain how lift is formulated. In fact, one must 

consider the many airfoils that are symmetrical, yet produce 

significant lift. 

The fundamental physical laws governing the forces acting 

upon an aircraft in flight were adopted from postulated 

theories developed before any human successfully flew 

an aircraft. The use of these physical laws grew out of the 

Scientific Revolution, which began in Europe in the 1600s. 

Driven by the belief the universe operated in a predictable 

manner open to human understanding, many philosophers, 

mathematicians, natural scientists, and inventors spent their 

lives unlocking the secrets of the universe. One of the most 

well-known was Sir Isaac Newton, who not only formulated 

the law of universal gravitation, but also described the three 

basic laws of motion. 

Newton’s First Law: “Every object persists in its state of rest 

or uniform motion in a straight line unless it is compelled to 

change that state by forces impressed on it.” 

This means that nothing starts or stops moving until some 

outside force causes it to do so. An aircraft at rest on the ramp 

remains at rest unless a force strong enough to overcome 

its inertia is applied. Once it is moving, its inertia keeps 

it moving, subject to the various other forces acting on it. 

These forces may add to its motion, slow it down, or change 

its direction. 

Newton’s Second Law: “Force is equal to the change in 

momentum per change in time. For a constant mass, force 

equals mass times acceleration.” 

4-5 
When a body is acted upon by a constant force, its resulting 

acceleration is inversely proportional to the mass of the body 

and is directly proportional to the applied force. This takes 

into account the factors involved in overcoming Newton’s 

First Law. It covers both changes in direction and speed, 

including starting up from rest (positive acceleration) and 

coming to a stop (negative acceleration or deceleration). 

Newton’s Third Law: “For every action, there is an equal 

and opposite reaction.” 

In an airplane, the propeller moves and pushes back the 

air; consequently, the air pushes the propeller (and thus the 

airplane) in the opposite direction—forward. In a jet airplane, 

the engine pushes a blast of hot gases backward; the force of 

equal and opposite reaction pushes against the engine and 

forces the airplane forward. 

Bernoulli’s Principle of Differential Pressure 

A half-century after Newton formulated his laws, Daniel 

Bernoulli, a Swiss mathematician, explained how the pressure 

of a moving fluid (liquid or gas) varies with its speed of 

motion. Bernoulli’s Principle states that as the velocity of a 

moving fluid (liquid or gas) increases, the pressure within 

the fluid decreases. This principle explains what happens to 

air passing over the curved top of the airplane wing. 

A practical application of Bernoulli’s Principle is the venturi 

tube. The venturi tube has an air inlet that narrows to a 

throat (constricted point) and an outlet section that increases 

in diameter toward the rear. The diameter of the outlet is 

the same as that of the inlet. The mass of air entering the 

tube must exactly equal the mass exiting the tube. At the 

constriction, the speed must increase to allow the same 

amount of air to pass in the same amount of time as in all 

other parts of the tube. When the air speeds up, the pressure 

also decreases. Past the constriction, the airflow slows and 

the pressure increases. [Figure 4-4] 

Since air is recognized as a body, and it is understood that 

air will follow the above laws, one can begin to see how 

and why an airplane wing develops lift. As the wing moves 

through the air, the flow of air across the curved top surface 

increases in velocity creating a low-pressure area. 

Although Newton, Bernoulli, and hundreds of other early 

scientists who studied the physical laws of the universe did 

not have the sophisticated laboratories available today, they 

provided great insight to the contemporary viewpoint of how 

lift is created. 

Airfoil Design 

An airfoil is a structure designed to obtain reaction upon its 

surface from the air through which it moves or that moves 

past such a structure. Air acts in various ways when submitted 

to different pressures and velocities; but this discussion 

is confined to the parts of an aircraft that a pilot is most 

concerned with in flight—namely, the airfoils designed to 

produce lift. By looking at a typical airfoil profile, such as 

the cross section of a wing, one can see several obvious 

characteristics of design. [Figure 4-5] Notice that there is 

a difference in the curvatures (called cambers) of the upper 

and lower surfaces of the airfoil. The camber of the upper 

surface is more pronounced than that of the lower surface, 

which is usually somewhat flat. 

NOTE: The two extremities of the airfoil profile also differ in 

appearance. The rounded end, which faces forward in flight, 

is called the leading edge; the other end, the trailing edge, is 

quite narrow and tapered. 

A reference line often used in discussing the airfoil is 

the chord line, a straight line drawn through the profile 

connecting the extremities of the leading and trailing edges. 

The distance from this chord line to the upper and lower 

surfaces of the wing denotes the magnitude of the upper and 

lower camber at any point. Another reference line, drawn 

8 

4 6

2 

0 I0 

VELOCITY 

8 

4 6

2 

0 I0 

PRESSURE 

8 

4 6

2 

0 I0 

VELOCITY 

8 

4 6

2 

0 I0 

PRESSURE 

8 

4 6

2 

0 I0 

VELOCITY 

8 

4 6

2 

0 I0 

PRESSURE 

Figure 4-4. Air pressure decreases in a venturi tube. 

4-6 
Camber of upper surface 

Camber of lower surface 

Trailing edge 

Leading edge 

Mean camber line 

Chord line 

Figure 4-5. Typical airfoil section. 

from the leading edge to the trailing edge, is the mean camber 

line. This mean line is equidistant at all points from the upper 

and lower surfaces. 

An airfoil is constructed in such a way that its shape takes 

advantage of the air’s response to certain physical laws. This 

develops two actions from the air mass: a positive pressure 

lifting action from the air mass below the wing, and a negative 

pressure lifting action from lowered pressure above the wing. 

As the air stream strikes the relatively flat lower surface of 

a wing or rotor blade when inclined at a small angle to its 

direction of motion, the air is forced to rebound downward, 

causing an upward reaction in positive lift. At the same time, 

the air stream striking the upper curved section of the leading 

edge is deflected upward. An airfoil is shaped to cause an 

action on the air, and forces air downward, which provides 

an equal reaction from the air, forcing the airfoil upward. If 

a wing is constructed in such form that it causes a lift force 

greater than the weight of the aircraft, the aircraft will fly. 

If all the lift required were obtained merely from the 

deflection of air by the lower surface of the wing, an aircraft 

would only need a flat wing like a kite. However, the balance 

of the lift needed to support the aircraft comes from the flow 

of air above the wing. Herein lies the key to flight. 

It is neither accurate nor useful to assign specific values to the 

percentage of lift generated by the upper surface of an airfoil 

versus that generated by the lower surface. These are not 

constant values. They vary, not only with flight conditions, 

but also with different wing designs. 

Different airfoils have different flight characteristics. Many 

thousands of airfoils have been tested in wind tunnels and in 

actual flight, but no one airfoil has been found that satisfies 

every flight requirement. The weight, speed, and purpose 

of each aircraft dictate the shape of its airfoil. The most 

efficient airfoil for producing the greatest lift is one that has 

a concave or “scooped out” lower surface. As a fixed design, 

this type of airfoil sacrifices too much speed while producing 

lift and is not suitable for high-speed flight. Advancements 

in engineering have made it possible for today’s high-speed 

jets to take advantage of the concave airfoil’s high lift 

characteristics. Leading edge (Kreuger) flaps and trailing 

edge (Fowler) flaps, when extended from the basic wing 

structure, literally change the airfoil shape into the classic 

concave form, thereby generating much greater lift during 

slow flight conditions. 

On the other hand, an airfoil that is perfectly streamlined 

and offers little wind resistance sometimes does not have 

enough lifting power to take the airplane off the ground. 

Thus, modern airplanes have airfoils that strike a medium 

between extremes in design. The shape varies according to 

the needs of the airplane for which it is designed. Figure 4-6 

shows some of the more common airfoil designs. 

Low Pressure Above 

In a wind tunnel or in flight, an airfoil is simply a streamlined 

object inserted into a moving stream of air. If the airfoil 

profile were in the shape of a teardrop, the speed and the 

pressure changes of the air passing over the top and bottom 

would be the same on both sides. But if the teardrop shaped 

airfoil were cut in half lengthwise, a form resembling the 

basic airfoil (wing) section would result. If the airfoil were 

then inclined so the airflow strikes it at an angle, the air 

moving over the upper surface would be forced to move 

faster than the air moving along the bottom of the airfoil. 

This increased velocity reduces the pressure above the airfoil. 

Applying Bernoulli’s Principle of Pressure, the increase in 

the speed of the air across the top of an airfoil produces a 

Early airfoil 

Later airfoil 

Laminar flow airfoil 

(Subsonic) 

Circular arc airfoil 

(Supersonic) 

Double wedge airfoil 

(Supersonic) 

Clark 'Y' airfoil 

(Subsonic) 

Figure 4-6. Airfoil designs. 

4-7 
Figure 2-8. Pressure distribution on an airfoil & CP changes 

with an angle of attack.

f

drop in pressure. This lowered pressure is a component of 

total lift. The pressure difference between the upper and 

lower surface of a wing alone does not account for the total 

lift force produced. 

The downward backward flow from the top surface of an 

airfoil creates a downwash. This downwash meets the flow 

from the bottom of the airfoil at the trailing edge. Applying 

Newton’s third law, the reaction of this downward backward 

flow results in an upward forward force on the airfoil. 

High Pressure Below 

A certain amount of lift is generated by pressure conditions 

underneath the airfoil. Because of the manner in which air 

flows underneath the airfoil, a positive pressure results, 

particularly at higher angles of attack. However, there is 

another aspect to this airflow that must be considered. At a 

point close to the leading edge, the airflow is virtually stopped 

(stagnation point) and then gradually increases speed. At 

some point near the trailing edge, it again reaches a velocity 

equal to that on the upper surface. In conformance with 

Bernoulli’s principle, where the airflow was slowed beneath 

the airfoil, a positive upward pressure was created (i.e., as 

the fluid speed decreases, the pressure must increase). Since 

the pressure differential between the upper and lower surface 

of the airfoil increases, total lift increases. Both Bernoulli’s 

Principle and Newton’s Laws are in operation whenever lift 

is being generated by an airfoil. 

Pressure Distribution 

From experiments conducted on wind tunnel models and on 

full size airplanes, it has been determined that as air flows 

along the surface of a wing at different angles of attack 

(AOA), there are regions along the surface where the pressure 

is negative, or less than atmospheric, and regions where the 

pressure is positive, or greater than atmospheric. This negative 

pressure on the upper surface creates a relatively larger force 

on the wing than is caused by the positive pressure resulting 

from the air striking the lower wing surface. Figure 4-7 shows 

the pressure distribution along an airfoil at three different 

angles of attack. The average of the pressure variation for 

any given AOA is referred to as the center of pressure (CP). 

Aerodynamic force acts through this CP. At high angles of 

attack, the CP moves forward, while at low angles of attack 

the CP moves aft. In the design of wing structures, this CP 

travel is very important, since it affects the position of the 

air loads imposed on the wing structure in both low and high 

AOA conditions. An airplane’s aerodynamic balance and 

controllability are governed by changes in the CP. 

Airfoil Behavior 

Although specific examples can be cited in which each of 

the principles predict and contribute to the formation of lift, 

High angle of attack 

Normal angle of attack 

Low angle of attack 

at at ck o

Angle 

-8° 

CP 

attack 

Angle

of 

+10° 

CP 

attack of Angle 

+4° 

CP 

Figure 4-7. Pressure distribution on an airfoil and CP changes 

with AOA. 

lift is a complex subject. The production of lift is much more 

complex than a simple differential pressure between upper 

and lower airfoil surfaces. In fact, many lifting airfoils do 

not have an upper surface longer than the bottom, as in the 

case of symmetrical airfoils. These are seen in high-speed 

aircraft having symmetrical wings, or on symmetrical rotor 

blades for many helicopters whose upper and lower surfaces 

4-8 
are identical. In both examples, the only difference is the 

relationship of the airfoil with the oncoming airstream 

(angle). A paper airplane, which is simply a flat plate, has a 

bottom and top exactly the same shape and length. Yet, these 

airfoils do produce lift, and “flow turning” is partly (or fully) 

responsible for creating lift. 

As an airfoil moves through air, the airfoil is inclined 

against the airflow, producing a different flow caused by the 

airfoil’s relationship to the oncoming air. Think of a hand 

being placed outside the car window at a high speed. If the 

hand is inclined in one direction or another, the hand will 

move upward or downward. This is caused by deflection, 

which in turn causes the air to turn about the object within 

the air stream. As a result of this change, the velocity about 

the object changes in both magnitude and direction, in turn 

resulting in a measurable velocity force and direction. 

A Third Dimension 

To this point, the discussion has centered on the flow across 

the upper and lower surfaces of an airfoil. While most of the 

lift is produced by these two dimensions, a third dimension, 

the tip of the airfoil also has an aerodynamic effect. The highpressure area on the bottom of an airfoil pushes around the tip 

to the low-pressure area on the top. [Figure 4-8] This action 

creates a rotating flow called a tip vortex. The vortex flows 

behind the airfoil creating a downwash that extends back to 

the trailing edge of the airfoil. This downwash results in an 

overall reduction in lift for the affected portion of the airfoil. 

Manufacturers have developed different methods to 

counteract this action. Winglets can be added to the tip of 

an airfoil to reduce this flow. The winglets act as a dam 

preventing the vortex from forming. Winglets can be on the 

top or bottom of the airfoil. Another method of countering 

the flow is to taper the airfoil tip, reducing the pressure 

differential and smoothing the airflow around the tip. 

v o r t e x 

Tip 

Figure 4-8. Tip vortex. 

Chapter Summary 

Modern general aviation aircraft have what may be considered 

high performance characteristics. Therefore, it is increasingly 

necessary that pilots appreciate and understand the principles 

upon which the art of flying is based. For additional 

information on the principles discussed in this chapter, visit 

the National Aeronautics and Space Administration (NASA) 

Beginner’s Guide to Aerodynamics at www.grc.nasa.gov/ 

www/k-12/airplane/bga.html. 

4-9 
4-10
 
5-1 

Forces Acting on the Aircraft 

Thrust, drag, lift, and weight are forces that act upon all 

aircraft in flight. Understanding how these forces work and 

knowing how to control them with the use of power and 

flight controls are essential to flight. This chapter discusses 

the aerodynamics of flight—how design, weight, load factors, 

and gravity affect an aircraft during flight maneuvers. 

The four forces acting on an aircraft in straight-and-level, 

unaccelerated flight are thrust, drag, lift, and weight. They 

are defined as follows: 

• Thrust—the forward force produced by the powerplant/ 

propeller or rotor. It opposes or overcomes the force 

of drag. As a general rule, it acts parallel to the 

longitudinal axis. However, this is not always the case, 

as explained later. 

• Drag—a rearward, retarding force caused by disruption 

of airflow by the wing, rotor, fuselage, and other 

protruding objects. As a general rule, drag opposes 

thrust and acts rearward parallel to the relative wind. 

• Lift—is a force that is produced by the dynamic effect 

of the air acting on the airfoil, and acts perpendicular 

to the flight path through the center of lift (CL) and 

perpendicular to the lateral axis. In level flight, lift 

opposes the downward force of weight. 

Aerodynamics

of Flight 

Chapter 5 
Thrust Drag 

•	 Weight—the combined load of the aircraft itself, the 

crew, the fuel, and the cargo or baggage. Weight is 

a force that pulls the aircraft downward because of 

the force of gravity. It opposes lift and acts vertically 

downward through the aircraft’s center of gravity (CG). 

In steady flight, the sum of these opposing forces is always 

zero. There can be no unbalanced forces in steady, straight 

flight based upon Newton’s Third Law, which states that for 

every action or force there is an equal, but opposite, reaction 

or force. This is true whether flying level or when climbing 

or descending. 

It does not mean the four forces are equal. It means the 

opposing forces are equal to, and thereby cancel, the effects of 

each other. In Figure 5-1, the force vectors of thrust, drag, lift, 

and weight appear to be equal in value. The usual explanation 

states (without stipulating that thrust and drag do not equal 

weight and lift) that thrust equals drag and lift equals weight. 

Although true, this statement can be misleading. It should be 

understood that in straight, level, unaccelerated flight, it is 

true that the opposing lift/weight forces are equal. They are 

also greater than the opposing forces of thrust/drag that are 

equal only to each other. Therefore, in steady flight: 

•	 The sum of all upward components of forces (not just 

lift) equals the sum of all downward components of 

forces (not just weight) 

•	 The sum of all forward components of forces (not just 

thrust) equals the sum of all backward components of 

forces (not just drag) 

This refinement of the old “thrust equals drag; lift equals 

weight” formula explains that a portion of thrust is directed Weight Lift 

upward in climbs and slow flight and acts as if it were lift 

while a portion of weight is directed backward opposite to the 

direction of flight and acts as if it were drag. In slow flight, 

Figure 5-1. Relationship of forces acting on an aircraft. Figure 5-2. Force vectors during a stabilized climb. 

thrust has an upward component. But because the aircraft is in 

level flight, weight does not contribute to drag. [Figure 5-2] 

In glides, a portion of the weight vector is directed along 

the forward flight path and, therefore, acts as thrust. In other 

words, any time the flight path of the aircraft is not horizontal, 

lift, weight, thrust, and drag vectors must each be broken down 

into two components. 

Another important concept to understand is angle of attack 

(AOA). Since the early days of flight, AOA is fundamental to 

understanding many aspects of airplane performance, stability, 

and control. The AOA is defined as the acute angle between the 

chord line of the airfoil and the direction of the relative wind. 

Discussions of the preceding concepts are frequently omitted 

in aeronautical texts/handbooks/manuals. The reason is 

not that they are inconsequential, but because the main 

ideas with respect to the aerodynamic forces acting upon 

an aircraft in flight can be presented in their most essential 

elements without being involved in the technicalities of the 

aerodynamicist. In point of fact, considering only level flight, 

and normal climbs and glides in a steady state, it is still true 

that lift provided by the wing or rotor is the primary upward 

force, and weight is the primary downward force. 

By using the aerodynamic forces of thrust, drag, lift, and 

weight, pilots can fly a controlled, safe flight. A more detailed 

discussion of these forces follows. 

Thrust 

For an aircraft to start moving, thrust must be exerted and be 

greater than drag. The aircraft continues to move and gain 

speed until thrust and drag are equal. In order to maintain a 

Rearward component of weight 

Thrust 

Drag 

Flight path

Relative wind 

Component of weight 

opposed to lift 

Lift 

CL 

CG 

5-2 
constant airspeed, thrust and drag must remain equal, just as 

lift and weight must be equal to maintain a constant altitude. 

If in level flight, the engine power is reduced, the thrust is 

lessened, and the aircraft slows down. As long as the thrust 

is less than the drag, the aircraft continues to decelerate. To 

a point, as the aircraft slows down, the drag force will also 

decrease. The aircraft will continue to slow down until thrust 

again equals drag at which point the airspeed will stabilize. 

Likewise, if the engine power is increased, thrust becomes 

greater than drag and the airspeed increases. As long as 

the thrust continues to be greater than the drag, the aircraft 

continues to accelerate. When drag equals thrust, the aircraft 

flies at a constant airspeed. 

Straight-and-level flight may be sustained at a wide range 

of speeds. The pilot coordinates AOA and thrust in all 

speed regimes if the aircraft is to be held in level flight. An 

important fact related to the principal of lift (for a given 

airfoil shape) is that lift varies with the AOA and airspeed. 

Therefore, a large AOA at low airspeeds produces an equal 

amount of lift at high airspeeds with a low AOA. The speed 

regimes of flight can be grouped in three categories: lowspeed flight, cruising flight, and high-speed flight. 

When the airspeed is low, the AOA must be relatively high 

if the balance between lift and weight is to be maintained. 

[Figure 5-3] If thrust decreases and airspeed decreases, lift 

will become less than weight and the aircraft will start to 

descend. To maintain level flight, the pilot can increase the 

AOA an amount that generates a lift force again equal to the 

weight of the aircraft. While the aircraft will be flying more 

slowly, it will still maintain level flight. The AOA is adjusted 

to maintain lift equal weight. The airspeed will naturally 

adjust until drag equals thrust and then maintain that airspeed 

(assumes the pilot is not trying to hold an exact speed). 

Straight-and-level flight in the slow-speed regime provides 

some interesting conditions relative to the equilibrium of 

forces. With the aircraft in a nose-high attitude, there is a 

vertical component of thrust that helps support it. For one 

thing, wing loading tends to be less than would be expected. 

In level flight, when thrust is increased, the aircraft speeds 

up and the lift increases. The aircraft will start to climb 

unless the AOA is decreased just enough to maintain the 

relationship between lift and weight. The timing of this 

decrease in AOA needs to be coordinated with the increase 

in thrust and airspeed. Otherwise, if the AOA is decreased too 

fast, the aircraft will descend, and if the AOA is decreased 

too slowly, the aircraft will climb. 

As the airspeed varies due to thrust, the AOA must also vary 

to maintain level flight. At very high speeds and level flight, 

it is even possible to have a slightly negative AOA. As thrust 

is reduced and airspeed decreases, the AOA must increase 

in order to maintain altitude. If speed decreases enough, the 

required AOA will increase to the critical AOA. Any further 

increase in the AOA will result in the wing stalling. Therefore, 

extra vigilance is required at reduced thrust settings and low 

speeds so as not to exceed the critical angle of attack. If the 

airplane is equipped with an AOA indicator, it should be 

referenced to help monitor the proximity to the critical AOA. 

Some aircraft have the ability to change the direction of the 

thrust rather than changing the AOA. This is accomplished 

either by pivoting the engines or by vectoring the exhaust 

gases. [Figure 5-4] 

Lift 

The pilot can control the lift. Any time the control yoke 

or stick is moved fore or aft, the AOA is changed. As the 

AOA increases, lift increases (all other factors being equal). 

When the aircraft reaches the maximum AOA, lift begins 

to diminish rapidly. This is the stalling AOA, known as 

CL-MAX critical AOA. Examine Figure 5-5, noting how the 

CL increases until the critical AOA is reached, then decreases 

rapidly with any further increase in the AOA. 

Before proceeding further with the topic of lift and how it 

can be controlled, velocity must be discussed. The shape of 

the wing or rotor cannot be effective unless it continually 

keeps “attacking” new air. If an aircraft is to keep flying, the 

lift-producing airfoil must keep moving. In a helicopter or 

gyroplane, this is accomplished by the rotation of the rotor 

blades. For other types of aircraft, such as airplanes, weightLevel high speed Level cruise speed Level low speed

Flight path 

Relative wind 

Flight path 

Relative wind 

Flight path 

Relative wind 

3°

6° 

12° 

Level high speed Level cruise speed Level low speed 

Figure 5-3. Angle of attack at various speeds. 

5-3 
 

 

 

Figure 5-4. Some aircraft have the ability to change the direction of thrust. 

shift control, or gliders, air must be moving across the lifting 

surface. This is accomplished by the forward speed of the 

aircraft. Lift is proportional to the square of the aircraft’s 

velocity. For example, an airplane traveling at 200 knots has 

four times the lift as the same airplane traveling at 100 knots, 

if the AOA and other factors remain constant. 

CL . ρ . V2 . S L = 2 

The above lift equation exemplifies this mathematically 

and supports that doubling of the airspeed will result in four 

times the lift. As a result, one can see that velocity is an 

important component to the production of lift, which itself 

can be affected through varying AOA. When examining the 

equation, lift (L) is determined through the relationship of the 

air density (ρ), the airfoil velocity (V), the surface area of the 

wing (S) and the coefficient of lift (CL) for a given airfoil. 

Taking the equation further, one can see an aircraft could 

not continue to travel in level flight at a constant altitude and 

maintain the same AOA if the velocity is increased. The lift 

would increase and the aircraft would climb as a result of 

the increased lift force or speed up. Therefore, to keep the 

aircraft straight and level (not accelerating upward) and in a 

state of equilibrium, as velocity is increased, lift must be kept 

constant. This is normally accomplished by reducing the AOA 

by lowering the nose. Conversely, as the aircraft is slowed, the 

decreasing velocity requires increasing the AOA to maintain 

lift sufficient to maintain flight. There is, of course, a limit to 

how far the AOA can be increased, if a stall is to be avoided. 

All other factors being constant, for every AOA there is 

a corresponding airspeed required to maintain altitude in 

steady, unaccelerated flight (true only if maintaining level 

flight). Since an airfoil always stalls at the same AOA, if 

increasing weight, lift must also be increased. The only 

Stall 

CL 

CLMAX 

CD 

L/D 

L/DMAX 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

.2000 

.1800 

.1600 

.1400 

.1200 

.1000 

.0800 

.0600 

.0400 

.0200 

0 

Coefficient of drag (CD ) 

Lift/drag 

Angle of attack 

0° 2° 4° 6° 8° 10° 12° 14° 16° 18° 20° 22° 

CL 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0 

Figure 5-5. Coefficients of lift and drag at various angles of attack. 

5-4 
 

 

method of increasing lift is by increasing velocity if the AOA 

is held constant just short of the “critical,” or stalling, AOA 

(assuming no flaps or other high lift devices). 

Lift and drag also vary directly with the density of the air. 

Density is affected by several factors: pressure, temperature, 

and humidity. At an altitude of 18,000 feet, the density of 

the air has one-half the density of air at sea level. In order to 

maintain its lift at a higher altitude, an aircraft must fly at a 

greater true airspeed for any given AOA. 

Warm air is less dense than cool air, and moist air is less 

dense than dry air. Thus, on a hot humid day, an aircraft 

must be flown at a greater true airspeed for any given AOA 

than on a cool, dry day. 

If the density factor is decreased and the total lift must equal 

the total weight to remain in flight, it follows that one of the 

other factors must be increased. The factor usually increased 

is the airspeed or the AOA because these are controlled 

directly by the pilot. 

Lift varies directly with the wing area, provided there is no 

change in the wing’s planform. If the wings have the same 

proportion and airfoil sections, a wing with a planform area 

of 200 square feet lifts twice as much at the same AOA as a 

wing with an area of 100 square feet. 

Two major aerodynamic factors from the pilot’s viewpoint 

are lift and airspeed because they can be controlled readily 

and accurately. Of course, the pilot can also control density by 

adjusting the altitude and can control wing area if the aircraft 

happens to have flaps of the type that enlarge wing area. 

However, for most situations, the pilot controls lift and airspeed 

to maneuver an aircraft. For instance, in straight-and-level flight, 

cruising along at a constant altitude, altitude is maintained by 

adjusting lift to match the aircraft’s velocity or cruise airspeed, 

while maintaining a state of equilibrium in which lift equals 

weight. In an approach to landing, when the pilot wishes to 

land as slowly as practical, it is necessary to increase AOA near 

maximum to maintain lift equal to the weight of the aircraft. 

Lift/Drag Ratio 

The lift-to-drag ratio (L/D) is the amount of lift generated by 

a wing or airfoil compared to its drag. A ratio of L/D indicates 

airfoil efficiency. Aircraft with higher L/D ratios are more 

efficient than those with lower L/D ratios. In unaccelerated 

flight with the lift and drag data steady, the proportions of 

the coefficient of lift (CL) and coefficient of drag (CD) can 

be calculated for specific AOA. [Figure 5-5] 

The coefficient of lift is dimensionless and relates the lift 

generated by a lifting body, the dynamic pressure of the fluid 

flow around the body, and a reference area associated with 

the body. The coefficient of drag is also dimensionless and is 

used to quantify the drag of an object in a fluid environment, 

such as air, and is always associated with a particular surface 

area. 

The L/D ratio is determined by dividing the CL by the CD, 

which is the same as dividing the lift equation by the drag 

equation as all of the variables, aside from the coefficients, 

cancel out. The lift and drag equations are as follows (L = 

Lift in pounds; D = Drag; CL = coefficient of lift; ρ = density 

(expressed in slugs per cubic feet); V = velocity (in feet per 

second); q = dynamic pressure per square foot (q = 1⁄2 ρv2); 

S = the area of the lifting body (in square feet); and 

CD = Ratio of drag pressure to dynamic pressure): 

CD . ρ . V2 . S D = 2 

Typically at low AOA, the coefficient of drag is low and 

small changes in AOA create only slight changes in the 

coefficient of drag. At high AOA, small changes in the AOA 

cause significant changes in drag. The shape of an airfoil, as 

well as changes in the AOA, affects the production of lift. 

Notice in Figure 5-5 that the coefficient of lift curve (red) 

reaches its maximum for this particular wing section at 20° 

AOA and then rapidly decreases. 20° AOA is therefore the 

critical angle of attack. The coefficient of drag curve (orange) 

increases very rapidly from 14° AOA and completely 

overcomes the lift curve at 21° AOA. The lift/drag ratio 

(green) reaches its maximum at 6° AOA, meaning that at this 

angle, the most lift is obtained for the least amount of drag. 

Note that the maximum lift/drag ratio (L/DMAX) occurs at 

one specific CL and AOA. If the aircraft is operated in steady 

flight at L/DMAX, the total drag is at a minimum. Any AOA 

lower or higher than that for L/DMAX reduces the L/D and 

consequently increases the total drag for a given aircraft’s Drag 

Airspeed 

Minimum 

drag 

Total drag 

Induced drag 

parasite

drag 

Figure 5-6. Drag versus speed. 

5-5 
 

 

lift. Figure 5-6 depicts the L/DMAX by the lowest portion of 

the blue line labeled “total drag.” The configuration of an 

aircraft has a great effect on the L/D. 

Drag 

Drag is the force that resists movement of an aircraft through 

the air. There are two basic types: parasite drag and induced 

drag. The first is called parasite because it in no way functions 

to aid flight, while the second, induced drag, is a result of an 

airfoil developing lift. 

Parasite Drag 

Parasite drag is comprised of all the forces that work to slow 

an aircraft’s movement. As the term parasite implies, it is the 

drag that is not associated with the production of lift. This 

includes the displacement of the air by the aircraft, turbulence 

generated in the airstream, or a hindrance of air moving over 

the surface of the aircraft and airfoil. There are three types of 

parasite drag: form drag, interference drag, and skin friction. 

Form Drag 

Form drag is the portion of parasite drag generated by the 

aircraft due to its shape and airflow around it. Examples include 

the engine cowlings, antennas, and the aerodynamic shape of 

other components. When the air has to separate to move around 

a moving aircraft and its components, it eventually rejoins 

after passing the body. How quickly and smoothly it rejoins is 

representative of the resistance that it creates, which requires 

additional force to overcome. [Figure 5-7] 

Notice how the flat plate in Figure 5-7 causes the air to swirl 

around the edges until it eventually rejoins downstream. Form 

FLAT PLATE 

SPHERE 

SPHERE WITH 

A FAIRING 

SPHERE INSIDE 

A HOUSING 

drag is the easiest to reduce when designing an aircraft. The 

solution is to streamline as many of the parts as possible. 

Interference Drag 

Interference drag comes from the intersection of airstreams 

that creates eddy currents, turbulence, or restricts smooth 

airflow. For example, the intersection of the wing and the 

fuselage at the wing root has significant interference drag. 

Air flowing around the fuselage collides with air flowing over 

the wing, merging into a current of air different from the two 

original currents. The most interference drag is observed when 

two surfaces meet at perpendicular angles. Fairings are used 

to reduce this tendency. If a jet fighter carries two identical 

wing tanks, the overall drag is greater than the sum of the 

individual tanks because both of these create and generate 

interference drag. Fairings and distance between lifting 

surfaces and external components (such as radar antennas 

hung from wings) reduce interference drag. [Figure 5-8] 

Skin Friction Drag 

Skin friction drag is the aerodynamic resistance due to the 

contact of moving air with the surface of an aircraft. Every 

surface, no matter how apparently smooth, has a rough, 

ragged surface when viewed under a microscope. The air 

molecules, which come in direct contact with the surface of 

the wing, are virtually motionless. Each layer of molecules 

above the surface moves slightly faster until the molecules 

are moving at the velocity of the air moving around the 

aircraft. This speed is called the free-stream velocity. The area 

between the wing and the free-stream velocity level is about as 

wide as a playing card and is called the boundary layer. At the 

top of the boundary layer, the molecules increase velocity and 

move at the same speed as the molecules outside the boundary 

layer. The actual speed at which the molecules move depends 

upon the shape of the wing, the viscosity (stickiness) of 

the air through which the wing or airfoil is moving, and its 

compressibility (how much it can be compacted). 

Figure 5-7. Figure 5-8. A wing root can cause interference drag. Form drag. 

5-6 
 

 

 

The airflow outside of the boundary layer reacts to the 

shape of the edge of the boundary layer just as it would 

to the physical surface of an object. The boundary layer 

gives any object an “effective” shape that is usually slightly 

different from the physical shape. The boundary layer may 

also separate from the body, thus creating an effective shape 

much different from the physical shape of the object. This 

change in the physical shape of the boundary layer causes a 

dramatic decrease in lift and an increase in drag. When this 

happens, the airfoil has stalled. 

In order to reduce the effect of skin friction drag, aircraft 

designers utilize flush mount rivets and remove any 

irregularities that may protrude above the wing surface. In 

addition, a smooth and glossy finish aids in transition of 

air across the surface of the wing. Since dirt on an aircraft 

disrupts the free flow of air and increases drag, keep the 

surfaces of an aircraft clean and waxed. 

Induced Drag 

The second basic type of drag is induced drag. It is an 

established physical fact that no system that does work in the 

mechanical sense can be 100 percent efficient. This means 

that whatever the nature of the system, the required work 

is obtained at the expense of certain additional work that is 

dissipated or lost in the system. The more efficient the system, 

the smaller this loss. 

In level flight, the aerodynamic properties of a wing or rotor 

produce a required lift, but this can be obtained only at the 

expense of a certain penalty. The name given to this penalty 

is induced drag. Induced drag is inherent whenever an airfoil 

is producing lift and, in fact, this type of drag is inseparable 

from the production of lift. Consequently, it is always present 

if lift is produced. 

An airfoil (wing or rotor blade) produces the lift force by 

making use of the energy of the free airstream. Whenever 

an airfoil is producing lift, the pressure on the lower surface 

of it is greater than that on the upper surface (Bernoulli’s 

Principle). As a result, the air tends to flow from the high 

pressure area below the tip upward to the low pressure area 

on the upper surface. In the vicinity of the tips, there is a 

tendency for these pressures to equalize, resulting in a lateral 

flow outward from the underside to the upper surface. This 

lateral flow imparts a rotational velocity to the air at the tips, 

creating vortices that trail behind the airfoil. 

When the aircraft is viewed from the tail, these vortices 

circulate counterclockwise about the right tip and clockwise 

about the left tip. [Figure 5-9] As the air (and vortices) roll off 

the back of your wing, they angle down, which is known as 

downwash. Figure 5-10 shows the difference in downwash at 

Figure 5-9. Wingtip vortex from a crop duster. 

altitude versus near the ground. Bearing in mind the direction 

of rotation of these vortices, it can be seen that they induce 

an upward flow of air beyond the tip and a downwash flow 

behind the wing’s trailing edge. This induced downwash has 

nothing in common with the downwash that is necessary to 

produce lift. It is, in fact, the source of induced drag. 

Downwash points the relative wind downward, so the more 

downwash you have, the more your relative wind points 

downward. That's important for one very good reason: lift is 

always perpendicular to the relative wind. In Figure 5-11, you 

can see that when you have less downwash, your lift vector 

is more vertical, opposing gravity. And when you have more 

downwash, your lift vector points back more, causing induced 

drag. On top of that, it takes energy for your wings to create 

downwash and vortices, and that energy creates drag. 

Figure 5-10. The difference in wingtip vortex size at altitude versus 

near the ground. 

5-7 
Figure 5-11. The difference in downwash at altitude versus near 

the ground. 

The greater the size and strength of the vortices and 

consequent downwash component on the net airflow over 

the airfoil, the greater the induced drag effect becomes. This 

downwash over the top of the airfoil at the tip has the same 

effect as bending the lift vector rearward; therefore, the lift 

is slightly aft of perpendicular to the relative wind, creating 

a rearward lift component. This is induced drag. 

In order to create a greater negative pressure on the top of an 

airfoil, the airfoil can be inclined to a higher AOA. If the AOA 

of a symmetrical airfoil were zero, there would be no pressure 

differential, and consequently, no downwash component and 

no induced drag. In any case, as AOA increases, induced 

drag increases proportionally. To state this another way—the 

lower the airspeed, the greater the AOA required to produce 

lift equal to the aircraft’s weight and, therefore, the greater 

induced drag. The amount of induced drag varies inversely 

with the square of the airspeed. 

Conversely, parasite drag increases as the square of the 

airspeed. Thus, in steady state, as airspeed decreases to 

near the stalling speed, the total drag becomes greater, due 

mainly to the sharp rise in induced drag. Similarly, as the 

aircraft reaches its never-exceed speed (VNE), the total drag 

increases rapidly due to the sharp increase of parasite drag. 

As seen in Figure 5-6, at some given airspeed, total drag is 

at its minimum amount. In figuring the maximum range of 

aircraft, the thrust required to overcome drag is at a minimum 

if drag is at a minimum. The minimum power and maximum 

endurance occur at a different point. 

Weight 

Gravity is the pulling force that tends to draw all bodies to 

the center of the earth. The CG may be considered as a point 

at which all the weight of the aircraft is concentrated. If the 

aircraft were supported at its exact CG, it would balance in

any attitude. It will be noted that CG is of major importance in 

an aircraft, for its position has a great bearing upon stability. 

The allowable location of the CG is determined by the general 

design of each particular aircraft. The designers determine 

how far the center of pressure (CP) will travel. It is important 

to understand that an aircraft’s weight is concentrated at the 

CG and the aerodynamic forces of lift occur at the CP. When 

the CG is forward of the CP, there is a natural tendency for 

the aircraft to want to pitch nose down. If the CP is forward 

of the CG, a nose up pitching moment is created. Therefore, 

designers fix the aft limit of the CG forward of the CP for the 

corresponding flight speed in order to retain flight equilibrium. 

Weight has a definite relationship to lift. This relationship 

is simple, but important in understanding the aerodynamics 

of flying. Lift is the upward force on the wing acting 

perpendicular to the relative wind and perpendicular to 

the aircraft’s lateral axis. Lift is required to counteract the 

aircraft’s weight. In stabilized level flight, when the lift force is 

equal to the weight force, the aircraft is in a state of equilibrium 

and neither accelerates upward or downward. If lift becomes 

less than weight, the vertical speed will decrease. When lift is 

greater than weight, the vertical speed will increase. 

Wingtip Vortices 

Formation of Vortices 

The action of the airfoil that gives an aircraft lift also causes 

induced drag. When an airfoil is flown at a positive AOA, 

a pressure differential exists between the upper and lower 

surfaces of the airfoil. The pressure above the wing is less 

than atmospheric pressure and the pressure below the wing 

is equal to or greater than atmospheric pressure. Since air 

always moves from high pressure toward low pressure, 

and the path of least resistance is toward the airfoil’s tips, 

there is a spanwise movement of air from the bottom of the 

airfoil outward from the fuselage around the tips. This flow 

of air results in “spillage” over the tips, thereby setting up a 

whirlpool of air called a vortex. [Figure 5-12] 

At the same time, the air on the upper surface has a tendency 

to flow in toward the fuselage and off the trailing edge. This 

air current forms a similar vortex at the inboard portion of the 

trailing edge of the airfoil, but because the fuselage limits the 

inward flow, the vortex is insignificant. Consequently, the 

deviation in flow direction is greatest at the outer tips where 

the unrestricted lateral flow is the strongest. 

5-8 
Vortex 

Figure 5-12. Wingtip vortices. 

As the air curls upward around the tip, it combines with the 

downwash to form a fast-spinning trailing vortex. These 

vortices increase drag because of energy spent in producing 

the turbulence. Whenever an airfoil is producing lift, induced 

drag occurs and wingtip vortices are created. 

Just as lift increases with an increase in AOA, induced 

drag also increases. This occurs because as the AOA is 

increased, there is a greater pressure difference between the 

top and bottom of the airfoil, and a greater lateral flow of air; 

consequently, this causes more violent vortices to be set up, 

resulting in more turbulence and more induced drag. 

In Figure 5-12, it is easy to see the formation of wingtip 

vortices. The intensity or strength of the vortices is directly 

proportional to the weight of the aircraft and inversely 

proportional to the wingspan and speed of the aircraft. The 

heavier and slower the aircraft, the greater the AOA and the 

stronger the wingtip vortices. Thus, an aircraft will create 

wingtip vortices with maximum strength occurring during 

the takeoff, climb, and landing phases of flight. These 

vortices lead to a particularly dangerous hazard to flight, 

wake turbulence. 

Avoiding Wake Turbulence 

Wingtip vortices are greatest when the generating aircraft is 

“heavy, clean, and slow.” This condition is most commonly 

encountered during approaches or departures because an 

aircraft’s AOA is at the highest to produce the lift necessary 

to land or take off. To minimize the chances of flying through 

an aircraft’s wake turbulence: 

•	 Avoid flying through another aircraft’s flight path. 

•	 Rotate prior to the point at which the preceding aircraft 

rotated when taking off behind another aircraft. 

•	 Avoid following another aircraft on a similar flight 

path at an altitude within 1,000 feet. [Figure 5-13] 

•	 Approach the runway above a preceding aircraft’s 

path when landing behind another aircraft and touch 

down after the point at which the other aircraft wheels 

contacted the runway. [Figure 5-14] 

A hovering helicopter generates a down wash from its main 

rotor(s) similar to the vortices of an airplane. Pilots of small 

aircraft should avoid a hovering helicopter by at least three 

rotor disc diameters to avoid the effects of this down wash. In 

forward flight, this energy is transformed into a pair of strong, 

high-speed trailing vortices similar to wing-tip vortices of larger 

fixed-wing aircraft. Helicopter vortices should be avoided 

because helicopter forward flight airspeeds are often very 

slow and can generate exceptionally strong wake turbulence. 

Wind is an important factor in avoiding wake turbulence 

because wingtip vortices drift with the wind at the speed of the 

wind. For example, a wind speed of 10 knots causes the vortices 

to drift at about 1,000 feet in a minute in the wind direction. 

When following another aircraft, a pilot should consider wind 

speed and direction when selecting an intended takeoff or 

landing point. If a pilot is unsure of the other aircraft’s takeoff 

or landing point, approximately 3 minutes provides a margin of 

AVOID 

Nominally 

500–1,000 ft 

Sink rate 

several hundred ft/min 

Figure 5-13. Avoid following another aircraft at an altitude within 1,000 feet. 

5-9 
25 

Rotation Touchdown

Wake ends 

Wake begins 

Figure 5-14. Avoid turbulence from another aircraft. 

Vortex Movement Near Ground - with Cross Winds 

Vortex Movement Near Ground - No Wind 

3K Wind 

6K 

(3K + 3K) 

3K 

No Wind 

3K 

0 (3K - 3K) 

Figure 5-15. When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the 

ground at a speed of 2 or 3 knots (top). A crosswind will decrease the lateral movement of the upwind vortex and increase the movement 

of the downwind vortex. Thus a light wind with a cross runway component of 1 to 5 knots could result in the upwind vortex remaining in 

the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway (bottom). 

5-10 
 

 

safety that allows wake turbulence dissipation. [Figure 5-15] 

For more information on wake turbulence, see Advisory 

Circular (AC) 90-23, Aircraft Wake Turbulence. 

Ground Effect 

Ever since the beginning of manned flight, pilots realized 

that just before touchdown it would suddenly feel like the 

aircraft did not want to go lower, and it would just want to go 

on and on. This is due to the air that is trapped between the 

wing and the landing surface, as if there were an air cushion. 

This phenomenon is called ground effect. 

When an aircraft in flight comes within several feet of the 

surface, ground or water, a change occurs in the threedimensional flow pattern around the aircraft because the 

vertical component of the airflow around the wing is 

restricted by the surface. This alters the wing’s upwash, 

downwash, and wingtip vortices. [Figure 5-16] Ground 

effect, then, is due to the interference of the ground (or water) 

surface with the airflow patterns about the aircraft in flight. 

While the aerodynamic characteristics of the tail surfaces 

and the fuselage are altered by ground effect, the principal 

effects due to proximity of the ground are the changes in 

the aerodynamic characteristics of the wing. As the wing 

encounters ground effect and is maintained at a constant 

AOA, there is consequent reduction in the upwash, 

downwash, and wingtip vortices. 

Induced drag is a result of the airfoil’s work of sustaining 

the aircraft, and a wing or rotor lifts the aircraft simply by 

accelerating a mass of air downward. It is true that reduced 

pressure on top of an airfoil is essential to lift, but that is 

only one of the things contributing to the overall effect of 

pushing an air mass downward. The more downwash there 

is, the harder the wing pushes the mass of air down. At high 

angles of attack, the amount of induced drag is high; since this 

corresponds to lower airspeeds in actual flight, it can be said 

that induced drag predominates at low speed. However, the 

reduction of the wingtip vortices due to ground effect alters 

14 

Figure 5-16. Ground effect changes airflow. 

the spanwise lift distribution and reduces the induced AOA 

and induced drag. Therefore, the wing will require a lower 

AOA in ground effect to produce the same CL. If a constant 

AOA is maintained, an increase in CL results. [Figure 5-17] 

Ground effect also alters the thrust required versus velocity. 

Since induced drag predominates at low speeds, the reduction 

of induced drag due to ground effect will cause a significant 

reduction of thrust required (parasite plus induced drag) at low 

speeds. Due to the change in upwash, downwash, and wingtip 

vortices, there may be a change in position (installation) error 

of the airspeed system associated with ground effect. In the 

majority of cases, ground effect causes an increase in the local 

pressure at the static source and produces a lower indication 

of airspeed and altitude. Thus, an aircraft may be airborne at 

an indicated airspeed less than that normally required. 

In order for ground effect to be of significant magnitude, the 

wing must be quite close to the ground. One of the direct 

results of ground effect is the variation of induced drag with 

wing height above the ground at a constant CL. When the 

wing is at a height equal to its span, the reduction in induced 

drag is only 1.4 percent. However, when the wing is at a 

height equal to one-fourth its span, the reduction in induced 

drag is 23.5 percent and, when the wing is at a height equal 

to one-tenth its span, the reduction in induced drag is 47.6 

percent. Thus, a large reduction in induced drag takes place 

only when the wing is very close to the ground. Because of 

this variation, ground effect is most usually recognized during 

the liftoff for takeoff or just prior to touchdown when landing. 

Thrust required 

Velocity 

Lift coefficient CL 

Angle of attack 

Out of ground effect 

In ground effect 

Out of ground effect 

In ground effect 

Figure 5-17. Ground effect changes drag and lift. 

5-11 
 

During the takeoff phase of flight, ground effect produces 

some important relationships. An aircraft leaving ground 

effect after takeoff encounters just the reverse of an aircraft 

entering ground effect during landing. The aircraft leaving 

ground effect will: 

•	 Require an increase in AOA to maintain the same CL 

•	 Experience an increase in induced drag and thrust 

required 

•	 Experience a decrease in stability and a nose-up 

change in moment 

•	 Experience a reduction in static source pressure and 

increase in indicated airspeed 

Ground effect must be considered during takeoffs and landings. 

For example, if a pilot fails to understand the relationship 

between the aircraft and ground effect during takeoff, a 

hazardous situation is possible because the recommended 

takeoff speed may not be achieved. Due to the reduced drag 

in ground effect, the aircraft may seem capable of takeoff well 

below the recommended speed. As the aircraft rises out of 

ground effect with a deficiency of speed, the greater induced 

drag may result in marginal initial climb performance. In 

extreme conditions, such as high gross weight, high density 

altitude, and high temperature, a deficiency of airspeed during 

takeoff may permit the aircraft to become airborne but be 

incapable of sustaining flight out of ground effect. In this case, 

the aircraft may become airborne initially with a deficiency 

of speed and then settle back to the runway. 

A pilot should not attempt to force an aircraft to become 

airborne with a deficiency of speed. The manufacturer’s 

recommended takeoff speed is necessary to provide adequate 

initial climb performance. It is also important that a definite 

climb be established before a pilot retracts the landing gear 

or flaps. Never retract the landing gear or flaps prior to 

establishing a positive rate of climb and only after achieving 

a safe altitude. 

If, during the landing phase of flight, the aircraft is brought 

into ground effect with a constant AOA, the aircraft 

experiences an increase in CL and a reduction in the thrust 

required, and a “floating” effect may occur. Because of the 

reduced drag and lack of power-off deceleration in ground 

effect, any excess speed at the point of flare may incur a 

considerable “float” distance. As the aircraft nears the point 

of touchdown, ground effect is most realized at altitudes less 

than the wingspan. During the final phases of the approach 

as the aircraft nears the ground, a reduction of power is 

necessary to offset the increase in lift caused from ground 

effect otherwise the aircraft will have a tendency to climb 

above the desired glidepath (GP). 

Axes of an Aircraft 

The axes of an aircraft are three imaginary lines that pass 

through an aircraft’s CG. The axes can be considered as 

imaginary axles around which the aircraft turns. The three 

axes pass through the CG at 90° angles to each other. The 

axis passes through the CG and parallel to a line from nose 

to tail is the longitudinal axis, the axis that passes parallel 

to a line from wingtip to wingtip is the lateral axis, and the 

axis that passes through the CG at right angles to the other 

two axes is the vertical axis. Whenever an aircraft changes 

its flight attitude or position in flight, it rotates about one or 

more of the three axes. [Figure 5-18] 

The aircraft’s motion about its longitudinal axis resembles 

the roll of a ship from side to side. In fact, the names 

used to describe the motion about an aircraft’s three axes 

were originally nautical terms. They have been adapted to 

aeronautical terminology due to the similarity of motion of 

aircraft and seagoing ships. The motion about the aircraft’s 

longitudinal axis is “roll,” the motion about its lateral axis is 

Pitching Rolling Yawing 

Lateral axis Longitudinal axis Vertical axis 

Figure 5-18. Axes of an airplane. 

5-12 
“pitch,” and the motion about its vertical axis is “yaw.” Yaw 

is the left and right movement of the aircraft’s nose. 

The three motions of the conventional airplane (roll, pitch, 

and yaw) are controlled by three control surfaces. Roll is 

controlled by the ailerons; pitch is controlled by the elevators; 

yaw is controlled by the rudder. The use of these controls 

is explained in Chapter 6, Flight Controls. Other types of 

aircraft may utilize different methods of controlling the 

movements about the various axes. 

For example, weight-shift control aircraft control two axes 

(roll and pitch) using an “A” frame suspended from the 

flexible wing attached to a three-wheeled carriage. These 

aircraft are controlled by moving a horizontal bar (called a 

control bar) in roughly the same way hang glider pilots fly. 

[Figure 5-19] They are termed weight-shift control aircraft 

because the pilot controls the aircraft by shifting the CG. 

For more information on weight-shift control aircraft, see 

the Federal Aviation Administration (FAA) Weight-Shift 

Control Flying Handbook, FAA-H-8083-5. In the case of 

powered parachutes, aircraft control is accomplished by 

altering the airfoil via steering lines. 

A powered parachute wing is a parachute that has a cambered 

upper surface and a flatter under surface. The two surfaces are 

separated by ribs that act as cells, which open to the airflow 

at the leading edge and have internal ports to allow lateral 

airflow. The principle at work holds that the cell pressure is 

greater than the outside pressure, thereby forming a wing that 

maintains its airfoil shape in flight. The pilot and passenger 

sit in tandem in front of the engine, which is located at the 

rear of a vehicle. The airframe is attached to the parachute 

via two attachment points and lines. Control is accomplished 

by both power and the changing of the airfoil via the control 

lines. [Figure 5-20] 

Figure 5-19. A weight-shift control aircraft. 

Figure 5-20. A powered parachute. 

Moment and Moment Arm 

A study of physics shows that a body that is free to rotate 

will always turn about its CG. In aerodynamic terms, the 

mathematical measure of an aircraft’s tendency to rotate 

about its CG is called a “moment.” A moment is said to be 

equal to the product of the force applied and the distance at 

which the force is applied. (A moment arm is the distance 

from a datum [reference point or line] to the applied force.) 

For aircraft weight and balance computations, “moments” 

are expressed in terms of the distance of the arm times the 

aircraft’s weight, or simply, inch-pounds. 

Aircraft designers locate the fore and aft position of the 

aircraft’s CG as nearly as possible to the 20 percent point 

of the mean aerodynamic chord (MAC). If the thrust line 

is designed to pass horizontally through the CG, it will not 

cause the aircraft to pitch when power is changed, and there 

will be no difference in moment due to thrust for a power-on 

or power-off condition of flight. Although designers have 

some control over the location of the drag forces, they are not 

always able to make the resultant drag forces pass through the 

CG of the aircraft. However, the one item over which they 

have the greatest control is the size and location of the tail. 

The objective is to make the moments (due to thrust, drag, and 

lift) as small as possible and, by proper location of the tail, 

to provide the means of balancing an aircraft longitudinally 

for any condition of flight. 

The pilot has no direct control over the location of forces 

acting on the aircraft in flight, except for controlling the 

center of lift by changing the AOA. The pilot can control 

the magnitude of the forces. Such a change, however, 

immediately involves changes in other forces. Therefore, 

the pilot cannot independently change the location of one 

force without changing the effect of others. For example, 

a change in airspeed involves a change in lift, as well as a 

change in drag and a change in the up or down force on the 

5-13 
 

tail. As forces such as turbulence and gusts act to displace 

the aircraft, the pilot reacts by providing opposing control 

forces to counteract this displacement. 

Some aircraft are subject to changes in the location of the CG 

with variations of load. Trimming devices, such as elevator 

trim tabs and adjustable horizontal stabilizers, are used to 

counteract the moments set up by fuel burnoff and loading 

or off-loading of passengers or cargo. 

Aircraft Design Characteristics 

Each aircraft handles somewhat differently because each 

resists or responds to control pressures in its own way. For 

example, a training aircraft is quick to respond to control 

applications, while a transport aircraft feels heavy on the 

controls and responds to control pressures more slowly. 

These features can be designed into an aircraft to facilitate 

the particular purpose of the aircraft by considering certain 

stability and maneuvering requirements. The following 

discussion summarizes the more important aspects of an 

aircraft’s stability, maneuverability, and controllability 

qualities; how they are analyzed; and their relationship to 

various flight conditions. 

Stability 

Stability is the inherent quality of an aircraft to correct for 

conditions that may disturb its equilibrium and to return to 

or to continue on the original flight path. It is primarily an 

aircraft design characteristic. The flight paths and attitudes an 

aircraft flies are limited by the aerodynamic characteristics of 

the aircraft, its propulsion system, and its structural strength. 

These limitations indicate the maximum performance and 

maneuverability of the aircraft. If the aircraft is to provide 

maximum utility, it must be safely controllable to the full 

extent of these limits without exceeding the pilot’s strength 

or requiring exceptional flying ability. If an aircraft is to fly 

straight and steady along any arbitrary flight path, the forces 

acting on it must be in static equilibrium. The reaction of 

any body when its equilibrium is disturbed is referred to as 

stability. The two types of stability are static and dynamic. 

Static Stability 

Static stability refers to the initial tendency, or direction of 

movement, back to equilibrium. In aviation, it refers to the 

aircraft’s initial response when disturbed from a given pitch, 

yaw, or bank. 

•	 Positive static stability—the initial tendency of the 

aircraft to return to the original state of equilibrium 

after being disturbed. [Figure 5-21] 

•	 Neutral static stability—the initial tendency of 

the aircraft to remain in a new condition after its 

equilibrium has been disturbed. [Figure 5-21] 

•	 Negative static stability—the initial tendency of the 

aircraft to continue away from the original state of 

equilibrium after being disturbed. [Figure 5-21] 

Dynamic Stability 

Static stability has been defined as the initial tendency to 

return to equilibrium that the aircraft displays after being 

disturbed from its trimmed condition. Occasionally, the 

initial tendency is different or opposite from the overall 

tendency, so a distinction must be made between the two. 

Dynamic stability refers to the aircraft response over time 

Positive Static Stability Neutral Static Stability Negative Static Stability CGCG CG CG 

Applied 

force 

Applied

force 

Applied

force 

Figure 5-21. Types of static stability. 

5-14 
when disturbed from a given pitch, yaw, or bank. This type 

of stability also has three subtypes: [Figure 5-22] 

•	 Positive dynamic stability—over time, the motion 

of the displaced object decreases in amplitude and, 

because it is positive, the object displaced returns 

toward the equilibrium state. 

•	 Neutral dynamic stability—once displaced, the 

displaced object neither decreases nor increases in 

amplitude. A worn automobile shock absorber exhibits 

this tendency. 

•	 Negative dynamic stability—over time, the motion 

of the displaced object increases and becomes more 

divergent. 

Stability in an aircraft affects two areas significantly: 

•	 Maneuverability—the quality of an aircraft that 

permits it to be maneuvered easily and to withstand 

the stresses imposed by maneuvers. It is governed by 

the aircraft’s weight, inertia, size and location of flight 

controls, structural strength, and powerplant. It too is 

an aircraft design characteristic. 

• Controllability—the capability of an aircraft to 

respond to the pilot’s control, especially with regard 

to flight path and attitude. It is the quality of the 

aircraft’s response to the pilot’s control application 

when maneuvering the aircraft, regardless of its 

stability characteristics. 

Longitudinal Stability (Pitching) 

In designing an aircraft, a great deal of effort is spent in 

developing the desired degree of stability around all three 

axes. But longitudinal stability about the lateral axis is 

considered to be the most affected by certain variables in 

various flight conditions. 

Longitudinal stability is the quality that makes an aircraft 

stable about its lateral axis. It involves the pitching motion 

as the aircraft’s nose moves up and down in flight. A 

longitudinally unstable aircraft has a tendency to dive or 

climb progressively into a very steep dive or climb, or even 

a stall. Thus, an aircraft with longitudinal instability becomes 

difficult and sometimes dangerous to fly. 

Static longitudinal stability, or instability in an aircraft, is 

dependent upon three factors: 

1.	 Location of the wing with respect to the CG 

2.	 Location of the horizontal tail surfaces with respect 

to the CG 

3.	 Area or size of the tail surfaces 

In analyzing stability, it should be recalled that a body free 

to rotate always turns about its CG. 

To obtain static longitudinal stability, the relation of the 

wing and tail moments must be such that, if the moments 

are initially balanced and the aircraft is suddenly nose up, 

the wing moments and tail moments change so that the sum 

of their forces provides an unbalanced but restoring moment 

which, in turn, brings the nose down again. Similarly, if the 

aircraft is nose down, the resulting change in moments brings 

the nose back up. 

The Center of Lift (CL) in most asymmetrical airfoils has a 

tendency to change its fore and aft positions with a change in 

the AOA. The CL tends to move forward with an increase in 

AOA and to move aft with a decrease in AOA. This means 

Displacement 

Positive static 

(neutral dynamic) 

Positive static 

(positive dynamic) 

Positive Static 

(negative dynamic) 

Time 

Damped oscillation 

Undamped oscillation 

Divergent oscillation 

Figure 5-22. Damped versus undamped stability. 

5-15 
 

that when the AOA of an airfoil is increased, the CL, by 

moving forward, tends to lift the leading edge of the wing 

still more. This tendency gives the wing an inherent quality 

of instability. (NOTE: CL is also known as the center of 

pressure (CP).) 

Figure 5-23 shows an aircraft in straight-and-level flight. The 

line CG-CL-T represents the aircraft’s longitudinal axis from 

the CG to a point T on the horizontal stabilizer. 

Most aircraft are designed so that the wing’s CL is to the rear 

of the CG. This makes the aircraft “nose heavy” and requires 

that there be a slight downward force on the horizontal 

stabilizer in order to balance the aircraft and keep the nose 

from continually pitching downward. Compensation for this 

nose heaviness is provided by setting the horizontal stabilizer 

at a slight negative AOA. The downward force thus produced 

holds the tail down, counterbalancing the “heavy” nose. It 

is as if the line CG-CL-T were a lever with an upward force 

at CL and two downward forces balancing each other, one 

a strong force at the CG point and the other, a much lesser 

force, at point T (downward air pressure on the stabilizer). 

To better visualize this physics principle: If an iron bar were 

suspended at point CL, with a heavy weight hanging on it at 

the CG, it would take downward pressure at point T to keep 

the “lever” in balance. 

Even though the horizontal stabilizer may be level when the 

aircraft is in level flight, there is a downwash of air from the 

wings. This downwash strikes the top of the stabilizer and 

produces a downward pressure, which at a certain speed is 

just enough to balance the “lever.” The faster the aircraft 

is flying, the greater this downwash and the greater the 

downward force on the horizontal stabilizer (except T-tails). 

[Figure 5-24] In aircraft with fixed-position horizontal 

stabilizers, the aircraft manufacturer sets the stabilizer at an 

angle that provides the best stability (or balance) during flight 

at the design cruising speed and power setting. 

If the aircraft’s speed decreases, the speed of the airflow 

over the wing is decreased. As a result of this decreased CG CL CG CL 

Figure 5-23. Longitudinal stability. 

CG 

CG 

CG 

Balanced tail load 

Lesser downward tail load 

Greater downward tail load 

Cruise Speed 

High Speed 

Low Speed 

Figure 5-24. Effect of speed on downwash. 

flow of air over the wing, the downwash is reduced, causing 

a lesser downward force on the horizontal stabilizer. In turn, 

the characteristic nose heaviness is accentuated, causing the 

aircraft’s nose to pitch down more. [Figure 5-25] This places 

the aircraft in a nose-low attitude, lessening the wing’s AOA 

and drag and allowing the airspeed to increase. As the aircraft 

continues in the nose-low attitude and its speed increases, 

the downward force on the horizontal stabilizer is once again 

increased. Consequently, the tail is again pushed downward 

and the nose rises into a climbing attitude. 

Normal downwash 

Reduced downwash 

Thrust 

Weight 

CG 

Lift 

Thrust 

Weight 

CG 

Lift 

Figure 5-25. Reduced power allows pitch down. 

5-16 
As this climb continues, the airspeed again decreases, causing 

the downward force on the tail to decrease until the nose 

lowers once more. Because the aircraft is dynamically stable, 

the nose does not lower as far this time as it did before. The 

aircraft acquires enough speed in this more gradual dive to 

start it into another climb, but the climb is not as steep as 

the preceding one. 

After several of these diminishing oscillations, in which 

the nose alternately rises and lowers, the aircraft finally 

settles down to a speed at which the downward force on the 

tail exactly counteracts the tendency of the aircraft to dive. 

When this condition is attained, the aircraft is once again in 

balanced flight and continues in stabilized flight as long as 

this attitude and airspeed are not changed. 

A similar effect is noted upon closing the throttle. The 

downwash of the wings is reduced and the force at T in 

Figure 5-23 is not enough to hold the horizontal stabilizer 

down. It seems as if the force at T on the lever were allowing 

the force of gravity to pull the nose down. This is a desirable 

characteristic because the aircraft is inherently trying to 

regain airspeed and reestablish the proper balance. 

Power or thrust can also have a destabilizing effect in that 

an increase of power may tend to make the nose rise. The 

aircraft designer can offset this by establishing a “high 

thrust line” wherein the line of thrust passes above the CG. 

[Figures 5-26 and 5-27] In this case, as power or thrust is 

Below center of gravity 

Through center of gravity 

Above center of gravity 

Thrust CG 

Thrust CG 

Thrust 

CG 

Figure 5-26. Thrust line affects longitudinal stability. 

Cruise power 

Idle power 

Full power Lift 

Thrust CG Lift 

Thrust CG Lift 

Thrust CG 

Figure 5-27. Power changes affect longitudinal stability. 

increased a moment is produced to counteract the down load 

on the tail. On the other hand, a very “low thrust line” would 

tend to add to the nose-up effect of the horizontal tail surface. 

Conclusion: with CG forward of the CL and with an 

aerodynamic tail-down force, the aircraft usually tries to 

return to a safe flying attitude. 

The following is a simple demonstration of longitudinal 

stability. Trim the aircraft for “hands off” control in level 

flight. Then, momentarily give the controls a slight push to 

nose the aircraft down. If, within a brief period, the nose rises 

towards the original position, the aircraft is statically stable. 

Ordinarily, the nose passes the original position (that of level 

flight) and a series of slow pitching oscillations follows. If the 

oscillations gradually cease, the aircraft has positive stability; 

if they continue unevenly, the aircraft has neutral stability; 

if they increase, the aircraft is unstable. 

Lateral Stability (Rolling) 

Stability about the aircraft’s longitudinal axis, which extends 

from the nose of the aircraft to its tail, is called lateral 

stability. Positive lateral stability helps to stabilize the lateral 

or “rolling effect” when one wing gets lower than the wing 

on the opposite side of the aircraft. There are four main 

design factors that make an aircraft laterally stable: dihedral, 

sweepback, keel effect, and weight distribution. 

5-17 
Dihedral 

Some aircraft are designed so that the outer tips of the wings 

are higher than the wing roots. The upward angle thus formed 

by the wings is called dihedral. [Figure 5-28] When a gust 

causes a roll, a sideslip will result. This sideslip causes the 

relative wind affecting the entire airplane to be from the 

direction of the slip. When the relative wind comes from the 

side, the wing slipping into the wind is subject to an increase 

in AOA and develops an increase in lift. The wing away 

from the wind is subject to a decrease in angle of attack, and 

develops a decrease in lift. The changes in lift effect a rolling 

moment tending to raise the windward wing, hence dihedral 

contributes to a stable roll due to sideslip. [Figure 5-29] 

Sweepback and Wing Location 

Many aspects of an aircraft's configuration can affect its 

effective dihedral, but two major components are wing 

sweepback and the wing location with respect to the fuselage 

(such as a low wing or high wing). As a rough estimation, 

10° of sweepback on a wing provides about 1° of effective 

dihedral, while a high wing configuration can provide about 

5° of effective dihedral over a low wing configuration. 

A sweptback wing is one in which the leading edge slopes 

backward. [Figure 5-30] When a disturbance causes an 

aircraft with sweepback to slip or drop a wing, the low 

wing presents its leading edge at an angle that is more 

perpendicular to the relative airflow. As a result, the low 

wing acquires more lift, rises, and the aircraft is restored to 

its original flight attitude. 

Keel Effect and Weight Distribution 

A high wing aircraft always has the tendency to turn the 

longitudinal axis of the aircraft into the relative wind, which is 

often referred to as the keel effect. These aircraft are laterally 

stable simply because the wings are attached in a high 

position on the fuselage, making the fuselage behave like a 

keel exerting a steadying influence on the aircraft laterally 

about the longitudinal axis. When a high-winged aircraft is 

Wing has decreased 

AOA, hence reduced lift 

due to sideslip. 

Wing has increased AOA, hence 

increased lift due to sideslip. 

Sideslip 

Restoring lift 

Figure 5-29. Sideslip causing different AOA on each blade. 

Figure 5-30. Sweepback wings. 

disturbed and one wing dips, the fuselage weight acts like a 

pendulum returning the aircraft to the horizontal level. 

Laterally stable aircraft are constructed so that the greater 

portion of the keel area is above the CG. [Figure 5-31] Thus, 

when the aircraft slips to one side, the combination of the 

Dihedral Dihedral

Figure 5-28. Dihedral is the upward angle of the wings from a horizontal (front/rear view) axis of the plane as shown in the graphic 

depiction and the rear view of a Ryanair Boeing 737. 

5-18 
 

CG 

CG 

CG centerline 

Figure 5-31. Keel area for lateral stability. 

aircraft’s weight and the pressure of the airflow against the 

upper portion of the keel area (both acting about the CG) 

tends to roll the aircraft back to wings-level flight. 

Directional Stability (Yawing) 

Stability about the aircraft’s vertical axis (the sideways 

moment) is called yawing or directional stability. Yawing 

or directional stability is the most easily achieved stability 

in aircraft design. The area of the vertical fin and the sides 

of the fuselage aft of the CG are the prime contributors that 

make the aircraft act like the well known weather vane or 

arrow, pointing its nose into the relative wind. 

In examining a weather vane, it can be seen that if exactly the 

same amount of surface were exposed to the wind in front 

of the pivot point as behind it, the forces fore and aft would 

be in balance and little or no directional movement would 

result. Consequently, it is necessary to have a greater surface 

aft of the pivot point than forward of it. 

Similarly, the aircraft designer must ensure positive 

directional stability by making the side surface greater aft 

than ahead of the CG. [Figure 5-32] To provide additional 

positive stability to that provided by the fuselage, a vertical 

fin is added. The fin acts similar to the feather on an arrow 

in maintaining straight flight. Like the weather vane and the 

arrow, the farther aft this fin is placed and the larger its size, 

the greater the aircraft’s directional stability. 

If an aircraft is flying in a straight line, and a sideward gust 

of air gives the aircraft a slight rotation about its vertical 

axis (i.e., the right), the motion is retarded and stopped by 

the fin because while the aircraft is rotating to the right, the 

air is striking the left side of the fin at an angle. This causes 

pressure on the left side of the fin, which resists the turning 

motion and slows down the aircraft’s yaw. In doing so, it 

acts somewhat like the weather vane by turning the aircraft 

into the relative wind. The initial change in direction of the 

aircraft’s flight path is generally slightly behind its change 

of heading. Therefore, after a slight yawing of the aircraft 

Area 

forward 

of CG 

Area aft of CG 

CG 

CG 

Relative wind 

Yaw 

yaw 

Figure 5-32. Fuselage and fin for directional stability. 

to the right, there is a brief moment when the aircraft is still 

moving along its original path, but its longitudinal axis is 

pointed slightly to the right. 

The aircraft is then momentarily skidding sideways and, 

during that moment (since it is assumed that although the 

yawing motion has stopped, the excess pressure on the left 

side of the fin still persists), there is necessarily a tendency 

for the aircraft to be turned partially back to the left. That is, 

there is a momentary restoring tendency caused by the fin. 

This restoring tendency is relatively slow in developing and 

ceases when the aircraft stops skidding. When it ceases, the 

aircraft is flying in a direction slightly different from the 

original direction. In other words, it will not return of its own 

accord to the original heading; the pilot must reestablish the 

initial heading. 

A minor improvement of directional stability may be obtained 

through sweepback. Sweepback is incorporated in the design 

of the wing primarily to delay the onset of compressibility 

during high-speed flight. In lighter and slower aircraft, 

sweepback aids in locating the center of pressure in the 

correct relationship with the CG. A longitudinally stable 

aircraft is built with the center of pressure aft of the CG. 

Because of structural reasons, aircraft designers sometimes 

cannot attach the wings to the fuselage at the exact desired 

5-19 
point. If they had to mount the wings too far forward, and at 

right angles to the fuselage, the center of pressure would not 

be far enough to the rear to result in the desired amount of 

longitudinal stability. By building sweepback into the wings, 

however, the designers can move the center of pressure toward 

the rear. The amount of sweepback and the position of the 

wings then place the center of pressure in the correct location. 

When turbulence or rudder application causes the aircraft to 

yaw to one side, the opposite wing presents a longer leading 

edge perpendicular to the relative airflow. The airspeed of 

the forward wing increases and it acquires more drag than 

the back wing. The additional drag on the forward wing pulls 

the wing back, turning the aircraft back to its original path. 

The contribution of the wing to static directional stability is 

usually small. The swept wing provides a stable contribution 

depending on the amount of sweepback, but the contribution 

is relatively small when compared with other components. 

Free Directional Oscillations (Dutch Roll) 

Dutch roll is a coupled lateral/directional oscillation that is 

usually dynamically stable but is unsafe in an aircraft because 

of the oscillatory nature. The damping of the oscillatory mode 

may be weak or strong depending on the properties of the 

particular aircraft. 

If the aircraft has a right wing pushed down, the positive 

sideslip angle corrects the wing laterally before the nose is 

realigned with the relative wind. As the wing corrects the 

position, a lateral directional oscillation can occur resulting in 

the nose of the aircraft making a figure eight on the horizon as 

a result of two oscillations (roll and yaw), which, although of 

about the same magnitude, are out of phase with each other. 

In most modern aircraft, except high-speed swept wing 

designs, these free directional oscillations usually die out 

automatically in very few cycles unless the air continues to 

be gusty or turbulent. Those aircraft with continuing Dutch 

roll tendencies are usually equipped with gyro-stabilized yaw 

dampers. Manufacturers try to reach a midpoint between too 

much and too little directional stability. Because it is more 

desirable for the aircraft to have “spiral instability” than 

Dutch roll tendencies, most aircraft are designed with that 

characteristic. 

Spiral Instability 

Spiral instability exists when the static directional stability 

of the aircraft is very strong as compared to the effect of its 

dihedral in maintaining lateral equilibrium. When the lateral 

equilibrium of the aircraft is disturbed by a gust of air and a 

sideslip is introduced, the strong directional stability tends 

to yaw the nose into the resultant relative wind while the 

comparatively weak dihedral lags in restoring the lateral 

balance. Due to this yaw, the wing on the outside of the 

turning moment travels forward faster than the inside wing 

and, as a consequence, its lift becomes greater. This produces 

an overbanking tendency which, if not corrected by the pilot, 

results in the bank angle becoming steeper and steeper. At 

the same time, the strong directional stability that yaws the 

aircraft into the relative wind is actually forcing the nose 

to a lower pitch attitude. A slow downward spiral begins 

which, if not counteracted by the pilot, gradually increases 

into a steep spiral dive. Usually the rate of divergence in the 

spiral motion is so gradual the pilot can control the tendency 

without any difficulty. 

Many aircraft are affected to some degree by this characteristic, 

although they may be inherently stable in all other normal 

parameters. This tendency explains why an aircraft cannot 

be flown “hands off” indefinitely. 

Much research has gone into the development of control 

devices (wing leveler) to correct or eliminate this instability. 

The pilot must be careful in application of recovery controls 

during advanced stages of this spiral condition or excessive 

loads may be imposed on the structure. Improper recovery 

from spiral instability leading to inflight structural failures 

has probably contributed to more fatalities in general aviation 

aircraft than any other factor. Since the airspeed in the spiral 

condition builds up rapidly, the application of back elevator 

force to reduce this speed and to pull the nose up only 

“tightens the turn,” increasing the load factor. The results 

of the prolonged uncontrolled spiral are inflight structural 

failure, crashing into the ground, or both. Common recorded 

causes for pilots who get into this situation are loss of horizon 

reference, inability to control the aircraft by reference to 

instruments, or a combination of both. 

Effect of Wing Planform 

Understanding the effects of different wing planforms 

is important when learning about wing performance and 

airplane flight characteristics. A planform is the shape of the 

wing as viewed from directly above and deals with airflow 

in three dimensions. Aspect ratio, taper ratio, and sweepback 

are factors in planform design that are very important to the 

overall aerodynamic characteristic of a wing. [Figure 5-33] 

Aspect ratio is the ratio of wing span to wing chord. Taper 

ratio can be either in planform or thickness, or both. In its 

simplest terms, it is a decrease from wing root to wingtip in 

wing chord or wing thickness. Sweepback is the rearward 

slant of a wing, horizontal tail, or other airfoil surface. 

There are two general means by which the designer can 

change the planform of a wing and both will affect the 

5-20 
Elliptical wing Regular wing 

Moderate taper wing High taper wing 

Pointed tip wing Sweepback wing 

Figure 5-33. Different types of wing planforms. 

aerodynamic characteristics of the wing. The first is to effect 

a change in the aspect ratio. Aspect ratio is the primary factor 

in determining the three dimensional characteristics of the 

ordinary wing and its lift/drag ratio. An increase in aspect 

ratio with constant velocity will decrease the drag, especially 

at high angles of attack, improving the performance of the 

wing when in a climbing attitude. 

A decrease in aspect ratio will give a corresponding increase 

in drag. It should be noted, however, that with an increase in 

aspect ratio there is an increase in the length of span, with a 

corresponding increase in the weight of the wing structure, 

which means the wing must be heavier to carry the same load. 

For this reason, part of the gain (due to a decrease in drag) is 

lost because of the increased weight, and a compromise in 

5-21 
design is necessary to obtain the best results from these two 

conflicting conditions. 

The second means of changing the planform is by tapering 

(decreasing the length of chord from the root to the tip of the 

wing). In general, tapering causes a decrease in drag (most 

effective at high speeds) and an increase in lift. There is also 

a structural benefit due to a saving in weight of the wing. 

Most training and general aviation type airplanes are operated 

at high coefficients of lift, and therefore require comparatively 

high aspect ratios. Airplanes that are developed to operate at 

very high speeds demand greater aerodynamic cleanness and 

greater strength, which require low aspect ratios. Very low 

aspect ratios result in high wing loadings and high stall speeds. 

When sweepback is combined with low aspect ratio, it results 

in flying qualities very different from a more conventional 

high aspect ratio airplane configuration. Such airplanes 

require very precise and professional flying techniques, 

especially at slow speeds, while airplanes with a high aspect 

ratio are usually more forgiving of improper pilot techniques. 

The elliptical wing is the ideal subsonic planform since it 

provides for a minimum of induced drag for a given aspect 

ratio, though as we shall see, its stall characteristics in 

some respects are inferior to the rectangular wing. It is also 

comparatively difficult to construct. The tapered airfoil is 

desirable from the standpoint of weight and stiffness, but 

again is not as efficient aerodynamically as the elliptical 

wing. In order to preserve the aerodynamic efficiency of the 

elliptical wing, rectangular and tapered wings are sometimes 

tailored through use of wing twist and variation in airfoil 

sections until they provide as nearly as possible the elliptical 

wing’s lift distribution. While it is true that the elliptical 

wing provides the best coefficients of lift before reaching an 

incipient stall, it gives little advance warning of a complete 

stall, and lateral control may be difficult because of poor 

aileron effectiveness. 

In comparison, the rectangular wing has a tendency to stall 

first at the wing root and provides adequate stall warning, 

adequate aileron effectiveness, and is usually quite stable. 

It is, therefore, favored in the design of low cost, low speed 

airplanes. 

Aerodynamic Forces in Flight Maneuvers 

Forces in Turns 

If an aircraft were viewed in straight-and-level flight from the 

front [Figure 5-34], and if the forces acting on the aircraft 

could be seen, lift and weight would be apparent: two forces. 

If the aircraft were in a bank it would be apparent that lift 

did not act directly opposite to the weight, rather it now acts 

in the direction of the bank. A basic truth about turns is that 

when the aircraft banks, lift acts inward toward the center of 

the turn, perpendicular to the lateral axis as well as upward. 

Newton’s First Law of Motion, the Law of Inertia, states that 

an object at rest or moving in a straight line remains at rest 

or continues to move in a straight line until acted on by some 

other force. An aircraft, like any moving object, requires a 

sideward force to make it turn. In a normal turn, this force 

is supplied by banking the aircraft so that lift is exerted 

inward, as well as upward. The force of lift during a turn is 

separated into two components at right angles to each other. 

One component, which acts vertically and opposite to the 

weight (gravity), is called the “vertical component of lift.” 

The other, which acts horizontally toward the center of the 

turn, is called the “horizontal component of lift” or centripetal 

force. The horizontal component of lift is the force that 

pulls the aircraft from a straight flight path to make it turn. 

Centrifugal force is the “equal and opposite reaction” of the 

aircraft to the change in direction and acts equal and opposite 

to the horizontal component of lift. This explains why, in a 

correctly executed turn, the force that turns the aircraft is 

not supplied by the rudder. The rudder is used to correct any 

deviation between the straight track of the nose and tail of the 

aircraft into the relative wind. A good turn is one in which the 

Level flight Medium banked turn Steeply banked turn 

Centrifugal

force 

Horizontal 

component 

component Vertical

Resultant load 

Centrifugal

force 

Horizontal 

component 

component Vertical

Resultant load 

Lift

Total lift 

Total lift

WeightWeight Weight

Figure 5-34. Forces during normal, coordinated turn at constant altitude. 

5-22 
 

 

nose and tail of the aircraft track along the same path. If no 

rudder is used in a turn, the nose of the aircraft yaws to the 

outside of the turn. The rudder is used rolling into the turn 

to bring the nose back in line with the relative wind. Once 

in the turn, the rudder should not be needed. 

An aircraft is not steered like a boat or an automobile. In 

order for an aircraft to turn, it must be banked. If it is not 

banked, there is no force available to cause it to deviate 

from a straight flight path. Conversely, when an aircraft is 

banked, it turns provided it is not slipping to the inside of the 

turn. Good directional control is based on the fact that the 

aircraft attempts to turn whenever it is banked. Pilots should 

keep this fact in mind when attempting to hold the aircraft 

in straight-and-level flight. 

Merely banking the aircraft into a turn produces no change in 

the total amount of lift developed. Since the lift during the bank 

is divided into vertical and horizontal components, the amount 

of lift opposing gravity and supporting the aircraft’s weight 

is reduced. Consequently, the aircraft loses altitude unless 

additional lift is created. This is done by increasing the AOA 

until the vertical component of lift is again equal to the weight. 

Since the vertical component of lift decreases as the bank 

angle increases, the AOA must be progressively increased 

to produce sufficient vertical lift to support the aircraft’s 

weight. An important fact for pilots to remember when making 

constant altitude turns is that the vertical component of lift 

must be equal to the weight to maintain altitude. 

At a given airspeed, the rate at which an aircraft turns 

depends upon the magnitude of the horizontal component 

of lift. It is found that the horizontal component of lift is 

proportional to the angle of bank—that is, it increases or 

decreases respectively as the angle of bank increases or 

decreases. As the angle of bank is increased, the horizontal 

component of lift increases, thereby increasing the rate of 

turn (ROT). Consequently, at any given airspeed, the ROT 

can be controlled by adjusting the angle of bank. 

To provide a vertical component of lift sufficient to hold 

altitude in a level turn, an increase in the AOA is required. 

Since the drag of the airfoil is directly proportional to its AOA, 

induced drag increases as the lift is increased. This, in turn, 

causes a loss of airspeed in proportion to the angle of bank. 

A small angle of bank results in a small reduction in airspeed 

while a large angle of bank results in a large reduction in 

airspeed. Additional thrust (power) must be applied to prevent 

a reduction in airspeed in level turns. The required amount of 

additional thrust is proportional to the angle of bank. 

To compensate for added lift, which would result if the 

airspeed were increased during a turn, the AOA must be 

decreased, or the angle of bank increased, if a constant 

altitude is to be maintained. If the angle of bank is held 

constant and the AOA decreased, the ROT decreases. In order 

to maintain a constant ROT as the airspeed is increased, the 

AOA must remain constant and the angle of bank increased. 

An increase in airspeed results in an increase of the turn radius, 

and centrifugal force is directly proportional to the radius of 

the turn. In a correctly executed turn, the horizontal component 

of lift must be exactly equal and opposite to the centrifugal 

force. As the airspeed is increased in a constant-rate level turn, 

the radius of the turn increases. This increase in the radius of 

turn causes an increase in the centrifugal force, which must 

be balanced by an increase in the horizontal component of lift, 

which can only be increased by increasing the angle of bank. 

In a slipping turn, the aircraft is not turning at the rate 

appropriate to the bank being used, since the aircraft is yawed 

toward the outside of the turning flight path. The aircraft is 

banked too much for the ROT, so the horizontal lift component 

is greater than the centrifugal force. [Figure 5-35] Equilibrium 

between the horizontal lift component and centrifugal force 

is reestablished by either decreasing the bank, increasing the 

ROT, or a combination of the two changes. 

A skidding turn results from an excess of centrifugal force 

over the horizontal lift component, pulling the aircraft 

toward the outside of the turn. The ROT is too great for the 

angle of bank. Correction of a skidding turn thus involves a 

reduction in the ROT, an increase in bank, or a combination 

of the two changes. 

To maintain a given ROT, the angle of bank must be varied 

with the airspeed. This becomes particularly important in 

high-speed aircraft. For instance, at 400 miles per hour (mph), 

an aircraft must be banked approximately 44° to execute a 

standard-rate turn (3° per second). At this angle of bank, 

only about 79 percent of the lift of the aircraft comprises the 

vertical component of the lift. This causes a loss of altitude 

unless the AOA is increased sufficiently to compensate for 

the loss of vertical lift. 

Forces in Climbs 

For all practical purposes, the wing’s lift in a steady state 

normal climb is the same as it is in a steady level flight at the 

same airspeed. Although the aircraft’s flight path changed 

when the climb was established, the AOA of the wing with 

respect to the inclined flight path reverts to practically the 

same values, as does the lift. There is an initial momentary 

change as shown in Figure 5-36. During the transition from 

straight-and-level flight to a climb, a change in lift occurs 

when back elevator pressure is first applied. Raising the 

aircraft’s nose increases the AOA and momentarily increases 

5-23 
W

W

W

Normal turn Slipping turn Skidding turn 

Centrifugal 

force equals 

horizontal lift 

Centrifugal 

force less than 

horizontal lift 

Centrifugal force 

greater than 

horizontal lift 

Vertical lift

Vertical lift

Vertical lift 

Load

Load

Load 

Centrifugal force 

Horizontal 

lift 

Centrifugal force 

Horizontal 

lift 

Centrifugal force 

Horizontal 

lift 

Lift

Lift

Lift 

WeightWeight Weight

Figure 5-35. Normal, slipping, and skidding turns at a constant altitude. 

the lift. Lift at this moment is now greater than weight and 

starts the aircraft climbing. After the flight path is stabilized 

on the upward incline, the AOA and lift again revert to about 

the level flight values. 

If the climb is entered with no change in power setting, the 

airspeed gradually diminishes because the thrust required 

to maintain a given airspeed in level flight is insufficient to 

maintain the same airspeed in a climb. When the flight path 

is inclined upward, a component of the aircraft’s weight 

acts in the same direction as, and parallel to, the total drag 

of the aircraft, thereby increasing the total effective drag. 

Consequently, the total effective drag is greater than the 

power, and the airspeed decreases. The reduction in airspeed 

gradually results in a corresponding decrease in drag until 

the total drag (including the component of weight acting 

in the same direction) equals the thrust. [Figure 5-37] Due 

to momentum, the change in airspeed is gradual, varying 

considerably with differences in aircraft size, weight, total 

drag, and other factors. Consequently, the total effective drag 

is greater than the thrust, and the airspeed decreases. 

Generally, the forces of thrust and drag, and lift and weight, 

again become balanced when the airspeed stabilizes but at 

a value lower than in straight-and-level flight at the same 

power setting. Since the aircraft’s weight is acting not only 

downward but rearward with drag while in a climb, additional 

power is required to maintain the same airspeed as in level 

flight. The amount of power depends on the angle of climb. 

When the climb is established steep enough that there is 

insufficient power available, a slower speed results. 

The thrust required for a stabilized climb equals drag plus a 

percentage of weight dependent on the angle of climb. For 

example, a 10° climb would require thrust to equal drag plus 

17 percent of weight. To climb straight up would require 

thrust to equal all of weight and drag. Therefore, the angle 

of climb for climb performance is dependent on the amount 

of excess thrust available to overcome a portion of weight. 

Note that aircraft are able to sustain a climb due to excess 

thrust. When the excess thrust is gone, the aircraft is no 

longer able to climb. At this point, the aircraft has reached 

its “absolute ceiling.” 

Forces in Descents 

As in climbs, the forces that act on the aircraft go through 

definite changes when a descent is entered from straightand-level flight. For the following example, the aircraft 

L 

L 

L 

L 

Steady climb 

normal lift Climb entry

increased lift 

Level flight

normal lift 

T 

D 

T 

D T D 

Steady climb

forces balanced 

constant speed 

Climb entry drag

greater than thrust

speed slowing 

Level flight

forces balanced 

constant speed 

L 

L 

L 

Figure 5-37. Changes in speed during climb entry. Figure 5-36. Changes in lift during climb entry. 

5-24 
 

 

is descending at the same power as used in straight-andlevel flight. 

As forward pressure is applied to the control yoke to initiate 

the descent, the AOA is decreased momentarily. Initially, 

the momentum of the aircraft causes the aircraft to briefly 

continue along the same flight path. For this instant, the AOA 

decreases causing the total lift to decrease. With weight now 

being greater than lift, the aircraft begins to descend. At the 

same time, the flight path goes from level to a descending 

flight path. Do not confuse a reduction in lift with the inability 

to generate sufficient lift to maintain level flight. The flight 

path is being manipulated with available thrust in reserve 

and with the elevator. 

To descend at the same airspeed as used in straight-andlevel flight, the power must be reduced as the descent is 

entered. Entering the descent, the component of weight 

acting forward along the flight path increases as the angle 

of descent increases and, conversely, when leveling off, the 

component of weight acting along the flight path decreases 

as the angle of descent decreases. 

Stalls 

An aircraft stall results from a rapid decrease in lift caused by 

the separation of airflow from the wing’s surface brought on 

by exceeding the critical AOA. A stall can occur at any pitch 

attitude or airspeed. Stalls are one of the most misunderstood 

areas of aerodynamics because pilots often believe an airfoil 

stops producing lift when it stalls. In a stall, the wing does 

not totally stop producing lift. Rather, it cannot generate 

adequate lift to sustain level flight. 

Since the CL increases with an increase in AOA, at some 

point the CL peaks and then begins to drop off. This peak is 

called the CL-MAX. The amount of lift the wing produces drops 

dramatically after exceeding the CL-MAX or critical AOA, but 

as stated above, it does not completely stop producing lift. 

In most straight-wing aircraft, the wing is designed to stall 

the wing root first. The wing root reaches its critical AOA 

first making the stall progress outward toward the wingtip. 

By having the wing root stall first, aileron effectiveness is 

maintained at the wingtips, maintaining controllability of 

the aircraft. Various design methods are used to achieve 

the stalling of the wing root first. In one design, the wing is 

“twisted” to a higher AOA at the wing root. Installing stall 

strips on the first 20–25 percent of the wing’s leading edge 

is another method to introduce a stall prematurely. 

The wing never completely stops producing lift in a stalled 

condition. If it did, the aircraft would fall to the Earth. Most 

training aircraft are designed for the nose of the aircraft to 

drop during a stall, reducing the AOA and “unstalling” the 

wing. The nose-down tendency is due to the CL being aft of 

the CG. The CG range is very important when it comes to 

stall recovery characteristics. If an aircraft is allowed to be 

operated outside of the CG range, the pilot may have difficulty 

recovering from a stall. The most critical CG violation would 

occur when operating with a CG that exceeds the rear limit. 

In this situation, a pilot may not be able to generate sufficient 

force with the elevator to counteract the excess weight aft of 

the CG. Without the ability to decrease the AOA, the aircraft 

continues in a stalled condition until it contacts the ground. 

The stalling speed of a particular aircraft is not a fixed value 

for all flight situations, but a given aircraft always stalls at 

the same AOA regardless of airspeed, weight, load factor, or 

density altitude. Each aircraft has a particular AOA where the 

airflow separates from the upper surface of the wing and the 

stall occurs. This critical AOA varies from approximately 16° 

to 20° depending on the aircraft’s design. But each aircraft 

has only one specific AOA where the stall occurs. 

There are three flight situations in which the critical AOA is 

most frequently exceeded: low speed, high speed, and turning. 

One way the aircraft can be stalled in straight-and-level flight 

by flying too slowly. As the airspeed decreases, the AOA 

must be increased to retain the lift required for maintaining 

altitude. The lower the airspeed becomes, the more the AOA 

must be increased. Eventually, an AOA is reached that results 

in the wing not producing enough lift to support the aircraft, 

which then starts settling. If the airspeed is reduced further, 

the aircraft stalls because the AOA has exceeded the critical 

angle and the airflow over the wing is disrupted. 

Low speed is not necessary to produce a stall. The wing 

can be brought into an excessive AOA at any speed. For 

example, an aircraft is in a dive with an airspeed of 100 

knots when the pilot pulls back sharply on the elevator 

control. [Figure 5-38] Gravity and centrifugal force prevent 

an immediate alteration of the flight path, but the aircraft’s 

AOA changes abruptly from quite low to very high. Since 

the flight path of the aircraft in relation to the oncoming air 

determines the direction of the relative wind, the AOA is 

suddenly increased, and the aircraft would reach the stalling 

angle at a speed much greater than the normal stall speed. 

The stalling speed of an aircraft is also higher in a level turn 

than in straight-and-level flight. [Figure 5-39] Centrifugal 

force is added to the aircraft’s weight and the wing must 

produce sufficient additional lift to counterbalance the load 

imposed by the combination of centrifugal force and weight. 

In a turn, the necessary additional lift is acquired by applying 

back pressure to the elevator control. This increases the wing’s 

5-25 
W

W

W

 

 

W 

CF 

L 

L 

CF 

CF 

L 

L CF 

Figure 5-38. Forces exerted when pulling out of a dive. 

AOA and results in increased lift. The AOA must increase 

as the bank angle increases to counteract the increasing load 

caused by centrifugal force. If at any time during a turn the 

AOA becomes excessive, the aircraft stalls. 

At this point, the action of the aircraft during a stall should be 

examined. To balance the aircraft aerodynamically, the CL 

is normally located aft of the CG. Although this makes the 

aircraft inherently nose-heavy, downwash on the horizontal 

stabilizer counteracts this condition. At the point of stall, 

when the upward force of the wing’s lift diminishes below 

that required for sustained flight and the downward tail 

force decreases to a point of ineffectiveness, or causes it to 

have an upward force, an unbalanced condition exists. This 

causes the aircraft to pitch down abruptly, rotating about its 

CG. During this nose-down attitude, the AOA decreases and 

the airspeed again increases. The smooth flow of air over 

the wing begins again, lift returns, and the aircraft begins 

to fly again. Considerable altitude may be lost before this 

cycle is complete. 

Airfoil shape and degradation of that shape must also be 

considered in a discussion of stalls. For example, if ice, snow, 

and frost are allowed to accumulate on the surface of an aircraft, 

the smooth airflow over the wing is disrupted. This causes the 

boundary layer to separate at an AOA lower than that of the 

critical angle. Lift is greatly reduced, altering expected aircraft 

performance. If ice is allowed to accumulate on the aircraft 

during flight, the weight of the aircraft is increased while the 

ability to generate lift is decreased. [Figure 5-40] As little as 

0.8 millimeter of ice on the upper wing surface increases drag 

and reduces aircraft lift by 25 percent. 

Pilots can encounter icing in any season, anywhere in the 

country, at altitudes of up to 18,000 feet and sometimes 

higher. Small aircraft, including commuter planes, are most 

vulnerable because they fly at lower altitudes where ice is more 

prevalent. They also lack mechanisms common on jet aircraft 

that prevent ice buildup by heating the front edges of wings. 

Icing can occur in clouds any time the temperature drops 

below freezing and super-cooled droplets build up on an 

aircraft and freeze. (Super-cooled droplets are still liquid 

even though the temperature is below 32 °Fahrenheit (F), 

or 0 °Celsius (C). 

Angle of Attack Indicators 

The FAA along with the General Aviation Joint Steering 

Committee (GAJSC) is promoting AOA indicators as one 

of the many safety initiatives aimed at reducing the general 

aviation accident rate. AOA indicators will specifically target 

Loss of Control (LOC) accidents. Loss of control is the 

number one root cause of fatalities in both general aviation 

and commercial aviation. More than 25 percent of general 

aviation fatal accidents occur during the maneuvering phase 

of flight. Of those accidents, half involve stall/spin scenarios. 

Technology such as AOA indicators can have a tremendous 

impact on reversing this trend and are increasingly affordable 

for general aviation airplanes. [Figure 5-41] 

100 

90 

80 

60 

40 

20 

0 

0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 

13 

12 

11 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

Percent increase in stall speed

Load factor or “G” 

Bank Angle 

Load factor 

Stall speed increase 

The purpose of an AOA indicator is to give the pilot better 

situation awareness pertaining to the aerodynamic health 

Figure 5-40. Inflight ice formation. Figure 5-39. Increase in stall speed and load factor. 

5-26 
 

 

of the airfoil. This can also be referred to as stall margin 

awareness. More simply explained, it is the margin that exists 

between the current AOA that the airfoil is operating at, and 

the AOA at which the airfoil will stall (critical AOA). 

Angle of attack is taught to student pilots as theory in ground 

training. When beginning flight training, students typically 

rely solely on airspeed and the published 1G stall speed to 

avoid stalls. This creates problems since this speed is only 

valid when the following conditions are met: 

• Unaccelerated flight (a 1G load factor) 

• Coordinated flight (inclinometer centered) 

• At one weight (typically maximum gross weight) 

Speed by itself is not a reliable parameter to avoid a stall. 

An airplane can stall at any speed. Angle of attack is a better 

parameter to use to avoid a stall. For a given configuration, 

the airplane always stalls at the same AOA, referred to as 

the critical AOA. This critical AOA does not change with: 

• Weight 

• Bank angle 

• Temperature 

• Density altitude 

• Center of gravity 

An AOA indicator can have several benefits when installed 

in general aviation aircraft, not the least of which is increased 

situational awareness. Without an AOA indicator, the AOA 

is “invisible” to pilots. These devices measure several 

parameters simultaneously and determine the current AOA 

providing a visual image to the pilot of the current AOA along 

with representations of the proximity to the critical AOA. 

[Figure 5-42] These devices can give a visual representation 

of the energy management state of the airplane. The energy 

state of an airplane is the balance between airspeed, altitude, 

drag, and thrust and represents how efficiently the airfoil is 

operating. The more efficiently the airfoil operates; the larger 

stall margin that is present. With this increased situational 

awareness pertaining to the energy condition of the airplane, 

pilots will have information that they need to aid in preventing 

a LOC scenario resulting from a stall/spin. Additionally, the 

less energy that is utilized to maintain flight means greater 

overall efficiency of the airplane, which is typically realized in 

fuel savings. This equates to a lower operating cost to the pilot. 

Just as training is required for any system on an aircraft, 

AOA indicators have training considerations also. A more 

comprehensive understanding of AOA in general should be 

the goal of this training along with the specific operating 

characteristics and limitations of the installed AOA indicator. 

Ground and flight instructors should make every attempt 

to receive training from an instructor knowledgeable about 

AOA indicators prior to giving instruction pertaining to or in 

airplanes equipped with AOA indicators. Pilot schools should 

incorporate training on AOA indicators in their syllabi, 

whether their training aircraft are equipped with them or not. 

Installation of AOA indicators not required by type 

certification in general aviation airplanes has recently been 

streamlined by the FAA. The FAA established policy in 

February 2014 pertaining to non-required AOA systems and 

how they may be installed as a minor alteration, depending 

upon their installation requirements and operational 

utilization, and the procedures to take for certification of 

these installations. For updated information, reference the 

FAA website at www.faa.gov. 

While AOA indicators provide a simple visual representation 

of the current AOA and its proximity to the critical AOA, they 

are not without their limitations. These limitations should 

be understood by operators of general aviation airplanes 

Figure 5-41. A variety of AOA indicators. 

5-27 
 

Coefficient of Lift Curve 

Direction of 

Alpha (angle of attack) 

CL 

Direction of 

Relative Wind Direction of 

Relative Wind 

Relative Wind 

2 

1 

3 

Calibration Set Points: 

Ground (Zero Set Point) 

Optimum Alpha Angle (OAA) (1.3 x Vs) 

Cruise Alpha (Va or Maneuvering Speed) 

1 

2 

3 

Direction of 

Relative Wind 

Figure 5-42. An AOA indicator has several benefits when installed in general aviation aircraft. 

equipped with these devices. Like advanced automation, 

such as autopilots and moving maps, the misunderstanding 

or misuse of the equipment can have disastrous results. Some 

items which may limit the effectiveness of an AOA indicator 

are listed below: 

• Calibration techniques 

• Probes or vanes not being heated 

• The type of indicator itself 

• Flap setting 

• Wing contamination 

Pilots of general aviation airplanes equipped with AOA 

indicators should contact the manufacturer for specific 

limitations applicable to that installation. 

Basic Propeller Principles 

The aircraft propeller consists of two or more blades and a 

central hub to which the blades are attached. Each blade of 

an aircraft propeller is essentially a rotating wing. As a result 

of their construction, the propeller blades are like airfoils 

and produce forces that create the thrust to pull, or push, 

the aircraft through the air. The engine furnishes the power 

needed to rotate the propeller blades through the air at high 

speeds, and the propeller transforms the rotary power of the 

engine into forward thrust. 

A cross-section of a typical propeller blade is shown in 

Figure 5-43. This section or blade element is an airfoil 

comparable to a cross-section of an aircraft wing. One 

surface of the blade is cambered or curved, similar to the 

upper surface of an aircraft wing, while the other surface is 

flat like the bottom surface of a wing. The chord line is an 

imaginary line drawn through the blade from its leading edge 

to its trailing edge. As in a wing, the leading edge is the thick 

edge of the blade that meets the air as the propeller rotates. 

Blade angle, usually measured in degrees, is the angle 

between the chord of the blade and the plane of rotation 

and is measured at a specific point along the length of the 

blade. [Figure 5-44] Because most propellers have a flat 

blade “face,” the chord line is often drawn along the face 

of the propeller blade. Pitch is not blade angle, but because 

pitch is largely determined by blade angle, the two terms are 

5-28 
 

Relative wind 

Chord line 

Thrust 

Forward velocity 

attac

A

k

ngle 

of 

Rotational veloc

Pit

ity

blad

c

e

h

a

o

ngle

r 

 

Figure 5-44. Propeller blade angle. 

Figure 5-43. Airfoil sections of propeller blade. 

often used interchangeably. An increase or decrease in one is 

usually associated with an increase or decrease in the other. 

The pitch of a propeller may be designated in inches. A 

propeller designated as a “74–48” would be 74 inches in 

length and have an effective pitch of 48 inches. The pitch 

is the distance in inches, which the propeller would screw 

through the air in one revolution if there were no slippage. 

When specifying a fixed-pitch propeller for a new type of 

aircraft, the manufacturer usually selects one with a pitch 

that operates efficiently at the expected cruising speed of the 

aircraft. Every fixed-pitch propeller must be a compromise 

because it can be efficient at only a given combination of 

airspeed and revolutions per minute (rpm). Pilots cannot 

change this combination in flight. 

When the aircraft is at rest on the ground with the engine 

operating, or moving slowly at the beginning of takeoff, 

the propeller efficiency is very low because the propeller is 

restrained from advancing with sufficient speed to permit 

its fixed-pitch blades to reach their full efficiency. In this 

situation, each propeller blade is turning through the air at 

an AOA that produces relatively little thrust for the amount 

of power required to turn it. 

To understand the action of a propeller, consider first its 

motion, which is both rotational and forward. As shown by 

the vectors of propeller forces in Figure 5-44, each section of 

a propeller blade moves downward and forward. The angle 

at which this air (relative wind) strikes the propeller blade 

is its AOA. The air deflection produced by this angle causes 

the dynamic pressure at the engine side of the propeller blade 

to be greater than atmospheric pressure, thus creating thrust. 

The shape of the blade also creates thrust because it is 

cambered like the airfoil shape of a wing. As the air flows 

past the propeller, the pressure on one side is less than that 

on the other. As in a wing, a reaction force is produced in the 

direction of the lesser pressure. The airflow over the wing 

has less pressure, and the force (lift) is upward. In the case 

of the propeller, which is mounted in a vertical instead of a 

horizontal plane, the area of decreased pressure is in front of 

the propeller, and the force (thrust) is in a forward direction. 

Aerodynamically, thrust is the result of the propeller shape 

and the AOA of the blade. 

Thrust can be considered also in terms of the mass of air 

handled by the propeller. In these terms, thrust equals mass 

of air handled multiplied by slipstream velocity minus 

velocity of the aircraft. The power expended in producing 

thrust depends on the rate of air mass movement. On average, 

thrust constitutes approximately 80 percent of the torque (total 

horsepower absorbed by the propeller). The other 20 percent 

is lost in friction and slippage. For any speed of rotation, 

the horsepower absorbed by the propeller balances the 

horsepower delivered by the engine. For any single revolution 

of the propeller, the amount of air handled depends on the 

blade angle, which determines how big a “bite” of air the 

propeller takes. Thus, the blade angle is an excellent means of 

adjusting the load on the propeller to control the engine rpm. 

The blade angle is also an excellent method of adjusting the 

AOA of the propeller. On constant-speed propellers, the blade 

angle must be adjusted to provide the most efficient AOA at 

all engine and aircraft speeds. Lift versus drag curves, which 

are drawn for propellers as well as wings, indicate that the 

most efficient AOA is small, varying from +2° to +4°. The 

actual blade angle necessary to maintain this small AOA 

varies with the forward speed of the aircraft. 

Fixed-pitch and ground-adjustable propellers are designed 

for best efficiency at one rotation and forward speed. They 

are designed for a given aircraft and engine combination. A 

propeller may be used that provides the maximum efficiency 

for takeoff, climb, cruise, or high-speed flight. Any change in 

these conditions results in lowering the efficiency of both the 

propeller and the engine. Since the efficiency of any machine 

is the ratio of the useful power output to the actual power 

input, propeller efficiency is the ratio of thrust horsepower 

to brake horsepower. Propeller efficiency varies from 50 to 

5-29 
87 percent, depending on how much the propeller “slips.” 

Propeller slip is the difference between the geometric pitch of 

the propeller and its effective pitch. [Figure 5-45] Geometric 

pitch is the theoretical distance a propeller should advance 

in one revolution; effective pitch is the distance it actually 

advances. Thus, geometric or theoretical pitch is based on 

no slippage, but actual or effective pitch includes propeller 

slippage in the air. 

The reason a propeller is “twisted” is that the outer parts of the 

propeller blades, like all things that turn about a central point, 

travel faster than the portions near the hub. [Figure 5-46] If the 

blades had the same geometric pitch throughout their lengths, 

portions near the hub could have negative AOAs while the 

propeller tips would be stalled at cruise speed. Twisting or 

variations in the geometric pitch of the blades permits the 

propeller to operate with a relatively constant AOA along its 

length when in cruising flight. Propeller blades are twisted 

to change the blade angle in proportion to the differences in 

speed of rotation along the length of the propeller, keeping 

thrust more nearly equalized along this length. 

Usually 1° to 4° provides the most efficient lift/drag ratio, 

but in flight the propeller AOA of a fixed-pitch propeller 

varies—normally from 0° to 15°. This variation is caused 

by changes in the relative airstream, which in turn results 

from changes in aircraft speed. Thus, propeller AOA is the 

product of two motions: propeller rotation about its axis and 

its forward motion. 

A constant-speed propeller automatically keeps the blade 

angle adjusted for maximum efficiency for most conditions 

encountered in flight. During takeoff, when maximum power 

and thrust are required, the constant-speed propeller is at a 

low propeller blade angle or pitch. The low blade angle keeps 

the AOA small and efficient with respect to the relative wind. 

At the same time, it allows the propeller to handle a smaller 

mass of air per revolution. This light load allows the engine to 

turn at high rpm and to convert the maximum amount of fuel 

into heat energy in a given time. The high rpm also creates 

maximum thrust because, although the mass of air handled 

per revolution is small, the rpm and slipstream velocity are 

Effective pitch 

Geometric pitch 

Slip 

Figure 5-45. Propeller slippage. 

60 in. 

40 in. 

20 in. 

Short travel distance—slow speed 

—129 kno s t

Moderate travel distance—moderate speed—259

knots 

Greater travel distance—very high speed—389 knots 

2,500 rpm 

2,500 rpm 

2,500 rpm 

Figure 5-46. Propeller tips travel faster than the hub. 

high, and with the low aircraft speed, there is maximum thrust. 

After liftoff, as the speed of the aircraft increases, the constantspeed propeller automatically changes to a higher angle (or 

pitch). Again, the higher blade angle keeps the AOA small 

and efficient with respect to the relative wind. The higher 

blade angle increases the mass of air handled per revolution. 

This decreases the engine rpm, reducing fuel consumption 

and engine wear, and keeps thrust at a maximum. 

After the takeoff climb is established in an aircraft having a 

controllable-pitch propeller, the pilot reduces the power output 

of the engine to climb power by first decreasing the manifold 

pressure and then increasing the blade angle to lower the rpm. 

At cruising altitude, when the aircraft is in level flight and 

less power is required than is used in takeoff or climb, the 

pilot again reduces engine power by reducing the manifold 

pressure and then increasing the blade angle to decrease the 

rpm. Again, this provides a torque requirement to match the 

reduced engine power. Although the mass of air handled per 

revolution is greater, it is more than offset by a decrease in 

slipstream velocity and an increase in airspeed. The AOA is 

still small because the blade angle has been increased with 

an increase in airspeed. 

Torque and P-Factor 

To the pilot, “torque” (the left turning tendency of the 

airplane) is made up of four elements that cause or produce 

a twisting or rotating motion around at least one of the 

airplane’s three axes. These four elements are: 

1. Torque reaction from engine and propeller 

5-30 
2. Corkscrewing effect of the slipstream

3. Gyroscopic action of the propeller

4. Asymmetric loading of the propeller (P-factor)

Torque Reaction 

Torque reaction involves Newton’s Third Law of Physics— 

for every action, there is an equal and opposite reaction. As 

applied to the aircraft, this means that as the internal engine 

parts and propeller are revolving in one direction, an equal 

force is trying to rotate the aircraft in the opposite direction. 

[Figure 5-47] 

When the aircraft is airborne, this force is acting around 

the longitudinal axis, tending to make the aircraft roll. To 

compensate for roll tendency, some of the older aircraft are 

rigged in a manner to create more lift on the wing that is being 

forced downward. The more modern aircraft are designed 

with the engine offset to counteract this effect of torque. 

NOTE: Most United States built aircraft engines rotate the 

propeller clockwise, as viewed from the pilot’s seat. The 

discussion here is with reference to those engines. 

Generally, the compensating factors are permanently set so 

that they compensate for this force at cruising speed, since 

most of the aircraft’s operating time is at that speed. However, 

aileron trim tabs permit further adjustment for other speeds. 

When the aircraft’s wheels are on the ground during the 

takeoff roll, an additional turning moment around the vertical 

axis is induced by torque reaction. As the left side of the 

aircraft is being forced down by torque reaction, more weight 

is being placed on the left main landing gear. This results in 

more ground friction, or drag, on the left tire than on the right, 

causing a further turning moment to the left. The magnitude 

of this moment is dependent on many variables. Some of 

these variables are: 

1. Size and horsepower of engine

2. Size of propeller and the rpm

3. Size of the aircraft

4. Condition of the ground surface

This yawing moment on the takeoff roll is corrected by the 

pilot’s proper use of the rudder or rudder trim. 

Corkscrew Effect 

The high-speed rotation of an aircraft propeller gives a 

corkscrew or spiraling rotation to the slipstream. At high 

propeller speeds and low forward speed (as in the takeoffs 

and approaches to power-on stalls), this spiraling rotation 

is very compact and exerts a strong sideward force on the 

aircraft’s vertical tail surface. [Figure 5-48] 

When this spiraling slipstream strikes the vertical fin, it 

causes a yawing moment about the aircraft’s vertical axis. 

The more compact the spiral, the more prominent this force 

is. As the forward speed increases, however, the spiral 

elongates and becomes less effective. The corkscrew 

flow of the slipstream also causes a rolling moment 

around the longitudinal axis. 

Note that this rolling moment caused by the corkscrew flow 

of the slipstream is to the right, while the yawing moment 

caused by torque reaction is to the left—in effect one may 

be counteracting the other. However, these forces vary 

greatly and it is the pilot’s responsibility to apply proper 

corrective action by use of the flight controls at all times. 

These forces must be counteracted regardless of which is 

the most prominent at the time. 

Gyroscopic Action 

Before the gyroscopic effects of the propeller can be 

understood, it is necessary to understand the basic principle 

of a gyroscope. All practical applications of the gyroscope 

are based upon two fundamental properties of gyroscopic 

action: rigidity in space and precession. The one of interest 

for this discussion is precession. 

Precession is the resultant action, or deflection, of a spinning 

rotor when a deflecting force is applied to its rim. As can be 

seen in Figure 5-49, when a force is applied, the resulting 

force takes effect 90° ahead of and in the direction of rotation. 

The rotating propeller of an airplane makes a very good 

Reaction 

Action 

Figure 5-47. Torque reaction. 

Yaw 

Force 

Slipstream 

Figure 5-48. Corkscrewing slipstream. 

5-31 
 

1. Intake 

Resultant force 90° Effective 

force 

Applied force 

Yaw 

Figure 5-49. Gyroscopic precession. 

gyroscope and thus has similar properties. Any time a force 

is applied to deflect the propeller out of its plane of rotation, 

the resulting force is 90° ahead of and in the direction of 

rotation and in the direction of application, causing a pitching 

moment, a yawing moment, or a combination of the two 

depending upon the point at which the force was applied. 

This element of torque effect has always been associated with 

and considered more prominent in tailwheel-type aircraft 

and most often occurs when the tail is being raised during 

the takeoff roll. [Figure 5-50] This change in pitch attitude 

has the same effect as applying a force to the top of the 

propeller’s plane of rotation. The resultant force acting 90° 

ahead causes a yawing moment to the left around the vertical 

axis. The magnitude of this moment depends on several 

variables, one of which is the abruptness with which the tail Applied force

is raised (amount of force applied). However, precession, 

or gyroscopic action, occurs when a force is applied to any 

point on the rim of the propeller’s plane of rotation; the 

resultant force will still be 90° from the point of application 

in the direction of rotation. Depending on where the force is 

applied, the airplane is caused to yaw left or right, to pitch 

up or down, or a combination of pitching and yawing. 

It can be said that, as a result of gyroscopic action, any yawing 

around the vertical axis results in a pitching moment, and any 

pitching around the lateral axis results in a yawing moment. 

To correct for the effect of gyroscopic action, it is necessary 

for the pilot to properly use elevator and rudder to prevent 

undesired pitching and yawing. 

Asymmetric Loading (P-Factor) 

When an aircraft is flying with a high AOA, the “bite” of 

the downward moving blade is greater than the “bite” of the 

upward moving blade. This moves the center of thrust to the 

right of the prop disc area, causing a yawing moment toward 

the left around the vertical axis. Proving this explanation is 

complex because it would be necessary to work wind vector 

problems on each blade while considering both the AOA of 

the aircraft and the AOA of each blade. 

This asymmetric loading is caused by the resultant velocity, 

which is generated by the combination of the velocity of the 

propeller blade in its plane of rotation and the velocity of the 

air passing horizontally through the propeller disc. With the 

aircraft being flown at positive AOAs, the right (viewed from 

the rear) or downswinging blade, is passing through an area of 

resultant velocity, which is greater than that affecting the left 

or upswinging blade. Since the propeller blade is an airfoil, 

increased velocity means increased lift. The downswinging 

blade has more lift and tends to pull (yaw) the aircraft’s nose 

to the left. 

When the aircraft is flying at a high AOA, the downward 

moving blade has a higher resultant velocity, creating more 

lift than the upward moving blade. [Figure 5-51] This might 

be easier to visualize if the propeller shaft was mounted 

perpendicular to the ground (like a helicopter). If there 

were no air movement at all, except that generated by the 

propeller itself, identical sections of each blade would have 

the same airspeed. With air moving horizontally across this 

vertically mounted propeller, the blade proceeding forward 

into the flow of air has a higher airspeed than the blade 

retreating with the airflow. Thus, the blade proceeding into 

the horizontal airflow is creating more lift, or thrust, moving 

the center of thrust toward that blade. Visualize rotating the 

vertically mounted propeller shaft to shallower angles relative 

to the moving air (as on an aircraft). This unbalanced thrust 

then becomes proportionately smaller and continues getting 

smaller until it reaches the value of zero when the propeller 

shaft is exactly horizontal in relation to the moving air. 

The effects of each of these four elements of torque vary 

in value with changes in flight situations. In one phase of 

flight, one of these elements may be more prominent than 

another. In another phase of flight, another element may be 

more prominent. The relationship of these values to each 

other varies with different aircraft depending on the airframe, 

engine, and propeller combinations, as well as other design 

features. To maintain positive control of the aircraft in all 

flight conditions, the pilot must apply the flight controls as 

necessary to compensate for these varying values. 

Resultant

force

Yaw 

Effective

force 

Figure 5-50. Raising tail produces gyroscopic precession. 

5-32 
 

Low angle of attack High angle of attack 

Load on 

upward moving

propeller blade 

Load on 

downward moving

propeller blade 

Load on 

downward moving

propeller blade 

Load on 

upward moving

propeller blade 

Figure 5-51. Asymmetrical loading of propeller (P-factor). 

Load Factors 

In aerodynamics, the maximum load factor (at given bank 

angle) is a proportion between lift and weight and has a 

trigonometric relationship. The load factor is measured in 

Gs (acceleration of gravity), a unit of force equal to the force 

exerted by gravity on a body at rest and indicates the force to 

which a body is subjected when it is accelerated. Any force 

applied to an aircraft to deflect its flight from a straight line 

produces a stress on its structure. The amount of this force 

is the load factor. While a course in aerodynamics is not a 

prerequisite for obtaining a pilot’s license, the competent 

pilot should have a solid understanding of the forces that act 

on the aircraft, the advantageous use of these forces, and the 

operating limitations of the aircraft being flown. 

For example, a load factor of 3 means the total load on an 

aircraft’s structure is three times its weight. Since load factors 

are expressed in terms of Gs, a load factor of 3 may be spoken 

of as 3 Gs, or a load factor of 4 as 4 Gs. 

If an aircraft is pulled up from a dive, subjecting the pilot to 

3 Gs, he or she would be pressed down into the seat with a 

force equal to three times his or her weight. Since modern 

aircraft operate at significantly higher speeds than older 

aircraft, increasing the potential for large load factors, this 

effect has become a primary consideration in the design of 

the structure of all aircraft. 

With the structural design of aircraft planned to withstand 

only a certain amount of overload, a knowledge of load 

factors has become essential for all pilots. Load factors are 

important for two reasons: 

1.	 It is possible for a pilot to impose a dangerous overload 

on the aircraft structures. 

2.	 An increased load factor increases the stalling speed and 

makes stalls possible at seemingly safe flight speeds. 

Load Factors in Aircraft Design 

The answer to the question “How strong should an aircraft 

be?” is determined largely by the use to which the aircraft is 

subjected. This is a difficult problem because the maximum 

possible loads are much too high for use in efficient design. 

It is true that any pilot can make a very hard landing or an 

extremely sharp pull up from a dive, which would result in 

abnormal loads. However, such extremely abnormal loads 

must be dismissed somewhat if aircraft are built that take off 

quickly, land slowly, and carry worthwhile payloads. 

The problem of load factors in aircraft design becomes how 

to determine the highest load factors that can be expected in 

normal operation under various operational situations. These 

load factors are called “limit load factors.” For reasons of 

safety, it is required that the aircraft be designed to withstand 

these load factors without any structural damage. Although 

the Code of Federal Regulations (CFR) requires the aircraft 

structure be capable of supporting one and one-half times 

these limit load factors without failure, it is accepted that 

parts of the aircraft may bend or twist under these loads and 

that some structural damage may occur. 

This 1.5 load limit factor is called the “factor of safety” and 

provides, to some extent, for loads higher than those expected 

under normal and reasonable operation. This strength reserve 

is not something that pilots should willfully abuse; rather, it is 

there for protection when encountering unexpected conditions. 

The above considerations apply to all loading conditions, 

whether they be due to gusts, maneuvers, or landings. The 

gust load factor requirements now in effect are substantially 

the same as those that have been in existence for years. 

Hundreds of thousands of operational hours have proven 

them adequate for safety. Since the pilot has little control over 

gust load factors (except to reduce the aircraft’s speed when 

rough air is encountered), the gust loading requirements are 

substantially the same for most general aviation type aircraft 

regardless of their operational use. Generally, the gust load 

factors control the design of aircraft which are intended for 

strictly nonacrobatic usage. 

An entirely different situation exists in aircraft design with 

maneuvering load factors. It is necessary to discuss this matter 

separately with respect to: (1) aircraft designed in accordance 

with the category system (i.e., normal, utility, acrobatic); and 

(2) older designs built according to requirements that did not 

provide for operational categories. 

Aircraft designed under the category system are readily 

identified by a placard in the flight deck, which states the 

operational category (or categories) in which the aircraft 

5-33 
 

 

is certificated. The maximum safe load factors (limit load 

factors) specified for aircraft in the various categories are: 

CATEGORY LIMIT LOAD FACTOR 

Normal1 3.8 to –1.52 

Utility (mild acrobatics, 4.4 to –1.76 

including spins) 

Acrobatic 6.0 to –3.00 

1 For aircraft with gross weight of more than 4,000 pounds, 

the limit load factor is reduced. To the limit loads given 

above, a safety factor of 50 percent is added. 

There is an upward graduation in load factor with the 

increasing severity of maneuvers. The category system 

provides for maximum utility of an aircraft. If normal 

operation alone is intended, the required load factor (and 

consequently the weight of the aircraft) is less than if the 

aircraft is to be employed in training or acrobatic maneuvers 

as they result in higher maneuvering loads. 

Aircraft that do not have the category placard are designs that 

were constructed under earlier engineering requirements in 

which no operational restrictions were specifically given to 

the pilots. For aircraft of this type (up to weights of about 

4,000 pounds), the required strength is comparable to presentday utility category aircraft, and the same types of operation 

are permissible. For aircraft of this type over 4,000 pounds, 

the load factors decrease with weight. These aircraft should 

be regarded as being comparable to the normal category 

aircraft designed under the category system, and they should 

be operated accordingly. 

Load Factors in Steep Turns 

At a constant altitude, during a coordinated turn in any 

aircraft, the load factor is the result of two forces: centrifugal 

force and weight. [Figure 5-52] For any given bank angle, 

the ROT varies with the airspeed—the higher the speed, the 

Load factor = 2 Gs 

Centrifugal 

force = 1.73 Gs 

Gravity = 1G 

60° 50° 40° 30° 20° 10° 

slower the ROT. This compensates for added centrifugal 

force, allowing the load factor to remain the same. 

Figure 5-53 reveals an important fact about turns—the load 

factor increases at a terrific rate after a bank has reached 

45° or 50°. The load factor for any aircraft in a coordinated 

level turn at 60° bank is 2 Gs. The load factor in an 80° bank 

is 5.76 Gs. The wing must produce lift equal to these load 

factors if altitude is to be maintained. 

It should be noted how rapidly the line denoting load factor 

rises as it approaches the 90° bank line, which it never quite 

reaches because a 90° banked, constant altitude turn is not 

mathematically possible. An aircraft may be banked to 90° 

in a coordinated turn if not trying to hold altitude. An aircraft 

that can be held in a 90° banked slipping turn is capable of 

straight knife-edged flight. At slightly more than 80°, the 

load factor exceeds the limit of 6 Gs, the limit load factor of 

an acrobatic aircraft. 

For a coordinated, constant altitude turn, the approximate 

maximum bank for the average general aviation aircraft is 60°. 

This bank and its resultant necessary power setting reach the 

limit of this type of aircraft. An additional 10° bank increases 

the load factor by approximately 1 G, bringing it close to the 

yield point established for these aircraft. [Figure 5-54] 

Load Factors and Stalling Speeds 

Any aircraft, within the limits of its structure, may be stalled 

at any airspeed. When a sufficiently high AOA is imposed, 

the smooth flow of air over an airfoil breaks up and separates, 

producing an abrupt change of flight characteristics and a 

sudden loss of lift, which results in a stall. 

A study of this effect has revealed that an aircraft’s stalling 

speed increases in proportion to the square root of the 

7 

6 

5 

4 

3 

2 

1 

0 

0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 

Load factor (G units)

 Bank angle 

Figure 5-52. Two forces cause load factor during turns. 

Figure 5-53. Angle of bank changes load factor in level flight. 

5-34 
Ratio of acceleration V to unaccelerated V s s 5 

4 

3 

2 

1 

0 

40 40

50 50

60 60

70 70

80 80

100 100

120 120

150 150

Unaccelerated stall speed

0 1 2 3 4 5 6 7 8 20 40 60 80 100 120 140 160 180 200 220 240 260 

“G” Load Accelerated stall speed 

 

load factor. This means that an aircraft with a normal 

unaccelerated stalling speed of 50 knots can be stalled at 100 

knots by inducing a load factor of 4 Gs. If it were possible 

for this aircraft to withstand a load factor of nine, it could 

be stalled at a speed of 150 knots. A pilot should be aware 

of the following: 

•	 The danger of inadvertently stalling the aircraft by 

increasing the load factor, as in a steep turn or spiral; 

•	 When intentionally stalling an aircraft above its 

design maneuvering speed, a tremendous load factor 

is imposed. 

Figures 5-53 and 5-54 show that banking an aircraft greater 

than 72° in a steep turn produces a load factor of 3, and the 

stalling speed is increased significantly. If this turn is made 

in an aircraft with a normal unaccelerated stalling speed of 

45 knots, the airspeed must be kept greater than 75 knots to 

prevent inducing a stall. A similar effect is experienced in a 

quick pull up or any maneuver producing load factors above 

1 G. This sudden, unexpected loss of control, particularly in 

a steep turn or abrupt application of the back elevator control 

near the ground, has caused many accidents. 

Since the load factor is squared as the stalling speed doubles, 

tremendous loads may be imposed on structures by stalling 

an aircraft at relatively high airspeeds. 

The following information primarily applies to fixed-wing 

airplanes. The maximum speed at which an airplane may 

be stalled safely is now determined for all new designs. 

This speed is called the “design maneuvering speed” (VA), 

which is the speed below which you can move a single 

flight control, one time, to its full deflection, for one axis 

of airplane rotation only (pitch, roll or yaw), in smooth 

air, without risk of damage to the airplane. VA must be 

entered in the FAA-approved Airplane Flight Manual/ 

Pilot’s Operating Handbook (AFM/POH) of all recently 

designed airplanes. For older general aviation airplanes, 

this speed is approximately 1.7 times the normal stalling 

speed. Thus, an older airplane that normally stalls at 60 

knots must never be stalled at above 102 knots (60 knots × 

1.7 = 102 knots). An airplane with a normal stalling speed 

of 60 knots stalled at 102 knots undergoes a load factor 

equal to the square of the increase in speed, or 2.89 Gs (1.7 

× 1.7 = 2.89 Gs). (The above figures are approximations to 

be considered as a guide, and are not the exact answers to 

any set of problems. The design maneuvering speed should 

be determined from the particular airplane’s operating 

limitations provided by the manufacturer.) Operating at or 

below design maneuvering speed does not provide structural 

protection against multiple full control inputs in one axis or 

full control inputs in more than one axis at the same time. 

Since the leverage in the control system varies with different 

aircraft (some types employ “balanced” control surfaces while 

others do not), the pressure exerted by the pilot on the controls 

cannot be accepted as an index of the load factors produced 

in different aircraft. In most cases, load factors can be judged 

by the experienced pilot from the feel of seat pressure. Load 

factors can also be measured by an instrument called an 

“accelerometer,” but this instrument is not common in general 

Figure 5-54. Load factor changes stall speed. 

5-35 
aviation training aircraft. The development of the ability to 

judge load factors from the feel of their effect on the body is 

important. A knowledge of these principles is essential to the 

development of the ability to estimate load factors. 

A thorough knowledge of load factors induced by varying 

degrees of bank and the VA aids in the prevention of two of 

the most serious types of accidents: 

1.	 Stalls from steep turns or excessive maneuvering near 

the ground 

2.	 Structural failures during acrobatics or other violent 

maneuvers resulting from loss of control 

Load Factors and Flight Maneuvers 

Critical load factors apply to all flight maneuvers except 

unaccelerated straight flight where a load factor of 1 G is 

always present. Certain maneuvers considered in this section 

are known to involve relatively high load factors. Full 

application of pitch, roll, or yaw controls should be confined 

to speeds below the maneuvering speed. Avoid rapid and 

large alternating control inputs, especially in combination 

with large changes in pitch, roll, or yaw (e.g., large sideslip 

angles) as they may result in structural failures at any speed, 

including below VA. 

Turns 

Increased load factors are a characteristic of all banked 

turns. As noted in the section on load factors in steep turns, 

load factors become significant to both flight performance 

and load on wing structure as the bank increases beyond 

approximately 45°. 

The yield factor of the average light plane is reached 

at a bank of approximately 70° to 75°, and the stalling 

speed is increased by approximately one-half at a bank of 

approximately 63°. 

Stalls 

The normal stall entered from straight-and-level flight, or an 

unaccelerated straight climb, does not produce added load 

factors beyond the 1 G of straight-and-level flight. As the 

stall occurs, however, this load factor may be reduced toward 

zero, the factor at which nothing seems to have weight. The 

pilot experiences a sensation of “floating free in space.” If 

recovery is effected by snapping the elevator control forward, 

negative load factors (or those that impose a down load on 

the wings and raise the pilot from the seat) may be produced. 

During the pull up following stall recovery, significant 

load factors are sometimes induced. These may be further 

increased inadvertently during excessive diving (and 

consequently high airspeed) and abrupt pull ups to level 

flight. One usually leads to the other, thus increasing the load 

factor. Abrupt pull ups at high diving speeds may impose 

critical loads on aircraft structures and may produce recurrent 

or secondary stalls by increasing the AOA to that of stalling. 

As a generalization, a recovery from a stall made by diving 

only to cruising or design maneuvering airspeed, with a 

gradual pull up as soon as the airspeed is safely above stalling, 

can be effected with a load factor not to exceed 2 or 2.5 Gs. A 

higher load factor should never be necessary unless recovery 

has been effected with the aircraft’s nose near or beyond the 

vertical attitude or at extremely low altitudes to avoid diving 

into the ground. 

Spins 

A stabilized spin is not different from a stall in any element 

other than rotation and the same load factor considerations 

apply to spin recovery as apply to stall recovery. Since spin 

recoveries are usually effected with the nose much lower than is 

common in stall recoveries, higher airspeeds and consequently 

higher load factors are to be expected. The load factor in a 

proper spin recovery usually is found to be about 2.5 Gs. 

The load factor during a spin varies with the spin characteristics 

of each aircraft, but is usually found to be slightly above the 

1 G of level flight. There are two reasons for this: 

1.	 Airspeed in a spin is very low, usually within 2 knots 

of the unaccelerated stalling speeds. 

2.	 An aircraft pivots, rather than turns, while it is in a spin. 

High Speed Stalls 

The average light plane is not built to withstand the repeated 

application of load factors common to high speed stalls. 

The load factor necessary for these maneuvers produces a 

stress on the wings and tail structure, which does not leave 

a reasonable margin of safety in most light aircraft. 

The only way this stall can be induced at an airspeed above 

normal stalling involves the imposition of an added load 

factor, which may be accomplished by a severe pull on the 

elevator control. A speed of 1.7 times stalling speed (about 

102 knots in a light aircraft with a stalling speed of 60 knots) 

produces a load factor of 3 Gs. Only a very narrow margin 

for error can be allowed for acrobatics in light aircraft. To 

illustrate how rapidly the load factor increases with airspeed, 

a high-speed stall at 112 knots in the same aircraft would 

produce a load factor of 4 Gs. 

Chandelles and Lazy Eights 

A chandelle is a maximum performance climbing turn 

beginning from approximately straight-and-level flight, 

and ending at the completion of a precise 180° turn in a 

wings-level, nose-high attitude at the minimum controllable 

5-36 
 

airspeed. In this flight maneuver, the aircraft is in a steep 

climbing turn and almost stalls to gain altitude while changing 

direction. A lazy eight derives its name from the manner in 

which the extended longitudinal axis of the aircraft is made 

to trace a flight pattern in the form of a figure “8” lying on 

its side. It would be difficult to make a definite statement 

concerning load factors in these maneuvers as both involve 

smooth, shallow dives and pull-ups. The load factors incurred 

depend directly on the speed of the dives and the abruptness 

of the pull-ups during these maneuvers. 

Generally, the better the maneuver is performed, the less 

extreme the load factor induced. A chandelle or lazy eight 

in which the pull-up produces a load factor greater than 2 Gs 

will not result in as great a gain in altitude; in low-powered 

aircraft, it may result in a net loss of altitude. 

The smoothest pull-up possible, with a moderate load factor, 

delivers the greatest gain in altitude in a chandelle and results 

in a better overall performance in both chandelles and lazy 

eights. The recommended entry speed for these maneuvers 

is generally near the manufacturer’s design maneuvering 

speed, which allows maximum development of load factors 

without exceeding the load limits. 

Rough Air 

All standard certificated aircraft are designed to withstand 

loads imposed by gusts of considerable intensity. Gust load 

factors increase with increasing airspeed, and the strength used 

for design purposes usually corresponds to the highest level 

flight speed. In extremely rough air, as in thunderstorms or 

frontal conditions, it is wise to reduce the speed to the design 

maneuvering speed. Regardless of the speed held, there may 

be gusts that can produce loads that exceed the load limits. 

Each specific aircraft is designed with a specific G loading 

that can be imposed on the aircraft without causing structural 

damage. There are two types of load factors factored into 

aircraft design: limit load and ultimate load. The limit load 

is a force applied to an aircraft that causes a bending of the 

aircraft structure that does not return to the original shape. 

The ultimate load is the load factor applied to the aircraft 

beyond the limit load and at which point the aircraft material 

experiences structural failure (breakage). Load factors lower 

than the limit load can be sustained without compromising 

the integrity of the aircraft structure. 

Speeds up to, but not exceeding, the maneuvering speed 

allow an aircraft to stall prior to experiencing an increase in 

load factor that would exceed the limit load of the aircraft. 

Most AFM/POH now include turbulent air penetration 

information, which help today’s pilots safely fly aircraft 

capable of a wide range of speeds and altitudes. It is important 

for the pilot to remember that the maximum “never-exceed” 

placard dive speeds are determined for smooth air only. High 

speed dives or acrobatics involving speed above the known 

maneuvering speed should never be practiced in rough or 

turbulent air. 

Vg Diagram 

The flight operating strength of an aircraft is presented 

on a graph whose vertical scale is based on load factor. 

[Figure 5-55] The diagram is called a Vg diagram—velocity 

versus G loads or load factor. Each aircraft has its own Vg 

diagram that is valid at a certain weight and altitude. 

The lines of maximum lift capability (curved lines) are the 

first items of importance on the Vg diagram. The aircraft in 

Figure 5-53 is capable of developing no more than +1 G at 

64 mph, the wing level stall speed of the aircraft. Since the 

maximum load factor varies with the square of the airspeed, 

the maximum positive lift capability of this aircraft is 2 G at 

92 mph, 3 G at 112 mph, 4.4 G at 137 mph, and so forth. Any 

load factor above this line is unavailable aerodynamically 

(i.e., the aircraft cannot fly above the line of maximum lift 

capability because it stalls). The same situation exists for 

negative lift flight with the exception that the speed necessary 

to produce a given negative load factor is higher than that to 

produce the same positive load factor. 

If the aircraft is flown at a positive load factor greater than the 

positive limit load factor of 4.4, structural damage is possible. 

When the aircraft is operated in this region, objectionable 

permanent deformation of the primary structure may take place 

and a high rate of fatigue damage is incurred. Operation above 

the limit load factor must be avoided in normal operation. 

There are two other points of importance on the Vg diagram. 

One point is the intersection of the positive limit load factor 

and the line of maximum positive lift capability. The airspeed 

at this point is the minimum airspeed at which the limit load 

can be developed aerodynamically. Any airspeed greater than 

this provides a positive lift capability sufficient to damage 

the aircraft. Conversely, any airspeed less than this does not 

provide positive lift capability sufficient to cause damage 

from excessive flight loads. The usual term given to this speed 

is “maneuvering speed,” since consideration of subsonic 

aerodynamics would predict minimum usable turn radius or 

maneuverability to occur at this condition. The maneuver 

speed is a valuable reference point, since an aircraft operating 

below this point cannot produce a damaging positive flight 

load. Any combination of maneuver and gust cannot create 

damage due to excess airload when the aircraft is below the 

maneuver speed. 

5-37 
 

0 

–1 

2 

–2 

1 

–3 

6 

5 

4 

7 

3 

20 40 60 80 100 120 140 160 180 200 220 240 

Load factor 

Indicated airspeed (mph) 

Structural damage 

Caution range 

Structural failure

Normal operating range

Accelerated stall 

Structural Damage 

Normal stall speed 

Maneuvering speed 

Level flight at 1 G 

Never exceed speed 

Figure 5-55. Typical Vg diagram. 

The other point of importance on the Vg diagram is the 

intersection of the negative limit load factor and line of 

maximum negative lift capability. Any airspeed greater than 

this provides a negative lift capability sufficient to damage 

the aircraft; any airspeed less than this does not provide 

negative lift capability sufficient to damage the aircraft from 

excessive flight loads. 

The limit airspeed (or redline speed) is a design reference point 

for the aircraft—this aircraft is limited to 225 mph. If flight 

is attempted beyond the limit airspeed, structural damage or 

structural failure may result from a variety of phenomena. 

The aircraft in flight is limited to a regime of airspeeds 

and Gs that do not exceed the limit (or redline) speed, do 

not exceed the limit load factor, and cannot exceed the 

maximum lift capability. The aircraft must be operated 

within this “envelope” to prevent structural damage and 

ensure the anticipated service lift of the aircraft is obtained. 

The pilot must appreciate the Vg diagram as describing the 

allowable combination of airspeeds and load factors for 

safe operation. Any maneuver, gust, or gust plus maneuver 

outside the structural envelope can cause structural damage 

and effectively shorten the service life of the aircraft. 

Rate of Turn 

The rate of turn (ROT) is the number of degrees (expressed in 

degrees per second) of heading change that an aircraft makes. 

The ROT can be determined by taking the constant of 1,091, 

multiplying it by the tangent of any bank angle and dividing 

that product by a given airspeed in knots as illustrated in 

Figure 5-55. If the airspeed is increased and the ROT desired 

is to be constant, the angle of bank must be increased, 

otherwise, the ROT decreases. Likewise, if the airspeed is 

held constant, an aircraft’s ROT increases if the bank angle 

is increased. The formula in Figures 5-56 through 5-58 

depicts the relationship between bank angle and airspeed as 

they affect the ROT. 

NOTE: All airspeed discussed in this section is true airspeed 

(TAS). 

Airspeed significantly effects an aircraft’s ROT. If airspeed is 

increased, the ROT is reduced if using the same angle of bank 

used at the lower speed. Therefore, if airspeed is increased 

as illustrated in Figure 5-57, it can be inferred that the angle 

of bank must be increased in order to achieve the same ROT 

achieved in Figure 5-58. 

5-38 
 

 

 

 

 1,091 x tangent of the bank angle 

airspeed (in knots) ROT =

 1,091 x tangent of 30° 

120 knots 

ROT =

 1,091 x 0.5773 (tangent of 30°) 

120 knots 

ROT = 

ROT = 5.25 degrees per second 

Example The rate of turn for an aircraft in a 

coordinated turn of 30° and traveling at 

120 knots would have a ROT as follows. 

1,091 x tangent of X 

240 knots ROT (5.25) = 

240 x 5.25 = 1,091 x tangent of X 

240 x 5.25 = tangent of X 1,091 

1.1549 = tangent of X 

49° = X 

Example Suppose we wanted to know what bank angle 

would give us a rate of turn of 5.25° per second 

at 240 knots. A slight rearrangement of the formula 

would indicate it will take a 49° angle of bank to 

achieve the same ROT used at the lower airspeed 

of 120 knots. 

Figure 5-56. Rate of turn for a given airspeed (knots, TAS) and 

bank angle.

What does this mean on a practicable side? If a given 

airspeed and bank angle produces a specific ROT, additional 

conclusions can be made. Knowing the ROT is a given number 

of degrees of change per second, the number of seconds it 

takes to travel 360° (a circle) can be determined by simple 

division. For example, if moving at 120 knots with a 30° bank 

angle, the ROT is 5.25° per second and it takes 68.6 seconds 

(360° divided by 5.25 = 68.6 seconds) to make a complete 

circle. Likewise, if flying at 240 knots TAS and using a 30° 

angle of bank, the ROT is only about 2.63° per second and it 

takes about 137 seconds to complete a 360° circle. Looking at 

the formula, any increase in airspeed is directly proportional 

to the time the aircraft takes to travel an arc. 

So why is this important to understand? Once the ROT is 

understood, a pilot can determine the distance required to 

make that particular turn, which is explained in radius of turn. 

Radius of Turn 

The radius of turn is directly linked to the ROT, which 

explained earlier is a function of both bank angle and 

airspeed. If the bank angle is held constant and the airspeed 

is increased, the radius of the turn changes (increases). A 

higher airspeed causes the aircraft to travel through a longer 

Figure 5-58. To achieve the same rate of turn of an aircraft traveling 

at 120 knots, an increase of bank angle is required. 

arc due to a greater speed. An aircraft traveling at 120 knots 

is able to turn a 360° circle in a tighter radius than an aircraft 

traveling at 240 knots. In order to compensate for the increase 

in airspeed, the bank angle would need to be increased. 

The radius of turn (R) can be computed using a simple 

formula. The radius of turn is equal to the velocity squared 

(V2) divided by 11.26 times the tangent of the bank angle. 

V2 

R = 11.26 × tangent of bank angle 

Using the examples provided in Figures 5-56 through 5-58, the 

turn radius for each of the two speeds can be computed. 

Note that if the speed is doubled, the radius is quadrupled. 

[Figures 5-59 and 5-60] 

Another way to determine the radius of turn is speed using 

feet per second (fps), π (3.1415), and the ROT. In one of the 

previous examples, it was determined that an aircraft with 

a ROT of 5.25 degrees per second required 68.6 seconds to 

make a complete circle. An aircraft’s speed (in knots) can 

1,091 x tangent of 30° 

240 knots 

ROT = 

ROT = 2.62 degrees per second 

An increase in speed causes a decrease in the 

ROT when using the same bank angle. 

Example Suppose we were to increase the speed to 240 

knots, what is the ROT? Using the same 

formula from above we see that: 

Figure 5-57. Rate of turn when increasing speed.

120 knots 

11.26 x tangent of bank angle 

R = 

1202 

11.26 x tangent of 30° 

R = 

V2 

R = 11.26 x 0.5773 

14,400 

R = 2,215 feet 

The radius of a turn required by an aircraft traveling at 120 knots 

and using a bank angle of 30° is 2,215 feet 

Figure 5-59. Radius at 120 knots with bank angle of 30°. 

5-39
 

 

 

240 knots 

11.26 x tangent of bank angle 

R = 

2402 

11.26 x tangent of 30° 

R = 

V2 

R = 11.26 x 0.57735

 57,600 

R = 8,861 feet

 (four times the radius at 120 knots) 

The radius of a turn required by an aircraft traveling at 240 knots 

using the same bank angle in Figure 4-51 is 8,861 feet. Speed 

is a major factor in a turn. 

Figure 5-60. Radius at 240 knots. 

be converted to fps by multiplying it by a constant of 1.69. 

Therefore, an aircraft traveling at 120 knots (TAS) travels 

at 202.8 fps. Knowing the speed in fps (202.8) multiplied by 

the time an aircraft takes to complete a circle (68.6 seconds) 

can determine the size of the circle; 202.8 times 68.6 equals 

13,912 feet. Dividing by π yields a diameter of 4,428 feet, 

which when divided by 2 equals a radius of 2,214 feet 

[Figure 5-61], a foot within that determined through use of 

the formula in Figure 5-59. 

In Figure 5-62, the pilot enters a canyon and decides to turn 

180° to exit. The pilot uses a 30° bank angle in his turn. 

Weight and Balance 

The aircraft’s weight and balance data is important 

information for a pilot that must be frequently reevaluated. 

Although the aircraft was weighed during the certification 

process, this information is not valid indefinitely. Equipment 

changes or modifications affect the weight and balance data. 

Too often pilots reduce the aircraft weight and balance into 

a rule of thumb, such as: “If I have three passengers, I can 

load only 100 gallons of fuel; four passengers, 70 gallons.” 

Weight and balance computations should be part of every 

preflight briefing. Never assume three passengers are always 

Figure 5-61. Another formula that can be used for radius. 

r = speed (fps) x 360 

ROT 

Pi (π) 

2 

202.8 x 68.6 

π

2 r = 

13,912 

π

2 r = 

4,428 

2 r = = 2,214 feet 

of equal weight. Instead, do a full computation of all items 

to be loaded on the aircraft, including baggage, as well as 

the pilot and passenger. It is recommended that all bags be 

weighed to make a precise computation of how the aircraft 

CG is positioned. 

The importance of the CG was stressed in the discussion 

of stability, controllability, and performance. Unequal load 

distribution causes accidents. A competent pilot understands 

and respects the effects of CG on an aircraft. 

Weight and balance are critical components in the utilization 

of an aircraft to its fullest potential. The pilot must know 

how much fuel can be loaded onto the aircraft without 

violating CG limits, as well as weight limits to conduct 

long or short flights with or without a full complement of 

allowable passengers. For example, an aircraft has four seats 

and can carry 60 gallons of fuel. How many passengers can 

the aircraft safely carry? Can all those seats be occupied at 

all times with the varying fuel loads? Four people who each 

weigh 150 pounds leads to a different weight and balance 

computation than four people who each weigh 200 pounds. 

The second scenario loads an additional 200 pounds onto the 

aircraft and is equal to about 30 gallons of fuel. 

The additional weight may or may not place the CG outside 

of the CG envelope, but the maximum gross weight could 

be exceeded. The excess weight can overstress the aircraft 

and degrade the performance. 

Aircraft are certificated for weight and balance for two 

principal reasons: 

1.	 The effect of the weight on the aircraft’s primary 

structure and its performance characteristics 

2.	 The effect of the location of this weight on flight 

characteristics, particularly in stall and spin recovery 

and stability 

Aircraft, such as balloons and weight-shift control, do not 

require weight and balance computations because the load 

is suspended below the lifting mechanism. The CG range 

in these types of aircraft is such that it is difficult to exceed 

loading limits. For example, the rear seat position and fuel 

of a weight-shift control aircraft are as close as possible to 

the hang point with the aircraft in a suspended attitude. Thus, 

load variations have little effect on the CG. This also holds 

true for the balloon basket or gondola. While it is difficult 

to exceed CG limits in these aircraft, pilots should never 

overload an aircraft because overloading causes structural 

damage and failures. Weight and balance computations are 

not required, but pilots should calculate weight and remain 

within the manufacturer’s established limit. 

5-40 
 

 

 

 

 

 

 

 

 

 

5,000 feet 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

2,215 feet

4,430 feet 

5 , 0 0 0 f e e t 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

3,014 feet

6,028 feet

 V2 

11.26 x tangent of the bank angle 30° 

R = 1202 

11.26 x 0.5773 

14,400 

6.50096 

R = = = 2,215 feet

 V2 

11.26 x tangent of the bank angle 30° 

R = 1402 

11.26 x 0.5773 

19,600 

6.50096 

R = = = 3,014 feet 

120 knots 

140 knots 

Figure 5-62. Two aircraft have flown into a canyon by error. The canyon is 5,000 feet across and has sheer cliffs on both sides. The pilot 

in the top image is flying at 120 knots. After realizing the error, the pilot banks hard and uses a 30° bank angle to reverse course. This 

aircraft requires about 4,000 feet to turn 180°, and makes it out of the canyon safely. The pilot in the bottom image is flying at 140 knots 

and also uses a 30° angle of bank in an attempt to reverse course. The aircraft, although flying just 20 knots faster than the aircraft in the 

top image, requires over 6,000 feet to reverse course to safety. Unfortunately, the canyon is only 5,000 feet across and the aircraft will hit 

the canyon wall. The point is that airspeed is the most influential factor in determining how much distance is required to turn. Many pilots 

have made the error of increasing the steepness of their bank angle when a simple reduction of speed would have been more appropriate. 

5-41 
 

 

 

Effect of Weight on Flight Performance 

The takeoff/climb and landing performance of an aircraft are 

determined on the basis of its maximum allowable takeoff and 

landing weights. A heavier gross weight results in a longer 

takeoff run and shallower climb, and a faster touchdown 

speed and longer landing roll. Even a minor overload may 

make it impossible for the aircraft to clear an obstacle that 

normally would not be a problem during takeoff under more 

favorable conditions. 

The detrimental effects of overloading on performance are 

not limited to the immediate hazards involved with takeoffs 

and landings. Overloading has an adverse effect on all 

climb and cruise performance, which leads to overheating 

during climbs, added wear on engine parts, increased fuel 

consumption, slower cruising speeds, and reduced range. 

The manufacturers of modern aircraft furnish weight and 

balance data with each aircraft produced. Generally, this 

information may be found in the FAA-approved AFM/POH 

and easy-to-read charts for determining weight and balance 

data are now provided. Increased performance and loadcarrying capability of these aircraft require strict adherence 

to the operating limitations prescribed by the manufacturer. 

Deviations from the recommendations can result in structural 

damage or complete failure of the aircraft’s structure. Even 

if an aircraft is loaded well within the maximum weight 

limitations, it is imperative that weight distribution be 

within the limits of CG location. The preceding brief study 

of aerodynamics and load factors points out the reasons for 

this precaution. The following discussion is background 

information into some of the reasons why weight and balance 

conditions are important to the safe flight of an aircraft. 

In some aircraft, it is not possible to fill all seats, baggage 

compartments, and fuel tanks, and still remain within 

approved weight or balance limits. For example, in several 

popular four-place aircraft, the fuel tanks may not be filled to 

capacity when four occupants and their baggage are carried. 

In a certain two-place aircraft, no baggage may be carried 

in the compartment aft of the seats when spins are to be 

practiced. It is important for a pilot to be aware of the weight 

and balance limitations of the aircraft being flown and the 

reasons for these limitations. 

Effect of Weight on Aircraft Structure 

The effect of additional weight on the wing structure of an 

aircraft is not readily apparent. Airworthiness requirements 

prescribe that the structure of an aircraft certificated in the 

normal category (in which acrobatics are prohibited) must 

be strong enough to withstand a load factor of 3.8 Gs to take 

care of dynamic loads caused by maneuvering and gusts. This 

means that the primary structure of the aircraft can withstand 

a load of 3.8 times the approved gross weight of the aircraft 

without structural failure occurring. If this is accepted as 

indicative of the load factors that may be imposed during 

operations for which the aircraft is intended, a 100-pound 

overload imposes a potential structural overload of 380 

pounds. The same consideration is even more impressive 

in the case of utility and acrobatic category aircraft, which 

have load factor requirements of 4.4 and 6.0, respectively. 

Structural failures that result from overloading may be 

dramatic and catastrophic, but more often they affect 

structural components progressively in a manner that 

is difficult to detect and expensive to repair. Habitual 

overloading tends to cause cumulative stress and damage 

that may not be detected during preflight inspections and 

result in structural failure later during completely normal 

operations. The additional stress placed on structural parts 

by overloading is believed to accelerate the occurrence of 

metallic fatigue failures. 

A knowledge of load factors imposed by flight maneuvers 

and gusts emphasizes the consequences of an increase in the 

gross weight of an aircraft. The structure of an aircraft about to 

undergo a load factor of 3 Gs, as in recovery from a steep dive, 

must be prepared to withstand an added load of 300 pounds 

for each 100-pound increase in weight. It should be noted that 

this would be imposed by the addition of about 16 gallons 

of unneeded fuel in a particular aircraft. FAA-certificated 

civil aircraft have been analyzed structurally and tested for 

flight at the maximum gross weight authorized and within the 

speeds posted for the type of flights to be performed. Flights at 

weights in excess of this amount are quite possible and often 

are well within the performance capabilities of an aircraft. 

This fact should not mislead the pilot, as the pilot may not 

realize that loads for which the aircraft was not designed are 

being imposed on all or some part of the structure. 

In loading an aircraft with either passengers or cargo, the 

structure must be considered. Seats, baggage compartments, 

and cabin floors are designed for a certain load or 

concentration of load and no more. For example, a light 

plane baggage compartment may be placarded for 20 pounds 

because of the limited strength of its supporting structure 

even though the aircraft may not be overloaded or out of CG 

limits with more weight at that location. 

Effect of Weight on Stability and Controllability 

Overloading also affects stability. An aircraft that is stable 

and controllable when loaded normally may have very 

different flight characteristics when overloaded. Although 

the distribution of weight has the most direct effect on this, 

an increase in the aircraft’s gross weight may be expected 

to have an adverse effect on stability, regardless of location 

5-42 
 

of the CG. The stability of many certificated aircraft is 

completely unsatisfactory if the gross weight is exceeded. 

Effect of Load Distribution 

The effect of the position of the CG on the load imposed 

on an aircraft’s wing in flight is significant to climb and 

cruising performance. An aircraft with forward loading is 

“heavier” and consequently, slower than the same aircraft 

with the CG further aft. 

Figure 5-63 illustrates why this is true. With forward loading, 

“nose-up” trim is required in most aircraft to maintain level 

cruising flight. Nose-up trim involves setting the tail surfaces 

to produce a greater down load on the aft portion of the 

fuselage, which adds to the wing loading and the total lift 

required from the wing if altitude is to be maintained. This 

requires a higher AOA of the wing, which results in more 

drag and, in turn, produces a higher stalling speed. 

With aft loading and “nose-down” trim, the tail surfaces 

exert less down load, relieving the wing of that much wing 

loading and lift required to maintain altitude. The required 

AOA of the wing is less, so the drag is less, allowing for a 

faster cruise speed. Theoretically, a neutral load on the tail 

surfaces in cruising flight would produce the most efficient 

overall performance and fastest cruising speed, but it would 

also result in instability. Modern aircraft are designed to 

require a down load on the tail for stability and controllability. 

A zero indication on the trim tab control is not necessarily 

the same as “neutral trim” because of the force exerted by 

downwash from the wings and the fuselage on the tail surfaces. 

The effects of the distribution of the aircraft’s useful load 

have a significant influence on its flight characteristics, even 

when the load is within the CG limits and the maximum 

Down load on tail

Stronger 

CG 

Down load on tail

Lighter 

CG 

Forward CG Center of lift

AFT CG 

Load imposed by tail 

Gross weight 

Load imposed by tail 

Gross weight 

Figure 5-63. Effect of load distribution on balance. 

permissible gross weight. Important among these effects 

are changes in controllability, stability, and the actual load 

imposed on the wing. 

Generally, an aircraft becomes less controllable, especially 

at slow flight speeds, as the CG is moved further aft. An 

aircraft that cleanly recovers from a prolonged spin with 

the CG at one position may fail completely to respond to 

normal recovery attempts when the CG is moved aft by one 

or two inches. 

It is common practice for aircraft designers to establish 

an aft CG limit that is within one inch of the maximum, 

which allows normal recovery from a one-turn spin. When 

certificating an aircraft in the utility category to permit 

intentional spins, the aft CG limit is usually established 

at a point several inches forward of that permissible for 

certification in the normal category. 

Another factor affecting controllability, which has become 

more important in current designs of large aircraft, is the 

effect of long moment arms to the positions of heavy 

equipment and cargo. The same aircraft may be loaded to 

maximum gross weight within its CG limits by concentrating 

fuel, passengers, and cargo near the design CG, or by 

dispersing fuel and cargo loads in wingtip tanks and cargo 

bins forward and aft of the cabin. 

With the same total weight and CG, maneuvering the 

aircraft or maintaining level flight in turbulent air requires 

the application of greater control forces when the load is 

dispersed. The longer moment arms to the positions of the 

heavy fuel and cargo loads must be overcome by the action 

of the control surfaces. An aircraft with full outboard wing 

tanks or tip tanks tends to be sluggish in roll when control 

situations are marginal, while one with full nose and aft cargo 

bins tends to be less responsive to the elevator controls. 

The rearward CG limit of an aircraft is determined largely 

by considerations of stability. The original airworthiness 

requirements for a type certificate specify that an aircraft in 

flight at a certain speed dampens out vertical displacement of 

the nose within a certain number of oscillations. An aircraft 

loaded too far rearward may not do this. Instead, when the 

nose is momentarily pulled up, it may alternately climb and 

dive becoming steeper with each oscillation. This instability 

is not only uncomfortable to occupants, but it could even 

become dangerous by making the aircraft unmanageable 

under certain conditions. 

The recovery from a stall in any aircraft becomes progressively 

more difficult as its CG moves aft. This is particularly 

important in spin recovery, as there is a point in rearward 

5-43 
 

 

loading of any aircraft at which a “flat” spin develops. A 

flat spin is one in which centrifugal force, acting through a 

CG located well to the rear, pulls the tail of the aircraft out 

away from the axis of the spin, making it impossible to get 

the nose down and recover. 

An aircraft loaded to the rear limit of its permissible CG 

range handles differently in turns and stall maneuvers and 

has different landing characteristics than when it is loaded 

near the forward limit. 

The forward CG limit is determined by a number of 

considerations. As a safety measure, it is required that the 

trimming device, whether tab or adjustable stabilizer, be 

capable of holding the aircraft in a normal glide with the power 

off. A conventional aircraft must be capable of a full stall, 

power-off landing in order to ensure minimum landing speed 

in emergencies. A tailwheel-type aircraft loaded excessively 

nose-heavy is difficult to taxi, particularly in high winds. It 

can be nosed over easily by use of the brakes, and it is difficult 

to land without bouncing since it tends to pitch down on the 

wheels as it is slowed down and flared for landing. Steering 

difficulties on the ground may occur in nosewheel-type 

aircraft, particularly during the landing roll and takeoff. The 

effects of load distribution are summarized as follows: 

•	 The CG position influences the lift and AOA of the 

wing, the amount and direction of force on the tail, 

and the degree of deflection of the stabilizer needed 

to supply the proper tail force for equilibrium. The 

latter is very important because of its relationship to 

elevator control force. 

•	 The aircraft stalls at a higher speed with a forward CG 

location. This is because the stalling AOA is reached 

at a higher speed due to increased wing loading. 

•	 Higher elevator control forces normally exist with a 

forward CG location due to the increased stabilizer 

deflection required to balance the aircraft. 

•	 The aircraft cruises faster with an aft CG location 

because of reduced drag. The drag is reduced because 

a smaller AOA and less downward deflection of the 

stabilizer are required to support the aircraft and 

overcome the nose-down pitching tendency. 

•	 The aircraft becomes less stable as the CG is moved 

rearward. This is because when the CG is moved 

rearward, it causes a decrease in the AOA. Therefore, 

the wing contribution to the aircraft’s stability is 

now decreased, while the tail contribution is still 

stabilizing. When the point is reached that the wing 

and tail contributions balance, then neutral stability 

exists. Any CG movement further aft results in an 

unstable aircraft. 

•	 A forward CG location increases the need for greater 

back elevator pressure. The elevator may no longer 

be able to oppose any increase in nose-down pitching. 

Adequate elevator control is needed to control the 

aircraft throughout the airspeed range down to the stall. 

A detailed discussion and additional information relating 

to weight and balance can be found in Chapter 10, Weight 

and Balance. 

High Speed Flight 

Subsonic Versus Supersonic Flow 

In subsonic aerodynamics, the theory of lift is based upon the 

forces generated on a body and a moving gas (air) in which 

it is immersed. At speeds of approximately 260 knots or 

less, air can be considered incompressible in that, at a fixed 

altitude, its density remains nearly constant while its pressure 

varies. Under this assumption, air acts the same as water and 

is classified as a fluid. Subsonic aerodynamic theory also 

assumes the effects of viscosity (the property of a fluid that 

tends to prevent motion of one part of the fluid with respect 

to another) are negligible and classifies air as an ideal fluid 

conforming to the principles of ideal-fluid aerodynamics such 

as continuity, Bernoulli’s principle, and circulation. 

In reality, air is compressible and viscous. While the effects of 

these properties are negligible at low speeds, compressibility 

effects in particular become increasingly important as speed 

increases. Compressibility (and to a lesser extent viscosity) is 

of paramount importance at speeds approaching the speed of 

sound. In these speed ranges, compressibility causes a change 

in the density of the air around an aircraft. 

During flight, a wing produces lift by accelerating the airflow 

over the upper surface. This accelerated air can, and does, 

reach sonic speeds even though the aircraft itself may be flying 

subsonic. At some extreme AOAs, in some aircraft, the speed 

of the air over the top surface of the wing may be double the 

aircraft’s speed. It is therefore entirely possible to have both 

supersonic and subsonic airflow on an aircraft at the same time. 

When flow velocities reach sonic speeds at some location on 

an aircraft (such as the area of maximum camber on the wing), 

further acceleration results in the onset of compressibility 

effects, such as shock wave formation, drag increase, buffeting, 

stability, and control difficulties. Subsonic flow principles are 

invalid at all speeds above this point. [Figure 5-64] 

Speed Ranges 

The speed of sound varies with temperature. Under standard 

temperature conditions of 15 °C, the speed of sound at sea 

level is 661 knots. At 40,000 feet, where the temperature is 

–55 °C, the speed of sound decreases to 574 knots. In high5-44 
 

Possible separation 

M = 0.50 

M = 0.72 

M = 0.77 

Maximum local velocity is less than sonic 

Critical mach number 

Maximum local velocity equal to sonic 

Normal shock wave

Supersonic 

flow 

Subsonic 

Figure 5-64. Wing airflow. 

speed flight and/or high-altitude flight, the measurement of 

speed is expressed in terms of a “Mach number”—the ratio 

of the true airspeed of the aircraft to the speed of sound in 

the same atmospheric conditions. An aircraft traveling at 

the speed of sound is traveling at Mach 1.0. Aircraft speed 

regimes are defined approximately as follows: 

Subsonic—Mach numbers below 0.75 

Transonic—Mach numbers from 0.75 to 1.20 

Supersonic—Mach numbers from 1.20 to 5.00 

Hypersonic—Mach numbers above 5.00 

While flights in the transonic and supersonic ranges are 

common occurrences for military aircraft, civilian jet aircraft 

normally operate in a cruise speed range of Mach 0.7 to 

Mach 0.90. 

The speed of an aircraft in which airflow over any part of 

the aircraft or structure under consideration first reaches 

(but does not exceed) Mach 1.0 is termed “critical Mach 

number” or “Mach Crit.” Thus, critical Mach number is 

the boundary between subsonic and transonic flight and is 

largely dependent on the wing and airfoil design. Critical 

Mach number is an important point in transonic flight. When 

shock waves form on the aircraft, airflow separation followed 

by buffet and aircraft control difficulties can occur. Shock 

waves, buffet, and airflow separation take place above critical 

Mach number. A jet aircraft typically is most efficient when 

cruising at or near its critical Mach number. At speeds 5–10 

percent above the critical Mach number, compressibility 

effects begin. Drag begins to rise sharply. Associated with 

the “drag rise” are buffet, trim, and stability changes and a 

decrease in control surface effectiveness. This is the point 

of “drag divergence.” [Figure 5-65] 

VMO/MMO is defined as the maximum operating limit speed. 

VMO is expressed in knots calibrated airspeed (KCAS), while 

MMO is expressed in Mach number. The VMO limit is usually 

associated with operations at lower altitudes and deals with 

structural loads and flutter. The MMO limit is associated with 

operations at higher altitudes and is usually more concerned 

with compressibility effects and flutter. At lower altitudes, 

structural loads and flutter are of concern; at higher altitudes, 

compressibility effects and flutter are of concern. 

Adherence to these speeds prevents structural problems due 

to dynamic pressure or flutter, degradation in aircraft control 

response due to compressibility effects (e.g., Mach Tuck, 

aileron reversal, or buzz), and separated airflow due to shock 

waves resulting in loss of lift or vibration and buffet. Any of 

these phenomena could prevent the pilot from being able to 

adequately control the aircraft. 

For example, an early civilian jet aircraft had a VMO limit of 

306 KCAS up to approximately FL 310 (on a standard day). 

At this altitude (FL 310), an MMO of 0.82 was approximately 

equal to 306 KCAS. Above this altitude, an MMO of 0.82 

always equaled a KCAS less than 306 KCAS and, thus, 

became the operating limit as you could not reach the VMO 

limit without first reaching the MMO limit. For example, at 

FL 380, an MMO of 0.82 is equal to 261 KCAS. 

Mach Number Versus Airspeed 

It is important to understand how airspeed varies with Mach 

number. As an example, consider how the stall speed of a 

jet transport aircraft varies with an increase in altitude. The 

increase in altitude results in a corresponding drop in air 

density and outside temperature. Suppose this jet transport 

is in the clean configuration (gear and flaps up) and weighs 

550,000 pounds. The aircraft might stall at approximately 152 

KCAS at sea level. This is equal to (on a standard day) a true 

velocity of 152 KTAS and a Mach number of 0.23. At FL 380, 

the aircraft will still stall at approximately 152 KCAS, but the 

true velocity is about 287 KTAS with a Mach number of 0.50. C D (Drag coefficient)

 M (Mach number) 

0.5 1.0 

CL= 0.3 

Force divergence Mach number 

Critical Mach number 

Figure 5-65. Critical Mach. 

5-45 
 

 

Although the stalling speed has remained the same for our 

purposes, both the Mach number and TAS have increased. 

With increasing altitude, the air density has decreased; this 

requires a faster true airspeed in order to have the same 

pressure sensed by the pitot tube for the same KCAS, or KIAS 

(for our purposes, KCAS and KIAS are relatively close to 

each other). The dynamic pressure the wing experiences at 

FL 380 at 287 KTAS is the same as at sea level at 152 KTAS. 

However, it is flying at higher Mach number. 

Another factor to consider is the speed of sound. A decrease 

in temperature in a gas results in a decrease in the speed of 

sound. Thus, as the aircraft climbs in altitude with outside 

temperature dropping, the speed of sound is dropping. At 

sea level, the speed of sound is approximately 661 KCAS, 

while at FL 380 it is 574 KCAS. Thus, for our jet transport 

aircraft, the stall speed (in KTAS) has gone from 152 at sea 

level to 287 at FL 380. Simultaneously, the speed of sound 

(in KCAS) has decreased from 661 to 574 and the Mach 

number has increased from 0.23 (152 KTAS divided by 661 

KTAS) to 0.50 (287 KTAS divided by 574 KTAS). All the 

while, the KCAS for stall has remained constant at 152. This 

describes what happens when the aircraft is at a constant 

KCAS with increasing altitude, but what happens when the 

pilot keeps Mach constant during the climb? In normal jet 

flight operations, the climb is at 250 KIAS (or higher (e.g. 

heavy)) to 10,000 feet and then at a specified en route climb 

airspeed (about 330 if a DC10) until reaching an altitude in 

the “mid-twenties” where the pilot then climbs at a constant 

Mach number to cruise altitude. 

Assuming for illustration purposes that the pilot climbs at a 

MMO of 0.82 from sea level up to FL 380. KCAS goes from 

543 to 261. The KIAS at each altitude would follow the 

same behavior and just differ by a few knots. Recall from 

the earlier discussion that the speed of sound is decreasing 

with the drop in temperature as the aircraft climbs. The Mach 

number is simply the ratio of the true airspeed to the speed 

of sound at flight conditions. The significance of this is that 

at a constant Mach number climb, the KCAS (and KTAS or 

KIAS as well) is falling off. 

If the aircraft climbed high enough at this constant MMO 

with decreasing KIAS, KCAS, and KTAS, it would begin to 

approach its stall speed. At some point, the stall speed of the 

aircraft in Mach number could equal the MMO of the aircraft, 

and the pilot could neither slow down (without stalling) nor 

speed up (without exceeding the max operating speed of the 

aircraft). This has been dubbed the “coffin corner.” 

Boundary Layer 

The viscous nature of airflow reduces the local velocities on 

a surface and is responsible for skin friction. As discussed 

earlier in the chapter, the layer of air over the wing’s surface 

that is slowed down or stopped by viscosity is the boundary 

layer. There are two different types of boundary layer flow: 

laminar and turbulent. 

Laminar Boundary Layer Flow 

The laminar boundary layer is a very smooth flow, while 

the turbulent boundary layer contains swirls or eddies. 

The laminar flow creates less skin friction drag than the 

turbulent flow but is less stable. Boundary layer flow over a 

wing surface begins as a smooth laminar flow. As the flow 

continues back from the leading edge, the laminar boundary 

layer increases in thickness. 

Turbulent Boundary Layer Flow 

At some distance back from the leading edge, the smooth 

laminar flow breaks down and transitions to a turbulent flow. 

From a drag standpoint, it is advisable to have the transition 

from laminar to turbulent flow as far aft on the wing as 

possible or have a large amount of the wing surface within 

the laminar portion of the boundary layer. The low energy 

laminar flow, however, tends to break down more suddenly 

than the turbulent layer. 

Boundary Layer Separation 

Another phenomenon associated with viscous flow is 

separation. Separation occurs when the airflow breaks away 

from an airfoil. The natural progression is from laminar 

boundary layer to turbulent boundary layer and then to 

airflow separation. Airflow separation produces high drag 

and ultimately destroys lift. The boundary layer separation 

point moves forward on the wing as the AOA is increased. 

[Figure 5-66] 

Vortex generators are used to delay or prevent shock wave 

induced boundary layer separation encountered in transonic 

flight. They are small low aspect ratio airfoils placed at a 12° 

to 15° AOA to the airstream. Usually spaced a few inches 

apart along the wing ahead of the ailerons or other control 

surfaces, vortex generators create a vortex that mixes the 

boundary airflow with the high energy airflow just above the 

surface. This produces higher surface velocities and increases 

the energy of the boundary layer. Thus, a stronger shock wave 

is necessary to produce airflow separation. 

Shock Waves 

When an airplane flies at subsonic speeds, the air ahead is 

“warned” of the airplane’s coming by a pressure change 

transmitted ahead of the airplane at the speed of sound. 

Because of this warning, the air begins to move aside before 

the airplane arrives and is prepared to let it pass easily. When 

the airplane’s speed reaches the speed of sound, the pressure 

5-46 
Transition region 

Laminar sublayer 

Laminar boundary layer 

Turbulent boundary layer 

Figure 5-66. Boundary layer. 

change can no longer warn the air ahead because the airplane 

is keeping up with its own pressure waves. Rather, the air 

particles pile up in front of the airplane causing a sharp 

decrease in the flow velocity directly in front of the airplane 

with a corresponding increase in air pressure and density. 

As the airplane’s speed increases beyond the speed of sound, 

the pressure and density of the compressed air ahead of it 

increase, the area of compression extending some distance 

ahead of the airplane. At some point in the airstream, the air 

particles are completely undisturbed, having had no advanced 

warning of the airplane’s approach, and in the next instant the 

same air particles are forced to undergo sudden and drastic 

changes in temperature, pressure, density, and velocity. 

The boundary between the undisturbed air and the region 

of compressed air is called a shock or “compression” wave. 

This same type of wave is formed whenever a supersonic 

airstream is slowed to subsonic without a change in direction, 

such as when the airstream is accelerated to sonic speed 

over the cambered portion of a wing, and then decelerated 

to subsonic speed as the area of maximum camber is passed. 

A shock wave forms as a boundary between the supersonic 

and subsonic ranges. 

Whenever a shock wave forms perpendicular to the airflow, it 

is termed a “normal” shock wave, and the flow immediately 

behind the wave is subsonic. A supersonic airstream passing 

through a normal shock wave experiences these changes: 

•	 The airstream is slowed to subsonic. 

•	 The airflow immediately behind the shock wave does 

not change direction. 

•	 The static pressure and density of the airstream behind 

the wave is greatly increased. 

•	 The energy of the airstream (indicated by total

pressure—dynamic plus static) is greatly reduced. 

Shock wave formation causes an increase in drag. One of 

the principal effects of a shock wave is the formation of a 

dense high pressure region immediately behind the wave. 

The instability of the high pressure region, and the fact that 

part of the velocity energy of the airstream is converted to 

heat as it flows through the wave, is a contributing factor 

in the drag increase, but the drag resulting from airflow 

separation is much greater. If the shock wave is strong, 

the boundary layer may not have sufficient kinetic energy 

to withstand airflow separation. The drag incurred in the 

transonic region due to shock wave formation and airflow 

separation is known as “wave drag.” When speed exceeds 

the critical Mach number by about 10 percent, wave drag 

increases sharply. A considerable increase in thrust (power) 

is required to increase flight speed beyond this point into the 

supersonic range where, depending on the airfoil shape and 

the AOA, the boundary layer may reattach. 

Normal shock waves form on the wing’s upper surface and 

form an additional area of supersonic flow and a normal shock 

wave on the lower surface. As flight speed approaches the 

speed of sound, the areas of supersonic flow enlarge and the 

shock waves move nearer the trailing edge. [Figure 5-67] 

M = 0.82 

M = 0.95 

M = 1.05 

Normal shock wave 

Supersonic flow 

Normal shock wave 

Supersonic flow 

Subsonic airflow 

Bow wave 

Figure 5-67. Shock waves. 

5-47 
 

 

Associated with “drag rise” are buffet (known as Mach 

buffet), trim, and stability changes and a decrease in control 

force effectiveness. The loss of lift due to airflow separation 

results in a loss of downwash and a change in the position of 

the center pressure on the wing. Airflow separation produces 

a turbulent wake behind the wing, which causes the tail 

surfaces to buffet (vibrate). The nose-up and nose-down pitch 

control provided by the horizontal tail is dependent on the 

downwash behind the wing. Thus, an increase in downwash 

decreases the horizontal tail’s pitch control effectiveness 

since it effectively increases the AOA that the tail surface is 

seeing. Movement of the wing CP affects the wing pitching 

moment. If the CP moves aft, a diving moment referred to 

as “Mach tuck” or “tuck under” is produced, and if it moves 

forward, a nose-up moment is produced. This is the primary 

reason for the development of the T-tail configuration on 

many turbine-powered aircraft, which places the horizontal 

stabilizer as far as practical from the turbulence of the wings. 

Sweepback 

Most of the difficulties of transonic flight are associated with 

shock wave induced flow separation. Therefore, any means of 

delaying or alleviating the shock induced separation improves 

aerodynamic performance. One method is wing sweepback. 

Sweepback theory is based upon the concept that it is only the 

component of the airflow perpendicular to the leading edge 

of the wing that affects pressure distribution and formation 

of shock waves. [Figure 5-68] 

On a straight wing aircraft, the airflow strikes the wing 

leading edge at 90°, and its full impact produces pressure and 

lift. A wing with sweepback is struck by the same airflow at 

an angle smaller than 90°. This airflow on the swept wing has 

the effect of persuading the wing into believing that it is flying 

slower than it really is; thus the formation of shock waves is 

delayed. Advantages of wing sweep include an increase in 

critical Mach number, force divergence Mach number, and 

the Mach number at which drag rise peaks. In other words, 

sweep delays the onset of compressibility effects. 

The Mach number that produces a sharp change in coefficient 

of drag is termed the “force divergence” Mach number and, 

for most airfoils, usually exceeds the critical Mach number by 

5 to 10 percent. At this speed, the airflow separation induced 

by shock wave formation can create significant variations in 

the drag, lift, or pitching moment coefficients. In addition to 

the delay of the onset of compressibility effects, sweepback 

reduces the magnitude in the changes of drag, lift, or moment 

coefficients. In other words, the use of sweepback “softens” 

the force divergence. 

A disadvantage of swept wings is that they tend to stall at the 

wingtips rather than at the wing roots. [Figure 5-69] This is 

Spanwise flow 

True airspeed 

Mach 0.85 

Airspeed sensed 

by wing Mach 0.70 

Figure 5-68. Sweepback effect. 

because the boundary layer tends to flow spanwise toward 

the tips and to separate near the leading edges. Because the 

tips of a swept wing are on the aft part of the wing (behind 

the CL), a wingtip stall causes the CL to move forward on 

the wing, forcing the nose to rise further. The tendency for 

tip stall is greatest when wing sweep and taper are combined. 

The stall situation can be aggravated by a T-tail configuration, 

which affords little or no pre-stall warning in the form of tail 

control surface buffet. [Figure 5-70] The T-tail, being above 

the wing wake remains effective even after the wing has begun 

to stall, allowing the pilot to inadvertently drive the wing 

into a deeper stall at a much greater AOA. If the horizontal 

tail surfaces then become buried in the wing’s wake, the 

elevator may lose all effectiveness, making it impossible to 

reduce pitch attitude and break the stall. In the pre-stall and 

immediate post-stall regimes, the lift/drag qualities of a swept 

wing aircraft (specifically the enormous increase in drag 

at low speeds) can cause an increasingly descending flight 

path with no change in pitch attitude, further increasing the 

5-48 
Stalled

Prestall 

 

Pre-stall 

Figure 5-69. Wingtip pre-stall. 

Stalled 

Figure 5-70. T-tail stall. 

AOA. In this situation, without reliable AOA information, 

a nose-down pitch attitude with an increasing airspeed is no 

guarantee that recovery has been affected, and up-elevator 

movement at this stage may merely keep the aircraft stalled. 

It is a characteristic of T-tail aircraft to pitch up viciously 

when stalled in extreme nose-high attitudes, making 

recovery difficult or violent. The stick pusher inhibits this 

type of stall. At approximately one knot above stall speed, 

pre-programmed stick forces automatically move the stick 

forward, preventing the stall from developing. A G-limiter 

may also be incorporated into the system to prevent the pitch 

down generated by the stick pusher from imposing excessive 

loads on the aircraft. A “stick shaker,” on the other hand, 

provides stall warning when the airspeed is five to seven 

percent above stall speed. 

Mach Buffet Boundaries 

Mach buffet is a function of the speed of the airflow over the 

wing—not necessarily the speed of the aircraft. Any time that 

too great a lift demand is made on the wing, whether from too 

fast an airspeed or from too high an AOA near the MMO, the 

“high-speed” buffet occurs. There are also occasions when 

the buffet can be experienced at much lower speeds known 

as the “low-speed Mach buffet.” 

An aircraft flown at a speed too slow for its weight and 

altitude necessitating a high AOA is the most likely situation 

to cause a low-speed Mach buffet. This very high AOA has 

the effect of increasing airflow velocity over the upper surface 

of the wing until the same effects of the shock waves and 

buffet occur as in the high-speed buffet situation. The AOA 

of the wing has the greatest effect on inducing the Mach 

buffet at either the high-speed or low-speed boundaries for 

the aircraft. The conditions that increase the AOA, the speed 

of the airflow over the wing, and chances of Mach buffet are: 

•	 High altitudes—the higher an aircraft flies, the thinner 

the air and the greater the AOA required to produce 

the lift needed to maintain level flight. 

•	 Heavy weights—the heavier the aircraft, the greater 

the lift required of the wing, and all other factors being 

equal, the greater the AOA. 

•	 G loading—an increase in the G loading on the aircraft 

has the same effect as increasing the weight of the 

aircraft. Whether the increase in G forces is caused 

by turns, rough control usage, or turbulence, the effect 

of increasing the wing’s AOA is the same. 

High Speed Flight Controls 

On high-speed aircraft, flight controls are divided into 

primary flight controls and secondary or auxiliary flight 

controls. The primary flight controls maneuver the aircraft 

about the pitch, roll, and yaw axes. They include the ailerons, 

elevator, and rudder. Secondary or auxiliary flight controls 

include tabs, leading edge flaps, trailing edge flaps, spoilers, 

and slats. 

Spoilers are used on the upper surface of the wing to spoil or 

reduce lift. High speed aircraft, due to their clean low drag 

design, use spoilers as speed brakes to slow them down. 

Spoilers are extended immediately after touchdown to dump 

lift and thus transfer the weight of the aircraft from the wings 

onto the wheels for better braking performance. [Figure 5-71] 

Jet transport aircraft have small ailerons. The space for 

ailerons is limited because as much of the wing trailing 

edge as possible is needed for flaps. Also, a conventional 

size aileron would cause wing twist at high speed. For that 

reason, spoilers are used in unison with ailerons to provide 

additional roll control. 

Some jet transports have two sets of ailerons, a pair of outboard 

low-speed ailerons and a pair of high-speed inboard ailerons. 

When the flaps are fully retracted after takeoff, the outboard 

ailerons are automatically locked out in the faired position. 

When used for roll control, the spoiler on the side of the 

up-going aileron extends and reduces the lift on that side, 

causing the wing to drop. If the spoilers are extended as speed 

brakes, they can still be used for roll control. If they are the 

5-49 
 

737 Control Surfaces 

727 Control Surfaces 

Takeoff Flaps 

Flaps Retracted 

Landing Flaps 

Aileron 

Leading edge slat 

Leading edge flap 

Foreflap Midflap Aftflap 

Inboard wing 

Outboard wing 

Inboard wing 

Outboard wing 

Foreflap 

Midflap 

Aftflap 

Aileron 

Inboard wing 

Outboard wing 

Aileron 

Rudder 

Elevator 

Tab 

Stabilizer 

Inboard flap 

Flight spoilers 

Ground spoiler 

Outboard flap 

Tab 

Aileron 

Leading edge slats 

Leading edge flaps 

Stabilizer 

Elevator 

Control tab 

Upper rudder 

Anti-balance tabs 

Control tab 

Inboard aileron 

Leading edge flaps 

Lower rudder 

Vortex generators 

Pitot tubes 

Ground spoilers 

Inboard flaps 

Flight spoilers 

Outboard flap 

Balance tab 

Outboard aileron 

Slats 

Fence 

Figure 5-71. Control surfaces. 

differential type, they extend further on one side and retract 

on the other side. If they are the non-differential type, they 

extend further on one side but do not retract on the other side. 

When fully extended as speed brakes, the non-differential 

spoilers remain extended and do not supplement the ailerons. 

To obtain a smooth stall and a higher AOA without airflow 

separation, the wing’s leading edge should have a wellrounded almost blunt shape that the airflow can adhere to 

at the higher AOA. With this shape, the airflow separation 

starts at the trailing edge and progresses forward gradually 

as AOA is increased. 

The pointed leading edge necessary for high-speed flight 

results in an abrupt stall and restricts the use of trailing edge 

flaps because the airflow cannot follow the sharp curve 

around the wing leading edge. The airflow tends to tear loose 

rather suddenly from the upper surface at a moderate AOA. 

To utilize trailing edge flaps, and thus increase the CL-MAX, 

the wing must go to a higher AOA without airflow separation. 

Therefore, leading edge slots, slats, and flaps are used to 

improve the low-speed characteristics during takeoff, climb, 

and landing. Although these devices are not as powerful as 

trailing edge flaps, they are effective when used full span in 

combination with high-lift trailing edge flaps. With the aid 

of these sophisticated high-lift devices, airflow separation is 

delayed and the CL-MAX is increased considerably. In fact, a 

50 knot reduction in stall speed is not uncommon. 

5-50 
The operational requirements of a large jet transport aircraft 

necessitate large pitch trim changes. Some requirements are: 

•	 A large CG range 

•	 A large speed range 

•	 The ability to perform large trim changes due to 

wing leading edge and trailing edge high-lift devices 

without limiting the amount of elevator remaining 

•	 Maintaining trim drag to a minimum 

These requirements are met by the use of a variable incidence 

horizontal stabilizer. Large trim changes on a fixed-tail 

aircraft require large elevator deflections. At these large 

deflections, little further elevator movement remains in the 

same direction. A variable incidence horizontal stabilizer 

is designed to take out the trim changes. The stabilizer is 

larger than the elevator, and consequently does not need to 

be moved through as large an angle. This leaves the elevator 

streamlining the tail plane with a full range of movement up 

and down. The variable incidence horizontal stabilizer can 

be set to handle the bulk of the pitch control demand, with 

the elevator handling the rest. On aircraft equipped with a 

variable incidence horizontal stabilizer, the elevator is smaller 

and less effective in isolation than it is on a fixed-tail aircraft. 

In comparison to other flight controls, the variable incidence 

horizontal stabilizer is enormously powerful in its effect. 

Because of the size and high speeds of jet transport aircraft, 

the forces required to move the control surfaces can be beyond 

the strength of the pilot. Consequently, the control surfaces are 

actuated by hydraulic or electrical power units. Moving the 

controls in the flight deck signals the control angle required, 

and the power unit positions the actual control surface. In the 

event of complete power unit failure, movement of the control 

surface can be affected by manually controlling the control 

tabs. Moving the control tab upsets the aerodynamic balance, 

which causes the control surface to move. 

Chapter Summary 

In order to sustain an aircraft in flight, a pilot must understand 

how thrust, drag, lift, and weight act on the aircraft. By 

understanding the aerodynamics of flight, how design, 

weight, load factors, and gravity affect an aircraft during 

flight maneuvers from stalls to high speed flight, the pilot 

learns how to control the balance between these forces. For 

information on stall speeds, load factors, and other important 

aircraft data, always consult the AFM/POH for specific 

information pertaining to the aircraft being flown. 

5-51 
6-1 

Introduction 

This chapter focuses on the flight control systems a pilot uses 

to control the forces of flight and the aircraft’s direction and 

attitude. It should be noted that flight control systems and 

characteristics can vary greatly depending on the type of 

aircraft flown. The most basic flight control system designs 

are mechanical and date back to early aircraft. They operate 

with a collection of mechanical parts, such as rods, cables, 

pulleys, and sometimes chains to transmit the forces of the 

flight deck controls to the control surfaces. Mechanical flight 

control systems are still used today in small general and 

sport category aircraft where the aerodynamic forces are not 

excessive. [Figure 6-1] 

Flight Controls 

Chapter 6 
Elevator 

Control stick 

Cable 

Pulleys 

Push rod 

Figure 6-1. Mechanical flight control system. 

As aviation matured and aircraft designers learned more about 

aerodynamics, the industry produced larger and faster aircraft. 

Therefore, the aerodynamic forces acting upon the control 

surfaces increased exponentially. To make the control force 

required by pilots manageable, aircraft engineers designed 

more complex systems. At first, hydromechanical designs, 

consisting of a mechanical circuit and a hydraulic circuit, 

were used to reduce the complexity, weight, and limitations 

of mechanical flight controls systems. [Figure 6-2] 

As aircraft became more sophisticated, the control surfaces 

were actuated by electric motors, digital computers, or fiber 

optic cables. Called “fly-by-wire,” this flight control system 

replaces the physical connection between pilot controls and 

the flight control surfaces with an electrical interface. In 

addition, in some large and fast aircraft, controls are boosted 

by hydraulically or electrically actuated systems. In both 

the fly-by-wire and boosted controls, the feel of the control 

reaction is fed back to the pilot by simulated means. 

Current research at the National Aeronautics and Space 

Administration (NASA) Dryden Flight Research Center 

involves Intelligent Flight Control Systems (IFCS). The goal 

of this project is to develop an adaptive neural network-based 

flight control system. Applied directly to flight control system 

feedback errors, IFCS provides adjustments to improve 

aircraft performance in normal flight, as well as with system 

failures. With IFCS, a pilot is able to maintain control and 

safely land an aircraft that has suffered a failure to a control 

surface or damage to the airframe. It also improves mission 

capability, increases the reliability and safety of flight, and 

eases the pilot workload. 

Today’s aircraft employ a variety of flight control systems. 

For example, some aircraft in the sport pilot category rely on 

weight-shift control to fly while balloons use a standard burn 

technique. Helicopters utilize a cyclic to tilt the rotor in the 

desired direction along with a collective to manipulate rotor 

pitch and anti-torque pedals to control yaw. [Figure 6-3] 

For additional information on flight control systems, refer 

to the appropriate handbook for information related to the 

flight control systems and characteristics of specific types 

of aircraft. 

Flight Control Systems 

Flight Controls 

Aircraft flight control systems consist of primary and 

secondary systems. The ailerons, elevator (or stabilator), 

and rudder constitute the primary control system and are 

required to control an aircraft safely during flight. Wing flaps, 

leading edge devices, spoilers, and trim systems constitute 

the secondary control system and improve the performance 

characteristics of the airplane or relieve the pilot of excessive 

control forces. 

Primary Flight Controls 

Aircraft control systems are carefully designed to provide 

adequate responsiveness to control inputs while allowing a 

Hydraulic pressure 

Hydraulic return 

Pivot point 

LEGEND 

Elevator (UP) 

Control stick (AFT—nose up) 

Control cables 

Power cylinder 

Neutral 

Neutral 

Control valves 

Power disconnect linkage Neutral Anti-torque pedals 

Cyclic stick 

Collective lever 

Cyclic 

Cyclic 

Cyclic

Cyclic 

Yaw 

Yaw 

Collective Collective 

Collective Collective 

Figure 6-2. Hydromechanical flight control system. Figure 6-3. Helicopter flight control system. 

6-2 
natural feel. At low airspeeds, the controls usually feel soft 

and sluggish, and the aircraft responds slowly to control 

applications. At higher airspeeds, the controls become 

increasingly firm and aircraft response is more rapid. 

Movement of any of the three primary flight control surfaces 

(ailerons, elevator or stabilator, or rudder), changes the 

airflow and pressure distribution over and around the airfoil. 

These changes affect the lift and drag produced by the airfoil/ 

control surface combination, and allow a pilot to control the 

aircraft about its three axes of rotation. 

Design features limit the amount of deflection of flight 

control surfaces. For example, control-stop mechanisms may 

be incorporated into the flight control linkages, or movement 

of the control column and/or rudder pedals may be limited. 

The purpose of these design limits is to prevent the pilot from 

inadvertently overcontrolling and overstressing the aircraft 

during normal maneuvers. 

A properly designed aircraft is stable and easily controlled 

during normal maneuvering. Control surface inputs cause 

movement about the three axes of rotation. The types of 

stability an aircraft exhibits also relate to the three axes of 

rotation. [Figure 6-4] 

Lateral axis

(longitudinal

stability) 

Aileron—Roll 

Elevator—Pitch 

Rudder—Yaw

Longitudinal

axis (lateral

stability) 

Vertical axis 

(directional

stability) 

Aileron Roll Longitudinal Lateral 

Rudder Yaw Vertical Directional 

Elevator/ 

Stabilator Pitch Lateral Longitudinal 

Primary

Control 

Surface 

Airplane

Movement 

Axes of 

Rotation 

Type of

Stability 

Figure 6-4. Airplane controls, movement, axes of rotation, and 

type of stability. 

Ailerons 

Ailerons control roll about the longitudinal axis. The ailerons 

are attached to the outboard trailing edge of each wing and 

move in the opposite direction from each other. Ailerons are 

connected by cables, bellcranks, pulleys, and/or push-pull 

tubes to a control wheel or control stick. 

Moving the control wheel, or control stick, to the right 

causes the right aileron to deflect upward and the left aileron 

to deflect downward. The upward deflection of the right 

aileron decreases the camber resulting in decreased lift on 

the right wing. The corresponding downward deflection of 

the left aileron increases the camber resulting in increased 

lift on the left wing. Thus, the increased lift on the left wing 

and the decreased lift on the right wing causes the aircraft 

to roll to the right. 

Adverse Yaw 

Since the downward deflected aileron produces more lift as 

evidenced by the wing raising, it also produces more drag. 

This added drag causes the wing to slow down slightly. 

This results in the aircraft yawing toward the wing which 

had experienced an increase in lift (and drag). From the 

pilot’s perspective, the yaw is opposite the direction of the 

bank. The adverse yaw is a result of differential drag and the 

slight difference in the velocity of the left and right wings. 

[Figure 6-5] 

Adverse yaw becomes more pronounced at low airspeeds. 

At these slower airspeeds, aerodynamic pressure on control 

surfaces are low, and larger control inputs are required to 

Figure 6-5. Adverse yaw is caused by higher drag on the outside 

wing that is producing more lift. Lift 

Drag 

Lift

A

Drag

d v e r s e yaw 

6-3 
Figure 5-4. Frise-type ailerons.

 

 

 

effectively maneuver the aircraft. As a result, the increase 

in aileron deflection causes an increase in adverse yaw. The 

yaw is especially evident in aircraft with long wing spans. 

Application of the rudder is used to counteract adverse 

yaw. The amount of rudder control required is greatest at 

low airspeeds, high angles of attack, and with large aileron 

deflections. Like all control surfaces at lower airspeeds, 

the vertical stabilizer/rudder becomes less effective and 

magnifies the control problems associated with adverse yaw. 

All turns are coordinated by use of ailerons, rudder, and 

elevator. Applying aileron pressure is necessary to place 

the aircraft in the desired angle of bank, while simultaneous 

application of rudder pressure is necessary to counteract the 

resultant adverse yaw. Additionally, because more lift is 

required during a turn than during straight-and-level flight, 

the angle of attack (AOA) must be increased by applying 

elevator back pressure. The steeper the turn, the more elevator 

back pressure that is needed. 

As the desired angle of bank is established, aileron and 

rudder pressures should be relaxed. This stops the angle of 

bank from increasing, because the aileron and rudder control 

surfaces are in a neutral and streamlined position. Elevator 

back pressure should be held constant to maintain altitude. 

The roll-out from a turn is similar to the roll-in, except the 

flight controls are applied in the opposite direction. The 

aileron and rudder are applied in the direction of the roll-out 

or toward the high wing. As the angle of bank decreases, 

the elevator back pressure should be relaxed as necessary 

to maintain altitude. 

In an attempt to reduce the effects of adverse yaw, 

manufacturers have engineered four systems: differential 

ailerons, frise-type ailerons, coupled ailerons and rudder, 

and flaperons. 

Differential Ailerons 

With differential ailerons, one aileron is raised a greater 

distance than the other aileron and is lowered for a given 

movement of the control wheel or control stick. This produces 

an increase in drag on the descending wing. The greater drag 

results from deflecting the up aileron on the descending wing 

to a greater angle than the down aileron on the rising wing. 

While adverse yaw is reduced, it is not eliminated completely. 

[Figure 6-6] 

Frise-Type Ailerons 

With a frise-type aileron, when pressure is applied to the 

control wheel, or control stick, the aileron that is being raised 

pivots on an offset hinge. This projects the leading edge of 

the aileron into the airflow and creates drag. It helps equalize 

Aileron deflected up 

Aileron deflected down 

Differential aileron 

Figure 6-6. Differential ailerons. 

the drag created by the lowered aileron on the opposite wing 

and reduces adverse yaw. [Figure 6-7] 

The frise-type aileron also forms a slot so air flows smoothly 

over the lowered aileron, making it more effective at high 

angles of attack. Frise-type ailerons may also be designed 

to function differentially. Like the differential aileron, the 

frise-type aileron does not eliminate adverse yaw entirely. 

Coordinated rudder application is still needed when ailerons 

are applied. 

Coupled Ailerons and Rudder 

Coupled ailerons and rudder are linked controls. This is 

accomplished with rudder-aileron interconnect springs, which 

help correct for aileron drag by automatically deflecting 

the rudder at the same time the ailerons are deflected. For 

Lowered 

Neutral 

Raised 

Drag 

Figure 6-7. Frise-type ailerons. 

6-4 
example, when the control wheel, or control stick, is moved 

to produce a left roll, the interconnect cable and spring pulls 

forward on the left rudder pedal just enough to prevent the 

nose of the aircraft from yawing to the right. The force applied 

to the rudder by the springs can be overridden if it becomes 

necessary to slip the aircraft. [Figure 6-8] 

Flaperons 

Flaperons combine both aspects of flaps and ailerons. In 

addition to controlling the bank angle of an aircraft like 

conventional ailerons, flaperons can be lowered together 

to function much the same as a dedicated set of flaps. The 

pilot retains separate controls for ailerons and flaps. A mixer 

is used to combine the separate pilot inputs into this single 

set of control surfaces called flaperons. Many designs that 

incorporate flaperons mount the control surfaces away from 

the wing to provide undisturbed airflow at high angles of 

attack and/or low airspeeds. [Figure 6-9] 

Elevator 

The elevator controls pitch about the lateral axis. Like the 

ailerons on small aircraft, the elevator is connected to the 

control column in the flight deck by a series of mechanical 

Rudder/Aileron interconnecting springs 

Rudder deflects with ailerons 

Figure 6-8. Coupled ailerons and rudder. 

Figure 6-9. Flaperons on a Skystar Kitfox MK 7. 

linkages. Aft movement of the control column deflects 

the trailing edge of the elevator surface up. This is usually 

referred to as the up-elevator position. [Figure 6-10] 

The up-elevator position decreases the camber of the elevator 

and creates a downward aerodynamic force, which is greater 

than the normal tail-down force that exists in straight-andlevel flight. The overall effect causes the tail of the aircraft 

to move down and the nose to pitch up. The pitching moment 

occurs about the center of gravity (CG). The strength of the 

pitching moment is determined by the distance between 

the CG and the horizontal tail surface, as well as by the 

aerodynamic effectiveness of the horizontal tail surface. 

Moving the control column forward has the opposite effect. 

In this case, elevator camber increases, creating more lift 

(less tail-down force) on the horizontal stabilizer/elevator. 

This moves the tail upward and pitches the nose down. Again, 

the pitching moment occurs about the CG. 

As mentioned earlier, stability, power, thrustline, and the 

position of the horizontal tail surfaces on the empennage 

are factors in elevator effectiveness controlling pitch. For 

Nose up 

Tail down

Control column 

aft 

Up elevator 

Downward 

aerodynamic force 

CG 

Figure 6-10. The elevator is the primary control for changing the 

pitch attitude of an aircraft. 

6-5 
 

 

example, the horizontal tail surfaces may be attached near 

the lower part of the vertical stabilizer, at the midpoint, or 

at the high point, as in the T-tail design. 

T-Tail 

In a T-tail configuration, the elevator is above most of the 

effects of downwash from the propeller, as well as airflow 

around the fuselage and/or wings during normal flight 

conditions. Operation of the elevators in this undisturbed air 

allows control movements that are consistent throughout most 

flight regimes. T-tail designs have become popular on many 

light and large aircraft, especially those with aft fuselagemounted engines because the T-tail configuration removes 

the tail from the exhaust blast of the engines. Seaplanes and 

amphibians often have T-tails in order to keep the horizontal 

surfaces as far from the water as possible. An additional 

benefit is reduced noise and vibration inside the aircraft. 

In comparison with conventional-tail aircraft, the elevator on a 

T-tail aircraft must be moved a greater distance to raise the nose 

a given amount when traveling at slow speeds. This is because 

the conventional-tail aircraft has the downwash from the 

propeller pushing down on the tail to assist in raising the nose. 

Aircraft controls are rigged so that an increase in control force 

is required to increase control travel. The forces required to 

raise the nose of a T-tail aircraft are greater than the forces 

required to raise the nose of a conventional-tail aircraft. 

Longitudinal stability of a trimmed aircraft is the same for 

both types of configuration, but the pilot must be aware that 

the required control forces are greater at slow speeds during 

takeoffs, landings, or stalls than for similar size aircraft 

equipped with conventional tails. 

T-tail aircraft also require additional design considerations 

to counter the problem of flutter. Since the weight of the 

horizontal surfaces is at the top of the vertical stabilizer, the 

moment arm created causes high loads on the vertical stabilizer 

that can result in flutter. Engineers must compensate for this by 

increasing the design stiffness of the vertical stabilizer, usually 

resulting in a weight penalty over conventional tail designs. 

When flying at a very high AOA with a low airspeed and 

an aft CG, the T-tail aircraft may be more susceptible to a 

deep stall. In this condition, the wake of the wing impinges 

on the tail surface and renders it almost ineffective. The 

wing, if fully stalled, allows its airflow to separate right after 

the leading edge. The wide wake of decelerated, turbulent 

air blankets the horizontal tail and hence its effectiveness 

diminished significantly. In these circumstances, elevator or 

stabilator control is reduced (or perhaps eliminated) making 

it difficult to recover from the stall. It should be noted that an 

aft CG is often a contributing factor in these incidents, since 

similar recovery problems are also found with conventional 

tail aircraft with an aft CG. [Figure 6-11] Deep stalls can 

occur on any aircraft but are more likely to occur on aircraft 

with “T” tails as a high AOA may be more likely to place 

the wings separated airflow into the path of the horizontal 

surface of the tail. Additionally, the distance between the 

wings and the tail, the position of the engines (such as being 

mounted on the tail) may increase the susceptibility of deep 

stall events. Therefore a deep stall may be more prevalent 

on transport versus general aviation aircraft. 

Since flight at a high AOA with a low airspeed and an aft 

CG position can be dangerous, many aircraft have systems to 

compensate for this situation. The systems range from control 

stops to elevator down springs. On transport category jets, stick 

pushers are commonly used. An elevator down spring assists in 

lowering the nose of the aircraft to prevent a stall caused by the 

aft CG position. The stall occurs because the properly trimmed 

airplane is flying with the elevator in a trailing edge down 

position, forcing the tail up and the nose down. In this unstable 

condition, if the aircraft encounters turbulence and slows down 

further, the trim tab no longer positions the elevator in the nosedown position. The elevator then streamlines, and the nose of 

the aircraft pitches upward, possibly resulting in a stall. 

The elevator down spring produces a mechanical load on the 

elevator, causing it to move toward the nose-down position if not 

otherwise balanced. The elevator trim tab balances the elevator 

down spring to position the elevator in a trimmed position. 

When the trim tab becomes ineffective, the down spring drives 

the elevator to a nose-down position. The nose of the aircraft 

lowers, speed builds up, and a stall is prevented. [Figure 6-12] 

The elevator must also have sufficient authority to hold the 

nose of the aircraft up during the roundout for a landing. In 

this case, a forward CG may cause a problem. During the 

landing flare, power is usually reduced, which decreases the 

CG 

Figure 6-11. Aircraft with a T-tail design at a high AOA and an aft CG. 

6-6 
Elevator 

Down spring 

Pivot points 

Bell crank 

Figure 6-12. When the aerodynamic efficiency of the horizontal tail 

surface is inadequate due to an aft CG condition, an elevator down 

spring may be used to supply a mechanical load to lower the nose. 

airflow over the empennage. This, coupled with the reduced 

landing speed, makes the elevator less effective. 

As this discussion demonstrates, pilots must understand and 

follow proper loading procedures, particularly with regard 

to the CG position. More information on aircraft loading, 

as well as weight and balance, is included in Chapter 10, 

Weight and Balance. 

Stabilator 

As mentioned in Chapter 3, Aircraft Structure, a stabilator is 

essentially a one-piece horizontal stabilizer that pivots from 

a central hinge point. When the control column is pulled 

back, it raises the stabilator’s trailing edge, pulling the nose 

of the aircraft. Pushing the control column forward lowers 

the trailing edge of the stabilator and pitches the nose of the 

aircraft down. 

Because stabilators pivot around a central hinge point, they 

are extremely sensitive to control inputs and aerodynamic 

loads. Antiservo tabs are incorporated on the trailing edge to 

decrease sensitivity. They deflect in the same direction as the 

stabilator. This results in an increase in the force required to 

move the stabilator, thus making it less prone to pilot-induced 

overcontrolling. In addition, a balance weight is usually 

incorporated in front of the main spar. The balance weight 

may project into the empennage or may be incorporated on 

the forward portion of the stabilator tips. [Figure 6-13] 

Canard 

The canard design utilizes the concept of two lifting surfaces. 

The canard functions as a horizontal stabilizer located in front 

Antiservo tab 

Balance weight 

Stabilator 

Pivot point 

Figure 6-13. The stabilator is a one-piece horizontal tail surface 

that pivots up and down about a central hinge point. 

of the main wings. In effect, the canard is an airfoil similar to 

the horizontal surface on a conventional aft-tail design. The 

difference is that the canard actually creates lift and holds 

the nose up, as opposed to the aft-tail design which exerts 

downward force on the tail to prevent the nose from rotating 

downward. [Figure 6-14] 

The canard design dates back to the pioneer days of aviation. 

Most notably, it was used on the Wright Flyer. Recently, the 

canard configuration has regained popularity and is appearing 

on newer aircraft. Canard designs include two types–one with 

a horizontal surface of about the same size as a normal aft-tail 

design, and the other with a surface of the same approximate 

size and airfoil of the aft-mounted wing known as a tandem 

wing configuration. Theoretically, the canard is considered 

more efficient because using the horizontal surface to help 

lift the weight of the aircraft should result in less drag for a 

given amount of lift. 

Figure 6-14. The Piaggio P180 includes a variable-sweep canard 

design that provides longitudinal stability about the lateral axis. 

6-7 
Rudder 

The rudder controls movement of the aircraft about its vertical 

axis. This motion is called yaw. Like the other primary control 

surfaces, the rudder is a movable surface hinged to a fixed 

surface in this case, to the vertical stabilizer or fin. The rudder 

is controlled by the left and right rudder pedals. 

When the rudder is deflected into the airflow, a horizontal 

force is exerted in the opposite direction. [Figure 6-15] By 

pushing the left pedal, the rudder moves left. This alters the 

airflow around the vertical stabilizer/rudder and creates a 

sideward lift that moves the tail to the right and yaws the nose 

of the airplane to the left. Rudder effectiveness increases with 

speed; therefore, large deflections at low speeds and small 

deflections at high speeds may be required to provide the 

desired reaction. In propeller-driven aircraft, any slipstream 

flowing over the rudder increases its effectiveness. 

V-Tail 

The V-tail design utilizes two slanted tail surfaces to perform 

the same functions as the surfaces of a conventional elevator 

and rudder configuration. The fixed surfaces act as both 

horizontal and vertical stabilizers. [Figure 6-16] 

The movable surfaces, which are usually called ruddervators, 

are connected through a special linkage that allows the control 

wheel to move both surfaces simultaneously. On the other 

hand, displacement of the rudder pedals moves the surfaces 

differentially, thereby providing directional control. 

When both rudder and elevator controls are moved by the 

pilot, a control mixing mechanism moves each surface the 

Aerodynamic force

Left rudder 

CG Left rudder forward 

Yaw 

Figure 6-15. The effect of left rudder pressure. 

Figure 6-16. Beechcraft Bonanza V35. 

appropriate amount. The control system for the V-tail is more 

complex than the control system for a conventional tail. In 

addition, the V-tail design is more susceptible to Dutch roll 

tendencies than a conventional tail, and total reduction in 

drag is minimal. 

Secondary Flight Controls 

Secondary flight control systems may consist of wing flaps, 

leading edge devices, spoilers, and trim systems. 

Flaps 

Flaps are the most common high-lift devices used on aircraft. 

These surfaces, which are attached to the trailing edge of 

the wing, increase both lift and induced drag for any given 

AOA. Flaps allow a compromise between high cruising 

speed and low landing speed because they may be extended 

when needed and retracted into the wing’s structure when not 

needed. There are four common types of flaps: plain, split, 

slotted, and Fowler flaps. [Figure 6-17] 

The plain flap is the simplest of the four types. It increases 

the airfoil camber, resulting in a significant increase in the 

coefficient of lift (CL) at a given AOA. At the same time, it 

greatly increases drag and moves the center of pressure (CP) 

aft on the airfoil, resulting in a nose-down pitching moment. 

The split flap is deflected from the lower surface of the airfoil 

and produces a slightly greater increase in lift than the plain 

flap. More drag is created because of the turbulent air pattern 

produced behind the airfoil. When fully extended, both plain 

and split flaps produce high drag with little additional lift. 

The most popular flap on aircraft today is the slotted flap. 

Variations of this design are used for small aircraft, as well 

as for large ones. Slotted flaps increase the lift coefficient 

significantly more than plain or split flaps. On small aircraft, 

the hinge is located below the lower surface of the flap, and 

6-8 
when the flap is lowered, a duct forms between the flap well 

in the wing and the leading edge of the flap. When the slotted 

flap is lowered, high energy air from the lower surface is 

ducted to the flap’s upper surface. The high energy air from 

the slot accelerates the upper surface boundary layer and 

delays airflow separation, providing a higher CL. Thus, the 

slotted flap produces much greater increases in maximum 

coefficient of lift (CL-MAX) than the plain or split flap. While 

there are many types of slotted flaps, large aircraft often 

have double- and even triple-slotted flaps. These allow the 

maximum increase in drag without the airflow over the flaps 

separating and destroying the lift they produce. 

Plain flap 

Basic section 

Split flap 

Slotted flap 

Fowler flap 

Fowler flaps are a type of slotted flap. This flap design not 

only changes the camber of the wing, it also increases the 

wing area. Instead of rotating down on a hinge, it slides 

backwards on tracks. In the first portion of its extension, it 

increases the drag very little, but increases the lift a great 

deal as it increases both the area and camber. Pilots should 

be aware that flap extension may cause a nose-up or down 

pitching moment, depending on the type of aircraft, which 

the pilot will need to compensate for, usually with a trim 

adjustment. As the extension continues, the flap deflects 

downward. During the last portion of its travel, the flap 

increases the drag with little additional increase in lift. 

Leading Edge Devices 

High-lift devices also can be applied to the leading edge of 

the airfoil. The most common types are fixed slots, movable 

slats, leading edge flaps, and cuffs. [Figure 6-18] 

Fixed slots direct airflow to the upper wing surface and delay 

airflow separation at higher angles of attack. The slot does not 

Leading edge flap 

Movable slot 

Fixed slot 

Slotted Fowler flap 

Leading edge cuff 

Figure 6-17. Five common types of flaps. Figure 6-18. Leading edge high lift devices. 

6-9 
 

increase the wing camber, but allows a higher maximum CL 

because the stall is delayed until the wing reaches a greater AOA. 

Movable slats consist of leading edge segments that move on 

tracks. At low angles of attack, each slat is held flush against 

the wing’s leading edge by the high pressure that forms at 

the wing’s leading edge. As the AOA increases, the highpressure area moves aft below the lower surface of the wing, 

allowing the slats to move forward. Some slats, however, are 

pilot operated and can be deployed at any AOA. Opening a 

slat allows the air below the wing to flow over the wing’s 

upper surface, delaying airflow separation. 

Leading edge flaps, like trailing edge flaps, are used to 

increase both CL-MAX and the camber of the wings. This type 

of leading edge device is frequently used in conjunction with 

trailing edge flaps and can reduce the nose-down pitching 

movement produced by the latter. As is true with trailing edge 

flaps, a small increment of leading edge flaps increases lift 

to a much greater extent than drag. As flaps are extended, 

drag increases at a greater rate than lift. 

Leading edge cuffs, like leading edge flaps and trailing edge 

flaps are used to increase both CL-MAX and the camber of 

the wings. Unlike leading edge flaps and trailing edge flaps, 

leading edge cuffs are fixed aerodynamic devices. In most 

cases, leading edge cuffs extend the leading edge down and 

forward. This causes the airflow to attach better to the upper 

surface of the wing at higher angles of attack, thus lowering 

an aircraft’s stall speed. The fixed nature of leading edge cuffs 

extracts a penalty in maximum cruise airspeed, but recent 

advances in design and technology have reduced this penalty. 

Spoilers 

Found on some fixed-wing aircraft, high drag devices called 

spoilers are deployed from the wings to spoil the smooth 

airflow, reducing lift and increasing drag. On gliders, spoilers 

are most often used to control rate of descent for accurate 

landings. On other aircraft, spoilers are often used for roll 

control, an advantage of which is the elimination of adverse 

yaw. To turn right, for example, the spoiler on the right wing 

is raised, destroying some of the lift and creating more drag 

on the right. The right wing drops, and the aircraft banks 

and yaws to the right. Deploying spoilers on both wings at 

the same time allows the aircraft to descend without gaining 

speed. Spoilers are also deployed to help reduce ground roll 

after landing. By destroying lift, they transfer weight to the 

wheels, improving braking effectiveness. [Figure 6-19] 

Trim Systems 

Although an aircraft can be operated throughout a wide range 

of attitudes, airspeeds, and power settings, it can be designed to 

fly hands-off within only a very limited combination of these 

Figure 6-19. Spoilers reduce lift and increase drag during descent 

and landing. 

variables. Trim systems are used to relieve the pilot of the 

need to maintain constant pressure on the flight controls, and 

usually consist of flight deck controls and small hinged devices 

attached to the trailing edge of one or more of the primary flight 

control surfaces. Designed to help minimize a pilot’s workload, 

trim systems aerodynamically assist movement and position of 

the flight control surface to which they are attached. Common 

types of trim systems include trim tabs, balance tabs, antiservo 

tabs, ground adjustable tabs, and an adjustable stabilizer. 

Trim Tabs 

The most common installation on small aircraft is a single 

trim tab attached to the trailing edge of the elevator. Most trim 

tabs are manually operated by a small, vertically mounted 

control wheel. However, a trim crank may be found in some 

aircraft. The flight deck control includes a trim tab position 

indicator. Placing the trim control in the full nose-down 

position moves the trim tab to its full up position. With 

the trim tab up and into the airstream, the airflow over the 

horizontal tail surface tends to force the trailing edge of the 

elevator down. This causes the tail of the aircraft to move 

up and the nose to move down. [Figure 6-20] 

If the trim tab is set to the full nose-up position, the tab moves 

to its full down position. In this case, the air flowing under the 

horizontal tail surface hits the tab and forces the trailing edge 

of the elevator up, reducing the elevator’s AOA. This causes 

the tail of the aircraft to move down and the nose to move up. 

In spite of the opposing directional movement of the trim 

tab and the elevator, control of trim is natural to a pilot. If 

the pilot needs to exert constant back pressure on a control 

column, the need for nose-up trim is indicated. The normal 

trim procedure is to continue trimming until the aircraft is 

balanced and the nose-heavy condition is no longer apparent. 

Pilots normally establish the desired power, pitch attitude, 

and configuration first, and then trim the aircraft to relieve 

6-10 
Figure 5-16. The movement of the elevator is opposite to the 

direction of movement of the elevator trim tab.

 

Nose-down trim 

Nose-up trim 

Trim tab 

Elevator 

Trim tab 

Elevator 

Tab up—elevator down 

Tab up—elevator up 

Figure 6-20. The movement of the elevator is opposite to the 

direction of movement of the elevator trim tab. 

control pressures that may exist for that flight condition. As 

power, pitch attitude, or configuration changes, retrimming 

is necessary to relieve the control pressures for the new 

flight condition. 

Balance Tabs 

The control forces may be excessively high in some aircraft, 

and, in order to decrease them, the manufacturer may use 

balance tabs. They look like trim tabs and are hinged in 

approximately the same places as trim tabs. The essential 

difference between the two is that the balancing tab is coupled 

to the control surface rod so that when the primary control 

surface is moved in any direction, the tab automatically 

moves in the opposite direction. The airflow striking the tab 

counterbalances some of the air pressure against the primary 

control surface and enables the pilot to move the control more 

easily and hold the control surface in position. 

If the linkage between the balance tab and the fixed 

surface is adjustable from the flight deck, the tab acts as a 

combination trim and balance tab that can be adjusted to a 

desired deflection. 

Servo Tabs 

Servo tabs are very similar in operation and appearance to the 

trim tabs previously discussed. A servo tab is a small portion 

of a flight control surface that deploys in such a way that it 

helps to move the entire flight control surface in the direction 

that the pilot wishes it to go. A servo tab is a dynamic device 

that deploys to decrease the pilots work load and de-stabilize 

the aircraft. Servo tabs are sometimes referred to as flight tabs 

and are used primarily on large aircraft. They aid the pilot in 

moving the control surface and in holding it in the desired 

position. Only the servo tab moves in response to movement 

of the pilot’s flight control, and the force of the airflow on 

the servo tab then moves the primary control surface. 

Antiservo Tabs 

Antiservo tabs work in the same manner as balance tabs 

except, instead of moving in the opposite direction, they move 

in the same direction as the trailing edge of the stabilator. 

In addition to decreasing the sensitivity of the stabilator, an 

antiservo tab also functions as a trim device to relieve control 

pressure and maintain the stabilator in the desired position. 

The fixed end of the linkage is on the opposite side of the 

surface from the horn on the tab; when the trailing edge of the 

stabilator moves up, the linkage forces the trailing edge of the 

tab up. When the stabilator moves down, the tab also moves 

down. Conversely, trim tabs on elevators move opposite of 

the control surface. [Figure 6-21] 

Ground Adjustable Tabs 

Many small aircraft have a nonmovable metal trim tab on the 

rudder. This tab is bent in one direction or the other while on 

the ground to apply a trim force to the rudder. The correct 

displacement is determined by trial and error. Usually, small 

Pivot point 

Stabilator 

Antiservo tab 

Figure 6-21. An antiservo tab attempts to streamline the control 

surface and is used to make the stabilator less sensitive by opposing 

the force exerted by the pilot. 

6-11 
adjustments are necessary until the aircraft no longer skids 

left or right during normal cruising flight. [Figure 6-22] 

Adjustable Stabilizer 

Rather than using a movable tab on the trailing edge of the 

elevator, some aircraft have an adjustable stabilizer. With this 

arrangement, linkages pivot the horizontal stabilizer about 

its rear spar. This is accomplished by the use of a jackscrew 

mounted on the leading edge of the stabilator. [Figure 6-23] 

On small aircraft, the jackscrew is cable operated with a trim 

wheel or crank. On larger aircraft, it is motor driven. The 

trimming effect and flight deck indications for an adjustable 

stabilizer are similar to those of a trim tab. 

Autopilot 

Autopilot is an automatic flight control system that keeps an 

aircraft in level flight or on a set course. It can be directed by 

the pilot, or it may be coupled to a radio navigation signal. 

Autopilot reduces the physical and mental demands on a pilot 

and increases safety. The common features available on an 

autopilot are altitude and heading hold. 

The simplest systems use gyroscopic attitude indicators and 

magnetic compasses to control servos connected to the flight 

control system. [Figure 6-24] The number and location of 

these servos depends on the complexity of the system. For 

example, a single-axis autopilot controls the aircraft about the 

longitudinal axis and a servo actuates the ailerons. A three-axis 

autopilot controls the aircraft about the longitudinal, lateral, and 

vertical axes. Three different servos actuate ailerons, elevator, 

and rudder. More advanced systems often include a vertical 

speed and/or indicated airspeed hold mode. Advanced autopilot 

systems are coupled to navigational aids through a flight director. 

Figure 6-23. Some aircraft, including most jet transports, use an 

adjustable stabilizer to provide the required pitch trim forces. 

Adjustable stabilizer 

Nose down 

Nose up 

Trim motor or trim cable 

Jackscrew 

Pivot 

The autopilot system also incorporates a disconnect safety 

feature to disengage the system automatically or manually. 

These autopilots work with inertial navigation systems, 

global positioning systems (GPS), and flight computers to 

control the aircraft. In fly-by-wire systems, the autopilot is 

an integrated component. 

Additionally, autopilots can be manually overridden. Because 

autopilot systems differ widely in their operation, refer to 

the autopilot operating instructions in the Airplane Flight 

Manual (AFM) or the Pilot’s Operating Handbook (POH). 

Chapter Summary 

Because flight control systems and aerodynamic 

characteristics vary greatly between aircraft, it is essential 

that a pilot become familiar with the primary and secondary 

flight control systems of the aircraft being flown. The 

primary source of this information is the AFM or the POH. 

Various manufacturer and owner group websites can also be 

a valuable source of additional information. 

Figure 6-22. A ground adjustable tab is used on the rudder of many 

small airplanes to correct for a tendency to fly with the fuselage 

slightly misaligned with the relative wind. 

Figure 6-24. Basic autopilot system integrated into the flight 

control system. 

6-12 
7-1 

Aircraft Systems 

Chapter 7 

Introduction 

This chapter covers the primary systems found on most 

aircraft. These include the engine, propeller, induction, 

ignition, as well as the fuel, lubrication, cooling, electrical, 

landing gear, and environmental control systems. 

Powerplant 

An aircraft engine, or powerplant, produces thrust to propel 

an aircraft. Reciprocating engines and turboprop engines 

work in combination with a propeller to produce thrust. 

Turbojet and turbofan engines produce thrust by increasing 

the velocity of air flowing through the engine. All of these 

powerplants also drive the various systems that support the 

operation of an aircraft. 
 

Reciprocating Engines 

Most small aircraft are designed with reciprocating 

engines. The name is derived from the back-and-forth, or 

reciprocating, movement of the pistons that produces the 

mechanical energy necessary to accomplish work. 

Driven by a revitalization of the general aviation (GA) 

industry and advances in both material and engine design, 

reciprocating engine technology has improved dramatically 

over the past two decades. The integration of computerized 

engine management systems has improved fuel efficiency, 

decreased emissions, and reduced pilot workload. 

Reciprocating engines operate on the basic principle of 

converting chemical energy (fuel) into mechanical energy. 

This conversion occurs within the cylinders of the engine 

through the process of combustion. The two primary 

reciprocating engine designs are the spark ignition and the 

compression ignition. The spark ignition reciprocating engine 

has served as the powerplant of choice for many years. In 

an effort to reduce operating costs, simplify design, and 

improve reliability, several engine manufacturers are turning 

to compression ignition as a viable alternative. Often referred 

to as jet fuel piston engines, compression ignition engines 

have the added advantage of utilizing readily available and 

lower cost diesel or jet fuel. 

The main mechanical components of the spark ignition and 

the compression ignition engine are essentially the same. 

Both use cylindrical combustion chambers and pistons that 

travel the length of the cylinders to convert linear motion 

into the rotary motion of the crankshaft. The main difference 

between spark ignition and compression ignition is the 

process of igniting the fuel. Spark ignition engines use a 

spark plug to ignite a pre-mixed fuel-air mixture. (Fuel-air 

mixture is the ratio of the “weight” of fuel to the “weight” 

of air in the mixture to be burned.) A compression ignition 

engine first compresses the air in the cylinder, raising its 

temperature to a degree necessary for automatic ignition 

when fuel is injected into the cylinder. 

These two engine designs can be further classified as: 

1.	 Cylinder arrangement with respect to the crankshaft— 

radial, in-line, v-type, or opposed 

2. Operating cycle—two or four 

3. Method of cooling—liquid or air 

Radial engines were widely used during World War II and 

many are still in service today. With these engines, a row or 

rows of cylinders are arranged in a circular pattern around 

the crankcase. The main advantage of a radial engine is the 

favorable power-to-weight ratio. [Figure 7-1] 

Figure 7-1. Radial engine. 

In-line engines have a comparatively small frontal area, but 

their power-to-weight ratios are relatively low. In addition, 

the rearmost cylinders of an air-cooled, in-line engine 

receive very little cooling air, so these engines are normally 

limited to four or six cylinders. V-type engines provide 

more horsepower than in-line engines and still retain a small 

frontal area. 

Continued improvements in engine design led to the 

development of the horizontally-opposed engine, which 

remains the most popular reciprocating engines used on 

smaller aircraft. These engines always have an even number 

of cylinders, since a cylinder on one side of the crankcase 

“opposes” a cylinder on the other side. [Figure 7-2] The 

majority of these engines are air cooled and usually are 

mounted in a horizontal position when installed on fixed-wing 

airplanes. Opposed-type engines have high power-to-weight 

ratios because they have a comparatively small, lightweight 

crankcase. In addition, the compact cylinder arrangement 

reduces the engine’s frontal area and allows a streamlined 

installation that minimizes aerodynamic drag. 

Opposed cylinders 

Figure 7-2. Horizontally opposed engine. 

7-2 
 

Depending on the engine manufacturer, all of these 

arrangements can be designed to utilize spark or compression 

ignition and operate on either a two- or four-stroke cycle. 

In a two-stroke engine, the conversion of chemical energy 

into mechanical energy occurs over a two-stroke operating 

cycle. The intake, compression, power, and exhaust processes 

occur in only two strokes of the piston rather than the more 

common four strokes. Because a two-stroke engine has 

a power stroke upon each revolution of the crankshaft, it 

typically has higher power-to-weight ratio than a comparable 

four-stroke engine. Due to the inherent inefficiency and 

disproportionate emissions of the earliest designs, use of the 

two-stroke engine has been limited in aviation. 

Recent advances in material and engine design have 

reduced many of the negative characteristics associated 

with two-stroke engines. Modern two-stroke engines often 

use conventional oil sumps, oil pumps, and full pressure 

fed lubrication systems. The use of direct fuel injection 

and pressurized air, characteristic of advanced compression 

ignition engines, make two-stroke compression ignition 

engines a viable alternative to the more common four-stroke 

spark ignition designs. [Figure 7-3] 

Spark ignition four-stroke engines remain the most common 

design used in GA today. [Figure 7-4] The main parts of a 

spark ignition reciprocating engine include the cylinders, 

crankcase, and accessory housing. The intake/exhaust valves, 

spark plugs, and pistons are located in the cylinders. The 

crankshaft and connecting rods are located in the crankcase. 

The magnetos are normally located on the engine accessory 

housing. 

Exhaust valve Fuel injector 

Piston 

Forced air 

2. Power stroke 

1. Intake/compression 

and exhaust 

Figure 7-3. Two-stroke compression ignition. 

Exhaust valve 

Intake valve 

Spark plug 

Piston 

Connecting rod Crankshaft

Crankcase 

Cylinder 

Figure 7-4. Main components of a spark ignition reciprocating 

engine. 

In a four-stroke engine, the conversion of chemical energy into 

mechanical energy occurs over a four-stroke operating cycle. 

The intake, compression, power, and exhaust processes occur 

in four separate strokes of the piston in the following order. 

1.	 The intake stroke begins as the piston starts its 

downward travel. When this happens, the intake 

valve opens and the fuel-air mixture is drawn into the 

cylinder. 

2. The compression stroke begins when the intake valve 

closes, and the piston starts moving back to the top of 

the cylinder. This phase of the cycle is used to obtain 

a much greater power output from the fuel-air mixture 

once it is ignited. 

3. The power stroke begins when the fuel-air mixture is 

ignited. This causes a tremendous pressure increase 

in the cylinder and forces the piston downward away 

from the cylinder head, creating the power that turns 

the crankshaft. 

7-3 
 

4. The exhaust stroke is used to purge the cylinder of 

burned gases. It begins when the exhaust valve opens, 

and the piston starts to move toward the cylinder head 

once again. 

Even when the engine is operated at a fairly low speed, 

the four-stroke cycle takes place several hundred times 

each minute. [Figure 7-5] In a four-cylinder engine, each 

cylinder operates on a different stroke. Continuous rotation 

of a crankshaft is maintained by the precise timing of the 

power strokes in each cylinder. Continuous operation of the 

engine depends on the simultaneous function of auxiliary 

systems, including the induction, ignition, fuel, oil, cooling, 

and exhaust systems. 

The latest advance in aircraft reciprocating engines was 

pioneered in the mid-1960s by Frank Thielert, who looked 

to the automotive industry for answers on how to integrate 

diesel technology into an aircraft engine. The advantage 

1. Intake 2. Compression 

3. Power 4. Exhaust 

Intake valve Exhaust valve

Piston Spark plug

Crankshaft Connecting rod 

Figure 7-5. The arrows in this illustration indicate the direction of 

motion of the crankshaft and piston during the four-stroke cycle. 

of a diesel-fueled reciprocating engine lies in the physical 

similarity of diesel and kerosene. Aircraft equipped with a 

diesel piston engine runs on standard aviation fuel kerosene, 

which provides more independence, higher reliability, lower 

consumption, and operational cost saving. 

In 1999, Thielert formed Thielert Aircraft Engines (TAE) 

to design, develop, certify, and manufacture a brand-new 

Jet-A-burning diesel cycle engine (also known as jet-fueled 

piston engine) for the GA industry. By March 2001, the first 

prototype engine became the first certified diesel engine 

since World War II. TAE continues to design and develop 

diesel cycle engines and other engine manufacturers, such as 

Société de Motorisations Aéronautiques (SMA), now offer 

jet-fueled piston engines as well. TAE engines can be found 

on the Diamond DA40 single and the DA42 Twin Star; the 

first diesel engine to be part of the type certificate of a new 

original equipment manufacturer (OEM) aircraft. 

These engines have also gained a toehold in the retrofit 

market with a supplemental type certificate (STC) to reengine the Cessna 172 models and the Piper PA-28 family. 

The jet-fueled piston engine’s technology has continued to 

progress and a full authority digital engine control (FADEC, 

discussed more fully later in the chapter) is standard on such 

equipped aircraft, which minimizes complication of engine 

control. By 2007, various jet-fueled piston aircraft had logged 

well over 600,000 hours of service. 

Propeller 

The propeller is a rotating airfoil, subject to induced drag, 

stalls, and other aerodynamic principles that apply to any 

airfoil. It provides the necessary thrust to pull, or in some 

cases push, the aircraft through the air. The engine power is 

used to rotate the propeller, which in turn generates thrust 

very similar to the manner in which a wing produces lift. 

The amount of thrust produced depends on the shape of the 

airfoil, the angle of attack (AOA) of the propeller blade, and 

the revolutions per minute (rpm) of the engine. The propeller 

itself is twisted so the blade angle changes from hub to tip. 

The greatest angle of incidence, or the highest pitch, is at the 

hub while the smallest angle of incidence or smallest pitch 

is at the tip. [Figure 7-6] 

The reason for the twist is to produce uniform lift from the 

hub to the tip. As the blade rotates, there is a difference in 

the actual speed of the various portions of the blade. The tip 

of the blade travels faster than the part near the hub, because 

the tip travels a greater distance than the hub in the same 

length of time. [Figure 7-7] Changing the angle of incidence 

(pitch) from the hub to the tip to correspond with the speed 

produces uniform lift throughout the length of the blade. A 

propeller blade designed with the same angle of incidence 

7-4 
 

Figure 7-6. Changes in propeller blade angle from hub to tip. 

throughout its entire length would be inefficient because as 

airspeed increases in flight, the portion near the hub would 

have a negative AOA while the blade tip would be stalled. 

Small aircraft are equipped with either one of two types of 

propellers: fixed-pitch or adjustable-pitch. 

Fixed-Pitch Propeller 

A propeller with fixed blade angles is a fixed-pitch propeller. 

The pitch of this propeller is set by the manufacturer and 

cannot be changed. Since a fixed-pitch propeller achieves 

the best efficiency only at a given combination of airspeed 

and rpm, the pitch setting is ideal for neither cruise nor 

climb. Thus, the aircraft suffers a bit in each performance 

category. The fixed-pitch propeller is used when low weight, 

simplicity, and low cost are needed. 

There are two types of fixed-pitch propellers: climb and 

cruise. Whether the airplane has a climb or cruise propeller 

60 in. 

40 in. 

20 in. 

Short travel distance—slow speed 

—129 kno s t

Moderate travel distance—moderate speed—259 knots 

Greater travel distance—very high speed—389 knots 

2,500 rpm 

2,500 rpm 

2,500 rpm 

Figure 7-7. Relationship of travel distance and speed of various 

portions of propeller blade. 

installed depends upon its intended use. The climb propeller 

has a lower pitch, therefore less drag. Less drag results in 

higher rpm and more horsepower capability, which increases 

performance during takeoffs and climbs but decreases 

performance during cruising flight. 

The cruise propeller has a higher pitch, therefore more 

drag. More drag results in lower rpm and less horsepower 

capability, which decreases performance during takeoffs and 

climbs but increases efficiency during cruising flight. 

The propeller is usually mounted on a shaft, which may be 

an extension of the engine crankshaft. In this case, the rpm 

of the propeller would be the same as the crankshaft rpm. On 

some engines, the propeller is mounted on a shaft geared to 

the engine crankshaft. In this type, the rpm of the propeller 

is different than that of the engine. 

In a fixed-pitch propeller, the tachometer is the indicator of 

engine power. [Figure 7-8] A tachometer is calibrated in 

hundreds of rpm and gives a direct indication of the engine 

and propeller rpm. The instrument is color coded with a green 

arc denoting the maximum continuous operating rpm. Some 

tachometers have additional markings to reflect engine and/or 

propeller limitations. The manufacturer’s recommendations 

should be used as a reference to clarify any misunderstanding 

of tachometer markings. 

The rpm is regulated by the throttle, which controls the fuelair flow to the engine. At a given altitude, the higher the 

tachometer reading, the higher the power output of the engine. 

When operating altitude increases, the tachometer may not 

show correct power output of the engine. For example, 2,300 

rpm at 5,000 feet produces less horsepower than 2,300 rpm 

at sea level because power output depends on air density. Air 

density decreases as altitude increases and a decrease in air 

RPM HUNDREDS 

25

3

5

I5

30

20

I0

35

25 

3

5 

I5 

30 

20 

I0 

35 HOURS 

AVOID CONTINUOUS 

OPERATION 

BETWEEN 2250 

AND 2350 RPM 

I 

I0 

Figure 7-8. Engine rpm is indicated on the tachometer. 

7-5 
 

density (higher density altitude) decreases the power output 

of the engine. As altitude changes, the position of the throttle 

must be changed to maintain the same rpm. As altitude is 

increased, the throttle must be opened further to indicate the 

same rpm as at a lower altitude. 

Adjustable-Pitch Propeller 

The adjustable-pitch propeller was the forerunner of the 

constant-speed propeller. It is a propeller with blades whose 

pitch can be adjusted on the ground with the engine not 

running, but which cannot be adjusted in flight. It is also 

referred to as a ground adjustable propeller. By the 1930s, 

pioneer aviation inventors were laying the ground work for 

automatic pitch-change mechanisms, which is why the term 

sometimes refers to modern constant-speed propellers that 

are adjustable in flight. 

The first adjustable-pitch propeller systems provided only two 

pitch settings: low and high. Today, most adjustable-pitch 

propeller systems are capable of a range of pitch settings. 

A constant-speed propeller is a controllable-pitch propeller 

whose pitch is automatically varied in flight by a governor 

maintaining constant rpm despite varying air loads. It is the 

most common type of adjustable-pitch propeller. The main 

advantage of a constant-speed propeller is that it converts 

a high percentage of brake horsepower (BHP) into thrust 

horsepower (THP) over a wide range of rpm and airspeed 

combinations. A constant-speed propeller is more efficient 

than other propellers because it allows selection of the most 

efficient engine rpm for the given conditions. 

An aircraft with a constant-speed propeller has two controls: 

the throttle and the propeller control. The throttle controls 

power output, and the propeller control regulates engine 

rpm. This regulates propeller rpm, which is registered on 

the tachometer. 

Once a specific rpm is selected, a governor automatically 

adjusts the propeller blade angle as necessary to maintain 

the selected rpm. For example, after setting the desired rpm 

during cruising flight, an increase in airspeed or decrease in 

propeller load causes the propeller blade angle to increase 

as necessary to maintain the selected rpm. A reduction in 

airspeed or increase in propeller load causes the propeller 

blade angle to decrease. 

The propeller’s constant-speed range, defined by the high 

and low pitch stops, is the range of possible blade angles for 

a constant-speed propeller. As long as the propeller blade 

angle is within the constant-speed range and not against 

either pitch stop, a constant engine rpm is maintained. If 

the propeller blades contact a pitch stop, the engine rpm 

will increase or decrease as appropriate, with changes in 

airspeed and propeller load. For example, once a specific 

rpm has been selected, if aircraft speed decreases enough to 

rotate the propeller blades until they contact the low pitch 

stop, any further decrease in airspeed will cause engine rpm 

to decrease the same way as if a fixed-pitch propeller were 

installed. The same holds true when an aircraft equipped with 

a constant-speed propeller accelerates to a faster airspeed. As 

the aircraft accelerates, the propeller blade angle increases to 

maintain the selected rpm until the high pitch stop is reached. 

Once this occurs, the blade angle cannot increase any further 

and engine rpm increases. 

On aircraft equipped with a constant-speed propeller, power 

output is controlled by the throttle and indicated by a manifold 

pressure gauge. The gauge measures the absolute pressure of 

the fuel-air mixture inside the intake manifold and is more 

correctly a measure of manifold absolute pressure (MAP). At 

a constant rpm and altitude, the amount of power produced 

is directly related to the fuel-air mixture being delivered to 

the combustion chamber. As the throttle setting is increased, 

more fuel and air flows to the engine and MAP increases. 

When the engine is not running, the manifold pressure gauge 

indicates ambient air pressure (i.e., 29.92 inches mercury 

(29.92 "Hg)). When the engine is started, the manifold 

pressure indication decreases to a value less than ambient 

pressure (i.e., idle at 12 "Hg). Engine failure or power loss 

is indicated on the manifold gauge as an increase in manifold 

pressure to a value corresponding to the ambient air pressure 

at the altitude where the failure occurred. [Figure 7-9] 

The manifold pressure gauge is color coded to indicate the 

engine’s operating range. The face of the manifold pressure 

gauge contains a green arc to show the normal operating 

range and a red radial line to indicate the upper limit of 

manifold pressure. 

IN Hg 

ALg. 

MANIFOLD 

PRESS 

35

10 50

15

25

40

30

20

45

35 

10 50

15 

25 

40 

30 

20 

45 

Figure 7-9. Engine power output is indicated on the manifold 

pressure gauge. 

7-6 
 

For any given rpm, there is a manifold pressure that should 

not be exceeded. If manifold pressure is excessive for a given 

rpm, the pressure within the cylinders could be exceeded, 

placing undue stress on the cylinders. If repeated too 

frequently, this stress can weaken the cylinder components 

and eventually cause engine failure. 

A pilot can avoid conditions that overstress the cylinders 

by being constantly aware of the rpm, especially when 

increasing the manifold pressure. Consult the manufacturer’s 

recommendations for power settings of a particular engine to 

maintain the proper relationship between manifold pressure 

and rpm. 

When both manifold pressure and rpm need to be changed, 

avoid engine overstress by making power adjustments in 

the proper order: 

•	 When power settings are being decreased, reduce 

manifold pressure before reducing rpm. If rpm is 

reduced before manifold pressure, manifold pressure 

automatically increases, possibly exceeding the 

manufacturer’s tolerances. 

•	 When power settings are being increased, reverse the 

order—increase rpm first, then manifold pressure. 

•	 To prevent damage to radial engines, minimize 

operating time at maximum rpm and manifold 

pressure, and avoid operation at maximum rpm and 

low manifold pressure. 

The engine and/or airframe manufacturer’s recommendations 

should be followed to prevent severe wear, fatigue, and 

damage to high-performance reciprocating engines. 

Propeller Overspeed in Piston Engine Aircraft 

On March 17, 2010, the Federal Aviation Administration 

(FAA) issued Special Airworthiness Information Bulletin 

(SAIB) CE-10-21. The subject was Propellers/Propulsers; 

Propeller Overspeed in Piston Engine Aircraft to alert 

operators, pilots, and aircraft manufacturers of concerns 

for an optimum response to a propeller overspeed in piston 

engine aircraft with variable pitch propellers. Although a 

SAIB is not regulatory in nature, the FAA recommends that 

the information be read and taken into consideration for the 

safety of flight. 

The document explains that a single-engine aircraft 

experienced a propeller overspeed during cruise flight at 

7,000 feet. The pilot reported that the application of throttle 

resulted in a propeller overspeed with no appreciable thrust. 

The pilot attempted to glide to a nearby airport and established 

the “best glide” speed of 110 knots, as published in the Pilot’s 

Operating Handbook (POH), but was unable to reach the 

airport and was forced to conduct an off-field landing. 

It was further explained that a determination was made that the 

propeller experienced a failure causing the blade pitch change 

mechanism to move to the low pitch stop position. This caused 

the propeller to operate as a fixed-pitch propeller such that it 

changes rpm with changes in power and airspeed. The low 

pitch setting allows for maximum power during takeoff but 

can result in a propeller overspeed at a higher airspeed. 

A performance evaluation of the flight condition was 

performed for the particular aircraft model involved in this 

incident. This evaluation indicated that an airspeed lower 

than the best glide speed would have resulted in increased 

thrust enabling the pilot to maintain level flight. There are 

numerous variables in aircraft, engines, and propellers 

that affect aircraft performance. For some aircraft models, 

the published best glide speed may not be low enough to 

generate adequate thrust for a given propeller installation in 

this situation (propeller blades at low pitch stop position). 

The operators of aircraft with variable pitch propellers should 

be aware that in certain instances of propeller overspeed, the 

airspeed necessary to maintain level flight may be different 

than the speed associated with engine-out best glide speed. 

The appropriate emergency procedures should be followed to 

mitigate the emergency situation in the event of a propeller 

overspeed; however, pilots should be aware that some 

reduction in airspeed may result in the ability for continued 

safe flight and landing. The determination of an airspeed that 

is more suitable than engine-out best glide speed should only 

be conducted at a safe altitude when the pilot has time to 

determine an alternative course of action other than landing 

immediately. 

Induction Systems 

The induction system brings in air from the outside, mixes 

it with fuel, and delivers the fuel-air mixture to the cylinder 

where combustion occurs. Outside air enters the induction 

system through an intake port on the front of the engine 

cowling. This port normally contains an air filter that inhibits 

the entry of dust and other foreign objects. Since the filter 

may occasionally become clogged, an alternate source of 

air must be available. Usually, the alternate air comes from 

inside the engine cowling, where it bypasses a clogged air 

filter. Some alternate air sources function automatically, 

while others operate manually. 

7-7 
 

Two types of induction systems are commonly used in small 

aircraft engines: 

1.	 The carburetor system mixes the fuel and air in 

the carburetor before this mixture enters the intake 

manifold. 

2.	 The fuel injection system mixes the fuel and air 

immediately before entry into each cylinder or injects 

fuel directly into each cylinder. 

Carburetor Systems 

Aircraft carburetors are separated into two categories: floattype carburetors and pressure-type carburetors. Float-type 

carburetors, complete with idling, accelerating, mixture 

control, idle cutoff, and power enrichment systems, are the 

most common of the two carburetor types. Pressure-type 

carburetors are usually not found on small aircraft. The basic 

difference between a float-type and a pressure-type carburetor 

is the delivery of fuel. The pressure-type carburetor delivers 

fuel under pressure by a fuel pump. 

In the operation of the float-type carburetor system, the 

outside air first flows through an air filter, usually located 

at an air intake in the front part of the engine cowling. This 

filtered air flows into the carburetor and through a venturi, a 

narrow throat in the carburetor. When the air flows through 

the venturi, a low-pressure area is created that forces the 

fuel to flow through a main fuel jet located at the throat. The 

fuel then flows into the airstream where it is mixed with the 

flowing air. [Figure 7-10] 

The fuel-air mixture is then drawn through the intake 

manifold and into the combustion chambers where it is 

ignited. The float-type carburetor acquires its name from a 

float that rests on fuel within the float chamber. A needle 

attached to the float opens and closes an opening at the 

bottom of the carburetor bowl. This meters the amount of 

fuel entering into the carburetor, depending upon the position 

of the float, which is controlled by the level of fuel in the 

float chamber. When the level of the fuel forces the float 

to rise, the needle valve closes the fuel opening and shuts 

off the fuel flow to the carburetor. The needle valve opens 

again when the engine requires additional fuel. The flow of 

the fuel-air mixture to the combustion chambers is regulated 

by the throttle valve, which is controlled by the throttle in 

the flight deck. 

The float-type carburetor has several distinct disadvantages. 

First, they do not function well during abrupt maneuvers. 

Secondly, the discharge of fuel at low pressure leads to 

incomplete vaporization and difficulty in discharging 

fuel into some types of supercharged systems. The chief 

disadvantage of the float-type carburetor, however, is its 

icing tendency. Since the float-type carburetor must discharge 

Fuel 

Fuel level is maintained 

by a float-type device. 

Float chamber 

Fuel is received into 

the carburetor through 

the fuel inlet. 

Fuel inlet 

The mixture needle 

controls fuel to the 

discharge nozzle. 

Mixture needle position 

can be adjusted using 

the mixture control. 

Mixture needle 

Air enters the carburetor 

through the air inlet. 

Air inlet 

The blend of fuel and 

air is routed to the 

combustion chambers 

to be burned. 

Fuel-air mixture 

The flow of the fuel-air 

mixture is controlled by 

the throttle valve. The 

throttle valve is adjusted 

from the flight deck by 

the throttle. 

Throttle valve 

Fuel is forced through 

the discharge nozzle 

into the venturi by 

greater atmospheric 

pressure in the float 

chamber. 

Discharge nozzle 

The shape of the venturi 

creates an area of low 

pressure. 

Venturi 

The air bleed allows air to be mixed 

with fuel being drawn out of the 

discharge nozzle to decrease fuel 

density and promote fuel vaporization. 

Air bleed 

Figure 7-10. Float-type carburetor. 

7-8 
fuel at a point of low pressure, the discharge nozzle must be 

located at the venturi throat, and the throttle valve must be 

on the engine side of the discharge nozzle. This means that 

the drop in temperature due to fuel vaporization takes place 

within the venturi. As a result, ice readily forms in the venturi 

and on the throttle valve. 

A pressure-type carburetor discharges fuel into the airstream 

at a pressure well above atmospheric pressure. This results 

in better vaporization and permits the discharge of fuel into 

the airstream on the engine side of the throttle valve. With the 

discharge nozzle in this position fuel vaporization takes place 

after the air has passed through the throttle valve and at a point 

where the drop in temperature is offset by heat from the engine. 

Thus, the danger of fuel vaporization icing is practically 

eliminated. The effects of rapid maneuvers and rough air on 

the pressure-type carburetors are negligible, since their fuel 

chambers remain filled under all operating conditions. 

Mixture Control 

Carburetors are normally calibrated at sea-level air pressure 

where the correct fuel-air mixture ratio is established with the 

mixture control set in the FULL RICH position. However, as 

altitude increases, the density of air entering the carburetor 

decreases, while the density of the fuel remains the same. This 

creates a progressively richer mixture that can result in engine 

roughness and an appreciable loss of power. The roughness 

normally is due to spark plug fouling from excessive carbon 

buildup on the plugs. Carbon buildup occurs because the 

rich mixture lowers the temperature inside the cylinder, 

inhibiting complete combustion of the fuel. This condition 

may occur during the runup prior to takeoff at high-elevation 

airports and during climbs or cruise flight at high altitudes. 

To maintain the correct fuel-air mixture, the mixture must 

be leaned using the mixture control. Leaning the mixture 

decreases fuel flow, which compensates for the decreased 

air density at high altitude. 

During a descent from high altitude, the fuel-air mixture 

must be enriched, or it may become too lean. An overly lean 

mixture causes detonation, which may result in rough engine 

operation, overheating, and/or a loss of power. The best way 

to maintain the proper fuel-air mixture is to monitor the 

engine temperature and enrich the mixture as needed. Proper 

mixture control and better fuel economy for fuel-injected 

engines can be achieved by using an exhaust gas temperature 

(EGT) gauge. Since the process of adjusting the mixture can 

vary from one aircraft to another, it is important to refer to 

the airplane flight manual (AFM) or the POH to determine 

the specific procedures for a given aircraft. 

Carburetor Icing 

As mentioned earlier, one disadvantage of the float-type 

carburetor is its icing tendency. Carburetor ice occurs due 

to the effect of fuel vaporization and the decrease in air 

pressure in the venturi, which causes a sharp temperature 

drop in the carburetor. If water vapor in the air condenses 

when the carburetor temperature is at or below freezing, ice 

may form on internal surfaces of the carburetor, including 

the throttle valve. [Figure 7-11] 

The reduced air pressure, as well as the vaporization of fuel, 

contributes to the temperature decrease in the carburetor. Ice 

generally forms in the vicinity of the throttle valve and in the 

venturi throat. This restricts the flow of the fuel-air mixture 

and reduces power. If enough ice builds up, the engine may 

cease to operate. Carburetor ice is most likely to occur when 

temperatures are below 70 degrees Fahrenheit (°F) or 21 

degrees Celsius (°C) and the relative humidity is above 80 

percent. Due to the sudden cooling that takes place in the 

carburetor, icing can occur even in outside air temperatures 

as high as 100 °F (38 °C) and humidity as low as 50 percent. 

This temperature drop can be as much as 60 to 70 absolute 

(versus relative) Fahrenheit degrees (70 x 100/180 = 38.89 

Incoming air 

Venturi 

Ice 

To engine Fuel-air mixture 

Ice 

Ice 

Figure 7-11. The formation of carburetor ice may reduce or block 

fuel-air flow to the engine. 

7-9 
Celsius degrees) (Remember there are 180 Fahrenheit degrees 

from freezing to boiling versus 100 degrees for the Celsius 

scale.) Therefore, an outside air temperature of 100 F (38 C), 

a temperature drop of an absolute 70 F degrees (38.89 Celsius 

degrees) results in an air temperature in the carburetor of 30 

F (-1 C). [Figure 7-12] 

The first indication of carburetor icing in an aircraft with 

a fixed-pitch propeller is a decrease in engine rpm, which 

may be followed by engine roughness. In an aircraft with a 

constant-speed propeller, carburetor icing is usually indicated 

by a decrease in manifold pressure, but no reduction in rpm. 

Propeller pitch is automatically adjusted to compensate for 

loss of power. Thus, a constant rpm is maintained. Although 

carburetor ice can occur during any phase of flight, it is 

particularly dangerous when using reduced power during a 

descent. Under certain conditions, carburetor ice could build 

unnoticed until power is added. To combat the effects of 

carburetor ice, engines with float-type carburetors employ a 

carburetor heat system. 

Carburetor Heat 

Carburetor heat is an anti-icing system that preheats the air 

before it reaches the carburetor and is intended to keep the 

fuel-air mixture above freezing to prevent the formation of 

carburetor ice. Carburetor heat can be used to melt ice that has 

already formed in the carburetor if the accumulation is not too 

great, but using carburetor heat as a preventative measure is 

the better option. Additionally, carburetor heat may be used 

as an alternate air source if the intake filter clogs, such as in 

sudden or unexpected airframe icing conditions. The carburetor 

heat should be checked during the engine runup. When using 

carburetor heat, follow the manufacturer’s recommendations. 

When conditions are conducive to carburetor icing during 

flight, periodic checks should be made to detect its Relative humidity 

Outside air temperature 

100% 

50% 

80% 

60% 

70% 

90% 

20°F/-7°C 32°F/0°C 70°F/21°C 100°F/38°C 

High carburetor

icing potential 

Carburetor icing possible 

Figure 7-12. Although carburetor ice is most likely to form when 

the temperature and humidity are in ranges indicated by this chart, 

carburetor icing is possible under conditions not depicted. 

presence. If detected, full carburetor heat should be applied 

immediately, and it should be left in the ON position until 

the pilot is certain that all the ice has been removed. If ice 

is present, applying partial heat or leaving heat on for an 

insufficient time might aggravate the situation. In extreme 

cases of carburetor icing, even after the ice has been removed, 

full carburetor heat should be used to prevent further ice 

formation. If installed, a carburetor temperature gauge is 

useful in determining when to use carburetor heat. 

Whenever the throttle is closed during flight, the engine cools 

rapidly and vaporization of the fuel is less complete than if 

the engine is warm. Also, in this condition, the engine is more 

susceptible to carburetor icing. If carburetor icing conditions 

are suspected and closed-throttle operation anticipated, adjust 

the carburetor heat to the full ON position before closing the 

throttle and leave it on during the closed-throttle operation. 

The heat aids in vaporizing the fuel and helps prevent the 

formation of carburetor ice. Periodically, open the throttle 

smoothly for a few seconds to keep the engine warm; 

otherwise, the carburetor heater may not provide enough 

heat to prevent icing. 

The use of carburetor heat causes a decrease in engine 

power, sometimes up to 15 percent, because the heated 

air is less dense than the outside air that had been entering 

the engine. This enriches the mixture. When ice is present 

in an aircraft with a fixed-pitch propeller and carburetor 

heat is being used, there is a decrease in rpm, followed by 

a gradual increase in rpm as the ice melts. The engine also 

should run more smoothly after the ice has been removed. 

If ice is not present, the rpm decreases and then remains 

constant. When carburetor heat is used on an aircraft with a 

constant-speed propeller and ice is present, a decrease in the 

manifold pressure is noticed, followed by a gradual increase. 

If carburetor icing is not present, the gradual increase in 

manifold pressure is not apparent until the carburetor heat 

is turned off. 

It is imperative for a pilot to recognize carburetor ice when it 

forms during flight to prevent a loss in power, altitude, and/or 

airspeed. These symptoms may sometimes be accompanied 

by vibration or engine roughness. Once a power loss is 

noticed, immediate action should be taken to eliminate ice 

already formed in the carburetor and to prevent further ice 

formation. This is accomplished by applying full carburetor 

heat, which will further reduce power and may cause engine 

roughness as melted ice goes through the engine. These 

symptoms may last from 30 seconds to several minutes, 

depending on the severity of the icing. During this period, the 

pilot must resist the temptation to decrease the carburetor heat 

usage. Carburetor heat must remain in the full-hot position 

until normal power returns. 

7-10 
Since the use of carburetor heat tends to reduce the output 

of the engine and to increase the operating temperature, 

carburetor heat should not be used when full power is required 

(as during takeoff) or during normal engine operation, except 

to check for the presence of, or to remove, carburetor ice. 

Carburetor Air Temperature Gauge 

Some aircraft are equipped with a carburetor air temperature 

gauge, which is useful in detecting potential icing conditions. 

Usually, the face of the gauge is calibrated in degrees Celsius 

with a yellow arc indicating the carburetor air temperatures 

where icing may occur. This yellow arc typically ranges 

between –15 °C and +5 °C (5 °F and 41 °F). If the air 

temperature and moisture content of the air are such that 

carburetor icing is improbable, the engine can be operated 

with the indicator in the yellow range with no adverse effects. 

If the atmospheric conditions are conducive to carburetor 

icing, the indicator must be kept outside the yellow arc by 

application of carburetor heat. 

Certain carburetor air temperature gauges have a red radial 

that indicates the maximum permissible carburetor inlet air 

temperature recommended by the engine manufacturer. If 

present, a green arc indicates the normal operating range. 

Outside Air Temperature Gauge 

Most aircraft are also equipped with an outside air 

temperature (OAT) gauge calibrated in both degrees 

Celsius and Fahrenheit. It provides the outside or ambient 

air temperature for calculating true airspeed and is useful in 

detecting potential icing conditions. 

Fuel Injection Systems 

In a fuel injection system, the fuel is injected directly into 

the cylinders, or just ahead of the intake valve. The air 

intake for the fuel injection system is similar to that used 

in a carburetor system, with an alternate air source located 

within the engine cowling. This source is used if the external 

air source is obstructed. The alternate air source is usually 

operated automatically, with a backup manual system that 

can be used if the automatic feature malfunctions. 

A fuel injection system usually incorporates six basic 

components: an engine-driven fuel pump, a fuel-air control 

unit, a fuel manifold (fuel distributor), discharge nozzles, 

an auxiliary fuel pump, and fuel pressure/flow indicators. 

[Figure 7-13] 

The auxiliary fuel pump provides fuel under pressure to the 

fuel-air control unit for engine starting and/or emergency 

use. After starting, the engine-driven fuel pump provides fuel 

under pressure from the fuel tank to the fuel-air control unit. 

This control unit, which essentially replaces the carburetor, 

meters fuel based on the mixture control setting and sends it 

to the fuel manifold valve at a rate controlled by the throttle. 

Fuel tank 

Auxiliary fuel pump 

Engine-driven fuel pump 

Fuel-air control unit 

Fuel lines Fuel manifold valve 

Figure 7-13. Fuel injection system. 

7-11 
 

 

 

After reaching the fuel manifold valve, the fuel is distributed 

to the individual fuel discharge nozzles. The discharge 

nozzles, which are located in each cylinder head, inject the 

fuel-air mixture directly into each cylinder intake port. 

A fuel injection system is considered to be less susceptible 

to icing than a carburetor system, but impact icing on the air 

intake is a possibility in either system. Impact icing occurs 

when ice forms on the exterior of the aircraft and blocks 

openings, such as the air intake for the injection system. 

The following are advantages of using fuel injection: 

•	 Reduction in evaporative icing 

•	 Better fuel flow 

•	 Faster throttle response 

•	 Precise control of mixture 

•	 Better fuel distribution 

•	 Easier cold weather starts 

The following are disadvantages of using fuel injection: 

•	 Difficulty in starting a hot engine 

•	 Vapor locks during ground operations on hot days 

•	 Problems associated with restarting an engine that 

quits because of fuel starvation 

Superchargers and Turbosuperchargers 

To increase an engine’s horsepower, manufacturers have 

developed forced induction systems called supercharger 

and turbosupercharger systems. They both compress the 

intake air to increase its density. The key difference lies in 

the power supply. A supercharger relies on an engine-driven 

air pump or compressor, while a turbocharger gets its power 

from the exhaust stream that runs through a turbine, which in 

turn spins the compressor. Aircraft with these systems have 

a manifold pressure gauge, which displays MAP within the 

engine’s intake manifold. 

On a standard day at sea level with the engine shut 

down, the manifold pressure gauge indicates the ambient 

absolute air pressure of 29.92 "Hg. Because atmospheric 

pressure decreases approximately 1 "Hg per 1,000 feet of 

altitude increase, the manifold pressure gauge indicates 

approximately 24.92 "Hg at an airport that is 5,000 feet above 

sea level with standard day conditions. 

As a normally aspirated aircraft climbs, it eventually reaches 

an altitude where the MAP is insufficient for a normal climb. 

This altitude limit is known as the aircraft’s service ceiling, 

and it is directly affected by the engine’s ability to produce 

power. If the induction air entering the engine is pressurized, 

or boosted, by either a supercharger or a turbosupercharger, 

the aircraft’s service ceiling can be increased. With these 

systems, an aircraft can fly at higher altitudes with the 

advantage of higher true airspeeds and the increased ability 

to circumnavigate adverse weather. 

Superchargers 

A supercharger is an engine-driven air pump or compressor 

that provides compressed air to the engine to provide 

additional pressure to the induction air so that the engine can 

produce additional power. It increases manifold pressure and 

forces the fuel-air mixture into the cylinders. Higher manifold 

pressure increases the density of the fuel-air mixture and 

increases the power an engine can produce. With a normally 

aspirated engine, it is not possible to have manifold pressure 

higher than the existing atmospheric pressure. A supercharger 

is capable of boosting manifold pressure above 30 "Hg. 

For example, at 8,000 feet, a typical engine may be able to 

produce 75 percent of the power it could produce at mean 

sea level (MSL) because the air is less dense at the higher 

altitude. The supercharger compresses the air to a higher 

density allowing a supercharged engine to produce the same 

manifold pressure at higher altitudes as it could produce 

at sea level. Thus, an engine at 8,000 feet MSL could still 

produce 25 "Hg of manifold pressure whereas, without a 

supercharger, it could only produce 22 "Hg. Superchargers 

are especially valuable at high altitudes (such as 18,000 feet) 

where the air density is 50 percent that of sea level. The use 

of a supercharger in many cases will supply air to the engine 

at the same density it did at sea level. 

The components in a supercharged induction system are similar 

to those in a normally aspirated system, with the addition of 

a supercharger between the fuel metering device and intake 

manifold. A supercharger is driven by the engine through a 

gear train at one speed, two speeds, or variable speeds. In 

addition, superchargers can have one or more stages. Each 

stage also provides an increase in pressure and superchargers 

may be classified as single stage, two stage, or multistage, 

depending on the number of times compression occurs. 

An early version of a single-stage, single-speed supercharger 

may be referred to as a sea-level supercharger. An engine 

equipped with this type of supercharger is called a sea-level 

engine. With this type of supercharger, a single gear-driven 

impeller is used to increase the power produced by an engine 

at all altitudes. The drawback with this type of supercharger is 

a decrease in engine power output with an increase in altitude. 

Single-stage, single-speed superchargers are found on many 

high-powered radial engines and use an air intake that faces 

forward so the induction system can take full advantage of 

7-12 
 

 

 

the ram air. Intake air passes through ducts to a carburetor, 

where fuel is metered in proportion to the airflow. The 

fuel-air charge is then ducted to the supercharger, or blower 

impeller, which accelerates the fuel-air mixture outward. 

Once accelerated, the fuel-air mixture passes through a 

diffuser, where air velocity is traded for pressure energy. 

After compression, the resulting high pressure fuel-air 

mixture is directed to the cylinders. 

Some of the large radial engines developed during World 

War II have a single-stage, two-speed supercharger. With 

this type of supercharger, a single impeller may be operated 

at two speeds. The low impeller speed is often referred to 

as the low blower setting, while the high impeller speed is 

called the high blower setting. On engines equipped with a 

two-speed supercharger, a lever or switch in the flight deck 

activates an oil-operated clutch that switches from one speed 

to the other. 

Under normal operations, takeoff is made with the 

supercharger in the low blower position. In this mode, the 

engine performs as a ground-boosted engine, and the power 

output decreases as the aircraft gains altitude. However, once 

the aircraft reaches a specified altitude, a power reduction is 

made, and the supercharger control is switched to the high 

blower position. The throttle is then reset to the desired 

manifold pressure. An engine equipped with this type of 

supercharger is called an altitude engine. [Figure 7-14] 

Turbosuperchargers 

The most efficient method of increasing horsepower in an 

engine is by using a turbosupercharger or turbocharger. 

Figure 7-14. Power output of normally aspirated engine compared 

to a single-stage, two-speed supercharged engine. Brake horsepower 

Sea level Density altitude 

Two-speed supercharged engine 

High blower

Low blower 

Normally aspirated engine 

Installed on an engine, this booster uses the engine’s exhaust 

gases to drive an air compressor to increase the pressure of 

the air going into the engine through the carburetor or fuel 

injection system to boost power at higher altitude. 

The major disadvantage of the gear-driven supercharger––use 

of a large amount of the engine’s power output for the amount 

of power increase produced––is avoided with a turbocharger 

because turbochargers are powered by an engine’s exhaust 

gases. This means a turbocharger recovers energy from hot 

exhaust gases that would otherwise be lost. 

A second advantage of turbochargers over superchargers is 

the ability to maintain control over an engine’s rated sealevel horsepower from sea level up to the engine’s critical 

altitude. Critical altitude is the maximum altitude at which 

a turbocharged engine can produce its rated horsepower. 

Above the critical altitude, power output begins to decrease 

like it does for a normally aspirated engine. 

Turbochargers increase the pressure of the engine’s induction 

air, which allows the engine to develop sea level or greater 

horsepower at higher altitudes. A turbocharger is comprised 

of two main elements: a compressor and turbine. The 

compressor section houses an impeller that turns at a high rate 

of speed. As induction air is drawn across the impeller blades, 

the impeller accelerates the air, allowing a large volume of 

air to be drawn into the compressor housing. The impeller’s 

action subsequently produces high-pressure, high-density 

air that is delivered to the engine. To turn the impeller, the 

engine’s exhaust gases are used to drive a turbine wheel 

that is mounted on the opposite end of the impeller’s drive 

shaft. By directing different amounts of exhaust gases to flow 

over the turbine, more energy can be extracted, causing the 

impeller to deliver more compressed air to the engine. The 

waste gate, essentially an adjustable butterfly valve installed 

in the exhaust system, is used to vary the mass of exhaust gas 

flowing into the turbine. When closed, most of the exhaust 

gases from the engine are forced to flow through the turbine. 

When open, the exhaust gases are allowed to bypass the 

turbine by flowing directly out through the engine’s exhaust 

pipe. [Figure 7-15] 

Since the temperature of a gas rises when it is compressed, 

turbocharging causes the temperature of the induction air to 

increase. To reduce this temperature and lower the risk of 

detonation, many turbocharged engines use an intercooler. 

This small heat exchanger uses outside air to cool the hot 

compressed air before it enters the fuel metering device. 

7-13 
 

 

Exhaust gas discharge 

Pressurized air from the 

turbocharger is supplied 

to the cylinders. 

Intake manifold 

Intake air is ducted to the 

turbocharger where it is 

compressed. 

Air intake This controls the amount 

of exhaust through the 

turbine. Waste gate 

position is actuated by 

engine oil pressure. 

Waste gas 

The turbocharger incorporates a turbine, 

which is driven by exhaust gases and a compressor that pressurizes 

the incoming air. 

Turbocharger 

This regulates airflow 

to the engine. 

Throttle body 

Exhaust gas is ducted 

through the exhaust manifold and is used to turn 

the turbine which drives 

the compressor. 

Exhaust manifold 

Figure 7-15. Turbocharger components. 

System Operation 

On most modern turbocharged engines, the position of 

the waste gate is governed by a pressure-sensing control 

mechanism coupled to an actuator. Engine oil directed into 

or away from this actuator moves the waste gate position. 

On these systems, the actuator is automatically positioned to 

produce the desired MAP simply by changing the position 

of the throttle control. 

Other turbocharging system designs use a separate manual 

control to position the waste gate. With manual control, 

the manifold pressure gauge must be closely monitored to 

determine when the desired MAP has been achieved. Manual 

systems are often found on aircraft that have been modified 

with aftermarket turbocharging systems. These systems 

require special operating considerations. For example, if the 

waste gate is left closed after descending from a high altitude, 

it is possible to produce a manifold pressure that exceeds the 

engine’s limitations. This condition, called an overboost, 

may produce severe detonation because of the leaning effect 

resulting from increased air density during descent. 

Although an automatic waste gate system is less likely to 

experience an overboost condition, it can still occur. If takeoff 

power is applied while the engine oil temperature is below its 

normal operating range, the cold oil may not flow out of the 

waste gate actuator quickly enough to prevent an overboost. 

To help prevent overboosting, advance the throttle cautiously 

to prevent exceeding the maximum manifold pressure limits. 

A pilot flying an aircraft with a turbocharger should be aware 

of system limitations. For example, a turbocharger turbine 

and impeller can operate at rotational speeds in excess of 

80,000 rpm while at extremely high temperatures. To achieve 

high rotational speed, the bearings within the system must be 

constantly supplied with engine oil to reduce the frictional 

forces and high temperature. To obtain adequate lubrication, 

the oil temperature should be in the normal operating range 

before high throttle settings are applied. In addition, allow 

the turbocharger to cool and the turbine to slow down before 

shutting the engine down. Otherwise, the oil remaining in 

the bearing housing will boil, causing hard carbon deposits 

to form on the bearings and shaft. These deposits rapidly 

deteriorate the turbocharger’s efficiency and service life. For 

further limitations, refer to the AFM/POH. 

High Altitude Performance 

As an aircraft equipped with a turbocharging system climbs, 

the waste gate is gradually closed to maintain the maximum 

allowable manifold pressure. At some point, the waste gate 

is fully closed and further increases in altitude cause the 

manifold pressure to decrease. This is the critical altitude, 

7-14 
which is established by the aircraft or engine manufacturer. 

When evaluating the performance of the turbocharging 

system, be aware that if the manifold pressure begins 

decreasing before the specified critical altitude, the engine 

and turbocharging system should be inspected by a qualified 

aviation maintenance technician (AMT) to verify that the 

system is operating properly. 

Ignition System 

In a spark ignition engine, the ignition system provides a 

spark that ignites the fuel-air mixture in the cylinders and is 

made up of magnetos, spark plugs, high-tension leads, and 

an ignition switch. [Figure 7-16] 

A magneto uses a permanent magnet to generate an electrical 

current completely independent of the aircraft’s electrical 

system. The magneto generates sufficiently high voltage 

to jump a spark across the spark plug gap in each cylinder. 

The system begins to fire when the starter is engaged and the 

crankshaft begins to turn. It continues to operate whenever 

the crankshaft is rotating. 

Most standard certificated aircraft incorporate a dual ignition 

system with two individual magnetos, separate sets of wires, 

and spark plugs to increase reliability of the ignition system. 

Each magneto operates independently to fire one of the two 

spark plugs in each cylinder. The firing of two spark plugs 

improves combustion of the fuel-air mixture and results in a 

slightly higher power output. If one of the magnetos fails, the 

other is unaffected. The engine continues to operate normally, 

although a slight decrease in engine power can be expected. 

The same is true if one of the two spark plugs in a cylinder fails. 

The operation of the magneto is controlled in the flight deck 

by the ignition switch. The switch has five positions: 

1. OFF 

2. R (right) 

3. L (left) 

4. BOTH 

5. START 

With RIGHT or LEFT selected, only the associated magneto 

is activated. The system operates on both magnetos when 

BOTH is selected. 

A malfunctioning ignition system can be identified during 

the pretakeoff check by observing the decrease in rpm that 

occurs when the ignition switch is first moved from BOTH 

to RIGHT and then from BOTH to LEFT. A small decrease 

in engine rpm is normal during this check. The permissible 

decrease is listed in the AFM or POH. If the engine stops 

running when switched to one magneto or if the rpm drop 

exceeds the allowable limit, do not fly the aircraft until 

the problem is corrected. The cause could be fouled plugs, 

Upper magneto wires 

Lower magneto wires 

4 

2 

3 

1 

Upper spark plugs Lower spark plugs 

Left magneto Right magneto

Figure 7-16. Ignition system components. 

7-15 
 

broken or shorted wires between the magneto and the plugs, 

or improperly timed firing of the plugs. It should be noted 

that “no drop” in rpm is not normal, and in that instance, the 

aircraft should not be flown. 

Following engine shutdown, turn the ignition switch to the 

OFF position. Even with the battery and master switches 

OFF, the engine can fire and turn over if the ignition switch 

is left ON and the propeller is moved because the magneto 

requires no outside source of electrical power. Be aware of 

the potential for serious injury in this situation. 

Even with the ignition switch in the OFF position, if 

the ground wire between the magneto and the ignition 

switch becomes disconnected or broken, the engine could 

accidentally start if the propeller is moved with residual fuel 

in the cylinder. If this occurs, the only way to stop the engine 

is to move the mixture lever to the idle cutoff position, then 

have the system checked by a qualified AMT. 

Oil Systems 

The engine oil system performs several important functions: 

• Lubrication of the engine’s moving parts 

• Cooling of the engine by reducing friction 

• Removing heat from the cylinders 

• Providing a seal between the cylinder walls and pistons 

• Carrying away contaminants 

Reciprocating engines use either a wet-sump or a dry-sump 

oil system. In a wet-sump system, the oil is located in a sump 

that is an integral part of the engine. In a dry-sump system, 

the oil is contained in a separate tank and circulated through 

the engine by pumps. [Figure 7-17] 

The main component of a wet-sump system is the oil pump, 

which draws oil from the sump and routes it to the engine. After 

the oil passes through the engine, it returns to the sump. In 

some engines, additional lubrication is supplied by the rotating 

crankshaft, which splashes oil onto portions of the engine. 

An oil pump also supplies oil pressure in a dry-sump 

system, but the source of the oil is located external to the 

engine in a separate oil tank. After oil is routed through 

the engine, it is pumped from the various locations in the 

engine back to the oil tank by scavenge pumps. Dry-sump 

systems allow for a greater volume of oil to be supplied to 

the engine, which makes them more suitable for very large 

reciprocating engines. 

The oil pressure gauge provides a direct indication of the oil 

system operation. It ensures the pressure in pounds per square 

inch (psi) of the oil supplied to the engine. Green indicates 

the normal operating range, while red indicates the minimum 

and maximum pressures. There should be an indication of 

oil pressure during engine start. Refer to the AFM/POH for 

manufacturer limitations. 

Engine

and 

Accessory

Bearings 

200 

245 

I50 

I00 

75 

°F P 

S 

I 

II5 

60 

I00 

20 

0 OIL 

P 

R 

E 

S 

S 

T 

E 

M 

P 

Oil cooler and filter 

Oil pressure relief valve 

Oil filler cap and dipstick 

High pressure oil screen 

Oil pump 

Low pressure oil screen 

Oil sump 

Pressure oil from 

oil pump 

Sump oil and return

oil from relief valve 

Figure 7-17. Wet-sump oil system. 

7-16 
The oil temperature gauge measures the temperature of oil. 

A green area shows the normal operating range, and the red 

line indicates the maximum allowable temperature. Unlike 

oil pressure, changes in oil temperature occur more slowly. 

This is particularly noticeable after starting a cold engine, 

when it may take several minutes or longer for the gauge to 

show any increase in oil temperature. 

Check oil temperature periodically during flight especially 

when operating in high or low ambient air temperature. 

High oil temperature indications may signal a plugged oil 

line, a low oil quantity, a blocked oil cooler, or a defective 

temperature gauge. Low oil temperature indications may 

signal improper oil viscosity during cold weather operations. 

The oil filler cap and dipstick (for measuring the oil quantity) 

are usually accessible through a panel in the engine cowling. If 

the quantity does not meet the manufacturer’s recommended 

operating levels, oil should be added. The AFM/POH or 

placards near the access panel provide information about 

the correct oil type and weight, as well as the minimum and 

maximum oil quantity. [Figure 7-18] 

Engine Cooling Systems 

The burning fuel within the cylinders produces intense 

heat, most of which is expelled through the exhaust system. 

Much of the remaining heat, however, must be removed, or 

at least dissipated, to prevent the engine from overheating. 

Otherwise, the extremely high engine temperatures can lead 

to loss of power, excessive oil consumption, detonation, and 

serious engine damage. 

While the oil system is vital to the internal cooling of the 

engine, an additional method of cooling is necessary for the 

engine’s external surface. Most small aircraft are air cooled, 

although some are liquid cooled. 

Air cooling is accomplished by air flowing into the engine 

compartment through openings in front of the engine 

cowling. Baffles route this air over fins attached to the engine 

cylinders, and other parts of the engine, where the air absorbs 

the engine heat. Expulsion of the hot air takes place through 

one or more openings in the lower, aft portion of the engine 

cowling. [Figure 7-19] 

The outside air enters the engine compartment through an 

inlet behind the propeller hub. Baffles direct it to the hottest 

parts of the engine, primarily the cylinders, which have fins 

that increase the area exposed to the airflow. 

The air cooling system is less effective during ground 

operations, takeoffs, go-arounds, and other periods of highpower, low-airspeed operation. Conversely, high-speed 

descents provide excess air and can shock cool the engine, 

subjecting it to abrupt temperature fluctuations. 

Operating the engine at higher than its designed temperature 

can cause loss of power, excessive oil consumption, and 

detonation. It will also lead to serious permanent damage, 

such as scoring the cylinder walls, damaging the pistons and 

rings, and burning and warping the valves. Monitoring the 

flight deck engine temperature instruments aids in avoiding 

high operating temperature. 

Under normal operating conditions in aircraft not equipped 

with cowl flaps, the engine temperature can be controlled 

Fixed cowl opening 

Baffle 

Baffle 

Cylinders 

Air inlet 

Figure 7-18. Always check the engine oil level during the preflight Figure 7-19. Outside air aids in cooling the engine. 

inspection. 

7-17 
 

by changing the airspeed or the power output of the engine. 

High engine temperatures can be decreased by increasing the 

airspeed and/or reducing the power. 

The oil temperature gauge gives an indirect and delayed 

indication of rising engine temperature, but can be used 

for determining engine temperature if this is the only 

means available. 

Most aircraft are equipped with a cylinder-head temperature 

gauge that indicates a direct and immediate cylinder 

temperature change. This instrument is calibrated in degrees 

Celsius or Fahrenheit and is usually color coded with a green 

arc to indicate the normal operating range. A red line on 

the instrument indicates maximum allowable cylinder head 

temperature. 

To avoid excessive cylinder head temperatures, increase 

airspeed, enrich the fuel-air mixture, and/or reduce 

power. Any of these procedures help to reduce the engine 

temperature. On aircraft equipped with cowl flaps, use the 

cowl flap positions to control the temperature. Cowl flaps 

are hinged covers that fit over the opening through which the 

hot air is expelled. If the engine temperature is low, the cowl 

flaps can be closed, thereby restricting the flow of expelled 

hot air and increasing engine temperature. If the engine 

temperature is high, the cowl flaps can be opened to permit 

a greater flow of air through the system, thereby decreasing 

the engine temperature. 

Exhaust Systems 

Engine exhaust systems vent the burned combustion gases 

overboard, provide heat for the cabin, and defrost the 

windscreen. An exhaust system has exhaust piping attached 

to the cylinders, as well as a muffler and a muffler shroud. 

The exhaust gases are pushed out of the cylinder through 

the exhaust valve and then through the exhaust pipe system 

to the atmosphere. 

For cabin heat, outside air is drawn into the air inlet and is 

ducted through a shroud around the muffler. The muffler is 

heated by the exiting exhaust gases and, in turn, heats the 

air around the muffler. This heated air is then ducted to the 

cabin for heat and defrost applications. The heat and defrost 

are controlled in the flight deck and can be adjusted to the 

desired level. 

Exhaust gases contain large amounts of carbon monoxide, 

which is odorless and colorless. Carbon monoxide is deadly, 

and its presence is virtually impossible to detect. To ensure 

that exhaust gases are properly expelled, the exhaust system 

must be in good condition and free of cracks. 

Some exhaust systems have an EGT probe. This probe 

transmits the EGT to an instrument in the flight deck. The 

EGT gauge measures the temperature of the gases at the 

exhaust manifold. This temperature varies with the ratio of 

fuel to air entering the cylinders and can be used as a basis 

for regulating the fuel-air mixture. The EGT gauge is highly 

accurate in indicating the correct fuel-air mixture setting. 

When using the EGT to aid in leaning the fuel-air mixture, 

fuel consumption can be reduced. For specific procedures, 

refer to the manufacturer’s recommendations for leaning the 

fuel-air mixture. 

Starting System 

Most small aircraft use a direct-cranking electric starter 

system. This system consists of a source of electricity, wiring, 

switches, and solenoids to operate the starter and a starter 

motor. Most aircraft have starters that automatically engage 

and disengage when operated, but some older aircraft have 

starters that are mechanically engaged by a lever actuated by 

the pilot. The starter engages the aircraft flywheel, rotating 

the engine at a speed that allows the engine to start and 

maintain operation. 

Electrical power for starting is usually supplied by an onboard 

battery, but can also be supplied by external power through 

an external power receptacle. When the battery switch is 

turned on, electricity is supplied to the main power bus bar 

through the battery solenoid. Both the starter and the starter 

switch draw current from the main bus bar, but the starter 

will not operate until the starting solenoid is energized by 

the starter switch being turned to the “start” position. When 

the starter switch is released from the “start” position, the 

solenoid removes power from the starter motor. The starter 

motor is protected from being driven by the engine through a 

clutch in the starter drive that allows the engine to run faster 

than the starter motor. [Figure 7-20] 

When starting an engine, the rules of safety and courtesy 

should be strictly observed. One of the most important safety 

rules is to ensure there is no one near the propeller prior to 

starting the engine. In addition, the wheels should be chocked 

and the brakes set to avoid hazards caused by unintentional 

movement. To avoid damage to the propeller and property, 

the aircraft should be in an area where the propeller will not 

stir up gravel or dust. 

Combustion 

During normal combustion, the fuel-air mixture burns in a 

very controlled and predictable manner. In a spark ignition 

engine, the process occurs in a fraction of a second. The 

mixture actually begins to burn at the point where it is ignited 

7-18 
M 

A 

I 

N 

B 

U 

S 

Starter 

Battery 

A

L

T 

B

A

T 

Battery

contactor 

(solenoid) 

Starter 

contactor 

External 

power

relay 

+ 

+ 

OFF 

L 

R B 

S 

Ignition switch 

External 

power plug 

Figure 7-20. Typical starting circuit. 

by the spark plugs. It then burns away from the plugs until it 

is completely consumed. This type of combustion causes a 

smooth build-up of temperature and pressure and ensures that 

the expanding gases deliver the maximum force to the piston 

at exactly the right time in the power stroke. [Figure 7-21] 

Detonation is an uncontrolled, explosive ignition of the 

fuel-air mixture within the cylinder’s combustion chamber. 

It causes excessive temperatures and pressures which, if not 

corrected, can quickly lead to failure of the piston, cylinder, 

or valves. In less severe cases, detonation causes engine 

overheating, roughness, or loss of power. 

Detonation is characterized by high cylinder head temperatures 

and is most likely to occur when operating at high power 

settings. Common operational causes of detonation are: 

•	 Use of a lower fuel grade than that specified by the 

aircraft manufacturer 

•	 Operation of the engine with extremely high manifold 

pressures in conjunction with low rpm 

•	 Operation of the engine at high power settings with 

an excessively lean mixture 

Normal combustion Explosion

Figure 7-21. Normal combustion and explosive combustion. 

•	 Maintaining extended ground operations or steep 

climbs in which cylinder cooling is reduced 

Detonation may be avoided by following these basic 

guidelines during the various phases of ground and flight 

operations: 

•	 Ensure that the proper grade of fuel is used. 

•	 Keep the cowl flaps (if available) in the full-open 

position while on the ground to provide the maximum 

airflow through the cowling. 

•	 Use an enriched fuel mixture, as well as a shallow 

climb angle, to increase cylinder cooling during 

takeoff and initial climb. 

•	 Avoid extended, high power, steep climbs. 

•	 Develop the habit of monitoring the engine instruments 

to verify proper operation according to procedures 

established by the manufacturer. 

Preignition occurs when the fuel-air mixture ignites prior 

to the engine’s normal ignition event. Premature burning 

is usually caused by a residual hot spot in the combustion 

chamber, often created by a small carbon deposit on a spark 

plug, a cracked spark plug insulator, or other damage in the 

cylinder that causes a part to heat sufficiently to ignite the 

fuel-air charge. Preignition causes the engine to lose power 

and produces high operating temperature. As with detonation, 

preignition may also cause severe engine damage because 

the expanding gases exert excessive pressure on the piston 

while still on its compression stroke. 

7-19 
 

Detonation and preignition often occur simultaneously and 

one may cause the other. Since either condition causes high 

engine temperature accompanied by a decrease in engine 

performance, it is often difficult to distinguish between the 

two. Using the recommended grade of fuel and operating 

the engine within its proper temperature, pressure, and rpm 

ranges reduce the chance of detonation or preignition. 

Full Authority Digital Engine Control

(FADEC) 

FADEC is a system consisting of a digital computer and 

ancillary components that control an aircraft’s engine 

and propeller. First used in turbine-powered aircraft, and 

referred to as full authority digital electronic control, these 

sophisticated control systems are increasingly being used in 

piston powered aircraft. 

In a spark-ignition reciprocating engine, the FADEC uses 

speed, temperature, and pressure sensors to monitor the status 

of each cylinder. A digital computer calculates the ideal pulse 

for each injector and adjusts ignition timing as necessary 

to achieve optimal performance. In a compression-ignition 

engine, the FADEC operates similarly and performs all of 

the same functions, excluding those specifically related to 

the spark ignition process. 

FADEC systems eliminate the need for magnetos, carburetor 

heat, mixture controls, and engine priming. A single throttle 

lever is characteristic of an aircraft equipped with a FADEC 

system. The pilot simply positions the throttle lever to a 

desired detent, such as start, idle, cruise power, or max power, 

and the FADEC system adjusts the engine and propeller 

automatically for the mode selected. There is no need for the 

pilot to monitor or control the fuel-air mixture. 

During aircraft starting, the FADEC primes the cylinders, 

adjusts the mixture, and positions the throttle based on engine 

temperature and ambient pressure. During cruise flight, the 

FADEC constantly monitors the engine and adjusts fuel flow 

and ignition timing individually in each cylinder. This precise 

control of the combustion process often results in decreased 

fuel consumption and increased horsepower. 

FADEC systems are considered an essential part of the 

engine and propeller control and may be powered by the 

aircraft’s main electrical system. In many aircraft, FADEC 

uses power from a separate generator connected to the engine. 

In either case, there must be a backup electrical source 

available because failure of a FADEC system could result in a 

complete loss of engine thrust. To prevent loss of thrust, two 

separate and identical digital channels are incorporated for 

redundancy. Each channel is capable of providing all engine 

and propeller functions without limitations. 

Turbine Engines 

An aircraft turbine engine consists of an air inlet, compressor, 

combustion chambers, a turbine section, and exhaust. Thrust 

is produced by increasing the velocity of the air flowing 

through the engine. Turbine engines are highly desirable 

aircraft powerplants. They are characterized by smooth 

operation and a high power-to-weight ratio, and they 

use readily available jet fuel. Prior to recent advances in 

material, engine design, and manufacturing processes, the 

use of turbine engines in small/light production aircraft was 

cost prohibitive. Today, several aviation manufacturers are 

producing or plan to produce small/light turbine-powered 

aircraft. These smaller turbine-powered aircraft typically 

seat between three and seven passengers and are referred to 

as very light jets (VLJs) or microjets. [Figure 7-22] 

Types of Turbine Engines 

Turbine engines are classified according to the type of 

compressors they use. There are three types of compressors— 

centrifugal flow, axial flow, and centrifugal-axial flow. 

Compression of inlet air is achieved in a centrifugal flow 

engine by accelerating air outward perpendicular to the 

longitudinal axis of the machine. The axial-flow engine 

compresses air by a series of rotating and stationary 

airfoils moving the air parallel to the longitudinal axis. The 

centrifugal-axial flow design uses both kinds of compressors 

to achieve the desired compression. 

The path the air takes through the engine and how power is 

produced determines the type of engine. There are four types 

of aircraft turbine engines—turbojet, turboprop, turbofan, 

and turboshaft. 

Turbojet 

The turbojet engine consists of four sections—compressor, 

combustion chamber, turbine section, and exhaust. The 

compressor section passes inlet air at a high rate of speed to 

Figure 7-22. Eclipse 500 VLJ. 

7-20 
 

the combustion chamber. The combustion chamber contains 

the fuel inlet and igniter for combustion. The expanding 

air drives a turbine, which is connected by a shaft to the 

compressor, sustaining engine operation. The accelerated 

exhaust gases from the engine provide thrust. This is a basic 

application of compressing air, igniting the fuel-air mixture, 

producing power to self-sustain the engine operation, and 

exhaust for propulsion. [Figure 7-23] 

Turbojet engines are limited in range and endurance. They 

are also slow to respond to throttle applications at slow 

compressor speeds. 

Turboprop 

A turboprop engine is a turbine engine that drives a propeller 

through a reduction gear. The exhaust gases drive a power 

turbine connected by a shaft that drives the reduction gear 

assembly. Reduction gearing is necessary in turboprop 

engines because optimum propeller performance is achieved 

at much slower speeds than the engine’s operating rpm. 

Turboprop engines are a compromise between turbojet 

engines and reciprocating powerplants. Turboprop engines 

are most efficient at speeds between 250 and 400 mph and 

altitudes between 18,000 and 30,000 feet. They also perform 

well at the slow airspeeds required for takeoff and landing and 

are fuel efficient. The minimum specific fuel consumption 

of the turboprop engine is normally available in the altitude 

range of 25,000 feet to the tropopause. [Figure 7-24] 

Turbofan 

Turbofans were developed to combine some of the best 

features of the turbojet and the turboprop. Turbofan engines 

are designed to create additional thrust by diverting a 

secondary airflow around the combustion chamber. The 

turbofan bypass air generates increased thrust, cools the 

engine, and aids in exhaust noise suppression. This provides 

turbojet-type cruise speed and lower fuel consumption. 

The inlet air that passes through a turbofan engine is usually 

divided into two separate streams of air. One stream passes 

through the engine core, while a second stream bypasses the 

engine core. It is this bypass stream of air that is responsible 

for the term “bypass engine.” A turbofan’s bypass ratio refers 

to the ratio of the mass airflow that passes through the fan 

divided by the mass airflow that passes through the engine 

core. [Figure 7-25] 

Turboshaft 

The fourth common type of jet engine is the turboshaft. 

[Figure 7-26] It delivers power to a shaft that drives 

something other than a propeller. The biggest difference 

between a turbojet and turboshaft engine is that on a 

Fuel injector 

Inlet 

Compressor Combustion chamber 

Turbine 

Hot gases 

Nozzle 

Figure 7-23. Turbojet engine. 

Gear box Compressor Combustion chamber

Exhaust 

Fuel injector 

Inlet 

Prop Turbine 

Figure 7-24. Turboprop engine. 

7-21 
 

Inlet Fuel injector 

Compressor Combustion chamber

Turbine 

Hot gases 

Nozzle 

Duct fan 

Secondary air stream 

Primary air stream 

Figure 7-25. Turbofan engine. 

Inlet Compressor Combustion chamber Exhaust

Free (power) turbine 

Compressor turbine 

Power shaft 

Figure 7-26. Turboshaft engine. 

turboshaft engine, most of the energy produced by the 

expanding gases is used to drive a turbine rather than produce 

thrust. Many helicopters use a turboshaft gas turbine engine. 

In addition, turboshaft engines are widely used as auxiliary 

power units on large aircraft. 

Turbine Engine Instruments 

Engine instruments that indicate oil pressure, oil temperature, 

engine speed, exhaust gas temperature, and fuel flow are 

common to both turbine and reciprocating engines. However, 

there are some instruments that are unique to turbine engines. 

These instruments provide indications of engine pressure 

ratio, turbine discharge pressure, and torque. In addition, 

most gas turbine engines have multiple temperature-sensing 

instruments, called thermocouples, which provide pilots with 

temperature readings in and around the turbine section. 

Engine Pressure Ratio (EPR) 

An engine pressure ratio (EPR) gauge is used to indicate the 

power output of a turbojet/turbofan engine. EPR is the ratio 

of turbine discharge to compressor inlet pressure. Pressure 

measurements are recorded by probes installed in the engine 

inlet and at the exhaust. Once collected, the data is sent to 

a differential pressure transducer, which is indicated on a 

flight deck EPR gauge. 

EPR system design automatically compensates for the effects 

of airspeed and altitude. Changes in ambient temperature 

require a correction be applied to EPR indications to provide 

accurate engine power settings. 

Exhaust Gas Temperature (EGT) 

A limiting factor in a gas turbine engine is the temperature 

of the turbine section. The temperature of a turbine section 

must be monitored closely to prevent overheating the turbine 

blades and other exhaust section components. One common 

way of monitoring the temperature of a turbine section is 

with an EGT gauge. EGT is an engine operating limit used 

to monitor overall engine operating conditions. 

Variations of EGT systems bear different names based on 

the location of the temperature sensors. Common turbine 

temperature sensing gauges include the turbine inlet 

temperature (TIT) gauge, turbine outlet temperature (TOT) 

gauge, interstage turbine temperature (ITT) gauge, and 

turbine gas temperature (TGT) gauge. 

Torquemeter 

Turboprop/turboshaft engine power output is measured 

by the torquemeter. Torque is a twisting force applied to a 

shaft. The torquemeter measures power applied to the shaft. 

7-22 
Turboprop and turboshaft engines are designed to produce 

torque for driving a propeller. Torquemeters are calibrated 

in percentage units, foot-pounds, or psi. 

N1 Indicator 

N1 represents the rotational speed of the low pressure 

compressor and is presented on the indicator as a percentage 

of design rpm. After start, the speed of the low pressure 

compressor is governed by the N1 turbine wheel. The N1 

turbine wheel is connected to the low pressure compressor 

through a concentric shaft. 

N2 Indicator 

N2 represents the rotational speed of the high pressure 

compressor and is presented on the indicator as a percentage of 

design rpm. The high pressure compressor is governed by the 

N2 turbine wheel. The N2 turbine wheel is connected to the high 

pressure compressor through a concentric shaft. [Figure 7-27] 

Turbine Engine Operational Considerations 

The great variety of turbine engines makes it impractical to 

cover specific operational procedures, but there are certain 

operational considerations common to all turbine engines. 

They are engine temperature limits, foreign object damage, 

hot start, compressor stall, and flameout. 

Engine Temperature Limitations 

The highest temperature in any turbine engine occurs at the 

turbine inlet. TIT is therefore usually the limiting factor in 

turbine engine operation. 

Thrust Variations 

Turbine engine thrust varies directly with air density. As air 

density decreases, so does thrust. Additionally, because air 

density decreases with an increase in temperature, increased 

Figure 7-27. Dual-spool axial-flow compressor. 

Low pressure 

compressor (N1) 

High pressure 

compressor (N2) 

Low pressure compressor drive shaft 

High pressure compressor drive shaft 

temperatures also results in decreased thrust. While both 

turbine and reciprocating powered engines are affected to 

some degree by high relative humidity, turbine engines will 

experience a negligible loss of thrust, while reciprocating 

engines a significant loss of brake horsepower. 

Foreign Object Damage (FOD) 

Due to the design and function of a turbine engine’s air inlet, 

the possibility of ingestion of debris always exists. This 

causes significant damage, particularly to the compressor 

and turbine sections. When ingestion of debris occurs, it is 

called foreign object damage (FOD). Typical FOD consists 

of small nicks and dents caused by ingestion of small objects 

from the ramp, taxiway, or runway, but FOD damage caused 

by bird strikes or ice ingestion also occur. Sometimes FOD 

results in total destruction of an engine. 

Prevention of FOD is a high priority. Some engine inlets 

have a tendency to form a vortex between the ground and 

the inlet during ground operations. A vortex dissipater may 

be installed on these engines. Other devices, such as screens 

and/or deflectors, may also be utilized. Preflight procedures 

include a visual inspection for any sign of FOD. 

Turbine Engine Hot/Hung Start 

When the EGT exceeds the safe limit of an aircraft, it 

experiences a “hot start.” This is caused by too much fuel 

entering the combustion chamber or insufficient turbine rpm. 

Any time an engine has a hot start, refer to the AFM/POH or an 

appropriate maintenance manual for inspection requirements. 

If the engine fails to accelerate to the proper speed after 

ignition or does not accelerate to idle rpm, a hung or false start 

has occurred. A hung start may be caused by an insufficient 

starting power source or fuel control malfunction. 

Compressor Stalls 

Compressor blades are small airfoils and are subject to the 

same aerodynamic principles that apply to any airfoil. A 

compressor blade has an AOA that is a result of inlet air 

velocity and the compressor’s rotational velocity. These two 

forces combine to form a vector, which defines the airfoil’s 

actual AOA to the approaching inlet air. 

A compressor stall is an imbalance between the two vector 

quantities, inlet velocity, and compressor rotational speed. 

Compressor stalls occur when the compressor blades’ AOA 

exceeds the critical AOA. At this point, smooth airflow 

is interrupted and turbulence is created with pressure 

fluctuations. Compressor stalls cause air flowing in the 

compressor to slow down and stagnate, sometimes reversing 

direction. [Figure 7-28] 

7-23 
 

 

Normal inlet airflow 

Distorted inlet airflow 

Figure 7-28. Comparison of normal and distorted airflow into the 

compressor section. 

Compressor stalls can be transient and intermittent or steady 

and severe. Indications of a transient/intermittent stall are 

usually an intermittent “bang” as backfire and flow reversal 

take place. If the stall develops and becomes steady, strong 

vibration and a loud roar may develop from the continuous 

flow reversal. Often, the flight deck gauges do not show 

a mild or transient stall, but they do indicate a developed 

stall. Typical instrument indications include fluctuations 

in rpm and an increase in exhaust gas temperature. Most 

transient stalls are not harmful to the engine and often correct 

themselves after one or two pulsations. The possibility of 

severe engine damage from a steady state stall is immediate. 

Recovery must be accomplished by quickly reducing power, 

decreasing the aircraft’s AOA, and increasing airspeed. 

Although all gas turbine engines are subject to compressor 

stalls, most models have systems that inhibit them. One 

system uses a variable inlet guide vane (VIGV) and variable 

stator vanes that direct the incoming air into the rotor blades 

at an appropriate angle. To prevent air pressure stalls, 

operate the aircraft within the parameters established by the 

manufacturer. If a compressor stall does develop, follow the 

procedures recommended in the AFM/POH. 

Flameout 

A flameout occurs in the operation of a gas turbine engine in 

which the fire in the engine unintentionally goes out. If the 

rich limit of the fuel-air ratio is exceeded in the combustion 

chamber, the flame will blow out. This condition is often 

referred to as a rich flameout. It generally results from 

very fast engine acceleration where an overly rich mixture 

causes the fuel temperature to drop below the combustion 

temperature. It may also be caused by insufficient airflow 

to support combustion. 

A more common flameout occurrence is due to low fuel 

pressure and low engine speeds, which typically are 

associated with high-altitude flight. This situation may also 

occur with the engine throttled back during a descent, which 

can set up the lean-condition flameout. A weak mixture can 

easily cause the flame to die out, even with a normal airflow 

through the engine. 

Any interruption of the fuel supply can result in a 

flameout. This may be due to prolonged unusual attitudes, 

a malfunctioning fuel control system, turbulence, icing, or 

running out of fuel. 

Symptoms of a flameout normally are the same as those 

following an engine failure. If the flameout is due to a 

transitory condition, such as an imbalance between fuel 

flow and engine speed, an airstart may be attempted once 

the condition is corrected. In any case, pilots must follow 

the applicable emergency procedures outlined in the AFM/ 

POH. Generally these procedures contain recommendations 

concerning altitude and airspeed where the airstart is most 

likely to be successful. 

Performance Comparison 

It is possible to compare the performance of a reciprocating 

powerplant and different types of turbine engines. For 

the comparison to be accurate, thrust horsepower (usable 

horsepower) for the reciprocating powerplant must be used 

rather than brake horsepower, and net thrust must be used 

for the turbine-powered engines. In addition, aircraft design 

configuration and size must be approximately the same. 

When comparing performance, the following definitions 

are useful: 

•	 Brake horsepower (BHP)—the horsepower actually 

delivered to the output shaft. Brake horsepower is the 

actual usable horsepower. 

•	 Net thrust—the thrust produced by a turbojet or 

turbofan engine. 

•	 Thrust horsepower (THP)—the horsepower equivalent 

of the thrust produced by a turbojet or turbofan engine. 

Equivalent shaft horsepower (ESHP)—with respect 

to turboprop engines, the sum of the shaft horsepower 

(SHP) delivered to the propeller and THP produced by the 

exhaust gases. 

Figure 7-29 shows how four types of engines compare in net 

thrust as airspeed is increased. This figure is for explanatory 

7-24 
Net thrust

 Airspeed 

Aircraft drag 

A B C D E F 

Reciprocating 

Turboprop 

Turbofan 

Turbojet 

Figure 7-29. Engine net thrust versus aircraft speed and drag. Points 

a through f are explained in the text below.

purposes only and is not for specific models of engines. The 

following are the four types of engines: 

• Reciprocating powerplant

• Turbine, propeller combination (turboprop)

• Turbine engine incorporating a fan (turbofan)

• Turbojet (pure jet)

By plotting the performance curve for each engine, a 

comparison can be made of maximum aircraft speed variation 

with the type of engine used. Since the graph is only a means 

of comparison, numerical values for net thrust, aircraft speed, 

and drag are not included. 

Comparison of the four powerplants on the basis of net thrust 

makes certain performance capabilities evident. In the speed 

range shown to the left of line A, the reciprocating powerplant 

outperforms the other three types. The turboprop outperforms 

the turbofan in the range to the left of line C. The turbofan 

engine outperforms the turbojet in the range to the left of 

line F. The turbofan engine outperforms the reciprocating 

powerplant to the right of line B and the turboprop to the 

right of line C. The turbojet outperforms the reciprocating 

powerplant to the right of line D, the turboprop to the right 

of line E, and the turbofan to the right of line F. 

The points where the aircraft drag curve intersects the net 

thrust curves are the maximum aircraft speeds. The vertical 

lines from each of the points to the baseline of the graph 

indicate that the turbojet aircraft can attain a higher maximum 

speed than aircraft equipped with the other types of engines. 

Aircraft equipped with the turbofan engine attains a higher 

maximum speed than aircraft equipped with a turboprop or 

reciprocating powerplant. 

Airframe Systems 

Fuel, electrical, hydraulic, and oxygen systems make up the 

airframe systems. 

Fuel Systems 

The fuel system is designed to provide an uninterrupted 

flow of clean fuel from the fuel tanks to the engine. The 

fuel must be available to the engine under all conditions 

of engine power, altitude, attitude, and during all approved 

flight maneuvers. Two common classifications apply to fuel 

systems in small aircraft: gravity-feed and fuel-pump systems. 

Gravity-Feed System 

The gravity-feed system utilizes the force of gravity to 

transfer the fuel from the tanks to the engine. For example, on 

high-wing airplanes, the fuel tanks are installed in the wings. 

This places the fuel tanks above the carburetor, and the fuel 

is gravity fed through the system and into the carburetor. If 

the design of the aircraft is such that gravity cannot be used 

to transfer fuel, fuel pumps are installed. For example, on 

low-wing airplanes, the fuel tanks in the wings are located 

below the carburetor. [Figure 7-30] 

Fuel-Pump System 

Aircraft with fuel-pump systems have two fuel pumps. The 

main pump system is engine driven with an electricallydriven auxiliary pump provided for use in engine starting 

and in the event the engine pump fails. The auxiliary pump, 

also known as a boost pump, provides added reliability to 

the fuel system. The electrically-driven auxiliary pump is 

controlled by a switch in the flight deck. 

Fuel Primer 

Both gravity-feed and fuel-pump systems may incorporate a 

fuel primer into the system. The fuel primer is used to draw 

fuel from the tanks to vaporize fuel directly into the cylinders 

prior to starting the engine. During cold weather, when 

engines are difficult to start, the fuel primer helps because 

there is not enough heat available to vaporize the fuel in the 

carburetor. It is important to lock the primer in place when 

it is not in use. If the knob is free to move, it may vibrate 

out of position during flight which may cause an excessively 

rich fuel-air mixture. To avoid overpriming, read the priming 

instructions for the aircraft. 

Fuel Tanks 

The fuel tanks, normally located inside the wings of an 

airplane, have a filler opening on top of the wing through 

which they can be filled. A filler cap covers this opening. 

7-25 
Gravity-feed system 

Fuel-pump system 

Engine-driven pump 

Right tank 

Right tank

 Left tank

 Left tank 

BOTH 

LEFT

RIGHT 

OFF 

BOTH 

LEFT

RIGHT 

OFF 

Selector valve 

Carburetor 

Primer 

Strainer 

Vent 

Selector valve 

Carburetor 

Electric pump 

Strainer 

Primer 

Figure 7-30. Gravity-feed and fuel-pump systems. 

The tanks are vented to the outside to maintain atmospheric 

pressure inside the tank. They may be vented through the 

filler cap or through a tube extending through the surface 

of the wing. Fuel tanks also include an overflow drain that 

may stand alone or be collocated with the fuel tank vent. 

This allows fuel to expand with increases in temperature 

without damage to the tank itself. If the tanks have been 

filled on a hot day, it is not unusual to see fuel coming from 

the overflow drain. 

Fuel Gauges 

The fuel quantity gauges indicate the amount of fuel 

measured by a sensing unit in each fuel tank and is displayed 

in gallons or pounds. Aircraft certification rules require 

accuracy in fuel gauges only when they read “empty.” Any 

reading other than “empty” should be verified. Do not depend 

solely on the accuracy of the fuel quantity gauges. Always 

visually check the fuel level in each tank during the preflight 

inspection, and then compare it with the corresponding fuel 

quantity indication. 

If a fuel pump is installed in the fuel system, a fuel pressure 

gauge is also included. This gauge indicates the pressure in 

the fuel lines. The normal operating pressure can be found 

in the AFM/POH or on the gauge by color coding. 

Fuel Selectors 

The fuel selector valve allows selection of fuel from various 

tanks. A common type of selector valve contains four 

positions: LEFT, RIGHT, BOTH, and OFF. Selecting the 

LEFT or RIGHT position allows fuel to feed only from the 

respective tank, while selecting the BOTH position feeds 

fuel from both tanks. The LEFT or RIGHT position may be 

used to balance the amount of fuel remaining in each wing 

tank. [Figure 7-31] 

Fuel placards show any limitations on fuel tank usage, such 

as “level flight only” and/or “both” for landings and takeoffs. 

Regardless of the type of fuel selector in use, fuel 

consumption should be monitored closely to ensure that a 

tank does not run completely out of fuel. Running a fuel tank 

dry does not only cause the engine to stop, but running for 

prolonged periods on one tank causes an unbalanced fuel load 

between tanks. Running a tank completely dry may allow air 

to enter the fuel system and cause vapor lock, which makes 

it difficult to restart the engine. On fuel-injected engines, the 

fuel becomes so hot it vaporizes in the fuel line, not allowing 

fuel to reach the cylinders. 

Figure 7-31. Fuel selector valve.

 LEFT 

19 gal 

LEVEL 

FLIGHT 

ONLY 

RIGHT 

19 gal 

LEVEL 

FLIGHT 

ONLY 

OFF 

TAKEOFF 

LANDING 

ALL FLIGHT 38 GAL ATTITUDES 

BOTH 

7-26 
 

 

Fuel Strainers, Sumps, and Drains 

After leaving the fuel tank and before it enters the carburetor, 

the fuel passes through a strainer that removes any moisture 

and other sediments in the system. Since these contaminants 

are heavier than aviation fuel, they settle in a sump at the 

bottom of the strainer assembly. A sump is a low point in a fuel 

system and/or fuel tank. The fuel system may contain a sump, 

a fuel strainer, and fuel tank drains, which may be collocated. 

The fuel strainer should be drained before each flight. Fuel 

samples should be drained and checked visually for water 

and contaminants. 

Water in the sump is hazardous because in cold weather the 

water can freeze and block fuel lines. In warm weather, it 

can flow into the carburetor and stop the engine. If water is 

present in the sump, more water in the fuel tanks is probable, 

and they should be drained until there is no evidence of water. 

Never take off until all water and contaminants have been 

removed from the engine fuel system. 

Because of the variation in fuel systems, become thoroughly 

familiar with the systems that apply to the aircraft being flown. 

Consult the AFM/POH for specific operating procedures. 

Fuel Grades 

Aviation gasoline (AVGAS) is identified by an octane or 

performance number (grade), which designates the antiknock 

value or knock resistance of the fuel mixture in the engine 

cylinder. The higher the grade of gasoline, the more pressure 

the fuel can withstand without detonating. Lower grades of 

fuel are used in lower-compression engines because these 

fuels ignite at a lower temperature. Higher grades are used 

in higher-compression engines because they ignite at higher 

temperatures, but not prematurely. If the proper grade of fuel 

is not available, use the next higher grade as a substitute. Never 

use a grade lower than recommended. This can cause the 

cylinder head temperature and engine oil temperature to exceed 

their normal operating ranges, which may result in detonation. 

Several grades of AVGAS are available. Care must be 

exercised to ensure that the correct aviation grade is being 

used for the specific type of engine. The proper fuel grade is 

stated in the AFM/POH, on placards in the flight deck, and 

next to the filler caps. Automobile gas should NEVER be 

used in aircraft engines unless the aircraft has been modified 

with a Supplemental Type Certificate (STC) issued by the 

Federal Aviation Administration (FAA). 

The current method identifies AVGAS for aircraft with 

reciprocating engines by the octane and performance number, 

along with the abbreviation AVGAS. These aircraft use 

AVGAS 80, 100, and 100LL. Although AVGAS 100LL 

performs the same as grade 100, the “LL” indicates it has 

a low lead content. Fuel for aircraft with turbine engines is 

classified as JET A, JET A-1, and JET B. Jet fuel is basically 

kerosene and has a distinctive kerosene smell. Since use of 

the correct fuel is critical, dyes are added to help identify the 

type and grade of fuel. [Figure 7-32] 

In addition to the color of the fuel itself, the color-coding 

system extends to decals and various airport fuel handling 

equipment. For example, all AVGAS is identified by name, 

using white letters on a red background. In contrast, turbine 

fuels are identified by white letters on a black background. 

Special Airworthiness Information Bulleting (SAIB) 

NE-11-15 advises that grade 100VLL AVGAS is acceptable 

for use on aircraft and engines. 100VLL meets all 

performance requirements of grades 80, 91, 100, and 100LL; 

meets the approved operating limitations for aircraft and 

engines certificated to operate with these other grades of 

AVGAS; and is basically identical to 100LL AVGAS. The 

lead content of 100VLL is reduced by about 19 percent. 

100VLL is blue like 100LL and virtually indistinguishable. 

Fuel Contamination 

Accidents attributed to powerplant failure from fuel 

contamination have often been traced to: 

•	 Inadequate preflight inspection by the pilot 

•	 Servicing aircraft with improperly filtered fuel from 

small tanks or drums 

•	 Storing aircraft with partially filled fuel tanks 

•	 Lack of proper maintenance 

Fuel should be drained from the fuel strainer quick drain and 

from each fuel tank sump into a transparent container and 

then checked for dirt and water. When the fuel strainer is 

being drained, water in the tank may not appear until all the 

fuel has been drained from the lines leading to the tank. This 

indicates that water remains in the tank and is not forcing the 

fuel out of the fuel lines leading to the fuel strainer. Therefore, 

drain enough fuel from the fuel strainer to be certain that 

fuel is being drained from the tank. The amount depends on 

Figure 7-32. Aviation fuel color-coding system. 

80 

AVGAS 

100 

AVGAS 

100LL 

AVGAS 

JET 

A 

AVGAS 

100LL 

AVGAS 

80 

AVGAS 

100 JET A 

RED GREEN BLUE COLORLESS 

OR STRAW 

7-27 
the length of fuel line from the tank to the drain. If water or 

other contaminants are found in the first sample, drain further 

samples until no trace appears. 

Water may also remain in the fuel tanks after the drainage 

from the fuel strainer has ceased to show any trace of water. 

This residual water can be removed only by draining the fuel 

tank sump drains. 

Water is the principal fuel contaminant. Suspended water 

droplets in the fuel can be identified by a cloudy appearance 

of the fuel, or by the clear separation of water from the colored 

fuel, which occurs after the water has settled to the bottom 

of the tank. As a safety measure, the fuel sumps should be 

drained before every flight during the preflight inspection. 

Fuel tanks should be filled after each flight or after the last 

flight of the day to prevent moisture condensation within the 

tank. To prevent fuel contamination, avoid refueling from 

cans and drums. 

In remote areas or in emergency situations, there may be no 

alternative to refueling from sources with inadequate anticontamination systems. While a chamois skin and funnel 

may be the only possible means of filtering fuel, using 

them is hazardous. Remember, the use of a chamois does 

not always ensure decontaminated fuel. Worn-out chamois 

do not filter water; neither will a new, clean chamois that is 

already water-wet or damp. Most imitation chamois skins 

do not filter water. 

Fuel System Icing 

Ice formation in the aircraft fuel system results from the 

presence of water in the fuel system. This water may be 

undissolved or dissolved. One condition of undissolved 

water is entrained water that consists of minute water 

particles suspended in the fuel. This may occur as a result of 

mechanical agitation of free water or conversion of dissolved 

water through temperature reduction. Entrained water settles 

out in time under static conditions and may or may not be 

drained during normal servicing, depending on the rate at 

which it is converted to free water. In general, it is not likely 

that all entrained water can ever be separated from fuel under 

field conditions. The settling rate depends on a series of 

factors including temperature, quiescence, and droplet size. 

The droplet size varies depending upon the mechanics 

of formation. Usually, the particles are so small as to be 

invisible to the naked eye, but in extreme cases, can cause 

slight haziness in the fuel. Water in solution cannot be 

removed except by dehydration or by converting it through 

temperature reduction to entrained, then to free water. 

Another condition of undissolved water is free water that 

may be introduced as a result of refueling or the settling of 

entrained water that collects at the bottom of a fuel tank. Free 

water is usually present in easily detected quantities at the 

bottom of the tank, separated by a continuous interface from 

the fuel above. Free water can be drained from a fuel tank 

through the sump drains, which are provided for that purpose. 

Free water, frozen on the bottom of reservoirs, such as the 

fuel tanks and fuel filter, may render water drains useless 

and can later melt releasing the water into the system thereby 

causing engine malfunction or stoppage. If such a condition 

is detected, the aircraft may be placed in a warm hangar to 

reestablish proper draining of these reservoirs, and all sumps 

and drains should be activated and checked prior to flight. 

Entrained water (i.e., water in solution with petroleum fuels) 

constitutes a relatively small part of the total potential water 

in a particular system, the quantity dissolved being dependent 

on fuel temperature and the existing pressure and the water 

volubility characteristics of the fuel. Entrained water freezes 

in mid fuel and tends to stay in suspension longer since the 

specific gravity of ice is approximately the same as that of 

AVGAS. 

Water in suspension may freeze and form ice crystals of 

sufficient size such that fuel screens, strainers, and filters 

may be blocked. Some of this water may be cooled further as 

the fuel enters carburetor air passages and causes carburetor 

metering component icing, when conditions are not otherwise 

conducive to this form of icing. 

Prevention Procedures 

The use of anti-icing additives for some aircraft has been 

approved as a means of preventing problems with water 

and ice in AVGAS. Some laboratory and flight testing 

indicates that the use of hexylene glycol, certain methanol 

derivatives, and ethylene glycol mononethyl ether (EGME) 

in small concentrations inhibit fuel system icing. These tests 

indicate that the use of EGME at a maximum 0.15 percent 

by volume concentration substantially inhibits fuel system 

icing under most operating conditions. The concentration 

of additives in the fuel is critical. Marked deterioration in 

additive effectiveness may result from too little or too much 

additive. Pilots should recognize that anti-icing additives are 

in no way a substitute or replacement for carburetor heat. 

Aircraft operating instructions involving the use of carburetor 

heat should be adhered to at all times when operating under 

atmospheric conditions conducive to icing. 

7-28 
 

 

Refueling Procedures 

Static electricity is formed by the friction of air passing 

over the surfaces of an aircraft in flight and by the flow of 

fuel through the hose and nozzle during refueling. Nylon, 

Dacron, or wool clothing is especially prone to accumulate 

and discharge static electricity from the person to the funnel 

or nozzle. To guard against the possibility of static electricity 

igniting fuel fumes, a ground wire should be attached to the 

aircraft before the fuel cap is removed from the tank. Because 

both the aircraft and refueler have different static charges, 

bonding both components to each other is critical. By bonding 

both components to each other, the static differential charge is 

equalized. The refueling nozzle should be bonded to the aircraft 

before refueling begins and should remain bonded throughout 

the refueling process. When a fuel truck is used, it should be 

grounded prior to the fuel nozzle contacting the aircraft. 

If fueling from drums or cans is necessary, proper bonding 

and grounding connections are important. Drums should be 

placed near grounding posts, and the following sequence of 

connections observed: 

1. Drum to ground 

2. Ground to aircraft 

3. Drum to aircraft or nozzle to aircraft before removing 

the fuel cap 

When disconnecting, reverse the order. 

The passage of fuel through a chamois increases the charge 

of static electricity and the danger of sparks. The aircraft 

must be properly grounded and the nozzle, chamois filter, 

and funnel bonded to the aircraft. If a can is used, it should 

be connected to either the grounding post or the funnel. 

Under no circumstances should a plastic bucket or similar 

nonconductive container be used in this operation. 

Heating System 

There are many different types of aircraft heating systems that 

are available depending on the type of aircraft. Regardless of 

which type or the safety features that accompany them, it is 

always important to reference the specific aircraft operator’s 

manual and become knowledgeable about the heating system. 

Each has different repair and inspection criteria that should 

be precisely followed. 

Fuel Fired Heaters 

A fuel fired heater is a small mounted or portable spaceheating device. The fuel is brought to the heater by using 

piping from a fuel tank, or taps into the aircraft’s fuel system. 

A fan blows air into a combustion chamber, and a spark plug 

or ignition device lights the fuel-air mixture. A built-in safety 

switch prevents fuel from flowing unless the fan is working. 

Outside the combustion chamber, a second, larger diameter 

tube conducts air around the combustion tube’s outer surface, 

and a second fan blows the warmed air into tubing to direct 

it towards the interior of the aircraft. Most gasoline heaters 

can produce between 5,000 and 50,000 British Thermal Units 

(BTU) per hour. 

Fuel fired heaters require electricity to operate and are 

compatible with a 12-volt and 24-volt aircraft electrical 

system. The heater requires routine maintenance, such as 

regular inspection of the combustion tube and replacement of 

the igniter at periodic intervals. Because gasoline heaters are 

required to be vented, special care must be made to ensure the 

vents do not leak into the interior of the aircraft. Combustion 

byproducts include soot, sulfur dioxide, carbon dioxide, and 

some carbon monoxide. An improperly adjusted, fueled, or 

poorly maintained fuel heater can be dangerous. 

Exhaust Heating Systems 

Exhaust heating systems are the simplest type of aircraft 

heating system and are used on most light aircraft. Exhaust 

heating systems are used to route exhaust gases away from 

the engine and fuselage while reducing engine noise. The 

exhaust systems also serve as a heat source for the cabin 

and carburetor. 

The risks of operating an aircraft with a defective exhaust 

heating system include carbon monoxide poisoning, a 

decrease in engine performance, and an increased potential 

for fire. Because of these risks, technicians should be aware 

of the rate of exhaust heating system deterioration and should 

thoroughly inspect all areas of the exhaust heating system to 

look for deficiencies inside and out. 

Combustion Heater Systems 

Combustion heaters or surface combustion heaters are often 

used to heat the cabin of larger, more expensive aircraft. 

This type of heater burns the aircraft’s fuel in a combustion 

chamber or tube to develop required heat, and the air 

flowing around the tube is heated and ducted to the cabin. 

A combustion heater is an airtight burner chamber with a 

stainless-steel jacket. Fuel from the aircraft fuel system is 

ignited and burns to provide heat. Ventilation air is forced 

over the airtight burn chamber picking up heat, which is then 

dispersed into the cabin area. 

When the heater control switch is turned on, airflow, ignition, 

and fuel are supplied to the heater. Airflow and ignition are 

constant within the burner chamber while the heater control 

switch is on. When heat is required, the temperature control 

is advanced, activating the thermostat. The thermostat (which 

7-29 
senses ventilation air temperature) turns on the fuel solenoid 

allowing fuel to spray into the burner chamber. Fuel mixes 

with air inside the chamber and is ignited by the spark plug, 

producing heat. 

The by-product, carbon monoxide, leaves the aircraft through 

the heater exhaust pipe. Air flowing over the outside of the 

burner chamber and inside the jacket of the heater absorbs 

the heat and carries it through ducts into the cabin. As the 

thermostat reaches its preset temperature, it turns off the fuel 

solenoid and stops the flow of fuel into the burner chamber. 

When ventilation air cools to the point that the thermostat 

again turns the fuel solenoid on, the burner starts again. 

This method of heat is very safe as an overheat switch is 

provided on all combustion heaters, which is wired into 

the heater’s electrical system to shut off the fuel in the case 

of malfunction. In the unlikely event that the heater fuel 

solenoid, located at the heater, remains open or the control 

switches fail, the remote fuel solenoid and/or fuel pump is 

shut off by the mechanical overheat switch, stopping all fuel 

flow to the system. 

As opposed to the fuel fired cabin heaters that are used 

on most single-engine aircraft, it is unlikely for carbon 

monoxide poisoning to occur in combustion heaters. 

Combustion heaters have low pressure in the combustion 

tube that is vented through its exhaust into the air stream. The 

ventilation air on the outside of the combustion chamber is 

of higher pressure than on the inside, and ram air increases 

the pressure on the outside of the combustion tube. In the 

event a leak would develop in the combustion chamber, the 

higher-pressure air outside the chamber would travel into the 

chamber and out the exhaust. 

Bleed Air Heating Systems 

Bleed air heating systems are used on turbine-engine 

aircraft. Extremely hot compressor bleed air is ducted into 

a chamber where it is mixed with ambient or re-circulated 

air to cool the air to a useable temperature. The air mixture 

is then ducted into the cabin. This type of system contains 

several safety features to include temperature sensors that 

prevent excessive heat from entering the cabin, check 

valves to prevent a loss of compressor bleed air when 

starting the engine and when full power is required, and 

engine sensors to eliminate the bleed system if the engine 

becomes inoperative. 

Electrical System 

Most aircraft are equipped with either a 14- or a 28-volt direct 

current (DC) electrical system. A basic aircraft electrical 

system consists of the following components: 

• Alternator/generator 

• Battery 

• Master/battery switch 

• Alternator/generator switch 

• Bus bar, fuses, and circuit breakers 

• Voltage regulator 

• Ammeter/loadmeter 

• Associated electrical wiring 

Engine-driven alternators or generators supply electric 

current to the electrical system. They also maintain a 

sufficient electrical charge in the battery. Electrical energy 

stored in a battery provides a source of electrical power for 

starting the engine and a limited supply of electrical power 

for use in the event the alternator or generator fails. 

Most DC generators do not produce a sufficient amount of 

electrical current at low engine rpm to operate the entire 

electrical system. During operations at low engine rpm, the 

electrical needs must be drawn from the battery, which can 

quickly be depleted. 

Alternators have several advantages over generators. 

Alternators produce sufficient current to operate the entire 

electrical system, even at slower engine speeds, by producing 

alternating current (AC), which is converted to DC. The 

electrical output of an alternator is more constant throughout 

a wide range of engine speeds. 

Some aircraft have receptacles to which an external ground 

power unit (GPU) may be connected to provide electrical 

energy for starting. These are very useful, especially 

during cold weather starting. Follow the manufacturer’s 

recommendations for engine starting using a GPU. 

The electrical system is turned on or off with a master switch. 

Turning the master switch to the ON position provides 

electrical energy to all the electrical equipment circuits 

except the ignition system. Equipment that commonly uses 

the electrical system for its source of energy includes: 

• Position lights 

• Anticollision lights 

• Landing lights 

• Taxi lights 

• Interior cabin lights 

• Instrument lights 

• Radio equipment 

• Turn indicator 

• Fuel gauges 

7-30 
 

• Electric fuel pump 

• Stall warning system 

• Pitot heat 

• Starting motor 

Many aircraft are equipped with a battery switch that 

controls the electrical power to the aircraft in a manner 

similar to the master switch. In addition, an alternator switch 

is installed that permits the pilot to exclude the alternator 

from the electrical system in the event of alternator failure. 

[Figure 7-33] 

With the alternator half of the switch in the OFF position, the 

entire electrical load is placed on the battery. All nonessential 

electrical equipment should be turned off to conserve 

battery power. 

A bus bar is used as a terminal in the aircraft electrical system 

to connect the main electrical system to the equipment using 

electricity as a source of power. This simplifies the wiring 

system and provides a common point from which voltage can 

be distributed throughout the system. [Figure 7-34] 

Fuses or circuit breakers are used in the electrical system to 

protect the circuits and equipment from electrical overload. 

Spare fuses of the proper amperage limit should be carried in 

the aircraft to replace defective or blown fuses. Circuit breakers 

have the same function as a fuse but can be manually reset, 

rather than replaced, if an overload condition occurs in the 

electrical system. Placards at the fuse or circuit breaker panel 

identify the circuit by name and show the amperage limit. 

Figure 7-33. On this master switch, the left half is for the alternator 

and the right half is for the battery. 

An ammeter is used to monitor the performance of the aircraft 

electrical system. The ammeter shows if the alternator/ 

generator is producing an adequate supply of electrical power. 

It also indicates whether or not the battery is receiving an 

electrical charge. 

Ammeters are designed with the zero point in the center 

of the face and a negative or positive indication on either 

side. [Figure 7-35] When the pointer of the ammeter is 

on the plus side, it shows the charging rate of the battery. 

A minus indication means more current is being drawn 

from the battery than is being replaced. A full-scale minus 

deflection indicates a malfunction of the alternator/generator. 

A full-scale positive deflection indicates a malfunction of 

the regulator. In either case, consult the AFM/POH for 

appropriate action to be taken. 

Not all aircraft are equipped with an ammeter. Some have 

a warning light that, when lighted, indicates a discharge in 

the system as a generator/alternator malfunction. Refer to the 

AFM/POH for appropriate action to be taken. 

Another electrical monitoring indicator is a loadmeter. 

This type of gauge has a scale beginning with zero and 

shows the load being placed on the alternator/generator. 

[Figure 7-35] The loadmeter reflects the total percentage of 

the load placed on the generating capacity of the electrical 

system by the electrical accessories and battery. When all 

electrical components are turned off, it reflects only the 

amount of charging current demanded by the battery. 

A voltage regulator controls the rate of charge to the battery 

by stabilizing the generator or alternator electrical output. The 

generator/alternator voltage output should be higher than the 

battery voltage. For example, a 12-volt battery would be fed 

by a generator/alternator system of approximately 14 volts. 

The difference in voltage keeps the battery charged. 

Hydraulic Systems 

There are multiple applications for hydraulic use in aircraft, 

depending on the complexity of the aircraft. For example, a 

hydraulic system is often used on small airplanes to operate 

wheel brakes, retractable landing gear, and some constantspeed propellers. On large airplanes, a hydraulic system is 

used for flight control surfaces, wing flaps, spoilers, and 

other systems. 

A basic hydraulic system consists of a reservoir, pump 

(either hand, electric, or engine-driven), a filter to keep the 

fluid clean, a selector valve to control the direction of flow, 

a relief valve to relieve excess pressure, and an actuator. 

[Figure 7-36] 

7-31 
 

Low-voltage

warning light 

ALT 

To wing

flap circuit

breaker 

Magnetos 

Starter 

contactor 

Clock 

Ammeter 

Alternator 

control unit 

Circuit breaker (auto-reset) 

Circuit breaker (push to reset) 

Circuit breaker (pull—off, 

push to reset) 

Fuse Diode 

Resistor 

Capacitor (Noise Filter) 

To inst 

LTS 

circuit 

breaker FUEL IND. 

BCN PITOT 

PULL 

OFF STROBE 

RADIO FAN 

LDG LTS 

FLAP 

INST LTS 

STBY VAC 

RADIO 1 

RADIO 2 

RADIO 3 

NAV 

DOME 

RADIO 4 

G 

F 

B 

Alternator 

B 

Master 

switch 

Pull off 

Alternator field 

circuit breaker 

Flight hour recorder 

Oil pressure

switch 

To fuel quantity indicators 

To flashing beacon 

To pitot heat 

To radio cooling fan 

To strobe lights 

To landing and taxi lights 

To ignition switch 

To wing flap system 

To red doorpost maplight 

To low-voltage warning light 

To instrument, radio, compass

and post lights 

To oil temperature gauge 

To turn coordinator 

To low-vacuum warning light 

Switch/circuit breaker to

standby vacuum pump 

To white doorpost light 

To audio muting relay 

To control wheel maplight 

To navigation lights 

To dome light 

To radio 

To radio 

To radio or transponder

and encoding altimeter 

To radio 

P 

R 

I 

M 

A 

R 

Y 

B 

U 

S 

A 

V 

I 

O 

N 

I 

C 

S 

B 

U 

S 

Low volt out 

Power in

 Sense (+)

 Field

 Sense (-) 

Ground 

Starter 

Battery 

A

L

T 

B

A

T 

+ 60 - 60 

-30 +30 0 

A M P 

L R 

Battery

contactor 

Ground service 

plug receptacle 

CODE 

Figure 7-34. Electrical system schematic. 

The hydraulic fluid is pumped through the system to an 

actuator or servo. A servo is a cylinder with a piston inside 

that turns fluid power into work and creates the power needed 

to move an aircraft system or flight control. Servos can be 

either single-acting or double-acting, based on the needs of 

the system. This means that the fluid can be applied to one 

or both sides of the servo, depending on the servo type. A 

single-acting servo provides power in one direction. The 

selector valve allows the fluid direction to be controlled. 

This is necessary for operations such as the extension and 

retraction of landing gear during which the fluid must work 

in two different directions. The relief valve provides an outlet 

7-32 
 

 

 

 

+ 60 - 60 

-30 +30 0 

A M P 

ALT AMPS 

0 30 60 

Ammeter Loadmeter 

Figure 7-35. Ammeter and loadmeter. 

for the system in the event of excessive fluid pressure in the 

system. Each system incorporates different components to 

meet the individual needs of different aircraft. 

A mineral-based hydraulic fluid is the most widely used type 

for small aircraft. This type of hydraulic fluid, a kerosene-like 

petroleum product, has good lubricating properties, as well 

as additives to inhibit foaming and prevent the formation 

of corrosion. It is chemically stable, has very little viscosity 

change with temperature, and is dyed for identification. Since 

several types of hydraulic fluids are commonly used, an aircraft 

must be serviced with the type specified by the manufacturer. 

Refer to the AFM/POH or the Maintenance Manual. 

Landing Gear 

The landing gear forms the principal support of an aircraft on 

the surface. The most common type of landing gear consists 

of wheels, but aircraft can also be equipped with floats for 

water operations or skis for landing on snow. [Figure 7-37] 

The landing gear on small aircraft consists of three wheels: 

two main wheels (one located on each side of the fuselage) 

and a third wheel positioned either at the front or rear of the 

Figure 7-36. Basic hydraulic system. 

Pump 

BOTH

LEFT

RIGHT

OFF

Selector valve 

System relief valve 

Double acting cylinder Motion 

Hydraulic fluid supply 

Return fluid 

Hydraulic pressure 

Figure 7-37. The landing gear supports the airplane during the 

takeoff run, landing, taxiing, and when parked. 

airplane. Landing gear employing a rear-mounted wheel is 

called conventional landing gear. Airplanes with conventional 

landing gear are often referred to as tailwheel airplanes. When 

the third wheel is located on the nose, it is called a nosewheel, 

and the design is referred to as a tricycle gear. A steerable 

nosewheel or tailwheel permits the airplane to be controlled 

throughout all operations while on the ground. 

Tricycle Landing Gear 

There are three advantages to using tricycle landing gear: 

1.	 It allows more forceful application of the brakes during 

landings at high speeds without causing the aircraft to 

nose over. 

2. It permits better forward visibility for the pilot during 

takeoff, landing, and taxiing. 

3.	 It tends to prevent ground looping (swerving) by 

providing more directional stability during ground 

operation since the aircraft’s center of gravity (CG) 

is forward of the main wheels. The forward CG keeps 

the airplane moving forward in a straight line rather 

than ground looping. 

Nosewheels are either steerable or castering. Steerable 

nosewheels are linked to the rudders by cables or rods, while 

castering nosewheels are free to swivel. In both cases, the 

aircraft is steered using the rudder pedals. Airplanes with a 

castering nosewheel may require the pilot to combine the 

use of the rudder pedals with independent use of the brakes. 

Tailwheel Landing Gear 

Tailwheel landing gear airplanes have two main wheels 

attached to the airframe ahead of its CG that support most of 

the weight of the structure. A tailwheel at the very back of the 

fuselage provides a third point of support. This arrangement 

7-33 
allows adequate ground clearance for a larger propeller 

and is more desirable for operations on unimproved fields. 

[Figure 7-38] 

With the CG located behind the main landing gear, directional 

control using this type of landing gear is more difficult while 

on the ground. This is the main disadvantage of the tailwheel 

landing gear. For example, if the pilot allows the aircraft to 

swerve while rolling on the ground at a low speed, he or 

she may not have sufficient rudder control and the CG will 

attempt to get ahead of the main gear, which may cause the 

airplane to ground loop. 

Diminished forward visibility when the tailwheel is on or near 

the ground is a second disadvantage of tailwheel landing gear 

airplanes. Because of these disadvantages, specific training 

is required to operate tailwheel airplanes. 

Fixed and Retractable Landing Gear 

Landing gear can also be classified as either fixed or 

retractable. Fixed landing gear always remains extended 

and has the advantage of simplicity combined with low 

Figure 7-38. Tailwheel landing gear. 

maintenance. Retractable landing gear is designed to 

streamline the airplane by allowing the landing gear to 

be stowed inside the structure during cruising flight. 

[Figure 7-39] 

Brakes 

Airplane brakes are located on the main wheels and are 

applied by either a hand control or by foot pedals (toe or heel). 

Foot pedals operate independently and allow for differential 

braking. During ground operations, differential braking can 

supplement nosewheel/tailwheel steering. 

Pressurized Aircraft 

Aircraft are flown at high altitudes for two reasons. First, an 

aircraft flown at high altitude consumes less fuel for a given 

airspeed than it does for the same speed at a lower altitude 

because the aircraft is more efficient at a high altitude. 

Second, bad weather and turbulence may be avoided by flying 

in relatively smooth air above the storms. Many modern 

aircraft are being designed to operate at high altitudes, 

taking advantage of that environment. In order to fly at 

higher altitudes, the aircraft must be pressurized or suitable 

supplemental oxygen must be provided for each occupant. 

It is important for pilots who fly these aircraft to be familiar 

with the basic operating principles. 

In a typical pressurization system, the cabin, flight 

compartment, and baggage compartments are incorporated 

into a sealed unit capable of containing air under a pressure 

higher than outside atmospheric pressure. On aircraft powered 

by turbine engines, bleed air from the engine compressor 

section is used to pressurize the cabin. Superchargers may 

be used on older model turbine-powered aircraft to pump 

air into the sealed fuselage. Piston-powered aircraft may use 

air supplied from each engine turbocharger through a sonic 

venturi (flow limiter). Air is released from the fuselage by 

Figure 7-39. Fixed (left) and retractable (right) gear airplanes. 

7-34 
a device called an outflow valve. By regulating the air exit, 

the outflow valve allows for a constant inflow of air to the 

pressurized area. [Figure 7-40] 

A cabin pressurization system typically maintains a cabin 

pressure altitude of approximately 8,000 feet at the maximum 

designed cruising altitude of an aircraft. This prevents rapid 

changes of cabin altitude that may be uncomfortable or cause 

injury to passengers and crew. In addition, the pressurization 

system permits a reasonably fast exchange of air from 

the inside to the outside of the cabin. This is necessary to 

eliminate odors and to remove stale air. [Figure 7-41] 

Pressurization of the aircraft cabin is necessary in order to 

protect occupants against hypoxia. Within a pressurized 

cabin, occupants can be transported comfortably and safely 

for long periods of time, particularly if the cabin altitude 

is maintained at 8,000 feet or below, where the use of 

oxygen equipment is not required. The flight crew in this 

type of aircraft must be aware of the danger of accidental 

loss of cabin pressure and be prepared to deal with such an 

emergency whenever it occurs. 

Figure 7-40. High performance airplane pressurization system. CODE 

Ambient air 

Compressor discharge air 

Pressurization air 

Pre-heated ambient air 

Conditioned pressurization air 

Pressurized cabin 

Air scoops 

Turbocharger 

compressor 

section 

Heat shroud 

Heat exchanger 

Forward 

air outlets 

Cabin heat 

valve 

Floor level outlets 

Safety/dump valve 

Flow control 

venturi 

To cabin altitude 

controller 

Outflow valve 

Altitude (ft) Pressure (psi) 

Atmosphere pressure 

Sea level 

2,000 

4,000 

6,000 

8,000 

10,000 

12,000 

14,000 

16,000 

18,000 

20,000 

22,000 

24,000 

26,000 

28,000 

30,000 

14.7 

13.7 

12.7 

11.8 

10.9 

10.1 

9.4 

8.6 

8.0 

7.3 

6.8 

6.2 

5.7 

5.2 

4.8 

4.4 

At an altitude of 28,000 

feet, standard atmospheric pressure is 4.8 

psi. By adding this 

pressure to the cabin 

pressure differential of 

6.1 psi difference (psid), 

a total air pressure of 

10.9 psi is obtained. 

The altitude at which the 

standard air pressure is 

equal to 10.9 psi can be 

found at 8,000 feet. 

Figure 7-41. Standard atmospheric pressure chart. 

The following terms will aid in understanding the operating 

principles of pressurization and air conditioning systems: 

•	 Aircraft altitude—the actual height above sea level at 

which the aircraft is flying 

•	 Ambient temperature—the temperature in the area 

immediately surrounding the aircraft 

•	 Ambient pressure—the pressure in the area 

immediately surrounding the aircraft 

•	 Cabin altitude—cabin pressure in terms of equivalent 

altitude above sea level 

•	 Differential pressure—the difference in pressure 

between the pressure acting on one side of a wall 

and the pressure acting on the other side of the 

wall. In aircraft air-conditioning and pressurizing 

systems, it is the difference between cabin pressure 

and atmospheric pressure. 

The cabin pressure control system provides cabin pressure 

regulation, pressure relief, vacuum relief, and the means 

for selecting the desired cabin altitude in the isobaric and 

differential range. In addition, dumping of the cabin pressure 

is a function of the pressure control system. A cabin pressure 

regulator, an outflow valve, and a safety valve are used to 

accomplish these functions. 

The cabin pressure regulator controls cabin pressure to a 

selected value in the isobaric range and limits cabin pressure 

to a preset differential value in the differential range. When an 

aircraft reaches the altitude at which the difference between 

the pressure inside and outside the cabin is equal to the 

highest differential pressure for which the fuselage structure 

is designed, a further increase in aircraft altitude will result 

7-35 
 

 

in a corresponding increase in cabin altitude. Differential 

control is used to prevent the maximum differential pressure, 

for which the fuselage was designed, from being exceeded. 

This differential pressure is determined by the structural 

strength of the cabin and often by the relationship of the 

cabin size to the probable areas of rupture, such as window 

areas and doors. 

The cabin air pressure safety valve is a combination 

pressure relief, vacuum relief, and dump valve. The pressure 

relief valve prevents cabin pressure from exceeding a 

predetermined differential pressure above ambient pressure. 

The vacuum relief prevents ambient pressure from exceeding 

cabin pressure by allowing external air to enter the cabin 

when ambient pressure exceeds cabin pressure. The flight 

deck control switch actuates the dump valve. When this 

switch is positioned to ram, a solenoid valve opens, causing 

the valve to dump cabin air into the atmosphere. 

The degree of pressurization and the operating altitude of 

the aircraft are limited by several critical design factors. 

Primarily, the fuselage is designed to withstand a particular 

maximum cabin differential pressure. 

Several instruments are used in conjunction with the 

pressurization controller. The cabin differential pressure gauge 

indicates the difference between inside and outside pressure. 

This gauge should be monitored to assure that the cabin does 

not exceed the maximum allowable differential pressure. A 

cabin altimeter is also provided as a check on the performance 

of the system. In some cases, these two instruments are 

combined into one. A third instrument indicates the cabin rate 

of climb or descent. A cabin rate-of-climb instrument and a 

cabin altimeter are illustrated in Figure 7-42. 

Decompression is defined as the inability of the aircraft’s 

pressurization system to maintain its designed pressure 

differential. This can be caused by a malfunction in the 

pressurization system or structural damage to the aircraft. 

Physiologically, decompressions fall into the following two 

categories: 

•	 Explosive decompression—a change in cabin pressure 

faster than the lungs can decompress, possibly 

resulting in lung damage. Normally, the time required 

to release air from the lungs without restrictions, such 

as masks, is 0.2 seconds. Most authorities consider any 

decompression that occurs in less than 0.5 seconds to 

be explosive and potentially dangerous. 

•	 Rapid decompression—a change in cabin pressure in 

which the lungs decompress faster than the cabin. 

During an explosive decompression, there may be noise, 

and one may feel dazed for a moment. The cabin air fills 

with fog, dust, or flying debris. Fog occurs due to the rapid 

drop in temperature and the change of relative humidity. 

Normally, the ears clear automatically. Air rushes from the 

mouth and nose due to the escape of air from the lungs and 

may be noticed by some individuals. 

Rapid decompression decreases the period of useful 

consciousness because oxygen in the lungs is exhaled rapidly, 

reducing pressure on the body. This decreases the partial 

pressure of oxygen in the blood and reduces the pilot’s 

effective performance time by one-third to one-fourth its 

normal time. For this reason, an oxygen mask should be 

worn when flying at very high altitudes (35,000 feet or 

higher). It is recommended that the crewmembers select the 

100 percent oxygen setting on the oxygen regulator at high 

altitude if the aircraft is equipped with a demand or pressure 

demand oxygen system. 

Cabin rate-of-climb indicator Cabin/differential pressure indicator 

4 

6 

I 

0 

2 

2 I 

4 

CABIN CLIMB THOUSAND FT PER MIN .5 

.5 

0 

5 

10 

15 

20 

25 

30 

35 0 

1 

2 

3 

4 

5 

6 

PSI 

CABIN ALT 

DIFF 

PRESS 

1000 Feet 

Cabin pressure 

altitude indicator 

(thousands of feet) 

Maximum cabin 

differential pressure 

limit 

Cabin differential 

pressure indicator 

(pounds per square 

inch differential) 

Figure 7-42. Cabin pressurization instruments. 

7-36 
 

 

 

The primary danger of decompression is hypoxia. Quick, 

proper utilization of oxygen equipment is necessary to avoid 

unconsciousness. Another potential danger that pilots, crew, 

and passengers face during high altitude decompressions is 

evolved gas decompression sickness. This occurs when the 

pressure on the body drops sufficiently, nitrogen comes out 

of solution, and forms bubbles inside the person that can have 

adverse effects on some body tissues. 

Decompression caused by structural damage to the aircraft 

presents another type of danger to pilots, crew, and 

passengers––being tossed or blown out of the aircraft if 

they are located near openings. Individuals near openings 

should wear safety harnesses or seatbelts at all times when 

the aircraft is pressurized and they are seated. Structural 

damage also has the potential to expose them to wind blasts 

and extremely cold temperatures. 

Rapid descent from altitude is necessary in order to minimize 

these problems. Automatic visual and aural warning systems 

are included in the equipment of all pressurized aircraft. 

Oxygen Systems 

Crew and passengers use oxygen systems, in conjunction 

with pressurization systems, to prevent hypoxia. Regulations 

require, at a minimum, flight crews have and use supplemental 

oxygen after 30 minutes exposure to cabin pressure altitudes 

between 12,500 and 14,000 feet. Use of supplemental 

oxygen is required immediately upon exposure to cabin 

pressure altitudes above 14,000 feet. Every aircraft occupant, 

above 15,000 feet cabin pressure altitude, must have 

supplemental oxygen. However, based on a person’s physical 

characteristics and condition, a person may feel the effects 

of oxygen deprivation at much lower altitudes. Some people 

flying above 10,000 feet during the day may experience 

disorientation due to the lack of adequate oxygen. At night, 

especially when fatigued, these effects may occur as low 

as 5,000 feet. Therefore, for optimum protection, pilots are 

encouraged to use supplemental oxygen above 10,000 feet 

cabin altitude during the day and above 5,000 feet at night. 

Most high altitude aircraft come equipped with some type 

of fixed oxygen installation. If the aircraft does not have 

a fixed installation, portable oxygen equipment must be 

readily accessible during flight. The portable equipment 

usually consists of a container, regulator, mask outlet, 

and pressure gauge. Aircraft oxygen is usually stored in 

high pressure system containers of 1,800–2,200 psi. When 

the ambient temperature surrounding an oxygen cylinder 

decreases, pressure within that cylinder decreases because 

pressure varies directly with temperature if the volume of a 

gas remains constant. A drop in the indicated pressure of a 

supplemental oxygen cylinder may be due to the container 

being stored in an unheated area of the aircraft rather than 

an actual depletion of the oxygen supply. High pressure 

oxygen containers should be marked with the psi tolerance 

(i.e., 1,800 psi) before filling the container to that pressure. 

The containers should be supplied with oxygen that meets 

or exceeds SAE AS8010 (as revised), Aviator’s Breathing 

Oxygen Purity Standard. To assure safety, periodic inspection 

and servicing of the oxygen system should be performed. 

An oxygen system consists of a mask or cannula and a 

regulator that supplies a flow of oxygen dependent upon 

cabin altitude. Most regulators approved for use up to 40,000 

feet are designed to provide zero percent cylinder oxygen 

and 100 percent cabin air at cabin altitudes of 8,000 feet or 

less, with the ratio changing to 100 percent oxygen and zero 

percent cabin air at approximately 34,000 feet cabin altitude. 

[Figure 7-43] Most regulators approved up to 45,000 feet 

are designed to provide 40 percent cylinder oxygen and 60 

percent cabin air at lower altitudes, with the ratio changing 

to 100 percent at the higher altitude. 

Pilots should be aware of the danger of fire when using 

oxygen. Materials that are nearly fireproof in ordinary air may 

be susceptible to combustion in oxygen. Oils and greases may 

ignite if exposed to oxygen and cannot be used for sealing 

the valves and fittings of oxygen equipment. Smoking during 

any kind of oxygen equipment use is prohibited. Before 

each flight, the pilot should thoroughly inspect and test all 

oxygen equipment. The inspection should include a thorough 

examination of the aircraft oxygen equipment, including 

available supply, an operational check of the system, and 

assurance that the supplemental oxygen is readily accessible. 

The inspection should be accomplished with clean hands and 

should include a visual inspection of the mask and tubing 

for tears, cracks, or deterioration; the regulator for valve 

and lever condition and positions; oxygen quantity; and the 

location and functioning of oxygen pressure gauges, flow 

indicators, and connections. The mask should be donned and 

the system should be tested. After any oxygen use, verify that 

all components and valves are shut off. 

Figure 7-43. Oxygen system regulator. 

7-37 
 

Oxygen Masks 

There are numerous types and designs of oxygen masks in 

use. The most important factor in oxygen mask use is to 

ensure that the masks and oxygen system are compatible. 

Crew masks are fitted to the user’s face with a minimum of 

leakage and usually contain a microphone. Most masks are 

the oronasal type that covers only the mouth and nose. 

A passenger mask may be a simple, cup-shaped rubber 

molding sufficiently flexible to obviate individual fitting. It 

may have a simple elastic head strap or the passenger may 

hold it to his or her face. 

All oxygen masks should be kept clean to reduce the danger 

of infection and prolong the life of the mask. To clean the 

mask, wash it with a mild soap and water solution and rinse 

it with clear water. If a microphone is installed, use a clean 

swab, instead of running water, to wipe off the soapy solution. 

The mask should also be disinfected. A gauze pad that has 

been soaked in a water solution of Merthiolate can be used 

to swab out the mask. This solution used should contain 

one-fifth teaspoon of Merthiolate per quart of water. Wipe 

the mask with a clean cloth and air dry. 

Cannula 

A cannula is an ergonomic piece of plastic tubing that runs 

under the nose to administer oxygen to the user. [Figure 7-44] 

Cannulas are typically more comfortable than masks, but 

may not provide an adequate flow of oxygen as reliably as 

masks when operating at higher altitudes. Airplanes certified 

to older regulations had cannulas installed with an on-board 

Figure 7-44. Cannula with green flow detector. 

oxygen system. However, current regulations require aircraft 

with oxygen systems installed and certified for operations 

above 18,000 feet to be equipped with oxygen masks instead 

of cannulas. Many cannulas have a flow meter in the oxygen 

supply line. If equipped, a periodic check of the green flow 

detector should be a part of the pilot’s regular scan. 

Diluter-Demand Oxygen Systems 

Diluter-demand oxygen systems supply oxygen only when 

the user inhales through the mask. An automix lever allows 

the regulators to automatically mix cabin air and oxygen or 

supply 100 percent oxygen, depending on the altitude. The 

demand mask provides a tight seal over the face to prevent 

dilution with outside air and can be used safely up to 40,000 

feet. A pilot who has a beard or mustache should be sure it is 

trimmed in a manner that will not interfere with the sealing 

of the oxygen mask. The fit of the mask around the beard or 

mustache should be checked on the ground for proper sealing. 

Pressure-Demand Oxygen Systems 

Pressure-demand oxygen systems are similar to diluter 

demand oxygen equipment, except that oxygen is supplied to 

the mask under pressure at cabin altitudes above 34,000 feet. 

Pressure-demand regulators create airtight and oxygen-tight 

seals, but they also provide a positive pressure application of 

oxygen to the mask face piece that allows the user’s lungs 

to be pressurized with oxygen. This feature makes pressure 

demand regulators safe at altitudes above 40,000 feet. Some 

systems may have a pressure demand mask with the regulator 

attached directly to the mask, rather than mounted on the 

instrument panel or other area within the flight deck. The 

mask-mounted regulator eliminates the problem of a long 

hose that must be purged of air before 100 percent oxygen 

begins flowing into the mask. 

Continuous-Flow Oxygen System 

Continuous-flow oxygen systems are usually provided for 

passengers. The passenger mask typically has a reservoir 

bag that collects oxygen from the continuous-flow oxygen 

system during the time when the mask user is exhaling. 

The oxygen collected in the reservoir bag allows a higher 

aspiratory flow rate during the inhalation cycle, which 

reduces the amount of air dilution. Ambient air is added to 

the supplied oxygen during inhalation after the reservoir bag 

oxygen supply is depleted. The exhaled air is released to the 

cabin. [Figure 7-45] 

Electrical Pulse-Demand Oxygen System 

Portable electrical pulse-demand oxygen systems deliver 

oxygen by detecting an individual’s inhalation effort and 

provide oxygen flow during the initial portion of inhalation. 

Pulse demand systems do not waste oxygen during the 

7-38 
Figure 7-46. EDS-011 portable pulse-demand oxygen system. 

Figure 7-45. Continuous flow mask and rebreather bag. 

breathing cycle because oxygen is only delivered during 

inhalation. Compared to continuous-flow systems, the pulsedemand method of oxygen delivery can reduce the amount 

of oxygen needed by 50–85 percent. Most pulse-demand 

oxygen systems also incorporate an internal barometer 

that automatically compensates for changes in altitude by 

increasing the amount of oxygen delivered for each pulse as 

altitude is increased. [Figure 7-46] 

Pulse Oximeters 

A pulse oximeter is a device that measures the amount of 

oxygen in an individual’s blood, in addition to heart rate. 

This non-invasive device measures the color changes that 

red blood cells undergo when they become saturated with 

oxygen. By transmitting a special light beam through a 

fingertip to evaluate the color of the red cells, a pulse 

oximeter can calculate the degree of oxygen saturation 

within one percent of directly measured blood oxygen. 

Because of their portability and speed, pulse oximeters are 

very useful for pilots operating in nonpressurized aircraft 

above 12,500 feet where supplemental oxygen is required. 

A pulse oximeter permits crewmembers and passengers of 

an aircraft to evaluate their actual need for supplemental 

oxygen. [Figure 7-47] 

Servicing of Oxygen Systems 

Before servicing any aircraft with oxygen, consult the 

specific aircraft service manual to determine the type of 

equipment required and procedures to be used. Certain 

precautions should be observed whenever aircraft oxygen 

systems are to be serviced. Oxygen system servicing should 

be accomplished only when the aircraft is located outside 

of the hangars. Personal cleanliness and good housekeeping 

are imperative when working with oxygen. Oxygen under 

pressure creates spontaneous results when brought in contact 

with petroleum products. Service people should be certain to 

wash dirt, oil, and grease (including lip salves and hair oil) 

from their hands before working around oxygen equipment. It 

is also essential that clothing and tools are free of oil, grease, 

Figure 7-47. Onyx pulse oximeter. 

7-39 
and dirt. Aircraft with permanently installed oxygen tanks 

usually require two persons to accomplish servicing of the 

system. One should be stationed at the service equipment 

control valves, and the other stationed where he or she 

can observe the aircraft system pressure gauges. Oxygen 

system servicing is not recommended during aircraft fueling 

operations or while other work is performed that could 

provide a source of ignition. Oxygen system servicing while 

passengers are on board the aircraft is not recommended. 

Anti-Ice and Deice Systems 

Anti-icing equipment is designed to prevent the formation 

of ice, while deicing equipment is designed to remove ice 

once it has formed. These systems protect the leading edge 

of wing and tail surfaces, pitot and static port openings, fuel 

tank vents, stall warning devices, windshields, and propeller 

blades. Ice detection lighting may also be installed on some 

aircraft to determine the extent of structural icing during 

night flights. 

Most light aircraft have only a heated pitot tube and are not 

certified for flight in icing. These light aircraft have limited 

cross-country capability in the cooler climates during late 

fall, winter, and early spring. Noncertificated aircraft must 

exit icing conditions immediately. Refer to the AFM/POH 

for details. 

Airfoil Anti-Ice and Deice 

Inflatable deicing boots consist of a rubber sheet bonded to 

the leading edge of the airfoil. When ice builds up on the 

leading edge, an engine-driven pneumatic pump inflates the 

rubber boots. Many turboprop aircraft divert engine bleed 

air to the wing to inflate the rubber boots. Upon inflation, 

the ice is cracked and should fall off the leading edge of the 

wing. Deicing boots are controlled from the flight deck by 

a switch and can be operated in a single cycle or allowed to 

cycle at automatic, timed intervals. [Figure 7-48] 

In the past, it was believed that if the boots were cycled 

too soon after encountering ice, the ice layer would expand 

instead of breaking off, resulting in a condition referred to as 

ice “bridging.” Consequently, subsequent deice boot cycles 

would be ineffective at removing the ice buildup. Although 

some residual ice may remain after a boot cycle, “bridging” 

does not occur with any modern boots. Pilots can cycle the 

boots as soon as an ice accumulation is observed. Consult 

the AFM/POH for information on the operation of deice 

boots on an aircraft. 

Many deicing boot systems use the instrument system suction 

gauge and a pneumatic pressure gauge to indicate proper boot 

operation. These gauges have range markings that indicate 

the operating limits for boot operation. Some systems may 

Tubes deflated 

Tubes inflated 

Figure 6-48. Deicing boots on the leading edge of the wing. 

also incorporate an annunciator light to indicate proper boot 

operation. 

Proper maintenance and care of deicing boots are important 

for continued operation of this system. They need to be 

carefully inspected during preflight. 

Another type of leading edge protection is the thermal anti-ice 

system. Heat provides one of the most effective methods for 

preventing ice accumulation on an airfoil. High performance 

turbine aircraft often direct hot air from the compressor 

section of the engine to the leading edge surfaces. The hot 

air heats the leading edge surfaces sufficiently to prevent the 

formation of ice. A newer type of thermal anti-ice system 

referred to as ThermaWing uses electrically heated graphite 

foil laminate applied to the leading edge of the wing and 

horizontal stabilizer. ThermaWing systems typically have 

two zones of heat application. One zone on the leading edge 

receives continuous heat; the second zone further aft receives 

heat in cycles to dislodge the ice allowing aerodynamic forces 

to remove it. Thermal anti-ice systems should be activated 

prior to entering icing conditions. 

An alternate type of leading edge protection that is not as 

common as thermal anti-ice and deicing boots is known 

7-40 
 

as a weeping wing. The weeping-wing design uses small 

holes located in the leading edge of the wing to prevent 

the formation and build-up of ice. An antifreeze solution 

is pumped to the leading edge and weeps out through the 

holes. Additionally, the weeping wing is capable of deicing 

an aircraft. When ice has accumulated on the leading edges, 

application of the antifreeze solution chemically breaks down 

the bond between the ice and airframe, allowing aerodynamic 

forces to remove the ice. [Figure 7-49] 

Windscreen Anti-Ice 

There are two main types of windscreen anti-ice systems. 

The first system directs a flow of alcohol to the windscreen. 

If used early enough, the alcohol prevents ice from building 

up on the windscreen. The rate of alcohol flow can be 

controlled by a dial in the flight deck according to procedures 

recommended by the aircraft manufacturer. 

Another effective method of anti-icing equipment is the 

electric heating method. Small wires or other conductive 

material is imbedded in the windscreen. The heater can be 

turned on by a switch in the flight deck, causing an electrical 

current to be passed across the shield through the wires to 

provide sufficient heat to prevent the formation of ice on 

the windscreen. The heated windscreen should only be used 

during flight. Do not leave it on during ground operations, as 

it can overheat and cause damage to the windscreen. Warning: 

the electrical current can cause compass deviation errors by 

as much as 40°. 

Propeller Anti-Ice 

Propellers are protected from icing by the use of alcohol or 

electrically heated elements. Some propellers are equipped 

with a discharge nozzle that is pointed toward the root of the 

blade. Alcohol is discharged from the nozzles, and centrifugal 

force drives the alcohol down the leading edge of the blade. 

The boots are also grooved to help direct the flow of alcohol. 

This prevents ice from forming on the leading edge of the 

propeller. Propellers can also be fitted with propeller anti-ice 

boots. The propeller boot is divided into two sections—the 

inboard and the outboard sections. The boots are imbedded 

with electrical wires that carry current for heating the 

propeller. The prop anti-ice system can be monitored for 

proper operation by monitoring the prop anti-ice ammeter. 

During the preflight inspection, check the propeller boots for 

proper operation. If a boot fails to heat one blade, an unequal 

blade loading can result and may cause severe propeller 

vibration. [Figure 7-50] 

Other Anti-Ice and Deice Systems 

Pitot and static ports, fuel vents, stall-warning sensors, 

and other optional equipment may be heated by electrical 

elements. Operational checks of the electrically heated 

systems are to be checked in accordance with the AFM /POH. 

Operation of aircraft anti-icing and deicing systems should be 

checked prior to encountering icing conditions. Encounters 

with structural ice require immediate action. Anti-icing and 

deicing equipment are not intended to sustain long-term flight 

in icing conditions. 

Chapter Summary 

All aircraft have a requirement for essential systems such 

as the engine, propeller, induction, ignition systems as well 

as the fuel, lubrication, cooling, electrical, landing gear, and 

The boot is divided into two sections: inboard and outboard. 

When the anti-ice is operating, the inboard section heats on 

each blade, and then cycles to the outboard section. If a boot 

fails to heat properly on one blade, unequal ice loading may 

result causing severe vibration. 

Prop anti-ice boot 

0 20

10 

PROP DEICER 

AMPS 

When the system is operating, 

the prop ammeter indicates 

normal operating range. As each 

boot section cycles, the ammeter 

fluctuates. 

Prop anti-ice ammeter 

Outboard section 

Inboard section 

Figure 7-49. TKS weeping wing anti-ice/deicing system. Figure 7-50. Prop ammeter and anti-ice boots. 

7-41 
environmental control systems to support flight. Understanding 

the aircraft systems of the aircraft being flown is critical to 

its safe operation and proper maintenance. Consult the AFM/ 

POH for specific information pertaining to the aircraft being 

flown. Various manufacturer and owners group websites can 

also be a valuable source of additional information. 

7-42
 
8-1 

Introduction 

In order to safely fly any aircraft, a pilot must understand 

how to interpret and operate the flight instruments. The 

pilot also needs to be able to recognize associated errors and 

malfunctions of these instruments. This chapter addresses the 

pitot-static system and associated instruments, the vacuum 

system and related instruments, gyroscopic instruments, and 

the magnetic compass. When a pilot understands how each 

instrument works and recognizes when an instrument is 

malfunctioning, he or she can safely utilize the instruments 

to their fullest potential. 

Pitot-Static Flight Instruments 

The pitot-static system is a combined system that utilizes the 

static air pressure and the dynamic pressure due to the motion 

of the aircraft through the air. These combined pressures are 

utilized for the operation of the airspeed indicator (ASI), 

altimeter, and vertical speed indicator (VSI). [Figure 8-1] 

Flight

Instruments 

Chapter 8 
 

30.0

29.9

29.8 

Altimeter 

Heater (35 watts) 

Static port 

Airspeed indicator (ASI) Vertical speed indicator (VSI)

Pitot heater switch 

Drain hole 

Pressure chamber 

Alternate static source 

Static hole 

Heater (100 watts) 

Pitot tube 

Baffle plate 

Static chamber 

Ram air 

Figure 8-1. Pitot-static system and instruments. 

Impact Pressure Chamber and Lines 

The pitot tube is utilized to measure the total combined 

pressures that are present when an aircraft moves through 

the air. Static pressure, also known as ambient pressure, is 

always present whether an aircraft is moving or at rest. It is 

simply the barometric pressure in the local area. Dynamic 

pressure is present only when an aircraft is in motion; 

therefore, it can be thought of as a pressure due to motion. 

Wind also generates dynamic pressure. It does not matter if 

the aircraft is moving through still air at 70 knots or if the 

aircraft is facing a wind with a speed of 70 knots, the same 

dynamic pressure is generated. 

When the wind blows from an angle less than 90° off the 

nose of the aircraft, dynamic pressure can be depicted on the 

ASI. The wind moving across the airfoil at 20 knots is the 

same as the aircraft moving through calm air at 20 knots. 

The pitot tube captures the dynamic pressure, as well as the 

static pressure that is always present. 

The pitot tube has a small opening at the front that allows 

the total pressure to enter the pressure chamber. The total 

pressure is made up of dynamic pressure plus static pressure. 

In addition to the larger hole in the front of the pitot tube, 

there is a small hole in the back of the chamber that allows 

moisture to drain from the system should the aircraft enter 

precipitation. Both openings in the pitot tube must be checked 

prior to flight to ensure that neither is blocked. Many aircraft 

have pitot tube covers installed when they sit for extended 

periods of time. This helps to keep bugs and other objects 

from becoming lodged in the opening of the pitot tube. 

The one instrument that utilizes the pitot tube is the ASI. The 

total pressure is transmitted to the ASI from the pitot tube’s 

pressure chamber via a small tube. The static pressure is 

also delivered to the opposite side of the ASI, which serves 

to cancel out the two static pressures, thereby leaving the 

dynamic pressure to be indicated on the instrument. When 

the dynamic pressure changes, the ASI shows either increase 

or decrease, corresponding to the direction of change. The 

two remaining instruments (altimeter and VSI) utilize only 

the static pressure that is derived from the static port. 

Static Pressure Chamber and Lines 

The static chamber is vented through small holes to the 

free undisturbed air on the side(s) of the aircraft. As the 

atmospheric pressure changes, the pressure is able to move 

freely in and out of the instruments through the small lines 

that connect the instruments to the static system. An alternate 

static source is provided in some aircraft to provide static 

pressure should the primary static source become blocked. 

The alternate static source is normally found inside the flight 

8-2 
 

 

deck. Due to the venturi effect of the air flowing around the 

fuselage, the air pressure inside the flight deck is lower than 

the exterior pressure. 

When the alternate static source pressure is used, the 

following instrument indications are observed: 

1. The altimeter indicates a slightly higher altitude than 

actual. 

2. The ASI indicates an airspeed greater than the actual 

airspeed. 

3.	 The VSI shows a momentary climb and then stabilizes 

if the altitude is held constant. 

Each pilot is responsible for consulting the Aircraft Flight 

Manual (AFM) or the Pilot’s Operating Handbook (POH) 

to determine the amount of error that is introduced into the 

system when utilizing the alternate static source. In an aircraft 

not equipped with an alternate static source, an alternate 

method of introducing static pressure into the system should 

a blockage occur is to break the glass face of the VSI. This 

most likely renders the VSI inoperative. The reason for 

choosing the VSI as the instrument to break is that it is the 

least important static source instrument for flight. 

Altimeter 

The altimeter is an instrument that measures the height of 

an aircraft above a given pressure level. Pressure levels 

are discussed later in detail. Since the altimeter is the only 

instrument that is capable of indicating altitude, this is one of 

the most vital instruments installed in the aircraft. To use the 

altimeter effectively, the pilot must understand the operation 

of the instrument, as well as the errors associated with the 

altimeter and how each affect the indication. 

A stack of sealed aneroid wafers comprise the main 

component of the altimeter. An aneroid wafer is a sealed 

wafer that is evacuated to an internal pressure of 29.92 

inches of mercury ("Hg). These wafers are free to expand 

and contract with changes to the static pressure. A higher 

static pressure presses down on the wafers and causes them 

to collapse. A lower static pressure (less than 29.92 "Hg) 

allows the wafers to expand. A mechanical linkage connects 

the wafer movement to the needles on the indicator face, 

which translates compression of the wafers into a decrease 

in altitude and translates an expansion of the wafers into an 

increase in altitude. [Figure 8-2] 

Notice how the static pressure is introduced into the rear of the 

sealed altimeter case. The altimeter’s outer chamber is sealed, 

which allows the static pressure to surround the aneroid 

wafers. If the static pressure is higher than the pressure in the 

aneroid wafers (29.92 "Hg), then the wafers are compressed 

Figure 8-2. Altimeter. 

Aneroid wafers 

Static port 

100 ft. pointer 

A crosshatched area appears on 

some altimeters when displaying 

an altitude below 10,000 feet MSL. 

Crosshatch flag 

Barometric scale adjustment knob 

10,000 ft. pointer 

1,000 ft. pointer 

Altimeter setting window 

until the pressure inside the wafers is equal to the surrounding 

static pressure. Conversely, if the static pressure is less than 

the pressure inside of the wafers, the wafers are able to expand 

which increases the volume. The expansion and contraction 

of the wafers moves the mechanical linkage which drives the 

needles on the face of the altimeter. 

Principle of Operation 

The pressure altimeter is an aneroid barometer that measures 

the pressure of the atmosphere at the level where the altimeter is 

located and presents an altitude indication in feet. The altimeter 

uses static pressure as its source of operation. Air is denser 

at sea level than aloft—as altitude increases, atmospheric 

pressure decreases. This difference in pressure at various levels 

causes the altimeter to indicate changes in altitude. 

The presentation of altitude varies considerably between 

different types of altimeters. Some have one pointer while 

others have two or more. Only the multipointer type is 

discussed in this handbook. The dial of a typical altimeter 

is graduated with numerals arranged clockwise from zero 

to nine. Movement of the aneroid element is transmitted 

through gears to the three hands that indicate altitude. In 

Figure 8-2, the long, thin needle with the inverted triangle 

at the end indicates tens of thousands of feet; the short, wide 

needle indicates thousands of feet; and the long needle on 

top indicates hundreds of feet. 

8-3 
° ° °

 

This indicated altitude is correct, however, only when the 

sea level barometric pressure is standard (29.92 "Hg), the sea 

level free air temperature is standard (+15 degrees Celsius 

(°C) or 59 degrees Fahrenheit (°F)), and the pressure and 

temperature decrease at a standard rate with an increase 

in altitude. Adjustments for nonstandard pressures are 

accomplished by setting the corrected pressure into a 

barometric scale located on the face of the altimeter. The 

barometric pressure window is sometimes referred to as 

the Kollsman window; only after the altimeter is set does it 

indicate the correct altitude. The word “correct” will need 

to be better explained when referring to types of altitudes, 

but is commonly used in this case to denote the approximate 

altitude above sea level. In other words, the indicated 

altitude refers to the altitude read off of the altitude which is 

uncorrected, after the barometric pressure setting is dialed 

into the Kollsman window. The additional types of altitudes 

are further explained later. 

Effect of Nonstandard Pressure and Temperature 

It is easy to maintain a consistent height above ground if 

the barometric pressure and temperature remain constant, 

but this is rarely the case. The pressure and temperature can 

change between takeoff and landing even on a local flight. 

If these changes are not taken into consideration, flight 

becomes dangerous. 

If altimeters could not be adjusted for nonstandard pressure, a 

hazardous situation could occur. For example, if an aircraft is 

flown from a high pressure area to a low pressure area without 

adjusting the altimeter, a constant altitude will be displayed, 

but the actual height of the aircraft above the ground would 

be lower then the indicated altitude. There is an old aviation 

axiom: “GOING FROM A HIGH TO A LOW, LOOK OUT 

BELOW.” Conversely, if an aircraft is flown from a low 

pressure area to a high pressure area without an adjustment 

of the altimeter, the actual altitude of the aircraft is higher 

than the indicated altitude. Once in flight, it is important to 

frequently obtain current altimeter settings en route to ensure 

terrain and obstruction clearance. 

Many altimeters do not have an accurate means of being 

adjusted for barometric pressures in excess of 31.00 

"Hg. When the altimeter cannot be set to the higher 

pressure setting, the aircraft actual altitude is higher than 

the altimeter indicates. When low barometric pressure 

conditions occur (below 28.00), flight operations by 

aircraft unable to set the actual altimeter setting are 

not recommended. 

Adjustments to compensate for nonstandard pressure do 

not compensate for nonstandard temperature. Since cold 

air is denser than warm air, when operating in temperatures 

that are colder than standard, the altitude is lower than the 

altimeter indication. [Figure 8-3] It is the magnitude of this 

“difference” that determines the magnitude of the error. It is 

the difference due to colder temperatures that concerns the 

pilot. When flying into a cooler air mass while maintaining a 

constant indicated altitude, true altitude is lower. If terrain or 

obstacle clearance is a factor in selecting a cruising altitude, 

particularly in mountainous terrain, remember to anticipate 

that a colder-than-standard temperature places the aircraft 

lower than the altimeter indicates. Therefore, a higher 

indicated altitude may be required to provide adequate terrain 

clearance. A variation of the memory aid used for pressure 

5,000 foot pressure level 

4,000 foot pressure level 

3,000 foot pressure level 

2,000 foot pressure level 

1,000 foot pressure level 

Sea level 

30 C 15 C 0 C 

Figure 8-3. Effects of nonstandard temperature on an altimeter. 

8-4 
 

 

 

 

 

 

 

can be employed: “FROM HOT TO COLD, LOOK OUT 

BELOW.” When the air is warmer than standard, the aircraft 

is higher than the altimeter indicates. Altitude corrections for 

temperature can be computed on the navigation computer. 

Extremely cold temperatures also affect altimeter indications. 

Figure 8-4, which was derived from ICAO formulas, 

indicates how much error can exist when the temperature is 

extremely cold. 

Setting the Altimeter 

Most altimeters are equipped with a barometric pressure 

setting window (or Kollsman window) providing a means 

to adjust the altimeter. A knob is located at the bottom of the 

instrument for this adjustment. 

To adjust the altimeter for variation in atmospheric pressure, 

the pressure scale in the altimeter setting window, calibrated 

in inches of mercury ("Hg) and/or millibars (mb), is adjusted 

to match the given altimeter setting. Altimeter setting is 

defined as station pressure reduced to sea level, but an 

altimeter setting is accurate only in the vicinity of the 

reporting station. Therefore, the altimeter must be adjusted as 

the flight progresses from one station to the next. Air traffic 

control (ATC) will advise when updated altimeter settings 

are available. If a pilot is not utilizing ATC assistance, 

local altimeter settings can be obtained by monitoring local 

automated weather observing system/automated surface 

observation system (AWOS/ASOS) or automatic terminal 

information service (ATIS) broadcasts. 

Many pilots confidently expect the current altimeter setting 

will compensate for irregularities in atmospheric pressure at 

all altitudes, but this is not always true. The altimeter setting 

broadcast by ground stations is the station pressure corrected 

to mean sea level. It does not account for the irregularities 

Figure 8-4. Look at the chart using a temperature of –10 °C and 

an aircraft altitude of 1,000 feet above the airport elevation. The 

chart shows that the reported current altimeter setting may place 

the aircraft as much as 100 feet below the altitude indicated by 

the altimeter. 

Height Above Airport in Feet 

+10 

0 

-10 

-20 

-30 

-40 

-50 

10 

20 

20 

30 

40 

50 

60 

10 

20 

30 

50 

60 

80 

90 

10 

30 

40 

60 

80 

100 

120 

10 

30 

50 

70 

100 

120 

150 

20 

40 

60 

90 

120 

150 

180 

20 

40 

70 

100 

140 

170 

210 

20 

50 

80 

120 

150 

190 

240 

20 

50 

90 

130 

170 

220 

270 

20 

60 

100 

140 

190 

240 

300 

30 

90 

150 

210 

280 

360 

450 

40 

120 

200 

280 

380 

480 

590 

60 

170 

290 

420 

570 

720 

890 

80 

230 

390 

570 

760 

970 

1,190 

90 

280 

490 

710 

950 

1,210 

1,500 

ReportedTemp 0 °C

200300400500600700800900

1,0001,500

2,0003,000

4,0005,000 

at higher levels, particularly the effect of nonstandard 

temperature. If each pilot in a given area is using the same 

altimeter setting, each altimeter should be equally affected 

by temperature and pressure variation errors, making it 

possible to maintain the desired vertical separation between 

aircraft. This does not guarantee vertical separation though. 

It is still imperative to maintain a regimented visual scan for 

intruding air traffic. 

When flying over high, mountainous terrain, certain 

atmospheric conditions cause the altimeter to indicate an 

altitude of 1,000 feet or more higher than the actual altitude. 

For this reason, a generous margin of altitude should be 

allowed—not only for possible altimeter error, but also for 

possible downdrafts that might be associated with high winds. 

To illustrate the use of the altimeter setting system, follow a 

flight from Dallas Love Field, Texas, to Abilene Municipal 

Airport, Texas, via Mineral Wells. Before taking off from 

Love Field, the pilot receives a current altimeter setting of 

29.85 "Hg from the control tower or ATIS and sets this value 

in the altimeter setting window. The altimeter indication 

should then be compared with the known airport elevation of 

487 feet. Since most altimeters are not perfectly calibrated, 

an error may exist. 

When over Mineral Wells, assume the pilot receives a current 

altimeter setting of 29.94 "Hg and sets this in the altimeter 

window. Before entering the traffic pattern at Abilene 

Municipal Airport, a new altimeter setting of 29.69 "Hg 

is received from the Abilene Control Tower and set in 

the altimeter setting window. If the pilot desires to fly the 

traffic pattern at approximately 800 feet above the terrain, 

and the field elevation of Abilene is 1,791 feet, an indicated 

altitude of 2,600 feet should be maintained (1,791 feet + 

800 feet = 2,591 feet, rounded to 2,600 feet). 

The importance of properly setting the altimeter cannot 

be overemphasized. Assume the pilot did not adjust the 

altimeter at Abilene to the current setting and continued using 

the Mineral Wells setting of 29.94 "Hg. When entering the 

Abilene traffic pattern at an indicated altitude of 2,600 feet, 

the aircraft would be approximately 250 feet below the proper 

traffic pattern altitude. Upon landing, the altimeter would 

indicate approximately 250 feet higher than the field elevation. 

Mineral Wells altimeter setting 29.94 

Abilene altimeter setting 29.69 

Difference 0.25 

(Since 1 inch of pressure is equal to approximately 1,000 feet 

of altitude, 0.25 × 1,000 feet = 250 feet.) 

8-5 
 

 

 

 

 

 

When determining whether to add or subtract the amount of 

altimeter error, remember that when the actual pressure is lower 

than what is set in the altimeter window, the actual altitude 

of the aircraft is lower than what is indicated on the altimeter. 

The following is another method of computing the altitude 

deviation. Start by subtracting the current altimeter setting 

from 29.94 "Hg. Always remember to place the original setting 

as the top number. Then subtract the current altimeter setting. 

Mineral Wells altimeter setting 29.94 

Abilene altimeter setting 29.69 

29.94 – 29.69 = Difference 0.25 

(Since 1 inch of pressure is equal to approximately 1,000 feet 

of altitude, 0.25 × 1,000 feet = 250 feet.) Always subtract 

the number from the indicated altitude. 

2,600 – 250 = 2,350 

Now, try a lower pressure setting. Adjust from altimeter 

setting 29.94 to 30.56 "Hg. 

Mineral Wells altimeter setting 29.94 

Altimeter setting 30.56 

29.94 – 30.56 = Difference –0.62 

(Since 1 inch of pressure is equal to approximately 1,000 feet 

of altitude, 0.62 × 1,000 feet = 620 feet.) Always subtract 

the number from the indicated altitude. 

2,600 – (–620) = 3,220 

The pilot will be 620 feet high. 

Notice the difference is a negative number. Starting with the 

current indicated altitude of 2,600 feet, subtracting a negative 

number is the same as adding the two numbers. By utilizing 

this method, a pilot will better understand the importance of 

using the current altimeter setting (miscalculation of where 

and in what direction an error lies can affect safety; if altitude 

is lower than indicated altitude, an aircraft could be in danger 

of colliding with an obstacle). 

Altimeter Operation 

There are two means by which the altimeter pointers can 

be moved. The first is a change in air pressure, while the 

other is an adjustment to the barometric scale. When the 

aircraft climbs or descends, changing pressure within the 

altimeter case expands or contracts the aneroid barometer. 

This movement is transmitted through mechanical linkage 

to rotate the pointers. 

A decrease in pressure causes the altimeter to indicate an 

increase in altitude, and an increase in pressure causes the 

altimeter to indicate a decrease in altitude. Accordingly, if 

the aircraft is sitting on the ground with a pressure level of 

29.98 "Hg and the pressure level changes to 29.68 "Hg, the 

altimeter would show an increase of approximately 300 feet 

in altitude. This pressure change is most noticeable when the 

aircraft is left parked over night. As the pressure falls, the 

altimeter interprets this as a climb. The altimeter indicates 

an altitude above the actual field elevation. If the barometric 

pressure setting is reset to the current altimeter setting of 29.68 

"Hg, then the field elevation is again indicated on the altimeter. 

This pressure change is not as easily noticed in flight since 

aircraft fly at specific altitudes. The aircraft steadily decreases 

true altitude while the altimeter is held constant through pilot 

action as discussed in the previous section. 

Knowing the aircraft’s altitude is vitally important to a 

pilot. The pilot must be sure that the aircraft is flying high 

enough to clear the highest terrain or obstruction along the 

intended route. It is especially important to have accurate 

altitude information when visibility is restricted. To clear 

obstructions, the pilot must constantly be aware of the altitude 

of the aircraft and the elevation of the surrounding terrain. To 

reduce the possibility of a midair collision, it is essential to 

maintain altitude in accordance with air traffic rules. 

Types of Altitude 

Altitude in itself is a relevant term only when it is specifically 

stated to which type of altitude a pilot is referring. Normally 

when the term “altitude” is used, it is referring to altitude 

above sea level since this is the altitude which is used to 

depict obstacles and airspace, as well as to separate air traffic. 

Altitude is vertical distance above some point or level used as 

a reference. There are as many kinds of altitude as there are 

reference levels from which altitude is measured, and each 

may be used for specific reasons. Pilots are mainly concerned 

with five types of altitudes: 

1. Indicated altitude—read directly from the altimeter 

(uncorrected) when it is set to the current altimeter 

setting. 

2. True altitude—the vertical distance of the aircraft 

above sea level—the actual altitude. It is often 

expressed as feet above mean sea level (MSL). Airport, 

terrain, and obstacle elevations on aeronautical charts 

are true altitudes. 

8-6 
I

0

I

UP

3. Absolute altitude—the vertical distance of an aircraft 

above the terrain, or above ground level (AGL). 

4. Pressure altitude—the altitude indicated when 

the altimeter setting window (barometric scale) is 

adjusted to 29.92 "Hg. This is the altitude above 

the standard datum plane, which is a theoretical 

plane where air pressure (corrected to 15 °C) equals 

29.92 "Hg. Pressure altitude is used to compute density 

altitude, true altitude, true airspeed (TAS), and other 

performance data. 

5. Density altitude—pressure altitude corrected 

for variations from standard temperature. When 

conditions are standard, pressure altitude and density 

altitude are the same. If the temperature is above 

standard, the density altitude is higher than pressure 

altitude. If the temperature is below standard, the 

density altitude is lower than pressure altitude. This 

is an important altitude because it is directly related 

to the aircraft’s performance. 

A pilot must understand how the performance of the aircraft 

is directly related to the density of the air. The density of 

the air affects how much power a naturally aspirated engine 

produces, as well as how efficient the airfoils are. If there are 

fewer air molecules (lower pressure) to accelerate through 

the propeller, the acceleration to rotation speed is longer 

and thus produces a longer takeoff roll, which translates to 

a decrease in performance. 

As an example, consider an airport with a field elevation 

of 5,048 feet MSL where the standard temperature is 5 °C. 

Under these conditions, pressure altitude and density altitude 

are the same—5,048 feet. If the temperature changes to 

30 °C, the density altitude increases to 7,855 feet. This 

means an aircraft would perform on takeoff as though the 

field elevation were 7,855 feet at standard temperature. 

Conversely, a temperature of –25 °C would result in a density 

altitude of 1,232 feet. An aircraft would perform much better 

under these conditions. 

Instrument Check 

Prior to each flight, a pilot should examine the altimeter for 

proper indications in order to verify its validity. To determine 

the condition of an altimeter, set the barometric scale to the 

current reported altimeter setting transmitted by the local 

airport traffic control tower, flight service station (FSS), or 

any other reliable source, such as ATIS, AWOS, or ASOS. 

The altimeter pointers should indicate the surveyed field 

elevation of the airport. If the indication is off more than 

75 feet from the surveyed field elevation, the instrument 

should be referred to a certificated instrument repair station 

for recalibration. 

Vertical Speed Indicator (VSI) 

The VSI, which is sometimes called a vertical velocity 

indicator (VVI), indicates whether the aircraft is climbing, 

descending, or in level flight. The rate of climb or descent is 

indicated in feet per minute (fpm). If properly calibrated, the 

VSI indicates zero in level flight. [Figure 8-5] 

Principle of Operation 

Although the VSI operates solely from static pressure, it is a 

differential pressure instrument. It contains a diaphragm with 

connecting linkage and gearing to the indicator pointer inside 

an airtight case. The inside of the diaphragm is connected 

directly to the static line of the pitot-static system. The area 

outside the diaphragm, which is inside the instrument case, 

is also connected to the static line but through a restricted 

orifice (calibrated leak). 

Both the diaphragm and the case receive air from the static 

line at existing atmospheric pressure. The diaphragm receives 

unrestricted air, while the case receives the static pressure via 

the metered leak. When the aircraft is on the ground or in level 

flight, the pressures inside the diaphragm and the instrument 

case are equal, and the pointer is at the zero indication. 

When the aircraft climbs or descends, the pressure inside 

the diaphragm changes immediately, but due to the metering 

action of the restricted passage, the case pressure remains 

higher or lower for a short time, causing the diaphragm to 

contract or expand. This causes a pressure differential that 

is indicated on the instrument needle as a climb or descent. 

When the pressure differential stabilizes at a definite ratio, 

the needle indicates the rate of altitude change. 

Figure 8-5. Vertical speed indicator (VSI). 

3 

4 

2 

2 

3 

VERTICAL SPEED 

THOUSAND FT PER MIN 

DOWN 

Diaphragm 

Direct static pressure 

Calibrated leak 

8-7 
4

The VSI displays two different types of information: 

• Trend information shows an immediate indication of 

an increase or decrease in the aircraft’s rate of climb 

or descent. 

• Rate information shows a stabilized rate of change in 

altitude. 

The trend information is the direction of movement of the 

VSI needle. For example, if an aircraft is maintaining level 

flight and the pilot pulls back on the control yoke causing the 

nose of the aircraft to pitch up, the VSI needle moves upward 

to indicate a climb. If the pitch attitude is held constant, 

the needle stabilizes after a short period (6–9 seconds) and 

indicates the rate of climb in hundreds of fpm. The time 

period from the initial change in the rate of climb, until the 

VSI displays an accurate indication of the new rate, is called 

the lag. Rough control technique and turbulence can extend 

the lag period and cause erratic and unstable rate indications. 

Some aircraft are equipped with an instantaneous vertical 

speed indicator (IVSI), which incorporates accelerometers 

to compensate for the lag in the typical VSI. [Figure 8-6] 

Instrument Check 

As part of a preflight check, proper operation of the VSI 

must be established. Make sure the VSI indicates a near zero 

reading prior to leaving the ramp area and again just before 

takeoff. If the VSI indicates anything other than zero, that 

indication can be referenced as the zero mark. Normally, if the 

needle is not exactly zero, it is only slightly above or below 

the zero line. After takeoff, the VSI should trend upward to 

indicate a positive rate of climb and then, once a stabilized 

climb is established, a rate of climb can be referenced. 

Figure 8-6. An IVSI incorporates accelerometers to help the 

instrument immediately indicate changes in vertical speed. 

3 

I 

0 

2 

I 2

3 

UP 

DOWN 

.5 

.5 

Accelerometer 

Inlet from static port 

Calibrated leak 

Airspeed Indicator (ASI) 

The ASI is a sensitive, differential pressure gauge that 

measures and promptly indicates the difference between pitot 

(impact/dynamic pressure) and static pressure. These two 

pressures are equal when the aircraft is parked on the ground 

in calm air. When the aircraft moves through the air, the 

pressure on the pitot line becomes greater than the pressure 

in the static lines. This difference in pressure is registered by 

the airspeed pointer on the face of the instrument, which is 

calibrated in miles per hour, knots (nautical miles per hour), 

or both. [Figure 8-7] 

The ASI is the one instrument that utilizes both the pitot, 

as well as the static system. The ASI introduces the static 

pressure into the airspeed case while the pitot pressure 

(dynamic) is introduced into the diaphragm. The dynamic 

pressure expands or contracts one side of the diaphragm, 

which is attached to an indicating system. The system drives 

the mechanical linkage and the airspeed needle. 

Just as in altitudes, there are multiple types of airspeeds. 

Pilots need to be very familiar with each type. 

• Indicated airspeed (IAS)—the direct instrument 

reading obtained from the ASI, uncorrected for 

variations in atmospheric density, installation error, 

or instrument error. Manufacturers use this airspeed 

as the basis for determining aircraft performance. 

Takeoff, landing, and stall speeds listed in the AFM/ 

POH are IAS and do not normally vary with altitude 

or temperature. 

Figure 8-7. Airspeed indicator (ASI). 

100 

200 

50 

150 

Diaphragm 

Static air line Handstaff pinion

Pitot tube 

Ram air 

Long lever Sector

Pitot connection 

8-8 
 

 

 

 

 

 

 

 

• Calibrated airspeed (CAS)—IAS corrected for 

installation error and instrument error. Although 

manufacturers attempt to keep airspeed errors to a 

minimum, it is not possible to eliminate all errors 

throughout the airspeed operating range. At certain 

airspeeds and with certain flap settings, the installation 

and instrument errors may total several knots. This 

error is generally greatest at low airspeeds. In the 

cruising and higher airspeed ranges, IAS and CAS 

are approximately the same. Refer to the airspeed 

calibration chart to correct for possible airspeed errors. 

• True airspeed (TAS)—CAS corrected for altitude 

and nonstandard temperature. Because air density 

decreases with an increase in altitude, an aircraft has 

to be flown faster at higher altitudes to cause the same 

pressure difference between pitot impact pressure 

and static pressure. Therefore, for a given CAS, TAS 

increases as altitude increases; or for a given TAS, 

CAS decreases as altitude increases. A pilot can find 

TAS by two methods. The most accurate method is 

to use a flight computer. With this method, the CAS 

is corrected for temperature and pressure variation by 

using the airspeed correction scale on the computer. 

Extremely accurate electronic flight computers are 

also available. Just enter the CAS, pressure altitude, 

and temperature, and the computer calculates the TAS. 

A second method, which is a rule of thumb, provides 

the approximate TAS. Simply add 2 percent to the 

CAS for each 1,000 feet of altitude. The TAS is the 

speed that is used for flight planning and is used when 

filing a flight plan. 

• Groundspeed (GS)—the actual speed of the airplane 

over the ground. It is TAS adjusted for wind. GS 

decreases with a headwind and increases with a 

tailwind. 

Airspeed Indicator Markings 

Aircraft weighing 12,500 pounds or less, manufactured after 

1945, and certificated by the FAA are required to have ASIs 

marked in accordance with a standard color-coded marking 

system. This system of color-coded markings enables a pilot 

to determine at a glance certain airspeed limitations that are 

important to the safe operation of the aircraft. For example, if 

during the execution of a maneuver, it is noted that the airspeed 

needle is in the yellow arc and rapidly approaching the red 

line, the immediate reaction should be to reduce airspeed. 

As shown in Figure 8-8, ASIs on single-engine small aircraft 

include the following standard color-coded markings: 

•	 White arc—commonly referred to as the flap operating 

range since its lower limit represents the full flap stall 

speed and its upper limit provides the maximum flap 

Figure 8-8. Single engine airspeed indicator (ASI). 

100 

80

120

140 

T.A.S.

KTS 

PRESS

ALT 0 5 10 15 20 

F° 120 90 60 30 0 -30 

100

120 

40 

60 

80 100 

120 

140 

160 

MPH

MPH 

AIRSPEED 

KNOTS 

VS0 

VNE (red line) 

Yellow arc 

VN0 

Green arc VFE 

White arc 

VS1 

speed. Approaches and landings are usually flown at 

speeds within the white arc. 

•	 Lower limit of white arc (VS0)—the stalling speed 

or the minimum steady flight speed in the landing 

configuration. In small aircraft, this is the power-off 

stall speed at the maximum landing weight in the 

landing configuration (gear and flaps down). 

• Upper limit of the white arc (VFE)—the maximum 

speed with the flaps extended. 

•	 Green arc—the normal operating range of the aircraft. 

Most flying occurs within this range. 

•	 Lower limit of green arc (VS1)—the stalling speed 

or the minimum steady flight speed obtained in a 

specified configuration. For most aircraft, this is the 

power-off stall speed at the maximum takeoff weight 

in the clean configuration (gear up, if retractable, and 

flaps up). 

•	 Upper limit of green arc (VN0)—the maximum 

structural cruising speed. Do not exceed this speed 

except in smooth air. 

•	 Yellow arc—caution range. Fly within this range only 

in smooth air and then only with caution. 

•	 Red line (VNE)—never exceed speed. Operating above 

this speed is prohibited since it may result in damage 

or structural failure. 

Other Airspeed Limitations 

Some important airspeed limitations are not marked on the 

face of the ASI, but are found on placards and in the AFM/ 

POH. These airspeeds include: 

8-9 
 

 

• Design maneuvering speed (VA)—the maximum 

speed at which the structural design’s limit load can 

be imposed (either by gusts or full deflection of the 

control surfaces) without causing structural damage. 

It is important to consider weight when referencing 

this speed. For example, VA may be 100 knots when 

an airplane is heavily loaded, but only 90 knots when 

the load is light. 

• Landing gear operating speed (VLO)—the maximum 

speed for extending or retracting the landing gear if 

flying an aircraft with retractable landing gear. 

• Landing gear extended speed (VLE)—the maximum 

speed at which an aircraft can be safely flown with 

the landing gear extended. 

• Best angle-of-climb speed (VX)—the airspeed at 

which an aircraft gains the greatest amount of altitude 

in a given distance. It is used during a short-field 

takeoff to clear an obstacle. 

• Best rate-of-climb speed (VY)—the airspeed that 

provides the most altitude gain in a given period of time. 

• Single-engine best rate-of-climb (VYSE)—the best 

rate-of-climb or minimum rate-of-sink in a light 

twin-engine aircraft with one engine inoperative. It is 

marked on the ASI with a blue line. VYSE is commonly 

referred to as “Blue Line.” 

• Minimum control speed (VMC)—the minimum flight 

speed at which a light, twin-engine aircraft can be 

satisfactorily controlled when an engine suddenly 

becomes inoperative and the remaining engine is at 

takeoff power. 

Instrument Check 

Prior to takeoff, the ASI should read zero. However, if there 

is a strong wind blowing directly into the pitot tube, the ASI 

may read higher than zero. When beginning the takeoff, 

make sure the airspeed is increasing at an appropriate rate. 

Blockage of the Pitot-Static System 

Errors almost always indicate blockage of the pitot tube, the 

static port(s), or both. Blockage may be caused by moisture 

(including ice), dirt, or even insects. During preflight, make 

sure the pitot tube cover is removed. Then, check the pitot and 

static port openings. A blocked pitot tube affects the accuracy 

of the ASI, but a blockage of the static port not only affects 

the ASI, but also causes errors in the altimeter and VSI. 

Blocked Pitot System 

The pitot system can become blocked completely or only 

partially if the pitot tube drain hole remains open. If the pitot 

tube becomes blocked and its associated drain hole remains 

clear, ram air is no longer able to enter the pitot system. Air 

already in the system vents through the drain hole, and the 

remaining pressure drops to ambient (outside) air pressure. 

Under these circumstances, the ASI reading decreases to 

zero because the ASI senses no difference between ram and 

static air pressure. The ASI no longer operates since dynamic 

pressure cannot enter the pitot tube opening. Static pressure 

is able to equalize on both sides since the pitot drain hole 

is still open. The apparent loss of airspeed is not usually 

instantaneous but happens very quickly. [Figure 8-9] 

If both the pitot tube opening and the drain hole should 

become clogged simultaneously, then the pressure in the pitot 

tube is trapped. No change is noted on the airspeed indication 

should the airspeed increase or decrease. If the static port 

is unblocked and the aircraft should change altitude, then a 

change is noted on the ASI. The change is not related to a 

change in airspeed but a change in static pressure. The total 

pressure in the pitot tube does not change due to the blockage; 

however, the static pressure will change. 

Because airspeed indications rely upon both static and 

dynamic pressure together, the blockage of either of these 

systems affects the ASI reading. Remember that the ASI has 

a diaphragm in which dynamic air pressure is entered. Behind 

this diaphragm is a reference pressure called static pressure 

that comes from the static ports. The diaphragm pressurizes 

against this static pressure and as a result changes the airspeed 

indication via levers and indicators. [Figure 8-10] 

For example, take an aircraft and slow it down to zero knots 

at a given altitude. If the static port (providing static pressure) 

and the pitot tube (providing dynamic pressure) are both 

unobstructed, the following claims can be made: 

1. The ASI would be zero. 

2. Dynamic pressure and static pressure are equal. 

3.	 Because both dynamic and static air pressure are equal 

at zero speed with increased speed, dynamic pressure 

Figure 8-9. A blocked pitot tube, but clear drain hole. 

Static port 

Drain hole 

Pitot tube 

Blockage 

8-10 
Climb 

Descent 

Static port 

Drain hole 

Pitot tube 

Blockage 

Figure 8-10. Blocked pitot system with clear static system. 

must include two components: static pressure and 

dynamic pressure. 

It can be inferred that airspeed indication must be based upon 

a relationship between these two pressures, and indeed it is. 

An ASI uses the static pressure as a reference pressure and 

as a result, the ASI’s case is kept at this pressure behind the 

diaphragm. On the other hand, the dynamic pressure through 

the pitot tube is connected to a highly sensitive diaphragm 

within the ASI case. Because an aircraft in zero motion 

(regardless of altitude) results in a zero airspeed, the pitot tube 

always provides static pressure in addition to dynamic pressure. 

Therefore, the airspeed indication is the result of two 

pressures: the pitot tube static and dynamic pressure within 

the diaphragm as measured against the static pressure in the 

ASI’s case. 

If the aircraft were to descend while the pitot tube is 

obstructed, the pressure in the pitot system, including the 

diaphragm, would remain constant. But as the descent 

is made, the static pressure would increase against the 

diaphragm causing it to compress, thereby resulting in an 

indication of decreased airspeed. Conversely, if the aircraft 

were to climb, the static pressure would decrease allowing 

the diaphragm to expand, thereby showing an indication of 

greater airspeed. [Figure 8-10] 

The pitot tube may become blocked during flight due to 

visible moisture. Some aircraft may be equipped with pitot 

heat for flight in visible moisture. Consult the AFM/POH for 

specific procedures regarding the use of pitot heat. 

Blocked Static System 

If the static system becomes blocked but the pitot tube 

remains clear, the ASI continues to operate; however, it 

is inaccurate. The airspeed indicates lower than the actual 

airspeed when the aircraft is operated above the altitude 

where the static ports became blocked because the trapped 

static pressure is higher than normal for that altitude. When 

operating at a lower altitude, a faster than actual airspeed is 

displayed due to the relatively low static pressure trapped 

in the system. 

Revisiting the ratios that were used to explain a blocked pitot 

tube, the same principle applies for a blocked static port. If 

the aircraft descends, the static pressure increases on the pitot 

side showing an increase on the ASI. This assumes that the 

aircraft does not actually increase its speed. The increase in 

static pressure on the pitot side is equivalent to an increase 

in dynamic pressure since the pressure cannot change on 

the static side. 

If an aircraft begins to climb after a static port becomes 

blocked, the airspeed begins to show a decrease as the 

aircraft continues to climb. This is due to the decrease in 

static pressure on the pitot side, while the pressure on the 

static side is held constant. 

A blockage of the static system also affects the altimeter and 

VSI. Trapped static pressure causes the altimeter to freeze 

at the altitude where the blockage occurred. In the case of 

the VSI, a blocked static system produces a continuous zero 

indication. [Figure 8-11] 

Some aircraft are equipped with an alternate static source in 

the flight deck. In the case of a blocked static source, opening 

the alternate static source introduces static pressure from the 

flight deck into the system. Flight deck static pressure is lower 

than outside static pressure. Check the aircraft AOM/POH for 

airspeed corrections when utilizing alternate static pressure. 

8-11 
3600

3500

3400

3300

3200

3100

 

 

°

30.0

29.9

29.8 

Pitot tube 

Blockage 

Static port 

Frozen altimeter 

Constant zero indication on VSI 

Inaccurate airspeed indications 

Figure 8-11. Blocked static system. 

Electronic Flight Display (EFD) 

Advances in technology have brought about changes in the 

instrumentation found in all types of aircraft; for example, 

Electronic Flight Displays (EFDs) commonly referred to 

as “glass cockpits.” EFDs include flight displays such as 

primary flight displays (PFD) and multi-function displays 

(MFD). This has changed not only what information is 

available to a pilot, but also how the information is displayed. 

In addition to the improvement in system reliability, which 

increases overall safety, EFDs have decreased the overall cost 

of equipping aircraft with state-of-the-art instrumentation. 

Primary electronic instrumentation packages are less prone 

to failure than their analogue counterparts. No longer is it 

necessary for aircraft designers to create cluttered panel 

layouts in order to accommodate all necessary flight 

instruments. Instead, multi-panel digital flight displays 

combine all flight instruments onto a single screen that is 

called a primary flight display (PFD). The traditional “six 

pack” of instruments is now displayed on one liquid crystal 

display (LCD) screen. 

Airspeed Tape 

Configured similarly to traditional panel layouts, the ASI 

is located on the left side of the screen and is displayed as 

a vertical speed tape. As the aircraft increases in speed, the 

larger numbers descend from the top of the tape. The TAS is 

displayed at the bottom of the tape through the input to the air 

data computer (ADC) from the outside air temperature probe. 

Airspeed markings for VX, VY, and rotation speed (VR) are 

displayed for pilot reference. An additional pilot-controlled 

airspeed bug is available to set at any desired reference speed. 

As on traditional analogue ASIs, the electronic airspeed tape 

displays the color-coded ranges for the flap operating range, 

XPDR 5537 IDNT LCL10:12:34 

INSET PFD OBS CDI DME XPDR IDENT TMR/REF NRST ALERTS 

VOR 1 

270 

2 

1 

1 

2 

4300 

4200 

4100 

3900 

3900 

3800 

4300 

20 

80 

4000 

4000 

130 

120 

110 

90 

80 

70 

1 

100 

9 

TAS 106KT 

OAT 6°C 

NAV1 108.00 113.00 NAV2 108.00 110.60 134.000 118.000 COM1 

123.800 118.000 COM2 

WPT _ _ _ _ _ _ DIS _ _ ._ NM DTK _ _ _°T TRK 360° Attitude indicator Altimeter 

Horizontal situation indicator 

Vertical speed indicator (VSI) 

Slip skid indicator 

Airspeed indicator 

Turn indicator 

VOR 1 

270°

270° 

Slip/skid indicator 

Turn rate indicator tick marks 

Turn rate trend vector 

Figure 8-12. Primary flight display (PFD). Note that the actual location of indications vary depending on manufacturers. 

8-12 
 

normal range, and caution range. [Figure 8-12] The number 

value changes color to red when the airspeed exceeds VNE to 

warn the pilot of exceeding the maximum speed limitation. 

Attitude Indicator 

One improvement over analogue instrumentation is the 

larger attitude indicator on EFD. The artificial horizon spans 

the entire width of the PFD. [Figure 8-12] This expanded 

instrumentation offers better reference through all phases of 

flight and all flight maneuvers. The attitude indicator receives 

its information from the Attitude Heading and Reference 

System (AHRS). 

Altimeter 

The altimeter is located on the right side of the PFD. 

[Figure 8-12] As the altitude increases, the larger numbers 

descend from the top of the display tape, with the current 

altitude being displayed in the black box in the center of the 

display tape. The altitude is displayed in increments of 20 feet. 

Vertical Speed Indicator (VSI) 

The VSI is displayed to the right of the altimeter tape and can 

take the form of an arced indicator or a vertical speed tape. 

[Figure 8-12] Both are equipped with a vertical speed bug. 

Heading Indicator 

The heading indicator is located below the artificial horizon 

and is normally modeled after a Horizontal Situation 

Indicator (HSI). [Figure 8-12] As in the case of the attitude 

indicator, the heading indicator receives its information from 

the magnetometer, which feeds information to the AHRS unit 

and then out to the PFD. 

Turn Indicator 

The turn indicator takes a slightly different form than the 

traditional instrumentation. A sliding bar moves left and right 

below the triangle to indicate deflection from coordinated 

flight. [Figure 8-12] Reference for coordinated flight comes 

from accelerometers contained in the AHRS unit. 

Tachometer 

The sixth instrument normally associated with the “six pack” 

package is the tachometer. This is the only instrument that is 

not located on the PFD. The tachometer is normally located 

on the multi-function display (MFD). In the event of a display 

screen failure, it is displayed on the remaining screen with 

the PFD flight instrumentation. [Figure 8-13] 

Slip/Skid Indicator 

The slip/skid indicator is the horizontal line below the roll 

pointer. [Figure 8-12] Like a ball in a turn-and-slip indicator, 

a bar width off center is equal to one ball width displacement. 

Turn Rate Indicator 

The turn rate indicator, illustrated in Figure 8-12, is typically 

found directly above the rotating compass card. Tick marks 

to the left and right of the lubber line denote the turn 

(standard­rate versus half standard-rate). Typically denoted 

by a trend line, if the trend vector is extended to the 

second tick mark the aircraft is in a standard-rate turn. 

Individual panel displays can be configured for a variety 

of aircraft by installing different software packages. 

[Figure 8-14] Manufacturers are also able to upgrade existing 

instrument displays in a similar manner, eliminating the need 

to replace individual gauges in order to upgrade. 

Figure 8-13. Multi-function display (MFD). 

8-13 
150

140

130

110

100

90

9

140 

120 

100 

80 

60 

40 

102 10 

10 

10 

10 

58 

70 

65 

70 

30.30 

6710 

200 210 220 230 240 250 260 270 

UY 

UX 

VS 

IFR APPR 

00:03:29 

2320B 

ANG 239 A 

MA239 5800’ 

239 2.3NM 

W 

S 

E N 

Figure 8-14. Chelton’s FlightLogic (top) and Avidyne’s Entegra 

(bottom) are examples of panel displays that are configurable. 

Air Data Computer (ADC) 

EFDs utilize the same type of instrument inputs as traditional 

analogue gauges; however, the processing system is different. 

The pitot static inputs are received by an ADC. The ADC 

computes the difference between the total pressure and the 

static pressure and generates the information necessary to 

display the airspeed on the PFD. Outside air temperatures 

are also monitored and introduced into various components 

within the system, as well as being displayed on the PFD 

screen. [Figure 8-15] 

The ADC is a separate solid state device that, in addition to 

providing data to the PFD, is capable of providing data to the 

autopilot control system. In the event of system malfunction, the 

ADC can quickly be removed and replaced in order to decrease 

downtime and decrease maintenance turn-around times. 

Altitude information is derived from the static pressure port 

just as an analogue system does; however, the static pressure 

Figure 8-15. Teledyne’s 90004 TAS/Plus Air Data Computer (ADC) 

computes air data information from the pitot-static pneumatic 

system, aircraft temperature probe, and barometric correction 

device to help create a clear picture of flight characteristics. 

does not enter a diaphragm. The ADC computes the received 

barometric pressure and sends a digital signal to the PFD to 

display the proper altitude readout. EFDs also show trend 

vectors, which show the pilot how the altitude and airspeed 

are progressing. 

Trend Vectors 

Trend vectors are magenta lines that move up and down both 

the ASI and the altimeter. [Figures 8-16 and 8-17] The ADC 

computes the rate of change and displays the 6-second projection 

of where the aircraft will be. Pilots can utilize the trend vectors 

to better control the aircraft’s attitude. By including the trend 

vectors in the instrument scan, pilots are able to precisely control 

airspeed and altitude. Additional information can be obtained 

by referencing the Instrument Flying Handbook or specific 

avionics manufacturer’s training material. 

Figure 8-16. Airspeed trend vector. 

150 

140 

130 

110 

100 

90 

1 

120 

9 

TAS 120KT 

1 

120 

Airspeed trend vector 

8-14 
3600

3500

3400

3300

3200

3100

Figure 4-27. Supporting Instruments

 

°

°

 

Figure 8-17. Altimeter trend vector. 

VOR 1 

270 

2 

1 

1 

2 

-500 

4200 

4100 

4000 

3900 

3800 

3700 

3700 

40 

80 

3900 

4000 

130 

120 

110 

90 

80 

70 

1 

100 

9 

TAS 100KT 

270 

4100

3000

3900

20

80

4000

3100

4000

3900

80

70

3975 -125

3100

4000

3900

70

30

3950 -250

4000

3000

3800

45

05

3925

-375

Altitude trend vector 

Turn rate trend vector 

Airspeed trend (increasing) 

Gyroscopic Flight Instruments 

Several flight instruments utilize the properties of a gyroscope 

for their operation. The most common instruments containing 

gyroscopes are the turn coordinator, heading indicator, and 

the attitude indicator. To understand how these instruments 

operate requires knowledge of the instrument power systems, 

gyroscopic principles, and the operating principles of each 

instrument. 

Gyroscopic Principles 

Any spinning object exhibits gyroscopic properties. A wheel 

or rotor designed and mounted to utilize these properties is 

called a gyroscope. Two important design characteristics 

of an instrument gyro are great weight for its size, or high 

density, and rotation at high speed with low friction bearings. 

There are two general types of mountings; the type used 

depends upon which property of the gyro is utilized. A freely 

or universally mounted gyroscope is free to rotate in any 

direction about its center of gravity. Such a wheel is said to 

have three planes of freedom. The wheel or rotor is free to 

rotate in any plane in relation to the base and is balanced so 

that, with the gyro wheel at rest, it remains in the position 

in which it is placed. Restricted or semi-rigidly mounted 

gyroscopes are those mounted so that one of the planes of 

freedom is held fixed in relation to the base. 

There are two fundamental properties of gyroscopic action: 

rigidity in space and precession. 

Rigidity in Space 

Rigidity in space refers to the principle that a gyroscope 

remains in a fixed position in the plane in which it is spinning. 

An example of rigidity in space is that of a bicycle wheel. As 

the bicycle wheels increase speed, they become more stable in 

their plane of rotation. This is why a bicycle is unstable and 

maneuverable at low speeds and stable and less maneuverable 

at higher speeds. 

By mounting this wheel, or gyroscope, on a set of gimbal 

rings, the gyro is able to rotate freely in any direction. Thus, 

if the gimbal rings are tilted, twisted, or otherwise moved, 

the gyro remains in the plane in which it was originally 

spinning. [Figure 8-18] 

Precession 

Precession is the tilting or turning of a gyro in response to a 

deflective force. The reaction to this force does not occur at 

the point at which it was applied; rather, it occurs at a point 

that is 90° later in the direction of rotation. This principle 

allows the gyro to determine a rate of turn by sensing the 

amount of pressure created by a change in direction. The rate 

at which the gyro precesses is inversely proportional to the 

speed of the rotor and proportional to the deflective force. 

Using the example of the bicycle, precession acts on the 

wheels in order to allow the bicycle to turn. While riding 

at normal speed, it is not necessary to turn the handle bars 

in the direction of the desired turn. A rider simply leans in 

the direction that he or she wishes to go. Since the wheels 

are rotating in a clockwise direction when viewed from the 

right side of the bicycle, if a rider leans to the left, a force is 

applied to the top of the wheel to the left. The force actually 

acts 90° in the direction of rotation, which has the effect of 

applying a force to the front of the tire, causing the bicycle 

Figure 8-18. Regardless of the position of its base, a gyro tends to 

remain rigid in space, with its axis of rotation pointed in a constant 

direction. 

8-15 
 

to move to the left. There is a need to turn the handlebars at 

low speeds because of the instability of the slowly turning 

gyros and also to increase the rate of turn. 

Precession can also create some minor errors in some 

instruments. [Figure 8-19] Precession can cause a freely 

spinning gyro to become displaced from its intended plane 

of rotation through bearing friction, etc. Certain instruments 

may require corrective realignment during flight, such as the 

heading indicator. 

Sources of Power 

In some aircraft, all the gyros are vacuum, pressure, or 

electrically operated. In other aircraft, vacuum or pressure 

systems provide the power for the heading and attitude 

indicators, while the electrical system provides the power for 

the turn coordinator. Most aircraft have at least two sources 

of power to ensure at least one source of bank information is 

available if one power source fails. The vacuum or pressure 

system spins the gyro by drawing a stream of air against the 

rotor vanes to spin the rotor at high speed, much like the 

operation of a waterwheel or turbine. The amount of vacuum 

or pressure required for instrument operation varies, but is 

usually between 4.5 "Hg and 5.5 "Hg. 

One source of vacuum for the gyros is a vane-type enginedriven pump that is mounted on the accessory case of the 

engine. Pump capacity varies in different aircraft, depending 

on the number of gyros. 

A typical vacuum system consists of an engine-driven 

vacuum pump, relief valve, air filter, gauge, and tubing 

necessary to complete the connections. The gauge is mounted 

in the aircraft’s instrument panel and indicates the amount 

Figure 8-19. Precession of a gyroscope resulting from an applied 

deflective force. 

Plane of Precession 

Plane of Force

Plane of Rotation 

FORCE 

of pressure in the system (vacuum is measured in inches of 

mercury less than ambient pressure). 

As shown in Figure 8-20, air is drawn into the vacuum 

system by the engine-driven vacuum pump. It first goes 

through a filter, which prevents foreign matter from entering 

the vacuum or pressure system. The air then moves through 

the attitude and heading indicators where it causes the gyros 

to spin. A relief valve prevents the vacuum pressure, or 

suction, from exceeding prescribed limits. After that, the air 

is expelled overboard or used in other systems, such as for 

inflating pneumatic deicing boots. 

It is important to monitor vacuum pressure during flight, 

because the attitude and heading indicators may not provide 

reliable information when suction pressure is low. The 

vacuum, or suction, gauge is generally marked to indicate 

the normal range. Some aircraft are equipped with a warning 

light that illuminates when the vacuum pressure drops below 

the acceptable level. 

When the vacuum pressure drops below the normal operating 

range, the gyroscopic instruments may become unstable and 

inaccurate. Cross-checking the instruments routinely is a 

good habit to develop. 

Turn Indicators 

Aircraft use two types of turn indicators: turn-and-slip 

indicators and turn coordinators. Because of the way the gyro 

is mounted, the turn-and-slip indicator shows only the rate of 

turn in degrees per second. The turn coordinator is mounted 

at an angle, or canted, so it can initially show roll rate. When 

the roll stabilizes, it indicates rate of turn. Both instruments 

indicate turn direction and quality (coordination), and also 

serve as a backup source of bank information in the event an 

attitude indicator fails. Coordination is achieved by referring 

to the inclinometer, which consists of a liquid-filled curved 

tube with a ball inside. [Figure 8-21] 

Turn-and-Slip Indicator 

The gyro in the turn-and-slip indicator rotates in the vertical 

plane corresponding to the aircraft’s longitudinal axis. A 

single gimbal limits the planes in which the gyro can tilt, 

and a spring works to maintain a center position. Because of 

precession, a yawing force causes the gyro to tilt left or right, 

as viewed from the pilot seat. The turn-and-slip indicator 

uses a pointer, called the turn needle, to show the direction 

and rate of turn. The turn-and-slip indicator is incapable of 

“tumbling” off its rotational axis because of the restraining 

springs. When extreme forces are applied to a gyro, the gyro 

is displaced from its normal plane of rotation, rendering its 

indications invalid. Certain instruments have specific pitch 

and bank limits that induce a tumble of the gyro. 

8-16 
 

 

 

 

 

8 

4 6

2 

0 I0 

SUCTION 

INCHES MERCURT 

33

30 

24

2I

I5

I2 

6 

3 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Vacuum relief valve 

Vacuum air filter 

Attitude indicator 

Vacuum pump 

Heading indicator 

Overboard vent line 

Suction 

gauge 

Figure 8-20. Typical vacuum system. 

Turn Coordinator 

The gimbal in the turn coordinator is canted; therefore, its 

gyro can sense both rate of roll and rate of turn. Since turn 

coordinators are more prevalent in training aircraft, this 

discussion concentrates on that instrument. When rolling into 

or out of a turn, the miniature aircraft banks in the direction 

the aircraft is rolled. A rapid roll rate causes the miniature 

aircraft to bank more steeply than a slow roll rate. 

The turn coordinator can be used to establish and maintain 

a standard-rate turn by aligning the wing of the miniature 

aircraft with the turn index. Figure 8-22 shows a picture of a 

turn coordinator. There are two marks on each side (left and 

right) of the face of the instrument. The first mark is used to 

reference a wings level zero rate of turn. The second mark 

on the left and right side of the instrument serve to indicate 

a standard rate of turn. A standard-rate turn is defined as a 

turn rate of 3° per second. The turn coordinator indicates only 

the rate and direction of turn; it does not display a specific 

angle of bank. 

Figure 8-21. Turn indicators rely on controlled precession for their operation. 

Turn coordinator Turn-and-slip indicator 

Gyro rotation 

Standard rate turn index 

Horizontal gyro 

Inclinometer Inclinometer

Gimbal rotation 

Standard rate turn index 

Gyro rotation 

Gimbal rotation 

Canted gyro 

Gimbal 

8-17 
20

I0

0

20

20

I0

I0

20

 

I 

 I

 

 

 I

 I

 

Slipping turn Skidding turn 

Coordinated turn 

TURN COORDINATOR 

2 MIN. 

D.C.

ELEC.

L R 

NO PITCH 

INFORMATION 

TURN COORDINATOR 

2 MIN. 

D.C.

ELEC.

L R 

NO PITCH 

INFORMATION 

TURN COORDINATOR 

2 MIN. 

D.C.

ELEC.

L R 

NO PITCH 

INFORMATION 

Figure 8-22. If inadequate right rudder is applied in a right turn, 

a slip results. Too much right rudder causes the aircraft to skid 

through the turn. Centering the ball results in a coordinated turn. 

Inclinometer 

The inclinometer is used to depict aircraft yaw, which is 

the side-to-side movement of the aircraft’s nose. During 

coordinated, straight-and-level flight, the force of gravity 

causes the ball to rest in the lowest part of the tube, centered 

between the reference lines. Coordinated flight is maintained 

by keeping the ball centered. If the ball is not centered, it can 

be centered by using the rudder. 

To center the ball, apply rudder pressure on the side to 

which the ball is deflected. Use the simple rule, “step on the 

ball,” to remember which rudder pedal to press. If aileron 

and rudder are coordinated during a turn, the ball remains 

centered in the tube. If aerodynamic forces are unbalanced, 

the ball moves away from the center of the tube. As shown 

in Figure 8-22, in a slip, the rate of turn is too slow for the 

angle of bank, and the ball moves to the inside of the turn. In 

a skid, the rate of turn is too great for the angle of bank, and 

the ball moves to the outside of the turn. To correct for these 

conditions, and improve the quality of the turn, remember to 

“step on the ball.” Varying the angle of bank can also help 

restore coordinated flight from a slip or skid. To correct for a 

slip, decrease bank and/or increase the rate of turn. To correct 

for a skid, increase the bank and/or decrease the rate of turn. 

Yaw String 

One additional tool that can be added to the aircraft is a yaw 

string. A yaw string is simply a string or piece of yarn attached 

to the center of the wind screen. When in coordinated flight, 

the string trails straight back over the top of the wind screen. 

When the aircraft is either slipping or skidding, the yaw 

string moves to the right or left depending on the direction 

of slip or skid. 

Instrument Check 

During preflight, ensure that the inclinometer is full of fluid 

and has no air bubbles. The ball should also be resting at 

its lowest point. When taxiing, the turn coordinator should 

indicate a turn in the correct direction while the ball moves 

opposite the direction of the turn. 

Attitude Indicator 

The attitude indicator, with its miniature aircraft and horizon 

bar, displays a picture of the attitude of the aircraft. The 

relationship of the miniature aircraft to the horizon bar is 

the same as the relationship of the real aircraft to the actual 

horizon. The instrument gives an instantaneous indication of 

even the smallest changes in attitude. 

The gyro in the attitude indicator is mounted in a horizontal 

plane and depends upon rigidity in space for its operation. 

The horizon bar represents the true horizon. This bar is 

fixed to the gyro and remains in a horizontal plane as the 

aircraft is pitched or banked about its lateral or longitudinal 

axis, indicating the attitude of the aircraft relative to the true 

horizon. [Figure 8-23] 

The gyro spins in the horizontal plane and resists deflection 

of the rotational path. Since the gyro relies on rigidity in 

space, the aircraft actually rotates around the spinning gyro. 

20 

0 

I0

20 

TEST

STBY PWR 

20

0 

0 

20 

Bank index 

Horizon reference arm Roll gimbal 

Gimbal rotation 

Gyro Pitch gimbal 

Figure 8-23. Attitude indicator. 

8-18 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An adjustment knob is provided with which the pilot may 

move the miniature aircraft up or down to align the miniature 

aircraft with the horizon bar to suit the pilot’s line of vision. 

Normally, the miniature aircraft is adjusted so that the wings 

overlap the horizon bar when the aircraft is in straight-andlevel cruising flight. 

The pitch and bank limits depend upon the make and model 

of the instrument. Limits in the banking plane are usually 

from 100° to 110°, and the pitch limits are usually from 60° 

to 70°. If either limit is exceeded, the instrument will tumble 

or spill and will give incorrect indications until realigned. A 

number of modern attitude indicators do not tumble. 

Every pilot should be able to interpret the banking scale 

illustrated in Figure 8-24. Most banking scale indicators on 

the top of the instrument move in the same direction from 

that in which the aircraft is actually banked. Some other 

models move in the opposite direction from that in which 

the aircraft is actually banked. This may confuse the pilot if 

the indicator is used to determine the direction of bank. This 

scale should be used only to control the degree of desired 

bank. The relationship of the miniature aircraft to the horizon 

bar should be used for an indication of the direction of bank. 

The attitude indicator is reliable and the most realistic flight 

instrument on the instrument panel. Its indications are very 

close approximations of the actual attitude of the aircraft. 

Heading Indicator 

The heading indicator is fundamentally a mechanical 

instrument designed to facilitate the use of the magnetic 

compass. Errors in the magnetic compass are numerous, 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Bank scale 

Descending left bank 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Straight descent 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Descending right bank 

20 20

I0 I0

I0 I0

20 20 

STBY PWR TEST

Level left bank 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Level right bank 

20 20

I0 I0 

I0 I0

20 20 

STBY PWR TEST

Climbing left bank 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Straight climb 

20 20 

I0 I0 

I0 I0 

20 20 

STBY PWR TEST

Climbing right bank 

20 20

I0 I0

I0 I0

20 20 

STBY PWR TEST

Artificial horizon Adjustment knob 

Pointer 

60° 

45° 

20° 10° 

30° 

90° 

Figure 8-24. Attitude representation by the attitude indicator corresponds to the relation of the aircraft to the real horizon. 

8-19 
30

24

making straight flight and precision turns to headings difficult 

to accomplish, particularly in turbulent air. A heading 

indicator, however, is not affected by the forces that make 

the magnetic compass difficult to interpret. [Figure 8-25] 

The operation of the heading indicator depends upon the 

principle of rigidity in space. The rotor turns in a vertical 

plane and fixed to the rotor is a compass card. Since the rotor 

remains rigid in space, the points on the card hold the same 

position in space relative to the vertical plane of the gyro. The 

aircraft actually rotates around the rotating gyro, not the other 

way around. As the instrument case and the aircraft revolve 

around the vertical axis of the gyro, the card provides clear 

and accurate heading information. 

Because of precession caused by friction, the heading 

indicator creeps or drifts from its set position. Among 

other factors, the amount of drift depends largely upon the 

condition of the instrument. If the bearings are worn, dirty, 

or improperly lubricated, the drift may be excessive. Another 

error in the heading indicator is caused by the fact that the 

gyro is oriented in space, and the Earth rotates in space at a 

rate of 15° in 1 hour. Thus, discounting precession caused 

by friction, the heading indicator may indicate as much as 

15° error per every hour of operation. 

Some heading indicators referred to as horizontal situation 

indicators (HSI) receive a magnetic north reference from 

a magnetic slaving transmitter and generally need no 

adjustment. The magnetic slaving transmitter is called 

a magnetometer. 

Attitude and Heading Reference System (AHRS) 

Electronic flight displays have replaced free-spinning gyros 

with solid-state laser systems that are capable of flight at 

any attitude without tumbling. This capability is the result 

of the development of the Attitude and Heading Reference 

System (AHRS). 

The AHRS sends attitude information to the PFD in order 

to generate the pitch and bank information of the attitude 

indicator. The heading information is derived from a 

magnetometer that senses the earth’s lines of magnetic flux. 

This information is then processed and sent out to the PFD 

to generate the heading display. [Figure 8-26] 

The Flux Gate Compass System 

As mentioned earlier, the lines of flux in the Earth’s magnetic 

field have two basic characteristics: a magnet aligns with 

them, and an electrical current is induced, or generated, in 

any wire crossed by them. 

The flux gate compass that drives slaved gyros uses the 

characteristic of current induction. The flux valve is a small, 

segmented ring, like the one in Figure 8-27, made of soft iron 

that readily accepts lines of magnetic flux. An electrical coil 

is wound around each of the three legs to accept the current 

induced in this ring by the Earth’s magnetic field. A coil 

wound around the iron spacer in the center of the frame has 

400 Hz alternating current (AC) flowing through it. During 

the times when this current reaches its peak, twice during 

each cycle, there is so much magnetism produced by this 

coil that the frame cannot accept the lines of flux from the 

Earth’s field. 

33 

2I

I5

I2

6 

3 

Compass card gear 

Gimbal Adjustment gears

Main drive gear 

Gyro Adjustment knob 

Gimbal rotation 

Figure 8-25. A heading indicator displays headings based on a 360° 

azimuth, with the final zero omitted. For example, “6” represents 

060°, while “21” indicates 210°. The adjustment knob is used to 

align the heading indicator with the magnetic compass. 

Figure 8-26. Attitude and heading reference system (AHRS). 

8-20 
Figure 3-23. The soft iron frame of the flux valve accepts the

flux from the Earth’s magnetic field each time the current in the 

center coil reverse.This flux causes current to flow in the three 

picked coils.

Figure 3-24. The current in each of the three pickup coils

changes with the heading of the aircraft.

 

 

Figure 8-27. The soft iron frame of the flux valve accepts the flux from 

the Earth’s magnetic field each time the current in the center coil 

reverses. This flux causes current to flow in the three pickup coils. 

As the current reverses between the peaks, it demagnetizes 

the frame so it can accept the flux from the Earth’s field. As 

this flux cuts across the windings in the three coils, it causes 

current to flow in them. These three coils are connected in 

such a way that the current flowing in them changes as the 

heading of the aircraft changes. [Figure 8-28] 

The three coils are connected to three similar but smaller 

coils in a synchro inside the instrument case. The synchro 

rotates the dial of a radio magnetic indicator (RMI) or a HSI. 

Remote Indicating Compass 

Remote indicating compasses were developed to compensate 

for the errors and limitations of the older type of heading 

indicators. The two panel-mounted components of a typical 

system are the pictorial navigation indicator and the slaving 

control and compensator unit. [Figure 8-29] The pictorial 

navigation indicator is commonly referred to as an HSI. 

The slaving control and compensator unit has a push button 

that provides a means of selecting either the “slaved gyro” 

or “free gyro” mode. This unit also has a slaving meter 

and two manual heading-drive buttons. The slaving meter 

indicates the difference between the displayed heading and 

the magnetic heading. A right deflection indicates a clockwise 

error of the compass card; a left deflection indicates a 

counterclockwise error. Whenever the aircraft is in a turn 

and the card rotates, the slaving meter shows a full deflection 

to one side or the other. When the system is in “free gyro” 

mode, the compass card may be adjusted by depressing the 

appropriate heading-drive button. 

A separate unit, the magnetic slaving transmitter, is mounted 

remotely, usually in a wingtip to eliminate the possibility of 

magnetic interference. It contains the flux valve, which is 

the direction-sensing device of the system. A concentration 

of lines of magnetic force, after being amplified, becomes 

Figure 8-29. Pictorial navigation indicator (HSI, top), slaving meter 

Figure 8-28. The current in each of the three pickup coils changes (lower right), and slaving control compensator unit (lower left).

with the heading of the aircraft. 

8-21 
 

 

a signal relayed to the heading indicator unit, which is also 

remotely mounted. This signal operates a torque motor in 

the heading indicator unit that processes the gyro unit until 

it is aligned with the transmitter signal. The magnetic slaving 

transmitter is connected electrically to the HSI. 

There are a number of designs of the remote indicating 

compass; therefore, only the basic features of the system are 

covered here. Instrument pilots must become familiar with 

the characteristics of the equipment in their aircraft. 

As instrument panels become more crowded and the pilot’s 

available scan time is reduced by a heavier flight deck 

workload, instrument manufacturers have worked toward 

combining instruments. One good example of this is the 

RMI in Figure 8-30. The compass card is driven by signals 

from the flux valve, and the two pointers are driven by an 

automatic direction finder (ADF) and a very high frequency 

(VHF) omni-directional radio range (VOR). 

Heading indicators that do not have this automatic 

northseeking capability are called “free” gyros and require 

periodic adjustment. It is important to check the indications 

frequently (approximately every 15 minutes) and reset the 

heading indicator to align it with the magnetic compass 

when required. Adjust the heading indicator to the magnetic 

compass heading when the aircraft is straight and level at a 

constant speed to avoid compass errors. 

The bank and pitch limits of the heading indicator vary 

with the particular design and make of instrument. On some 

heading indicators found in light aircraft, the limits are 

approximately 55° of pitch and 55° of bank. When either of 

these attitude limits is exceeded, the instrument “tumbles” 

Figure 8-30. Driven by signals from a flux valve, the compass card 

in this RMI indicates the heading of the aircraft opposite the upper 

center index mark. The green pointer is driven by the ADF. 

or “spills” and no longer gives the correct indication until 

reset. After spilling, it may be reset with the caging knob. 

Many of the modern instruments used are designed in such 

a manner so that they do not tumble. 

An additional precession error may occur due to a gyro not 

spinning fast enough to maintain its alignment. When the 

vacuum system stops producing adequate suction to maintain 

the gyro speed, the heading indicator and the attitude indicator 

gyros begin to slow down. As they slow, they become more 

susceptible to deflection from the plane of rotation. Some 

aircraft have warning lights to indicate that a low vacuum 

situation has occurred. Other aircraft may have only a vacuum 

gauge that indicates the suction. 

Instrument Check 

As the gyro spools up, make sure there are no abnormal 

sounds. While taxiing, the instrument should indicate turns in 

the correct direction, and precession should be normal. At idle 

power settings, the gyroscopic instruments using the vacuum 

system might not be up to operating speeds and precession 

might occur more rapidly than during flight. 

Angle of Attack Indicators 

The purpose of an AOA indicator is to give the pilot better 

situational awareness pertaining to the aerodynamic health 

of the airfoil. This can also be referred to as stall margin 

awareness. More simply explained, it is the margin that exists 

between the current AOA that the airfoil is operating at, and 

the AOA at which the airfoil will stall (critical AOA). 

Speed by itself is not a reliable parameter to avoid a stall. 

An airplane can stall at any speed. Angle of attack is a better 

parameter to use to avoid a stall. For a given configuration, 

the airplane always stalls at the same AOA, referred to as 

the critical AOA. This critical AOA does not change with: 

• Weight 

• Bank Angle 

• Temperature 

• Density Altitude 

• Center of Gravity 

An AOA indicator can have several benefits when installed in 

General Aviation aircraft, not the least of which is increased 

situational awareness. Without an AOA indicator, the AOA 

is “invisible” to pilots. These devices measure several 

parameters simultaneously and determine the current AOA 

providing a visual image to the pilot of the current AOA along 

with representations of the proximity to the critical AOA. 

[Figure 8-31] These devices can give a visual representation 

of the energy management state of the airplane. The energy 

8-22 
Figure 8-31. Angle of attack indicators. 

state of an airplane is the balance between airspeed, altitude, 

drag, and thrust and represents how efficiently the airfoil is 

operating. 

Compass Systems 

The Earth is a huge magnet, spinning in space, surrounded 

by a magnetic field made up of invisible lines of flux. These 

lines leave the surface at the magnetic North Pole and reenter 

at the magnetic South Pole. 

Lines of magnetic flux have two important characteristics: 

any magnet that is free to rotate will align with them, and 

an electrical current is induced into any conductor that cuts 

across them. Most direction indicators installed in aircraft 

make use of one of these two characteristics. 

Magnetic Compass 

One of the oldest and simplest instruments for indicating 

direction is the magnetic compass. It is also one of the basic 

instruments required by Title 14 of the Code of Federal 

Regulations (14 CFR) part 91 for both VFR and IFR flight. 

A magnet is a piece of material, usually a metal containing 

iron, that attracts and holds lines of magnetic flux. Regardless 

of size, every magnet has two poles: north and south. When 

one magnet is placed in the field of another, the unlike poles 

attract each other, and like poles repel. 

An aircraft magnetic compass, such as the one in Figure 8-32, 

has two small magnets attached to a metal float sealed inside a 

bowl of clear compass fluid similar to kerosene. A graduated 

scale, called a card, is wrapped around the float and viewed 

through a glass window with a lubber line across it. The card 

is marked with letters representing the cardinal directions, 

north, east, south, and west, and a number for each 30° 

between these letters. The final “0” is omitted from these 

directions. For example, 3 = 30°, 6 = 60°, and 33 = 330°. 

There are long and short graduation marks between the letters 

and numbers, each long mark representing 10° and each short 

mark representing 5°. 

The float and card assembly has a hardened steel pivot in its 

center that rides inside a special, spring-loaded, hard glass 

jewel cup. The buoyancy of the float takes most of the weight 

off of the pivot, and the fluid damps the oscillation of the 

float and card. This jewel-and-pivot type mounting allows the 

float freedom to rotate and tilt up to approximately 18° angle 

of bank. At steeper bank angles, the compass indications are 

erratic and unpredictable. 

The compass housing is entirely full of compass fluid. To 

prevent damage or leakage when the fluid expands and 

contracts with temperature changes, the rear of the compass 

case is sealed with a flexible diaphragm, or with a metal 

bellows in some compasses. 

The magnets align with the Earth’s magnetic field and the 

pilot reads the direction on the scale opposite the lubber 

line. Note that in Figure 8-32, the pilot views the compass 

N-S E-W 

Figure 8-32. A magnetic compass. The vertical line is called the 

lubber line. 

8-23 
60 

50 

40 

30 

20 

10 

10 

20 

0 

0 

10 

0 

20 

10 

0 

0 

20 

10 

130 

110 100 90 

80 70 

60 50 

40 

30 

80 

70 

20 

10 

-40 

-90 

-100 

-110 

-120

-130 

-50 

-40 

-30 

-20 

-10 

-30 

-20 

-10 

-20 

-30 

-10 

-10 

-80 

-70 

-60 

-20 

-10 

-10 

card from its backside. When the pilot is flying north, as the 

compass indicates, east is to the pilot’s right. On the card, 

“33,” which represents 330° (west of north), is to the right of 

north. The reason for this apparent backward graduation is 

that the card remains stationary, and the compass housing and 

the pilot rotate around it. Because of this setup, the magnetic 

compass can be confusing to read. 

Magnetic Compass Induced Errors 

The magnetic compass is the simplest instrument in

the panel, but it is subject to a number of errors that must

be considered. 

Variation 

The Earth rotates about its geographic axis; maps and charts 

are drawn using meridians of longitude that pass through the 

geographic poles. Directions measured from the geographic 

poles are called true directions. The magnetic North Pole to 

which the magnetic compass points is not collocated with 

the geographic North Pole, but is some 1,300 miles away; 

directions measured from the magnetic poles are called 

magnetic directions. In aerial navigation, the difference 

between true and magnetic directions is called variation. This 

same angular difference in surveying and land navigation is 

called declination. 

Figure 8-33 shows the isogonic lines that identify the number 

of degrees of variation in their area. The line that passes near 

Chicago is called the agonic line. Anywhere along this line 

180 ̊W 165 ̊W 150 ̊W 135 ̊W 120 ̊W 105 ̊W 90 ̊W 75 ̊W 60 ̊W 45 ̊W 30 ̊W 15 ̊W 

the two poles are aligned, and there is no variation. East 

of this line, the magnetic North Pole is to the west of the 

geographic North Pole and a correction must be applied to 

a compass indication to get a true direction. 

Flying in the Washington, D.C., area, for example, the 

variation is 10° west. If a pilot wants to fly a true course of 

south (180°), the variation must be added to this, resulting in 

a magnetic course of 190° to fly. Flying in the Los Angeles, 

California area, the variation is 14° east. To fly a true course 

of 180° there, the pilot would have to subtract the variation 

and fly a magnetic course of 166°. The variation error does 

not change with the heading of the aircraft; it is the same 

anywhere along the isogonic line. 

Deviation 

The magnets in a compass align with any magnetic field. 

Some causes for magnetic fields in aircraft include flowing 

electrical current, magnetized parts, and conflict with the 

Earth’s magnetic field. These aircraft magnetic fields create 

a compass error called deviation. 

Deviation, unlike variation, depends on the aircraft heading. 

Also unlike variation, the aircraft’s geographic location 

does not affect deviation. While no one can reduce or 

change variation error, an aviation maintenance technician 

(AMT) can provide the means to minimize deviation error 

by performing the maintenance task known as “swinging 

the compass.” 

0 ̊ 15 ̊E 30 ̊E 45 ̊E 60 ̊E 75 ̊E 90 ̊E 105 ̊E 120 ̊E 135 ̊E 150 ̊E 165 ̊E 180 ̊W

70 ̊N 70 ̊N

60 ̊N 60 ̊N 

45 ̊N 45 ̊N 

30 ̊N 30 ̊N 

15 ̊N 15 ̊N 

0 ̊ 0 ̊

15 ̊S 15 ̊S 

30 ̊S 30 ̊S 

Main field declination (D) 

Contour interval: 

45 ̊S 2 degrees 45 ̊S 

red contours positive (east) 

blue negative (west) 

pink (agonic) zero line. 

Mercator Projection. 60 ̊N 60 ̊N 

Position of dip poles 

70 ̊N 70 ̊N

180 ̊W 165 ̊W 150 ̊W 135 ̊W 120 ̊W 105 ̊W 90 ̊W 75 ̊W 60 ̊W 45 ̊W 30 ̊W 15 ̊W 0 ̊ 15 ̊E 30 ̊E 45 ̊E 60 ̊E 75 ̊E 90 ̊E 105 ̊E 120 ̊E 135 ̊E 150 ̊E 165 ̊E 180 ̊W

Figure 8-33. Isogonic lines are lines of equal variation. 

8-24 
To swing the compass, an AMT positions the aircraft 

on a series of known headings, usually at a compass 

rose. [Figure 8-34] A compass rose consists of a series 

of lines marked every 30° on an airport ramp, oriented to 

magnetic north. There is minimal magnetic interference at 

the compass rose. The pilot or the AMT, if authorized, can 

taxi the aircraft to the compass rose and maneuver the aircraft 

to the headings prescribed by the AMT. 

As the aircraft is “swung” or aligned to each compass rose 

heading, the AMT adjusts the compensator assembly located 

on the top or bottom of the compass. The compensator 

assembly has two shafts whose ends have screwdriver slots 

accessible from the front of the compass. Each shaft rotates 

one or two small compensating magnets. The end of one shaft 

is marked E-W, and its magnets affect the compass when the 

aircraft is pointed east or west. The other shaft is marked 

N-S and its magnets affect the compass when the aircraft is 

pointed north or south. 

The adjustments position the compensating magnets to 

minimize the difference between the compass indication and 

the actual aircraft magnetic heading. The AMT records any 

remaining error on a compass correction card like the one 

in Figure 8-35 and places it in a holder near the compass. 

Only AMTs can adjust the compass or complete the compass 

correction card. Pilots determine and fly compass headings 

using the deviation errors noted on the card. Pilots must also 

note the use of any equipment causing operational magnetic 

interference such as radios, deicing equipment, pitot heat, 

radar, or magnetic cargo. 

The corrections for variation and deviation must be applied 

in the correct sequence as shown below, starting from the 

true course desired. 

030 

060 

E 

120 

S 

150

210 

240 

W 

300 

330 

N 

True north 

Figure 8-34. Utilization of a compass rose aids compensation for 

deviation errors. 

Figure 8-35. A compass correction card shows the deviation 

correction for any heading. 

Step 1: Determine the Magnetic Course
 

True Course (180°) ± Variation (+10°) = Magnetic Course 

(190°)
 

The magnetic course (190°) is steered if there is no deviation
 

error to be applied. The compass card must now be considered
 

for the compass course of 190°.
 

Step 2: Determine the Compass Course
 

Magnetic Course (190°, from step 1) ± Deviation (–2°, from 

correction card) = Compass Course (188°)
 

NOTE: Intermediate magnetic courses between those listed 

on the compass card need to be interpreted. Therefore, to 

steer a true course of 180°, the pilot would follow a compass 

course of 188°.
 

To find the true course that is being flown when the compass 

course is known:
 

Compass Course ± Deviation = Magnetic Course ±
 

Variation= True Course 

Dip Errors 

The Earth's magnetic field runs parallel to its surface only at 

the Magnetic Equator, which is the point halfway between 

the Magnetic North and South Poles. As you move away 

from the Magnetic Equator towards the magnetic poles, the 

angle created by the vertical pull of the Earth's magnetic field 

in relation to the Earth’s surface increases gradually. This 

angle is known as the dip angle. The dip angle increases in 

a downward direction as you move towards the Magnetic 

North Pole and increases in an upward direction as you move 

towards the Magnetic South Pole. 

If the compass needle were mounted so that it could pivot 

freely in three dimensions, it would align itself with the 

magnetic field, pointing up or down at the dip angle in the 

direction of local Magnetic North. Because the dip angle is 

of no navigational interest, the compass is made so that it can 

8-25 
 

 

rotate only in the horizontal plane. This is done by lowering Southerly Turning Errors 

the center of gravity below the pivot point and making the 

assembly heavy enough that the vertical component of the 

magnetic force is too weak to tilt it significantly out of the 

horizontal plane. The compass can then work effectively at 

all latitudes without specific compensation for dip. However, 

close to the magnetic poles, the horizontal component of

the Earth’s field is too small to align the compass which 

makes the compass unuseable for navigation. Because of 

this constraint, the compass only indicates correctly if the 

card is horizontal. Once tilted out of the horizontal plane, 

it will be affected by the vertical component of the Earth’s 

field which leads to the following discussions on northerly 

and southerly turning errors. 

Northerly Turning Errors 

The center of gravity of the float assembly is located lower 

than the pivotal point. As the aircraft turns, the force that 

results from the magnetic dip causes the float assembly to 

swing in the same direction that the float turns. The result is 

a false northerly turn indication. Because of this lead of the 

compass card, or float assembly, a northerly turn should be 

stopped prior to arrival at the desired heading. This compass 

error is amplified with the proximity to either magnetic pole. 

One rule of thumb to correct for this leading error is to stop 

the turn 15 degrees plus half of the latitude (i.e., if the aircraft 

is being operated in a position near 40 degrees latitude, the 

turn should be stopped 15+20=35 degrees prior to the desired 

heading). [Figure 8-36A] 

When turning in a southerly direction, the forces are such that 

the compass float assembly lags rather than leads. The result 

is a false southerly turn indication. The compass card, or float 

assembly, should be allowed to pass the desired heading prior 

to stopping the turn. As with the northerly error, this error 

is amplified with the proximity to either magnetic pole. To 

correct this lagging error, the aircraft should be allowed to 

pass the desired heading prior to stopping the turn. The same 

rule of 15 degrees plus half of the latitude applies here (i.e., 

if the aircraft is being operated in a position near 30 degrees 

latitude, the turn should be stopped 15+15+30 degrees after 

passing the desired heading). [Figure 8-36B] 

Acceleration Error 

The magnetic dip and the forces of inertia cause magnetic 

compass errors when accelerating and decelerating on 

easterly and westerly headings. Because of the penduloustype mounting, the aft end of the compass card is tilted 

upward when accelerating and downward when decelerating 

during changes of airspeed. When accelerating on either 

an easterly or westerly heading, the error appears as a 

turn indication toward north. When decelerating on either 

of these headings, the compass indicates a turn toward 

south. A mnemonic, or memory jogger, for the effect of 

acceleration error is the word “ANDS” (AccelerationNorth/Deceleration-South) may help you to remember the 

acceleration error. [Figure 8-37] Acceleration causes an 

21 S 15 12 21 S 15 12 21 S 15 12 

Dip effect

CARD 

CARD 

Left turn No error Right turn 

Dip effect

DIP DIP DIP 

B 

3 N 33 30

3 N 33 30 

3 N 33 30

CARD 

Dip effect

CARD 

Dip effectDip effect 

Left turn No error Right turn A 

DIP DIP 

DIP 

Dip effect 

Dip effect 

Dip effect 

Figure 8-36. Northerly and southerly turning errors. 

8-26 
Figure 3-21. The effects of acceleration error.

N 

E 

S 

W 

3 

33 

24 21 

12 

6 

NAV

GS 

NORTH 

South 

OBS 

15 

30 

View is from the pilot’s 

perspective, and the 

movable card is reset 

after each turn. 

Figure 8-37. The effects of acceleration error. 

indication toward north; deceleration causes an indication 

toward south. 

Oscillation Error 

Oscillation is a combination of all of the errors previously 

mentioned and results in fluctuation of the compass card in 

relation to the actual heading direction of the aircraft. When 

setting the gyroscopic heading indicator to agree with the 

magnetic compass, use the average indication between the 

swings. 

The Vertical Card Magnetic Compass 

The vertical card magnetic compass eliminates some of the 

errors and confusion encountered with the magnetic compass. 

The dial of this compass is graduated with letters representing 

the cardinal directions, numbers every 30°, and tick marks 

every 5°. The dial is rotated by a set of gears from the shaftmounted magnet, and the nose of the symbolic aircraft on 

the instrument glass represents the lubber line for reading the 

heading of the aircraft from the dial. [Figure 8-38] 

Lags or Leads 

When starting a turn from a northerly heading, the compass 

lags behind the turn. When starting a turn from a southerly 

heading, the compass leads the turn. 

N 

W 

S 

E 

33

30 

24

21

15

12

6 

3 

Figure 8-38. Vertical card magnetic compass. 

Eddy Current Damping 

In the case of a vertical card magnetic compass, flux from 

the oscillating permanent magnet produces eddy currents in 

a damping disk or cup. The magnetic flux produced by the 

eddy currents opposes the flux from the permanent magnet 

and decreases the oscillations. 

8-27 
Outside Air Temperature (OAT) Gauge 

The outside air temperature (OAT) gauge is a simple and 

effective device mounted so that the sensing element is 

exposed to the outside air. The sensing element consists 

of a bimetallic-type thermometer in which two dissimilar 

materials are welded together in a single strip and twisted 

into a helix. One end is anchored into protective tube and the 

other end is affixed to the pointer, which reads against the 

calibration on a circular face. OAT gauges are calibrated in 

degrees °C, °F, or both. An accurate air temperature provides 

the pilot with useful information about temperature lapse rate 

with altitude change. [Figure 8-39] 

Chapter Summary 

Flight instruments enable an aircraft to be operated with 

maximum performance and enhanced safety, especially when 

flying long distances. Manufacturers provide the necessary 

flight instruments, but to use them effectively, pilots need 

to understand how they operate. As a pilot, it is important to 

become very familiar with the operational aspects of the pitotstatic system and associated instruments, the vacuum system 

and associated instruments, the gyroscopic instruments, and 

the magnetic compass. 

20 

0 

-20 

-40 

-60 

40 

60 

100 

140 

120 

80 

F 

20 

0 

-20 

-40 

40 

60 

C 

Figure 8-39. Outside air temperature (OAT) gauge. 

8-28 
 

9-1 

Introduction 

Each aircraft comes with documentation and a set of manuals 

with which a pilot must be familiar in order to fly that aircraft. 

This chapter covers airplane flight manuals (AFM), the 

pilot’s operating handbook (POH), and aircraft documents 

pertaining to ownership, airworthiness, maintenance, and 

operations with inoperative equipment. Knowledge of these 

required documents and manuals is essential for a pilot to 

conduct a safe flight. 

Airplane Flight Manuals (AFM) 

Flight manuals and operating handbooks are concise reference 

books that provide specific information about a particular 

aircraft or subject. They contain basic facts, information, 

and/or instructions for the pilot about the operation of an 

aircraft, flying techniques, etc., and are intended to be kept 

on hand for ready reference. 

Flight Manuals and

Other Documents 

Chapter 9 
 

 

 

The aircraft owner/information manual is a document 

developed by the aircraft manufacturer and contains general 

information about the make and model of the aircraft. 

The manual is not approved by the Federal Aviation 

Administration (FAA) and is not specific to an individual 

aircraft. The manual provides general information about the 

operation of an aircraft, is not kept current, and cannot be 

substituted for the AFM/POH. 

An AFM is a document developed by the aircraft manufacturer 

and approved by the FAA. This book contains the information 

and instructions required to operate an aircraft safely. A 

pilot must comply with this information which is specific 

to a particular make and model of aircraft, usually by serial 

number. An AFM contains the operating procedures and 

limitations of that aircraft. Title 14 of the Code of Federal 

Regulations (14 CFR) part 91 requires that pilots comply 

with the operating limitations specified in the approved flight 

manuals, markings, and placards. 

Originally, flight manuals followed whatever format and 

content the manufacturer felt was appropriate, but this 

changed with the acceptance of Specification No. 1 prepared 

by the General Aviation Manufacturers Association (GAMA). 

Specification No. 1 established a standardized format for all 

general aviation airplane and helicopter flight manuals. 

The POH is a document developed by the aircraft 

manufacturer and contains FAA-approved AFM information. 

If “POH” is used in the main title, a statement must be 

included on the title page indicating that sections of the 

document are FAA approved as the AFM. 

The POH for most light aircraft built after 1975 is also 

designated as the FAA-approved flight manual. The typical 

AFM/POH contains the following nine sections: General; 

Limitations; Emergency Procedures; Normal Procedures; 

Performance; Weight and Balance/Equipment List; Systems 

Description; Handling, Service, and Maintenance; and 

Supplements. Manufacturers also have the option of including 

additional sections, such as one on Safety and Operational 

Tips or an alphabetical index at the end of the POH. 

Preliminary Pages 

While the AFM/POH may appear similar for the same make 

and model of aircraft, each manual is unique and contains 

specific information about a particular aircraft, such as the 

equipment installed and weight and balance information. 

Manufacturers are required to include the serial number and 

registration on the title page to identify the aircraft to which 

the manual belongs. If a manual does not indicate a specific 

aircraft registration and serial number, it is limited to general 

study purposes only. 

Most manufacturers include a table of contents that identifies 

the order of the entire manual by section number and title. 

Usually, each section also contains a table of contents for that 

section. Page numbers reflect the section and page within that 

section (1-1, 1-2, 2-1, 3-1, etc.). If the manual is published 

in loose-leaf form, each section is usually marked with a 

divider tab indicating the section number, title, or both. The 

Emergency Procedures section may have a red tab for quick 

identification and reference. 

General (Section 1) 

The General section provides the basic descriptive 

information on the airframe and powerplant(s). Some 

manuals include a three-dimensional drawing of the aircraft 

that provides dimensions of various components. Included 

are such items as wingspan, maximum height, overall length, 

wheelbase length, main landing gear track width, diameter 

of the rotor system, maximum propeller diameter, propeller 

ground clearance, minimum turning radius, and wing area. 

This section serves as a quick reference and helps a pilot 

become familiar with the aircraft. 

The last segment of the General section contains definitions, 

abbreviations, explanations of symbology, and some of 

the terminology used in the POH. At the discretion of the 

manufacturer, metric and other conversion tables may also 

be included. 

Limitations (Section 2) 

The Limitations section contains only those limitations required 

by regulation or that are necessary for the safe operation of 

the aircraft, powerplant, systems, and equipment. It includes 

operating limitations, instrument markings, color-coding, 

and basic placards. Some of the limitation areas are airspeed, 

powerplant, weight and loading distribution, and flight. 

Airspeed 

Airspeed limitations are shown on the airspeed indicator 

(ASI) by color coding and on placards or graphs in the 

aircraft. [Figure 9-1] A red line on the ASI shows the airspeed 

limit beyond which structural damage could occur. This is 

called the never-exceed speed (VNE). A yellow arc indicates 

the speed range between maximum structural cruising speed 

(VN0) and VNE. Operation of an aircraft in the yellow airspeed 

arc is for smooth air only and then only with caution. A green 

arc depicts the normal operating speed range, with the upper 

end at VN0 and the lower end at stalling speed at maximum 

weight with the landing gear and flaps retracted (VS1). For 

airplanes, the flap operating range is depicted by the white 

arc, with the upper end at the maximum flap extended speed 

(VFE), and the lower end at the stalling speed with the landing 

gear and flaps in the landing configuration (VS0). 

9-2 
 

 

Figure 9-1. Single-engine airspeed indicator. 

200 

245 

I50 

I00 

75 

°F P 

S 

I 

II5 

60 

I00 

20 

0 

OIL 

P 

R 

E 

S 

S 

T 

E 

M 

P 

Minimum 

Maximum 

Normal operating range 

In addition to the markings listed above, small multi-engine 

airplanes have a red radial line to indicate single-engine 

minimum controllable airspeed (VMC). A blue radial line 

is used to indicate single-engine best rate of climb speed at 

maximum weight at sea level (VYSE). [Figure 9-2] 

Powerplant 

The Powerplant Limitations portion describes operating 

limitations on an aircraft’s reciprocating or turbine engine(s). 

These include limitations for takeoff power, maximum 

continuous power, and maximum normal operating power, 

which is the maximum power the engine can produce without 

any restrictions and is depicted by a green arc. Other items 

that can be included in this area are the minimum and 

maximum oil and fuel pressures, oil and fuel grades, and 

propeller operating limits. [Figure 9-3] 

All reciprocating-engine powered aircraft must have a 

revolutions per minute (rpm) indicator for each engine. 

Aircraft equipped with a constant-speed propeller or rotor 

system use a manifold pressure gauge to monitor power 

output and a tachometer to monitor propeller or rotor speed. 

Both instruments depict the maximum operating limit with 

Figure 9-3. Minimum, maximum, and normal operating range 

markings on oil gauge. 

a red radial line and the normal operating range with a green 

arc. [Figure 9-4] Some instruments may have a yellow arc 

to indicate a caution area. 

Weight and Loading Distribution 

Weight and Loading Distribution contains the maximum 

certificated weights, as well as the center of gravity (CG) 

range. The location of the reference datum used in balance 

computations is included in this section. Weight and balance 

computations are not provided in this area, but rather in the 

weight and balance section of the AFM/POH. 

RPM HUNDREDS

25

3

5

I5

30

20

I0

35

25 

3

5 

I5 

30 

20 

I0 

35 HOURS 

AVOID CONTINUOUS 

OPERATION 

BETWEEN 2250 

AND 2350 RPM 

I 

I0 

IN Hg 

ALg. 

MANIFOLD 

PRESSURE 

35

10 50

15

25

40

30

20

45

35 

10 50

15 

25 

40 

30 

20 

45

160 

140

200 

250 

AIRSPEED 

KNOTS 

IAS 

TAS 

40 

60 

80 

100 

120 140 

160 

180 

200 

260 

Figure 9-4. Manifold pressure gauge (top) and tachometer (bottom). Figure 9-2. Multi-engine airspeed indicator. 

9-3 
Flight Limits 

Flight Limits list authorized maneuvers with appropriate 

entry speeds, flight load factor limits, and types of operation 

limits. It also indicates those maneuvers that are prohibited, 

such as spins or acrobatic flight, as well as operational 

limitations such as flight into known icing conditions. 

Placards 

Most aircraft display one or more placards that contain 

information having a direct bearing on the safe operation of 

the aircraft. These placards are located in conspicuous places 

and are reproduced in the Limitations section or as directed by 

an Airworthiness Directive (AD). [Figure 9-5] Airworthiness 

Directives are explained in detail later in this chapter. 

Emergency Procedures (Section 3) 

Checklists describing the recommended procedures and 

airspeeds for coping with various types of emergencies or 

critical situations are located in the Emergency Procedures 

section. Some of the emergencies covered include: 

engine failure, fire, and system failure. The procedures 

for inflight engine restarting and ditching may also be 

included. Manufacturers may first show an emergency 

checklist in an abbreviated form with the order of items 

reflecting the sequence of action. Amplified checklists that 

provide additional information on the procedures follow 

the abbreviated checklist. To be prepared for emergency 

situations, memorize the immediate action items and, after 

completion, refer to the appropriate checklist. 

Figure 9-5. Placards are used to depict aircraft limitations. 

Manufacturers may include an optional subsection 

entitled Abnormal Procedures. This subsection describes 

recommended procedures for handling malfunctions that are 

not considered emergencies. 

Normal Procedures (Section 4) 

This section begins with a list of the airspeeds for normal 

operations. The next area consists of several checklists that 

may include preflight inspection, before starting procedures, 

starting engine, before taxiing, taxiing, before takeoff, climb, 

cruise, descent, before landing, balked landing, after landing, 

and post flight procedures. An Amplified Procedures area 

follows the checklists to provide more detailed information 

about the various previously mentioned procedures. 

To avoid missing important steps, always use the appropriate 

checklists when available. Consistent adherence to approved 

checklists is a sign of a disciplined and competent pilot. 

Performance (Section 5) 

The Performance section contains all the information required 

by the aircraft certification regulations and any additional 

performance information the manufacturer deems important 

to pilot ability to safely operate the aircraft. Performance 

charts, tables, and graphs vary in style, but all contain the 

same basic information. Examples of the performance 

information found in most flight manuals include a graph or 

table for converting calibrated airspeed to true airspeed; stall 

speeds in various configurations; and data for determining 

takeoff and climb performance, cruise performance, and 

landing performance. Figure 9-6 is an example of a typical 

performance graph. For more information on use of the 

charts, graphs, and tables, refer to Chapter 10, Aircraft 

Performance. 

Weight and Balance/Equipment List (Section 6) 

The Weight and Balance/Equipment List section contains 

all the information required by the FAA to calculate the 

weight and balance of an aircraft. Manufacturers include 

sample weight and balance problems. Weight and balance is 

discussed in greater detail in Chapter 10, Weight and Balance. 

Systems Description (Section 7) 

This section describes the aircraft systems in a manner 

appropriate to the pilot most likely to operate the aircraft. 

For example, a manufacturer might assume an experienced 

pilot will be reading the information for an advanced aircraft. 

For more information on aircraft systems, refer to Chapter 

7, Aircraft Systems. 

9-4 
 

60 

50 

40 

70 

30 

2,400 2,200 2,000 1,800 1,600 0° 20° 40° 60° 

Stall speed (knots) 

Gross weight (pounds) Angle of bank (degrees) 

0° Flaps 

0° Flaps 40° Flaps

Maximum weight - 2,440 (pounds) 

Calibrated stall speed 

Indicated stall speed

EXAMPLE

Gross weight: 2,170 pounds 

Angle of bank: 20° 

Flap position: 40° 

Stall speed, indicated: 44 knots 

40° Flaps 

Figure 9-6. Stall speed chart. 

Handling, Service, and Maintenance (Section 8) 

The Handling, Service, and Maintenance section describes 

the maintenance and inspections recommended by the 

manufacturer (and the regulations). Additional maintenance 

or inspections may be required by the issuance of ADs 

applicable to the airframe, engine, propeller, or components. 

This section also describes preventive maintenance that 

may be accomplished by certificated pilots, as well as the 

manufacturer’s recommended ground handling procedures. It 

includes considerations for hangaring, tie-down, and general 

storage procedures for the aircraft. 

Supplements (Section 9) 

The Supplements section contains information necessary 

to safely and efficiently operate the aircraft when equipped 

with optional systems and equipment (not provided with the 

standard aircraft). Some of this information may be supplied 

by the aircraft manufacturer or by the manufacturer of the 

optional equipment. The appropriate information is inserted 

into the flight manual at the time the equipment is installed. 

Autopilots, navigation systems, and air-conditioning 

systems are examples of equipment described in this section. 

[Figure 9-7] 

Figure 9-7. Supplements provide information on optional equipment. 

9-5 
Safety Tips (Section 10) 

The Safety Tips section is an optional section containing a 

review of information that enhances the safe operation of the 

aircraft. For example, physiological factors, general weather 

information, fuel conservation procedures, high altitude 

operations, or cold weather operations might be discussed. 

Aircraft Documents 

Certificate of Aircraft Registration 

Before an aircraft can be flown legally, it must be registered 

with the FAA Aircraft Registry. The Certificate of Aircraft 

Registration, which is issued to the owner as evidence of 

the registration, must be carried in the aircraft at all times. 

[Figure 9-8] 

The Certificate of Aircraft Registration cannot be used for 

operations when: 

•	 The aircraft is registered under the laws of a foreign 

country 

•	 The aircraft’s registration is canceled upon written 

request of the certificate holder 

•	 The aircraft is totally destroyed or scrapped 

•	 The ownership of the aircraft is transferred 

•	 The certificate holder loses United States citizenship 

For additional information, see 14 CFR part 47, section 47.41. 

When one of the events listed in 14 CFR part 47, section 

47.41 occurs, the previous owner must notify the FAA by 

filling in the back of the Certificate of Aircraft Registration, 

and mailing it to: 

FAA Aircraft Registration Branch, AFS-750 

P.O. Box 25504 

Oklahoma City, OK 73125-0504 

A dealer’s aircraft registration certificate is another form of 

registration certificate, but is valid only for required flight 

tests by the manufacturer or in flights that are necessary for 

Figure 9-8. AC Form 8050-3, Certificate of Aircraft Registration. 

9-6 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

the sale of the aircraft by the manufacturer or a dealer. The 

dealer must remove the certificate when the aircraft is sold. 

Upon complying with 14 CFR part 47, section 47.31, the 

pink copy of the application for an Aircraft Registration 

Application, Aeronautical Center (AC) Form 8050-1, 

provides authorization to operate an unregistered aircraft 

for a period not to exceed 90 days. Since the aircraft is 

unregistered, it cannot be operated outside of the United 

States until a permanent Certificate of Aircraft Registration 

is received and placed in the aircraft. 

The FAA does not issue any certificate of ownership or 

endorse any information with respect to ownership on a 

Certificate of Aircraft Registration. 

NOTE: For additional information concerning the Aircraft 

Registration Application or the Aircraft Bill of Sale, contact 

the nearest FAA Flight Standards District Office (FSDO). 

Airworthiness Certificate 

An Airworthiness Certificate is issued by a representative of 

the FAA after the aircraft has been inspected, is found to meet 

the requirements of 14 CFR part 21, and is in condition for safe 

operation. The Airworthiness Certificate must be displayed in 

the aircraft so it is legible to the passengers and crew whenever 

it is operated. The Airworthiness Certificate must remain with 

the aircraft unless it is sold to a foreign purchaser. 

A Standard Airworthiness Certificate is issued for aircraft 

type certificated in the normal, utility, acrobatic, commuter, 

transport categories, and manned free balloons. Figure 9-9 

illustrates a Standard Airworthiness Certificate, and an 

explanation of each item in the certificate follows. 

1. Nationality and Registration Marks. The “N” 

indicates the aircraft is registered in the United States. 

Registration marks consist of a series of up to five 

numbers or numbers and letters. In this case, N2631A 

is the registration number assigned to this aircraft. 

2.	 Manufacturer and Model. Indicates the manufacturer, 

make, and model of the aircraft. 

3.	 Aircraft Serial Number. Indicates the manufacturer’s 

serial number assigned to the aircraft, as noted on the 

aircraft data plate. 

4.	 Category. Indicates the category in which the aircraft 

must be operated. In this case, it must be operated 

in accordance with the limitations specified for the 

“NORMAL” category. 

5.	 Authority and Basis for Issuance. Indicates the aircraft 

conforms to its type certificate and is considered in 

condition for safe operation at the time of inspection 

and issuance of the certificate. Any exemptions from 

the applicable airworthiness standards are briefly 

noted here and the exemption number given. The word 

“NONE” is entered if no exemption exists. 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION-FEDERAL AVIATION ADMINISTRATION 

STANDARD AIRWORTHINESS CERTIFICATE 

1 NATIONALITY AND 

REGISTRATION MARKS 

N12345 

2 MANUFACTURER AND MODEL 

Douglas DC-6A 

3 AIRCRAFT SERIAL 

NUMBER 

43219 

4 CATEGORY 

Transport 

5 AUTHORITY AND BASIS FOR ISSUANCE 

This airworthiness certificate is issued pursuant to the Federal Aviation Act of 1958 and certifies that, as of the date of issuance, the
 

aircraft to which issued has been inspected and found to conform to the type certificate therefor, to be in condition for safe operation,
 

and has been shown to meet the requirements of the applicable comprehensive and detailed airworthiness code as provided by Annex 8 

to the Convention on International Civil Aviation, except as noted herein. 

Exceptions:
 

None 

6 TERMS AND CONDITIONS 

Unless sooner surrendered, suspended, revoked, or a termination date is otherwise established by the Administrator, this airworthiness 

certificate is effective as long as the maintenance, preventative maintenance, and alterations are performed in accordance with 

Parts 21, 43, and 91 of the Federal Aviation Regulations, as appropriate, and the aircraft is registered in the United States. 

DATE OF ISSUANCE 

01/20/00 

FAA REPRESENTATIVE 

E.R. White E.R. White 

DESIGNATION NUMBER 

NE-XX 

Any iteration, reproduction, or misuse of this certificate may be punishable by a fine not exceeding $1,000 or imprisonment not exceeding 3 years or both. 

THIS CERTIFICATE MUST BE DISPLAYED IN THE AIRCRAFT IN ACCORDANCE WITH APPLICABLE FEDERAL AVIATION REGULATIONS. 

FAA Form 8100-2 (04-11) Supersedes Previous Edition 

Figure 9-9. FAA Form 8100-2, Standard Airworthiness Certificate. 

9-7 
 

6.	 Terms and Conditions. Indicates the Airworthiness 

Certificate is in effect indefinitely if the aircraft is 

maintained in accordance with 14 CFR parts 21, 43, and 

91, and the aircraft is registered in the United States. 

Also included are the date the certificate was issued and the 

signature and office identification of the FAA representative. 

A Standard Airworthiness Certificate remains in effect 

if the aircraft receives the required maintenance and is 

properly registered in the United States. Flight safety relies 

in part on the condition of the aircraft, which is determined 

by inspections performed by mechanics, approved repair 

stations, or manufacturers that meet specific requirements 

of 14 CFR part 43. 

A Special Airworthiness Certificate is issued for all aircraft 

certificated in other than the Standard classifications, such 

as Experimental, Restricted, Limited, Provisional, and 

Light-Sport Aircraft (LSA). LSA receive a pink special 

airworthiness certificate; however, there are exceptions. 

For example, the Piper Cub is in the LSA category, but it 

was certificated as a normal aircraft during its manufacture. 

When purchasing an aircraft classified as other than Standard, 

it is recommended that the local FSDO be contacted for an 

explanation of the pertinent airworthiness requirements and 

the limitations of such a certificate. 

Aircraft Maintenance 

Maintenance is defined as the preservation, inspection, 

overhaul, and repair of an aircraft, including the replacement 

of parts. Regular and proper maintenance ensures that 

an aircraft meets an acceptable standard of airworthiness 

throughout its operational life. 

Although maintenance requirements vary for different 

types of aircraft, experience shows that aircraft need some 

type of preventive maintenance every 25 hours of flying 

time or less and minor maintenance at least every 100 

hours. This is influenced by the kind of operation, climatic 

conditions, storage facilities, age, and construction of the 

aircraft. Manufacturers supply maintenance manuals, parts 

catalogs, and other service information that should be used 

in maintaining the aircraft. 

Aircraft Inspections 

Under 14 CFR part 91, the primary responsibility for 

maintaining an aircraft in an airworthy condition falls on the 

owner or operator of the aircraft. Certain inspections must be 

performed on the aircraft, and the owner must maintain the 

airworthiness of the aircraft during the time between required 

inspections by having any defects corrected. 

Under 14 CFR, part 91, subpart E, all civil aircraft are 

required to be inspected at specific intervals to determine 

the overall condition. The interval depends upon the type 

of operations in which the aircraft is engaged. All aircraft 

need to be inspected at least once every 12 calendar months, 

while inspection is required for others after every 100 hours 

of operation. Some aircraft are inspected in accordance with 

an inspection system set up to provide for total inspection 

of the aircraft on the basis of calendar time, time in service, 

number of system operations, or any combination of these. 

All inspections should follow the current manufacturer’s 

maintenance manual, including the Instructions for 

Continued Airworthiness concerning inspection intervals, 

parts replacement, and life-limited items as applicable to 

the aircraft. 

Annual Inspection 

Any reciprocating engine or single-engine turbojet/ 

turbopropeller-powered small aircraft (weighing 12,500 

pounds or less) flown for business or pleasure and not 

flown for compensation or hire is required to be inspected 

at least annually. The inspection shall be performed by a 

certificated airframe and powerplant (A&P) mechanic who 

holds an inspection authorization (IA) by the manufacturer 

of the aircraft or by a certificated and appropriately rated 

repair station. The aircraft may not be operated unless the 

annual inspection has been performed within the preceding 

12 calendar months. A period of 12 calendar months extends 

from any day of a month to the last day of the same month the 

following year. An aircraft overdue for an annual inspection 

may be operated under a Special Flight Permit issued by 

the FAA for the purpose of flying the aircraft to a location 

where the annual inspection can be performed. However, all 

applicable ADs that are due must be complied with before 

the flight. 

100-Hour Inspection 

All aircraft under 12,500 pounds (except turbojet/ 

turbopropeller-powered multi-engine airplanes and turbine 

powered rotorcraft), used to carry passengers for hire, must 

receive a 100-hour inspection within the preceding 100 hours 

of time in service and must be approved for return to service. 

Additionally, an aircraft used for flight instruction for hire, 

when provided by the person giving the flight instruction, 

must also have received a 100-hour inspection. This inspection 

must be performed by an FAA-certificated A&P mechanic, 

an appropriately rated FAA-certificated repair station, or 

by the aircraft manufacturer. An annual inspection, or an 

inspection for the issuance of an Airworthiness Certificate, 

may be substituted for a required 100-hour inspection. The 

100-hour limitation may be exceeded by no more than 10 

9-8 
hours for the purpose of traveling to a location at which the 

required inspection can be performed. Any excess time used 

for this purpose must be included in computing the next 100 

hours of time in service. 

Other Inspection Programs 

The annual and 100-hour inspection requirements do not 

apply to large (over 12,500 pounds) airplanes, turbojets, or 

turbopropeller-powered multi-engine airplanes or to aircraft 

for which the owner complies with a progressive inspection 

program. Details of these requirements may be determined 

by referencing 14 CFR, part 43, section 43.11 and 14 CFR 

part 91, subpart E, or by inquiring at a local FSDO. 

Altimeter System Inspection 

Under 14 CFR, part 91, section 91.411, requires that the 

altimeter, encoding altimeter, and related system must be 

tested and inspected within the 24 months prior to operating in 

controlled airspace under instrument flight rules (IFR). This 

applies to all aircraft being operated in controlled airspace. 

Transponder Inspection 

Title 14 CFR, part 91, section 91.413, requires that before 

a transponder can be used under 14 CFR, part 91, section 

91.215(a), it shall be tested and inspected within the 24 

months prior to operation of the aircraft regardless of airspace 

restrictions. 

Emergency Locator Transmitter 

An emergency locator transmitter (ELT) is required by 14 

CFR, part 91, section 91.207, and must be inspected within 

12 calendar months after the last inspection for the following: 

•	 Proper installation 

•	 Battery corrosion 

•	 Operation of the controls and crash sensor 

•	 The presence of a sufficient signal radiated from its 

antenna 

The ELT must be attached to the airplane in such a manner 

that the probability of damage to the transmitter in the event 

of crash impact is minimized. Fixed and deployable automatic 

type transmitters must be attached to the airplane as far aft 

as practicable. Batteries used in the ELTs must be replaced 

(or recharged, if the batteries are rechargeable): 

•	 When the transmitter has been in use for more than 1 

cumulative hour 

•	 When 50 percent of the battery useful life or, for 

rechargeable batteries, 50 percent of useful life of the 

charge has expired 

An expiration date for replacing (or recharging) the battery 

must be legibly marked on the outside of the transmitter 

and entered in the aircraft maintenance record. This does 

not apply to batteries that are essentially unaffected during 

storage intervals, such as water-activated batteries. 

Preflight Inspections 

The preflight inspection is a thorough and systematic means 

by which a pilot determines if an aircraft is airworthy and in 

condition for safe operation. POHs and owner/information 

manuals contain a section devoted to a systematic method 

of performing a preflight inspection. 

Minimum Equipment Lists (MEL) and 

Operations With Inoperative Equipment 

Under 14 CFR, all aircraft instruments and installed equipment 

are required to be operative prior to each departure. When the 

FAA adopted the minimum equipment list (MEL) concept for 

14 CFR part 91 operations, it allowed aircraft to be operated 

with inoperative equipment determined to be nonessential for 

safe flight. At the same time, it allowed part 91 operators, 

without an MEL, to defer repairs on nonessential equipment 

within the guidelines of part 91. 

The FAA has two acceptable methods of deferring 

maintenance on small rotorcraft, non-turbine powered 

airplanes, gliders, or lighter-than-air aircraft operated under 

part 91. They are the deferral provision of 14 CFR, part 91, 

section 91.213(d) and an FAA-approved MEL. 

The deferral provision of 14 CFR, part 91, section 91.213(d) 

is widely used by most pilot/operators. Its popularity is due 

to simplicity and minimal paperwork. When inoperative 

equipment is found during a preflight inspection or prior to 

departure, the decision should be to cancel the flight, obtain 

maintenance prior to flight, or to defer the item or equipment. 

Maintenance deferrals are not used for inflight discrepancies. 

The manufacturer’s AFM/POH procedures are to be used in 

those situations. The discussion that follows assumes that 

the pilot wishes to defer maintenance that would ordinarily 

be required prior to flight. 

Using the deferral provision of 14 CFR, part 91, section 

91.213(d), the pilot determines whether the inoperative 

equipment is required by type design, 14 CFR, or ADs. If 

the inoperative item is not required, and the aircraft can be 

safely operated without it, the deferral may be made. The 

inoperative item shall be deactivated or removed and an 

INOPERATIVE placard placed near the appropriate switch, 

control, or indicator. If deactivation or removal involves 

9-9 
 

 

 

 

maintenance (removal always will), it must be accomplished 

by certificated maintenance personnel and recorded in 

accordance with 14 CFR part 43. 

For example, if the position lights (installed equipment) 

were discovered to be inoperative prior to a daytime flight, 

the pilot would follow the requirements of 14 CFR, part 91, 

section 91.213(d). 

The deactivation may be a process as simple as the pilot 

positioning a circuit breaker to the OFF position or as 

complex as rendering instruments or equipment totally 

inoperable. Complex maintenance tasks require a certificated 

and appropriately rated maintenance person to perform the 

deactivation. In all cases, the item or equipment must be 

placarded INOPERATIVE. 

All small rotorcraft, non-turbine powered airplanes, gliders, 

or lighter-than-air aircraft operated under 14 CFR part 91 

are eligible to use the maintenance deferral provisions of 14 

CFR, part 91, section 91.213(d). However, once an operator 

requests an MEL, and a Letter of Authorization (LOA) 

is issued by the FAA, then the use of the MEL becomes 

mandatory for that aircraft. All maintenance deferrals must 

be accomplished in accordance with the terms and conditions 

of the MEL and the operator-generated procedures document. 

The use of an MEL for an aircraft operated under 14 

CFR part 91 also allows for the deferral of inoperative 

items or equipment. The primary guidance becomes the 

FAA-approved MEL issued to that specific operator and 

N-numbered aircraft. 

The FAA has developed master minimum equipment lists 

(MMELs) for aircraft in current use. Upon written request by 

an operator, the local FSDO may issue the appropriate make 

and model MMEL, along with an LOA, and the preamble. 

The operator then develops operations and maintenance 

(O&M) procedures from the MMEL. This MMEL with O&M 

procedures now becomes the operator’s MEL. The MEL, 

LOA, preamble, and procedures document developed by the 

operator must be on board the aircraft during each operation. 

The FAA considers an approved MEL to be a supplemental 

type certificate (STC) issued to an aircraft by serial number 

and registration number. It, therefore, becomes the authority 

to operate that aircraft in a condition other than originally 

type certificated. 

With an approved MEL, if the position lights were discovered 

inoperative prior to a daytime flight, the pilot would make 

an entry in the maintenance record or discrepancy record 

provided for that purpose. The item would then either be 

repaired or deferred in accordance with the MEL. Upon 

confirming that daytime flight with inoperative position 

lights is acceptable in accordance with the provisions of the 

MEL, the pilot would leave the position lights switch OFF, 

open the circuit breaker (or whatever action is called for in 

the procedures document), and placard the position light 

switch as INOPERATIVE. 

There are exceptions to the use of the MEL for deferral. For 

example, should a component fail that is not listed in the MEL 

as deferrable (the tachometer, flaps, or stall warning device, 

for example), then repairs are required to be performed prior 

to departure. If maintenance or parts are not readily available 

at that location, a special flight permit can be obtained from 

the nearest FSDO. This permit allows the aircraft to be 

flown to another location for maintenance. This allows an 

aircraft that may not currently meet applicable airworthiness 

requirements, but is capable of safe flight, to be operated 

under the restrictive special terms and conditions attached 

to the special flight permit. 

Deferral of maintenance is not to be taken lightly, and due 

consideration should be given to the effect an inoperative 

component may have on the operation of an aircraft, 

particularly if other items are inoperative. Further information 

regarding MELs and operations with inoperative equipment 

can be found in AC 91-67, Minimum Equipment Requirements 

for General Aviation Operations Under FAR Part 91. 

Preventive Maintenance 

Preventive maintenance is regarded as simple or minor 

preservation operations and the replacement of small standard 

parts, not involving complex assembly operations. Allowed 

items of preventative maintenance are listed and limited to 

the items of 14 CFR part 43, appendix A(c). 

Maintenance Entries 

All pilots who perform preventive maintenance must make 

an entry in the maintenance record of the aircraft. The entry 

must include the following information: 

1.	 A description of the work, such as “changed oil (Shell 

Aero-50) at 2,345 hours” 

2. The date of completion of the work performed 

3. The pilot’s name, signature, certificate number, and 

type of certificate held 

Examples of Preventive Maintenance 

The following examples of preventive maintenance are taken 

from 14 CFR, part 43, Maintenance, Preventive Maintenance, 

Rebuilding, and Alternation, which should be consulted for a 

more in-depth look at the preventive maintenance a pilot can 

perform on an aircraft. Remember, preventive maintenance 

9-10 
 

 

 

 

is limited to work that does not involve complex assembly • Cleaning or replacing fuel and oil strainers or filter 

operations including the following: elements; servicing batteries, cleaning balloon burner 

•	 Removal, installation, and repair of landing gear 

tires and shock cords; servicing landing gear shock 

struts by adding oil, air, or both; servicing gear wheel 

bearings; replacing defective safety wiring or cotter 

keys; lubrication not requiring disassembly other than 

removal of nonstructural items, such as cover plates, 

cowlings, and fairings; making simple fabric patches 

not requiring rib stitching or the removal of structural 

parts or control surfaces. In the case of balloons, 

the making of small fabric repairs to envelopes 

(as defined in, and in accordance with, the balloon 

manufacturer’s instructions) not requiring load tape 

repair or replacement. 

•	 Replenishing hydraulic fluid in the hydraulic 

reservoir; refinishing decorative coating of fuselage, 

balloon baskets, wings, tail group surfaces (excluding 

balanced control surfaces), fairings, cowlings, 

landing gear, cabin, or flight deck interior when 

removal or disassembly of any primary structure 

or operating system is not required; applying 

preservative or protective material to components 

where no disassembly of any primary structure or 

operating system is involved and where such coating 

is not prohibited or is not contrary to good practices; 

repairing upholstery and decorative furnishings of the 

cabin, flight deck, or balloon basket interior when the 

repair does not require disassembly of any primary 

structure or operating system or interfere with an 

operating system or affect the primary structure of 

the aircraft; making small, simple repairs to fairings, 

nonstructural cover plates, cowlings, and small 

patches and reinforcements not changing the contour 

to interfere with proper air flow; replacing side 

windows where that work does not interfere with the 

structure or any operating system, such as controls, 

electrical equipment, etc. 

•	 Replacing safety belts, seats or seat parts with 

replacement parts approved for the aircraft, not 

involving disassembly of any primary structure or 

operating system, bulbs, reflectors, and lenses of 

position and landing lights. 

•	 Replacing wheels and skis where no weight-andbalance computation is involved; replacing any 

cowling not requiring removal of the propeller or 

disconnection of flight controls; replacing or cleaning 

spark plugs and setting of spark plug gap clearance; 

replacing any hose connection, except hydraulic 

connections; however, prefabricated fuel lines may 

be replaced. 

pilot and main nozzles in accordance with the balloon 

manufacturer’s instructions. 

•	 The interchange of balloon baskets and burners on 

envelopes when the basket or burner is designated as 

interchangeable in the balloon type certificate data 

and the baskets and burners are specifically designed 

for quick removal and installation; adjustment 

of nonstructural standard fasteners incidental to 

operations. 

•	 The installations of anti-misfueling devices to reduce 

the diameter of fuel tank filler openings only if the 

specific device has been made a part of the aircraft type 

certificate data by the aircraft manufacturer, the aircraft 

manufacturer has provided FAA-approved instructions 

for installation of the specific device, and installation 

does not involve the disassembly of the existing tank 

filler opening; troubleshooting and repairing broken 

circuits in landing light wiring circuits. 

•	 Removing and replacing self-contained, front 

instrument panel-mounted navigation and 

communication devices that employ tray-mounted 

connectors which connect the unit when the unit 

is installed into the instrument panel (excluding 

automatic flight control systems, transponders, and 

microwave frequency distance measuring equipment 

(DME)). The approved unit must be designed to be 

readily and repeatedly removed and replaced, and 

pertinent instructions must be provided. Prior to the 

unit’s intended use, an operational check must be 

performed in accordance with the applicable sections 

of 14 CFR part 91 on checking, removing, and 

replacing magnetic chip detectors. 

•	 Inspection and maintenance tasks prescribed and 

specifically identified as preventive maintenance in 

a primary category aircraft type certificate or STC 

holder’s approved special inspection and preventive 

maintenance program when accomplished on a 

primary category aircraft. 

•	 Updating self-contained, front instrument panelmounted air traffic control (ATC) navigational 

software databases (excluding those of automatic 

flight control systems, transponders, and microwave 

frequency DME), only if no disassembly of the unit is 

required and pertinent instructions are provided; prior 

to the unit’s intended use, an operational check must 

be performed in accordance with applicable sections 

of 14 CFR part 91. 

9-11 
 

 

Certificated pilots, excluding student pilots, sport pilots, and 

recreational pilots, may perform preventive maintenance on 

any aircraft that is owned or operated by them provided that 

the aircraft is not used in air carrier service and does not 

qualify under 14 CFR parts 121, 129, or 135. A pilot holding 

a sport pilot certificate may perform preventive maintenance 

on an aircraft owned or operated by that pilot if that aircraft is 

issued a special airworthiness certificate in the LSA category. 

(Sport pilots operating LSA should refer to 14 CFR part 65 

for maintenance privileges.) 14 CFR part 43, appendix A, 

contains a list of the operations that are considered to be 

preventive maintenance. 

Repairs and Alterations 

Repairs and alterations are classified as either major or minor. 

14 CFR part 43, appendix A, describes the alterations and 

repairs considered major. Major repairs or alterations shall 

be approved for return to service on FAA Form 337, Major 

Repair and Alteration, by an appropriately rated certificated 

repair station, an FAA-certificated A&P mechanic holding an 

IA, or a representative of the Administrator. Minor repairs and 

minor alterations may be approved for return to service with a 

proper entry in the maintenance records by an FAA-certificated 

A&P mechanic or an appropriately certificated repair station. 

For modifications of experimental aircraft, refer to the 

operating limitations issued to that aircraft. Modifications 

in accordance with FAA Order 8130.2, Airworthiness 

Certification of Aircraft and Related Products, may require 

the notification of the issuing authority. 

Special Flight Permits 

A special flight permit is a Special Airworthiness Certificate 

authorizing operation of an aircraft that does not currently 

meet applicable airworthiness requirements but is safe 

for a specific flight. Before the permit is issued, an FAA 

inspector may personally inspect the aircraft or require it to 

be inspected by an FAA-certificated A&P mechanic or an 

appropriately certificated repair station to determine its safety 

for the intended flight. The inspection shall be recorded in 

the aircraft records. 

The special flight permit is issued to allow the aircraft to be 

flown to a base where repairs, alterations, or maintenance 

can be performed; for delivering or exporting the aircraft; or 

for evacuating an aircraft from an area of impending danger. 

A special flight permit may be issued to allow the operation 

of an overweight aircraft for flight beyond its normal range 

over water or land areas where adequate landing facilities 

or fuel is not available. 

If a special flight permit is needed, assistance and the 

necessary forms may be obtained from the local FSDO 

or Designated Airworthiness Representative (DAR). 

[Figure 9-10] 

Airworthiness Directives (ADs) 

A primary safety function of the FAA is to require correction 

of unsafe conditions found in an aircraft, aircraft engine, 

propeller, or appliance when such conditions exist and are 

likely to exist or develop in other products of the same design. 

The unsafe condition may exist because of a design defect, 

maintenance, or other causes. Airworthiness Directives 

(ADs), under 14 CFR, part 39, define the authority and 

responsibility of the Administrator for requiring the necessary 

corrective action. ADs are used to notify aircraft owners and 

other interested persons of unsafe conditions and to specify 

the conditions under which the product may continue to be 

operated. ADs are divided into two categories: 

1.	 Those of an emergency nature requiring immediate 

compliance prior to further flight 

2.	 Those of a less urgent nature requiring compliance 

within a specified period of time 

ADs are regulatory and shall be complied with unless a 

specific exemption is granted. It is the responsibility of the 

aircraft owner or operator to ensure compliance with all 

pertinent ADs, including those ADs that require recurrent 

or continuing action. For example, an AD may require a 

repetitive inspection each 50 hours of operation, meaning 

the particular inspection shall be accomplished and recorded 

every 50 hours of time in service. Owners/operators are 

reminded that there is no provision to overfly the maximum 

hour requirement of an AD unless it is specifically written 

into the AD. To help determine if an AD applies to an 

amateur-built aircraft, contact the local FSDO. 

14 CFR, part 91, section 91.417 requires a record to be 

maintained that shows the current status of applicable 

ADs, including the method of compliance; the AD number 

and revision date, if recurring; next due date and time; the 

signature; type of certificate; and certificate number of the 

repair station or mechanic who performed the work. For ready 

reference, many aircraft owners have a chronological listing 

of the pertinent ADs in the back of their aircraft, engine, and 

propeller maintenance records. 

All ADs and the AD Biweekly are free on the Internet 

at http://rgl.faa.gov and are available through e-mail. 

Individuals can enroll for the e-mail service at the website 

above. Paper copies of the Summary of Airworthiness 

Directives and the AD Biweekly may be purchased from 

the Superintendent of Documents. The Summary contains 

all the valid ADs previously published and is divided into 

9-12 
 

 

 

 

 

 

 

 

 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION - FEDERAL AVIATION ADMINISTRATION 

SPECIAL AIRWORTHINESS CERTIFICATE 

A CATEGORY/DESIGNATION Special Flight Permit

PURPOSE Production Flight Testing or Customer Demonstration 

B MANUFACTURER 

NAME The Boeing Company 

ADDRESS P.O. Box 767, Renton WA 13567 

C FLIGHT 

FROM N/A 

TO N/A 

D N- N/A SERIAL NO. N/A 

BUILDER N/A MODEL N/A 

E 

DATE OF ISSUANCE 01/31/2001 EXPIRY 01/31/2001 

OPERATING LIMITATIONS DATED 01/31/2001 ARE PART OF THIS CERTIFICATE 

SIGNATURE OF FAA REPRESENTATIVE 

Sam T. Smith 

Sam T. Smith 

DESIGNATION OR OFFICE NO. 

NM-XX 

Any alteration, reproduction or misuse of this certificate may be punishable by a fine not exceeding $1,000 or imprisonment not exceeding 3 years, or 

both. THIS CERTIFICATE MUST BE DISPLAYED IN THE AIRCRAFT IN ACCORDANCE WITH APPLICABLE TITLE 14, CODE OF FEDERAL 

REGULATIONS (CFR). 

FAA Form 8130-7 (07/04) SEE REVERSE SIDE 

 

Figure 9-10. FAA Form 8130-7, Special Airworthiness Certificate. 

two areas. The small aircraft and helicopter books contain 

all ADs applicable to small aircraft (12,500 pounds or less 

maximum certificated takeoff weight) and ADs applicable 

to all helicopters. The large aircraft books contain all ADs 

applicable to large aircraft. 

For current information on how to order paper copies of AD 

books and the AD Biweekly, visit the FAA online regulatory 

and guidance library at: http://rgl.faa.gov. 

Aircraft Owner/Operator Responsibilities 

The registered owner/operator of an aircraft is responsible for: 

•	 Having a current Airworthiness Certificate and a 

Certificate of Aircraft Registration in the aircraft. 

•	 Maintaining the aircraft in an airworthy condition, 

including compliance with all applicable ADs and 

assuring that maintenance is properly recorded. 

•	 Keeping abreast of current regulations concerning the 

operation and maintenance of the aircraft. 

•	 Notifying the FAA Aircraft Registry immediately of 

any change of permanent mailing address, of the sale 

or export of the aircraft, or of the loss of the eligibility 

to register an aircraft. (Refer to 14 CFR, part 47, 

section 47.41.) 

•	 Having a current Federal Communications Commission 

(FCC) radio station license if equipped with radios, 

including emergency locator transmitter (ELT), if 

operated outside of the United States. 

Chapter Summary 

Knowledge of an aircraft’s AFM/POH and documents, 

such as ADs, provide pilots with ready access to pertinent 

information needed to safely fly a particular aircraft. By 

understanding the operations, limitations, and performance 

characteristics of the aircraft, the pilot can make educated 

flight decisions. By learning what preventive maintenance 

is allowed on the aircraft, a pilot can maintain his or her 

aircraft in an airworthy condition. The goal of every pilot is 

a safe flight. Flight manuals and aircraft documentation are 

essential tools used to reach that goal. 

9-13 
9-14
 
10-1 

Introduction 

Compliance with the weight and balance limits of any aircraft 

is critical to flight safety. Operating above the maximum 

weight limitation compromises the structural integrity of 

an aircraft and adversely affects its performance. Operation 

with the center of gravity (CG) outside the approved limits 

results in control difficulty. 

Weight Control 

As discussed in Chapter 5, Aerodynamics of Flight, weight 

is the force with which gravity attracts a body toward the 

center of the Earth. It is a product of the mass of a body and 

the acceleration acting on the body. Weight is a major factor 

in aircraft construction and operation and demands respect 

from all pilots. 

The force of gravity continuously attempts to pull an aircraft 

down toward Earth. The force of lift is the only force that 

counteracts weight and sustains an aircraft in flight. The 

amount of lift produced by an airfoil is limited by the airfoil 

design, angle of attack (AOA), airspeed, and air density. To 

assure that the lift generated is sufficient to counteract weight, 

loading an aircraft beyond the manufacturer’s recommended 

weight must be avoided. If the weight is greater than the lift 

generated, the aircraft may be incapable of flight. 

Weight and Balance 

Chapter 10 
 

Effects of Weight 

Any item aboard an aircraft that increases the total weight is 

undesirable for performance. Manufacturers attempt to make 

an aircraft as light as possible without sacrificing strength 

or safety. 

The pilot should always be aware of the consequences of 

overloading. An overloaded aircraft may not be able to leave 

the ground, or if it does become airborne, it may exhibit 

unexpected and unusually poor flight characteristics. If not 

properly loaded, the initial indication of poor performance 

usually takes place during takeoff. 

Excessive weight reduces the flight performance in almost 

every respect. For example, the most important performance 

deficiencies of an overloaded aircraft are: 

• Higher takeoff speed 

• Longer takeoff run 

• Reduced rate and angle of climb 

• Lower maximum altitude 

• Shorter range 

• Reduced cruising speed 

• Reduced maneuverability 

• Higher stalling speed 

• Higher approach and landing speed 

• Longer landing roll 

• Excessive weight on the nose wheel or tail wheel 

The pilot must be knowledgeable about the effect of weight 

on the performance of the particular aircraft being flown. 

Preflight planning should include a check of performance 

charts to determine if the aircraft’s weight may contribute 

to hazardous flight operations. Excessive weight in itself 

reduces the safety margins available to the pilot and becomes 

even more hazardous when other performance-reducing 

factors are combined with excess weight. The pilot must 

also consider the consequences of an overweight aircraft if 

an emergency condition arises. If an engine fails on takeoff 

or airframe ice forms at low altitude, it is usually too late to 

reduce an aircraft’s weight to keep it in the air. 

Weight Changes 

The operating weight of an aircraft can be changed by 

simply altering the fuel load. Gasoline has considerable 

weight—6 pounds per gallon. Thirty gallons of fuel may 

weigh more than one passenger. If a pilot lowers airplane 

weight by reducing fuel, the resulting decrease in the range 

of the airplane must be taken into consideration during flight 

planning. During flight, fuel burn is normally the only weight 

change that takes place. As fuel is used, an aircraft becomes 

lighter and performance is improved. 

Changes of fixed equipment have a major effect upon the 

weight of an aircraft. The installation of extra radios or 

instruments, as well as repairs or modifications, may also 

affect the weight of an aircraft. 

Balance, Stability, and Center of Gravity 

Balance refers to the location of the CG of an aircraft, and is 

important to stability and safety in flight. The CG is a point 

at which the aircraft would balance if it were suspended at 

that point. 

The primary concern in balancing an aircraft is the fore 

and aft location of the CG along the longitudinal axis. The 

CG is not necessarily a fixed point; its location depends on 

the distribution of weight in the aircraft. As variable load 

items are shifted or expended, there is a resultant shift in 

CG location. The distance between the forward and back 

limits for the position of the center for gravity or CG range 

is certified for an aircraft by the manufacturer. The pilot 

should realize that if the CG is displaced too far forward 

on the longitudinal axis, a nose-heavy condition will 

result. Conversely, if the CG is displaced too far aft on the 

longitudinal axis, a tail heavy condition results. It is possible 

that the pilot could not control the aircraft if the CG location 

produced an unstable condition. [Figure 10-1] 

Location of the CG with reference to the lateral axis is also 

important. For each item of weight existing to the left of 

Lateral unbalance will cause wing heaviness. 

Empty Full 

Excess baggage 

Longitudinal unbalance will cause 

either nose or tail heaviness. 

Figure 10-1. Lateral and longitudinal unbalance. 

10-2 
 

the fuselage centerline, there is an equal weight existing at 

a corresponding location on the right. This may be upset 

by unbalanced lateral loading. The position of the lateral 

CG is not computed in all aircraft, but the pilot must be 

aware that adverse effects arise as a result of a laterally 

unbalanced condition. In an airplane, lateral unbalance occurs 

if the fuel load is mismanaged by supplying the engine(s) 

unevenly from tanks on one side of the airplane. The pilot 

can compensate for the resulting wing-heavy condition by 

adjusting the trim or by holding a constant control pressure. 

This action places the aircraft controls in an out-of-streamline 

condition, increases drag, and results in decreased operating 

efficiency. Since lateral balance is addressed when needed in 

the aircraft flight manual (AFM) and longitudinal balance is 

more critical, further reference to balance in this handbook 

means longitudinal location of the CG. 

Flying an aircraft that is out of balance can produce increased 

pilot fatigue with obvious effects on the safety and efficiency 

of flight. The pilot’s natural correction for longitudinal 

unbalance is a change of trim to remove the excessive control 

pressure. Excessive trim, however, has the effect of reducing 

not only aerodynamic efficiency but also primary control 

travel distance in the direction the trim is applied. 

Effects of Adverse Balance 

Adverse balance conditions affect flight characteristics in 

much the same manner as those mentioned for an excess 

weight condition. It is vital to comply with weight and 

balance limits established for all aircraft. Operating above 

the maximum weight limitation compromises the structural 

integrity of the aircraft and can adversely affect performance. 

Stability and control are also affected by improper balance. 

Stability 

Loading in a nose-heavy condition causes problems in 

controlling and raising the nose, especially during takeoff 

and landing. Loading in a tail heavy condition has a serious 

effect upon longitudinal stability, and reduces the capability 

to recover from stalls and spins. Tail heavy loading also 

produces very light control forces, another undesirable 

characteristic. This makes it easy for the pilot to inadvertently 

overstress an aircraft. 

Stability and Center of Gravity 

Limits for the location of the CG are established by the 

manufacturer. These are the fore and aft limits beyond 

which the CG should not be located for flight. These limits 

are published for each aircraft in the Type Certificate Data 

Sheet (TCDS), or aircraft specification and the AFM or 

pilot’s operating handbook (POH). If the CG is not within the 

allowable limits after loading, it will be necessary to relocate 

some items before flight is attempted. 

The forward CG limit is often established at a location that 

is determined by the landing characteristics of an aircraft. 

During landing, one of the most critical phases of flight, 

exceeding the forward CG limit may result in excessive loads 

on the nosewheel, a tendency to nose over on tailwheel type 

airplanes, decreased performance, higher stalling speeds, and 

higher control forces. 

Control 

In extreme cases, a CG location that is beyond the forward 

limit may result in nose heaviness, making it difficult or 

impossible to flare for landing. Manufacturers purposely 

place the forward CG limit as far rearward as possible to 

aid pilots in avoiding damage when landing. In addition to 

decreased static and dynamic longitudinal stability, other 

undesirable effects caused by a CG location aft of the 

allowable range may include extreme control difficulty, 

violent stall characteristics, and very light control forces 

which make it easy to overstress an aircraft inadvertently. 

A restricted forward CG limit is also specified to assure 

that sufficient elevator/control deflection is available at 

minimum airspeed. When structural limitations do not limit 

the forward CG position, it is located at the position where 

full-up elevator/control deflection is required to obtain a high 

AOA for landing. 

The aft CG limit is the most rearward position at which the 

CG can be located for the most critical maneuver or operation. 

As the CG moves aft, a less stable condition occurs, which 

decreases the ability of the aircraft to right itself after 

maneuvering or turbulence. 

For some aircraft, both fore and aft CG limits may be 

specified to vary as gross weight changes. They may also 

be changed for certain operations, such as acrobatic flight, 

retraction of the landing gear, or the installation of special 

loads and devices that change the flight characteristics. 

The actual location of the CG can be altered by many variable 

factors and is usually controlled by the pilot. Placement of 

baggage and cargo items determines the CG location. The 

assignment of seats to passengers can also be used as a means 

of obtaining a favorable balance. If an aircraft is tail heavy, 

it is only logical to place heavy passengers in forward seats. 

Fuel burn can also affect the CG based on the location of the 

fuel tanks. For example, most small aircraft carry fuel in the 

wings very near the CG and burning off fuel has little effect 

on the loaded CG. 

10-3 
 

Management of Weight and Balance Control 

Title 14 of the Code of Federal Regulations (14 CFR) part 23, 

section 23.23 requires establishment of the ranges of weights 

and CGs within which an aircraft may be operated safely. The 

manufacturer provides this information, which is included in 

the approved AFM, TCDS, or aircraft specifications. 

While there are no specified requirements for a pilot operating 

under 14 CFR part 91 to conduct weight and balance 

calculations prior to each flight, 14 CFR part 91, section 

91.9 requires the pilot in command (PIC) to comply with the 

operating limits in the approved AFM. These limits include 

the weight and balance of the aircraft. To enable pilots to 

make weight and balance computations, charts and graphs 

are provided in the approved AFM. 

Weight and balance control should be a matter of concern to 

all pilots. The pilot controls loading and fuel management 

(the two variable factors that can change both total weight 

and CG location) of a particular aircraft. The aircraft owner 

or operator should make certain that up-to-date information 

is available for pilot use, and should ensure that appropriate 

entries are made in the records when repairs or modifications 

have been accomplished. The removal or addition of 

equipment results in changes to the CG. 

Weight changes must be accounted for and the proper 

notations made in weight and balance records. The 

equipment list must be updated, if appropriate. Without such 

information, the pilot has no foundation upon which to base 

the necessary calculations and decisions. 

Standard parts with negligible weight or the addition of minor 

items of equipment such as nuts, bolts, washers, rivets, and 

similar standard parts of negligible weight on fixed-wing 

aircraft do not require a weight and balance check. The 

following criteria for negligible weight change is outlined 

in Advisory Circular (AC) 43.13-1 (as revised), Methods 

Techniques and Practices—Aircraft Inspection and Repair: 

•	 One pound or less for an aircraft whose weight empty 

is less than 5,000 pounds 

•	 Two pounds or less for aircraft with an empty weight 

of more than 5,000 pounds to 50,000 pounds 

•	 Five pounds or less for aircraft with an empty weight 

of more than 50,000 pounds 

Negligible CG change is any change of less than 0.05 percent 

Mean Aerodynamic Chord (MAC) for fixed-wing aircraft 

or 0.2 percent for rotary wing aircraft. MAC is the average 

distance from the leading edge to the trailing edge of the 

wing. Exceeding these limits would require a weight and 

balance check. 

Before any flight, the pilot should determine the weight 

and balance condition of the aircraft. Simple and orderly 

procedures based on sound principles have been devised 

by the manufacturer for the determination of loading 

conditions. The pilot uses these procedures and exercises 

good judgment when determining weight and balance. In 

many modern aircraft, it is not possible to fill all seats, 

baggage compartments, and fuel tanks, and still remain within 

the approved weight and balance limits. If the maximum 

passenger load is carried, the pilot must often reduce the fuel 

load or reduce the amount of baggage. 

14 CFR part 125 requires aircraft with 20 or more seats 

or maximum payload capacity of 6,000 pounds or more 

to be weighed every 36 calendar months. Multi-engine 

aircraft operated under 14 CFR part 135 are also required 

to be weighed every 36 months. Aircraft operated under 14 

CFR part 135 are exempt from the 36 month requirement 

if operated under a weight and balance system approved in 

the operations specifications of the certificate holder. For 

additional information on approved weight and balance 

control programs for operations under parts 121 and 135, 

reference the current edition of AC 120-27, Aircraft Weight 

and Balance Control. AC 43.13-l, Acceptable Methods, 

Techniques and Practices—Aircraft Inspection and Repair 

also requires that the aircraft mechanic ensure that the weight 

and balance data in the aircraft records is current and accurate 

after a 100-hour or annual inspection. 

Terms and Definitions 

The pilot should be familiar with the appropriate terms 

regarding weight and balance. The following list of terms 

and their definitions is standardized, and knowledge of these 

terms aids the pilot to better understand weight and balance 

calculations of any aircraft. Terms defined by the General 

Aviation Manufacturers Association (GAMA) as industry 

standard are marked in the titles with GAMA. 

• Arm (moment arm)—the horizontal distance in inches 

from the reference datum line to the CG of an item. 

The algebraic sign is plus (+) if measured aft of the 

datum and minus (–) if measured forward of the datum. 

• Basic empty weight (GAMA)—the standard empty 

weight plus the weight of optional and special 

equipment that have been installed. 

• Center of gravity (CG)—the point about which an 

aircraft would balance if it were possible to suspend it 

at that point. It is the mass center of the aircraft or the 

theoretical point at which the entire weight of the aircraft 

is assumed to be concentrated. It may be expressed in 

inches from the reference datum or in percent of MAC. 

The CG is a three-dimensional point with longitudinal, 

lateral, and vertical positioning in the aircraft. 

10-4 
• CG limits—the specified forward and aft points within 

which the CG must be located during flight. These 

limits are indicated on pertinent aircraft specifications. 

• CG range—the distance between the forward and aft 

CG limits indicated on pertinent aircraft specifications. 

• Datum (reference datum)—an imaginary vertical 

plane or line from which all measurements of arm are 

taken. The datum is established by the manufacturer. 

Once the datum has been selected, all moment arms 

and the location of CG range are measured from this 

point. 

• Delta—a Greek letter expressed by the symbol r to 

indicate a change of values. As an example, rCG 

indicates a change (or movement) of the CG. 

• Floor load limit—the maximum weight the floor 

can sustain per square inch/foot as provided by the 

manufacturer. 

• Fuel load—the expendable part of the load of the 

aircraft. It includes only usable fuel, not fuel required 

to fill the lines or that which remains trapped in the 

tank sumps. 

• Licensed empty weight—the empty weight that 

consists of the airframe, engine(s), unusable fuel, and 

undrainable oil plus standard and optional equipment 

as specified in the equipment list. Some manufacturers 

used this term prior to GAMA standardization. 

• Maximum landing weight—the greatest weight that 

an aircraft is normally allowed to have at landing. 

• Maximum ramp weight—the total weight of a loaded 

aircraft including all fuel. It is greater than the takeoff 

weight due to the fuel that will be burned during the 

taxi and run-up operations. Ramp weight may also be 

referred to as taxi weight. 

• Maximum takeoff weight—the maximum allowable 

weight for takeoff. 

• Maximum weight—the maximum authorized weight 

of the aircraft and all of its equipment as specified in 

the TCDS for the aircraft. 

• Maximum zero fuel weight (GAMA)—the maximum 

weight, exclusive of usable fuel. 

• Mean aerodynamic chord (MAC)—the average 

distance from the leading edge to the trailing edge of 

the wing. 

• Moment—the product of the weight of an item 

multiplied by its arm. Moments are expressed in 

pound-inches (in-lb). Total moment is the weight of 

the airplane multiplied by the distance between the 

datum and the CG. 

• Moment index (or index)—a moment divided by a 

constant such as 100, 1,000, or 10,000. The purpose 

of using a moment index is to simplify weight and 

balance computations of aircraft where heavy items 

and long arms result in large, unmanageable numbers. 

• Payload (GAMA)—the weight of occupants, cargo, 

and baggage. 

• Standard empty weight (GAMA)—aircraft weight 

that consists of the airframe, engines, and all items of 

operating equipment that have fixed locations and are 

permanently installed in the aircraft, including fixed 

ballast, hydraulic fluid, unusable fuel, and full engine 

oil. 

• Standard weights—established weights for numerous 

items involved in weight and balance computations. 

These weights should not be used if actual weights 

are available. Some of the standard weights are: 

Gasoline.................................................. 6 lb/US gal
 

Jet A, Jet A-1....................................... 6.8 lb/US gal
 

Jet B......................................................6.5 lb/US gal
 

Oil.........................................................7.5 lb/US gal
 

Water................................................. 8.35 lb/US gal
 

• Station—a location in the aircraft that is identified by 

a number designating its distance in inches from the 

datum. The datum is, therefore, identified as station 

zero. An item located at station +50 would have an 

arm of 50 inches. 

• Useful load—the weight of the pilot, copilot, 

passengers, baggage, usable fuel, and drainable oil. 

It is the basic empty weight subtracted from the 

maximum allowable gross weight. This term applies 

to general aviation (GA) aircraft only. 

Principles of Weight and Balance Computations 

It is imperative that all pilots understand the basic principles 

of weight and balance determination. The following methods 

of computation can be applied to any object or vehicle for 

which weight and balance information is essential. 

By determining the weight of the empty aircraft and adding 

the weight of everything loaded on the aircraft, a total weight 

can be determined—a simple concept. A greater problem, 

particularly if the basic principles of weight and balance are 

not understood, is distributing this weight in such a manner 

that the entire mass of the loaded aircraft is balanced around 

a point (CG) that must be located within specified limits. 

The point at which an aircraft balances can be determined by 

locating the CG, which is, as stated in the definitions of terms, 

10-5 
 

 

the imaginary point at which all the weight is concentrated. 

To provide the necessary balance between longitudinal 

stability and elevator control, the CG is usually located 

slightly forward of the center of lift. This loading condition 

causes a nose-down tendency in flight, which is desirable 

during flight at a high AOA and slow speeds. 

As mentioned earlier, a safe zone within which the balance 

point (CG) must fall is called the CG range. The extremities 

of the range are called the forward CG limits and aft CG 

limits. These limits are usually specified in inches, along the 

longitudinal axis of the airplane, measured from a reference 

point called a datum reference. The datum is an arbitrary 

point, established by aircraft designers that may vary in 

location between different aircraft. [Figure 10-2] 

The distance from the datum to any component part or any 

object loaded on the aircraft is called the arm. When the 

object or component is located aft of the datum, it is measured 

in positive inches; if located forward of the datum, it is 

measured as negative inches or minus inches. The location 

of the object or part is often referred to as the station. If 

the weight of any object or component is multiplied by the 

distance from the datum (arm), the product is the moment. 

The moment is the measurement of the gravitational force 

that causes a tendency of the weight to rotate about a point 

or axis and is expressed in inch-pounds (in-lb). 

To illustrate, assume a weight of 50 pounds is placed on 

the board at a station or point 100 inches from the datum. 

The downward force of the weight can be determined by 

multiplying 50 pounds by 100 inches, which produces a 

moment of 5,000 in-lb. [Figure 10-3] 

To establish a balance, a total of 5,000 in-lb must be applied 

to the other end of the board. Any combination of weight 

and distance which, when multiplied, produces a 5,000 inlb moment will balance the board. For example (illustrated 

50 

lb 

100" 

Moment = 5,000 in-lb 

Fulcrum 

Datum 

Wt x Arm = Moment 

(lb) x (in) = (in-lb) 

50 x 100 = 5,000 Note: The datum is assumed to be 

located at the fulcrum. 

Figure 10-3. Determining moment. 

in Figure 10-4), if a 100-pound weight is placed at a point 

(station) 25 inches from the datum, and another 50-pound 

weight is placed at a point (station) 50 inches from the datum, 

the sum of the product of the two weights and their distances 

total a moment of 5,000 in-lb, which will balance the board. 

Weight and Balance Restrictions 

An aircraft’s weight and balance restrictions should be 

closely followed. The loading conditions and empty weight 

of a particular aircraft may differ from that found in the 

AFM/POH because modifications or equipment changes 

may have been made. Sample loading problems in the 

AFM/POH are intended for guidance only; therefore, each 

aircraft must be treated separately. Although an aircraft is 

certified for a specified maximum gross takeoff weight, it 

may not safely take off at this weight under all conditions. 

Conditions that affect takeoff and climb performance, such as 

high elevations, high temperatures, and high humidity (high 

density altitudes), may require a reduction in weight before 

flight is attempted. Other factors to consider when computing 

Fwd limit Aft limit

Datum 

CG 

range 

( + ) 

Arm 

( – ) 

Arm 

( + ) Arm 70" 

Moment = 700 in-lb 

Sta 0 Sta 70 

10 lb 

Figure 10-2. Weight and balance. 

100 50 lb lb 

50 

lb 

25" 

50" 100" 

2,500 

in-lb 

2,500 

in-lb 

5,000 

in-lb 

Fulcrum 

Datum 

100 x 25 = 2,500 

50 x 50 = 2,500 

Total = 5,000 

Wt x Arm = Moment 

(lb) x (in) = (in-lb) 

Figure 10-4. Establishing a balance. 

10-6 
 

 

 

 

 

 

weight and balance distribution prior to takeoff are runway 

length, runway surface, runway slope, surface wind, and the 

presence of obstacles. These factors may require a reduction 

in or redistribution of weight prior to flight. 

Some aircraft are designed so that it is difficult to load them 

in a manner that places the CG out of limits. These are 

usually small aircraft with the seats, fuel, and baggage areas 

located near the CG limit. Pilots must be aware that while 

within CG limits these aircraft can be overloaded in weight. 

Other aircraft can be loaded in such a manner that they will 

be out of CG limits even though the useful load has not been 

exceeded. Because of the effects of an out-of-balance or 

overweight condition, a pilot should always be sure that an 

aircraft is properly loaded. 

Determining Loaded Weight and CG 

There are various methods for determining the loaded weight 

and CG of an aircraft. There is the computational method as 

well as methods that utilize graphs and tables provided by 

the aircraft manufacturer. 

Computational Method 

The following is an example of the computational method 

involving the application of basic math functions. 

Aircraft Allowances: 

Maximum gross weight......................3,400 pounds 

CG range.............................................78–86 inches 

Given: 

Weight of front seat occupants.............340 pounds 

Weight of rear seat occupants..............350 pounds 

Fuel...........................................................75 gallons 

Weight of baggage in area 1....................80 pounds 

1.	 List the weight of the aircraft, occupants, fuel, and 

baggage. Remember that aviation gas (AVGAS) 

weighs 6 pounds per gallon and is used in this 

example. 

2.	 Enter the moment for each item listed. Remember 

“weight x arm = moment.” 

3.	 Find the total weight and total moment. 

4.	 To determine the CG, divide the total moment by the 

total weight. 

NOTE: The weight and balance records for a particular 

aircraft provide the empty weight and moment, as well as the 

information on the arm distance. [Figure 10-5] 

The total loaded weight of 3,320 pounds does not exceed 

the maximum gross weight of 3,400 pounds, and the CG of 

Item Weight Arm Moment 

Aircraft Empty Weight 2,100 78.3 164,430 

Front Seat Occupants 340 85.0 28,900 

Rear Seat Occupants 350 121.0 42,350 

Fuel 450 75.0 33,750 

Baggage Area 1 80 150.0 12,000 

Total 3,320 281,430 

281,430 ÷ 3,320 = 84.8 

Figure 10-5. Example of weight and balance computations. 

84.8 is within the 78–86 inch range; therefore, the aircraft is 

loaded within limits. 

Graph Method 

Another method for determining the loaded weight and CG is 

the use of graphs provided by the manufacturers. To simplify 

calculations, the moment may sometimes be divided by 100, 

1,000, or 10,000. [Figures 10-6, 10-7, and 10-8] 

Front seat occupants....................................340 pounds
 

Rear seat occupants ......................................300 pounds
 

Fuel.................................................................40 gallons
 

Baggage area 1 ...............................................20 pounds
 

The same steps should be followed in the graph method as 

were used in the computational method except the graphs 

provided will calculate the moments and allow the pilot to 

determine if the aircraft is loaded within limits. To determine 

the moment using the loading graph, find the weight and draw 

a line straight across until it intercepts the item for which the 

moment is to be calculated. Then draw a line straight down 

to determine the moment. (The red line on the loading graph 

in Figure 10-7 represents the moment for the pilot and front 

passenger. All other moments were determined the same 

Sample Loading Problem Weight (lb) Moment 

(in-lb/1,000) 

1. Basic empty weight (Use data pertaining 

to aircraft as it is presently equipped) 

includes unusable fuel and full oil 

2. Usable fuel (At 6 lb/gal) 

Standard tanks (40 gal maximum) 

Long range tanks (50 gal maximum) 

Integral tanks (62 gal maximum) 

Integral reduced fuel (42 gal) 

3. Pilot and front passenger (Station 34 

to 46) 

4. Rear passengers 

5. Baggage area 1 or passenger on child’s 

seat (Station 82 to 108, 120 lb maximum) 

6. Baggage area 2 

(Station 108 to 142, 50 lb maximum) 

7. Weight and moment 

1,467 57.3

 240 11.5

 340 12.7

 300 21.8

 20 1.9 

2,367 105.2 

Figure 10-6. Weight and balance data. 

10-7 
 

400 

350 

300 

250 

200 

150 

100 

50 

0 5 10 15 20 25 30 

340

12.7

0 50 100 150 200 250 300 350 400 

Load Moment/1,000 (kilogram-millimeters) 

0 

25 

50 

75 

100 

125 

150 

175 

200 

Load Weight (kilograms) 

Load Moment/1,000 (inch-pounds) 

Load Weight (pounds)

 Maximum Usable Fuel

 * Standard tanks

 ** Long range tanks

 *** Internal tanks 

Pilot & front passenger 

Rear passengers 

Baggage area 1 or 

passenger on child’s seat 

Fuel (6 lb/gal; 0.72 kg/liter)

62 gal***(234.7 liters) 

Baggage area 2 

60 gal (227.1 liters) 

50 gal**(189.3 liters) 

42 gal reduced***(159 liters) 

40 gal*(189.3 liters) 

30 gal (113.6 liters) 

20 gal (75.7 liters) 

10 gal (37.9 liters) 

Figure 10-7. Loading graph. 

2,400 

2,300 

2,200 

2,100 

2,000 

1,900 

1,800 

1,700 

1,600 

1,50045 50 55 60 65 70 75 80 85 90 95 100 105 110 

2,367

105.2

Loaded Aircraft Moment/1,000 (kilogram-millimeters) 

700 

750 

800 

850 

900 

950 

1,000 

1,050 

1,100 

Loaded Airplane Weight (kilograms) 

Loaded Aircraft Moment/1,000 (inch-pounds) 

Loaded Aircraft Weight (pounds) 

600 700 800 900 1,000 1,100 1,200 1,300 

Utility category 

Normal 

category 

Figure 10-8. CG moment envelope. 

10-8 
130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

196

210

224

238

252

266

280

294

308

322

336

350

364

378

 

way.) Once this has been done for each item, total the weight Table Method 

and moments and draw a line for both weight and moment The table method applies the same principles as the 

on the CG envelope graph. If the lines intersect within the computational and graph methods. The information 

envelope, the aircraft is loaded within limits. In this sample and limitations are contained in tables provided by the 

loading problem, the aircraft is loaded within limits. manufacturer. Figure 10-9 is an example of a table and a 

OIL 

FUEL TANK 

FUEL TANK 

Occupants 

Front Seat 

Arm 85 

Rear Seats 

Arm 121 

Moment 

100 Weight Moment 

100 Weight 

120 

130 

140 

150 

160 

170 

180 

190 

200 

120 

130 

140 

150 

160 

170 

180 

190 

200 

102 

110 

119 

128 

136 

144 

153 

162 

170 

145 

157 

169 

182 

194 

206 

218 

230 

242 

Usable Fuel 

Main Wing Tanks Arm 75 

Gallons Weight Moment 

100 

5 

10 

15 

20 

25 

30 

35 

40 

44 

30

 60

 90 

120 

150 

180 

210 

240 

264 

22 

45 

68 

90 

112 

135 

158 

180 

198 

Moment Limits vs Weight 

Moment limits are based on the following weight and 

center of gravity limit data (landing gear down). 

2,950 lb (takeoff

or landing)

2,525 lb 

2,475 lb or less 

82.1 

77.5 

77.0 

84.7 

85.7 

85.7 

Forward 

CG Limit 

Weight 

Condition 

AFT 

CG Limit 

Moment 

100 Weight 

Baggage or 5th 

Seat Occupant 

Arm 140

 10

 20

 30

 40

 50

 60

 70

 80

 90 

100 

110 

120

 14

 28

 42

 56

 70

 84

 98 

112 

126 

140 

154 

168 

182 

Weight 

Maximum 

Moment 

100 

Minimum 

Moment 

100 

1,800 

1,808 

1,817 

1,825 

1,834 

1,843 

1,851 

1,860 

1,868 

1,877 

1,885 

1,894 

1,903 

1,911 

1,920 

1,928 

1,937 

1,945 

1,954 

1,963 

1,971 

1,980 

1,988 

1,997 

2,005 

2,014 

2,023 

2,031 

2,040 

2,048 

2,100 

2,110 

2,120 

2,130 

2,140 

2,150 

2,160 

2,170 

2,180 

2,190 

2,200 

2,210 

2,220 

2,230 

2,240 

2,250 

2,260 

2,270 

2,280 

2,290 

2,300 

2,310 

2,320 

2,330 

2,340 

2,350 

2,360 

2,370 

2,380 

2,390 

1,617 

1,625 

1,632 

1,640 

1,648 

1,656 

1,663 

1,671 

1,679 

1,686 

1,694 

1,702 

1,709 

1,717 

1,725 

1,733 

1,740 

1,748 

1,756 

1,763 

1,771 

1,779 

1,786 

1,794 

1,802 

1,810 

1,817 

1,825 

1,833 

1,840 

Weight 

Maximum 

Moment 

100 

Minimum 

Moment 

100 

2,057 

2,065 

2,074 

2,083 

2,091 

2,100 

2,108 

2,117 

2,125 

2,134 

2,143 

2,151 

2,160 

2,168 

2,176 

2,184 

2,192 

2,200 

2,208 

2,216 

2,224 

2,232 

2,239 

2,247 

2,255 

2,263 

2,271 

2,279 

2,287 

2,295 

2,303 

2,311 

2,319 

2,326 

2,334 

2,342 

2,350 

2,358 

2,366 

2,374 

2,381 

2,389 

2,397 

2,405 

2,413 

2,421 

2,426 

2,436 

2,444 

2,452 

3,460 

2,468 

2,475 

2,483 

2,491 

2,499 

2,400 

2,410 

2,420 

2,430 

2,440 

2,450 

2,460 

2,470 

2,480 

2,490 

2,500 

2,510 

2,520 

2,530 

2,540 

2,550 

2,560 

2,570 

2,580 

2,590 

2,600 

2,610 

2,620 

2,630 

2,640 

2,650 

2,660 

2,670 

2,680 

2,690 

2,700 

2,710 

2,720 

2,730 

2,740 

2,750 

2,760 

2,770 

2,780 

2,790 

2,800 

2,810 

2,820 

2,830 

2,840 

2,850 

2,860 

2,870 

2,880 

2,890 

2,900 

2,910 

2,920 

2,930 

2,940 

2,950 

1,848 

1,856 

1,863 

1,871 

1,879 

1,887 

1,894 

1,092 

1,911 

1,921 

1,932 

1,942 

1,953 

1,963 

1,974 

1,984 

1,995 

2,005 

2,016 

2,026 

2,037 

2,048 

2,058 

2,069 

2,080 

2,090 

2,101 

2,112 

2,123 

2,133 

2,144 

2,155 

2,166 

2,177 

2,188 

2,199 

2,210 

2,221 

2,232 

2,243 

2,254 

2,265 

2,276 

2,287 

2,298 

2,309 

2,320 

2,332 

2,343 

2,354 

2,365 

2,377 

2,388 

2,399 

2,411 

2,422 

Sample Loading Problem Weight Moment

 Basic empty weight 2,015 1,554

 Fuel main tanks (44 gal) 264 198 

*Front seat passengers 300 254 

*Rear seat passengers 190 230

 Baggage 30 42

 Total 2,799 2,278/100 

* Interpolate or, as in this case, add appropriate numbers. 

Empty Weight ~ 2,015 

MOM/ 100 ~ 1,554 

*Oil 

Quarts Weight Moment 

100 

10 19 5 

*Included in basic empty weight 

BAGGAGE AREA

SEATING AREA 

Figure 10-9. Loading schedule placard. 

10-9 
 

 

 

 

weight and balance calculation based on that table. In this 

problem, the total weight of 2,799 pounds and moment of 

2,278/100 are within the limits of the table. 

Computations With a Negative Arm 

Figure 10-10 is a sample of weight and balance computation 

using an aircraft with a negative arm. It is important to 

remember that a positive times a negative equals a negative, 

and a negative would be subtracted from the total moments. 

Computations With Zero Fuel Weight 

Figure 10-11 is a sample of weight and balance computation 

using an aircraft with a zero fuel weight. In this example, 

the total weight of the aircraft less fuel is 4,240 pounds, 

which is under the zero fuel weight of 4,400 pounds. If the 

total weight of the aircraft without fuel had exceeded 4,400 

pounds, passengers or cargo would have needed to be reduced 

to bring the weight at or below the max zero fuel weight. 

Shifting, Adding, and Removing Weight 

A pilot must be able to solve any problems accurately that 

involve the shift, addition, or removal of weight. For example, 

the pilot may load the aircraft within the allowable takeoff 

weight limit, then find that the CG limit has been exceeded. 

The most satisfactory solution to this problem is to shift 

baggage, passengers, or both. The pilot should be able to 

determine the minimum load shift needed to make the aircraft 

safe for flight. Pilots should be able to determine if shifting a 

load to a new location will correct an out-of-limit condition. 

There are some standardized calculations that can help make 

these determinations. 

Weight Shifting 

When weight is shifted from one location to another, the 

total weight of the aircraft is unchanged. The total moments, 

however, do change in relation and proportion to the 

direction and distance the weight is moved. When weight is 

moved forward, the total moments decrease; when weight 

is moved aft, total moments increase. The moment change 

is proportional to the amount of weight moved. Since many 

Item Weight Arm Moment 

Licensed empty weight 

Oil (6 quarts) 

Fuel (18 gallons) 

Fuel, auxiliary (18 gallons) 

Pilot 

Passenger 

Baggage 

1,011.9 

11.0 

108.0 

108.0 

170.0 

170.0 

70.0 

68.6 

−31.0 

84.0 

84.0 

81.0 

81.0 

105.0 

69,393.0 

−341.0 

9,072.0 

9,072.0 

13,770.0 

13,770.0 

7,350.0 

Total 1,648.9 122,086.0 

CG 74.0 

Item Weight Arm Moment 

Basic empty weight 

Front seat occupants 

3rd & 4th seat occupants

forward facing 

5th & 6th seat occupants 

Nose baggage 

Aft baggage 

Subtotal 

Fuel 

Subtotal ramp weight 

* Less fuel for start, 

taxi, and takeoff 

Subtotal 

takeoff weight 

Less fuel to destination 

Actual landing weight 

*Fuel for start, taxi, and takeoff is normally 24 pounds.

 3,230

 335

 350

 200

 100

 25

 4,240 

822 

5,062

 −24

 5,038

 −450

 4,588 

292,315.0

 29,815.0

 44,100.0

 31,400.0

 1,000.0 

4,575.0

 403,205.0

 92,886.0

 496,091.0 

−2,712.0 

493,379.0

 −50,850.0

 442,529.0

 CG 90.5

 89.0

 126.0

 157.0

 10.0

 183.0

 CG 95.1

 113.0

 CG 98.0

 113.0

 CG 97.9

 113.0

 CG 96.5 

Zero fuel weight max 4,400 pounds 

Ramp weight max 5,224 pounds 

Max landing weight 4,940 pounds 

Figure 10-11. Sample weight and balance using an aircraft with a 

published zero fuel weight. 

aircraft have forward and aft baggage compartments, weight 

may be shifted from one to the other to change the CG. If 

starting with a known aircraft weight, CG, and total moments, 

calculate the new CG (after the weight shift) by dividing the 

new total moments by the total aircraft weight. 

To determine the new total moments, find out how many 

moments are gained or lost when the weight is shifted. 

Assume that 100 pounds has been shifted from station 30 to 

station 150. This movement increases the total moments of 

the aircraft by 12,000 in-lb. 

Moment when 

at station 150 = 100 lb x 150 in = 15,000 in-lb 

Moment when 

at station 30 = 100 lb x 30 in = 3,000 in-lb 

Moment change = [15,000 – 3,000] = 12,000 in-lb 

By adding the moment change to the original moment (or 

subtracting if the weight has been moved forward instead of 

aft), the new total moments are obtained. Then determine the 

new CG by dividing the new moments by the total weight: 

Total moments = 

616,000 in-lb + 12,000 in-lb = 628,000 in-lb
 

CG = 628,000 in-lb = 78.5 in

 8,000 lb 

The shift has caused the CG to shift to station 78.5. 

Figure 10-10. Sample weight and balance using a negative. 

10-10 
 

 

Example 

The change of CG is added to (or subtracted from when appropriate) 

the original CG to determine the new CG: 

77 + 1.5 = 78.5 inches aft of datum 

The shifting weight proportion formula can also be used to determine 

how much weight must be shifted to achieve a particular shift of the CG. 

The following problem illustrates a solution of this type. 

Weight shifted 

Total weight 

∆CG (change of CG) 

Distance weight is shifted = 

100 

8,000 

∆CG 

120 = 

∆CG 1.5 in= 

Example 

Weight to be shifted 

Total weight 

CG 

Distance weight is shifted = 

Weight to be shifted 

7,800 lb 

Weight to be shifted 

1.0 in 

120 in = 

65 lb= 

Given: 

Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,800 lb 

CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5 in 

Aft CG limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.5 in 

Determine how much cargo must be shifted from the aft cargo compartment at station 150 to the forward cargo compartment at station 30 to 

move the CG to exactly the aft limit. 

Solution: 

A simpler solution may be obtained by using a computer 

or calculator and a proportional formula. This can be done 

because the CG will shift a distance that is proportional to 

the distance the weight is shifted. 

Weight Addition or Removal 

In many instances, the weight and balance of the aircraft will 

be changed by the addition or removal of weight. When this 

happens, a new CG must be calculated and checked against 

the limitations to see if the location is acceptable. This type 

of weight and balance problem is commonly encountered 

when the aircraft burns fuel in flight, thereby reducing the 

weight located at the fuel tanks. Most small aircraft are 

designed with the fuel tanks positioned close to the CG; 

therefore, the consumption of fuel does not affect the CG to 

any great extent. 

The addition or removal of cargo presents a CG change 

problem that must be calculated before flight. The problem 

may always be solved by calculations involving total 

moments. A typical problem may involve the calculation 

of a new CG for an aircraft which, when loaded and ready 

for flight, receives some additional cargo or passengers just 

before departure time. 

Example 

Added weight 

New total weight 

∆CG 

Distance between weight and old CG 

∆CG 

150 in − 80 in 

= 

140 lb 

6,860 lb + 140 lb = 

140 lb 

7,000 lb = ∆CG 

70 in 

CG = 1.4 in aft

Given: 

Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6,860 lb 

CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.0 in 

Determine the location of the CG if 140 pounds of baggage is added to 

station 150. 

Solution: 

Add ∆CG to old CG 

New CG = 80 in + 1.4 in = 81.4 in 

Example 

Weight removed 

New total weight 

∆CG 

Distance between weight and old CG 

∆CG 

150 in − 80 in 

= 

100 lb 

6,100 lb − 100 lb = 

100 lb 

6,000 lb = ∆CG 

70 in 

CG = 1.2 in forward

Given: 

Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6,100 lb 

CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.0 in 

Determine the location of the CG if 100 pounds is removed from 

station 150. 

Solution: 

Subtract ∆CG from old CG 

New CG = 80 in − 1.2 in = 78.8 in 

In the previous examples, the rCG is either added or 

subtracted from the old CG. Deciding which to accomplish is 

best handled by mentally calculating which way the CG will 

shift for the particular weight change. If the CG is shifting 

aft, the rCG is added to the old CG; if the CG is shifting 

forward, the rCG is subtracted from the old CG. 

Chapter Summary 

Operating an aircraft within the weight and balance limits 

is critical to flight safety. Pilots must ensure that the CG is 

and remains within approved limits throughout all phases of 

a flight. For additional information on weight, balance, CG, 

and aircraft stability refer to the FAA handbook appropriate 

to the specific aircraft category. 

10-11 
10-12
 
11-1 

Introduction 

This chapter discusses the factors that affect aircraft 

performance, which include the aircraft weight, atmospheric 

conditions, runway environment, and the fundamental 

physical laws governing the forces acting on an aircraft. 

Importance of Performance Data 

The performance or operational information section of the 

Aircraft Flight Manual/Pilot’s Operating Handbook (AFM/ 

POH) contains the operating data for the aircraft; that is, the 

data pertaining to takeoff, climb, range, endurance, descent, 

and landing. The use of this data in flying operations is 

mandatory for safe and efficient operation. Considerable 

knowledge and familiarity of the aircraft can be gained by 

studying this material. 

Aircraft 

Performance 

Chapter 11 
It must be emphasized that the manufacturers’ information 

and data furnished in the AFM/POH is not standardized. 

Some provide the data in tabular form, while others use 

graphs. In addition, the performance data may be presented 

on the basis of standard atmospheric conditions, pressure 

altitude, or density altitude. The performance information in 

the AFM/POH has little or no value unless the user recognizes 

those variations and makes the necessary adjustments. 

To be able to make practical use of the aircraft’s capabilities 

and limitations, it is essential to understand the significance 

of the operational data. The pilot must be cognizant of the 

basis for the performance data, as well as the meanings of 

the various terms used in expressing performance capabilities 

and limitations. 

Since the characteristics of the atmosphere have a major 

effect on performance, it is necessary to review two dominant 

factors—pressure and temperature. 

Structure of the Atmosphere 

The atmosphere is an envelope of air that surrounds the 

Earth and rests upon its surface. It is as much a part of the 

Earth as is land and water. However, air differs from land 

and water in that it is a mixture of gases. It has mass, weight, 

and indefinite shape. 

Air, like any other fluid, is able to flow and change its shape 

when subjected to even minute pressures because of the 

lack of strong molecular cohesion. For example, gas will 

completely fill any container into which it is placed, expanding 

or contracting to adjust its shape to the limits of the container. 

The atmosphere is composed of 78 percent nitrogen, 21 

percent oxygen, and 1 percent other gases, such as argon 

or helium. Most of the oxygen is contained below 35,000 

feet altitude. 

Atmospheric Pressure 

Though there are various kinds of pressure, pilots are mainly 

concerned with atmospheric pressure. It is one of the basic 

factors in weather changes, helps to lift the aircraft, and 

actuates some of the most important flight instruments in the 

aircraft. These instruments often include the altimeter, the 

airspeed indicator (ASI), the vertical speed indicator (VSI), 

and the manifold pressure gauge. 

Though air is very light, it has mass and is affected by the 

attraction of gravity. Therefore, like any other substance, it 

has weight; because it has weight, it has force. Since it is a 

fluid substance, this force is exerted equally in all directions, 

and its effect on bodies within the air is called pressure. 

Under standard conditions at sea level, the average pressure 

exerted by the weight of the atmosphere is approximately 14.7 

pounds per square inch (psi). The density of air has significant 

effects on the aircraft’s performance. As air becomes less 

dense, it reduces: 

• Power, because the engine takes in less air 

• Thrust, because the propeller is less efficient in thin air 

• Lift, because the thin air exerts less force on the airfoils 

The pressure of the atmosphere may vary with time but more 

importantly, it varies with altitude and temperature. Due to 

the changing atmospheric pressure, a standard reference 

was developed. The standard atmosphere at sea level has 

a surface temperature of 59 degrees Fahrenheit (°F) or 15 

degrees Celsius (°C) and a surface pressure of 29.92 inches 

of mercury ("Hg) or 1013.2 millibars (mb). [Figure 11-1] 

A standard temperature lapse rate is one in which the 

temperature decreases at the rate of approximately 3.5 °F or 

2 °C per thousand feet up to 36,000 feet. Above this point, 

the temperature is considered constant up to 80,000 feet. A 

standard pressure lapse rate is one in which pressure decreases 

at a rate of approximately 1 "Hg per 1,000 feet of altitude gain 

to 10,000 feet. [Figure 11-2] The International Civil Aviation 

Organization (ICAO) has established this as a worldwide 

standard, and it is often referred to as International Standard 

Atmosphere (ISA) or ICAO Standard Atmosphere. Any 

temperature or pressure that differs from the standard lapse 

rates is considered nonstandard temperature and pressure. 

Adjustments for nonstandard temperatures and pressures are 

provided on the manufacturer’s performance charts. 

30 

25 

20 

15 

10

 5

 0

 Inches of 

Mercury Millibars 

1016 

847 

677 

508 

339

 170

 0 

29.92" 

Standard 

Sea Level 

Pressure 

Hg 1013 

Standard 

Sea Level 

Pressure 

mb 

Atmospheric Pressure 

Figure 11-1. Standard sea level pressure. 

11-2 
 

 

 

 

 

Altitude (ft) Pressure 

("Hg) 

Temperature 

(°C) (°F) 

0 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

9,000 

10,000 

11,000 

12,000 

13,000 

14,000 

15,000 

16,000 

17,000 

18,000 

19,000 

20,000 

29.92 

28.86 

27.82 

26.82 

25.84 

24.89 

23.98 

23.09 

22.22 

21.38 

20.57 

19.79 

19.02 

18.29 

17.57 

16.88 

16.21 

15.56 

14.94 

14.33 

13.74 

15.0 

13.0 

11.0 

9.1 

7.1 

5.1 

3.1 

1.1 

−0.9

−2.8

−4.8

−6.8

−8.8

−10.8

−12.7

−14.7

−16.7

−18.7

−20.7

−22.6

−24.6

59.0 

55.4 

51.9 

48.3 

44.7 

41.2 

37.6 

34.0 

30.5 

26.9 

23.3 

19.8 

16.2 

12.6 

9.1 

5.5 

1.9 

−1.6

−5.2

−8.8

−12.3

Figure 11-2. Properties of standard atmosphere. 

Since all aircraft performance is compared and evaluated 

using the standard atmosphere, all aircraft instruments 

are calibrated for the standard atmosphere. Thus, certain 

corrections must apply to the instrumentation, as well as the 

aircraft performance, if the actual operating conditions do 

not fit the standard atmosphere. In order to account properly 

for the nonstandard atmosphere, certain related terms must 

be defined. 

Pressure Altitude 

Pressure altitude is the height above the standard datum 

plane (SDP). The aircraft altimeter is essentially a sensitive 

barometer calibrated to indicate altitude in the standard 

atmosphere. If the altimeter is set for 29.92 "Hg SDP, the 

altitude indicated is the pressure altitude—the altitude in the 

standard atmosphere corresponding to the sensed pressure. 

The SDP is a theoretical level at which the pressure of the 

atmosphere is 29.92 "Hg and the weight of air is 14.7 psi. As 

atmospheric pressure changes, the SDP may be below, at, or 

above sea level. Pressure altitude is important as a basis for 

determining aircraft performance, as well as for assigning 

flight levels to aircraft operating at above 18,000 feet. 

The pressure altitude can be determined by any of the three 

following methods: 

1.	 By setting the barometric scale of the altimeter to 

29.92 "Hg and reading the indicated altitude, 

2.	 By applying a correction factor to the indicated 

altitude according to the reported “altimeter setting,” 

[Figure 11-3] 

3. By using a flight computer 

Density Altitude 

The more appropriate term for correlating aerodynamic 

performance in the nonstandard atmosphere is density 

altitude—the altitude in the standard atmosphere 

corresponding to a particular value of air density. 

Density altitude is pressure altitude corrected for nonstandard 

temperature. As the density of the air increases (lower 

density altitude), aircraft performance increases. Conversely, 

Altimeter 

setting 

Altitude 

correction 

28.0 

28.1 

28.2 

28.3 

28.4 

28.5 

28.6 

28.7 

28.8 

28.9 

29.0 

29.1 

29.2 

29.3 

29.4 

29.5 

29.6 

29.7 

29.8 

29.9 

29.92 

30.0 

30.1 

30.2 

30.3 

30.4 

30.5 

30.6 

30.7 

30.8 

30.9 

31.0 

1,824 

1,727 

1,630 

1,533 

1,436 

1,340 

1,244 

1,148 

1,053 

957 

863 

768 

673 

579 

485 

392 

298 

205 

112 

20 

0 

−73

−165

−257

−348

−440

−531

−622

−712

−803

−893

−983

Subtract Add

To field 

elevation 

From field 

elevation 

To get 

pressure altitude 

Alternate Method for Determining 

Pressure Altitude 

Method for Determining 

Pressure Altitude 

Field elevation is sea level 

Figure 11-3. Field elevation versus pressure. The aircraft is located 

on a field that happens to be at sea level. Set the altimeter to the 

current altimeter setting (29.7). The difference of 205 feet is added 

to the elevation or a PA of 205 feet. 

11-3 
 

as air density decreases (higher density altitude), aircraft 

performance decreases. A decrease in air density means a 

high density altitude; an increase in air density means a lower 

density altitude. Density altitude is used in calculating aircraft 

performance. Under standard atmospheric condition, air at 

each level in the atmosphere has a specific density; under 

standard conditions, pressure altitude and density altitude 

identify the same level. Density altitude, then, is the vertical 

distance above sea level in the standard atmosphere at which 

a given density is to be found. 

Density altitude is computed using pressure altitude and 

temperature. Since aircraft performance data at any level is 

based upon air density under standard day conditions, such 

performance data apply to air density levels that may not be 

identical to altimeter indications. Under conditions higher 

or lower than standard, these levels cannot be determined 

directly from the altimeter. 

Density altitude is determined by first finding pressure 

altitude and then correcting this altitude for nonstandard 

temperature variations. Since density varies directly with 

pressure, and inversely with temperature, a given pressure 

altitude may exist for a wide range of temperature by allowing 

the density to vary. However, a known density occurs for 

any one temperature and pressure altitude. The density of the 

air, of course, has a pronounced effect on aircraft and engine 

performance. Regardless of the actual altitude at which 

the aircraft is operating, it will perform as though it were 

operating at an altitude equal to the existing density altitude. 

For example, when set at 29.92 "Hg, the altimeter may 

indicate a pressure altitude of 5,000 feet. According to the 

AFM/POH, the ground run on takeoff may require a distance 

of 790 feet under standard temperature conditions. However, 

if the temperature is 20 °C above standard, the expansion of 

air raises the density level. Using temperature correction data 

from tables or graphs, or by deriving the density altitude with 

a computer, it may be found that the density level is above 

7,000 feet, and the ground run may be closer to 1,000 feet. 

Air density is affected by changes in altitude, temperature, 

and humidity. High density altitude refers to thin air while 

low density altitude refers to dense air. The conditions that 

result in a high density altitude are high elevations, low 

atmospheric pressures, high temperatures, high humidity, or 

some combination of these factors. Lower elevations, high 

atmospheric pressure, low temperatures, and low humidity 

are more indicative of low density altitude. 

Using a flight computer, density altitude can be computed by 

inputting the pressure altitude and outside air temperature at 

flight level. Density altitude can also be determined by referring 

to the table and chart in Figures 11-3 and 11-4 respectively. 

Effects of Pressure on Density 

Since air is a gas, it can be compressed or expanded. When 

air is compressed, a greater amount of air can occupy a 

given volume. Conversely, when pressure on a given volume 

of air is decreased, the air expands and occupies a greater 

space. That is, the original column of air at a lower pressure 

Outside air temperature (OAT) 

Density altitude (feet) 

15,000 

14,000 

13,000 

12,000 

11,000 

10,000 

9,000 

8,000 

7,000 

6,000 

5,000 

4,000 

3,000 

2,000 

1,000 

Sea level 

14,000

13,000 

12,000

11,000 

10,000 

9,000 

Pressure altitude (feet)

8,000

7,000 

6,000 

5,000 

4,000 

3,000 

2,000 

1,000 

-1,000

Sea level

-2,000 

-20° -10° 0° 10° 20° 30° 40° 

0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100° 

Standard temperature 

C 

F 

Figure 11-4. Density altitude chart. 

11-4 
 

contains a smaller mass of air. In other words, the density is 

decreased. In fact, density is directly proportional to pressure. 

If the pressure is doubled, the density is doubled, and if the 

pressure is lowered, so is the density. This statement is true 

only at a constant temperature. 

Effects of Temperature on Density 

Increasing the temperature of a substance decreases its 

density. Conversely, decreasing the temperature increases 

the density. Thus, the density of air varies inversely with 

temperature. This statement is true only at a constant pressure. 

In the atmosphere, both temperature and pressure decrease 

with altitude and have conflicting effects upon density. 

However, the fairly rapid drop in pressure as altitude is 

increased usually has the dominant effect. Hence, pilots can 

expect the density to decrease with altitude. 

Effects of Humidity (Moisture) on Density 

The preceding paragraphs are based on the presupposition of 

perfectly dry air. In reality, it is never completely dry. The 

small amount of water vapor suspended in the atmosphere 

may be negligible under certain conditions, but in other 

conditions humidity may become an important factor in the 

performance of an aircraft. Water vapor is lighter than air; 

consequently, moist air is lighter than dry air. Therefore, as the 

water content of the air increases, the air becomes less dense, 

increasing density altitude and decreasing performance. It is 

lightest or least dense when, in a given set of conditions, it 

contains the maximum amount of water vapor. 

Humidity, also called relative humidity, refers to the amount 

of water vapor contained in the atmosphere and is expressed 

as a percentage of the maximum amount of water vapor 

the air can hold. This amount varies with the temperature; 

warm air can hold more water vapor, while colder air can 

hold less. Perfectly dry air that contains no water vapor has 

a relative humidity of zero percent, while saturated air that 

cannot hold any more water vapor has a relative humidity 

of 100 percent. Humidity alone is usually not considered an 

essential factor in calculating density altitude and aircraft 

performance; however, it does contribute. 

The higher the temperature, the greater amount of water 

vapor that the air can hold. When comparing two separate air 

masses, the first warm and moist (both qualities making air 

lighter) and the second cold and dry (both qualities making 

it heavier), the first must be less dense than the second. 

Pressure, temperature, and humidity have a great influence 

on aircraft performance because of their effect upon density. 

There is no rule-of-thumb or chart used to compute the effects 

of humidity on density altitude, but it must be taken into 

consideration. Expect a decrease in overall performance in 

high humidity conditions. 

Performance 

Performance is a term used to describe the ability of an 

aircraft to accomplish certain things that make it useful for 

certain purposes. For example, the ability of an aircraft to land 

and take off in a very short distance is an important factor 

to the pilot who operates in and out of short, unimproved 

airfields. The ability to carry heavy loads, fly at high altitudes 

at fast speeds, and/or travel long distances is essential for the 

performance of airline and executive type aircraft. 

The primary factors most affected by performance are the 

takeoff and landing distance, rate of climb, ceiling, payload, 

range, speed, maneuverability, stability, and fuel economy. 

Some of these factors are often directly opposed: for example, 

high speed versus short landing distance, long range versus 

great payload, and high rate of climb versus fuel economy. 

It is the preeminence of one or more of these factors that 

dictates differences between aircraft and explains the high 

degree of specialization found in modern aircraft. 

The various items of aircraft performance result from the 

combination of aircraft and powerplant characteristics. The 

aerodynamic characteristics of the aircraft generally define 

the power and thrust requirements at various conditions of 

flight, while powerplant characteristics generally define the 

power and thrust available at various conditions of flight. 

The matching of the aerodynamic configuration with the 

powerplant is accomplished by the manufacturer to provide 

maximum performance at the specific design condition (e.g., 

range, endurance, and climb). 

Straight-and-Level Flight 

All of the principal components of flight performance involve 

steady-state flight conditions and equilibrium of the aircraft. 

For the aircraft to remain in steady, level flight, equilibrium 

must be obtained by a lift equal to the aircraft weight and a 

powerplant thrust equal to the aircraft drag. Thus, the aircraft 

drag defines the thrust required to maintain steady, level 

flight. As presented in Chapter 4, Aerodynamics of Flight, 

all parts of an aircraft contribute to the drag, either induced 

(from lifting surfaces) or parasite drag. 

While parasite drag predominates at high speed, induced drag 

predominates at low speed. [Figure 11-5] For example, if 

an aircraft in a steady flight condition at 100 knots is then 

accelerated to 200 knots, the parasite drag becomes four 

times as great, but the power required to overcome that 

drag is eight times the original value. Conversely, when the 

11-5 
 

 

 

 

 

 

Drag 

Speed 

Total drag 

Parasite drag 

Stall 

Induced drag 

L/DMAX 

energy comes in two forms: (1) Kinetic Energy (KE), the 

energy of speed; (2) Potential Energy (PE), the stored energy 

of position. 

Aircraft motion (KE) is described by its velocity (airspeed). 

Aircraft position (PE) is described by its height (altitude). 

Both KE and PE are directly proportional to the object’s 

mass. KE is directly proportional to the square of the object’s 

velocity (airspeed). PE is directly proportional to the object’s 

height (altitude). The formulas below summarize these 

energy relationships: 

Figure 11-5. Drag versus speed. 

aircraft is operated in steady, level flight at twice as great a 

speed, the induced drag is one-fourth the original value, and 

the power required to overcome that drag is only one-half 

the original value. 

When an aircraft is in steady, level flight, the condition of 

equilibrium must prevail. The unaccelerated condition of 

flight is achieved with the aircraft trimmed for lift equal 

to weight and the powerplant set for a thrust to equal the 

aircraft drag. 

The maximum level flight speed for the aircraft is obtained 

when the power or thrust required equals the maximum power 

or thrust available from the powerplant. [Figure 11-6] The 

minimum level flight airspeed is not usually defined by thrust 

or power requirement since conditions of stall or stability and 

control problems generally predominate. 

Climb Performance 

If an aircraft is to move, fly, and perform, work must act 

upon it. Work involves force moving the aircraft. The aircraft 

acquires mechanical energy when it moves. Mechanical 

m = object mass KE = 1⁄2 × m × v2 

v = object velocity 

m = object mass 

PE = m × g × h g = gravity field strength 

h = object height 

We sometimes use the terms “power” and “thrust” 

interchangeably when discussing climb performance. This 

erroneously implies the terms are synonymous. It is important 

to distinguish between these terms. Thrust is a force or 

pressure exerted on an object. Thrust is measured in pounds 

(lb) or newtons (N). Power, however, is a measurement of 

the rate of performing work or transferring energy (KE and 

PE). Power is typically measured in horsepower (hp) or 

kilowatts (kw). We can think of power as the motion (KE 

and PE) a force (thrust) creates when exerted on an object 

over a period of time. 

Positive climb performance occurs when an aircraft gains PE 

by increasing altitude. Two basic factors, or a combination 

of the two factors, contribute to positive climb performance 

in most aircraft: 

1.	 The aircraft climbs (gains PE) using excess power 

above that required to maintain level flight, or 

Power required 

Speed 

Low cruise speed 

Min. speed 

High cruise speed 

Maximum available power Maximum level flight speed 

Figure 11-6. Power versus speed. 

2. The aircraft climbs by converting airspeed (KE) to 

altitude (PE). 

As an example of factor 1 above, an aircraft with an engine 

capable of producing 200 horsepower (at a given altitude) 

is using only 130 horsepower to maintain level flight at that 

altitude. This leaves 70 horsepower available to climb. The 

pilot holds airspeed constant and increases power to perform 

the climb. 

As an example of factor 2, an aircraft is flying level at 120 

knots. The pilot leaves the engine power setting constant but 

applies other control inputs to perform a climb. The climb, 

sometimes called a zoom climb, converts the airspeed (KE) 

11-6 
 

 

 

to altitude (PE); the airspeed decreases to something less 

than 120 knots as the altitude increases. 

There are two primary reasons to evaluate climb performance. 

First, aircraft must climb over obstacles to avoid hitting 

them. Second, climbing to higher altitudes can provide 

better weather, fuel economy, and other benefits. Maximum 

Angle of Climb (AOC), obtained at VX, may provide climb 

performance to ensure an aircraft will clear obstacles. 

Maximum Rate of Climb (ROC), obtained at VY, provides 

climb performance to achieve the greatest altitude gain over 

time. Maximum ROC may not be sufficient to avoid obstacles 

in some situations, while maximum AOC may be sufficient 

to avoid the same obstacles. [Figure 11-7] 

Angle of Climb (AOC) 

AOC is a comparison of altitude gained relative to distance 

traveled. AOC is the inclination (angle) of the flight path. For 

maximum AOC performance, a pilot flies the aircraft at VX Altitude 

Distance 

Max AOC

Max ROC 

Figure 11-7. Maximum angle of climb (AOC) versus maximum rate 

of climb (ROC). 

so as to achieve maximum altitude increase with minimum 

horizontal travel over the ground. A good use of maximum 

AOC is when taking off from a short airfield surrounded by 

high obstacles, such as trees or power lines. The objective is 

to gain sufficient altitude to clear the obstacle while traveling 

the least horizontal distance over the surface. 

One method to climb (have positive AOC performance) is 

to have excess thrust available. Essentially, the greater the 

force that pushes the aircraft upward, the steeper it can climb. 

Maximum AOC occurs at the airspeed and angle of attack 

(AOA) combination which allows the maximum excess 

thrust. The airspeed and AOA combination where excess 

thrust exists varies amongst aircraft types. As an example, 

Figure 11-8 provides a comparison between jet and propeller 

airplanes as to where maximum excess thrust (for maximum 

AOC) occurs. In a jet, maximum excess thrust normally 

occurs at the airspeed where the thrust required is at a 

minimum (approximately L/DMAX). In a propeller airplane, 

maximum excess thrust normally occurs at an airspeed below 

L/DMAX and frequently just above stall speed. 

Rate of Climb (ROC) 

ROC is a comparison of altitude gained relative to the time 

needed to reach that altitude. ROC is simply the vertical 

component of the aircraft’s flight path velocity vector. For 

maximum ROC performance, a pilot flies the aircraft at VY 

so as to achieve a maximum gain in altitude over a given 

period of time. 

Maximum ROC expedites a climb to an assigned altitude. 

This gains the greatest vertical distance over a period of 

time. For example, in a maximum AOC profile, a certain 

aircraft takes 30 seconds to reach 1,000 feet AGL, but 

covers only 3,000 feet over the ground. By comparison, 

using its maximum ROC profile, the same aircraft climbs 

Thrust 

Velocity (TAS) 

Thrust 

Velocity (TAS) 

(Full PCL) 

(Full Throttle) 

L/D MAX L/D MAX 

TE 

TE 

TA 

TA 

TR 

TR 

LEGEND 

TE thrust 

excess 

TA thrust 

available 

TR thrust 

required 

AOC angle of 

climb 

TAS true 

airspeed 

L/D MAX lift to drag 

ratio 

maximum 

PCL power 

control lever 

Max AOC (jet) 

Max AOC (prop) 

Figure 11-8. Comparison of maximum AOC between jet and propeller airplanes. 

11-7 
 

 

 

 

 

 

 

 

 

to 1,500 feet in 30 seconds but covers 6,000 feet across the 

ground. Note that both ROC and AOC maximum climb 

profiles use the aircraft’s maximum throttle setting. Any 

differences between max ROC and max AOC lie primarily 

in the velocity (airspeed) and AOA combination the aircraft 

manual specifies. [Figure 11-7] 

ROC performance depends upon excess power. Since 

climbing is work and power is the rate of performing work, 

a pilot can increase the climb rate by using any power not 

used to maintain level flight. Maximum ROC occurs at an 

airspeed and AOA combination that produces the maximum 

excess power. Therefore, maximum ROC for a typical jet 

airplane occurs at an airspeed greater than L/DMAX and at an 

AOA less than L/DMAX AOA. In contrast, maximum ROC for 

a typical propeller airplane occurs at an airspeed and AOA 

combination closer to L/DMAX. [Figure 11-9] 

Climb Performance Factors 

Since weight, altitude and configuration changes affect 

excess thrust and power, they also affect climb performance. 

Climb performance is directly dependent upon the ability to 

produce either excess thrust or excess power. Earlier in the 

book it was shown that an increase in weight, an increase in 

altitude, lowering the landing gear, or lowering the flaps all 

decrease both excess thrust and excess power for all aircraft. 

Therefore, maximum AOC and maximum ROC performance 

decreases under any of these conditions. 

Weight has a very pronounced effect on aircraft performance. 

If weight is added to an aircraft, it must fly at a higher AOA 

to maintain a given altitude and speed. This increases the 

induced drag of the wings, as well as the parasite drag of the 

aircraft. Increased drag means that additional thrust is needed 

to overcome it, which in turn means that less reserve thrust is 

available for climbing. Aircraft designers go to great lengths 

to minimize the weight, since it has such a marked effect on 

the factors pertaining to performance. 

A change in an aircraft’s weight produces a twofold effect 

on climb performance. First, a change in weight changes the 

drag and the power required. This alters the reserve power 

available, which in turn, affects both the climb angle and 

the climb rate. Secondly, an increase in weight reduces the 

maximum ROC, but the aircraft must be operated at a higher 

climb speed to achieve the smaller peak climb rate. 

An increase in altitude also increases the power required 

and decreases the power available. Therefore, the climb 

performance of an aircraft diminishes with altitude. The 

speeds for maximum ROC, maximum AOC, and maximum 

and minimum level flight airspeeds vary with altitude. As 

altitude is increased, these various speeds finally converge 

at the absolute ceiling of the aircraft. At the absolute ceiling, 

there is no excess of power and only one speed allows steady, 

level flight. Consequently, the absolute ceiling of an aircraft 

produces zero ROC. The service ceiling is the altitude at 

which the aircraft is unable to climb at a rate greater than 100 

feet per minute (fpm). Usually, these specific performance 

reference points are provided for the aircraft at a specific 

design configuration. [Figure 11-10] 

The terms “power loading,” “wing loading,” “blade loading,” 

and “disk loading” are commonly used in reference to 

performance. Power loading is expressed in pounds per 

horsepower and is obtained by dividing the total weight 

of the aircraft by the rated horsepower of the engine. It 

is a significant factor in an aircraft’s takeoff and climb 

capabilities. Wing loading is expressed in pounds per square 

foot and is obtained by dividing the total weight of an airplane 

in pounds by the wing area (including ailerons) in square feet. 

It is the airplane’s wing loading that determines the landing 

Power 

LEGEND 

PE power 

excess 

PA power 

available 

PR power 

required 

ROC rate of 

climb 

TAS true 

airspeed 

L/D MAX lift to drag 

ratio 

maximum 

PCL power 

control lever 

Power 

(Full PCL) (Full Throttle) 

L/D 

PE 

A R 

A 

PE 

P

Max ROC (jet) Max ROC (prop) 

P

P P

R 

MAX L/D MAX 

Velocity (TAS) Velocity (TAS) 

Figure 11-9. Comparison of maximum ROC between jet and propeller airplanes. 

11-8 
 

 

 

 

Indicated airspeed (knots) 

Standard altitude (feet)

Service ceiling 

Absolute ceiling 

Best angle 

of climb (Vx) 

Best rate 

of climb (Vy) 

24,000 

22,000 

20,000 

18,000 

16,000 

14,000 

12,000 

10,000 

8,000 

6,000 

4,000 

2,000 

Sea level 

70 80 90 100 110 120 

Figure 11-10. Absolute and service ceiling. 

speed. Blade loading is expressed in pounds per square foot 

and is obtained by dividing the total weight of a helicopter by 

the area of the rotor blades. Blade loading is not to be confused 

with disk loading, which is the total weight of a helicopter 

divided by the area of the disk swept by the rotor blades. 

Range Performance 

The ability of an aircraft to convert fuel energy into flying 

distance is one of the most important items of aircraft 

performance. In flying operations, the problem of efficient 

range operation of an aircraft appears in two general forms: 

1. To extract the maximum flying distance from a given 

fuel load 

2.	 To fly a specified distance with a minimum 

expenditure of fuel 

A common element for each of these operating problems 

is the specific range; that is, nautical miles (NM) of flying 

distance versus the amount of fuel consumed. Range must 

be clearly distinguished from the item of endurance. Range 

involves consideration of flying distance, while endurance 

involves consideration of flying time. Thus, it is appropriate 

to define a separate term, specific endurance. 

flight hours specific endurance = pounds of fuel 

or 

flight hours/hour specific endurance = pounds of fuel/hour 

or 

1 specific endurance = fuel flow 

Fuel flow can be defined in either pounds or gallons. If 

maximum endurance is desired, the flight condition must 

provide a minimum fuel flow. In Figure 11-11 at point A, 

the airspeed is low and fuel flow is high. This would occur 

during ground operations or when taking off and climbing. 

As airspeed is increased, power requirements decrease due 

to aerodynamic factors, and fuel flow decreases to point B. 

This is the point of maximum endurance. Beyond this point, 

increases in airspeed come at a cost. Airspeed increases 

require additional power and fuel flow increases with 

additional power. 

Cruise flight operations for maximum range should be 

conducted so that the aircraft obtains maximum specific range 

throughout the flight. The specific range can be defined by 

the following relationship. 

Fuel flow/power required (HP) 

Speed 

Reference line 

At altitude 

A 

B Maximum range at L/DMAX 

Maximum endurance at 

minimum power required Applicable for a particular

 Weight

 Altitude

 Configuration 

Figure 11-11. Airspeed for maximum endurance. 

11-9 
 

 

 

 

 

 NM specific range = pounds of fuel 

or 

NM/hour specific range = pounds of fuel/hour 

or 

knots specific range = fuel flow 

If maximum specific range is desired, the flight condition 

must provide a maximum of speed per fuel flow. While 

the peak value of specific range would provide maximum 

range operation, long-range cruise operation is generally 

recommended at a slightly higher airspeed. Most long-range 

cruise operations are conducted at the flight condition that 

provides 99 percent of the absolute maximum specific range. 

The advantage of such operation is that one percent of range 

is traded for three to five percent higher cruise speed. Since 

the higher cruise speed has a great number of advantages, the 

small sacrifice of range is a fair bargain. The values of specific 

range versus speed are affected by three principal variables: 

1. Aircraft gross weight

2. Altitude

3. The external aerodynamic configuration of the aircraft. 

These are the source of range and endurance operating data 

included in the performance section of the AFM/POH. 

Cruise control of an aircraft implies that the aircraft is 

operated to maintain the recommended long-range cruise 

condition throughout the flight. Since fuel is consumed during 

cruise, the gross weight of the aircraft varies and optimum 

airspeed, altitude, and power setting can also vary. Cruise 

control means the control of the optimum airspeed, altitude, 

and power setting to maintain the 99 percent maximum 

specific range condition. At the beginning of cruise flight, the 

relatively high initial weight of the aircraft requires specific 

values of airspeed, altitude, and power setting to produce the 

recommended cruise condition. As fuel is consumed and the 

aircraft’s gross weight decreases, the optimum airspeed and 

power setting may decrease, or the optimum altitude may 

increase. In addition, the optimum specific range increases. 

Therefore, the pilot must provide the proper cruise control 

procedure to ensure that optimum conditions are maintained. 

Total range is dependent on both fuel available and specific 

range. When range and economy of operation are the principal 

goals, the pilot must ensure that the aircraft is operated at the 

recommended long-range cruise condition. By this procedure, 

the aircraft is capable of its maximum design-operating radius 

or can achieve flight distances less than the maximum with 

a maximum of fuel reserve at the destination. 

A propeller-driven aircraft combines the propeller with the 

reciprocating engine for propulsive power. Fuel flow is 

determined mainly by the shaft power put into the propeller 

rather than thrust. Thus, the fuel flow can be related directly 

to the power required to maintain the aircraft in steady, level 

flight, and on performance charts power can be substituted 

for fuel flow. This fact allows for the determination of range 

through analysis of power required versus speed. 

The maximum endurance condition would be obtained at the 

point of minimum power required since this would require the 

lowest fuel flow to keep the airplane in steady, level flight. 

Maximum range condition would occur where the ratio of 

speed to power required is greatest. [Figure 11-11] 

The maximum range condition is obtained at maximum lift/ 

drag ratio (L/DMAX), and it is important to note that for a given 

aircraft configuration, the L/DMAX occurs at a particular AOA 

and lift coefficient and is unaffected by weight or altitude. A 

variation in weight alters the values of airspeed and power 

required to obtain the L/DMAX. [Figure 11-12] Different 

theories exist on how to achieve max range when there is a 

headwind or tailwind present. Many say that speeding up in 

a headwind or slowing down in a tail wind helps to achieve 

max range. While this theory may be true in a lot of cases, 

it is not always true as there are different variables to every 

situation. Each aircraft configuration is different, and there 

is not a rule of thumb that encompasses all of them as to how 

to achieve the max range. Power required 

t 

L/

DMAX er weigh

t 

High

ic w

g

ig

h

e

t h

B

w

as

r e

wei Lo

Constant altitude 

Speed 

Figure 11-12. Effect of weight. 

11-10 
 

The variations of speed and power required must be 

monitored by the pilot as part of the cruise control procedure 

to maintain the L/DMAX. When the aircraft’s fuel weight is a 

small part of the gross weight and the aircraft’s range is small, 

the cruise control procedure can be simplified to essentially 

maintaining a constant speed and power setting throughout 

the time of cruise flight. However, a long-range aircraft has a 

fuel weight that is a considerable part of the gross weight, and 

cruise control procedures must employ scheduled airspeed 

and power changes to maintain optimum range conditions. 

The effect of altitude on the range of a propeller-driven 

aircraft is illustrated in Figure 11-13. A flight conducted at 

high altitude has a greater true airspeed (TAS), and the power 

required is proportionately greater than when conducted at 

sea level. The drag of the aircraft at altitude is the same as the 

drag at sea level, but the higher TAS causes a proportionately 

greater power required. 

NOTE: The straight line that is tangent to the sea level power 

curve is also tangent to the altitude power curve. 

The effect of altitude on specific range can also be appreciated 

from the previous relationships. If a change in altitude causes 

identical changes in speed and power required, the proportion 

of speed to power required would be unchanged. The fact 

implies that the specific range of a propeller-driven aircraft 

would be unaffected by altitude. Actually, this is true to the 

extent that specific fuel consumption and propeller efficiency 

are the principal factors that could cause a variation of 

specific range with altitude. If compressibility effects are 

negligible, any variation of specific range with altitude is 

strictly a function of engine/propeller performance. 

An aircraft equipped with a reciprocating engine experiences 

very little, if any, variation of specific range up to its 

absolute altitude. There is negligible variation of brake Power required 

Speed 

L/DMAX 

Constant weight 

Sea level 

At altitude 

Figure 11-13. Effect of altitude on range. 

specific fuel consumption for values of brake horsepower 

below the maximum cruise power rating of the engine that 

is the lean range of engine operation. Thus, an increase in 

altitude produces a decrease in specific range only when the 

increased power requirement exceeds the maximum cruise 

power rating of the engine. One advantage of supercharging 

is that the cruise power may be maintained at high altitude, 

and the aircraft may achieve the range at high altitude with 

the corresponding increase in TAS. The principal differences 

in the high altitude cruise and low altitude cruise are the TAS 

and climb fuel requirements. 

Region of Reversed Command 

The aerodynamic properties of an aircraft generally determine 

the power requirements at various conditions of flight, while 

the powerplant capabilities generally determine the power 

available at various conditions of flight. When an aircraft 

is in steady, level flight, a condition of equilibrium must 

prevail. An unaccelerated condition of flight is achieved 

when lift equals weight, and the powerplant is set for thrust 

equal to drag. The power required to achieve equilibrium in 

constant-altitude flight at various airspeeds is depicted on a 

power required curve. The power required curve illustrates 

the fact that at low airspeeds near the stall or minimum 

controllable airspeed, the power setting required for steady, 

level flight is quite high. 

Flight in the region of normal command means that while 

holding a constant altitude, a higher airspeed requires a higher 

power setting and a lower airspeed requires a lower power 

setting. The majority of aircraft flying (climb, cruise, and 

maneuvers) is conducted in the region of normal command. 

Flight in the region of reversed command means flight in 

which a higher airspeed requires a lower power setting 

and a lower airspeed requires a higher power setting to 

hold altitude. It does not imply that a decrease in power 

produces lower airspeed. The region of reversed command is 

encountered in the low speed phases of flight. Flight speeds 

below the speed for maximum endurance (lowest point 

on the power curve) require higher power settings with a 

decrease in airspeed. Since the need to increase the required 

power setting with decreased speed is contrary to the normal 

command of flight, the regime of flight speeds between the 

speed for minimum required power setting and the stall speed 

(or minimum control speed) is termed the region of reversed 

command. In the region of reversed command, a decrease in 

airspeed must be accompanied by an increased power setting 

in order to maintain steady flight. 

Figure 11-14 shows the maximum power available as a 

curved line. Lower power settings, such as cruise power, 

would also appear in a similar curve. The lowest point on 

11-11 
Power setting 

Speed 

Best endurance speed 

Power required

Region of 

reversed 

command 

Maximum power available 

Excess power 

Figure 11-14. Power required curve. 

the power required curve represents the speed at which the 

lowest brake horsepower sustains level flight. This is termed 

the best endurance airspeed. 

An airplane performing a low airspeed, high pitch attitude 

power approach for a short-field landing is an example 

of operating in the region of reversed command. If an 

unacceptably high sink rate should develop, it may be 

possible for the pilot to reduce or stop the descent by applying 

power. But without further use of power, the airplane would 

probably stall or be incapable of flaring for the landing. 

Merely lowering the nose of the airplane to regain flying 

speed in this situation, without the use of power, would 

result in a rapid sink rate and corresponding loss of altitude. 

If during a soft-field takeoff and climb, for example, the pilot 

attempts to climb out of ground effect without first attaining 

normal climb pitch attitude and airspeed, the airplane may 

inadvertently enter the region of reversed command at a 

dangerously low altitude. Even with full power, the airplane 

may be incapable of climbing or even maintaining altitude. 

The pilot’s only recourse in this situation is to lower the pitch 

attitude in order to increase airspeed, which inevitably results 

in a loss of altitude. 

Airplane pilots must give particular attention to precise 

control of airspeed when operating in the low flight speeds 

of the region of reversed command. 

Takeoff and Landing Performance 

The majority of pilot-caused aircraft accidents occur during 

the takeoff and landing phase of flight. Because of this fact, 

the pilot must be familiar with all the variables that influence 

the takeoff and landing performance of an aircraft and must 

strive for exacting, professional procedures of operation 

during these phases of flight. 

Takeoff and landing performance is a condition of 

accelerated and decelerated motion. For instance, during 

takeoff an aircraft starts at zero speed and accelerates to 

the takeoff speed to become airborne. During landing, the 

aircraft touches down at the landing speed and decelerates 

to zero speed. The important factors of takeoff or landing 

performance are: 

•	 The takeoff or landing speed is generally a function 

of the stall speed or minimum flying speed. 

•	 The rate of acceleration/deceleration during the 

takeoff or landing roll. The speed (acceleration and 

deceleration) experienced by any object varies directly 

with the imbalance of force and inversely with the 

mass of the object. An airplane on the runway moving 

at 75 knots has four times the energy it has traveling 

at 37 knots. Thus, an airplane requires four times as 

much distance to stop as required at half the speed. 

•	 The takeoff or landing roll distance is a function of 

both acceleration/deceleration and speed. 

Runway Surface and Gradient 

Runway conditions affect takeoff and landing performance. 

Typically, performance chart information assumes paved, 

level, smooth, and dry runway surfaces. Since no two 

runways are alike, the runway surface differs from one 

runway to another, as does the runway gradient or slope. 

[Figure 11-15] 

Runway surfaces vary widely from one airport to another. 

The runway surface encountered may be concrete, asphalt, 

gravel, dirt, or grass. The runway surface for a specific 

airport is noted in the Chart Supplement U.S. (formerly 

Airport/Facility Directory). Any surface that is not hard 

and smooth increases the ground roll during takeoff. This 

is due to the inability of the tires to roll smoothly along the 

runway. Tires can sink into soft, grassy, or muddy runways. 

Potholes or other ruts in the pavement can be the cause of 

poor tire movement along the runway. Obstructions such 

as mud, snow, or standing water reduce the airplane’s 

acceleration down the runway. Although muddy and wet 

surface conditions can reduce friction between the runway 

and the tires, they can also act as obstructions and reduce 

the landing distance. [Figure 11-16] Braking effectiveness 

is another consideration when dealing with various runway 

types. The condition of the surface affects the braking ability 

of the aircraft. 

The amount of power that is applied to the brakes without 

skidding the tires is referred to as braking effectiveness. 

Ensure that runways are adequate in length for takeoff 

acceleration and landing deceleration when less than ideal 

surface conditions are being reported. 

11-12 
Figure 11-15. Takeoff distance chart. 

The gradient or slope of the runway is the amount of change 

in runway height over the length of the runway. The gradient 

is expressed as a percentage, such as a 3 percent gradient. This 

means that for every 100 feet of runway length, the runway 

height changes by 3 feet. A positive gradient indicates the 

runway height increases, and a negative gradient indicates the 

runway decreases in height. An upsloping runway impedes 

acceleration and results in a longer ground run during takeoff. 

However, landing on an upsloping runway typically reduces 

the landing roll. A downsloping runway aids in acceleration 

on takeoff resulting in shorter takeoff distances. The opposite 

is true when landing, as landing on a downsloping runway 

increases landing distances. Runway slope information is 

contained in the Chart Supplement U.S. (formerly Airport/ 

Facility Directory). [Figure 11-17] 

Water on the Runway and Dynamic Hydroplaning 

Water on the runways reduces the friction between the tires 

and the ground and can reduce braking effectiveness. The 

ability to brake can be completely lost when the tires are 

hydroplaning because a layer of water separates the tires from 

the runway surface. This is also true of braking effectiveness 

when runways are covered in ice. 

When the runway is wet, the pilot may be confronted with 

dynamic hydroplaning. Dynamic hydroplaning is a condition 

in which the aircraft tires ride on a thin sheet of water rather 

than on the runway’s surface. Because hydroplaning wheels 

are not touching the runway, braking and directional control 

are almost nil. To help minimize dynamic hydroplaning, 

some runways are grooved to help drain off water; most 

runways are not. 

Figure 11-16. An aircraft’s performance during takeoff depends greatly on the runway surface. 

11-13 
 

 

 

 

Airport name 

Runway slope and direction of slope 

Runway surface 

Runway 

Figure 11-17. Chart Supplement U.S. (formerly Airport/Facility Directory) information. 

Tire pressure is a factor in dynamic hydroplaning. Using 

the simple formula in Figure 11-18, a pilot can calculate 

the minimum speed, in knots, at which hydroplaning begins. 

In plain language, the minimum hydroplaning speed is 

determined by multiplying the square root of the main gear 

tire pressure in psi by nine. For example, if the main gear tire 

pressure is at 36 psi, the aircraft would begin hydroplaning 

at 54 knots. 

Landing at higher than recommended touchdown speeds 

exposes the aircraft to a greater potential for hydroplaning. 

And once hydroplaning starts, it can continue well below the 

minimum initial hydroplaning speed. 

On wet runways, directional control can be maximized 

by landing into the wind. Abrupt control inputs should be 

avoided. When the runway is wet, anticipate braking problems 

Figure 11-18. Tire pressure. 

9 x Tire pressure (in psi) 

9 x 6 = 54 knots 

36 = 6 

Minimum dynamic hydroplaning speed (rounded off) = 

well before landing and be prepared for hydroplaning. Opt for 

a suitable runway most aligned with the wind. Mechanical 

braking may be ineffective, so aerodynamic braking should 

be used to its fullest advantage. 

Takeoff Performance 

The minimum takeoff distance is of primary interest in 

the operation of any aircraft because it defines the runway 

requirements. The minimum takeoff distance is obtained by 

taking off at some minimum safe speed that allows sufficient 

margin above stall and provides satisfactory control and 

initial ROC. Generally, the lift-off speed is some fixed 

percentage of the stall speed or minimum control speed for 

the aircraft in the takeoff configuration. As such, the lift-off is 

accomplished at some particular value of lift coefficient and 

AOA. Depending on the aircraft characteristics, the lift-off 

speed is anywhere from 1.05 to 1.25 times the stall speed or 

minimum control speed. 

To obtain minimum takeoff distance at the specific lift-off 

speed, the forces that act on the aircraft must provide the 

maximum acceleration during the takeoff roll. The various 

forces acting on the aircraft may or may not be under the 

control of the pilot, and various procedures may be necessary 

in certain aircraft to maintain takeoff acceleration at the 

highest value. 

The powerplant thrust is the principal force to provide the 

acceleration and, for minimum takeoff distance, the output 

thrust should be at a maximum. Lift and drag are produced 

as soon as the aircraft has speed, and the values of lift and 

drag depend on the AOA and dynamic pressure. 

11-14 
 

 

As discussed in Chapter 6, engine pressure ratio (EPR) is the 

ratio between exhaust pressure (jet blast) and inlet (static) 

pressure on a turbo jet or turbo fan engine. An EPR gauge 

tells the pilot how much power the engines are generating. 

The higher the EPR, the higher the engine thrust. EPR is 

used to avoid over-boosting an engine and to set takeoff and 

go around power if needed. This information is important to 

know before taking off as it helps determine the performance 

of the aircraft. 

In addition to the important factors of proper procedures, 

many other variables affect the takeoff performance of an 

aircraft. Any item that alters the takeoff speed or acceleration 

rate during the takeoff roll affects the takeoff distance. 

For example, the effect of gross weight on takeoff distance 

is significant, and proper consideration of this item must be 

made in predicting the aircraft’s takeoff distance. Increased 

gross weight can be considered to produce a threefold effect 

on takeoff performance: 

1. Higher lift-off speed 

2. Greater mass to accelerate 

3. Increased retarding force (drag and ground friction) 

If the gross weight increases, a greater speed is necessary to 

produce the greater lift necessary to get the aircraft airborne 

at the takeoff lift coefficient. As an example of the effect of 

a change in gross weight, a 21 percent increase in takeoff 

weight requires a 10 percent increase in lift-off speed to 

support the greater weight. 

A change in gross weight changes the net accelerating force 

and changes the mass that is being accelerated. If the aircraft 

has a relatively high thrust-to-weight ratio, the change in the 

net accelerating force is slight and the principal effect on 

acceleration is due to the change in mass. 

For example, a 10 percent increase in takeoff gross weight 

would cause: 

• A 5 percent increase in takeoff velocity 

• At least a 9 percent decrease in rate of acceleration 

• At least a 21 percent increase in takeoff distance 

With ISA conditions, increasing the takeoff weight of the 

average Cessna 182 from 2,400 pounds to 2,700 pounds (11 

percent increase) results in an increased takeoff distance from 

440 feet to 575 feet (23 percent increase). 

For the aircraft with a high thrust-to-weight ratio, the increase 

in takeoff distance might be approximately 21 to 22 percent, 

but for the aircraft with a relatively low thrust-to-weight 

ratio, the increase in takeoff distance would be approximately 

25 to 30 percent. Such a powerful effect requires proper 

consideration of gross weight in predicting takeoff distance. 

The effect of wind on takeoff distance is large, and proper 

consideration must also be provided when predicting takeoff 

distance. The effect of a headwind is to allow the aircraft to 

reach the lift-off speed at a lower groundspeed, while the 

effect of a tailwind is to require the aircraft to achieve a 

greater groundspeed to attain the lift-off speed. 

A headwind that is 10 percent of the takeoff airspeed reduces 

the takeoff distance approximately 19 percent. However, a 

tailwind that is 10 percent of the takeoff airspeed increases 

the takeoff distance approximately 21 percent. In the case 

where the headwind speed is 50 percent of the takeoff speed, 

the takeoff distance would be approximately 25 percent of 

the zero wind takeoff distance (75 percent reduction). 

The effect of wind on landing distance is identical to its 

effect on takeoff distance. Figure 11-19 illustrates the general 

effect of wind by the percent change in takeoff or landing 

distance as a function of the ratio of wind velocity to takeoff 

or landing speed. 

The effect of proper takeoff speed is especially important 

when runway lengths and takeoff distances are critical. The 

takeoff speeds specified in the AFM/POH are generally 

the minimum safe speeds at which the aircraft can become 

airborne. Any attempt to take off below the recommended 

speed means that the aircraft could stall, be difficult to 

control, or have a very low initial ROC. In some cases, an 

Figure 11-19. Effect of wind on takeoff and landing. 

Percent increase 

in takeoff or 

landing distance 

Percent decrease 

in takeoff or 

landing distance 

Ratio of wind 

velocity to takeoff 

or landing speed 

Headwind 

Tailwind 

Reference line

80 

70 

60 

50 

40 

30 

20 

10

 30% 20% 10% 

10% 20% 30% 

10 

20 

30 

40 

50 

60 

Ratio of wind 

velocity to takeoff 

or landing speed 

11-15 
 

 

excessive AOA may not allow the aircraft to climb out of 

ground effect. On the other hand, an excessive airspeed at 

takeoff may improve the initial ROC and “feel” of the aircraft 

but produces an undesirable increase in takeoff distance. 

Assuming that the acceleration is essentially unaffected, the 

takeoff distance varies with the square of the takeoff velocity. 

Thus, ten percent excess airspeed would increase the takeoff 

distance 21 percent. In most critical takeoff conditions, such 

an increase in takeoff distance would be prohibitive, and the 

pilot must adhere to the recommended takeoff speeds. 

The effect of pressure altitude and ambient temperature 

is to define the density altitude and its effect on takeoff 

performance. While subsequent corrections are appropriate 

for the effect of temperature on certain items of powerplant 

performance, density altitude defines specific effects on 

takeoff performance. An increase in density altitude can 

produce a twofold effect on takeoff performance: 

1. Greater takeoff speed 

2. Decreased thrust and reduced net accelerating force 

If an aircraft of given weight and configuration is operated at 

greater heights above standard sea level, the aircraft requires 

the same dynamic pressure to become airborne at the takeoff 

lift coefficient. Thus, the aircraft at altitude takes off at the 

same indicated airspeed (IAS) as at sea level, but because of 

the reduced air density, the TAS is greater. 

The effect of density altitude on powerplant thrust depends 

much on the type of powerplant. An increase in altitude 

above standard sea level brings an immediate decrease in 

power output for the unsupercharged reciprocating engine. 

However, an increase in altitude above standard sea level does 

not cause a decrease in power output for the supercharged 

reciprocating engine until the altitude exceeds the critical 

operating altitude. For those powerplants that experience 

a decay in thrust with an increase in altitude, the effect 

on the net accelerating force and acceleration rate can be 

approximated by assuming a direct variation with density. 

Actually, this assumed variation would closely approximate 

the effect on aircraft with high thrust-to-weight ratios. 

Proper accounting of pressure altitude and temperature is 

mandatory for accurate prediction of takeoff roll distance. 

The most critical conditions of takeoff performance are the 

result of some combination of high gross weight, altitude, 

temperature, and unfavorable wind. In all cases, the pilot 

must make an accurate prediction of takeoff distance from 

the performance data of the AFM/POH, regardless of the 

runway available, and strive for a polished, professional 

takeoff procedure. 

In the prediction of takeoff distance from the AFM/POH 

data, the following primary considerations must be given: 

•	 Pressure altitude and temperature—to define the effect 

of density altitude on distance 

•	 Gross weight—a large effect on distance 

•	 Wind—a large effect due to the wind or wind 

component along the runway 

•	 Runway slope and condition—the effect of an incline 

and retarding effect of factors such as snow or ice 

Landing Performance 

In many cases, the landing distance of an aircraft defines the 

runway requirements for flight operations. The minimum 

landing distance is obtained by landing at some minimum safe 

speed, that allows sufficient margin above stall and provides 

satisfactory control and capability for a go-around. Generally, 

the landing speed is some fixed percentage of the stall speed 

or minimum control speed for the aircraft in the landing 

configuration. As such, the landing is accomplished at some 

particular value of lift coefficient and AOA. The exact values 

depend on the aircraft characteristics but, once defined, the 

values are independent of weight, altitude, and wind. 

To obtain minimum landing distance at the specified landing 

speed, the forces that act on the aircraft must provide 

maximum deceleration during the landing roll. The forces 

acting on the aircraft during the landing roll may require 

various procedures to maintain landing deceleration at the 

peak value. 

A distinction should be made between the procedures for 

minimum landing distance and an ordinary landing roll 

with considerable excess runway available. Minimum 

landing distance is obtained by creating a continuous peak 

deceleration of the aircraft; that is, extensive use of the brakes 

for maximum deceleration. On the other hand, an ordinary 

landing roll with considerable excess runway may allow 

extensive use of aerodynamic drag to minimize wear and tear 

on the tires and brakes. If aerodynamic drag is sufficient to 

cause deceleration, it can be used in deference to the brakes 

in the early stages of the landing roll (i.e., brakes and tires 

suffer from continuous hard use, but aircraft aerodynamic 

drag is free and does not wear out with use). The use of 

aerodynamic drag is applicable only for deceleration to 60 

or 70 percent of the touchdown speed. At speeds less than 

60 to 70 percent of the touchdown speed, aerodynamic drag 

is so slight as to be of little use, and braking must be utilized 

to produce continued deceleration. Since the objective during 

the landing roll is to decelerate, the powerplant thrust should 

be the smallest possible positive value (or largest possible 

negative value in the case of thrust reversers). 

11-16 
 

In addition to the important factors of proper procedures, 

many other variables affect the landing performance. Any 

item that alters the landing speed or deceleration rate during 

the landing roll affects the landing distance. 

The effect of gross weight on landing distance is one of the 

principal items determining the landing distance. One effect 

of an increased gross weight is that a greater speed is required 

to support the aircraft at the landing AOA and lift coefficient. 

For an example of the effect of a change in gross weight, a 

21 percent increase in landing weight requires a ten percent 

increase in landing speed to support the greater weight. 

When minimum landing distances are considered, braking 

friction forces predominate during the landing roll and, for 

the majority of aircraft configurations, braking friction is the 

main source of deceleration. 

The minimum landing distance varies in direct proportion 

to the gross weight. For example, a ten percent increase in 

gross weight at landing would cause a: 

•	 Five percent increase in landing velocity 

•	 Ten percent increase in landing distance 

A contingency of this is the relationship between weight and 

braking friction force. 

The effect of wind on landing distance is large and deserves 

proper consideration when predicting landing distance. Since 

the aircraft lands at a particular airspeed independent of the 

wind, the principal effect of wind on landing distance is 

the change in the groundspeed at which the aircraft touches 

down. The effect of wind on deceleration during the landing 

is identical to the effect on acceleration during the takeoff. 

The effect of pressure altitude and ambient temperature is to 

define density altitude and its effect on landing performance. 

An increase in density altitude increases the landing speed 

but does not alter the net retarding force. Thus, the aircraft 

at altitude lands at the same IAS as at sea level but, because 

of the reduced density, the TAS is greater. Since the aircraft 

lands at altitude with the same weight and dynamic pressure, 

the drag and braking friction throughout the landing roll have 

the same values as at sea level. As long as the condition is 

within the capability of the brakes, the net retarding force 

is unchanged, and the deceleration is the same as with the 

landing at sea level. Since an increase in altitude does not 

alter deceleration, the effect of density altitude on landing 

distance is due to the greater TAS. 

The minimum landing distance at 5,000 feet is 16 percent 

greater than the minimum landing distance at sea level. The 

approximate increase in landing distance with altitude is 

approximately three and one-half percent for each 1,000 feet 

of altitude. Proper accounting of density altitude is necessary 

to accurately predict landing distance. 

The effect of proper landing speed is important when runway 

lengths and landing distances are critical. The landing speeds 

specified in the AFM/POH are generally the minimum safe 

speeds at which the aircraft can be landed. Any attempt to 

land at below the specified speed may mean that the aircraft 

may stall, be difficult to control, or develop high rates of 

descent. On the other hand, an excessive speed at landing may 

improve the controllability slightly (especially in crosswinds) 

but causes an undesirable increase in landing distance. 

A ten percent excess landing speed causes at least a 21 

percent increase in landing distance. The excess speed 

places a greater working load on the brakes because of the 

additional kinetic energy to be dissipated. Also, the additional 

speed causes increased drag and lift in the normal ground 

attitude, and the increased lift reduces the normal force on 

the braking surfaces. The deceleration during this range of 

speed immediately after touchdown may suffer, and it is more 

probable for a tire to be blown out from braking at this point. 

The most critical conditions of landing performance are 

combinations of high gross weight, high density altitude, 

and unfavorable wind. These conditions produce the greatest 

required landing distances and critical levels of energy 

dissipation on the brakes. In all cases, it is necessary to 

make an accurate prediction of minimum landing distance to 

compare with the available runway. A polished, professional 

landing procedure is necessary because the landing phase of 

flight accounts for more pilot-caused aircraft accidents than 

any other single phase of flight. 

In the prediction of minimum landing distance from the 

AFM/POH data, the following considerations must be given: 

•	 Pressure altitude and temperature—to define the effect 

of density altitude 

•	 Gross weight—which defines the CAS for landing 

•	 Wind—a large effect due to wind or wind component 

along the runway 

•	 Runway slope and condition—relatively small 

correction for ordinary values of runway slope, but a 

significant effect of snow, ice, or soft ground 

A tail wind of ten knots increases the landing distance by 

about 21 percent. An increase of landing speed by ten percent 

increases the landing distance by 20 percent. Hydroplaning 

makes braking ineffective until a decrease of speed that can 

be determined by using Figure 11-18. 

11-17 
 

For instance, a pilot is downwind for runway 18, and the 

tower asks if runway 27 could be accepted. There is a light 

rain and the winds are out of the east at ten knots. The pilot 

accepts because he or she is approaching the extended 

centerline of runway 27. The turn is tight and the pilot must 

descend (dive) to get to runway 27. After becoming aligned 

with the runway and at 50 feet AGL, the pilot is already 1,000 

feet down the 3,500 feet runway. The airspeed is still high 

by about ten percent (should be at 70 knots and is at about 

80 knots). The wind of ten knots is blowing from behind. 

First, the airspeed being high by about ten percent (80 knots 

versus 70 knots), as presented in the performance chapter, 

results in a 20 percent increase in the landing distance. 

In performance planning, the pilot determined that at 70 

knots the distance would be 1,600 feet. However, now it 

is increased by 20 percent and the required distance is now 

1,920 feet. 

The newly revised landing distance of 1,920 feet is also 

affected by the wind. In looking at Figure 11-19, the affect 

of the wind is an additional 20 percent for every ten miles 

per hour (mph) in wind. This is computed not on the original 

estimate but on the estimate based upon the increased 

airspeed. Now the landing distance is increased by another 

320 feet for a total requirement of 2,240 feet to land the 

airplane after reaching 50 feet AGL. 

That is the original estimate of 1,600 under planned conditions 

plus the additional 640 feet for excess speed and the tailwind. 

Given the pilot overshot the threshhold by 1,000 feet, the 

total length required is 3,240 on a 3,500 foot runway; 260 

feet to spare. But this is in a perfect environment. Most pilots 

become fearful as the end of the runway is facing them just 

ahead. A typical pilot reaction is to brake—and brake hard. 

Because the aircraft does not have antilock braking features 

like a car, the brakes lock, and the aircraft hydroplanes on 

the wet surface of the runway until decreasing to a speed of 

about 54 knots (the square root of the tire pressure (√36) × 

9). Braking is ineffective when hydroplaning. 

The 260 feet that a pilot might feel is left over has long since 

evaporated as the aircraft hydroplaned the first 300–500 feet 

when the brakes locked. This is an example of a true story, 

but one which only changes from year to year because of new 

participants and aircraft with different N-numbers. 

In this example, the pilot actually made many bad decisions. 

Bad decisions, when combined, have a synergy greater 

than the individual errors. Therefore, the corrective 

actions become larger and larger until correction is almost 

impossible. Aeronautical decision-making is discussed more 

fully in Chapter 2, Aeronautical Decision-Making (ADM). 

Performance Speeds 

True airspeed (TAS)—the speed of the aircraft in relation to 

the air mass in which it is flying. 

Indicated airspeed (IAS)—the speed of the aircraft as 

observed on the ASI. It is the airspeed without correction for 

indicator, position (or installation), or compressibility errors. 

Calibrated airspeed (CAS)—the ASI reading corrected for 

position (or installation) and instrument errors. (CAS is 

equal to TAS at sea level in standard atmosphere.) The color 

coding for various design speeds marked on ASIs may be 

IAS or CAS. 

Equivalent airspeed (EAS)—the ASI reading corrected 

for position (or installation), for instrument error, and for 

adiabatic compressible flow for the particular altitude. (EAS 

is equal to CAS at sea level in standard atmosphere.) 

VS0—the calibrated power-off stalling speed or the minimum 

steady flight speed at which the aircraft is controllable in the 

landing configuration. 

VS1—the calibrated power-off stalling speed or the minimum 

steady flight speed at which the aircraft is controllable in a 

specified configuration. 

VY—the speed at which the aircraft obtains the maximum 

increase in altitude per unit of time. This best ROC speed 

normally decreases slightly with altitude. 

VX—the speed at which the aircraft obtains the highest 

altitude in a given horizontal distance. This best AOC speed 

normally increases slightly with altitude. 

VLE—the maximum speed at which the aircraft can be safely 

flown with the landing gear extended. This is a problem 

involving stability and controllability. 

VLO—the maximum speed at which the landing gear can 

be safely extended or retracted. This is a problem involving 

the air loads imposed on the operating mechanism during 

extension or retraction of the gear. 

VFE—the highest speed permissible with the wing flaps in a 

prescribed extended position. This is because of the air loads 

imposed on the structure of the flaps. 

VA—the calibrated design maneuvering airspeed. This is 

the maximum speed at which the limit load can be imposed 

(either by gusts or full deflection of the control surfaces) 

without causing structural damage. Operating at or below 

11-18 
 

maneuvering speed does not provide structural protection 

against multiple full control inputs in one axis or full control 

inputs in more than one axis at the same time. 

VN0—the maximum speed for normal operation or the 

maximum structural cruising speed. This is the speed at 

which exceeding the limit load factor may cause permanent 

deformation of the aircraft structure. 

VNE—the speed that should never be exceeded. If flight is 

attempted above this speed, structural damage or structural 

failure may result. 

Performance Charts 

Performance charts allow a pilot to predict the takeoff, climb, 

cruise, and landing performance of an aircraft. These charts, 

provided by the manufacturer, are included in the AFM/POH. 

Information the manufacturer provides on these charts has 

been gathered from test flights conducted in a new aircraft, 

under normal operating conditions while using average 

piloting skills, and with the aircraft and engine in good 

working order. Engineers record the flight data and create 

performance charts based on the behavior of the aircraft 

during the test flights. By using these performance charts, 

a pilot can determine the runway length needed to take off 

and land, the amount of fuel to be used during flight, and the 

time required to arrive at the destination. It is important to 

remember that the data from the charts will not be accurate 

if the aircraft is not in good working order or when operating 

under adverse conditions. Always consider the necessity to 

compensate for the performance numbers if the aircraft is not 

in good working order or piloting skills are below average. 

Each aircraft performs differently and, therefore, has different 

performance numbers. Compute the performance of the 

aircraft prior to every flight, as every flight is different. (See 

appendix for examples of performance charts for a Cessna 

Model 172R and Challenger 605.) 

Every chart is based on certain conditions and contains 

notes on how to adapt the information for flight conditions. 

It is important to read every chart and understand how to 

use it. Read the instructions provided by the manufacturer. 

For an explanation on how to use the charts, refer to the 

example provided by the manufacturer for that specific chart. 

[Figure 11-20] 

The information manufacturers furnish is not standardized. 

Information may be contained in a table format and 

other information may be contained in a graph format. 

Sometimes combined graphs incorporate two or more graphs 

into one chart to compensate for multiple conditions of 

flight. Combined graphs allow the pilot to predict aircraft 

performance for variations in density altitude, weight, 

and winds all on one chart. Because of the vast amount of 

information that can be extracted from this type of chart, it 

is important to be very accurate in reading the chart. A small 

error in the beginning can lead to a large error at the end. 

The remainder of this section covers performance information 

for aircraft in general and discusses what information the 

charts contain and how to extract information from the charts 

by direct reading and interpolation methods. Every chart 

contains a wealth of information that should be used when 

flight planning. Examples of the table, graph, and combined 

graph formats for all aspects of flight are discussed. 

, 

, , 

Figure 11-20. Conditions notes chart. 

11-19 
To find the takeoff distance for a pressure altitude of 2,500 feet 

at 20 °C, average the ground roll for 2,000 feet and 3,000 feet. 

1,115 + 1,230 

= 1,173 feet 

2 

ns 

Flaps 10° TAKEOFF DISTANCE 

Full throttle prior to brake release

itio

MAXIMUM WEIGHT 2,400 LB

Cond

Paved level runway 

Zero wind 

Weight 

(lb) Lift AT 

Takeoff 

speed KIAS Press 

ALT 

(ft) 

0 °C 10 °C 20 °C 30 °C 40 °C 

Total feet 

to clear 

Grnd 

roll 

Total feet 

to clear 

Grnd 

roll 

Grnd 

roll 

Total feet 

to clear 

Grnd 

roll 

Total feet 

to clear 

Grnd 

roll 

Total feet 

to clear 

off 50 ft (ft) 50 ft OBS (ft) 50 ft OBS (ft) 50 ft OBS (ft) 50 ft OBS (ft) 50 ft OBS 

2,400 51 56 S.L. 795 1,460 860 1,570 925 1,685 995 1,810 1,065 1,945

1,000 875 1,605 940 1,725 1,015 1,860 1,090 2,000 1,170 2,155

2,000 

3,000 

960 

1,055 

1,770 

1,960 

1,035 

1,140 

1,910 

2,120 

1,115 

1,230 

2,060 

2,295 

1,200 

1,325 

2,220 

2,480 

2,395 

2,685 

1,290 

1,425 

4,000 1,165 2,185 1,260 2,365 1,355 2,570 1,465 2,790 1,575 3,030

5,000 

6,000 

1,285 

1,425 

2,445 

2,755 

1,390 

1,540 

2,660 

3,015 

1,500 

1,665 

2,895 

3,300 

1,620 

1,800 

3,160 

3,620 

3,455 

3,990 

1,745 

1,940 

7,000 1,580 3,140 1,710 3,450 1,850 3,805 2,000 4,220 - - - - - -

8,000 1,755 3,615 1,905 4,015 2,060 4,480 - - - - - ­ - - - - - -

Interpolation 

Not all of the information on the charts is easily extracted. 

Some charts require interpolation to find the information for 

specific flight conditions. Interpolating information means 

that by taking the known information, a pilot can compute 

intermediate information. However, pilots sometimes round 

off values from charts to a more conservative figure. 

Using values that reflect slightly more adverse conditions 

provides a reasonable estimate of performance information 

and gives a slight margin of safety. The following illustration 

is an example of interpolating information from a takeoff 

distance chart. [Figure 11-21] 

Density Altitude Charts 

Use a density altitude chart to figure the density altitude at the 

departing airport. Using Figure 11-22, determine the density 

altitude based on the given information. 

Sample Problem 1 

Airport Elevation...............................................5,883 feet
 

OAT...........................................................................70 °F
 

Altimeter...........................................................30.10 "Hg
 

First, compute the pressure altitude conversion. Find 30.10 

under the altimeter heading. Read across to the second 

column. It reads “–165.” Therefore, it is necessary to subtract 

165 from the airport elevation giving a pressure altitude of 

5,718 feet. Next, locate the outside air temperature on the 

scale along the bottom of the graph. From 70°, draw a line up 

to the 5,718 feet pressure altitude line, which is about twothirds of the way up between the 5,000 and 6,000 foot lines. 

Draw a line straight across to the far left side of the graph 

Figure 11-21. Interpolating charts. 

and read the approximate density altitude. The approximate 

density altitude in thousands of feet is 7,700 feet. 

Takeoff Charts 

Takeoff charts are typically provided in several forms and 

allow a pilot to compute the takeoff distance of the aircraft 

with no flaps or with a specific flap configuration. A pilot can 

also compute distances for a no flap takeoff over a 50 foot 

obstacle scenario, as well as with flaps over a 50 foot obstacle. 

The takeoff distance chart provides for various aircraft 

weights, altitudes, temperatures, winds, and obstacle heights. 

Sample Problem 2 

Pressure Altitude...............................................2,000 feet
 

OAT..........................................................................22 °C
 

Takeoff Weight.............................................2,600 pounds
 

Headwind...............................................................6 knots
 

Obstacle Height.......................................50 foot obstacle
 

Refer to Figure 11-23. This chart is an example of a combined 

takeoff distance graph. It takes into consideration pressure 

altitude, temperature, weight, wind, and obstacles all on one 

chart. First, find the correct temperature on the bottom left 

side of the graph. Follow the line from 22 °C straight up until 

it intersects the 2,000 foot altitude line. From that point, draw 

a line straight across to the first dark reference line. Continue 

to draw the line from the reference point in a diagonal 

direction following the surrounding lines until it intersects 

the corresponding weight line. From the intersection of 2,600 

pounds, draw a line straight across until it reaches the second 

reference line. Once again, follow the lines in a diagonal 

manner until it reaches the six knot headwind mark. Follow 

11-20 
 

Approximate density altitude (thousand feet) 

15 

14 

13 

12 

11 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

S.L. 

C 

F 

14,000

13,000 

12,000

11,000 

10,000 

9,000 

Pressure altitude (feet)

8,000

7,000 

6,000 

5,000 

4,000 

3,000 

2,000 

1,000 

–1,000 

Sea level 

-18 -12° -7° -1° 4° 10° 16° 21° 27° 32° 38° 

0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100° 

Standard temperature 

Altimeter setting

("Hg)

Pressure altitude

conversion factor 

28.0 1,824 

28.1 1,727 

28.2 1,630 

28.3 1,533 

28.4 1,436 

28.5 1,340 

28.6 1,244 

28.7 1,148 

28.8 1,053 

28.9 957 

29.0 863 

29.1 768 

29.2 673 

29.3 579 

29.4 485 

29.5 392 

29.6 298 

29.7 205 

29.8 112 

29.9 20 

29.92 0 

30.0 −73 

30.1 −165 

30.2 −257 

30.3 −348 

30.4 −440 

30.5 −531 

30.6 −622 

30.7 −712 

30.8 −803 Outside air temperature 

Figure 11-22. Density altitude chart. 

straight across to the third reference line and from here, draw 

a line in two directions. First, draw a line straight across to 

figure the ground roll distance. Next, follow the diagonal lines 

again until they reach the corresponding obstacle height. In 

this case, it is a 50 foot obstacle. Therefore, draw the diagonal 

line to the far edge of the chart. This results in a 700 foot 

ground roll distance and a total distance of 1,400 feet over a 

50 foot obstacle. To find the corresponding takeoff speeds 

at lift-off and over the 50 foot obstacle, refer to the table on 

the top of the chart. In this case, the lift-off speed at 2,600 

pounds would be 63 knots and over the 50 foot obstacle 

would be 68 knots. 

Sample Problem 3 

Pressure Altitude...............................................3,000 feet
 

OAT.........................................................................30 °C
 

Takeoff Weight............................................2,400 pounds
 

Headwind............................................................18 knots
 

Refer to Figure 11-24. This chart is an example of a takeoff 

distance table for short-field takeoffs. For this table, first find 

the takeoff weight. Once at 2,400 pounds, begin reading from 

left to right across the table. The takeoff speed is in the second 

column and, in the third column under pressure altitude, find 

the pressure altitude of 3,000 feet. Carefully follow that line 

to the right until it is under the correct temperature column 

of 30 °C. The ground roll total reads 1,325 feet and the total 

required to clear a 50 foot obstacle is 2,480 feet. At this point, 

there is an 18 knot headwind. According to the notes section 

under point number two, decrease the distances by ten percent 

for each 9 knots of headwind. With an 18 knot headwind, it 

is necessary to decrease the distance by 20 percent. Multiply 

1,325 feet by 20 percent (1,325 × .20 = 265), subtract the 

product from the total distance (1,325 – 265 = 1,060). Repeat 

this process for the total distance over a 50 foot obstacle. The 

ground roll distance is 1,060 feet and the total distance over 

a 50 foot obstacle is 1,984 feet. 

Climb and Cruise Charts 

Climb and cruise chart information is based on actual flight 

tests conducted in an aircraft of the same type. This information 

is extremely useful when planning a cross-country flight to 

predict the performance and fuel consumption of the aircraft. 

Manufacturers produce several different charts for climb and 

cruise performance. These charts include everything from 

fuel, time, and distance to climb to best power setting during 

cruise to cruise range performance. 

The first chart to check for climb performance is a fuel, 

time, and distance-to-climb chart. This chart gives the fuel 

amount used during the climb, the time it takes to accomplish 

the climb, and the ground distance that is covered during 

the climb. To use this chart, obtain the information for 

the departing airport and for the cruise altitude. Using 

Figure 11-25, calculate the fuel, time, and distance to climb 

based on the information provided. 

Sample Problem 4 

Departing Airport Pressure Altitude.................6,000 feet
 

Departing Airport OAT............................................25 °C 

Cruise Pressure Altitude..................................10,000 feet 

Cruise OAT..............................................................10 °C 

11-21 
Reference line

Reference line

Reference line

 

 

 

 

TAKEOFF DISTANCE 

MAXIMUM WEIGHT 2,400 LB 

Notes Conditions 

Weight 

(lb) 

2,400 

2,200 

2,000 

Press 

ALT 

(ft) 

S.L. 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

S.L. 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

S.L. 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

795 

875 

960 

1,055 

1,165 

1,285 

1,425 

1,580 

1,755 

650 

710 

780 

855 

945 

1,040 

1,150 

1,270 

1,410 

525 

570 

625 

690 

755 

830 

920 

1,015 

1,125 

Total feet 

to clear 

50 ft OBS 

1,460 

1,605 

1,770 

1,960 

2,185 

2,445 

2,755 

3,140 

3,615 

1,195 

1,310 

1,440 

1,585 

1,750 

1,945 

2,170 

2,440 

2,760

 970 

1,060 

1,160 

1,270 

1,400 

1,545 

1,710 

1,900 

2,125 

860 

940 

1,035 

1,140 

1,260 

1,390 

1,540 

1,710 

1,905 

700 

765 

840 

925 

1,020 

1,125 

1,240 

1,375 

1,525 

565 

615 

675 

740 

815 

900 

990 

1,095 

1,215 

Total feet 

to clear 

50 ft OBS 

1,570 

1,725 

1,910 

2,120 

2,365 

2,660 

3,015 

3,450 

4,015 

1,280 

1,405 

1,545 

1,705 

1,890 

2,105 

2,355 

2,655 

3,015 

1,035 

1,135 

1,240 

1,365 

1,500 

1,660 

1,845 

2,055 

2,305 

995 

1,090 

1,200 

1,325 

1,465 

1,620 

1,800 

2,000 

- - -

805 

885 

975 

1,070 

1,180 

1,305 

1,445 

1,605 

1,785 

650 

710 

780 

860 

945 

2,145 

2,405 

2,715 

1,410 

Total feet 

to clear 

50 ft OBS 

1,810 

2,000 

2,220 

2,480 

2,790 

3,160 

3,620 

4,220 

- - ­

1,470 

1,615 

1,785 

1,975 

2,200 

2,465 

2,775 

3,155 

3,630 

1,185 

1,295 

1,425 

1,570 

1,735 

1,925 

2,145 

2,405 

2,715 

1,065 

1,170 

1,290 

1,425 

1,575 

1,745 

1,940 

- - -

- - -

865

 950 

1,045 

1,150 

1,270 

1,405 

1,555 

1,730 

1,925 

695 

765 

840 

920 

1,015 

1,120 

1,235 

1,370 

1,520 

Total feet 

to clear 

50 ft OBS 

1,945 

2,155 

2,395 

2,685 

3,030 

3,455 

3,990 

- - -

- - -

1,575 

1,735 

1,915 

2,130 

2,375 

2,665 

3,020 

3,450 

4,005 

1,265 

1,385 

1,525 

1,685 

1,865 

2,070 

2,315 

2,605 

2,950 

Lift 

off 

51 

49 

46 

AT 

50 ft 

56 

54 

51 

Takeoff 

speed KIAS 

0 °C 10 °C 20 °C 30 °C 

925 

1,015 

1,115 

1,230 

1,355 

1,500 

1,665 

1,850 

2,060 

750 

825 

905 

995 

1,100 

1,210 

1,340 

1,485 

1,650 

605 

665 

725 

800 

880 

970 

1,070 

1,180 

1,310 

Total feet 

to clear 

50 ft OBS 

1,685 

1,860 

2,060 

2,295 

2,570 

2,895 

3,300 

3,805 

4,480 

1,375 

1,510 

1,660 

1,835 

2,040 

2,275 

2,555 

2,890 

3,305 

1,110 

1,215 

1,330 

1,465 

1,615 

1,790 

1,990 

2,225 

2,500 

40 °C 

Grnd 

roll 

(ft) 

Grnd 

roll 

(ft) 

Grnd 

roll 

(ft) 

Grnd 

roll 

(ft) 

Grnd 

roll 

(ft) 

SHORT FIELD 

Flaps 10° 

Full throttle prior to brake release 

Paved level runway 

Zero wind 

1. Prior to takeoff from fields above 3,000 feet elevation, the mixture should be leaned to give maximum rpm in a full throttle, static runup. 

2. Decrease distances 10% for each 9 knots headwind. For operation with tailwind up to 10 knots, increase distances by 10% for each 2 knots. 

3. For operation on a dry, grass runway, increase distances by 15% of the “ground roll” figure. 

Figure 11-23. Takeoff distance graph. 

C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 2,800 2,600 2,400 2,200 0 10 20 30 0 50 

Outside air temperature Weight Wind component Obstacle 

(pounds) (knots) height (feet) F -40° -20° 0° 20° 40° 60° 80° 100° 120° 

6,000 

5,000 

4,000 

3,000 

2,000 

1,000 

0 

10,000

8,000

6,000

4,000

2,000

S.L.

 Guide lines not

applicable for

Intermediate

Tailwind 

Headwind

Pressure altitude - feet ISA 

Obstacle heights 

Weight 

pounds

 kts MPH 

Takeoff speed 

Lift-off 50 ft

 kts MPH 

2,950 

2,800 

2,600 

2,400 

2,200 

66 

64 

63 

61 

58 

76 

74 

72 

70 

67 

72 

70 

68 

66 

63 

83 

81 

78 

76 

73 

Associated conditions 

Power Full throttle 2,600 rpm 

Mixture Lean to appropriate fuel 

pressure 

Flaps Up 

Landing Retract after positive 

gear climb established 

Cowl Open 

flaps 

Figure 11-24. Takeoff distance short field charts. 

11-22 
Notes Conditions

NORMAL CLIMB

 110 KIAS 

Flaps up 

Gear up 

2,500 rpm 

30 "Hg 

120 PPH fuel flow 

Cowl flaps open 

Standard temperature 

1. Add 16 pounds of fuel for engine start, taxi, and takeoff allowance. 

2. Increase time, fuel, and distance by 10% for each 7 °C above standard 

temperature. 

3. Distances shown are based on zero wind. 

Weight 

(pounds) 

Press 

ALT 

(feet) 

Rate of 

climb 

fpm 

From sea level 

Time 

(minutes) 

Fuel used 

(pounds) 

Distance 

(nautical

miles) 

4,000 S.L. 605 0 0 0 

4,000 570 7 14 13 

8,000 530 14 28 27 

12,000 485 22 44 43 

16,000 430 31 62 63 

20,000 365 41 82 87 

3,700 S.L. 700 0 0 0 

4,000 665 6 12 11 

8,000 625 12 24 23 

12,000 580 19 37 37 

16,000 525 26 52 53 

20,000 460 34 68 72 

S.L. 810 0 0 0 

4,000 775 5 10 9 

3,400 8,000 735 10 21 20 

12,000 690 16 32 31 

16,000 635 22 44 45 

20,000 565 29 57 61 

 

 

20,000 

18,000 

16,000 

14,000 

12,000 

10,000 

8,000 

6,000 

4,000 

2,000 

Sea level 

Pressure ALT - feet 

Fuel - gallons 

Cruise 

Departure 

Associated conditions 

Maximum continuous power* 

3,600 lb gross weight 

Flaps up 

90 KIAS 

No wind 

* 2,700 rpm & 36 in M.P. (3-blade prop) 

2,575 rpm & 36 in M.P. (2-blade prop) 

Time - minutes 

Distance - nautical miles 

-40° -30° -20° -10° 0° 10° 20° 30° 40°C 0 10 20 30 40 50 

Outside air temperature Fuel, time and distance to climb 

Figure 11-25. Fuel, time, and distance climb chart. 

First, find the information for the departing airport. Find the 

OAT for the departing airport along the bottom, left side of the 

graph. Follow the line from 25 °C straight up until it intersects 

the line corresponding to the pressure altitude of 6,000 feet. 

Continue this line straight across until it intersects all three 

lines for fuel, time, and distance. Draw a line straight down 

from the intersection of altitude and fuel, altitude and time, and 

a third line at altitude and distance. It should read three and 

one-half gallons of fuel, 6 minutes of time, and nine NM. Next, 

repeat the steps to find the information for the cruise altitude. 

It should read six gallons of fuel, 10.5 minutes of time, and 

15 NM. Take each set of numbers for fuel, time, and distance 

and subtract them from one another (6.0 – 3.5 = 2.5 gallons of 

fuel). It takes two and one-half gallons of fuel and 4 minutes 

of time to climb to 10,000 feet. During that climb, the distance 

covered is six NM. Remember, according to the notes at the 

top of the chart, these numbers do not take into account wind, 

and it is assumed maximum continuous power is being used. 

The next example is a fuel, time, and distance-to-climb table. 

For this table, use the same basic criteria as for the previous 

chart. However, it is necessary to figure the information in a 

different manner. Refer to Figure 11-26 to work the following 

sample problem. 

Sample Problem 5 

Departing Airport Pressure Altitude..................Sea level
 

Departing Airport OAT............................................22 °C
 

Cruise Pressure Altitude....................................8,000 feet
 

Takeoff Weight.............................................3,400 pounds
 

To begin, find the given weight of 3,400 in the first column of 

the chart. Move across to the pressure altitude column to find 

the sea level altitude numbers. At sea level, the numbers read 

zero. Next, read the line that corresponds with the cruising 

altitude of 8,000 feet. Normally, a pilot would subtract these 

Figure 11-26. Fuel time distance climb. 

11-23 
 

 

two sets of numbers from one another, but given the fact that 

the numbers read zero at sea level, it is known that the time 

to climb from sea level to 8,000 feet is 10 minutes. It is also 

known that 21 pounds of fuel is used and 20 NM is covered 

during the climb. However, the temperature is 22 °C, which is 

7° above the standard temperature of 15 °C. The notes section 

of this chart indicate that the findings must be increased by ten 

percent for each 7° above standard. Multiply the findings by 

ten percent or .10 (10 × .10 = 1, 1 + 10 = 11 minutes). After 

accounting for the additional ten percent, the findings should 

read 11 minutes, 23.1 pounds of fuel, and 22 NM. Notice that 

the fuel is reported in pounds of fuel, not gallons. Aviation 

fuel weighs six pounds per gallon, so 23.1 pounds of fuel is 

equal to 3.85 gallons of fuel (23.1 ÷ 6 = 3.85). 

The next example is a cruise and range performance chart. 

This type of table is designed to give TAS, fuel consumption, 

endurance in hours, and range in miles at specific cruise 

configurations. Use Figure 11-27 to determine the cruise and 

range performance under the given conditions. 

Sample Problem 6 

Pressure Altitude...............................................5,000 feet
 

RPM..................................................................2,400 rpm
 

Fuel Carrying Capacity..................38 gallons, no reserve
 

Find 5,000 feet pressure altitude in the first column on the 

left side of the table. Next, find the correct rpm of 2,400 

in the second column. Follow that line straight across and 

read the TAS of 116 mph and a fuel burn rate of 6.9 gallons 

per hour. As per the example, the aircraft is equipped with 

a fuel carrying capacity of 38 gallons. Under this column, 

read that the endurance in hours is 5.5 hours and the range 

in miles is 635 miles. 

Cruise power setting tables are useful when planning crosscountry flights. The table gives the correct cruise power 

settings, as well as the fuel flow and airspeed performance 

numbers at that altitude and airspeed. 

Sample Problem 7 

Pressure Altitude at Cruise................................6,000 feet 

OAT..................................................36 °F above standard
 

Refer to Figure 11-28 for this sample problem. First, locate 

the pressure altitude of 6,000 feet on the far left side of the 

table. Follow that line across to the far right side of the table 

under the 20 °C (or 36 °F) column. At 6,000 feet, the rpm 

setting of 2,450 will maintain 65 percent continuous power 

at 21.0 "Hg with a fuel flow rate of 11.5 gallons per hour and 

airspeed of 161 knots. 

Figure 11-27. Cruise and range performance. Notes Conditions 

ALT 

2,500 

5,000 

7,500 

10,000 

GAL/ 

Hour 

9.7 

8.6 

7.8 

7.2 

6.7 

6.3 

9.0 

8.1 

7.4 

6.9 

6.5 

6.0 

8.4 

7.7 

7.1 

6.7 

6.2 

7.6 

7.3 

6.9 

6.4 

6.0 

Endr. 

hours 

3.9 

4.4 

4.9 

5.3 

5.7 

6.1 

4.2 

4.7 

5.1 

5.5 

5.9 

6.3 

4.5 

4.9 

5.3 

5.7 

6.1 

5.0 

5.2 

5.5 

5.9 

6.3 

Range

miles 

525 

570 

600 

620 

630 

625 

565 

600 

625 

635 

635 

630 

600 

625 

645 

645 

640 

640 

650 

655 

650 

635 

Endr. 

hours 

4.9 

5.6 

6.2 

6.7 

7.2 

7.7 

5.3 

5.9 

6.4 

6.9 

7.4 

7.9 

5.7 

6.2 

6.7 

7.2 

7.7 

6.3 

6.5 

7.0 

7.5 

8.0 

Range

miles 

660 

720 

760 

780 

795 

790 

710 

760 

790 

805 

805 

795 

755 

790 

810 

820 

810 

810 

820 

830 

825 

800 

% 

BHP 

86 

79 

72 

65 

58 

52 

82 

75 

68 

61 

55 

49 

78 

71 

64 

58 

52 

70 

67 

61 

55 

49 

TAS 

MPH 

134 

129 

123 

117 

111 

103 

134 

128 

122 

116 

108 

100 

133 

127 

121 

113 

105 

129 

125 

118 

110 

100 

38 gal (no reserve) 48 gal RPM (no reserve)

2,700 

2,600 

2,500 

2,400 

2,300 

2,200 

2,700 

2,600 

2,500 

2,400 

2,300 

2,200 

2,700 

2,600 

2,500 

2,400 

2,300 

2,650 

2,600 

2,500 

2,400 

2,300 

Gross weight—2,300 lb. 

Standard conditions 

Zero wind 

Lean mixture 

Maximum cruise is normally limited to 75% power. 

Another type of cruise chart is a best power mixture range 

graph. This graph gives the best range based on power 

setting and altitude. Using Figure 11-29, find the range at 

65 percent power with and without a reserve based on the 

provided conditions. 

Sample Problem 8 

OAT....................................................................Standard
 

Pressure Altitude...............................................5,000 feet
 

First, move up the left side of the graph to 5,000 feet and 

standard temperature. Follow the line straight across the 

graph until it intersects the 65 percent line under both the 

reserve and no reserve categories. Draw a line straight down 

from both intersections to the bottom of the graph. At 65 

percent power with a reserve, the range is approximately 

522 miles. At 65 percent power with no reserve, the range 

should be 581 miles. 

The last cruise chart referenced is a cruise performance graph. 

This graph is designed to tell the TAS performance of the 

airplane depending on the altitude, temperature, and power 

setting. Using Figure 11-30, find the TAS performance based 

on the given information. 

11-24 
 

 

Figure 11-29. Best power mixture range. 

Range (nautical miles) 

(Includes distance to climb and descend) 

14 

12 

10 

8 

6 

4 

2 

S.L. 

-13°

 -9°

 -5°

 -1°

 3°

 7°

 11°

 15° 

450 500 550 600 500 550 600 650 

Pressure ALT (1,000 feet)

Standard Temperature °C

Associated conditions 

Power 75% 

Power 65%

Power 55% 

Power 75% 

Power 65%

Power 55% 

Notes

Range may be reduced 

by up to 7% if wheel 

fairings are not installed 

Notes 

Add 0.6 NM for each 

degree Celsius above 

standard temperature 

and subtract 1 NM for 

each degree Celsius 

below standard 

temperature. 

45 minutes reserve at 55% 

power best economy mixture No reserve 

CRUISE POWER SETTING 

65% MAXIMUM CONTINUOUS POWER (OR FULL THROTTLE) 

2,800 POUNDS 

Press 

ALT 

27 

19 

12 

5 

–2 

–8 

–15 

–22 

–29 

–3 

–7 

–11 

–15 

–19 

–22 

–26 

–30 

–34 

°F °C RPM "HG PSI GPH kts MPH

IOAT TAS Engine

speed 

Man. 

press 

Fuel 

flow per

engine 

S.L. 

2,000 

4,000 

6,000 

8,000 

10,000 

12,000 

14,000 

16,000 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

20.7 

20.4 

20.1 

19.8 

19.5 

19.2 

18.8 

17.4 

16.1 

6.6 

6.6 

6.6 

6.6 

6.6 

6.6 

6.4 

5.8 

5.3 

11.5 

11.5 

11.5 

11.5 

11.5 

11.5 

11.3 

10.5 

9.7 

147 

149 

152 

155 

157 

160 

162 

159 

156 

169 

171 

175 

178 

181 

184 

186 

183 

180 

°F °C RPM "HG PSI GPH kts MPH

IOAT TAS Engine

speed 

Man. 

press 

Fuel 

flow per

engine 

°F °C RPM "HG PSI GPH kts MPH

IOAT TAS Engine

speed 

Man. 

press 

Fuel 

flow per

engine 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

2,450 

6.6 

6.6 

6.6 

6.6 

6.6 

6.6 

6.1 

5.6 

5.1 

6.6 

6.6 

6.6 

6.6 

6.6 

6.5 

5.9 

5.4 

4.9 

11.5 

11.5 

11.5 

11.5 

11.5 

11.5 

10.9 

10.1 

9.4 

11.5 

11.5 

11.5 

11.5 

11.5 

11.4 

10.6 

9.8 

9.1 

63 

55 

48 

41 

36 

28 

21 

14 

7 

17 

13 

9 

5 

2 

–2 

–6 

–10 

–14 

21.2 

21.0 

20.7 

20.4 

20.2 

19.9 

18.8 

17.4 

16.1 

150 

153 

156 

158 

161 

163 

163 

160 

156 

173 

176 

180 

182 

185 

188 

188 

184 

180 

99 

91 

84 

79 

72 

64 

57 

50 

43 

37 

33 

29 

26 

22 

18 

14 

10 

6 

21.8 

21.5 

21.3 

21.0 

20.8 

20.3 

18.8 

17.4 

16.1 

153 

156 

159 

161 

164 

166 

163 

160 

155 

176 

180 

183 

185 

189 

191 

188 

184 

178 

ISA –20° (–36 °F) Standard day (ISA) ISA +20° (+36 °F) 

1. Full throttle manifold pressure settings are approximate. 

2. Shaded area represents operation with full throttle.

Notes 

Figure 11-28. Cruise power setting. 

Sample Problem 9 

OAT.........................................................................16 °C
 

Pressure Altitude...............................................6,000 feet
 

Power Setting................................65 percent, best power
 

Wheel Fairings..............................................Not installed
 

Begin by finding the correct OAT on the bottom left side of 

the graph. Move up that line until it intersects the pressure 

altitude of 6,000 feet. Draw a line straight across to the 

Mixture Leaned per section 4 

Weight 2,300 lb. 

Wings No 

Fuel 48 gal usable 

Wheel Fairings installed 

Cruise Mid cruise 

65 percent, best power line. This is the solid line, that 

represents best economy. Draw a line straight down from 

this intersection to the bottom of the graph. The TAS at 65 

percent best power is 140 knots. However, it is necessary 

to subtract 8 knots from the speed since there are no wheel 

fairings. This note is listed under the title and conditions. 

The TAS is 132 knots. 

Crosswind and Headwind Component Chart 

Every aircraft is tested according to Federal Aviation 

Administration (FAA) regulations prior to certification. The 

aircraft is tested by a pilot with average piloting skills in 

90° crosswinds with a velocity up to 0.2 VS0 or two-tenths 

of the aircraft’s stalling speed with power off, gear down, 

and flaps down. This means that if the stalling speed of the 

aircraft is 45 knots, it must be capable of landing in a 9-knot, 

90° crosswind. The maximum demonstrated crosswind 

component is published in the AFM/POH. The crosswind and 

headwind component chart allows for figuring the headwind 

and crosswind component for any given wind direction and 

velocity. 

Sample Problem 10 

Runway..........................................................................17
 

Wind........................................................140° at 25 knots
 

Refer to Figure 11-31 to solve this problem. First, determine 

how many degrees difference there is between the runway 

and the wind direction. It is known that runway 17 means 

a direction of 170°; from that subtract the wind direction 

of 140°. This gives a 30° angular difference or wind angle. 

Next, locate the 30° mark and draw a line from there until 

it intersects the correct wind velocity of 25 knots. From 

11-25 
 

 

 

 

 

 

 

20,000

18,000

16,000

14,000

12,000

10,000

8,000

6,000

4,000

2,000 

Sea level 

–40° –30° –20° –10° 0° 10° 20° 30° 40° 100 120 140 160 180 200 

Outside air temperature (°C) True airspeed (knots) 

Pressure ALT (feet) 

Associated conditions 

Weight 3,600 lb. gross weight 

Flaps Up 

Best power Mixture leaned to 100° 

rich of peak EGT 

Best economy Mixture leaned to peak EGT 

1,650° Max allowable EGT 

Wheel Fairings installed 

Power 55%Power 65%

Power 75% 

Notes

Subtract 8 knots if wheel 

fairings are not installed. 

Best power 

Best economy 

Standard temperature 

2,575 rpm at

36 IN. M.P. – 2-blade prop 

2,700 rpm at 36 IN. M.P. – 3-blade prop 

Figure 11-30. Cruise performance graph. 

there, draw a line straight down and a line straight across. 

The headwind component is 22 knots and the crosswind 

component is 13 knots. This information is important when 

taking off and landing so that, first of all, the appropriate 

runway can be picked if more than one exists at a particular 

airport, but also so that the aircraft is not pushed beyond its 

tested limits. 

Landing Charts 

Landing performance is affected by variables similar to those 

affecting takeoff performance. It is necessary to compensate 

for differences in density altitude, weight of the airplane, and 

headwinds. Like takeoff performance charts, landing distance 

information is available as normal landing information, 

as well as landing distance over a 50 foot obstacle. As 

Figure 10-31. Crosswind component chart. 

Crosswind component 

Headwind component 

70 

60 

50 

40 

30 

20 

10 

10 20 30 40 50 60 70 0 

Wind velocity 

10° 0° 

20° 

30° 

40° 

50° 

60° 

70° 

80° 

90° 

usual, read the associated conditions and notes in order to 

ascertain the basis of the chart information. Remember, when 

calculating landing distance that the landing weight is not the 

same as the takeoff weight. The weight must be recalculated 

to compensate for the fuel that was used during the flight. 

Sample Problem 11 

Pressure Altitude...............................................1,250 feet
 

Temperature.........................................................Standard
 

Refer to Figure 10-32. This example makes use of a landing 

distance table. Notice that the altitude of 1,250 feet is not 

on this table. It is, therefore, necessary to interpolate to find 

the correct landing distance. The pressure altitude of 1,250 

is halfway between sea level and 2,500 feet. First, find the 

column for sea level and the column for 2,500 feet. Take the 

total distance of 1,075 for sea level and the total distance of 

1,135 for 2,500 and add them together. Divide the total by 

two to obtain the distance for 1,250 feet. The distance is 1,105 

feet total landing distance to clear a 50 foot obstacle. Repeat 

this process to obtain the ground roll distance for the pressure 

altitude. The ground roll should be 457.5 feet. 

Sample Problem 12 

OAT.......................................................................... 57 °F
 

Pressure Altitude.............................................. 4,000 feet
 

Landing Weight...........................................2,400 pounds
 

Headwind.............................................................. 6 knots
 

Obstacle Height..................................................... 50 feet
 

Using the given conditions and Figure 11-33, determine the 

landing distance for the aircraft. This graph is an example of 

11-26 
Reference line

Reference line

Reference line

 

 

 Note 

LANDING DISTANCE

Conditions 

Gross 

weight 

lb Ground roll Total to clear 

50 ft OBS 

Approach speed

IAS, MPH 

At sea level & 59 °F 

Flaps lowered to 40° 

Power off 

Hard surface runway 

Zero wind 

1,600 60 445 1,075 470 1,135 495 1,195 520 1,255 

Ground roll Total to clear 

50 ft OBS 

At 2,500 ft & 50 °F 

Ground roll Total to clear 

50 ft OBS 

At 5,000 ft & 41 °F 

Ground roll Total to clear 

50 ft OBS 

At 7,500 ft & 32 °F 

1. Decrease the distances shown by 10% for each 4 knots of headwind. 

2. Increase the distance by 10% for each 60 °F temperature increase above standard. 

3. For operation on a dry, grass runway, increase distances (both “ground roll” and “total to clear 50 ft obstacle”) by 20% of the “total to clear 50 ft obstacle” figure. 

Figure 11-32. Landing distance table. 

a combined landing distance graph and allows compensation 

for temperature, weight, headwinds, tailwinds, and varying 

obstacle height. Begin by finding the correct OAT on the 

scale on the left side of the chart. Move up in a straight 

line to the correct pressure altitude of 4,000 feet. From this 

intersection, move straight across to the first dark reference 

line. Follow the lines in the same diagonal fashion until the 

correct landing weight is reached. At 2,400 pounds, continue 

in a straight line across to the second dark reference line. 

Once again, draw a line in a diagonal manner to the correct 

wind component and then straight across to the third dark 

reference line. From this point, draw a line in two separate 

directions: one straight across to figure the ground roll and 

one in a diagonal manner to the correct obstacle height. This 

should be 975 feet for the total ground roll and 1,500 feet for 

the total distance over a 50 foot obstacle. 

Stall Speed Performance Charts 

Stall speed performance charts are designed to give an 

understanding of the speed at which the aircraft stalls in 

a given configuration. This type of chart typically takes 

into account the angle of bank, the position of the gear and 

flaps, and the throttle position. Use Figure 11-34 and the 

accompanying conditions to find the speed at which the 

airplane stalls. 

Sample Problem 13 

Power........................................................................ OFF
 

Flaps....................................................................... Down
 

Gear........................................................................ Down
 

Angle of Bank............................................................. 45° 

First, locate the correct flap and gear configuration. The 

bottom half of the chart should be used since the gear and 

C –40° –30° –20° –10° 0° 10° 20° 30° 40° 50° 2,800 2,600 2,400 2,200 0 10 20 30 0 50 

Outside air temperature Weight Wind component Obstacle 

(pounds) (knots) height (feet) F –40° –20° 0° 20° 40° 60° 80° 100° 120° 

3,500 

3,000 

2,500 

2,000 

1,500 

1,000 

500

 Guide lines not applicable for Intermediate 

Tailwind 

Pressure altitude (feet) 

Headwind

Obstacle heights

Weight 

(pounds) kts MPH 

Speed 

at 50 feet 

2,950 

2,800 

2,600 

2,400 

2,200 

70 

68 

65 

63 

60 

80 

78 

75 

72 

69 

Associated conditions 

Power Retarded to maintain 

900 feet/on final approach 

Flaps Down 

Landing gear Down 

Runway Paved, level, dry surface 

Approach speed IAS as tabulated 

Braking Maximum 

10,000

8,000

6,000

2,000

4,000

S.L. 

ISA 

Figure 11-33. Landing distance graph.

11-27 
Gross weight 

2,750 lb Level 

Angle of bank 

Gear and flaps up 

30° 45° 60° 

Power

On MPH 62 67 74 88

knots 54 58 64 76

Off MPH 75 81 89 106

knots 65 70 77 92

Gear and flaps down 

Power

On MPH 54 58 64 76 

knots 47 50 56 66

Off MPH 66 71 78 93

knots 57 62 68 81

Figure 11-34. Stall speed table. 

flaps are down. Next, choose the row corresponding to a 

power-off situation. Now, find the correct angle of bank 

column, which is 45°. The stall speed is 78 mph, and the 

stall speed in knots would be 68 knots. 

Performance charts provide valuable information to the pilot. 

By using these charts, a pilot can predict the performance of 

the aircraft under most flying conditions, providing a better 

plan for every flight. The Code of Federal Regulations (CFR) 

requires that a pilot be familiar with all information available 

prior to any flight. Pilots should use the information to their 

advantage as it can only contribute to safety in flight. 

Transport Category Aircraft Performance 

Transport category aircraft are certificated under Title 14 

of the CFR (14 CFR) part 25. For additional information 

concerning transport category airplanes, consult the Airplane 

Flying Handbook, FAA-H-8083-3 (as revised). 

Transport category helicopters are certificated under 14 

CFR part 29. 

Air Carrier Obstacle Clearance 

Requirements 

For information on air carrier obstacle clearance 

requirements consult the Instrument Procedures Handbook, 

FAA-H-8083-16 (as revised). 

Chapter Summary 

Performance characteristics and capabilities vary greatly 

among aircraft. As transport aircraft become more capable 

and more complex, most operators find themselves having 

to rely increasingly on computerized flight mission planning 

systems. These systems may be on board or used during 

the planning phase of the flight. Moreover, aircraft weight, 

atmospheric conditions, and external environmental factors 

can significantly affect aircraft performance. It is essential 

that a pilot become intimately familiar with the mission 

planning programs, performance characteristics, and 

capabilities of the aircraft being flown, as well as all of the 

onboard computerized systems in today’s complex aircraft. 

The primary source of this information is the AFM/POH. 

11-28 
 

12-1 

Weather Theory 

Chapter 12 

Introduction 

Weather is an important factor that influences aircraft 

performance and flying safety. It is the state of the atmosphere 

at a given time and place with respect to variables, such as 

temperature (heat or cold), moisture (wetness or dryness), 

wind velocity (calm or storm), visibility (clearness or 

cloudiness), and barometric pressure (high or low). The 

term “weather” can also apply to adverse or destructive 

atmospheric conditions, such as high winds. 

This chapter explains basic weather theory and offers pilots 

background knowledge of weather principles. It is designed 

to help them gain a good understanding of how weather 

affects daily flying activities. Understanding the theories 

behind weather helps a pilot make sound weather decisions 

based on the reports and forecasts obtained from a Flight 

Service Station (FSS) weather specialist and other aviation 

weather services. 

Be it a local flight or a long cross-country flight, decisions 

based on weather can dramatically affect the safety of the flight. 
21%

778%NNiittrrooggeenn 

OOxxyyggeenn 

1% 

T

S

roposphere 

tratosphere 

Mesosphere 

Thermosphere 

280,000 feet 

160,000 feet 

20,000 feet 

Atmosphere 

The atmosphere is a blanket of air made up of a mixture of 

gases that surrounds the Earth and reaches almost 350 miles 

from the surface of the Earth. This mixture is in constant 

motion. If the atmosphere were visible, it might look like 

an ocean with swirls and eddies, rising and falling air, and 

waves that travel for great distances. 

Life on Earth is supported by the atmosphere, solar energy, 

and the planet’s magnetic fields. The atmosphere absorbs 

energy from the sun, recycles water and other chemicals, and 

works with the electrical and magnetic forces to provide a 

moderate climate. The atmosphere also protects life on Earth 

from high energy radiation and the frigid vacuum of space. 

Composition of the Atmosphere 

In any given volume of air, nitrogen accounts for 78 percent 

of the gases that comprise the atmosphere, while oxygen 

makes up 21 percent. Argon, carbon dioxide, and traces 

of other gases make up the remaining one percent. This 

volume of air also contains some water vapor, varying from 

zero to about five percent by volume. This small amount of 

water vapor is responsible for major changes in the weather. 

[Figure 12-1] 

The envelope of gases surrounding the Earth changes 

from the ground up. Four distinct layers or spheres of the 

Figure 12-1. Composition of the atmosphere. 

atmosphere have been identified using thermal characteristics 

(temperature changes), chemical composition, movement, 

and density. [Figure 12-2] 

The first layer, known as the troposphere, extends from 6 

to 20 kilometers (km) (4 to 12 miles) over the northern and 

southern poles and up to 48,000 feet (14.5 km) over the 

equatorial regions. The vast majority of weather, clouds, 

storms, and temperature variances occur within this first 

layer of the atmosphere. Inside the troposphere, the average 

temperature decreases at a rate of about 2 °Celsius (C) every 

Figure 12-2. Layers of the atmosphere. 

12-2 
 

 

 

1,000 feet of altitude gain, and the pressure decreases at a rate 

of about one inch per 1,000 feet of altitude gain. 

At the top of the troposphere is a boundary known as the 

tropopause, which traps moisture and the associated weather 

in the troposphere. The altitude of the tropopause varies with 

latitude and with the season of the year; therefore, it takes 

on an elliptical shape as opposed to round. Location of the 

tropopause is important because it is commonly associated with 

the location of the jet stream and possible clear air turbulence. 

Above the tropopause are three more atmospheric levels. The 

first is the stratosphere, which extends from the tropopause to 

a height of about 160,000 feet (50 km). Little weather exists 

in this layer and the air remains stable, although certain types 

of clouds occasionally extend in it. Above the stratosphere 

are the mesosphere and thermosphere, which have little 

influence over weather. 

Atmospheric Circulation 

As noted earlier, the atmosphere is in constant motion. 

Certain factors combine to set the atmosphere in motion, but a 

major factor is the uneven heating of the Earth’s surface. This 

heating upsets the equilibrium of the atmosphere, creating 

changes in air movement and atmospheric pressure. The 

movement of air around the surface of the Earth is called 

atmospheric circulation. 

Heating of the Earth’s surface is accomplished by several 

processes, but in the simple convection-only model used for 

this discussion, the Earth is warmed by energy radiating from 

the sun. The process causes a circular motion that results 

when warm air rises and is replaced by cooler air. 

Warm air rises because heat causes air molecules to spread 

apart. As the air expands, it becomes less dense and lighter 

than the surrounding air. As air cools, the molecules pack 

together more closely, becoming denser and heavier than 

warm air. As a result, cool, heavy air tends to sink and replace 

warmer, rising air. 

Because the Earth has a curved surface that rotates on a tilted 

axis while orbiting the sun, the equatorial regions of the Earth 

receive a greater amount of heat from the sun than the polar 

regions. The amount of solar energy that heats the Earth 

depends on the time of year and the latitude of the specific 

region. All of these factors affect the length of time and the 

angle at which sunlight strikes the surface. 

Solar heating causes higher temperatures in equatorial areas, 

which causes the air to be less dense and rise. As the warm 

air flows toward the poles, it cools, becoming denser and 

sinks back toward the surface. [Figure 12-3] 

Figure 12-3. Circulation pattern in a static environment. 

Atmospheric Pressure 

The unequal heating of the Earth’s surface not only modifies 

air density and creates circulation patterns; it also causes 

changes in air pressure or the force exerted by the weight 

of air molecules. Although air molecules are invisible, they 

still have weight and take up space. 

Imagine a sealed column of air that has a footprint of one 

square inch and is 350 miles high. It would take 14.7 pounds 

of effort to lift that column. This represents the air’s weight; 

if the column is shortened, the pressure exerted at the bottom 

(and its weight) would be less. 

The weight of the shortened column of air at 18,000 feet is 

approximately 7.4 pounds; almost 50 percent that at sea level. 

For instance, if a bathroom scale (calibrated for sea level) 

were raised to 18,000 feet, the column of air weighing 14.7 

pounds at sea level would be 18,000 feet shorter and would 

weigh approximately 7.3 pounds (50 percent) less than at 

sea level. [Figure 12-4] 

The actual pressure at a given place and time differs with 

altitude, temperature, and density of the air. These conditions 

also affect aircraft performance, especially with regard to 

takeoff, rate of climb, and landings. 

Coriolis Force 

In general atmospheric circulation theory, areas of low 

pressure exist over the equatorial regions and areas of high 

pressure exist over the polar regions due to a difference in 

temperature. The resulting low pressure allows the highpressure air at the poles to flow along the planet’s surface 

toward the equator. While this pattern of air circulation is 

12-3 
18,000 feet

14.7 lb 

1

7.4

18,000 feetlb 

1

Sea level 

 1 Square Inch

1 Square Inch

1 Square Inch

1 Square Inch

Figure 12-4. Atmosphere weights. 

correct in theory, the circulation of air is modified by several 

forces, the most important of which is the rotation of the Earth. 

The force created by the rotation of the Earth is known as 

the Coriolis force. This force is not perceptible to humans as 

they walk around because humans move slowly and travel 

relatively short distances compared to the size and rotation 

rate of the Earth. However, the Coriolis force significantly 

affects motion over large distances, such as an air mass or 

body of water. 

The Coriolis force deflects air to the right in the Northern 

Hemisphere, causing it to follow a curved path instead of a 

straight line. The amount of deflection differs depending on 

the latitude. It is greatest at the poles and diminishes to zero 

at the equator. The magnitude of Coriolis force also differs 

with the speed of the moving body—the greater the speed, 

the greater the deviation. In the Northern Hemisphere, the 

rotation of the Earth deflects moving air to the right and 

changes the general circulation pattern of the air. 

The Coriolis force causes the general flow to break up into 

three distinct cells in each hemisphere. [Figure 12-5] In 

the Northern Hemisphere, the warm air at the equator rises 

upward from the surface, travels northward, and is deflected 

eastward by the rotation of the Earth. By the time it has 

traveled one-third of the distance from the equator to the 

North Pole, it is no longer moving northward, but eastward. 

This air cools and sinks in a belt-like area at about 30° 

latitude, creating an area of high pressure as it sinks toward 

Figure 12-5. Three-cell circulation pattern due to the rotation of 

the Earth. 

the surface. Then, it flows southward along the surface back 

toward the equator. Coriolis force bends the flow to the right, 

thus creating the northeasterly trade winds that prevail from 

30° latitude to the equator. Similar forces create circulation 

cells that encircle the Earth between 30° and 60° latitude and 

between 60° and the poles. This circulation pattern results in 

the prevailing upper level westerly winds in the conterminous 

United States. 

Circulation patterns are further complicated by seasonal 

changes, differences between the surfaces of continents and 

oceans, and other factors such as frictional forces caused 

by the topography of the Earth’s surface that modify the 

movement of the air in the atmosphere. For example, within 

2,000 feet of the ground, the friction between the surface and 

the atmosphere slows the moving air. The wind is diverted 

from its path because of the frictional force. Thus, the wind 

direction at the surface varies somewhat from the wind 

direction just a few thousand feet above the Earth. 

Measurement of Atmosphere Pressure 

Atmospheric pressure historically was measured in inches of 

mercury ("Hg) by a mercurial barometer. [Figure 12-6] The 

barometer measures the height of a column of mercury inside a 

glass tube. A section of the mercury is exposed to the pressure 

of the atmosphere, which exerts a force on the mercury. An 

increase in pressure forces the mercury to rise inside the tube. 

When the pressure drops, mercury drains out of the tube 

decreasing the height of the column. This type of barometer is 

typically used in a laboratory or weather observation station, 

is not easily transported, and difficult to read. 

12-4 
29.92 "Hg = 1,013.2 mb (hPa) = 14.7 lb/in2 

Sea level 

29.92" (760 mm)

Height of mercury

Atmospheric pressure

At sea level in a standard 

atmosphere, the weight 

of the atmosphere 

(14.7 lb/in2) supports 

a column of mercury 

29.92 inches high. 

Figure 12-6. Although mercurial barometers are no longer used 

in the U. S., they are still a good historical reference for where the 

altimeter setting came from (inches of mercury). 

An aneroid barometer is the standard instrument used 

to measure pressure; it is easier to read and transport. 

[Figure 12-7] The aneroid barometer contains a closed vessel 

called an aneroid cell that contracts or expands with changes 

in pressure. The aneroid cell attaches to a pressure indicator 

with a mechanical linkage to provide pressure readings. The 

pressure sensing part of an aircraft altimeter is essentially 

an aneroid barometer. It is important to note that due to 

Lower 

Higher 

Atmospheric pressure 

Sealed aneroid cell Sealed aneroid cell Sealed aneroid cell 

Figure 12-7. Aneroid barometer. 

the linkage mechanism of an aneroid barometer, it is not as 

accurate as a mercurial barometer. 

To provide a common reference, the International Standard 

Atmosphere (ISA) has been established. These standard 

conditions are the basis for certain flight instruments and 

most aircraft performance data. Standard sea level pressure 

is defined as 29.92 "Hg and a standard temperature of 59 °F 

(15 °C). Atmospheric pressure is also reported in millibars 

(mb), with 1 "Hg equal to approximately 34 mb. Standard sea 

level pressure is 1,013.2 mb. Typical mb pressure readings 

range from 950.0 to 1,040.0 mb. Surface charts, high and low 

pressure centers, and hurricane data are reported using mb. 

Since weather stations are located around the globe, all local 

barometric pressure readings are converted to a sea level 

pressure to provide a standard for records and reports. To 

achieve this, each station converts its barometric pressure by 

adding approximately 1 "Hg for every 1,000 feet of elevation. 

For example, a station at 5,000 feet above sea level, with a 

reading of 24.92 "Hg, reports a sea level pressure reading of 

29.92 "Hg. [Figure 12-8] Using common sea level pressure 

readings helps ensure aircraft altimeters are set correctly, 

based on the current pressure readings. 

By tracking barometric pressure trends across a large area, 

weather forecasters can more accurately predict movement 

of pressure systems and the associated weather. For example, 

tracking a pattern of rising pressure at a single weather station 

generally indicates the approach of fair weather. Conversely, 

decreasing or rapidly falling pressure usually indicates 

approaching bad weather and, possibly, severe storms. 

Altitude and Atmospheric Pressure 

As altitude increases, atmospheric pressure decreases. On 

average, with every 1,000 feet of increase in altitude, the 

atmospheric pressure decreases 1 "Hg. As pressure decreases, 

the air becomes less dense or thinner. This is the equivalent of 

being at a higher altitude and is referred to as density altitude. 

As pressure decreases, density altitude increases and has a 

pronounced effect on aircraft performance. 

Differences in air density caused by changes in temperature 

result in a change in pressure. This, in turn, creates motion in 

the atmosphere, both vertically and horizontally, in the form 

of currents and wind. The atmosphere is almost constantly in 

motion as it strives to reach equilibrium. These never-ending 

air movements set up chain reactions that cause a continuing 

variety in the weather. 

12-5 
Standard Atmosphere 

Denver 29.92 "Hg 

24.92 "Hg 

Station Pressure 

Denver 

29.92 "Hg 

Station Pressure 

New Orleans 

New Orleans 29.92 "Hg 

Figure 12-8. Station pressure is converted to and reported in sea level pressure. 

Altitude and Flight	 is longer. An aircraft that requires 745 feet of ground run at 

sea level requires more than double that at a pressure altitude Altitude affects every aspect of flight from aircraft of 8,000 feet. [Figure 12-9]. It is also true that at higher performance to human performance. At higher altitudes, altitudes, due to the decreased density of the air, aircraft with a decreased atmospheric pressure, takeoff and landing engines and propellers are less efficient. This leads to reduced distances are increased, while climb rates decrease. rates of climb and a greater ground run for obstacle clearance. 

When an aircraft takes off, lift is created by the flow of air Altitude and the Human Body around the wings. If the air is thin, more speed is required 

to obtain enough lift for takeoff; therefore, the ground run As discussed earlier, nitrogen and other trace gases make 

up 79 percent of the atmosphere, while the remaining 21 

1,590 feet 

745 feet 

Pressure Altitude: Sea level 

Pressure Altitude: 8,000 feet 

TAKEOFF DISTANCE 

MAXIMUM WEIGHT 2,400 LB 

Pressure 

altitude 

(feet) 

S.L. 

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

7,000 

8,000 

Ground 

roll 

(feet)

 745

 815

 895

 980 

1,075 

1,185 

1,305 

1,440 

1,590 

Total feet 

to clear 

50 foot obstacle 

1,320 

1,445 

1,585 

1,740 

1,920 

2,125 

2,360 

2,635 

2,960 

0 °C 

Figure 12-9. Takeoff distances increase with increased altitude. 

12-6 
 

percent is life sustaining atmospheric oxygen. At sea level, 

atmospheric pressure is great enough to support normal 

growth, activity, and life. By 18,000 feet, the partial pressure 

of oxygen is reduced and adversely affects the normal 

activities and functions of the human body. 

The reactions of the average person become impaired at an 

altitude of about 10,000 feet, but for some people impairment 

can occur at an altitude as low as 5,000 feet. The physiological 

reactions to hypoxia or oxygen deprivation are insidious and 

affect people in different ways. These symptoms range from 

mild disorientation to total incapacitation, depending on 

body tolerance and altitude. Supplemental oxygen or cabin 

pressurization systems help pilots fly at higher altitudes and 

overcome the effects of oxygen deprivation. 

Wind and Currents 

Air flows from areas of high pressure into areas of low 

pressure because air always seeks out lower pressure. The 

combination of atmospheric pressure differences, Coriolis 

force, friction, and temperature differences of the air near 

the earth cause two kinds of atmospheric motion: convective 

currents (upward and downward motion) and wind 

(horizontal motion). Currents and winds are important as 

they affect takeoff, landing, and cruise flight operations. Most 

importantly, currents and winds or atmospheric circulation 

cause weather changes. 

Wind Patterns 

In the Northern Hemisphere, the flow of air from areas of 

high to low pressure is deflected to the right and produces 

a clockwise circulation around an area of high pressure. 

This is known as anticyclonic circulation. The opposite 

is true of low-pressure areas; the air flows toward a low 

and is deflected to create a counterclockwise or cyclonic 

circulation. [Figure 12-10] 

High-pressure systems are generally areas of dry, descending 

air. Good weather is typically associated with high-pressure 

systems for this reason. Conversely, air flows into a lowpressure area to replace rising air. This air usually brings 

increasing cloudiness and precipitation. Thus, bad weather 

is commonly associated with areas of low pressure. 

A good understanding of high- and low-pressure wind patterns 

can be of great help when planning a flight because a pilot can 

take advantage of beneficial tailwinds. [Figure 12-11] When 

planning a flight from west to east, favorable winds would 

be encountered along the northern side of a high-pressure 

system or the southern side of a low-pressure system. On 

the return flight, the most favorable winds would be along 

the southern side of the same high-pressure system or the 

northern side of a low-pressure system. An added advantage 

Figure 12-10. Circulation pattern about areas of high and low 

pressure. 

is a better understanding of what type of weather to expect 

in a given area along a route of flight based on the prevailing 

areas of highs and lows. 

While the theory of circulation and wind patterns is accurate for 

large scale atmospheric circulation, it does not take into account 

changes to the circulation on a local scale. Local conditions, 

geological features, and other anomalies can change the wind 

direction and speed close to the Earth’s surface. 

Convective Currents 

Plowed ground, rocks, sand, and barren land absorb solar 

energy quickly and can therefore give off a large amount 

of heat; whereas, water, trees, and other areas of vegetation 

tend to more slowly absorb heat and give off heat. The 

resulting uneven heating of the air creates small areas of 

local circulation called convective currents. 

Convective currents cause the bumpy, turbulent air sometimes 

experienced when flying at lower altitudes during warmer 

weather. On a low-altitude flight over varying surfaces, 

updrafts are likely to occur over pavement or barren places, 

and downdrafts often occur over water or expansive areas 

of vegetation like a group of trees. Typically, these turbulent 

conditions can be avoided by flying at higher altitudes, even 

above cumulus cloud layers. [Figure 12-12] 

Convective currents are particularly noticeable in areas with a 

land mass directly adjacent to a large body of water, such as an 

ocean, large lake, or other appreciable area of water. During 

the day, land heats faster than water, so the air over the land 

becomes warmer and less dense. It rises and is replaced by 

12-7 
Figure 12-11. Favorable winds near a high pressure system. 

Figure 12-12. Convective turbulence avoidance. 

cooler, denser air flowing in from over the water. This causes 

an onshore wind called a sea breeze. Conversely, at night land 

cools faster than water, as does the corresponding air. In this 

case, the warmer air over the water rises and is replaced by 

the cooler, denser air from the land, creating an offshore wind 

called a land breeze. This reverses the local wind circulation 

pattern. Convective currents can occur anywhere there is an 

uneven heating of the Earth’s surface. [Figure 12-13] 

Convective currents close to the ground can affect a pilot’s 

ability to control the aircraft. For example, on final approach, 

the rising air from terrain devoid of vegetation sometimes 

produces a ballooning effect that can cause a pilot to overshoot 

the intended landing spot. On the other hand, an approach over 

a large body of water or an area of thick vegetation tends to 

create a sinking effect that can cause an unwary pilot to land 

short of the intended landing spot. [Figure 12-14] 

Effect of Obstructions on Wind 

Another atmospheric hazard exists that can create problems 

for pilots. Obstructions on the ground affect the flow of 

wind and can be an unseen danger. Ground topography and 

large buildings can break up the flow of the wind and create 

wind gusts that change rapidly in direction and speed. These 

obstructions range from man-made structures, like hangars, 

to large natural obstructions, such as mountains, bluffs, or 

canyons. It is especially important to be vigilant when flying 

in or out of airports that have large buildings or natural 

obstructions located near the runway. [Figure 12-15] 

The intensity of the turbulence associated with ground 

obstructions depends on the size of the obstacle and the 

primary velocity of the wind. This can affect the takeoff and 

landing performance of any aircraft and can present a very 

serious hazard. During the landing phase of flight, an aircraft 

12-8 
Return flow 

Land breeze 

Return flow 

Sea breeze 

Warm

Cool 

Cool

Warm 

Figure 12-13. Sea breeze and land breeze wind circulation patterns. 

Warm 

air

rising 

Cool 

air

sinking 

Intended Flight path 

Figure 12-14. Currents generated by varying surface conditions. 

12-9 
I N D W 

Figure 12-15. Turbulence caused by manmade obstructions. 

may “drop in” due to the turbulent air and be too low to clear 

obstacles during the approach. 

This same condition is even more noticeable when flying in 

mountainous regions. [Figure 12-16] While the wind flows 

smoothly up the windward side of the mountain and the 

upward currents help to carry an aircraft over the peak of 

the mountain, the wind on the leeward side does not act in 

a similar manner. As the air flows down the leeward side of 

the mountain, the air follows the contour of the terrain and 

is increasingly turbulent. This tends to push an aircraft into 

the side of a mountain. The stronger the wind, the greater the 

downward pressure and turbulence become. 

Due to the effect terrain has on the wind in valleys or canyons, 

downdrafts can be severe. Before conducting a flight in or 

WIND 

Figure 12-16. Turbulence in mountainous regions. 

12-10 
 

 

near mountainous terrain, it is helpful for a pilot unfamiliar 

with a mountainous area to get a checkout with a mountain 

qualified flight instructor. 

Low-Level Wind Shear 

Wind shear is a sudden, drastic change in wind speed and/or 

direction over a very small area. Wind shear can subject an 

aircraft to violent updrafts and downdrafts, as well as abrupt 

changes to the horizontal movement of the aircraft. While 

wind shear can occur at any altitude, low-level wind shear is 

especially hazardous due to the proximity of an aircraft to the 

ground. Low-level wind shear is commonly associated with 

passing frontal systems, thunderstorms, temperature inversions, 

and strong upper level winds (greater than 25 knots). 

Wind shear is dangerous to an aircraft. It can rapidly change 

the performance of the aircraft and disrupt the normal flight 

attitude. For example, a tailwind quickly changing to a 

headwind causes an increase in airspeed and performance. 

Conversely, a headwind changing to a tailwind causes a 

decrease in airspeed and performance. In either case, a pilot 

must be prepared to react immediately to these changes to 

maintain control of the aircraft. 

The most severe type of low-level wind shear, a microburst, 

is associated with convective precipitation into dry air at 

cloud base. Microburst activity may be indicated by an 

intense rain shaft at the surface but virga at cloud base 

and a ring of blowing dust is often the only visible clue. 

A typical microburst has a horizontal diameter of 1–2 

miles and a nominal depth of 1,000 feet. The lifespan of a 

microburst is about 5–15 minutes during which time it can 

produce downdrafts of up to 6,000 feet per minute (fpm) 

and headwind losses of 30–90 knots, seriously degrading 

performance. It can also produce strong turbulence and 

hazardous wind direction changes. Consider Figure 12-17: 

During an inadvertent takeoff into a microburst, the plane 

may first experience a performance-increasing headwind 

(1), followed by performance-decreasing downdrafts (2), 

followed by a rapidly increasing tailwind (3). This can result 

in terrain impact or flight dangerously close to the ground (4). 

An encounter during approach involves the same sequence 

of wind changes and could force the plane to the ground 

short of the runway. 

The FAA has made a substantial investment in microburst 

accident prevention. The totally redesigned LLWAS-NE, the 

TDWR, and the ASR-9 WSP are skillful microburst alerting 

systems installed at major airports. These three systems were 

extensively evaluated over a 3-year period. Each was seen 

to issue very few false alerts and to detect microbursts well 

above the 90 percent detection requirement established by 

Congress. Many flights involve airports that lack microburst 

alert equipment, so the FAA has also prepared wind shear 

training material: Advisory Circular (AC) 00-54, FAA 

Pilot Wind Shear Guide. Included is information on how to 

recognize the risk of a microburst encounter, how to avoid an 

encounter, and the best flight strategy for successful escape 

should an encounter occur. 

It is important to remember that wind shear can affect any 

flight and any pilot at any altitude. While wind shear may be 

reported, it often remains undetected and is a silent danger 

to aviation. Always be alert to the possibility of wind shear, 

especially when flying in and around thunderstorms and 

frontal systems. 

Intended Path 

1 

2 

3 4 

Increasing tailwind 

Increasing headwind 

Strong downdraft 

Outflow 

Outflow 

Figure 12-17. Effects of a microburst wind. 

12-11 
Wind and Pressure Representation on Surface 

Weather Maps 

Surface weather maps provide information about fronts, areas 

of high and low pressure, and surface winds and pressures 

for each station. This type of weather map allows pilots to 

see the locations of fronts and pressure systems, but more 

importantly, it depicts the wind and pressure at the surface 

for each location. For more information on surface analysis 

and weather depiction charts, see Chapter 13, Aviation 

Weather Services. 

Wind conditions are reported by an arrow attached to the 

station location circle. [Figure 12-18] The station circle 

represents the head of the arrow, with the arrow pointing 

in the direction from which the wind is blowing. Winds 

are described by the direction from which they blow, thus 

a northwest wind means that the wind is blowing from the 

northwest toward the southeast. The speed of the wind is 

depicted by barbs or pennants placed on the wind line. Each 

barb represents a speed of ten knots, while half a barb is equal 

to five knots, and a pennant is equal to 50 knots. 

The pressure for each station is recorded on the weather chart 

and is shown in mb. Isobars are lines drawn on the chart to 

depict lines of equal pressure. These lines result in a pattern 

that reveals the pressure gradient or change in pressure over 

distance. [Figure 12-19] Isobars are similar to contour lines 

on a topographic map that indicate terrain altitudes and 

slope steepness. For example, isobars that are closely spaced 

indicate a steep pressure gradient and strong winds prevail. 

Shallow gradients, on the other hand, are represented by 

isobars that are spaced far apart and are indicative of light 

winds. Isobars help identify low- and high-pressure systems, 

as well as the location of ridges and troughs. A high is an 

area of high pressure surrounded by lower pressure; a low 

is an area of low pressure surrounded by higher pressure. A 

ridge is an elongated area of high pressure, and a trough is 

an elongated area of low pressure. 

Isobars furnish valuable information about winds in the first 

few thousand feet above the surface. Close to the ground, 

NW/5 kts SW/20 kts 

E/35 kts N/50 kts W/105 kts 

Calm 

Figure 12-18. Depiction of winds on a surface weather chart. 

1028 

1024 

1020 

1016 

1012 

1008 

Isobars 

Isobars 

Closely spaced isobars mean a steep 

pressure gradient and strong winds. 

Widely spaced isobars 

mean a shallow pressure 

gradient and relatively 

light winds. 

L 

Figure 12-19. Isobars reveal the pressure gradient of an area of 

high- or low-pressure areas. 

wind direction is modified by the friction and wind speed 

decreases due to friction with the surface. At levels 2,000 to 

3,000 feet above the surface, however, the speed is greater 

and the direction becomes more parallel to the isobars. 

Generally, the wind 2,000 feet above ground level (AGL) is 

20° to 40° to the right of surface winds, and the wind speed is 

greater. The change of wind direction is greatest over rough 

terrain and least over flat surfaces, such as open water. In the 

absence of winds aloft information, this rule of thumb allows 

for a rough estimate of the wind conditions a few thousand 

feet above the surface. 

Atmospheric Stability 

The stability of the atmosphere depends on its ability to 

resist vertical motion. A stable atmosphere makes vertical 

movement difficult, and small vertical disturbances dampen 

out and disappear. In an unstable atmosphere, small vertical air 

movements tend to become larger, resulting in turbulent airflow 

and convective activity. Instability can lead to significant 

turbulence, extensive vertical clouds, and severe weather. 

Rising air expands and cools due to the decrease in air 

pressure as altitude increases. The opposite is true of 

descending air; as atmospheric pressure increases, the 

temperature of descending air increases as it is compressed. 

Adiabatic heating and adiabatic cooling are terms used to 

describe this temperature change. 

12-12 
 

The adiabatic process takes place in all upward and 

downward moving air. When air rises into an area of lower 

pressure, it expands to a larger volume. As the molecules 

of air expand, the temperature of the air lowers. As a result, 

when a parcel of air rises, pressure decreases, volume 

increases, and temperature decreases. When air descends, 

the opposite is true. The rate at which temperature decreases 

with an increase in altitude is referred to as its lapse rate. 

As air ascends through the atmosphere, the average rate of 

temperature change is 2 °C (3.5 °F) per 1,000 feet. 

Since water vapor is lighter than air, moisture decreases air 

density, causing it to rise. Conversely, as moisture decreases, 

air becomes denser and tends to sink. Since moist air cools 

at a slower rate, it is generally less stable than dry air since 

the moist air must rise higher before its temperature cools 

to that of the surrounding air. The dry adiabatic lapse rate 

(unsaturated air) is 3 °C (5.4 °F) per 1,000 feet. The moist 

adiabatic lapse rate varies from 1.1 °C to 2.8 °C (2 °F to 

5 °F) per 1,000 feet. 

The combination of moisture and temperature determine the 

stability of the air and the resulting weather. Cool, dry air 

is very stable and resists vertical movement, which leads to 

good and generally clear weather. The greatest instability 

occurs when the air is moist and warm, as it is in the tropical 

regions in the summer. Typically, thunderstorms appear on 

a daily basis in these regions due to the instability of the 

surrounding air. 

Inversion 

As air rises and expands in the atmosphere, the temperature 

decreases. There is an atmospheric anomaly that can occur; 

however, that changes this typical pattern of atmospheric 

behavior. When the temperature of the air rises with altitude, a 

temperature inversion exists. Inversion layers are commonly 

shallow layers of smooth, stable air close to the ground. The 

temperature of the air increases with altitude to a certain 

point, which is the top of the inversion. The air at the top 

of the layer acts as a lid, keeping weather and pollutants 

trapped below. If the relative humidity of the air is high, it 

can contribute to the formation of clouds, fog, haze, or smoke 

resulting in diminished visibility in the inversion layer. 

Surface-based temperature inversions occur on clear, cool 

nights when the air close to the ground is cooled by the 

lowering temperature of the ground. The air within a few 

hundred feet of the surface becomes cooler than the air above 

it. Frontal inversions occur when warm air spreads over a 

layer of cooler air, or cooler air is forced under a layer of 

warmer air. 

Moisture and Temperature 

The atmosphere, by nature, contains moisture in the form 

of water vapor. The amount of moisture present in the 

atmosphere is dependent upon the temperature of the air. 

Every 20 °F increase in temperature doubles the amount of 

moisture the air can hold. Conversely, a decrease of 20 °F 

cuts the capacity in half. 

Water is present in the atmosphere in three states: liquid, 

solid, and gaseous. All three forms can readily change to 

another, and all are present within the temperature ranges of 

the atmosphere. As water changes from one state to another, 

an exchange of heat takes place. These changes occur through 

the processes of evaporation, sublimation, condensation, 

deposition, melting, or freezing. However, water vapor 

is added into the atmosphere only by the processes of 

evaporation and sublimation. 

Evaporation is the changing of liquid water to water vapor. 

As water vapor forms, it absorbs heat from the nearest 

available source. This heat exchange is known as the latent 

heat of evaporation. A good example is the evaporation of 

human perspiration. The net effect is a cooling sensation 

as heat is extracted from the body. Similarly, sublimation 

is the changing of ice directly to water vapor, completely 

bypassing the liquid stage. Though dry ice is not made of 

water, but rather carbon dioxide, it demonstrates the principle 

of sublimation when a solid turns directly into vapor. 

Relative Humidity 

Humidity refers to the amount of water vapor present in the 

atmosphere at a given time. Relative humidity is the actual 

amount of moisture in the air compared to the total amount of 

moisture the air could hold at that temperature. For example, 

if the current relative humidity is 65 percent, the air is 

holding 65 percent of the total amount of moisture that it is 

capable of holding at that temperature and pressure. While 

much of the western United States rarely sees days of high 

humidity, relative humidity readings of 75 to 90 percent are 

not uncommon in the southern United States during warmer 

months. [Figure 12-20] 

Temperature/Dew Point Relationship 

The relationship between dew point and temperature defines 

the concept of relative humidity. The dew point, given in 

degrees, is the temperature at which the air can hold no 

more moisture. When the temperature of the air is reduced 

to the dew point, the air is completely saturated and moisture 

begins to condense out of the air in the form of fog, dew, 

frost, clouds, rain, or snow. 

12-13 
A cubic meter of air with 17g of water 

vapor at 20 °C is at saturation 

or 100% relative humidity. Any further 

cooling will cause condensation (fog,

clouds, dew) to form. Thus, 20 °C is 

the dew point for this situation. 

If the same cubic meter of air warms 

to 30 °C, the 17 g of water vapor will 

produce a relative humidity of 56%. 

(17 g is 56% of the 30 g the air could

hold at this temperature.) 

If the temperature is lowered to 10 °C, 

the air can hold only 9 g of water 

vapor, and 8 g of water will condense 

as water droplets. The relative 

humidity will still be at 100%. 

At sea level pressure, air can hold 

9 g H2O/cubic meter of air at 10 °C 

17 g H2O/cubic meter of air at 20 °C 

30 g H2O/cubic meter of air at 30 °C 

Figure 12-20. Relationship between relative humidity, temperature, and dewpoint. 

As moist, unstable air rises, clouds often form at the altitude 

where temperature and dew point reach the same value. When 

lifted, unsaturated air cools at a rate of 5.4 °F per 1,000 feet 

and the dew point temperature decreases at a rate of 1 °F per 

1,000 feet. This results in a convergence of temperature and 

dew point at a rate of 4.4 °F. Apply the convergence rate 

to the reported temperature and dew point to determine the 

height of the cloud base. 

Given: 

Temperature (T) = 85 °F 

Dew point (DP) = 71 °F 

Convergence Rate (CR) = 4.4° 

T – DP = Temperature Dew Point Spread (TDS) 

TDS ÷ CR = X 

X × 1,000 feet = height of cloud base AGL 

Example: 

85 °F – 71 °F = 14 °F 

14 °F ÷ 4.4 °F = 3.18 

3.18 × 1,000 = 3,180 feet AGL
 

The height of the cloud base is 3,180 feet AGL.
 

Explanation: 

With an outside air temperature (OAT) of 85 °F at the surface 

and dew point at the surface of 71 °F, the spread is 14°. Divide 

the temperature dew point spread by the convergence rate of 

4.4 °F, and multiply by 1,000 to determine the approximate 

height of the cloud base. 

Methods by Which Air Reaches the Saturation Point 

If air reaches the saturation point while temperature and 

dew point are close together, it is highly likely that fog, low 

clouds, and precipitation will form. There are four methods 

by which air can reach the saturation point. First, when warm 

air moves over a cold surface, the air temperature drops and 

reaches the saturation point. Second, the saturation point may 

be reached when cold air and warm air mix. Third, when air 

cools at night through contact with the cooler ground, air 

reaches its saturation point. The fourth method occurs when 

air is lifted or is forced upward in the atmosphere. 

As air rises, it uses heat energy to expand. As a result, the rising 

air loses heat rapidly. Unsaturated air loses heat at a rate of 

3.0 °C (5.4 °F) for every 1,000 feet of altitude gain. No matter 

what causes the air to reach its saturation point, saturated air 

brings clouds, rain, and other critical weather situations. 

12-14 
Dew and Frost 

On cool, clear, calm nights, the temperature of the ground 

and objects on the surface can cause temperatures of the 

surrounding air to drop below the dew point. When this 

occurs, the moisture in the air condenses and deposits itself on 

the ground, buildings, and other objects like cars and aircraft. 

This moisture is known as dew and sometimes can be seen 

on grass and other objects in the morning. If the temperature 

is below freezing, the moisture is deposited in the form of 

frost. While dew poses no threat to an aircraft, frost poses a 

definite flight safety hazard. Frost disrupts the flow of air over 

the wing and can drastically reduce the production of lift. It 

also increases drag, which when combined with lowered lift 

production, can adversely affect the ability to take off. An 

aircraft must be thoroughly cleaned and free of frost prior 

to beginning a flight. 

Fog 

Fog is a cloud that is on the surface. It typically occurs when 

the temperature of air near the ground is cooled to the air’s 

dew point. At this point, water vapor in the air condenses and 

becomes visible in the form of fog. Fog is classified according 

to the manner in which it forms and is dependent upon the 

current temperature and the amount of water vapor in the air. 

On clear nights, with relatively little to no wind present, 

radiation fog may develop. [Figure 12-21] Usually, it forms 

in low-lying areas like mountain valleys. This type of fog 

occurs when the ground cools rapidly due to terrestrial 

radiation, and the surrounding air temperature reaches its 

dew point. As the sun rises and the temperature increases, 

radiation fog lifts and eventually burns off. Any increase in 

wind also speeds the dissipation of radiation fog. If radiation 

fog is less than 20 feet thick, it is known as ground fog. 

When a layer of warm, moist air moves over a cold surface, 

advection fog is likely to occur. Unlike radiation fog, wind 

is required to form advection fog. Winds of up to 15 knots 

Figure 12-21. Radiation fog. 

allow the fog to form and intensify; above a speed of 15 knots, 

the fog usually lifts and forms low stratus clouds. Advection 

fog is common in coastal areas where sea breezes can blow 

the air over cooler landmasses. 

Upslope fog occurs when moist, stable air is forced up sloping 

land features like a mountain range. This type of fog also 

requires wind for formation and continued existence. Upslope 

and advection fog, unlike radiation fog, may not burn off with 

the morning sun but instead can persist for days. They can 

also extend to greater heights than radiation fog. 

Steam fog, or sea smoke, forms when cold, dry air moves over 

warm water. As the water evaporates, it rises and resembles 

smoke. This type of fog is common over bodies of water 

during the coldest times of the year. Low-level turbulence 

and icing are commonly associated with steam fog. 

Ice fog occurs in cold weather when the temperature is 

much below freezing and water vapor forms directly into ice 

crystals. Conditions favorable for its formation are the same 

as for radiation fog except for cold temperature, usually –25 

°F or colder. It occurs mostly in the arctic regions but is not 

unknown in middle latitudes during the cold season. 

Clouds 

Clouds are visible indicators and are often indicative of 

future weather. For clouds to form, there must be adequate 

water vapor and condensation nuclei, as well as a method by 

which the air can be cooled. When the air cools and reaches 

its saturation point, the invisible water vapor changes into 

a visible state. Through the processes of deposition (also 

referred to as sublimation) and condensation, moisture 

condenses or sublimates onto miniscule particles of matter 

like dust, salt, and smoke known as condensation nuclei. The 

nuclei are important because they provide a means for the 

moisture to change from one state to another. 

Cloud type is determined by its height, shape, and 

characteristics. They are classified according to the height of 

their bases as low, middle, or high clouds, as well as clouds 

with vertical development. [Figure 12-22] 

Low clouds are those that form near the Earth’s surface and 

extend up to about 6,500 feet AGL. They are made primarily 

of water droplets but can include supercooled water droplets 

that induce hazardous aircraft icing. Typical low clouds 

are stratus, stratocumulus, and nimbostratus. Fog is also 

classified as a type of low cloud formation. Clouds in this 

family create low ceilings, hamper visibility, and can change 

rapidly. Because of this, they influence flight planning and 

can make visual flight rules (VFR) flight impossible. 

12-15 
 

20,000 AGL 

6,500 AGL 

Low clouds Middle clouds High clouds 

Nimbostratus 

Altocumulus 

Cirrostratus 

Cirrocumulus 

Cirrus 

Altostratus 

Stratus 

Stratocumulus 

Cumulonimbus 

Clouds with vertical development 

Towering Cumulus 

Figure 12-22. Basic cloud types. 

Middle clouds form around 6,500 feet AGL and extend up to 

20,000 feet AGL. They are composed of water, ice crystals, 

and supercooled water droplets. Typical middle-level clouds 

include altostratus and altocumulus. These types of clouds 

may be encountered on cross-country flights at higher 

altitudes. Altostratus clouds can produce turbulence and may 

contain moderate icing. Altocumulus clouds, which usually 

form when altostratus clouds are breaking apart, also may 

contain light turbulence and icing. 

High clouds form above 20,000 feet AGL and usually form 

only in stable air. They are made up of ice crystals and pose 

no real threat of turbulence or aircraft icing. Typical high 

level clouds are cirrus, cirrostratus, and cirrocumulus. 

Clouds with extensive vertical development are cumulus 

clouds that build vertically into towering cumulus or 

cumulonimbus clouds. The bases of these clouds form in 

the low to middle cloud base region but can extend into high 

altitude cloud levels. Towering cumulus clouds indicate areas 

of instability in the atmosphere, and the air around and inside 

them is turbulent. These types of clouds often develop into 

cumulonimbus clouds or thunderstorms. Cumulonimbus 

clouds contain large amounts of moisture and unstable air 

and usually produce hazardous weather phenomena, such 

as lightning, hail, tornadoes, gusty winds, and wind shear. 

These extensive vertical clouds can be obscured by other 

cloud formations and are not always visible from the ground 

or while in flight. When this happens, these clouds are said 

to be embedded, hence the term, embedded thunderstorms. 

To pilots, the cumulonimbus cloud is perhaps the most 

dangerous cloud type. It appears individually or in groups and 

is known as either an air mass or orographic thunderstorm. 

Heating of the air near the Earth’s surface creates an air mass 

thunderstorm; the upslope motion of air in the mountainous 

regions causes orographic thunderstorms. Cumulonimbus 

clouds that form in a continuous line are nonfrontal bands 

of thunderstorms or squall lines. 

Since rising air currents cause cumulonimbus clouds, they 

are extremely turbulent and pose a significant hazard to flight 

safety. For example, if an aircraft enters a thunderstorm, 

the aircraft could experience updrafts and downdrafts that 

exceed 3,000 fpm. In addition, thunderstorms can produce 

large hailstones, damaging lightning, tornadoes, and large 

quantities of water, all of which are potentially hazardous 

to aircraft. 

12-16 
 

Cloud classification can be further broken down into specific 

cloud types according to the outward appearance and cloud 

composition. Knowing these terms can help a pilot identify 

visible clouds. 

The following is a list of cloud classifications: 

•	 Cumulus—heaped or piled clouds 

•	 Stratus—formed in layers 

•	 Cirrus—ringlets, fibrous clouds, also high level clouds 

above 20,000 feet 

•	 Castellanus—common base with separate vertical 

development, castle-like 

•	 Lenticularus—lens-shaped, formed over mountains 

in strong winds 

•	 Nimbus—rain-bearing clouds 

•	 Fracto—ragged or broken 

•	 Alto—middle level clouds existing at 5,000 to 20,000 

feet 

Ceiling 

For aviation purposes, a ceiling is the lowest layer of clouds 

reported as being broken or overcast, or the vertical visibility 

into an obscuration like fog or haze. Clouds are reported 

as broken when five-eighths to seven-eighths of the sky is 

covered with clouds. Overcast means the entire sky is covered 

with clouds. Current ceiling information is reported by the 

aviation routine weather report (METAR) and automated 

weather stations of various types. 

Visibility 

Closely related to cloud cover and reported ceilings is 

visibility information. Visibility refers to the greatest 

horizontal distance at which prominent objects can be 

viewed with the naked eye. Current visibility is also reported 

in METAR and other aviation weather reports, as well as 

by automated weather systems. Visibility information, as 

predicted by meteorologists, is available for a pilot during a 

preflight weather briefing. 

Precipitation 

Precipitation refers to any type of water particles that 

form in the atmosphere and fall to the ground. It has a 

profound impact on flight safety. Depending on the form of 

precipitation, it can reduce visibility, create icing situations, 

and affect landing and takeoff performance of an aircraft. 

Precipitation occurs because water or ice particles in clouds 

grow in size until the atmosphere can no longer support 

them. It can occur in several forms as it falls toward the 

Earth, including drizzle, rain, ice pellets, hail, snow, and ice. 

Drizzle is classified as very small water droplets, smaller 

than 0.02 inches in diameter. Drizzle usually accompanies 

fog or low stratus clouds. Water droplets of larger size are 

referred to as rain. Rain that falls through the atmosphere but 

evaporates prior to striking the ground is known as virga. 

Freezing rain and freezing drizzle occur when the temperature 

of the surface is below freezing; the rain freezes on contact 

with the cooler surface. 

If rain falls through a temperature inversion, it may freeze 

as it passes through the underlying cold air and fall to the 

ground in the form of ice pellets. Ice pellets are an indication 

of a temperature inversion and that freezing rain exists at a 

higher altitude. In the case of hail, freezing water droplets are 

carried up and down by drafts inside cumulonimbus clouds, 

growing larger in size as they come in contact with more 

moisture. Once the updrafts can no longer hold the freezing 

water, it falls to the Earth in the form of hail. Hail can be 

pea sized, or it can grow as large as five inches in diameter, 

larger than a softball. 

Snow is precipitation in the form of ice crystals that falls 

at a steady rate or in snow showers that begin, change in 

intensity, and end rapidly. Snow also varies in size, from very 

small grains to large flakes. Snow grains are the equivalent 

of drizzle in size. 

Precipitation in any form poses a threat to safety of flight. 

Often, precipitation is accompanied by low ceilings and 

reduced visibility. Aircraft that have ice, snow, or frost on 

their surfaces must be carefully cleaned prior to beginning 

a flight because of the possible airflow disruption and 

loss of lift. Rain can contribute to water in the fuel tanks. 

Precipitation can create hazards on the runway surface itself, 

making takeoffs and landings difficult, if not impossible, 

due to snow, ice, or pooling water and very slick surfaces. 

Air Masses 

Air masses are classified according to the regions where 

they originate. They are large bodies of air that take on the 

characteristics of the surrounding area or source region. A 

source region is typically an area in which the air remains 

relatively stagnant for a period of days or longer. During 

this time of stagnation, the air mass takes on the temperature 

and moisture characteristics of the source region. Areas of 

stagnation can be found in polar regions, tropical oceans, and 

dry deserts. Air masses are generally identified as polar or 

tropical based on temperature characteristics and maritime 

or continental based on moisture content. 

A continental polar air mass forms over a polar region and 

brings cool, dry air with it. Maritime tropical air masses form 

12-17 
Standard air mass abbreviations: arctic (A), continental polar (cP), A maritime polar (mP), continental tropical (cT), and maritime tropical 

(mT).

cP 

mP 

mP 

mT 

mT 

cT 

mT 

over warm tropical waters like the Caribbean Sea and bring 

warm, moist air. As the air mass moves from its source region 

and passes over land or water, the air mass is subjected to 

the varying conditions of the land or water which modify the 

nature of the air mass. [Figure 12-23] 

An air mass passing over a warmer surface is warmed from 

below, and convective currents form, causing the air to rise. 

This creates an unstable air mass with good surface visibility. 

Moist, unstable air causes cumulus clouds, showers, and 

turbulence to form. 

Conversely, an air mass passing over a colder surface does not 

form convective currents but instead creates a stable air mass 

with poor surface visibility. The poor surface visibility is due 

to the fact that smoke, dust, and other particles cannot rise 

out of the air mass and are instead trapped near the surface. 

A stable air mass can produce low stratus clouds and fog. 

Fronts 

As an air mass moves across bodies of water and land, it 

eventually comes in contact with another air mass with 

different characteristics. The boundary layer between two 

types of air masses is known as a front. An approaching 

front of any type always means changes to the weather 

are imminent. 

There are four types of fronts that are named according to the 

temperature of the advancing air relative to the temperature 

of the air it is replacing: [Figure 12-24] 

• Warm 

• Cold 

• Stationary 

• Occluded 

Any discussion of frontal systems must be tempered with 

the knowledge that no two fronts are the same. However, 

generalized weather conditions are associated with a specific 

type of front that helps identify the front. 

Warm Front 

A warm front occurs when a warm mass of air advances and 

replaces a body of colder air. Warm fronts move slowly, 

typically 10 to 25 miles per hour (mph). The slope of the 

advancing front slides over the top of the cooler air and 

gradually pushes it out of the area. Warm fronts contain 

warm air that often has very high humidity. As the warm 

air is lifted, the temperature drops and condensation occurs. 

Generally, prior to the passage of a warm front, cirriform 

or stratiform clouds, along with fog, can be expected to 

form along the frontal boundary. In the summer months, 

cumulonimbus clouds (thunderstorms) are likely to develop. 

Figure 12-23. North American air mass source regions. 

12-18 
 

Symbols for surface fronts and other significant lines 

shown on the surface analysis chart 

* Note: Fronts may be black and white or color depending on their 

source. Also, fronts shown in color code do not necessarily show 

frontal symbols. 

Warm front (red)* 

Cold front (blue)* 

Stationary front (red/blue)* 

Occluded front (purple)* 

Figure 12-24. Common chart symbology to depict weather front 

location. 

Light to moderate precipitation is probable, usually in the 

form of rain, sleet, snow, or drizzle, accentuated by poor 

visibility. The wind blows from the south-southeast, and the 

outside temperature is cool or cold with an increasing dew 

point. Finally, as the warm front approaches, the barometric 

pressure continues to fall until the front passes completely. 

During the passage of a warm front, stratiform clouds are 

visible and drizzle may be falling. The visibility is generally 

poor, but improves with variable winds. The temperature rises 

steadily from the inflow of relatively warmer air. For the most 

part, the dew point remains steady and the pressure levels off. 

After the passage of a warm front, stratocumulus clouds 

predominate and rain showers are possible. The visibility 

eventually improves, but hazy conditions may exist for a 

short period after passage. The wind blows from the southsouthwest. With warming temperatures, the dew point 

rises and then levels off. There is generally a slight rise in 

barometric pressure, followed by a decrease of barometric 

pressure. 

Flight Toward an Approaching Warm Front 

By studying a typical warm front, much can be learned 

about the general patterns and atmospheric conditions 

that exist when a warm front is encountered in flight. 

Figure 12-25 depicts a warm front advancing eastward from 

St. Louis, Missouri, toward Pittsburgh, Pennsylvania during 

a flight from Pittsburgh to St. Louis. 

At the time of departure from Pittsburgh, the weather is good 

VFR with a scattered layer of cirrus clouds at 15,000 feet. 

As the flight progresses westward to Columbus and closer 

to the oncoming warm front, the clouds deepen and become 

increasingly stratiform in appearance with a ceiling of 6,000 

feet. The visibility decreases to six miles in haze with a falling 

St. Louis Indianapolis

200 miles 

Columbus 

400 miles 

Pittsburgh

600 miles 

St. Louis 

Indianapolis 

1005 

1002 

999 

999 1002 1005 1008 1011 1014 

1008 1011 1014 1017 

1017 

Columbus Pittsburgh 

65 

1 

10 

65 

59 

3 

59 56 

60 6 

50 

53 

10 20 34

068 

020 

10 

40 125 

26 

166 

18 

METAR KSTL 1950Z 21018KT 1SM –RA

 0VC010 18/18 A2960 

METAR KIND 1950Z 16012KT 3SM RA 

BKN020 15/15 A2973 

METAR KCMH 1950Z 13018KT 6SM HZ

 0VC060 14/10 A2990 

METAR KPIT 1950Z 13012KT 10SM 

SCT150 12/01 A3002 

COLD AIR 

WARM AIR 

NIMBOSTRATUS 

ALTOSTRATUS 

CIRROSTRATUS 

CIRRUS 

Figure 12-25. Warm front cross-section with surface weather chart depiction and associated METAR. 

12-19 
 

 

barometric pressure. Approaching Indianapolis, the weather 

deteriorates to broken clouds at 2,000 feet with three miles 

visibility and rain. With the temperature and dew point the 

same, fog is likely to develop. At St. Louis, the sky is overcast 

with low clouds and drizzle and the visibility is one mile. 

Beyond Indianapolis, the ceiling and visibility are too low 

to continue VFR. Therefore, it would be wise to remain in 

Indianapolis until the warm front passes, which may take 

up to two days. 

Cold Front 

A cold front occurs when a mass of cold, dense, and stable 

air advances and replaces a body of warmer air. 

Cold fronts move more rapidly than warm fronts, progressing 

at a rate of 25 to 30 mph. However, extreme cold fronts 

have been recorded moving at speeds of up to 60 mph. 

A typical cold front moves in a manner opposite that of a 

warm front. It is so dense, it stays close to the ground and 

acts like a snowplow, sliding under the warmer air and 

forcing the less dense air aloft. The rapidly ascending air 

causes the temperature to decrease suddenly, forcing the 

creation of clouds. The type of clouds that form depends 

on the stability of the warmer air mass. A cold front in the 

Northern Hemisphere is normally oriented in a northeast to 

southwest manner and can be several hundred miles long, 

encompassing a large area of land. 

Prior to the passage of a typical cold front, cirriform or 

towering cumulus clouds are present, and cumulonimbus 

clouds may develop. Rain showers may also develop due 

to the rapid development of clouds. A high dew point and 

falling barometric pressure are indicative of imminent cold 

front passage. 

As the cold front passes, towering cumulus or cumulonimbus 

clouds continue to dominate the sky. Depending on the 

intensity of the cold front, heavy rain showers form and may 

be accompanied by lightning, thunder, and/or hail. More 

severe cold fronts can also produce tornadoes. During cold 

front passage, the visibility is poor with winds variable and 

gusty, and the temperature and dew point drop rapidly. A 

quickly falling barometric pressure bottoms out during frontal 

passage, then begins a gradual increase. 

After frontal passage, the towering cumulus and 

cumulonimbus clouds begin to dissipate to cumulus clouds 

with a corresponding decrease in the precipitation. Good 

visibility eventually prevails with the winds from the westnorthwest. Temperatures remain cooler and the barometric 

pressure continues to rise. 

Fast-Moving Cold Front 

Fast-moving cold fronts are pushed by intense pressure 

systems far behind the actual front. The friction between 

the ground and the cold front retards the movement of the 

front and creates a steeper frontal surface. This results in a 

very narrow band of weather, concentrated along the leading 

edge of the front. If the warm air being overtaken by the 

cold front is relatively stable, overcast skies and rain may 

occur for some distance behind the front. If the warm air 

is unstable, scattered thunderstorms and rain showers may 

form. A continuous line of thunderstorms, or squall line, 

may form along or ahead of the front. Squall lines present 

a serious hazard to pilots as squall-type thunderstorms are 

intense and move quickly. Behind a fast-moving cold front, 

the skies usually clear rapidly, and the front leaves behind 

gusty, turbulent winds and colder temperatures. 

Flight Toward an Approaching Cold Front 

Like warm fronts, not all cold fronts are the same. Examining 

a flight toward an approaching cold front, pilots can get a 

better understanding of the type of conditions that can be 

encountered in flight. Figure 12-26 depicts a flight from 

Pittsburgh, Pennsylvania, toward St. Louis, Missouri. 

At the time of departure from Pittsburgh, the weather is VFR 

with three miles visibility in smoke and a scattered layer of 

clouds at 3,500 feet. As the flight progresses westward to 

Columbus and closer to the oncoming cold front, the clouds 

show signs of vertical development with a broken layer at 

2,500 feet. The visibility is six miles in haze with a falling 

barometric pressure. Approaching Indianapolis, the weather 

has deteriorated to overcast clouds at 1,000 feet and three 

miles visibility with thunderstorms and heavy rain showers. 

At St. Louis, the weather gets better with scattered clouds at 

1,000 feet and a ten mile visibility. 

A pilot using sound judgment based on the knowledge of 

frontal conditions will likely remain in Indianapolis until the 

front has passed. Trying to fly below a line of thunderstorms 

or a squall line is hazardous, and flight over the top of or 

around the storm is not an option. Thunderstorms can extend 

up to well over the capability of small airplanes and can 

extend in a line for 300 to 500 miles. 

Comparison of Cold and Warm Fronts 

Warm fronts and cold fronts are very different in nature as are 

the hazards associated with each front. They vary in speed, 

composition, weather phenomenon, and prediction. Cold fronts, 

which move at 20 to 35 mph, travel faster than warm fronts, 

which move at only 10 to 25 mph. Cold fronts also possess a 

12-20 
 

St. Louis Indianapolis

200 miles 

Columbus 

400 miles 

Pittsburgh

600 miles 

METAR KSTL 1950Z 30018KT 10SM 

SCT010 08/02 A2979 

METAR KIND 1950Z 20024KT 3SM +TSRA 

OVC010 24/23 A2974 

METAR KCMH 1950Z 20012KT 6SM HZ

 BKN025 25/24 A2983 

METAR KPIT 1950Z 20012KT 3SM FU 

SCT035 24/22 A2989 

1011 

1008 1005 1005 1008

1011 

1011 1011 1014 

1014 

St. Louis Indianapolis Columbus Pittsburgh 

46 

42 

10 

066 10 

33 

74 071 

3 

71 77 

6 

73 

75 

3 

70 

35 

4 

8 12 

102 122 

10 

25 

WARM AIR 

COLD AIR 

CUMULONIMBUS 

Figure 12-26. Cold front cross-section with surface weather chart depiction and associated METAR. 

steeper frontal slope. Violent weather activity is associated with 

cold fronts, and the weather usually occurs along the frontal 

boundary, not in advance. However, squall lines can form 

during the summer months as far as 200 miles in advance of 

a strong cold front. Whereas warm fronts bring low ceilings, 

poor visibility, and rain, cold fronts bring sudden storms, gusty 

winds, turbulence, and sometimes hail or tornadoes. 

Cold fronts are fast approaching with little or no warning, 

and they bring about a complete weather change in just a 

few hours. The weather clears rapidly after passage and drier 

air with unlimited visibilities prevail. Warm fronts, on the 

other hand, provide advance warning of their approach and 

can take days to pass through a region. 

Wind Shifts 

Wind around a high-pressure system rotates clockwise, while 

low-pressure winds rotate counter-clockwise. When two 

high pressure systems are adjacent, the winds are almost in 

direct opposition to each other at the point of contact. Fronts 

are the boundaries between two areas of high pressure, and 

therefore, wind shifts are continually occurring within a front. 

Shifting wind direction is most pronounced in conjunction 

with cold fronts. 

Stationary Front 

When the forces of two air masses are relatively equal, the 

boundary or front that separates them remains stationary and 

influences the local weather for days. This front is called a 

stationary front. The weather associated with a stationary 

front is typically a mixture that can be found in both warm 

and cold fronts. 

Occluded Front 

An occluded front occurs when a fast-moving cold front 

catches up with a slow-moving warm front. As the occluded 

front approaches, warm front weather prevails but is 

immediately followed by cold front weather. There are two 

types of occluded fronts that can occur, and the temperatures 

of the colliding frontal systems play a large part in defining 

the type of front and the resulting weather. A cold front 

occlusion occurs when a fast moving cold front is colder 

than the air ahead of the slow moving warm front. When 

this occurs, the cold air replaces the cool air and forces the 

warm front aloft into the atmosphere. Typically, the cold 

front occlusion creates a mixture of weather found in both 

warm and cold fronts, providing the air is relatively stable. 

A warm front occlusion occurs when the air ahead of the 

12-21 
 

 

warm front is colder than the air of the cold front. When this 

is the case, the cold front rides up and over the warm front. If 

the air forced aloft by the warm front occlusion is unstable, 

the weather is more severe than the weather found in a cold 

front occlusion. Embedded thunderstorms, rain, and fog are 

likely to occur. 

Figure 12-27 depicts a cross-section of a typical cold 

front occlusion. The warm front slopes over the prevailing 

cooler air and produces the warm front type weather. Prior 

to the passage of the typical occluded front, cirriform and 

stratiform clouds prevail, light to heavy precipitation falls, 

visibility is poor, dew point is steady, and barometric pressure 

drops. During the passage of the front, nimbostratus and 

cumulonimbus clouds predominate, and towering cumulus 

clouds may also form. Light to heavy precipitation falls, 

visibility is poor, winds are variable, and the barometric 

pressure levels off. After the passage of the front, nimbostratus 

and altostratus clouds are visible, precipitation decreases, and 

visibility improves. 

Thunderstorms 

A thunderstorm makes its way through three distinct stages 

before dissipating. It begins with the cumulus stage, in 

which lifting action of the air begins. If sufficient moisture 

and instability are present, the clouds continue to increase 

in vertical height. Continuous, strong updrafts prohibit 

moisture from falling. Within approximately 15 minutes, 

the thunderstorm reaches the mature stage, which is the most 

violent time period of the thunderstorm’s life cycle. At this 

point, drops of moisture, whether rain or ice, are too heavy 

for the cloud to support and begin falling in the form of rain 

or hail. This creates a downward motion of the air. Warm, 

rising air; cool, precipitation-induced descending air; and 

violent turbulence all exist within and near the cloud. Below 

the cloud, the down-rushing air increases surface winds and 

decreases the temperature. Once the vertical motion near the 

top of the cloud slows down, the top of the cloud spreads 

out and takes on an anvil-like shape. At this point, the storm 

enters the dissipating stage. This is when the downdrafts 

spread out and replace the updrafts needed to sustain the 

storm. [Figure 12-28] 

It is impossible to fly over thunderstorms in light aircraft. 

Severe thunderstorms can punch through the tropopause and 

reach staggering heights of 50,000 to 60,000 feet depending 

on latitude. Flying under thunderstorms can subject aircraft 

to rain, hail, damaging lightning, and violent turbulence. 

A good rule of thumb is to circumnavigate thunderstorms 

identified as severe or giving an extreme radar echo by at 

St. Louis Indianapolis

200 miles 

Columbus 

400 miles 

Pittsburgh

600 miles 

METAR KSTL 1950Z 31023G40KT 8SM 

SCT035 05/M03 A2976 

METAR KIND 1950Z 29028G45KT 1/2SM TSRAGR 

VV005 18/16 A2970 

METAR KCMH 1950Z 16017KT 2SM BR 

OVC080 11/10 A2970 

METAR KPIT 1950Z 13012KT 75SM 

BKN130 08/04 A3012 

St. Louis Indianapolis Columbus Pittsburgh 

1023 

999100210051006 100610051002999 1011 1014 1017 1020

1011 1014 1017 1020 1023 

42 

8 32 

076 

26 

52 

2 

51 

47 

7 

40 

2 

058 142 8 34 200 

20 66 

62 

12 

WARM AIR 

CUMULONIMBUS 

COLD AIR 

NIMBOSTRATUS 

ALTOSTRATUS 

CIRROSTRATUS 

CIRRUS 

COLD AIR 

Figure 12-27. Occluded front cross-section with a weather chart depiction and associated METAR. 

12-22 
 

Cumulus Stage (3–5 mile height) Mature Stage (5–10 mile height) Dissipating Stage (5–7 mile height) 

32 °F 

0 °C 

Equilibrium level 

40,000 ft. 

30,000 ft. 

20,000 ft. 

10,000 ft. 

5,000 ft. 

Figure 12-28. Life cycle of a thunderstorm. 

least 20 nautical miles (NM) since hail may fall for miles 

outside of the clouds. If flying around a thunderstorm is not 

an option, stay on the ground until it passes. 

For a thunderstorm to form, the air must have sufficient water 

vapor, an unstable lapse rate, and an initial lifting action to 

start the storm process. Some storms occur at random in 

unstable air, last for only an hour or two, and produce only 

moderate wind gusts and rainfall. These are known as air 

mass thunderstorms and are generally a result of surface 

heating. Steady-state thunderstorms are associated with 

weather systems. Fronts, converging winds, and troughs 

aloft force upward motion spawning these storms that often 

form into squall lines. In the mature stage, updrafts become 

stronger and last much longer than in air mass storms, hence 

the name steady state. [Figure 12-29] 

Knowledge of thunderstorms and the hazards associated with 

them is critical to the safety of flight. 

Hazards 

All thunderstorms have conditions that are a hazard to aviation. 

These hazards occur in numerous combinations. While not 

every thunderstorm contains all hazards, it is not possible to 

visually determine which hazards a thunderstorm contains. 

Squall Line 

A squall line is a narrow band of active thunderstorms. Often 

it develops on or ahead of a cold front in moist, unstable 

air, but it may develop in unstable air far removed from 

any front. The line may be too long to detour easily and too 

wide and severe to penetrate. It often contains steady-state 

thunderstorms and presents the single most intense weather 

hazard to aircraft. It usually forms rapidly, generally reaching 

maximum intensity during the late afternoon and the first 

few hours of darkness. 

Tornadoes 

The most violent thunderstorms draw air into their cloud 

bases with great vigor. If the incoming air has any initial 

rotating motion, it often forms an extremely concentrated 

vortex from the surface well into the cloud. Meteorologists 

have estimated that wind in such a vortex can exceed 200 

knots with pressure inside the vortex quite low. The strong 

winds gather dust and debris and the low pressure generates 

a funnel-shaped cloud extending downward from the 

cumulonimbus base. If the cloud does not reach the surface, 

it is a funnel cloud; if it touches a land surface, it is a tornado; 

and if it touches water, it is a “waterspout.” 

12-23 
 

 

Turbulence 

Anvil 

Storm movement 

First gust 

Roll cloud 

Wind shear turbulence 

Dust 

Wind shear turbulance 

Figure 12-29. Movement and turbulence of a maturing thunderstorm. 

Tornadoes occur with both isolated and squall line 

thunderstorms. Reports for forecasts of tornadoes indicate 

that atmospheric conditions are favorable for violent 

turbulence. An aircraft entering a tornado vortex is almost 

certain to suffer loss of control and structural damage. Since 

the vortex extends well into the cloud, any pilot inadvertently 

caught on instruments in a severe thunderstorm could 

encounter a hidden vortex. 

Families of tornadoes have been observed as appendages of 

the main cloud extending several miles outward from the area 

of lightning and precipitation. Thus, any cloud connected to 

a severe thunderstorm carries a threat of violence. 

Turbulence 

Potentially hazardous turbulence is present in all 

thunderstorms, and a severe thunderstorm can destroy an 

aircraft. Strongest turbulence within the cloud occurs with 

shear between updrafts and downdrafts. Outside the cloud, 

shear turbulence has been encountered several thousand feet 

above and 20 miles laterally from a severe storm. A low-level 

turbulent area is the shear zone associated with the gust front. 

Often, a “roll cloud” on the leading edge of a storm marks the 

top of the eddies in this shear, and it signifies an extremely 

turbulent zone. Gust fronts often move far ahead (up to 15 

miles) of associated precipitation. The gust front causes a 

rapid, and sometimes drastic, change in surface wind ahead 

of an approaching storm. Advisory Circular (AC) 00-54, Pilot 

Windshear Guide, explains gust front hazards associated with 

thunderstorms. Figure 2 in the AC shows a cross section of a 

mature stage thunderstorm with a gust front area where very 

serious turbulence may be encountered. 

Icing 

Updrafts in a thunderstorm support abundant liquid water 

with relatively large droplet sizes. When carried above 

the freezing level, the water becomes supercooled. When 

temperature in the upward current cools to about –15 °C, 

much of the remaining water vapor sublimates as ice crystals. 

Above this level, at lower temperatures, the amount of 

supercooled water decreases. 

Supercooled water freezes on impact with an aircraft. Clear 

icing can occur at any altitude above the freezing level, but at 

high levels, icing from smaller droplets may be rime or mixed 

rime and clear ice. The abundance of large, supercooled 

water droplets makes clear icing very rapid between 0 °C and 

–15 °C and encounters can be frequent in a cluster of cells. 

Thunderstorm icing can be extremely hazardous. 

Thunderstorms are not the only area where pilots could 

encounter icing conditions. Pilots should be alert for icing 

anytime the temperature approaches 0 °C and visible moisture 

is present. 

12-24 
 

Hail 

Hail competes with turbulence as the greatest thunderstorm 

hazard to aircraft. Supercooled drops above the freezing level 

begin to freeze. Once a drop has frozen, other drops latch on 

and freeze to it, so the hailstone grows—sometimes into a 

huge ice ball. Large hail occurs with severe thunderstorms 

with strong updrafts that have built to great heights. 

Eventually, the hailstones fall, possibly some distance from 

the storm core. Hail may be encountered in clear air several 

miles from thunderstorm clouds. 

As hailstones fall through air whose temperature is above 0 

°C, they begin to melt and precipitation may reach the ground 

as either hail or rain. Rain at the surface does not mean the 

absence of hail aloft. Possible hail should be anticipated 

with any thunderstorm, especially beneath the anvil of a 

large cumulonimbus. Hailstones larger than one-half inch 

in diameter can significantly damage an aircraft in a few 

seconds. 

Ceiling and Visibility 

Generally, visibility is near zero within a thunderstorm 

cloud. Ceiling and visibility also may be restricted in 

precipitation and dust between the cloud base and the ground. 

The restrictions create the same problem as all ceiling and 

visibility restrictions; but the hazards are multiplied when 

associated with the other thunderstorm hazards of turbulence, 

hail, and lightning. 

Effect on Altimeters 

Pressure usually falls rapidly with the approach of a 

thunderstorm, rises sharply with the onset of the first gust 

and arrival of the cold downdraft and heavy rain showers, 

and then falls back to normal as the storm moves on. This 

cycle of pressure change may occur in 15 minutes. If the pilot 

does not receive a corrected altimeter setting, the altimeter 

may be more than 100 feet in error. 

Lightning 

A lightning strike can puncture the skin of an aircraft 

and damage communications and electronic navigational 

equipment. Although lightning has been suspected of igniting 

fuel vapors and causing an explosion, serious accidents due 

to lightning strikes are rare. Nearby lightning can blind the 

pilot, rendering him or her momentarily unable to navigate 

either by instrument or by visual reference. Nearby lightning 

can also induce permanent errors in the magnetic compass. 

Lightning discharges, even distant ones, can disrupt radio 

communications on low and medium frequencies. Though 

lightning intensity and frequency have no simple relationship 

to other storm parameters, severe storms, as a rule, have a 

high frequency of lightning. 

Engine Water Ingestion 

Turbine engines have a limit on the amount of water they 

can ingest. Updrafts are present in many thunderstorms, 

particularly those in the developing stages. If the updraft 

velocity in the thunderstorm approaches or exceeds the 

terminal velocity of the falling raindrops, very high 

concentrations of water may occur. It is possible that these 

concentrations can be in excess of the quantity of water 

turbine engines are designed to ingest. Therefore, severe 

thunderstorms may contain areas of high water concentration, 

which could result in flameout and/or structural failure of 

one or more engines. 

Chapter Summary 

Knowledge of the atmosphere and the forces acting within 

it to create weather is essential to understand how weather 

affects a flight. By understanding basic weather theories, a 

pilot can make sound decisions during flight planning after 

receiving weather briefings. For additional information on the 

topics discussed in this chapter, see the following publications 

as amended: AC 00-6, Aviation Weather For Pilots and Flight 

Operations Personnel; AC 00-24, Thunderstorms; AC 00-45, 

Aviation Weather Services; AC 91-74, Pilot Guide: Flight in 

Icing Conditions; and chapter 7, section 2 of the Aeronautical 

Information Manual (AIM). 

12-25 
12-26
 
13-1 

Introduction 

In aviation, weather service is a combined effort of the 

National Weather Service (NWS), Federal Aviation 

Administration (FAA), Department of Defense (DOD), other 

aviation groups, and individuals. Because of the increasing 

need for worldwide weather services, foreign weather 

organizations also provide vital input. 

While weather forecasts are not 100 percent accurate, 

meteorologists, through careful scientific study and computer 

modeling, have the ability to predict weather patterns, trends, 

and characteristics with increasing accuracy. Through a 

complex system of weather services, government agencies, 

and independent weather observers, pilots and other aviation 

professionals receive the benefit of this vast knowledge base 

in the form of up-to-date weather reports and forecasts. 

These reports and forecasts enable pilots to make informed 

decisions regarding weather and flight safety before and 

during a flight. 

Aviation Weather Services 

Chapter 13 
 

 

Observations 

The data gathered from surface and upper altitude 

observations form the basis of all weather forecasts, 

advisories, and briefings. There are four types of weather 

observations: surface, upper air, radar, and satellite. 

Surface Aviation Weather Observations 

Surface aviation weather observations (METARs) are a 

compilation of elements of the current weather at individual 

ground stations across the United States. The network is 

made up of government and privately contracted facilities 

that provide continuous up-to-date weather information. 

Automated weather sources, such as the Automated Weather 

Observing Systems (AWOS), Automated Surface Observing 

Systems (ASOS), as well as other automated facilities, also 

play a major role in the gathering of surface observations. 

Surface observations provide local weather conditions 

and other relevant information for a specific airport. This 

information includes the type of report, station identifier, 

date and time, modifier (as required), wind, visibility, 

runway visual range (RVR), weather phenomena, sky 

condition, temperature/dew point, altimeter reading, and 

applicable remarks. The information gathered for the surface 

observation may be from a person, an automated station, or 

an automated station that is updated or enhanced by a weather 

observer. In any form, the surface observation provides 

valuable information about individual airports around the 

country. Although the reports cover only a small radius, the 

pilot can generate a good picture of the weather over a wide 

area when many reporting stations are viewed together. 

Air Route Traffic Control Center (ARTCC) 

The Air Route Traffic Control Center (ARTCC) facilities 

are responsible for maintaining separation between flights 

conducted under instrument flight rules (IFR) in the en 

route structure. Center radars (Air Route Surveillance Radar 

(ARSR)) acquire and track transponder returns using the same 

basic technology as terminal radars. Earlier center radars 

displayed weather as an area of slashes (light precipitation) 

and Hs (moderate rainfall). Because the controller could not 

detect higher levels of precipitation, pilots had to be wary 

of areas showing moderate rainfall. Newer radar displays 

show weather as three shades of blue. Controllers can select 

the level of weather to be displayed. Weather displays of 

higher levels of intensity make it difficult for controllers to 

see aircraft data blocks, so pilots should not expect air traffic 

control (ATC) to keep weather displayed continuously. 

Upper Air Observations 

Observations of upper air weather are more challenging 

than surface observations. There are several methods by 

which upper air weather phenomena can be observed: 

radiosonde observations, pilot weather reports (PIREPs), 

Aircraft Meteorological Data Relay (AMDAR) and the 

Meteorological Data Collection and Reporting System 

(MDCRS). A radiosonde is a small cubic instrumentation 

package that is suspended below a six foot hydrogen- or 

helium-filled balloon. Once released, the balloon rises at a rate 

of approximately 1,000 feet per minute (fpm). As it ascends, 

the instrumentation gathers various pieces of data, such as air 

temperature, moisture, and pressure, as well as wind speed 

and direction. Once the information is gathered, it is relayed 

to ground stations via a 300 milliwatt radio transmitter. 

The balloon flight can last as long as 2 hours or more and 

can ascend to altitudes as high as 115,000 feet and drift as 

far as 125 miles. The temperatures and pressures experienced 

during the flight can be as low as -130 °F and pressures as 

low as a few thousandths of what is experienced at sea level. 

Since the pressure decreases as the balloon rises in the 

atmosphere, the balloon expands until it reaches the limits 

of its elasticity. This point is reached when the diameter has 

increased to over 20 feet. At this point, the balloon pops and 

the radiosonde falls back to Earth. The descent is slowed by 

means of a parachute. The parachute aids in protecting people 

and objects on the ground. Each year over 75,000 balloons 

are launched. Of that number, 20 percent are recovered and 

returned for reconditioning. Return instructions are printed 

on the side of each radiosonde. 

Pilots also provide vital information regarding upper air 

weather observations and remain the only real-time source 

of information regarding turbulence, icing, and cloud 

heights. This information is gathered and filed by pilots 

in flight. Together, PIREPs and radiosonde observations 

provide information on upper air conditions important for 

flight planning. Many domestic and international airlines 

have equipped their aircraft with instrumentation that 

automatically transmits in flight weather observations 

through the DataLink system. 

The Aircraft Meteorological Data Relay (AMDAR) is 

an international program utilizing commercial aircraft to 

provide automated weather observations. The AMDAR 

program provides approximately 220,000-230,000 aircraft 

observations per day on a worldwide basis utilizing aircraft 

onboard sensors and probes that measure wind, temperature, 

humidity/water vapor, turbulence and icing data. AMDAR 

vertical profiles and en route observations provide significant 

benefits to the aviation community by enhancing aircraft 

safety and operating efficiency through improved weather 

analysis and forecasting. The AMDAR program also 

contributes to improved short and medium term numerical 

weather forecasts for a wide range of services including 

13-2 
 

severe weather, defense, marine, public weather and 

environmental monitoring. The information is down linked 

either via Very High Frequency (VHF) communications 

through the Aircraft Communications Addressing and 

Reporting System (ACARS) or via satellite link through the 

Aircraft to Satellite Data Acquisition and Relay (ASDAR). 

The Meteorological Data Collection and Reporting System 

(MDCRS) is an automated airborne weather observation 

program that is used in the U.S. This program collects and 

disseminates real-time upper-air weather observations from 

participating airlines. The weather elements are down linked 

via ACARS and are managed by Aeronautical Radio, Inc. 

(ARINC) who then forwards them in Binary Universal Form 

for the Representation of Meteorological Data (BUFR) 

format to the NWS and in raw data form to the Earth Science 

Research Laboratory (ESRL) and the participating airline. 

More than 1,500 aircraft report wind and temperature data 

with some of these same aircraft also providing turbulence 

and humidity/water vapor information. In conjunction with 

avionics manufacturers, each participating airline programs 

their equipment to provide certain levels of meteorological 

data. The monitoring and collection of climb, en route, and 

descent data is accomplished through the aircraft’s Flight Data 

Acquisition and Monitoring System (FDAMS) and is then 

transmitted via ACARS. When aircraft are out of ACARS 

range, reports can be relayed through ASDAR. However, in 

most cases, the reports are buffered until the aircraft comes 

within ACARS range, at which point they are downloaded. 

Radar Observations 

There are four types of radars which provide information 

about precipitation and wind. 

1.	 The WSR-88D NEXRAD radar, commonly called 

Doppler radar, provides in-depth observations that 

inform surrounding communities of impending 

weather. Doppler radar has two operational modes: 

clear air and precipitation. In clear air mode, the radar 

is in its most sensitive operational mode because a 

slow antenna rotation allows the radar to sample the 

atmosphere longer. Images are updated about every 

10 minutes in this mode. 

Precipitation targets provide stronger return signals; 

therefore, the radar is operated in the Precipitation 

mode when precipitation is present. A faster antenna 

rotation in this mode allows images to update at 

a faster rate, approximately every 4 to 6 minutes. 

Intensity values in both modes are measured in 

dBZ (decibels of Z) and are depicted in color on the 

radar image. [Figure 13-1] Intensities are correlated 

to intensity terminology (phraseology) for ATC 

purposes. [Figures 13-2 and 13-3] 

Figure 13-1. Example of a weather radar scope. 

Figure 13-2. WSR-88D Weather Radar Echo Intensity Legend. 

Weather Radar Echo Intensity 

Light 

Moderate 

Heavy 

Extreme 

Reflectivity (dBZ) Ranges 

<30 dBZ 

30–40 dBZ 

>40–50 

50+ dBZ 

Figure 13-3. WSR-88D Weather Radar Precipitation Intensity 

Terminology. 

13-3 
 

 

2.	 FAA terminal Doppler weather radar (TDWR), 

installed at some major airports around the country, 

also aids in providing severe weather alerts and 

warnings to ATC. Terminal radar ensures pilots 

are aware of wind shear, gust fronts, and heavy 

precipitation, all of which are dangerous to arriving 

and departing aircraft. 

3.	 The third type of radar commonly used in the detection 

of precipitation is the FAA airport surveillance radar. 

This radar is used primarily to detect aircraft, but it 

also detects the location and intensity of precipitation, 

which is used to route aircraft traffic around severe 

weather in an airport environment. 

4. Airborne radar is equipment carried by aircraft to 

locate weather disturbances. The airborne radars 

generally operate in the C or X bands (around 6 

GHz or around 10 GHz, respectively) permitting 

both penetration of heavy precipitation, required for 

determining the extent of thunderstorms, and sufficient 

reflection from less intense precipitation. 

Satellite 

Advancement in satellite technologies has recently allowed 

for commercial use to include weather uplinks. Through the 

use of satellite subscription services, individuals are now able 

to receive satellite transmitted signals that provide near realtime weather information for the North American continent. 

Service Outlets 

Service outlets are government, government contract, or 

private facilities that provide aviation weather services. Several 

different government agencies, including the FAA, National 

Oceanic and Atmospheric Administration (NOAA), and the 

NWS work in conjunction with private aviation companies 

to provide different means of accessing weather information. 

Flight Service Station (FSS) 

The FSS is the primary source for preflight weather 

information. A preflight weather briefing from an FSS can be 

obtained 24 hours a day by calling 1-800-WX BRIEF from 

anywhere in the United States and Puerto Rico. Telephone 

numbers for FSS can be found in the Chart Supplement U.S. 

(formerly Airport/Facility Directory) or in the United States 

Government section of the telephone book. 

The FSS also provides inflight weather briefing services 

and weather advisories to flights within the FSS area of 

responsibility. 

Telephone Information Briefing Service (TIBS) 

The Telephone Information Briefing Service (TIBS), 

provided by FSS, is a system of automated telephone 

recordings of meteorological and aeronautical information. 

TIBS provides area and route briefings, airspace procedures, 

and special announcements. The recordings are automatically 

updated as changes occur. It is designed to be a preliminary 

briefing tool and is not intended to replace a standard briefing 

from a FSS specialist. The TIBS service can only be accessed 

by a touchtone phone. The phone numbers for the TIBS 

service are listed in the Chart Supplement U.S. (formerly 

Airport/Facility Directory). 

Hazardous Inflight Weather Advisory Service 

(HIWAS) 

Hazardous Inflight Weather Advisory Service (HIWAS), 

available in the 48 conterminous states, is an automated 

continuous broadcast of hazardous weather information 

over selected VOR navigational aids (NAVAIDs). The 

broadcasts include advisories such as AIRMETS, SIGMETS, 

convective SIGMETS, and urgent PIREPs. The broadcasts 

are automatically updated as changes occur. Pilots should 

contact a FSS or EFAS for additional information. VORs that 

have HIWAS capability are depicted on aeronautical charts 

with an “H” in the upper right corner of the identification 

box. [Figure 13-4] 

Transcribed Weather Broadcast (TWEB) (Alaska 

Only) 

A continuous automated broadcast of meteorological and 

aeronautical data over selected low or medium frequency (L/ 

MF) and very high frequency (VHF) omnidirectional range 

(VOR) NAVAID facilities. The broadcasts are automatically 

updated as changes occur. The broadcast contains adverse 

conditions, surface weather observations, PIREPS, and 

a density altitude statement (if applicable). Recordings 

may also include a synopsis, winds aloft forecast, en route 

and terminal forecast data, and radar reports. At selected 

locations, telephone access to the TWEB has been provided 

(TEL-TWEB). Telephone numbers for this service are found 

Symbol indicates HIWAS 

Figure 13-4. HIWAS availability is shown on sectional chart. 

13-4 
 

in the Alaska Chart Supplement U.S. (formerly Airport/ 

Facility Directory). These broadcasts are made available 

primarily for preflight and inflight planning, and as such, 

should not be considered as a substitute for specialistprovided preflight briefings. 

Weather Briefings 

Prior to every flight, pilots should gather all information 

vital to the nature of the flight. This includes an appropriate 

weather briefing obtained from a specialist at a FSS. 

For weather specialists to provide an appropriate weather 

briefing, they need to know which of the three types of 

briefings is needed—standard, abbreviated, or outlook. Other 

helpful information is whether the flight is visual flight rules 

(VFR) or IFR, aircraft identification and type, departure 

point, estimated time of departure (ETD), flight altitude, route 

of flight, destination, and estimated time en route (ETE). 

This information is recorded in the flight plan system and a 

note is made regarding the type of weather briefing provided. 

If necessary, it can be referenced later to file or amend a 

flight plan. It is also used when an aircraft is overdue or is 

reported missing. 

Standard Briefing 

A standard briefing provides the most complete information 

and a more complete weather picture. This type of briefing 

should be obtained prior to the departure of any flight and 

should be used during flight planning. A standard briefing 

provides the following information in sequential order if it 

is applicable to the route of flight. 

1.	 Adverse conditions—this includes information about 

adverse conditions that may influence a decision to 

cancel or alter the route of flight. Adverse conditions 

include significant weather, such as thunderstorms or 

aircraft icing, or other important items such as airport 

closings. 

2.	 VFR flight not recommended—if the weather for 

the route of flight is below VFR minimums, or if 

it is doubtful the flight could be made under VFR 

conditions due to the forecast weather, the briefer may 

state “VFR flight not recommended.” It is the pilot’s 

decision whether or not to continue the flight under 

VFR, but this advisory should be weighed carefully. 

3.	 Synopsis—an overview of the larger weather picture. 

Fronts and major weather systems that affect the 

general area are provided. 

4.	 Current conditions—the current ceilings, visibility, 

winds, and temperatures. If the departure time is more 

than 2 hours away, current conditions are not included 

in the briefing. 

5.	 En route forecast—a summary of the weather forecast 

for the proposed route of flight. 

6.	 Destination forecast—a summary of the expected 

weather for the destination airport at the estimated 

time of arrival (ETA). 

7.	 Forecast winds and temperatures aloft—a forecast of 

the winds at specific altitudes for the route of flight. 

The forecast temperature information aloft is provided 

only upon request. 

8.	 Notices to Airmen (NOTAM)—information pertinent 

to the route of flight that has not been published in the 

NOTAM publication. Published NOTAM information 

is provided during the briefing only when requested. 

9.	 ATC delays—an advisory of any known ATC delays 

that may affect the flight. 

10.	 Other information—at the end of the standard briefing, 

the FSS specialist provides the radio frequencies 

needed to open a flight plan and to contact EFAS. Any 

additional information requested is also provided at 

this time. 

Abbreviated Briefing 

An abbreviated briefing is a shortened version of the standard 

briefing. It should be requested when a departure has been 

delayed or when weather information is needed to update 

the previous briefing. When this is the case, the weather 

specialist needs to know the time and source of the previous 

briefing so the necessary weather information is not omitted 

inadvertently. It is always a good idea for the pilot to update 

the weather information whenever he/she has additional time. 

Outlook Briefing 

An outlook briefing should be requested when a planned 

departure is 6 hours or more away. It provides initial forecast 

information that is limited in scope due to the time frame 

of the planned flight. This type of briefing is a good source 

of flight planning information that can influence decisions 

regarding route of flight, altitude, and ultimately the go/no-go 

decision. A prudent pilot requests a follow-up briefing prior 

to departure since an outlook briefing generally only contains 

information based on weather trends and existing weather in 

geographical areas at or near the departure airport. A standard 

briefing near the time of departure ensures that the pilot has 

the latest information available prior to his/her flight. 

Aviation Weather Reports 

Aviation weather reports are designed to give accurate 

depictions of current weather conditions. Each report 

provides current information that is updated at different times. 

Some typical reports are METARs and PIREPs. 

13-5 
 

 

 

 

 

Aviation Routine Weather Report (METAR) 

A METAR is an observation of current surface weather 

reported in a standard international format. While the 

METAR code has been adopted worldwide, each country is 

allowed to make modifications to the code. Normally, these 

differences are minor but necessary to accommodate local 

procedures or particular units of measure. This discussion of 

METAR covers elements used in the United States. 

METARs are issued on a regularly scheduled basis unless 

significant weather changes have occurred. A special 

METAR (SPECI) can be issued at any time between routine 

METAR reports. 

Example: 

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM 

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK 

PRESFR 

A typical METAR report contains the following information 

in sequential order: 

1.	 Type of report—there are two types of METAR 

reports. The first is the routine METAR report that is 

transmitted on a regular time interval. The second is 

the aviation selected SPECI. This is a special report 

that can be given at any time to update the METAR for 

rapidly changing weather conditions, aircraft mishaps, 

or other critical information. 

2.	 Station identifier—a four-letter code as established by 

the International Civil Aviation Organization (ICAO). 

In the 48 contiguous states, a unique three-letter 

identifier is preceded by the letter “K.” For example, 

Gregg County Airport in Longview, Texas, is 

identified by the letters “KGGG,” K being the country 

designation and GGG being the airport identifier. 

In other regions of the world, including Alaska and 

Hawaii, the first two letters of the four-letter ICAO 

identifier indicate the region, country, or state. Alaska 

identifiers always begin with the letters “PA” and 

Hawaii identifiers always begin with the letters “PH.” 

Station identifiers can be found by calling the FSS, a 

NWS office, or by searching various websites such 

as DUATS and NOAA's Aviation Weather Aviation 

Digital Data Services (ADDS). 

3.	 Date and time of report—depicted in a six-digit group 

(161753Z). The first two digits are the date. The last 

four digits are the time of the METAR/SPECI, which 

is always given in coordinated universal time (UTC). 

A “Z” is appended to the end of the time to denote 

the time is given in Zulu time (UTC) as opposed to 

local time. 

4.	 Modifier—denotes that the METAR/SPECI came from 

an automated source or that the report was corrected. If 

the notation “AUTO” is listed in the METAR/SPECI, 

the report came from an automated source. It also lists 

“AO1” (for no precipitation discriminator) or “AO2” 

(with precipitation discriminator) in the “Remarks” 

section to indicate the type of precipitation sensors 

employed at the automated station. 

When the modifier “COR” is used, it identifies a 

corrected report sent out to replace an earlier report 

that contained an error (for example: METAR KGGG 

161753Z COR). 

5.	 Wind—reported with five digits (14021KT) unless 

the speed is greater than 99 knots, in which case the 

wind is reported with six digits. The first three digits 

indicate the direction the true wind is blowing from in 

tens of degrees. If the wind is variable, it is reported 

as “VRB.” The last two digits indicate the speed of 

the wind in knots unless the wind is greater than 99 

knots, in which case it is indicated by three digits. If 

the winds are gusting, the letter “G” follows the wind 

speed (G26KT). After the letter “G,” the peak gust 

recorded is provided. If the wind direction varies more 

than 60° and the wind speed is greater than six knots, 

a separate group of numbers, separated by a “V,” will 

indicate the extremes of the wind directions. 

6.	 Visibility—the prevailing visibility (3⁄4 SM) is reported 

in statute miles as denoted by the letters “SM.” It is 

reported in both miles and fractions of miles. At times, 

runway visual range (RVR) is reported following the 

prevailing visibility. RVR is the distance a pilot can 

see down the runway in a moving aircraft. When RVR 

is reported, it is shown with an R, then the runway 

number followed by a slant, then the visual range 

in feet. For example, when the RVR is reported as 

R17L/1400FT, it translates to a visual range of 1,400 

feet on runway 17 left. 

7.	 Weather—can be broken down into two different 

categories: qualifiers and weather phenomenon 

(+TSRA BR). First, the qualifiers of intensity, 

proximity, and the descriptor of the weather are given. 

The intensity may be light (–), moderate ( ), or heavy 

(+). Proximity only depicts weather phenomena that 

are in the airport vicinity. The notation “VC” indicates 

a specific weather phenomenon is in the vicinity 

of five to ten miles from the airport. Descriptors 

are used to describe certain types of precipitation 

and obscurations. Weather phenomena may be 

reported as being precipitation, obscurations, and 

other phenomena, such as squalls or funnel clouds. 

13-6 
Descriptions of weather phenomena as they begin or 

end and hailstone size are also listed in the “Remarks” 

sections of the report. [Figure 13-5] 

8. Sky condition—always reported in the sequence of

amount, height, and type or indefinite ceiling/height

(vertical visibility) (BKN008 OVC012CB, VV003).

The heights of the cloud bases are reported with a

three-digit number in hundreds of feet AGL. Clouds

above 12,000 feet are not detected or reported by an

automated station. The types of clouds, specifically

towering cumulus (TCU) or cumulonimbus (CB)

clouds, are reported with their height. Contractions

are used to describe the amount of cloud coverage and 

obscuring phenomena. The amount of sky coverage is 

reported in eighths of the sky from horizon to horizon. 

[Figure 13-6]

9. Temperature and dew point—the air temperature and

dew point are always given in degrees Celsius (C) or

(18/17). Temperatures below 0 °C are preceded by

the letter “M” to indicate minus.

10. Altimeter setting—reported as inches of mercury

("Hg) in a four-digit number group (A2970). It is

always preceded by the letter “A.” Rising or falling

pressure may also be denoted in the “Remarks”

sections as “PRESRR” or “PRESFR,” respectively.

11. Zulu time—a term used in aviation for UTC, which

places the entire world on one time standard.

Contraction 

SKC, CLR, FEW 

FEW 

SCT 

BKN 

OVC 

Sky Cover 

Less than 1∕8

(Clear) 1∕8–

2

∕8 (Few) 

3∕8–

4

∕8 (Scattered) 

5∕8–7∕8 (Broken) 

8∕8 or (Overcast) 

Figure 13-6. Reportable contractions for sky condition. 

12. Remarks—the remarks section always begins with the 

letters “RMK.” Comments may or may not appear in

this section of the METAR. The information contained 

in this section may include wind data, variable

visibility, beginning and ending times of particular

phenomenon, pressure information, and various other 

information deemed necessary. An example of a

remark regarding weather phenomenon that does not

fit in any other category would be: OCNL LTGICCG. 

This translates as occasional lightning in the clouds

and from cloud to ground. Automated stations also use 

the remarks section to indicate the equipment needs

maintenance.

Example: 

METAR KGGG 161753Z AUTO 14021G26KT 3/4SM 

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK 

PRESFR 

Intensity or Proximity 1 Descriptor 2 Precipitation 3 Obscuration 4 Other 5

– Light

 Moderate (no qualifier) 

+ Heavy 

VC in the vicinity 

MI Shallow 

BC Patches 

DR Low drifting 

BL Blowing 

SH Showers 

TS Thunderstorms 

FZ Freezing 

PR Partial 

DZ Drizzle 

RA Rain 

SN Snow 

SG Snow grains 

IC Ice crystals (diamond dust) 

PL Ice pellets 

GR Hail 

GS Small hail or snow pellets 

UP *Unknown precipitation 

BR Mist 

FG Fog 

FU Smoke 

DU Dust 

SA Sand 

HZ Haze 

PY Spray 

VA Volcanic ash 

PO Dust/sand whirls 

SQ Squalls 

FC Funnel cloud 

+FC Tornado or waterspout 

SS Sandstorm 

DS Dust storm 

The weather groups are constructed by considering columns 1–5 in this table in sequence: 

intensity, followed by descriptor, followed by weather phenomena (e.g., heavy rain showers(s) is coded as +SHRA). 

* Automated stations only

Qualifier Weather Phenomena 

Figure 13-5. Descriptors and weather phenomena used in a typical METAR. 

13-7 
 

Explanation:
 

Routine METAR for Gregg County Airport for the 16th
 

day of the month at 1753Z automated source. Winds are
 

140 at 21 knots gusting to 26. Visibility is 3⁄4 statute mile. 

Thunderstorms with heavy rain and mist. Ceiling is broken 

at 800 feet, overcast at 1,200 feet with cumulonimbus clouds.
 

Temperature 18 °C and dew point 17 °C. Barometric pressure
 

is 29.70 "Hg and falling rapidly. 

Pilot Weather Reports (PIREPs) 

PIREPs provide valuable information regarding the 

conditions as they actually exist in the air, which cannot be 

gathered from any other source. Pilots can confirm the height 

of bases and tops of clouds, locations of wind shear and 

turbulence, and the location of inflight icing. If the ceiling is 

below 5,000 feet, or visibility is at or below five miles, ATC 

facilities are required to solicit PIREPs from pilots in the area. 

When unexpected weather conditions are encountered, pilots 

are encouraged to make a report to a FSS or ATC. When a 

pilot weather report is filed, the ATC facility or FSS adds it 

to the distribution system to brief other pilots and provide 

inflight advisories. 

PIREPs are easy to file and a standard reporting form outlines 

the manner in which they should be filed. Figure 13-7 shows 

the elements of a PIREP form. Item numbers 1 through 5 are 

required information when making a report, as well as at least 

one weather phenomenon encountered. A PIREP is normally
 

transmitted as an individual report but may be appended to 

a surface report. Pilot reports are easily decoded, and most 

contractions used in the reports are self-explanatory.
 

Example:
 

UA/OV GGG 090025/TM 1450/FL 060/TP C182/SK
 

080 OVC/WX FV04SM RA/TA 05/WV 270030KT/TB
 

LGT/RM HVY RAIN
 

Explanation:
 

Type: .................................Routine pilot report
 

Location: .......................... 25 NM out on the 090° radial, 

Gregg County VOR
 

Time: ................................ 1450 Zulu
 

Altitude or Flight Level: 6,000 feet
 

Aircraft Type: ...................Cessna 182
 

Sky Cover: ........................8,000 overcast
 

Visibility/Weather: ...........4 miles in rain
 

Temperature: .....................5 °Celsius
 

Wind: ................................270° at 30 knots
 

Turbulence: .......................Light
 

Icing: ................................ None reported
 

Remarks: .......................... Rain is heavy
 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

XXX 

UA 

/OV 

/TM 

/FL 

/TP 

/SK 

/WX 

/TA 

/WV 

/TB 

/IC 

/RM 

3-letter station identifier 

Routine PIREP, UUA-Urgent PIREP. 

Location 

Time 

Altitude/flight level 

Type aircraft 

Sky cover/cloud layers 

Weather 

Air temperature in celsius (C) 

Wind 

Turbulence 

Icing 

Remarks 

Nearest weather reporting location to the reported phenomenon 

Use 3-letter NAVAID idents only. 

a. Fix: /OV ABC, /OV ABC 090025. 

b. Fix: /OV ABC 045020-DEF, /OV ABC-DEF-GHI 

4 digits in UTC: /TM 0915. 

3 digits for hundreds of feet. If not known, use UNKN: /FL095, /FL310, /FLUNKN. 

4 digits maximum. If not known, use UNKN: /TP L329, /TP B727, /TP UNKN. 

Describe as follows: 

a. Height of cloud base in hundreds of feet. If unknown, use UNKN. 

b. Cloud cover symbol. 

c. Height of cloud tops in hundreds of feet. 

Flight visibility reported first: 

Use standard weather symbols: 

/WX FV02SM RA HZ, /WX FV01SM TSRA. 

If below zero, prefix with a hyphen: /TA 15, /TA M06. 

Direction in degrees magnetic north and speed in six digits: 

/WV270045KT, WV 280110KT. 

Use standard contractions for intensity and type (use CAT or CHOP when 

appropriate). Include altitude only if different from /FL, /TB EXTRM, /TB 

LGT-MOD BLO 090. 

Describe using standard intensity and type contractions. Include altitude only if 

different than /FL: /IC LGT-MOD RIME, /IC SEV CLR 028-045. 

Use free form to clarify the report and type hazardous elements first: 

/RM LLWS -15KT SFC-030 DURC RY22 JFK. 

Encoding Pilot Weather Reports (PIREPS) 

Figure 13-7. PIREP encoding and decoding. 

13-8 
Aviation Forecasts 

Observed weather condition reports are often used in the 

creation of forecasts for the same area. A variety of different 

forecast products are produced and designed to be used in the 

preflight planning stage. The printed forecasts that pilots need 

to be familiar with are the terminal aerodrome forecast (TAF), 

aviation area forecast (FA), inflight weather advisories 

(SIGMET, AIRMET), and the winds and temperatures aloft 

forecast (FB). 

Terminal Aerodrome Forecasts (TAF) 

A TAF is a report established for the five statute mile 

radius around an airport. TAF reports are usually given for 

larger airports. Each TAF is valid for a 24 or 30-hour time 

period and is updated four times a day at 0000Z, 0600Z, 

1200Z, and 1800Z. The TAF utilizes the same descriptors 

and abbreviations as used in the METAR report. The TAF 

includes the following information in sequential order: 

1.	 Type of report—a TAF can be either a routine forecast 

(TAF) or an amended forecast (TAF AMD). 

2.	 ICAO station identifier—the station identifier is the 

same as that used in a METAR. 

3.	 Date and time of origin—time and date (081125Z) 

of TAF origination is given in the six-number code 

with the first two being the date, the last four being 

the time. Time is always given in UTC as denoted by 

the Z following the time block. 

4.	 Valid period dates and times—The TAF valid period 

(0812/0912) follows the date/time of forecast origin 

group. Scheduled 24 and 30 hour TAFs are issued 

four times per day, at 0000, 0600, 1200, and 1800Z. 

The first two digits (08) are the day of the month for 

the start of the TAF. The next two digits (12) are the 

starting hour (UTC). 09 is the day of the month for 

the end of the TAF, and the last two digits (12) are 

the ending hour (UTC) of the valid period. A forecast 

period that begins at midnight UTC is annotated as 00. 

If the end time of a valid period is at midnight UTC, 

it is annotated as 24. For example, a 00Z TAF issued 

on the 9th of the month and valid for 24 hours would 

have a valid period of 0900/0924. 

5.	 Forecast wind—the wind direction and speed forecast 

are coded in a five-digit number group. An example 

would be 15011KT. The first three digits indicate the 

direction of the wind in reference to true north. The 

last two digits state the windspeed in knots appended 

with “KT.” Like the METAR, winds greater than 99 

knots are given in three digits. 

6.	 Forecast visibility—given in statute miles and may 

be in whole numbers or fractions. If the forecast is 

greater than six miles, it is coded as “P6SM.” 

7.	 Forecast significant weather—weather phenomena 

are coded in the TAF reports in the same format as 

the METAR. 

8.	 Forecast sky condition—given in the same format as 

the METAR. Only cumulonimbus (CB) clouds are 

forecast in this portion of the TAF report as opposed 

to CBs and towering cumulus in the METAR. 

9.	 Forecast change group—for any significant weather 

change forecast to occur during the TAF time period, 

the expected conditions and time period are included 

in this group. This information may be shown as from 

(FM), and temporary (TEMPO). “FM” is used when a 

rapid and significant change, usually within an hour, is 

expected. “TEMPO” is used for temporary fluctuations 

of weather, expected to last less than 1 hour. 

10. PROB30—a given percentage that describes the 

probability of thunderstorms and precipitation 

occurring in the coming hours. This forecast is not 

used for the first 6 hours of the 24-hour forecast. 

Example: 

TAF 

KPIR 111130Z 1112/1212 

TEMPO 1112/1114 5SM BR 

FM1500 16015G25KT P6SM SCT040 BKN250 

FM120000 14012KT P6SM BKN080 OVC150 PROB30 

1200/1204 3SM TSRA BKN030CB 

FM120400 1408KT P6SM SCT040 OVC080 

TEMPO 1204/1208 3SM TSRA OVC030CB 

Explanation: 

Routine TAF for Pierre, South Dakota...on the 11th day of 

the month, at 1130Z...valid for 24 hours from 1200Z on the 

11th to 1200Z on the 12th...wind from 150° at 12 knots... 

visibility greater than 6 SM...broken clouds at 9,000 feet... 

temporarily, between 1200Z and 1400Z, visibility 5 SM in 

mist...from 1500Z winds from 160° at 15 knots, gusting 

to 25 knots visibility greater than 6 SM...clouds scattered 

at 4,000 feet and broken at 25,000 feet...from 0000Z wind 

from 140° at 12 knots...visibility greater than 6 SM...clouds 

broken at 8,000 feet, overcast at 15,000 feet...between 0000Z 

and 0400Z, there is 30 percent probability of visibility 3 

SM...thunderstorm with moderate rain showers...clouds 

broken at 3,000 feet with cumulonimbus clouds...from 

0400Z...winds from 140° at 8 knots...visibility greater than 

6 miles...clouds at 4,000 scattered and overcast at 8,000... 

temporarily between 0400Z and 0800Z...visibility 3 miles... 

thunderstorms with moderate rain showers...clouds overcast 

at 3,000 feet with cumulonimbus clouds...end of report (=). 

13-9 
Area Forecasts (FA) 

The FA gives a picture of clouds, general weather conditions, 

and visual meteorological conditions (VMC) expected over 

a large area encompassing several states. There are six areas 

for which area forecasts are published in the contiguous 48 

states. Area forecasts are issued three times a day and are 

valid for 18 hours. This type of forecast gives information 

vital to en route operations, as well as forecast information 

for smaller airports that do not have terminal forecasts. 

Area forecasts are typically disseminated in four sections and 

include the following information: 

1.	 Header—gives the location identifier of the source of 

the FA, the date and time of issuance, the valid forecast 

time, and the area of coverage. 

Example: 

DFWC FA 120945 

SYNOPSIS AND VFR CLDS/WX 

SYNOPSIS VALID UNTIL 130400 

CLDS/WX VALID UNTIL 122200...OTLK VALID 

122200-130400 

OK TX AR LA MS AL AND CSTL WTRS 

Explanation: 

The area forecast shows information given by Dallas Fort 

Worth, for the region of Oklahoma, Texas, Arkansas, 

Louisiana, Mississippi, and Alabama, as well as a portion 

of the Gulf coastal waters. It was issued on the 12th day 

of the month at 0945. The synopsis is valid from the time 

of issuance until 0400 hours on the 13th. VFR clouds and 

weather information on this area forecast are valid until 2200 

hours on the 12th and the outlook is valid from 2200Z on the 

12th to 0400Z on the 13th. 

2.	 Precautionary statements—IFR conditions, mountain 

obscurations, and thunderstorm hazards are described 

in this section. Statements made here regarding height 

are given in MSL, and if given otherwise, AGL or 

ceiling (CIG) is noted. 

Example:
 

SEE AIRMET SIERRA FOR IFR CONDS AND MTN
 

OBSCN.
 

TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND 

IFR CONDS.
 

NON MSL HGTS DENOTED BYAGL OR CIG.
 

Explanation:
 

The area forecast covers VFR clouds and weather, so the 

precautionary statement warns that AIRMET Sierra should 

be referenced for IFR conditions and mountain obscuration. 

The code TS indicates the possibility of thunderstorms
 

and implies there may be occurrences of severe or greater 

turbulence, severe icing, low-level wind shear, and IFR 

conditions. The final line of the precautionary statement alerts 

the user that heights, for the most part, are MSL. Those that 

are not MSL will state AGL or CIG. 

3.	 Synopsis—gives a brief summary identifying the 

location and movement of pressure systems, fronts, 

and circulation patterns. 

Example:
 

SYNOPSIS...LOW PRES TROF 10Z OK/TX PNHDL AREA
 

FCST MOV EWD INTO CNTRL-SWRN OK BY 04Z.
 

WRMFNT 10Z CNTRL OK-SRN AR-NRN MS FCST LIFT
 

NWD INTO NERN OK-NRN AR EXTRM NRN MS BY 04Z.
 

Explanation:
 

As of 1000Z, there is a low pressure trough over the Oklahoma
 

and Texas panhandle area, which is forecast to move eastward
 

into central to southwestern Oklahoma by 0400Z. A warm
 

front located over central Oklahoma, southern Arkansas, and
 

northern Mississippi at 1000Z is forecast to lift northwestward
 

into northeastern Oklahoma, northern Arkansas, and extreme
 

northern Mississippi by 0400Z.
 

4.	 VFR Clouds and Weather—This section lists expected 

sky conditions, visibility, and weather for the next 12 

hours and an outlook for the following 6 hours. 

Example:
 

S CNTRL AND SERN TX
 

AGL SCT-BKN010. TOPS 030. VIS 3-5SM BR. 14-16Z 

BECMG AGL SCT030. 19Z AGL SCT050.
 

OTLK...VFR
 

OK
 

PNDLAND NW...AGL SCT030 SCT-BKN100.
 

TOPS FL200.
 

15Z AGL SCT040 SCT100. AFT 20Z SCT TSRA DVLPG..
 

FEW POSS SEV. CB TOPS FL450.
 

OTLK...VFR
 

Explanation:
 

In south central and southeastern Texas, there is a scattered 

to broken layer of clouds from 1,000 feet AGL with tops at 

3,000 feet, visibility is 3 to 5 SM in mist. Between 1400Z and
 

1600Z, the cloud bases are expected to increase to 3,000 feet 

AGL. After 1900Z, the cloud bases are expected to continue 

to increase to 5,000 feet AGL and the outlook is VFR.
 

In northwestern Oklahoma and panhandle, the clouds are 

scattered at 3,000 feet with another scattered to broken layer 

at 10,000 feet AGL, with the tops at 20,000 feet. At 1500 

Z, the lowest cloud base is expected to increase to 4,000 

feet AGL with a scattered layer at 10,000 feet AGL. After 

13-10 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2000Z, the forecast calls for scattered thunderstorms with rain 

developing and a few becoming severe; the CB clouds have 

tops at flight level (FL) 450 or 45,000 feet MSL. 

It should be noted that when information is given in the area 

forecast, locations may be given by states, regions, or specific 

geological features such as mountain ranges. Figure 13-8 

shows an area forecast chart with six regions of forecast, 

states, regional areas, and common geographical features. 

Inflight Weather Advisories 

Inflight weather advisories, which are provided to en route 

aircraft, are forecasts that detail potentially hazardous 

weather. These advisories are also available to pilots prior 

to departure for flight planning purposes. An inflight 

weather advisory is issued in the form of either an AIRMET, 

SIGMET, or convective SIGMET. 

AIRMET 

AIRMETs (WAs) are examples of inflight weather advisories 

that are issued every 6 hours with intermediate updates 

issued as needed for a particular area forecast region. The 

information contained in an AIRMET is of operational 

interest to all aircraft, but the weather section concerns 

South 

Delta Area 

NW NE North 

Central 

SW SE 

NW NE 

Ozarks 

Boot 

Heel 

SW Missouri 

Lakes Area 

Lake of the 

Ozarks Area 

Extreme 

SRN 

IL 

SW SE 

Central 

NW NE 

NW NE 

SW SE 

Central 

Iowa 

SW SE 

Extrm 

SE 

NW NE 

Northeast Lakes Region 

Upper Mississippi Valley 

Arrowhead 

Lake Superior 

Shoreline 

WRN Upper MI 

Cntrl 

Upper

MI 

ERN Upper MI 

Door PeninsulaMackinac Area 

NRN Highlands 

The 

Thumb 

Saginaw 

Valley Grand 

Valley Irish Hills 

Near Lake 

Mi Extrm

N 

NW NE 

SW SE 

Near Ohio River 

SW 

SE 

West 

N

Cntrl 

Northern 

Southern 

Cntrl

EastNE 

West 

Middle East Appalachian Mountains 

SE 

NW NE Along Ohio River 

Extrm

NW 

SWRN 

Southern 

W

Cntrl E

Cntrl 

N Third 

S

Third 

Near Lake Erie 

Lee 

Lake 

Erie 

Lower Great 

Lakes Basin 

Extrm

NW 

Allegheny Plateau 

NW 

SW S

Cntrl 

NE 

SE 

N

Cntrl 

Lee Lake Ontario 

NRN 

SRN NE 

Eastern 

Shore Coastal 

Waters 

NE

NW 

SW SE 

Coastal Plain

NE 

SE 

Piedmont

West 

Mtns 

of 

SC 

Coastal Plain 

NW Hills

Mtns of 

Alabama 

West 

Cntrl 

East 

Cntrl 

Extrm 

SE Extrm Southern 

Georgia Mobile 

Area 

FL W 85 

Extrm

North 

North 

Central 

Apalachee

Bay 

South 

Extrm 

South Upper 

Keys 

Lower Keys 

Gulf Stream 

Florida Straits 

Coastal 

Waters 

Catskill 

Mtns 

E Cntrl 

Cape Cod 

Coastal Plains 

Hudson Valley 

Mohawk 

Valley 

West of 

Catskills 

Adirondack

Mtns 

Champlain 

Valley 

Green 

Mtns 

N of Catskills 

White Mtns NW NE 

Coastal Sectio

SE 

n SW 

MN 

IA 

MI 

IL IN 

MO 

AR 

LA 

MS 

AL 

TN 

GA 

FL 

SC 

NC 

VA 

MD 

DC 

NJ 

OH 

WI 

WV 

PA 

NY 

ME 

VT 

NH MA 

RI 

CT 

Coastal Waters–from 

coast outward to the 

flight information 

region border 

SW 

SE 

Northern 

NE

Mtns 

Central 

Strait of Juan De Fuca 

Olympic Mtns 

Sacramento 

Valley 

Northwest 

North Central 

South Central 

Lower 

Rio 

Grande 

Valley 

Lower 

Coastal 

Plain 

Mid Coastal 

Plain 

Upper Coastal 

Plain 

Northwest 

Texas 

Puget 

Sound 

Cascade Mtns 

Cascade Mtns 

of Cascades 

Mtns 

NE WA 

Columbia 

Basin Interior 

Valley 

Columbia Gorge Blue 

Mtns 

Wallowa 

Mtns 

Mtns of 

NE OR

Costal Range 

Willamette Valley 

Coast and 

Costal Valley 

High Plateau 

East Slopes 

WA 

OR 

Shasta 

Siskiyous 

NE CA 

NRN 

Sierra 

Mtns 

Coastal Mtns and Valleys 

San Joaquin 

Valley 

SRN 

Sierra 

Mtns 

Coastal Mtns and Valleys 

Western

Nevada 

Eastern

Nevada 

Coastal 

Areas 

Death 

Valley 

Lake Tahoe 

Lake 

Mead 

Lake 

Mojave 

Mojave 

Desert

Antelope

Valley

Coastal Range 

SRN 

Deserts 

Santa 

Barbara 

Channel 

Santa Monica 

Bay Coastal Plain 

Gulf of 

Santa Catalina 

Coacnella

and

Imperial

Valleys 

Great 

Basin 

Colorado 

River 

Valley 

Gilariver Valley 

Mogollon Rim 

Chiricahua 

Mtns 

White 

Mtns 

Little 

Colorado 

Valley 

Grand Canyon 

Four 

Corners 

Area 

Extrm

SW 

Uinta Basin 

S Cntrl 

Mtns 

Great 

Salt 

Lake Wasatch Mtns 

West Central

Valleys 

San Juan

Mtns 

NW 

Cntrl 

Colorado 

Mtns 

So Platte Valley 

NE 

Palmer Lake Ridge 

or Divide 

Eastern Plains 

Lower Arkansas Valley 

SE 

San Luis

Valley 

North Park 

Rio Grande Valley

Continental Divide 

Sacremento

Mtns 

Sangre De Cristo 

Mtns 

Eastern 

New Mexico Eastern

Plains 

Green River 

Basin 

So Central

Mtns 

SW 

WY Laramie Mtns 

N Platte River Valley

SE 

WY 

Black

Hills 

NE WY 

Big Horn Mtns Big Horn

Basin Wind River Mtns 

Teton 

Mtns 

Snake River Valley 

Central

Mtns

(Sawtooth) 

Yellowstone

Park 

Bitterroot Range 

Flathead Valley 

East 

Slopes of 

Cont Dvd 

SWRN 

Mtns 

Fort Peck Reservoir 

Wind River 

Basin 

E of Cont Dvd 

Pecos River 

West of

Pecos 

Big Bend

Area 

East of

Pecos 

Southwest 

Panhandle 

Northeast 

Southeast 

Coastal Bend 

Southwest Southeast 

Panhandle 

Northeast 

High Plains 

Flint 

Hills 

Marais des Cygnes Basin 

Kansas River Valley 

Blue River Valley Republican

Lower

Valley 

Cheyenne River 

James 

River 

NE Lakes

Region 

Rosebud 

Country 

Pine 

Ridge Area 

Big Bend

Reservoir 

North of 

Black 

Hills 

Lake Lewis and Francis Case Clark 

Dame 

Reservoir 

Missouri 

Slope 

River Valley 

Souris

Sand Hills 

Central Nebraska 

Nebraska

pan

Handle 

Platte River Basin 

SE 

NE 

CA 

NV 

ID 

MT 

ND 

SD 

NE 

KS 

OK 

TX 

WY 

UT 

CO 

AZ 

NM 

Lake Powell 

Red River Valley 

Lower Mississippi Valley 

CHI Chicago BOS Boston 

MIA Miami SFO 

San Francisco 

SLC Salt Lake City 

DFW 

Dallas/Fort Worth 

Lake Mich Shoreline 

phenomena considered potentially hazardous to light aircraft 

and aircraft with limited operational capabilities. 

An AIRMET includes forecast of moderate icing, moderate 

turbulence, sustained surface winds of 30 knots or 

greater, widespread areas of ceilings less than 1,000 feet 

and/or visibilities less than three miles, and extensive 

mountain obscurement. 

Each AIRMET bulletin has a fixed alphanumeric designator, 

numbered sequentially for easy identification, beginning with 

the first issuance of the day. Sierra is the AIRMET code used 

to denote IFR and mountain obscuration; Tango is used to 

denote turbulence, strong surface winds, and low-level wind 

shear; and Zulu is used to denote icing and freezing levels. 

Example: 

BOSS WA 211945 

AIRMET SIERRA UPDT 3 FOR IFR AND MTN OBSCN 

VALID UNTIL 220200 

AIRMET IFT...ME NH VT MA CT RI NY NJ AND CSTL 

WTRS FROM CAR TO YSJ TO 150E ACK TO EWR TO 

YOW TO CAR OCNL CIG BLW 010/VIS BLW 3SM 

PCPN/BR. CONDS CONT BYD 02Z THRU 08Z 

Figure 13-8. Area forecast region map. 

13-11 
 

 

AIRMET MTN OBSCN...ME NH VT MA NY PA 

FROM CAR TO MLT TO CON TO SLT TO SYR TO CAR 

MTNS OCNLY OBSCD BY CLDS/PCPN/BR. CONDS 

CONT BYD 02Z THRU 08Z 

Explanation: 

AIRMET SIERRA was issued for the Boston area at 1945Z 

on the 21st day of the month. SIERRA contains information 

on IFR and/or mountain obscurations. This is the third 

updated issuance of this Boston AIRMET series as indicated 

by “SIERRA UPDT 3” and is valid until 0200Z on the 

22nd. The affected states within the BOS area are: Maine, 

New Hampshire, Vermont, Massachusetts, New York, and 

Pennsylvania. Within an area bounded by: Caribou, ME; 

to Saint Johns, New Brunswick; to 150 nautical miles east 

of Nantucket, MA; to Newark, NJ; to Ottawa, Ontario; 

to Caribou, ME. The effected states within Caribou, ME 

to Millinocket, ME to Concord, NH to Slate Run, PA to 

Syracuse, NY to Caribou, ME will experience ceilings 

below 1,000 feet/visibility below 3 SM, precipitation/mist. 

Conditions will continue beyond 0200Z through 0800Z. 

SIGMET 

SIGMETs (WSs) are inflight advisories concerning nonconvective weather that is potentially hazardous to all 

aircraft. They report weather forecasts that include severe 

icing not associated with thunderstorms, severe or extreme 

turbulence or clear air turbulence (CAT) not associated with 

thunderstorms, dust storms or sandstorms that lower surface 

or inflight visibilities to below three miles, and volcanic ash. 

SIGMETs are unscheduled forecasts that are valid for 4 hours 

unless the SIGMET relates to a hurricane, in which case it 

is valid for 6 hours. 

A SIGMET is issued under an alphabetic identifier, from 

November through Yankee. The first issuance of a SIGMET 

is designated as an Urgent Weather SIGMET (UWS). 

Reissued SIGMETs for the same weather phenomenon are 

sequentially numbered until the weather phenomenon ends. 

Example: 

SFOR WS 100130 

SIGMET ROME02 VALID UNTIL 100530 

OR WA 

FROM SEA TO PDT TO EUG TO SEA 

OCNL SEV CAT BTN FL280 AND FL350 EXPCD 

DUE TO JTSTR. 

CONDS BGNG AFT 0200Z CONTG BYD 0530Z . 

Explanation: 

This is SIGMET Romeo 2, the second issuance for this 

weather phenomenon. It is valid until the 10th day of the 

month at 0530Z time. This SIGMET is for Oregon and 

Washington, for a defined area from Seattle to Portland to 

Eugene to Seattle. It calls for occasional severe clear air 

turbulence between FL280 and FL350 due to the location of 

the jet stream. These conditions will begin after 0200Z and 

continue beyond the forecast scope of this SIGMET of 0530Z. 

Convective Significant Meteorological Information 

(WST) 

A Convective SIGMET (WST) is an inflight weather 

advisory issued for hazardous convective weather that affects 

the safety of every flight. Convective SIGMETs are issued 

for severe thunderstorms with surface winds greater than 50 

knots, hail at the surface greater than or equal to 3⁄4 inch in 

diameter, or tornadoes. They are also issued to advise pilots 

of embedded thunderstorms, lines of thunderstorms, or 

thunderstorms with heavy or greater precipitation that affect 

40 percent or more of a 3,000 square mile or greater region. 

Convective SIGMETs are issued for each area of the 

contiguous 48 states but not Alaska or Hawaii. Convective 

SIGMETs are issued for the eastern (E), western (W), and 

central (C) United States. Each report is issued at 55 minutes 

past the hour, but special Convective SIGMETs can be 

issued during the interim for any reason. Each forecast is 

valid for 2 hours. They are numbered sequentially each day 

from 1–99, beginning at 00Z time. If no hazardous weather 

exists, the convective SIGMET is still issued; however, it 

states “CONVECTIVE SIGMET...NONE.” 

Example: 

MKCC WST 221855 

CONVECTIVE SIGMET 20C 

VALID UNTIL 2055Z 

ND SD 

FROM 90W MOT-GFK-ABR-90W MOT 

INTSFYG AREA SEV TS MOVG FROM 24045KT. TOPS 

ABV FL450. WIND GUSTS TO 60KTS RPRTD. 

TORNADOES...HAIL TO 2 IN... WIND GUSTS TO 

65KTS 

POSS ND PTN 

Explanation: 

Convective SIGMET was issued for the central portion of 

the United States on the 22nd at 1855Z. This is the 20th 

Convective SIGMET issued on the 22nd for the central 

United States as indicated by “20C” and is valid until 2055Z. 

The affected states are North and South Dakota, from 90 

nautical miles west of Minot, ND; to Grand Forks, ND; to 

Aberdeen, SD; to 90 nautical miles west of Minot, ND. An 

intensifying area of severe thunderstorms moving from 240 

degrees at 45 knots (to the northeast). Thunderstorm tops will 

be above FL 450. Wind gusts up to 60 knots were reported. 

13-12 
 

 

Also reported were tornadoes, hail to 2 inches in diameter, and 

wind gusts to 65 knots possible in the North Dakota portion. 

Winds and Temperature Aloft Forecast (FB) 

Winds and temperatures aloft forecasts (FB) provide wind 

and temperature forecasts for specific locations throughout 

the United States, including network locations in Hawaii 

and Alaska. The forecasts are made twice a day based on the 

radiosonde upper air observations taken at 0000Z and 1200Z. 

Altitudes through 12,000 feet are classified as true altitudes, 

while altitudes 18,000 feet and above are classified as 

altitudes and are termed flight levels. Wind direction is 

always in reference to true north, and wind speed is given in 

knots. The temperature is given in degrees Celsius. No winds 

are forecast when a given level is within 1,500 feet of the 

station elevation. Similarly, temperatures are not forecast for 

any station within 2,500 feet of the station elevation. 

If the wind speed is forecast to be greater than 99 knots but 

less than 199 knots, the computer adds 50 to the direction 

and subtracts 100 from the speed. To decode this type of data 

group, the reverse must be accomplished. For example, when 

the data appears as “731960,” subtract 50 from the 73 and 

add 100 to the 19, and the wind would be 230° at 119 knots 

with a temperature of –60 °C. If the wind speed is forecast to 

be 200 knots or greater, the wind group is coded as 99 knots. 

For example, when the data appears as “7799,” subtract 50 

from 77 and add 100 to 99, and the wind is 270° at 199 knots 

or greater. When the forecast wind speed is calm, or less than 

5 knots, the data group is coded “9900,” which means light 

and variable. [Figure 13-9] 

Explanation of Figure 13-9: 

The heading indicates that this FB was transmitted on the 

15th of the month at 1640Z and is based on the 1200Z upper 

air data. The valid time is 1800Z on the same day and should 

be used for the period between 1400Z and 2100Z. The 

heading also indicates that the temperatures above FL240 

are negative. Therefore, the minus sign will be omitted for 

all forecast temperatures above FL240. 

A four-digit data group shows the wind direction in reference 

to true north and the wind speed in knots. The elevation at 

Amarillo, Texas (AMA) is 3,605 feet, so the lowest reportable 

FB KWBC 151640 

DATA BASED ON 151200Z 

VALID 151800Z FOR USE 1400-2100Z 

TEMPS NEGATIVE ABV 24000 

FB 3000 6000 9000 12000 18000 24000 30000 

AMA 2714 2725+00 2625-04 2531-15 2542-27 265842 

DEN 2321-04 2532-08 2434-19 2441-31 235347 

Figure 13-9. Winds and temperature aloft forecast. 

altitude is 6,000 feet for the forecast winds. In this case, 

“2714” means the wind is forecast to be from 270° at a speed 

of 14 knots. 

A six-digit group includes the forecast temperature aloft. 

The elevation at Denver (DEN) is 5,431 feet, so the lowest 

reportable altitude is 9,000 feet for the winds and temperature 

forecast. In this case, “2321-04” indicates the wind is forecast to 

be from 230° at a speed of 21 knots with a temperature of –4 °C. 

Weather Charts 

Weather charts are graphic charts that depict current or 

forecast weather. They provide an overall picture of the 

United States and should be used in the beginning stages of 

flight planning. Typically, weather charts show the movement 

of major weather systems and fronts. Surface analysis, 

weather depiction, and significant weather prognostic charts 

are sources of current weather information. Significant 

weather prognostic charts provide an overall forecast weather 

picture. 

Surface Analysis Chart 

The surface analysis chart depicts an analysis of the current 

surface weather. [Figure 13-10] This chart is transmitted 

every 3 hours and covers the contiguous 48 states and 

adjacent areas. A surface analysis chart shows the areas of 

high and low pressure, fronts, temperatures, dew points, wind 

directions and speeds, local weather, and visual obstructions. 

Surface weather observations for reporting points across 

the United States are also depicted on this chart. Each of 

these reporting points is illustrated by a station model. 

[Figure 13-11] A station model includes: 

•	 Sky cover—the station model depicts total sky cover 

and is shown as clear, scattered, broken, overcast, or 

obscured/partially obscured. 

•	 Sea level pressure—given in three digits to the nearest 

tenth of a millibar (mb). For 1,000 mbs or greater, 

prefix a 10 to the three digits. For less than 1,000 mbs, 

prefix a 9 to the three digits. 

•	 Pressure change/tendency—pressure change in tenths 

of mb over the past 3 hours. This is depicted directly 

below the sea level pressure. 

•	 Dew point—given in degrees Fahrenheit. 

•	 Present weather—over 100 different standard weather 

symbols are used to describe the current weather. 

•	 Temperature—given in degrees Fahrenheit. 

•	 Wind—true direction of wind is given by the wind 

pointer line, indicating the direction from which the 

wind is blowing. A short barb is equal to 5 knots of 

wind, a long barb is equal to 10 knots of wind, and a 

pennant is equal to 50 knots. 

13-13 
 

 

 

Figure 13-10. Surface analysis chart. 

1. Total sky cover: Overcast 

2. Temperature/dew point: 34 °F/32 °F 

3. Wind: From the northwest at 20 knots (relative to true north) 

4. Present weather: Continuous light snow 

5. Sea level pressure: 1014.7 millibars (mb) 

Note: Pressure is always shown in 3 digits to the nearest tenth of a millibar. 

For 1,000 mb or greater, prefix a “10” to the 3 digits 

For less than 1,000 mb, prefix a “9” to the 3 digits 

6. Pressure change in past 3 hours: Increased steadily or unsteadily by 2.8 mb 

Examples of Wind Speed and Direction Plots 

Calm NE/5 kts SW/10 kts N/15 kts W/50 kts S/60 kts

147 

28 / 

34 

32 

** 

Pressure change in past 3 hours 

Pressure tendency 

Sea level pressure 

Wind speed 

Wind direction 

Temperature 

Total sky cover 

Present weather 

Dew point 

Figure 13-11. Sample station model and weather chart symbols. 

13-14 
Weather Depiction Chart 

A weather depiction chart details surface conditions as 

derived from METAR and other surface observations. The 

weather depiction chart is prepared and transmitted by 

computer every 3 hours beginning at 0100Z time and is valid 

data for the forecast period. It is designed to be used for flight 

planning by giving an overall picture of the weather across 

the United States. [Figure 13-12] 

The weather depiction chart also provides a graphic display 

of IFR, VFR, and marginal VFR (MVFR) weather. Areas of 

IFR conditions (ceilings less than 1,000 feet and visibility 

less than three miles) are shown by a hatched area outlined 

by a smooth line. MVFR regions (ceilings 1,000 to 3,000 

feet, visibility 3 to 5 miles) are shown by a nonhatched area 

outlined by a smooth line. Areas of VFR (no ceiling or ceiling 

greater than 3,000 feet and visibility greater than five miles) 

are not outlined. Also plotted are fronts, troughs, and squall 

lines from the previous hours surface analysis chart. 

Weather depiction charts show a modified station model 

that provides sky conditions in the form of total sky cover, 

ceiling height, weather, and obstructions to visibility, but 

does not include winds or pressure readings like the surface 

analysis chart. A bracket ( ] ) symbol to the right of the station 

indicates the observation was made by an automated station. 

Significant Weather Prognostic Charts 

Significant weather prognostic charts are available for lowlevel significant weather from the surface to FL 240 (24,000 

feet), also referred to as the 400 mb level and high-level 

significant weather from FL 250 to FL 630 (25,000 to 63,000 

feet). The primary concern of this discussion is the low-level 

significant weather prognostic chart. 

The low-level chart is is a forecast of aviation weather 

hazards, primarily intended to be used as a guidance product 

for briefing the VFR pilot. The forecast domain covers the 48 

contiguous states, southern Canada and the coastal waters for 

altitudes below 24,000 ft. Low altitude Significant Weather 

charts are issued four times daily and are valid at fixed times: 

0000, 0600, 1200, and 1800 UTC. Each chart is divided on 

the left and right into 12 and 24 hour forecast intervals (based 

on the current NAM model available). 

Figure 13-12. Weather depiction chart. 

13-15 
 

 

Effective September 1, 2015, the four-panel Low Level 

SFC-240 chart was replaced with a two-panel chart. The new 

two-panel chart will be the same as the top two panels in the 

former four-panel chart, depicting the freezing level and areas 

of IFR, MVFR, and moderate or greater turbulence. The bottom 

two panels of the chart have been removed. In lieu of these 

bottom two panels, an enhanced surface chart that includes 

fronts, pressure, precipitation type, precipitation intensity, and 

weather type, is displayed. The green precipitation polygons 

will be replaced by shaded precipitation areas using the 

National Digital Forecast Database (NDFD) weather grid. 

Figure 13-13 depicts the new two-panel significant weather 

prognostic chart, as well as the symbols typically used to 

depict precipitation. The two panels depict freezing levels, 

turbulence, and low cloud ceilings and/or restrictions to 

visibility (shown as contoured areas of MVFR and IFR 

conditions). These charts enable the pilot to pictorially 

evaluate existing and potential weather hazards they may 

encounter. Pilots can balance weather phenomena with 

their aircraft capability and skill set resulting in aeronautical 

decision-making appropriate to the flight. Prognostic charts 

are an excellent source of information for preflight planning; 

however, this chart should be viewed in light of current 

conditions and specific local area forecasts. 

The 36- and 48-hour significant weather prognostic chart is 

an extension of the 12- and 24-hour forecast. This chart is 

issued twice a day. It typically contains forecast positions and 

characteristics of pressure patterns, fronts, and precipitation. 

An example of a 36- and 48-hour surface prognostic chart is 

shown in Figure 13-14. 

ATC Radar Weather Displays 

Although ATC systems cannot always detect the presence 

or absence of clouds, they can often determine the intensity 

of a precipitation area, but the specific character of that area 

(snow, rain, hail, VIRGA, etc.) cannot be determined. For 

this reason, ATC refers to all weather areas displayed on ATC 

radar scopes as “precipitation.” 

ARTCC facilities normally use a Weather and Radar 

Processor (WARP) to display a mosaic of data obtained 

from multiple NEXRAD sites. There is a time delay between 

actual conditions and those displayed to the controller. 

The precipitation data on the ARTCC controller’s display 

could be up to 6 minutes old. The WARP processor is only 

used in ARTCC facilities. All ATC facilities using radar 

weather processors with the ability to determine precipitation 

intensity, describe the intensity to pilots as: 

• Light 

• Moderate 

• Heavy 

• Extreme 

When the WARP is not available, a second system, the 

narrowband Air Route Surveillance Radar (ARSR) can 

display two distinct levels of precipitation intensity that 

is described to pilots as “MODERATE and “HEAVY TO 

EXTREME.” 

ATC facilities that cannot display the intensity levels of 

precipitation due to equipment limitations describe the 

location of the precipitation area by geographic position or 

position relative to the aircraft. Since the intensity level is not 

available, the controller states “INTENSITY UNKNOWN.” 

ATC radar is not able to detect turbulence. Generally, 

turbulence can be expected to occur as the rate of rainfall or 

intensity of precipitation increases. Turbulence associated 

with greater rates of precipitation is normally more severe than 

Figure 13-13. Significant weather prognostic chart. 

13-16 
Figure 13-14. 36- (top) and 48-hour (bottom) surface prognostic chart. 

13-17 
any associated with lesser rates of precipitation. Turbulence 

should be expected to occur near convective activity, even 

in clear air. Thunderstorms are a form of convective activity 

that imply severe or greater turbulence. Operation within 

20 miles of thunderstorms should be approached with great 

caution, as the severity of turbulence can be much greater than 

the precipitation intensity might indicate. 

Weather Avoidance Assistance 

To the extent possible, controllers will issue pertinent 

information on weather and assist pilots in avoiding such 

areas when requested. Pilots should respond to a weather 

advisory by either acknowledging the advisory or by 

acknowledging the advisory and requesting an alternative 

course of action as follows: 

•	 Request to deviate off course by stating the number 

of miles and the direction of the requested deviation. 

•	 Request a new route to avoid the affected area. 

•	 Request a change of altitude. 

•	 Request radar vectors around the affected areas. 

The controller’s primary function is to provide safe separation 

between aircraft. Any additional service, such as weather 

avoidance assistance, can only be provided to the extent 

that it does not detract from the primary function. It’s also 

worth noting that the separation workload is generally greater 

than normal when weather disrupts the usual flow of traffic. 

ATC radar limitations and frequency congestion may also 

be a factor in limiting the controller’s capability to provide 

additional service. 

Electronic Flight Displays (EFD) /MultiFunction Display (MFD) Weather 

Many aircraft manufacturers now include data link weather 

services with new electronic flight display (EFD) systems. 

EFDs give a pilot access to many of the data link weather 

services available. 

Products available to a pilot on the display pictured in 

Figure 13-15 are listed as follows. The letters in parentheses 

indicate the soft key to press in order to access the data. 

•	 Graphical NEXRAD data (NEXRAD) 

•	 Graphical METAR data (METAR) 

•	 Textual METAR data 

•	 Textual terminal aerodrome forecasts (TAF) 

•	 City forecast data 

•	 Graphical wind data (WIND) 

•	 Graphical echo tops (ECHO T,,,OPS) 

•	 Graphical cloud tops (CLD TOPS) 

•	 Graphical lightning strikes (LTNG) 

•	 Graphical storm cell movement (CELL MOV) 

•	 NEXRAD radar coverage (information displayed with 

the NEXRAD data) 

•	 SIGMETs/AIRMETs (SIG/AIR) 

•	 Surface analysis to include city forecasts (SFC) 

•	 County warnings (COUNTY) 

•	 Freezing levels (FRZ LVL) 

•	 Hurricane track (CYCLONE) 

•	 Temporary flight restrictions (TFR) 

Pilots must be familiar with any EFD or MFD used and the 

data link weather products available on the display. 

Weather Products Age and Expiration 

The information displayed using a data link weather link is 

near real time but should not be thought of as instantaneous, 

up-to-date information. Each type of weather display is 

stamped with the age information on the MFD. The time is 

referenced from Zulu when the information was assembled at 

the ground station. The age should not be assumed to be the 

time when the FIS received the information from the data link. 

Two types of weather are displayed on the screen: “current” 

weather and forecast data. Current information is displayed 

by an age while the forecast data has a data stamp in the form 

of “__ / __ __ : __.” [Figure 13-16] 

The Next Generation Weather Radar System 

(NEXRAD) 

The NEXRAD system is comprised of a series of 159 Weather 

Surveillance Radar–1988 Doppler (WSR-88D) sites situated 

throughout the United States, as well as selected overseas 

sites. The NEXRAD system is a joint venture between the 

United States Department of Commerce (DOC), the United 

States DOD, as well as the United States Department of 

Transportation (DOT). The individual agencies that have 

control over the system are the NWS, Air Force Weather 

Agency (AFWA) and the FAA. [Figure 13-17] 

NEXRAD data for up to a 2,000 mile range can be displayed. 

It is important to realize that the radar image is not real time 

and can be up to 5 minutes old. The NTSB has reported on 2 

fatal accidents where in-cockpit NEXRAD mosaic imagery 

was available to pilots operating near quickly-developing and 

fast-moving convective weather. In one of these accidents, 

the images were from 6 to 8 minutes old. In some cases, 

NEXRAD data can age significantly by the time the mosaic 

image is created. In some extreme latency cases, the actual 

13-18 
Figure 13-15. Information page. 

age of the oldest NEXRAD data in the mosaic can exceed 

the age indication in the cockpit by 15 to 20 minutes. Even 

small-time differences between the age indicator and actual 

conditions can be important for safety of flight, especially 

when considering fast-moving weather hazards, quickly 

developing weather scenarios, and/or fast-moving aircraft. 

At no time should the images be used as storm penetrating 

radar nor to navigate through a line of storms. The images 

display should only be used as a reference. 

NEXRAD radar is mutually exclusive of Topographic 

(TOPO), TERRAIN and STORMSCOPE. When NEXRAD 

is turned on, TOPO, TERRAIN, and STORMSCOPE are 

turned off because the colors used to display intensities are 

very similar. 

Lightning information is available to assist when NEXRAD 

is enabled. This presents a more comprehensive picture of 

the weather in the surrounding area. 

In addition to utilizing the soft keys to activate the NEXRAD 

display, the pilot also has the option of setting the desired 

range. It is possible to zoom in on a specific area of the 

display in order to gain a more detailed picture of the radar 

display. [Figure 13-18] 

What Can Pilots Do? 

Remember that the in-cockpit NEXRAD display depicts 

where the weather WAS, not where it IS. The age indicator 

does not show the age of the actual weather conditions, 

but rather the age of the mosaic image. The actual weather 

conditions could be up to 15 to 20 minutes OLDER than 

the age indicated on the display. You should consider this 

NORTH UP 

NEXRAD 

RAIN 

MIX 

SNOW 

H 

E 

A 

V 

Y 

L 

I 

G 

H 

T 

SIGMET 

AIRMET 

__/__ __:__ 

__/__ __:__ 

Figure 13-16. List of weather products and the expiration times of each. 

13-19 
Figure 13-17. NEXRAD radar display. 

Figure 13-18. NEXRAD radar display (500 mile range). The individual color gradients can be easily discerned and interpreted via the 

legend in the upper right corner of the screen. Additional information can be gained by pressing the LEGEND soft key, which displays 

the legend page. 

13-20 
 

 

 

 

 

potential delay when using in-cockpit NEXRAD capabilities, 

as the movement and/or intensification of weather could 

adversely affect safety of flight. 

•	 Understand that the common perception of a “5-minute 

latency” with radar data is not always correct. 

•	 Get your preflight weather briefing! Having in-cockpit 

weather capabilities does not circumvent the need for 

a complete weather briefing before takeoff. 

• Use all appropriate sources of weather information to 

make in-flight decisions. 

• Let your fellow pilots know about the limitations of 

in-cockpit NEXRAD. 

NEXRAD Abnormalities 

Although NEXRAD is a compilation of stations across 

the country, there can be abnormalities associated with the 

system. Some of the abnormalities are listed below. 

•	 Ground clutter 

•	 Strobes and spurious radar data 

•	 Sun strobes, when the radar antenna points directly at 

the sun 

•	 Interference from buildings or mountains that may 

cause shadows 

•	 Military aircraft that deploy metallic dust and may 

reflect the radar signature 

NEXRAD Limitations 

In addition to the abnormalities listed, the NEXRAD system 

does have some specific limitations. 

Base Reflectivity 

The NEXRAD base reflectivity does not provide adequate 

information from which to determine cloud layers or type 

of precipitation with respect to hail versus rain. Therefore, a 

pilot may mistake rain for hail. 

In addition, the base reflectivity is sampled at the minimum 

antenna elevation angle. With this minimum angle, an 

individual site cannot depict high altitude storms directly 

over the station. This leaves an area of null coverage if an 

adjacent site does not also cover the affected area. 

Resolution Display 

The resolution of the displayed data poses additional concerns 

when the range is decreased. The minimum resolution for 

NEXRAD returns is 1.24 miles. This means that when the 

display range is zoomed in to approximately ten miles, the 

individual square return boxes are more prevalent. Each 

square indicates the strongest display return within that 1.24 

mile square area. 

AIRMET/SIGMET Display 

AIRMET/SIGMET information is available for the displayed 

viewing range on the MFD. Some displays are capable of 

displaying weather information for a 2,000 mile range. 

AIRMETS/SIGMETS are displayed by dashed lines on the 

map. [Figure 13-19] 

The legend box denotes the various colors used to depict the 

AIRMETs, such as icing, turbulence, IFR weather, mountain 

obscuration, and surface winds. [Figure 13-20] The great 

advantage of the graphically displayed AIRMET/SIGMET 

boundary box is the pilot can see the extent of the area that 

the advisory covers. The pilot does not need to manually plot 

the points to determine the full extent of the coverage area. 

Graphical METARs 

METARs can be displayed on the MFD. Each reporting 

station that has a METAR/TAF available is depicted by a flag 

from the center of the airport symbol. Each flag is color coded 

to depict the type of weather that is currently reported at that 

station. A legend is available to assist users in determining 

what each flag color represents. [Figure 13-21] 

The graphical METAR display shows all available reporting 

stations within the set viewing range. By setting the range 

knob up to a 2,000 mile range, pilots can pan around the 

display map to check the current conditions of various 

airports along the route of flight. 

By understanding what each colored flag indicates, a pilot can 

quickly determine where weather patterns display marginal 

weather, IFR, or areas of VFR. These flags make it easy to 

determine weather at a specific airport should the need arise 

to divert from the intended airport of landing. 

Data Link Weather 

Pilots now have the capability of receiving continuously 

updated weather across the entire country at any altitude. 

No longer are pilots restricted by radio range or geographic 

isolations, such as mountains or valleys. 

In addition, pilots no longer have to request specific 

information from weather briefing personnel directly. When 

the weather becomes questionable, radio congestion often 

increases, delaying the timely exchange of valuable inflight 

weather updates for a pilot’s specific route of flight. Flight 

Service Station (FSS) personnel can communicate with only 

one pilot at a time, which leaves other pilots waiting and 

flying in uncertain weather conditions. Data link weather 

13-21 
Figure 13-19. The AIRMET information box instructs the pilot to press the ENTER button soft key (ENT) to gain additional information 

on the selected area of weather. Once the ENTER soft key (ENT) is depressed, the specific textual information is displayed on the right 

side of the screen. 

Figure 13-20. SIGMET/AIRMET legend display. 

13-22 
 

Figure 13-21. Graphical METAR legend display. 

provides the pilot with a powerful resource for enhanced 

situational awareness at any time. Due to continuous data link 

broadcasts, pilots can obtain a weather briefing by looking at 

a display screen. Pilots have a choice between FAA-certified 

devices or portable receivers as a source of weather data. 

Data Link Weather Products 

Flight Information Service- Broadcast (FIS-B) 

Flight Information Service–Broadcast (FIS-B) is a ground 

broadcast service provided through the Automatic Dependent 

Surveillance–Broadcast (ADS-B) Services network over 

the 978 MHz UAT data link. The FAA FIS-B system 

provides pilots and flight crews of properly-equipped aircraft 

with a flightdeck display of certain aviation weather and 

aeronautical information which are listed below. 

•	 Aviation Routine Weather Reports (METARs) 

•	 Special Aviation Reports (SPECIs) 

•	 Terminal Area Forecasts (TAFs) and their amendments 

•	 NEXRAD (regional and CONUS) precipitation maps 

•	 Notice to Airmen (NOTAM) Distant and Flight Data 

Center 

•	 Airmen’s Meteorological Conditions (AIRMET) 

•	 Significant Meteorological Conditions (SIGMET) and 

Convective SIGMET 

•	 Status of Special Use Airspace (SUA) 

•	 Temporary Flight Restrictions (TFRs) 

•	 Winds and Temperatures Aloft. 

•	 Pilot Reports (PIREPS) 

•	 TIS-B service status 

The weather products provided by FIS-B are for information 

only. Therefore, these products do notmeet the safety and 

regulatory requirements of official weather products. The 

weather products displayed on FIS-B should not be used 

as primary weather products (i.e., aviation weather to meet 

operational and safety requirements). Each aircraft system is 

different and some of the data that is rendered can be up to 

20 or 30 minutes old and not current. Pilots should consult 

the individual equipment manuals for specific delay times. 

13-23 
 

 

 

 

 

 

Pilot Responsibility 

It is important for pilots to understand the realization that the 

derived safety benefits of data link depends heavily upon the 

pilot’s understanding of the specific system’s capabilities and 

limitations which are listed below. 

•	 Product latency—be aware of the time stamp or “valid 

until” time on the particular data link information 

displayed in the flightdeck. For example, since initial 

processing and transmission of NEXRAD data can 

take several minutes, pilots must assume that data 

link weather information will always be a minimum 

of seven to eight minutes older than shown on the time 

stamp and only use data link weather radar images for 

broad strategic avoidance of adverse weather. 

• Product update cycles—be aware of when and how 

often a product is updated as well as the Data Link 

Service Providers (DLSP) update rate for particular 

products. 

• Indication of system failure—be aware of partial or 

total system failure indications. 

•	 Coverage areas/service volume—coverage limitations 

are associated with the type of data link network 

being used. For example, ground-based systems that 

require a line-of-sight may have relatively limited 

coverage below 5,000 feet AGL. Satellite-based data 

link weather systems can have limitations stemming 

from whether the network is in geosynchronous orbit 

or low earth orbit. Also, NWS NEXRAD coverage 

has gaps, especially in the western states. 

• Content/format—since service providers often refine 

or enhance data link products for flightdeck display, 

pilots must be familiar with the content, format, and 

meaning of symbols and displays (i.e., the legend) in 

the specific system. 

•	 Data integrity/limitations to use—reliability of 

information depicted. Be aware of any applicable 

disclaimer provided by the service provider. 

•	 Use of equipment/avionics display—pilots remain 

responsible for the proper use of an electronic flight 

bag (EFB) or installed avionics. Pilots should be 

cognizant that, per the FAA Practical Test Standards, 

they may be evaluated on the use and interpretation 

of an EFB or installed avionics on the aircraft. 

•	 Overload of Information—most DLSPs offer 

numerous products with information that can be 

layered on top of each other. Pilots need to be aware 

that too much information can have a negative effect 

on their cognitive work load. Pilots need to manage the 

amount of information to a level that offers the most 

pertinent information to that specific flight without 

creating a distraction. Pilots may need to adjust the 

amount of information based on numerous factors 

including, but not limited to, the phase of flight, single 

pilot operation, autopilot availability, class of airspace, 

and the weather conditions encountered. 

Chapter Summary 

While no weather forecast is guaranteed to be 100 percent 

accurate, pilots have access to a myriad of weather information 

on which to base flight decisions. Weather products available 

for preflight planning to en route information received over 

the radio or via data link provide the pilot with the most 

accurate and up-to-date information available. Each report 

provides a piece of the weather puzzle. Pilots must use several 

reports to get an overall picture and gain an understanding 

of the weather that affects the safe completion of a flight. 

13-24 
14-1 

Introduction 

Each time a pilot operates an aircraft, the flight normally 

begins and ends at an airport. An airport may be a small sod 

field or a large complex utilized by air carriers. This chapter 

examines airport operations, identifies features of an airport 

complex, and provides information on operating on or in the 

vicinity of an airport. 

Airport Categories 

The definition for airports refers to any area of land or water 

used or intended for landing or takeoff of aircraft. This 

includes, within the five categories of airports listed below, 

special types of facilities including seaplane bases, heliports, 

and facilities to accommodate tilt rotor aircraft. An airport 

includes an area used or intended for airport buildings, 

facilities, as well as rights of way together with the buildings 

and facilities. 

Airport

Operations 

Chapter 14 
 

The law defines airports by categories of airport activities, Towered Airport 

including commercial service, primary, cargo service, A towered airport has an operating control tower. Air traffic 

reliever, and general aviation airports, as shown below: control (ATC) is responsible for providing the safe, orderly, 

•	 Commercial Service Airports—publicly owned 

airports that have at least 2,500 passenger boardings 

each calendar year and receive scheduled passenger 

service. Passenger boardings refer to revenue passenger 

boardings on an aircraft in service in air commerce 

whether or not in scheduled service. The definition 

also includes passengers who continue on an aircraft 

in international flight that stops at an airport in any of 

the 50 States for a non-traffic purpose, such as refueling 

or aircraft maintenance rather than passenger activity. 

Passenger boardings at airports that receive scheduled 

passenger service are also referred to as Enplanements. 

•	 Cargo Service Airports—airports that, in addition to any 

other air transportation services that may be available, 

are served by aircraft providing air transportation of 

only cargo with a total annual landed weight of more 

than 100 million pounds. “Landed weight” means the 

weight of aircraft transporting only cargo in intrastate, 

interstate, and foreign air transportation. An airport 

may be both a commercial service and a cargo service 

airport. 

•	 Reliever Airports—airports designated by the FAA 

to relieve congestion at Commercial Service Airports 

and to provide improved general aviation access to the 

overall community. These may be publicly or privatelyowned. 

•	 General Aviation Airports — the remaining airports 

are commonly described as General Aviation Airports. 

This airport type is the largest single group of airports 

in the U.S. system. The category also includes privately 

owned, public use airports that enplane 2500 or more 

passengers annually and receive scheduled airline 

service. 

Types of Airports 

There are two types of airports—towered and nontowered. 

These types can be further subdivided to: 

•	 Civil Airports—airports that are open to the general 

public. 

•	 Military/Federal Government airports—airports 

operated by the military, National Aeronautics and 

Space Administration (NASA), or other agencies of 

the Federal Government. 

•	 Private Airports—airports designated for private or 

restricted use only, not open to the general public. 

and expeditious flow of air traffic at airports where the 

type of operations and/or volume of traffic requires such a 

service. Pilots operating from a towered airport are required 

to maintain two-way radio communication with ATC and to 

acknowledge and comply with their instructions. Pilots must 

advise ATC if they cannot comply with the instructions issued 

and request amended instructions. A pilot may deviate from 

an air traffic instruction in an emergency, but must advise 

ATC of the deviation as soon as possible. 

Nontowered Airport 

A nontowered airport does not have an operating control 

tower. Two-way radio communications are not required, 

although it is a good operating practice for pilots to transmit 

their intentions on the specified frequency for the benefit 

of other traffic in the area. The key to communicating at an 

airport without an operating control tower is selection of the 

correct common frequency. The acronym CTAF, which stands 

for Common Traffic Advisory Frequency, is synonymous 

with this program. A CTAF is a frequency designated for 

the purpose of carrying out airport advisory practices while 

operating to or from an airport without an operating control 

tower. The CTAF may be a Universal Integrated Community 

(UNICOM), MULTICOM, Flight Service Station (FSS), or 

tower frequency and is identified in appropriate aeronautical 

publications. UNICOM is a nongovernment air/ground radio 

communication station that may provide airport information 

at public use airports where there is no tower or FSS. On pilot 

request, UNICOM stations may provide pilots with weather 

information, wind direction, the recommended runway, or 

other necessary information. If the UNICOM frequency 

is designated as the CTAF, it is identified in appropriate 

aeronautical publications. Figure 14-1 lists recommended 

communication procedures. More information regarding 

radio communications is provided later in this chapter. 

Nontowered airport traffic patterns are always entered at 

pattern altitude. How you enter the pattern depends upon the 

direction of arrival. The preferred method for entering from 

the downwind side of the pattern is to approach the pattern 

on a course 45 degrees to the downwind leg and join the 

pattern at midfield. 

There are several ways to enter the pattern if you’re coming 

from the upwind leg side of the airport. One method of entry 

from the opposite side of the pattern is to announce your 

intentions and cross over midfield at least 500 feet above 

14-2 
 

 

UNICOM 

(no tower or FSS) 

No tower, FSS, 

or UNICOM 

No tower in 

operation, FSS open 

FSS closed 

(no tower) 

Tower or FSS 

not in operation 

Communicate with UNICOM 

station on published CTAF 

frequency (122.7, 122.8, 122.725, 

122.975, or 123.0). If unable to 

contact UNICOM station, use selfannounce procedures on CTAF. 

Self-announce on MULTICOM 

frequency 122.9. 

Communicate with FSS on CTAF 

frequency. 

Self-announce on CTAF. 

Self-announce on CTAF. 

Before taxiing and 

before taxiing on the 

runway for departure. 

Before taxiing and 

before taxiing on the 

runway for departure. 

Before taxiing and 

before taxiing on the 

runway for departure. 

Before taxiing and 

before taxiing on the 

runway for departure. 

Before taxiing and 

before taxiing on the 

runway for departure. 

10 miles out. 

Entering downwind, 

base, and final. 

Leaving the runway. 

10 miles out. 

Entering downwind, 

base, and final. 

Leaving the runway. 

10 miles out. 

Entering downwind, 

base, and final. 

Leaving the runway. 

10 miles out. 

Entering downwind, 

base, and final. 

Leaving the runway. 

10 miles out. 

Entering downwind, 

base, and final. 

Leaving the runway. 

Facility at Airport Frequency Use 

Communication/Broadcast Procedures 

Departing final 

approach fix (name) 

or on final approach 

segment inbound. 

Approach 

completed/terminated. 

Practice Instrument 

Approach Outbound Inbound 

Figure 14-1. Recommended communication procedures. 

pattern altitude (normally 1,500 feet AGL.) However, if large or 

turbine aircraft operate at your airport, it is best to remain 2,000 

feet AGL so you are not in conflict with their traffic pattern. 

When well clear of the pattern—approximately 2 miles–scan 

carefully for traffic, descend to pattern altitude, then turn right 

to enter at 45° to the downwind leg at midfield. [Figure 14-2] 

An alternate method is to enter on a midfield crosswind at 

pattern altitude, carefully scan for traffic, announce your 

intentions, and then turn downwind. [Figure 14-3] This 

technique should not be used if the pattern is busy. Always 

remember to give way to aircraft on the preferred 45° entry 

and to aircraft already established on downwind. 

In either case, it is vital to announce your intentions, and 

remember to scan outside. Before joining the downwind 

leg, adjust your course or speed to blend into the traffic. 

Adjust power on the downwind leg, or sooner, to fit into 

the flow of traffic. Avoid flying too fast or too slow. Speeds 

recommended by the airplane manufacturer should be used. 

They will generally fall between 70 to 80 knots for fixed-gear 

singles and 80 to 90 knots for high-performance retractable. 

Sources for Airport Data 

When a pilot flies into a different airport, it is important to 

review the current data for that airport. This data provides the 

pilot with information, such as communication frequencies, 

services available, closed runways, or airport construction. 

Three common sources of information are: 

•	 Aeronautical Charts 

•	 Chart Supplement U.S. (formerly Airport/Facility 

Directory) 

•	 Notices to Airmen (NOTAMs) 

•	 Automated Terminal Information Service (ATIS) 

Aeronautical Charts 

Aeronautical charts provide specific information on airports. 

Chapter 16, “Navigation,” contains an excerpt from an 

aeronautical chart and an aeronautical chart legend, which 

provides guidance on interpreting the information on the chart. 

Chart Supplement U.S. (formerly Airport/Facility 

Directory) 

The Chart Supplement U.S. (formerly Airport/Facility 

Directory) provides the most comprehensive information on 

a given airport. It contains information on airports, heliports, 

and seaplane bases that are open to the public. The Chart 

Supplement U.S. is published in seven books, which are 

organized by regions and are revised every 56 days. The 

Chart Supplement U.S. is also available digitally at www. 

14-3 
 

 

Pattern altitude 

+500 feet 

Descend to 

pattern altitude, 

then turn 

Yield to 

downwind 

traffic and 

enter 

midfield 

downwind 

at 45° 

1 

3 

4 

Fly clear of 

traffic pattern 

(approx. 2 mi.) 

2 

Yield to the preferred

45° and downwind 

traffic, then turn

downwind 

Pattern altitude 

Figure 14-2. Preferred Entry-Crossing Midfield. Figure 14-3. Alternate Midfield Entry. 

faa.gov/air_traffic/flight_info/aeronav. Figure 14-4 contains 

an excerpt from a directory. For a complete listing 

of information provided in a Chart Supplement U.S. 

and how the information may be decoded, refer to the 

“Legend Sample” located in the front of each Chart 

Supplement U.S. 

In addition to airport information, each Chart Supplement 

U.S. contains information such as special notices, Federal 

Aviation Administration (FAA) and National Weather 

Service (NWS) telephone numbers, preferred instrument 

flight rules (IFR) routing, visual flight rules (VFR) waypoints, 

a listing of very high frequency (VHF) omnidirectional range 

(VOR) receiver checkpoints, aeronautical chart bulletins, land 

and hold short operations (LAHSO) for selected airports, 

airport diagrams for selected towered airports, en route 

flight advisory service (EFAS) outlets, parachute jumping 

areas, and facility telephone numbers. It is beneficial 

to review a Chart Supplement U.S. to become familiar 

with the information it contains. 

Notices to Airmen (NOTAM) 

Time-critical aeronautical information, which is of a temporary 

nature or not sufficiently known in advance to permit 

publication, on aeronautical charts or in other operational Figure 14-4. Chart Supplement U.S. (formerly Airport/Facility

Directory excerpt. 

14-4 
 

 

 

 

publications receives immediate dissemination by the 

NOTAM system. The NOTAM information could affect your 

decision to make the flight. It includes such information as 

taxiway and runway closures, construction, communications, 

changes in status of navigational aids, and other information 

essential to planned en route, terminal, or landing operations. 

Exercise good judgment and common sense by carefully 

regarding the information readily available in NOTAMs. 

Prior to any flight, pilots should check for any NOTAMs that 

could affect their intended flight. For more information on 

NOTAMs, refer back to Chapter 1, “Pilot and Aeronautical 

Information” section. 

Automated Terminal Information Service (ATIS) 

The Automated Terminal Information Service (ATIS) is a 

recording of the local weather conditions and other pertinent 

non-control information broadcast on a local frequency in a 

looped format. It is normally updated once per hour but is 

updated more often when changing local conditions warrant. 

Important information is broadcast on ATIS including 

weather, runways in use, specific ATC procedures, and any 

airport construction activity that could affect taxi planning. 

When the ATIS is recorded, it is given a code. This code is 

changed with every ATIS update. For example, ATIS Alpha 

is replaced by ATIS Bravo. The next hour, ATIS Charlie is 

recorded, followed by ATIS Delta and progresses down the 

alphabet. 

Prior to calling ATC, tune to the ATIS frequency and listen to 

the recorded broadcast. The broadcast ends with a statement 

containing the ATIS code. For example, “Advise on initial 

contact, you have information Bravo.” Upon contacting the 

tower controller, state information Bravo was received. This 

allows the tower controller to verify the pilot has the current 

local weather and airport information without having to 

state it all to each pilot who calls. This also clears the tower 

frequency from being overtaken by the constant relay of 

the same information, which would result without an ATIS 

broadcast. The use of ATIS broadcasts at departure and arrival 

airports is not only a sound practice but a wise decision. 

Airport Markings and Signs 

There are markings and signs used at airports that provide 

directions and assist pilots in airport operations. It is important 

for you to know the meanings of the signs, markings, and lights 

that are used on airports as surface navigational aids. All airport 

markings are painted on the surface, whereas some signs are 

vertical and some are painted on the surface. An overview of the 

most common signs and markings are described on the following 

pages. Additional information may be found in Chapter 2, 

“Aeronautical Lighting and Other Airport Visual Aids,” of 

the Aeronautical Information Manual (AIM). 

Runway Markings and Signs 

Runway markings vary depending on the type of operations 

conducted at the airport. A basic VFR runway may only 

have centerline markings and runway numbers. Refer to 

Appendix C of this publication for an example of the most 

common runway markings that are found at airports. 

Since aircraft are affected by the wind during takeoffs and 

landings, runways are laid out according to the local prevailing 

winds. Runway numbers are in reference to magnetic north. 

Certain airports have two or even three runways laid out in the 

same direction. These are referred to as parallel runways and 

are distinguished by a letter added to the runway number (e.g., 

runway 36L (left), 36C (center), and 36R (right)). 

Relocated Runway Threshold 

It is sometimes necessary, due to construction or runway 

maintenance, to close only a portion of a runway. When 

a portion of a runway is closed, the runway threshold is 

relocated as necessary. It is referred to as a relocated threshold 

and methods for identifying the relocated threshold vary. A 

common way for the relocated threshold to be marked is 

a ten foot wide white bar across the width of the runway. 

[Figure 14-5A and B] 

When the threshold is relocated, the closed portion of the 

runway is not available for use by aircraft for takeoff or 

landing, but it is available for taxi. When a threshold is 

relocated, it closes not only a set portion of the approach 

end of a runway, but also shortens the length of the opposite 

direction runway. Yellow arrow heads are placed across the 

width of the runway just prior to the threshold bar. 

Displaced Threshold 

A displaced threshold is a threshold located at a point on 

the runway other than the designated beginning of the 

runway. Displacement of a threshold reduces the length 

of runway available for landings. The portion of runway 

behind a displaced threshold is available for takeoffs in either 

direction, or landings from the opposite direction. A ten feet 

wide white threshold bar is located across the width of the 

runway at the displaced threshold, and white arrows are 

located along the centerline in the area between the beginning 

of the runway and displaced threshold. White arrow heads 

are located across the width of the runway just prior to the 

threshold bar. [Figure 14-6A and B] 

14-5 
A B 

36

Figure 14-5. (A) Relocated runway threshold drawing. (B) Relocated threshold for Runway 36 at Joplin Regional Airport (JLN). 

Runway Safety Area 

The runway safety area (RSA) is a defined surface 

surrounding the runway prepared, or suitable, for reducing 

the risk of damage to airplanes in the event of an undershoot, 

overshoot, or excursion from the runway. The dimensions 

of the RSA vary and can be determined by using the 

criteria contained within AC 150/5300-13, Airport Design, 

Chapter 3. Figure 3-1 in AC 150/5300-13 depicts the RSA. 

Additionally, it provides greater accessibility for firefighting 

and rescue equipment in emergency situations. 

The RSA is typically graded and mowed. The lateral 

boundaries are usually identified by the presence of the 

runway holding position signs and markings on the adjoining 

taxiway stubs. Aircraft should not enter the RSA without 

making sure of adequate separation from other aircraft during 

operations at uncontrolled airports. [Figure 14-7] 

Runway Safety Area Boundary Sign 

Some taxiway stubs also have a runway safety area boundary 

sign that faces the runway and is visible to you only when 

exiting the runway. This sign has a yellow background with 

black markings and is typically used at towered airports 

where a controller commonly requests you to report clear of 

a runway. This sign is intended to provide you with another 

visual cue that is used as a guide to determine when you are 

clear of the runway safety boundary area. The sign shown in 

Figure 14-8 is what you would see when exiting the runway at 

Taxiway Kilo. You are out of the runway safety area boundary 

when the entire aircraft passes the sign and the accompanying 

surface painted marking. 

Runway Holding Position Sign 

Noncompliance with a runway holding position sign may 

result in the FAA filing a Pilot Deviation against you. A 

14-6 
A 

17

×

×

B 

Figure 14-6. (A) Displaced runway threshold drawing. (B) Displaced threshold for Runway 17 at Albuquerque International Airport (ABQ). 

runway holding position sign is an airport version of a 

stop sign. [Figure 14-9] It may be seen as a sign and/or its 

characters painted on the airport pavement. The sign has 

white characters outlined in black on a red background. It is 

always collocated with the surface painted holding position 

markings and is located where taxiways intersect runways. 

On taxiways that intersect the threshold of the takeoff runway, 

only the designation of the runway may appear on the sign. 

If a taxiway intersects a runway somewhere other than at 

the threshold, the sign has the designation of the intersecting 

runway. The runway numbers on the sign are arranged to 

correspond to the relative location of the respective runway 

thresholds. Figure 14-10 shows “18-36” to indicate the 

threshold for Runway 18 is to the left and the threshold for 

Figure 14-8. Runway safety area boundary sign and marking located 

on Taxiway Kilo. 

27

9

A 9 B 27

9 C 

Typical Runway Safety Area 

Figure 14-7. Runway Safety Area. 

Figure 14-9. Runway holding position sign at takeoff end of Runway 

14 with collocated Taxiway Alpha location sign. 

14-7 
 

Figure 14-10. Runway holding position sign at a location other 

than the takeoff end of Runway 18-36 with collocated Taxiway 

Alpha location sign. 

Runway 36 is to the right. The sign also indicates that you 

are located on Taxiway Alpha. 

If the runway holding position sign is located on a taxiway 

at the intersection of two runways, the designations for 

both runways are shown on the sign along with arrows 

showing the approximate alignment of each runway. 

[Figure 14-11A and B] In addition to showing the 

approximate runway alignment, the arrows indicate the 

direction(s) to the threshold of the runway whose designation 

is immediately next to each corresponding arrow. 

This type of taxiway and runway/runway intersection 

geometry can be very confusing and create navigational 

challenges. Extreme caution must be exercised when taxiing 

onto or crossing this type of intersection. Figure 14-11A and 

B shows a depiction of a taxiway, runway/runway intersection 

and is also designated as a “hot spot” on the airport diagram. 

In the example, Taxiway Bravo intersects with two runways, 

31-13 and 35-17, which cross each other. 

Surface painted runway holding position signs may also be 

used to aid you in determining the holding position. These 

markings consist of white characters on a red background 

and are painted on the left side of the taxiway centerline. 

Figure 14-12 shows a surface painted runway holding 

position sign that is the holding point for Runway 32R-14L. 

You should never allow any part of your aircraft to cross the 

runway holding position sign (either a vertical or surface 

painted sign) without a clearance from ATC. Doing so poses 

a hazard to yourself and others. 

When the tower is closed or you are operating at a nontowered 

airport, you may taxi past a runway holding position sign only 

when the runway is clear of aircraft, and there are no aircraft on 

final approach. You may then proceed with extreme caution. 

Runway Holding Position Marking 

Noncompliance with a runway holding position marking 

may result in the FAA filing a Pilot Deviation against you. 

Runway holding position markings consist of four yellow 

lines, two solid and two dashed, that are painted on the surface 

and extend across the width of the taxiway to indicate where 

the aircraft should stop when approaching a runway. These 

markings are painted across the entire taxiway pavement, are 

in alignment, and are collocated with the holding position 

sign as described above. 

As you approach the runway, two solid yellow lines and two 

dashed lines will be visible. Prior to reaching the solid lines, it 

is imperative to stop and ensure that no portion of the aircraft 

intersects the first solid yellow line. Do not cross the double 

solid lines until a clearance from ATC has been received. 

[Figure 14-13] When the tower is closed or when operating at 

a nontowered airport, you may taxi onto or across the runway 

only when the runway is clear and there are no aircraft on final 

approach. You should use extreme caution when crossing or 

taxiing onto the runway and always look both ways. 

When exiting the runway, the same markings will be seen 

except the aircraft will be approaching the double dashed 

lines. [Figure 14-14] In order to be clear of the runway, the 

entire aircraft must cross both the dashed and solid lines. 

An ATC clearance is not needed to cross this marking when 

exiting the runway. 

Runway Distance Remaining Signs 

Runway distance remaining signs have a black background 

with a white number and may be installed along one or both 

sides of the runway. [Figure 14-15] The number on the 

signs indicates the distance, in thousands of feet, of landing 

runway remaining. The last sign, which has the numeral “1,” 

is located at least 950 feet from the runway end. 

Runway Designation Marking 

Runway numbers and letters are determined from the 

approach direction. The runway number is the whole number 

nearest one-tenth the magnetic azimuth of the centerline of the 

runway, measured clockwise from the magnetic north. In the 

case where there are parallel runways, the letters differentiate 

between left (L), right (R), or center (C). [Figure 14-16] For 

example, if there are two parallel runways, they would show 

the designation number and then either L or R beneath it. 

For three parallel runways, the designation number would 

be presented with L, C, or R beneath it. 

14-8 
NC-3, 08 MAR 2012 to 05 APR 2012 

NC-3, 08 MAR 2012 to 05 APR 2012 

Not to be used for navigation

35 35-17 

31-13 

B 31-13 35-17 

A 

B 

Runway 13 

Runway 31 

Figure 14-11. (A) Taxiway Bravo location sign collocated with runway/runway intersection holding signs at Sioux Gateway Airport 

(SUX) (B) Airport diagram of Sioux Gateway Airport (SUX), Sioux City, Iowa. The area outlined in red is a designated “hot spot” (HS1). 

14-9 
Figure 14-12. Surface painted runway holding position signs for 

Runway 32R-14L along with the enhanced taxiway centerline marking. 

Figure 14-13. Surface painted holding position marking along with 

enhanced taxiway centerline. 

Figure 14-14. Runway holding position markings as seen when 

exiting the runway. When exiting the runway, no ATC clearance 

is required to cross. 

Land and Hold Short Operations (LAHSO) 

When simultaneous operations (takeoffs and landings) are 

being conducted on intersecting runways, Land and Hold 

Short Operations (LAHSO) may also be in effect. LAHSO 

is an ATC procedure that may require your participation and 

Figure 14-15. Runway distance remaining sign indicating that there 

is 2,000 feet of runway remaining. 

compliance. As pilot in command (PIC), you have the final 

authority to accept or decline any LAHSO clearance. 

If issued a land and hold short clearance, you must be aware 

of the reduced runway distances and whether or not you can 

comply before accepting the clearance. You do not have 

to accept a LAHSO clearance. Pilots should only receive a 

LAHSO clearance when there is a minimum ceiling of 1,000 

feet and 3 statute miles of visibility. 

Runway holding position signs and markings are installed 

on those runways used for LAHSO. The signs and markings 

are placed at the LAHSO point to aid you in determining 

where to stop and hold the aircraft and are located prior to 

the runway/runway intersection. [Figure 14-17] 

The holding position sign has a white inscription with black 

border around the numbers on a red background and is installed 

adjacent to the holding position markings. If you accept a land 

and hold short clearance, you must comply so that no portion 

of the aircraft extends beyond these hold markings. 

If receiving “cleared to land” instructions from ATC, you 

are authorized to use the entire landing length of the runway 

and should disregard any LAHSO holding position markings 

located on the runway. If you receive and accept LAHSO 

instructions, you must stop short of the intersecting runway 

prior to the LAHSO signs and markings. 

Below is a list of items which, if thoroughly understood 

and complied with, will ensure that LAHSO operations are 

conducted properly. 

•	 Know landing distance available. 

•	 Be advised by ATC as to why LAHSO are being 

conducted. 

14-10 
 

35

L

35

C

Figure 14-16. Two of three parallel runways. 

•	 Advise ATC if you cannot comply with LAHSO. 

•	 Know what signs and markings are at the LAHSO point. 

•	 LAHSO are not authorized for student pilots who are 

performing a solo flight. 

•	 At many airports air carrier aircraft are not authorized 

to participate in LAHSO if the other aircraft is a 

general aviation aircraft. 

•	 Generally, LAHSO are not authorized at night. 

•	 LAHSO are not authorized on wet runways. 

Figure 14-17. Runway holding position sign and marking for LAHSO. 

If you accept the following clearance from ATC: “Cleared to 

land Runway 36 hold short of Runway 23,” you must either exit 

Runway 36 or stop at the holding position prior to Runway 23. 

Taxiway Markings and Signs 

Taxiway direction signs have a yellow background and 

black characters, which identifies the designation or 

intersecting taxiways. Arrows indicate the direction of turn 

that would place the aircraft on the designated taxiway. 

[Figure 14-18] Direction signs are normally located on 

the left side of the taxiway and prior to the intersection. 

These signs and markings (with a yellow background and 

black characters) indicate the direction toward a different 

taxiway, leading off a runway, or out of an intersection. 

Figure 14-18 shows Taxiway Delta and how Taxiway Bravo 

intersects ahead at 90° both left and right. 

Taxiway direction signs can also be displayed as surface 

painted markings. Figure 14-19 shows Taxiway Bravo as 

proceeding straight ahead while Taxiway Alpha turns to the 

right at approximately 45°. 

14-11 
 

Figure 14-18. Taxiway Bravo direction sign with a collocated 

Taxiway Delta location sign. When the arrow on the direction 

sign indicates a turn, the sign is located prior to the intersection. 

Figure 14-20A and B shows an example of a direction sign at 

a complex taxiway intersection. Figure 14-20A and B shows 

Taxiway Bravo intersects with Taxiway Sierra at 90°, but at 

45° with Taxiway Foxtrot. This type of array can be displayed 

with or without the taxiway location sign, which in this case 

would be Taxiway Bravo. 

Enhanced Taxiway Centerline Markings 

At most towered airports, the enhanced taxiway centerline 

marking is used to warn you of an upcoming runway. It consists 

of yellow dashed lines on either side of the normal solid taxiway 

centerline and the dashes extend up to 150 feet prior to a 

runway holding position marking. [Figure 14-21A and B] They 

are used to aid you in maintaining awareness during surface 

movement to reduce runway incursions. 

Destination Signs 

Destination signs have black characters on a yellow 

background indicating a destination at the airport. These 

Figure 14-19. Surface painted taxiway direction signs. 

signs always have an arrow showing the direction of the taxi 

route to that destination. [Figure 14-22] When the arrow on 

the destination sign indicates a turn, the sign is located prior 

to the intersection. Destinations commonly shown on these 

types of signs include runways, aprons, terminals, military 

areas, civil aviation areas, cargo areas, international areas, 

and fixed-base operators. When the inscription for two or 

more destinations having a common taxi route are placed 

on a sign, the destinations are separated by a “dot” (•) and 

one arrow would be used as shown in Figure 14-22. When 

the inscription on a sign contains two or more destinations 

having different taxi routes, each destination is accompanied 

by an arrow and separated from the other destination(s) on 

the sign with a vertical black message divider as shown in 

Figure 14-23. The example shown in Figure 14-23 shows 

two signs. The sign in the foreground explains that Runway 

20 threshold is to the left, and Runways 32, 2, and 14 are to 

the right. The sign in the background indicates that you are 

located on Taxiway Bravo and Taxiway November will take 

you to those runways. 

Holding Position Signs and Markings for an 

Instrument Landing System (ILS) Critical Area 

The instrument landing system (ILS) broadcasts signals to 

arriving instrument aircraft to guide them to the runway. Each 

of these ILSs have critical areas that must be kept clear of all 

obstacles in order to ensure quality of the broadcast signal. At 

many airports, taxiways extend into the ILS critical area. Most 

of the time, this is of no concern; however, during times of 

poor weather, an aircraft on approach may depend on a good 

signal quality. When necessary, ATC will protect the ILS 

critical area for arrival instrument traffic by instructing taxiing 

aircraft to “hold short” of Runway (XX) ILS critical area. 

The ILS critical area hold sign has white characters, outlined 

in black, on a red background and is installed adjacent to the 

ILS holding position markings. [Figure 14-24] The holding 

position markings for the ILS critical area appear on the 

pavement as a horizontal yellow ladder extending across the 

width of the taxiway. 

When instructed to “hold short of Runway (XX) ILS critical 

area,” you must ensure no portion of the aircraft extends 

beyond these markings. [Figure 14-25] If ATC does not 

instruct you to hold at this point, then you may bypass the ILS 

critical area hold position markings and continue with your 

taxi. Figure 14-24 shows that the ILS hold sign is located 

on Taxiway Golf and the ILS ladder hold position marking 

is adjacent to the hold sign. 

14-12 
B

Enhanced taxiway centerline marking extends 150 feet prior 

to a runway holding position marking. Prepare to STOP.

A

B

F

S S

B

F

A 

S F B S F

Figure 14-20. Orientation of signs is from left to right in a clockwise manner. Left turn signs are on the left and right turn on the right. 

In this view, the pilot is on Taxiway Bravo. 

Prepare to STOP unless you have been cleared onto 

or across the runway by ATC. 

B 

Enhanced taxiway centerline marking extends 150 feet prior

to a runway holding position marking. Prepare to STOP. 

A 

Figure 14-21. (A) Enhanced taxiway centerline marking. (B) Enhanced taxiway centerline marking and runway holding position marking. 

14-13 
ILS Critical Area boundary 

ILS 

Hold only

when 

specifically

instructed by ATC 

19 

The yellow surface

painted “ladder” 

marking and red ILS 

sign are located

on taxiways where 

the taxiways intersect 

the ILS critical area. 

Figure 14-25. Holding position sign and marking for instrument 

landing system (ILS) critical area boundary. 

Figure 14-22. Destination sign to the fixed-base operator (FBO). 

Figure 14-23. Runway destination sign with different taxi routes. 

Figure 14-24. Instrument landing system (ILS) holding position sign 

and marking on Taxiway Golf. 

Holding Position Markings for Taxiway/Taxiway 

Intersections 

Holding position markings for taxiway/taxiway intersections 

consist of a single dashed yellow line extending across the 

width of the taxiway. [Figure 14-26] They are painted on 

taxiways where ATC normally holds aircraft short of a 

taxiway intersection. When instructed by ATC “hold short 

of Taxiway X,” you should stop so that no part of your 

aircraft extends beyond the holding position marking. When 

the marking is not present, you should stop your aircraft at 

a point that provides adequate clearance from an aircraft on 

the intersecting taxiway. 

Marking and Lighting of Permanently Closed 

Runways and Taxiways 

For runways and taxiways that are permanently closed, the 

lighting circuits are disconnected. The runway threshold, 

runway designation, and touchdown markings are obliterated 

and yellow “Xs” are placed at each end of the runway and 

at 1,000-foot intervals. 

14-14 
 

G B 

G 

G 

B 

B G 

B G 

Figure 14-26. Holding position marking on a taxiway. 

Temporarily Closed Runways and Taxiways 

For temporarily closed runways and taxiways, a visual 

indication is often provided with yellow “Xs” or raised 

lighted yellow “Xs” placed at each end of the runway. 

Depending on the reason for the closure, duration of closure, 

airfield configuration, and the existence and the hours of 

operation of an ATC tower, a visual indication may not be 

present. As discussed previously in the chapter, you must 

always check NOTAMs and ATIS for runway and taxiway 

closure information. 

Figure 14-27A shows an example of a yellow “X” laid flat 

with an adequate number of heavy sand bags to keep the 

wind from getting under and displacing the vinyl material. 

A very effective and preferable visual aid to depict temporary 

closure is the lighted “X” placed on or near the runway 

designation numbers. [Figure 14-27B and C] This device is 

much more discernible to approaching aircraft than the other 

materials described above. 

Other Markings 

Some other markings found on the airport include vehicle 

roadway markings, VOR receiver checkpoint markings, and 

non-movement area boundary markings. 

Airport Signs 

There are six types of signs that may be found at airports. The 

more complex the layout of an airport, the more important 

the signs become to pilots. Appendix C of this publication 

shows examples of some signs that are found at most airports, 

their purpose, and appropriate pilot action. The six types of 

signs are: 

•	 Mandatory instruction signs—red background with 

white inscription. These signs denote an entrance to a 

runway, critical area, or prohibited area. 

A 

C 

B 

Figure 14-27. (A) Yellow “X” placed on surface of temporarily closed 

runways. (B) Lighted “X” placed on temporarily closed runways. 

(C) Lighted “X” at night showing a temporarily closed runway. 

•	 Location signs—black with yellow inscription and a 

yellow border, no arrows. They are used to identify a 

taxiway or runway location, to identify the boundary 

of the runway, or identify an instrument landing 

system (ILS) critical area. 

14-15 
 

•	 Direction signs—yellow background with black 

inscription. The inscription identifies the designation 

of the intersecting taxiway(s) leading out of an 

intersection. 

•	 Destination signs—yellow background with black 

inscription and arrows. These signs provide information 

on locating areas, such as runways, terminals, cargo 

areas, and civil aviation areas. 

•	 Information signs—yellow background with black 

inscription. These signs are used to provide the pilot 

with information on areas that cannot be seen from the 

control tower, applicable radio frequencies, and noise 

abatement procedures. The airport operator determines 

the need, size, and location of these signs. 

•	 Runway distance remaining signs—black background 

with white numbers. The numbers indicate the 

distance of the remaining runway in thousands of feet. 

Airport Lighting 

The majority of airports have some type of lighting for night 

operations. The variety and type of lighting systems depends 

on the volume and complexity of operations at a given airport. 

Airport lighting is standardized so that airports use the same 

light colors for runways and taxiways. 

Airport Beacon 

Airport beacons help a pilot identify an airport at night. 

The beacons are normally operated from dusk until dawn. 

Sometimes they are turned on if the ceiling is less than 1,000 

feet and/or the ground visibility is less than 3 statute miles (VFR 

minimums). However, there is no requirement for this, so a 

pilot has the responsibility of determining if the weather meets 

VFR requirements. The beacon has a vertical light distribution 

to make it most effective from 1–10° above the horizon, 

although it can be seen well above or below this spread. The 

beacon may be an omnidirectional capacitor-discharge device, 

or it may rotate at a constant speed, that produces the visual 

effect of flashes at regular intervals. The combination of light 

colors from an airport beacon indicates the type of airport. 

[Figure 14-28] Some of the most common beacons are: 

•	 Flashing white and green for civilian land airports 

•	 Flashing white and yellow for a water airport 

•	 Flashing white, yellow, and green for a heliport 

•	 Two quick white flashes alternating with a green flash 

identifying a military airport 

Approach Light Systems 

Approach light systems are primarily intended to provide a 

means to transition from instrument flight to visual flight for 

landing. The system configuration depends on whether the 

White Green White Yellow

Figure 14-28. Airport rotating beacons. 

runway is a precision or nonprecision instrument runway. 

Some systems include sequenced flashing lights that appear 

to the pilot as a ball of light traveling toward the runway at 

high speed. Approach lights can also aid pilots operating 

under VFR at night. 

Visual Glideslope Indicators 

Visual glideslope indicators provide the pilot with glidepath 

information that can be used for day or night approaches. By 

maintaining the proper glidepath as provided by the system, 

a pilot should have adequate obstacle clearance and should 

touch down within a specified portion of the runway. 

Visual Approach Slope Indicator (VASI) 

VASI installations are the most common visual glidepath 

systems in use. The VASI provides obstruction clearance 

within 10° of the extended runway centerline and up to four 

nautical miles (NM) from the runway threshold. 

The VASI consists of light units arranged in bars. There are 

2-bar and 3-bar VASIs. The 2-bar VASI has near and far light 

bars and the 3-bar VASI has near, middle, and far light bars. 

Two-bar VASI installations provide one visual glidepath 

that is normally set at 3°. The 3-bar system provides two 

glidepaths, the lower glidepath normally set at 3° and the 

upper glidepath 1⁄4 degree above the lower glidepath. 

The basic principle of the VASI is that of color differentiation 

between red and white. Each light unit projects a beam of 

light, a white segment in the upper part of the beam and a 

red segment in the lower part of the beam. The lights are 

arranged so the pilot sees the combination of lights shown in 

Figure 14-29 to indicate below, on, or above the glidepath. 

Other Glidepath Systems 

A precision approach path indicator (PAPI) uses lights similar 

to the VASI system, except they are installed in a single row, 

normally on the left side of the runway. [Figure 14-30] 

14-16 
Below Glidepath On Glidepath Above Glidepath 

Far Bar 

Near Bar 

Far Bar 

Near Bar 

Far Bar 

Near Bar 

Figure 14-29. Two-bar VASI system. 

A tri-color system consists of a single-light unit projecting 

a three-color visual approach path. Below the glidepath is 

indicated by red, on the glidepath is indicated by green, and 

above the glidepath is indicated by amber. When descending 

below the glidepath, there is a small area of dark amber. Pilots 

should not mistake this area for an “above the glidepath” 

indication. [Figure 14-31] 

Pulsating VASIs normally consist of a single-light unit 

projecting a two-color visual approach path into the final 

approach area of the runway upon which the indicator is 

installed. The “on glidepath” indication is a steady white 

light. The “slightly below glidepath” indication is a steady red 

light. If the aircraft descends further below the glidepath, the 

red light starts to pulsate. The “above glidepath” indication 

is a pulsating white light. The pulsating rate increases as the 

aircraft gets further above or below the desired glideslope. 

The useful range of the system is about four miles during the 

day and up to ten miles at night. [Figure 14-32] 

Runway Lighting 

There are various lights that identify parts of the runway 

complex. These assist a pilot in safely making a takeoff or 

landing during night operations. 

Runway End Identifier Lights (REIL) 

Runway end identifier lights (REIL) are installed at many 

airfields to provide rapid and positive identification of the 

approach end of a particular runway. The system consists 

of a pair of synchronized flashing lights located laterally 

on each side of the runway threshold. REILs may be either 

omnidirectional or unidirectional facing the approach area. 

Runway Edge Lights 

Runway edge lights are used to outline the edges of 

runways at night or during low visibility conditions. 

[Figure 14-33] These lights are classified according to the 

intensity they are capable of producing: high intensity runway 

lights (HIRL), medium intensity runway lights (MIRL), and 

High 

more than 3.5° 

Slightly High

 3.2° 

On Glidepath

 3° 

Slightly Low

 2.8° 

Low 

less than 2.5° 

Figure 14-30. Precision approach path indicator for a typical 3° glide slope. 

Below glidepath 

Above glidepath

On glidepath 

Amber

Red

Green

Amber 

Figure 14-31. Tri-color visual approach slope indicator. 

14-17 
Below glidepath 

Above glidepath 

On glidepath 

Pulsating white

Pulsating red

Steady

white 

Threshold 

Slightly below glidepath 

Steady

red 

Figure 14-32. Pulsating visual approach slope indicator. 

low intensity runway lights (LIRL). The HIRL and MIRL 

have variable intensity settings. These lights are white, except 

on instrument runways where amber lights are used on the 

last 2,000 feet or half the length of the runway, whichever 

is less. The lights marking the end of the runway are red. 

In-Runway Lighting 

Runway centerline lighting system (RCLS)—installed on some 

precision approach runways to facilitate landing under adverse 

visibility conditions. They are located along the runway 

centerline and are spaced at 50-foot intervals. When viewed 

from the landing threshold, the runway centerline lights are 

white until the last 3,000 feet of the runway. The white lights 

begin to alternate with red for the next 2,000 feet. For the 

remaining 1,000 feet of the runway, all centerline lights are red. 

Touchdown zone lights (TDZL)—installed on some precision 

approach runways to indicate the touchdown zone when 

landing under adverse visibility conditions. They consist of 

two rows of transverse light bars disposed symmetrically 

about the runway centerline. The system consists of steadyburning white lights that start 100 feet beyond the landing 

threshold and extend to 3,000 feet beyond the landing 

threshold or to the midpoint of the runway, whichever is less. 

Figure 14-33. Runway lights. 

Taxiway centerline lead-off lights—provide visual guidance 

to persons exiting the runway. They are color-coded to warn 

pilots and vehicle drivers that they are within the runway 

environment or ILS critical area, whichever is more restrictive. 

Alternate green and yellow lights are installed, beginning 

with green, from the runway centerline to one centerline light 

position beyond the runway holding position or ILS critical 

area holding position. 

Taxiway centerline lead-on lights—provide visual guidance 

to persons entering the runway. These “lead-on” lights are 

also color-coded with the same color pattern as lead-off 

lights to warn pilots and vehicle drivers that they are within 

the runway environment or ILS critical area, whichever is 

more conservative. The fixtures used for lead-on lights are 

bidirectional (i.e., one side emits light for the lead-on function 

while the other side emits light for the lead-off function). Any 

fixture that emits yellow light for the lead-off function also 

emits yellow light for the lead-on function. 

Land and hold short lights—used to indicate the hold short 

point on certain runways which are approved for LAHSO. 

Land and hold short lights consist of a row of pulsing white 

lights installed across the runway at the hold short point. 

Where installed, the lights are on anytime LAHSO is in effect. 

These lights are off when LAHSO is not in effect. 

Control of Airport Lighting 

Airport lighting is controlled by ATC at towered airports. At 

nontowered airports, the lights may be on a timer, or where an 

FSS is located at an airport, the FSS personnel may control the 

lighting. A pilot may request various light systems be turned 

on or off and also request a specified intensity, if available, 

from ATC or FSS personnel. At selected nontowered airports, 

the pilot may control the lighting by using the radio. This 

is done by selecting a specified frequency and clicking the 

radio microphone. [Figure 14-34] For information on pilot 

controlled lighting at various airports, refer to the Chart 

Supplement U.S. (formerly Airport/Facility Directory). 

14-18 
 

Key Mike Function

Highest intensity available 

Medium or lower intensity

(Lower REIL or REIL off) 

Lowest intensity available

(Lower REIL or REIL off) 

7 times within 5 seconds 

5 times within 5 seconds 

3 times within 5 seconds 

Figure 14-34. Radio controlled runway lighting. 

Taxiway Lights 

Similar to runway lighting, taxiways also have various lights 

which help pilots identify areas of the taxiway and any 

surrounding runways. 

Omnidirectional 

Omnidirectional taxiway lights outline the edges of the 

taxiway and are blue in color. At many airports, these 

edge lights may have variable intensity settings that may 

be adjusted by an ATC when deemed necessary or when 

requested by the pilot. Some airports also have taxiway 

centerline lights that are green in color. 

Clearance Bar Lights 

Clearance bar lights are installed at holding positions on 

taxiways in order to increase the conspicuity of the holding 

position in low visibility conditions. They may also be 

installed to indicate the location of an intersecting taxiway 

during periods of darkness. Clearance bars consist of three 

in-pavement steady-burning yellow lights. 

Runway Guard Lights 

Runway guard lights are installed at taxiway/runway 

intersections. They are primarily used to enhance the 

conspicuity of taxiway/runway intersections during low 

visibility conditions, but may be used in all weather conditions. 

Runway guard lights consist of either a pair of elevated flashing 

yellow lights installed on either side of the taxiway, or a row of 

in-pavement yellow lights installed across the entire taxiway, 

at the runway holding position marking. 

Note: Some airports may have a row of three or five 

in-pavement yellow lights installed at taxiway/runway 

intersections. They should not be confused with clearance 

bar lights described previously in this section. 

Stop Bar Lights 

Stop bar lights, when installed, are used to confirm the ATC 

clearance to enter or cross the active runway in low visibility 

conditions (below 1,200 ft Runway Visual Range (RVR)). 

A stop bar consists of a row of red, unidirectional, steadyburning in-pavement lights installed across the entire taxiway 

at the runway holding position, and elevated steady-burning 

red lights on each side. A controlled stop bar is operated in 

conjunction with the taxiway centerline lead-on lights which 

extend from the stop bar toward the runway. Following the 

ATC clearance to proceed, the stop bar is turned off and the 

lead-on lights are turned on. The stop bar and lead-on lights 

are automatically reset by a sensor or backup timer. 

Obstruction Lights 

Obstructions are marked or lighted to warn pilots of 

their presence during daytime and nighttime conditions. 

Obstruction lighting can be found both on and off an airport 

to identify obstructions. They may be marked or lighted in 

any of the following conditions. 

•	 Red obstruction lights—flash or emit a steady red 

color during nighttime operations, and the obstructions 

are painted orange and white for daytime operations. 

•	 High intensity white obstruction lights—flash high 

intensity white lights during the daytime with the 

intensity reduced for nighttime. 

•	 Dual lighting—a combination of flashing red beacons 

and steady red lights for nighttime operation and high 

intensity white lights for daytime operations. 

New Lighting Technologies 

A top priority of the FAA is to continue to enhance airport 

safety while maintaining airport capacity. Reducing runway 

incursions is a major component of this effort. Runway 

incursions develop quickly and without warning during routine 

traffic situations on the airport surface, leaving little time for 

corrective action. The Runway Status Lights (RWSL) System 

is designed to provide a direct indication to you that it is unsafe 

to enter a runway, cross a runway, or takeoff from or land on 

a runway when the system is activated. 

Runway status lights are red in color and indicate runway 

status only; they do not indicate clearance to enter a runway 

or clearance to takeoff. The RWSL system provides warning 

lights on runways and taxiways, illuminating when it is unsafe 

to enter, cross, or begin takeoff on a runway. Currently, there 

are two types: Runway Entrance Lights (REL) and Takeoff 

Hold Lights (THL). [Figures 14-35 and 14-36] 

REL provide a warning to aircraft crossing or entering a 

runway from intersecting taxiways that there is conflicting 

traffic on the runway. THL provide a warning signal to 

aircraft in position for takeoff that the runway is occupied 

and it is unsafe to take off. As of 2016, the RWSL system is 

operational at 14 of the nation’s busiest airports with 3 more 

airports scheduled to receive the system by 2017. 

14-19 
Figure 14-35. Runway Entrance Lights (REL). 

Figure 14-36. Takeoff Hold Lights (THL). 

Wind Direction Indicators 

It is important for a pilot to know the direction of the wind. At 

facilities with an operating control tower, this information is 

provided by ATC. Information may also be provided by FSS 

personnel either located at a particular airport or remotely 

available through a remote communication outlet (RCO), or 

by requesting information on a CTAF at airports that have the 

capacity to receive and broadcast on this frequency. 

When none of these services is available, it is possible 

to determine wind direction and runway in use by visual 

wind indicators. A pilot should check these wind indicators 

even when information is provided on the CTAF at a given 

airport because there is no assurance that the information 

provided is accurate. 

The wind direction indicator can be a wind cone, wind sock, 

tetrahedron, or wind tee. These are usually located in a central 

location near the runway and may be placed in the center 

of a segmented circle, which identifies the traffic pattern 

direction if it is other than the standard left-hand pattern. 

[Figures 14-37 and 14-38] 

The wind sock is a good source of information since it not 

only indicates wind direction but allows the pilot to estimate 

the wind velocity and/or gust factor. The wind sock extends 

out straighter in strong winds and tends to move back and 

forth when the wind is gusting. Wind tees and tetrahedrons 

can swing freely and align themselves with the wind direction. 

Since a wind tee or tetrahedron can also be manually set to 

align with the runway in use, a pilot should also look at the 

wind sock for wind information, if one is available. 

Traffic Patterns 

At airports without an operating control tower, a segmented 

circle visual indicator system, if installed, is designed to 

provide traffic pattern information. [Figure 14-38] Usually 

located in a position affording maximum visibility to pilots in 

the air and on the ground and providing a centralized location 

for other elements of the system, the segmented circle consists 

of the following components: wind direction indicators, 

landing direction indicators, landing strip indicators, and 

traffic pattern indicators. 

A tetrahedron is installed to indicate the direction of landings 

and takeoffs when conditions at the airport warrant its use. 

It may be located at the center of a segmented circle and 

may be lighted for night operations. The small end of the 

tetrahedron points in the direction of landing. Pilots are 

cautioned against using a tetrahedron for any purpose other 

than as an indicator of landing direction. At airports with 

control towers, the tetrahedron should only be referenced 

when the control tower is not in operation. Tower instructions 

supersede tetrahedron indications. 

Landing strip indicators are installed in pairs and are used to 

show the alignment of landing strips. [Figure 14-38] Traffic 

pattern indicators are arranged in pairs in conjunction with 

landing strip indicators and used to indicate the direction of 

turns when there is a variation from the normal left traffic 

pattern. (If there is no segmented circle installed at the airport, 

traffic pattern indicators may be installed on or near the end 

of the runway.) 

At most airports and military air bases, traffic pattern altitudes 

for propeller-driven aircraft generally extend from 600 feet 

to as high as 1,500 feet above ground level (AGL). Pilots 

can obtain the traffic pattern altitude for an airport from the 

Chart Supplement U.S. (formerly Airport/Facility Directory). 

Also, traffic pattern altitudes for military turbojet aircraft 

sometimes extend up to 2,500 feet AGL. Therefore, pilots of 

en route aircraft should be constantly on alert for other aircraft 

in traffic patterns and avoid these areas whenever possible. 

When operating at an airport, traffic pattern altitudes should 

be maintained unless otherwise required by the applicable 

distance from cloud criteria according to Title 14 of the Code 

of Federal Regulations (14 CFR) part 91, section 91.155. 

Additional information on airport traffic pattern operations 

14-20 
 

 

 

 

 

 

 

 

 

Tetrahedron 

Wind sock or cone 

Wind tee 

WIND 

Figure 14-37. Wind direction indicators. 

Landing runway Wind cone

or landing strip

indicators 

Landing direction 

indicator 

Traffic pattern

indicators 

Figure 14-38. Segmented circle. 

can be found in Chapter 4, “Air Traffic Control,” of the AIM. 

Pilots can find traffic pattern information and restrictions, such 

as noise abatement in the Chart Supplement U.S. (formerly 

Airport/Facility Directory). 

Example: Key to Traffic Pattern Operations— 

Single Runway 

1.	 Enter pattern in level flight, abeam the midpoint 

of the runway, at pattern altitude. (1,000' AGL is 

recommended pattern altitude unless otherwise 

established.) [Figure 14-39] 

2.	 Maintain pattern altitude until abeam approach end of 

the landing runway on downwind leg. [Figure 14-39] 

3.	 Complete turn to final at least 1⁄4 mile from the runway. 

[Figure 14-39] 

4. After takeoff or go-around, continue straight ahead 

until beyond departure end of runway. [Figure 14-39] 

5. If remaining in the traffic pattern, commence turn to 

crosswind leg beyond the departure end of the runway 

within 300 feet of pattern altitude. [Figure 14-39] 

6. If departing the traffic pattern, continue straight out, 

or exit with a 45° turn (to the left when in a left-hand 

traffic pattern; to the right when in a right-hand traffic 

pattern) beyond the departure end of the runway, after 

reaching pattern altitude. [Figure 14-39] 

Example: Key to Traffic Pattern Operations— 

Parallel Runways 

1.	 Enter pattern in level flight, abeam the midpoint 

of the runway, at pattern altitude. (1,000' AGL is 

recommended pattern altitude unless otherwise 

established.) [Figure 14-40] 

2.	 Maintain pattern altitude until abeam approach end of 

the landing runway on downwind leg. [Figure 14-40] 

3.	 Complete turn to final at least 1⁄4 mile from the runway. 

[Figure 14-40] 

4.	 Do not overshoot final or continue on a track that 

penetrates the final approach of the parallel runway 

5. After takeoff or go-around, continue straight ahead 

until beyond departure end of runway. [Figure 14-40] 

14-21 
 

 

LEGEND 

Recommended standard left-hand traffic 

pattern (depicted) (standard right-hand 

traffic pattern would be mirror image) 

RUNWAY 

Final Departure 

Downwind 

Base

Crosswind 

Departure 

Departure 

Entry

Application of traffic 

pattern indicators 

Segmented circle 

3 

4 6 

6 

5 

2 

1 

Figure 14-39. Traffic pattern operations—single runway. 

6. If remaining in the traffic pattern, commence turn to 

crosswind leg beyond the departure end of the runway 

within 300 feet of pattern altitude. [Figure 14-40] 

7. If departing the traffic pattern, continue straight out, 

or exit with a 45° turn (to the left when in a left-hand 

traffic pattern; to the right when in a right-hand traffic 

pattern) beyond the departure end of the runway, after 

reaching pattern altitude. [Figure 14-40] 

8.	 Do not continue on a track that penetrates the departure 

path of the parallel runway. [Figure 14-40] 

Radio Communications 

Operating in and out of a towered airport, as well as in a good 

portion of the airspace system, requires that an aircraft have twoway radio communication capability. For this reason, a pilot 

should be knowledgeable of radio station license requirements 

and radio communications equipment and procedures. 

Radio License 

There is no license requirement for a pilot operating in the 

United States; however, a pilot who operates internationally 

is required to hold a restricted radiotelephone permit issued 

by the Federal Communications Commission (FCC). There 

is also no station license requirement for most general 

aviation aircraft operating in the United States. A station 

license is required, however, for an aircraft that is operating 

internationally, that uses other than a VHF radio, and that 

meets other criteria. 

Radio Equipment 

In general aviation, the most common types of radios are 

VHF. A VHF radio operates on frequencies between 118.0 

megahertz (MHz) and 136.975 MHz and is classified as 

720 or 760 depending on the number of channels it can 

accommodate. The 720 and 760 use .025 MHz (25 kilohertz 

(KHz) spacing (118.025, 118.050) with the 720 having a 

frequency range up to 135.975 MHz and the 760 reaching 

up to 136.975 MHz. VHF radios are limited to line of sight 

transmissions; therefore, aircraft at higher altitudes are able 

to transmit and receive at greater distances. 

In March of 1997, the International Civil Aviation Organization 

(ICAO) amended its International Standards and Recommended 

Practices to incorporate a channel plan specifying 8.33 kHz 

channel spacings in the Aeronautical Mobile Service. The 

8.33 kHz channel plan was adopted to alleviate the shortage of 

VHF ATC channels experienced in western Europe and in the 

United Kingdom. Seven western European countries and the 

United Kingdom implemented the 8.33 kHz channel plan on 

January 1, 1999. Accordingly, aircraft operating in the airspace 

of these countries must have the capability of transmitting and 

receiving on the 8.33 kHz spaced channels. 

Using Proper Radio Procedures 

Using proper radio phraseology and procedures contribute to 

a pilot’s ability to operate safely and efficiently in the airspace 

system. A review of the Pilot/Controller Glossary contained 

in the AIM assists a pilot in the use and understanding of 

14-22 
LEGEND 

Standard left-hand 

traffic pattern (depicted) 

Right-hand traffic 

pattern (depicted) 

Final Departure 

Base

Crosswind 

Final Departure 

Base

Crosswind 

Downwind 

Entry 

No transgression zone Segmented circle No transgression zone

3 4 

6 

6 

5 

2 

1 

3 

4 6 

6 

5 

2 

1 

Figure 14-40. Traffic pattern operation—parallel runways. 

standard terminology. The AIM also contains many examples 

of radio communications. 

ICAO has adopted a phonetic alphabet that should be used in 

radio communications. When communicating with ATC, pilots 

should use this alphabet to identify their aircraft. [Figure 14-41] 

Lost Communication Procedures 

It is possible that a pilot might experience a malfunction of 

the radio. This might cause the transmitter, receiver, or both 

to become inoperative. If a receiver becomes inoperative and a 

pilot needs to land at a towered airport, it is advisable to remain 

outside or above Class D airspace until the direction and flow 

of traffic is determined. A pilot should then advise the tower of 

the aircraft type, position, altitude, and intention to land. The 

pilot should continue, enter the pattern, report a position as 

appropriate, and watch for light signals from the tower. Light 

signal colors and their meanings are contained in Figure 14-42. 

If the transmitter becomes inoperative, a pilot should follow 

the previously stated procedures and also monitor the 

appropriate ATC frequency. During daylight hours, ATC 

transmissions may be acknowledged by rocking the wings 

and at night by blinking the landing light. 

When both receiver and transmitter are inoperative, the pilot 

should remain outside of Class D airspace until the flow of 

traffic has been determined and then enter the pattern and 

watch for light signals. 

Radio malfunctions should be repaired before further 

flight. If this is not possible, ATC may be contacted by 

telephone requesting a VFR departure without two-way radio 

communications. No radio (NORDO) procedure arrivals 

are not accepted at busy airports. If authorization is given 

to depart, the pilot is advised to monitor the appropriate 

frequency and/or watch for light signals as appropriate. 

14-23 
Character Morse Code Telephony Phonic Pronunciation

r

R0

q Q9

p P8

o

O7

n N6

5 55

4 44

3 33

2 22

1 11

z

ZZ

Yy Y

x XX

WWw

V

U

v V

u

U

t TT

s SS

r

RR

Q

P

q Q

p P

o

OO

n NN

MMm

L LL

k KK

j JJ

i II

h hH

GGg

f FF

e

EE

d DD

c

CC

Bb B

a AA

Figure 14-41. Phonetic alphabet. 

If radio communication is lost, it may be a prudent decision 

to land at a non-towered airport with lower traffic volume, if 

practical. When operating at a non-towered airport, no radio 

communication is necessary. However, pilots should be extra 

vigilant when not using the radio. Other traffic may not as 

easily be aware of your presence when they are expecting 

the standard radio calls. 

Air Traffic Control (ATC) Services 

Besides the services provided by an FSS as discussed in 

Chapter 12, “Aviation Weather Services,” numerous other 

services are provided by ATC. In many instances a pilot 

is required to have contact with ATC, but even when not 

required, a pilot may find their services helpful. 

Primary Radar 

Radar is a device that provides information on range, azimuth, 

and/or elevation of objects in the path of the transmitted 

pulses. It measures the time interval between transmission and 

reception of radio pulses and correlates the angular orientation 

of the radiated antenna beam or beams in azimuth and/or 

elevation. Range is determined by measuring the time it takes 

for the radio wave to go out to the object and then return to the 

receiving antenna. The direction of a detected object from a 

radar site is determined by the position of the rotating antenna 

when the reflected portion of the radio wave is received. 

Modern radar is very reliable and there are seldom outages. 

This is due to reliable maintenance and improved equipment. 

There are, however, some limitations that may affect ATC 

services and prevent a controller from issuing advisories 

concerning aircraft that are not under his or her control and 

cannot be seen on radar. 

The characteristics of radio waves are such that they normally 

travel in a continuous straight line unless they are “bent” by 

atmospheric phenomena, such as temperature inversions, 

reflected or attenuated by dense objects such as heavy clouds 

and precipitation, or screened by high terrain features. Radar 

signals degrade over distance, cannot penetrate through solid 

objects such as mountains, and the fastest radar updates every 

4.7 seconds. By contrast, the satellite signals used with 

Automatic Dependent Surveillance−Broadcast (ADS−B) do

not degrade over distance, provide better visibility around 

mountainous terrain and allows equipped aircraft to update 

their own position once a second with better accuracy. 

ATC Radar Beacon System (ATCRBS) 

The ATC radar beacon system (ATCRBS) is often referred to 

as “secondary surveillance radar.” This system consists of three 

components and helps in alleviating some of the limitations 

associated with primary radar. The three components are an 

interrogator, transponder, and radarscope. The advantages of 

ATCRBS are the reinforcement of radar targets, rapid target 

identification, and a unique display of selected codes. 

Growing air traffic in the National Airspace System (NAS) 

will be addressed through the use of ADS-B, which not only 

14-24 
Color and Type of Signal Movement of Vehicles, 

Equipment and Personnel Aircraft on the Ground Aircraft in Flight 

Steady green 

Flashing green 

Steady red 

Flashing red 

Flashing white 

Alternating red and green 

Cleared to cross, 

proceed or go 

Not applicable 

Stop 

Clear the taxiway/runway 

Return to starting point

on airport 

Exercise extreme caution!!!! 

Cleared for takeoff 

Cleared for taxi 

Stop 

Taxi clear of the runway 

in use 

Return to starting point 

on airport 

Exercise extreme caution!!!! 

Cleared to land 

Return for landing (to be followed 

by steady green at the proper time) 

Give way to other aircraft and 

continue circling 

Airport unsafe, do not land 

Not applicable 

Exercise extreme caution!!!! 

Figure 14-42. Light gun signals. 

provides all the same information the ATCRBS, but will do 

so more rapidly and with significantly more accuracy. By 

broadcasting aircraft position information to a ground station, 

ADS–B can also provide coverage in areas that do not have 

radar coverage. In addition, ADS–B provides trajectory 

information that includes speed and direction of motion. 

Transponder 

The transponder is the airborne portion of the secondary 

surveillance radar system and a system with which a pilot 

should be familiar. The ATCRBS cannot display the secondary 

information unless an aircraft is equipped with a transponder. 

A transponder is also required to operate in certain controlled 

airspace as discussed in Chapter 15, “Airspace.” 

A transponder code consists of four numbers from 0 to 7 

(4,096 possible codes). There are some standard codes or ATC 

may issue a four-digit code to an aircraft. When a controller 

requests a code or function on the transponder, the word 

“squawk” may be used. Figure 14-43 lists some standard 

transponder phraseology. Additional information concerning 

transponder operation can be found in the AIM, Chapter 4. 

Radar Beacon Phraseology 

SQUAWK (number) 

IDENT 

SQUAWK (number) and IDENT 

SQUAWK Standby 

SQUAWK Low/Normal 

SQUAWK Altitude 

STOP Altitude SQUAWK 

STOP SQUAWK (mode in use) 

STOP SQUAWK 

SQUAWK Mayday 

SQUAWK VFR 

Operate radar beacon transponder on designated code in MODE A/3. 

Engage the “IDENT” feature (military I/P) of the transponder. 

Operate transponder on specified code in MODE A/3 and engage the “IDENT” 

(military I/P) feature. 

Switch transponder to standby position. 

Operate transponder on low or normal sensitivity as specified. Transponder is 

operated in “NORMAL” position unless ATC specifies “LOW” (“ON” is used instead of 

“NORMAL” as a master control label on some types of transponders). 

Activate MODE C with automatic altitude reporting. 

Turn off altitude reporting switch and continue transmitting MODE C framing pulses. 

If your equipment does not have this capability, turn off MODE C. 

Switch off specified mode. (Used for military aircraft when the controller is unaware of 

military service requirements for the aircraft to continue operation on another MODE.) 

Switch off transponder. 

Operate transponder in the emergency position (MODE A Code 7700 for civil 

transponder, MODE 3 Code 7700 and emergency feature for military transponder). 

Operate radar beacon transponder on Code 1200 in MODE A/3, or other 

appropriate VFR code. 

Figure 14-43. Transponder phraseology. 

14-25 
Automatic Dependent Surveillance–Broadcast 

(ADS-B) 

Automatic Dependent Surveillance−Broadcast (ADS−B) is a

surveillance technology being deployed throughout the NAS 

to facilitate improvements needed to increase the capacity 

and efficiency of the NAS, while maintaining safety. ADS-B 

supports these improvements by providing a higher update rate 

and enhanced accuracy of surveillance information over the 

current radar-based surveillance system. In addition, ADS-B 

enables the expansion of air traffic control (ATC) surveillance 

services into areas where none existed previously. The ADS-B 

ground system also provides Traffic Information ServicesBroadcast (TIS-B) and Flight Information Services-Broadcast 

(FIS-B) for use on appropriately equipped aircraft, enhancing 

the user’s situational awareness (SA) and improving the 

overall safety of the NAS. 

The ADS−B system is composed of aircraft avionics and a

ground infrastructure. Onboard avionics determine the position 

of the aircraft by using the GPS and transmit its position, 

along with additional information about the aircraft, to ground 

stations for use by ATC and nearby ADS-B equipped aircraft. 

In the United States, ADS−B equipped aircraft exchange

information on one of two frequencies: 978 or 1090 MHz. 

The 1090 MHz frequency is associated with Mode A, C, and S 

transponder operations. 1090 MHz transponders with integrated 

ADS−B functionality extend the transponder message sets with

additional ADS−B information. This additional information

is known as an “extended squitter” message and referred to as 

1090ES. ADS−B equipment operating on 978 MHz is known

as the Universal Access Transceiver (UAT). 

Radar Traffic Advisories 

Radar equipped ATC facilities provide radar assistance 

to aircraft on instrument flight plans and VFR aircraft 

provided the aircraft can communicate with the facility and 

are within radar coverage. This basic service includes safety 

alerts, traffic advisories, limited vectoring when requested, 

and sequencing at locations where this procedure has been 

established. ATC issues traffic advisories based on observed 

radar targets. The traffic is referenced by azimuth from the 

aircraft in terms of the 12-hour clock. Also, distance in 

nautical miles, direction in which the target is moving, and 

type and altitude of the aircraft, if known, are given. 

An example would be: “Traffic 10 o’clock 5 miles east 

bound, Cessna 152, 3,000 feet.” The pilot should note that 

traffic position is based on the aircraft track and that wind 

correction can affect the clock position at which a pilot locates 

traffic. This service is not intended to relieve the pilot of the 

responsibility to see and avoid other aircraft. [Figure 14-44] 

In addition to basic radar service, terminal radar service 

TRACK TRACK 

Traffic information would be issued to the pilot of aircraft “A” 

as 12 o’clock. The actual position of the traffic as seen by 

the pilot of aircraft “A” would be 1 o’clock. Traffic information 

issued to aircraft “B” would also be given as 12 o’clock, but 

in this case, the pilot of “B” would see traffic at 10 o’clock. 

Wind 

A B 

Figure 14-44. Traffic advisories. 

area (TRSA) has been implemented at certain terminal 

locations. TRSAs are depicted on sectional aeronautical 

charts and listed in the Chart Supplement U.S. (formerly 

Airport/Facility Directory). The purpose of this service is to 

provide separation between all participating VFR aircraft and 

all IFR aircraft operating within the TRSA. Class C service 

provides approved separation between IFR and VFR aircraft 

and sequencing of VFR aircraft to the primary airport. Class 

B service provides approved separation of aircraft based on 

IFR, VFR, and/or weight and sequencing of VFR arrivals to 

the primary airport(s). 

Wake Turbulence 

All aircraft generate wake turbulence during flight. This 

disturbance is caused by a pair of counter-rotating vortices 

trailing from the wingtips. The vortices from larger aircraft 

pose problems to encountering aircraft. The wake of these 

aircraft can impose rolling moments exceeding the rollcontrol authority of the encountering aircraft. Also, the 

turbulence generated within the vortices can damage aircraft 

components and equipment if encountered at close range. For 

this reason, a pilot must envision the location of the vortex 

wake and adjust the flight path accordingly. 

Vortex Generation 

Lift is generated by the creation of a pressure differential over 

the wing surface. The lowest pressure occurs over the upper 

wing surface and the highest pressure under the wing. This 

pressure differential triggers the rollup of the airflow aft of 

the wing resulting in swirling air masses trailing downstream 

of the wingtips. After the rollup is completed, the wake 

consists of two counter rotating cylindrical vortices. Most of 

the energy lies within a few feet of the center of each vortex. 

[Figure 14-45] 

14-26 
 

Figure 14-45. Vortex generation. 

Vortex Strength 

Terminal Area 

Wake turbulence has historically been thought of as only 

a function of aircraft weight, but recent research considers 

additional parameters, such as speed, aspects of the wing, wake 

decay rates, and aircraft resistance to wake, just to name a few. 

The vortex characteristics of any aircraft will be changed with 

the extension of flaps or other wing configuration devices, as 

well as changing speed. However, as the basic factors are weight 

and speed, the vortex strength increases proportionately with 

an increase in aircraft operating weight or decrease in aircraft 

speed. The greatest vortex strength occurs when the generating 

aircraft is heavy, slow, and clean, since the turbulence from a 

“dirty” aircraft configuration hastens wake decay. 

En Route 

En route wake turbulence events have been influenced by 

changes to the aircraft fleet mix that have more “Super” 

(A380) and “Heavy” (B-747, B-777, A340, etc.) aircraft 

operating in the NAS. There have been wake turbulence 

events in excess of 30NM and 2000 feet lower than the wake 

generating aircraft. Air density is also a factor in wake strength. 

Even though the speeds are higher in cruise at high altitude, 

the reduced air density may result in wake strength comparable 

to that in the terminal area. In addition, for a given separation 

distance, the higher speeds in cruise result in less time for the 

wake to decay before being encountered by a trailing aircraft. 

Vortex Behavior 

Trailing vortices have certain behavioral characteristics 

that can help a pilot visualize the wake location and take 

avoidance precautions. 

Vortices are generated from the moment an aircraft leaves the 

ground (until it touches down), since trailing vortices are the 

byproduct of wing lift. [Figure 14-46] The vortex circulation 

is outward, upward, and around the wingtips when viewed 

from either ahead or behind the aircraft. Tests with large 

25 

Wake begins 

Rotation Touchdown

Wake ends 

Figure 14-46. Vortex behavior. 

14-27 
 

 

 

 

 

 

aircraft have shown that vortices remain spaced a bit less than 

a wingspan apart, drifting with the wind, at altitudes greater 

than a wingspan from the ground. Tests have also shown that 

the vortices sink at a rate of several hundred feet per minute, 

slowing their descent and diminishing in strength with time 

and distance behind the generating aircraft. 

When the vortices of larger aircraft sink close to the ground 

(within 100 to 200 feet), they tend to move laterally over 

the ground at a speed of 2–3 knots. A crosswind decreases 

the lateral movement of the upwind vortex and increases 

the movement of the downwind vortex. A light quartering 

tailwind presents the worst case scenario as the wake 

vortices could be all present along a significant portion of 

the final approach and extended centerline and not just in the 

touchdown zone as typically expected. 

Vortex Avoidance Procedures 

The following procedures are in place to assist pilots in vortex 

avoidance in the given scenario. 

•	 Landing behind a larger aircraft on the same runway— 

stay at or above the larger aircraft’s approach 

flight path and land beyond its touchdown point. 

[Figure 14-47A] 

•	 Landing behind a larger aircraft on a parallel runway 

closer than 2,500 feet—consider the possibility of drift 

and stay at or above the larger aircraft’s final approach 

flight path and note its touchdown point. [Figure 14-47B] 

•	 Landing behind a larger aircraft on crossing runway— 

cross above the larger aircraft’s flight path. 

•	 Landing behind a departing aircraft on the same 

runway—land prior to the departing aircraft’s 

rotating point. 

•	 Landing behind a larger aircraft on a crossing 

runway—note the aircraft’s rotation point and, if that 

point is past the intersection, continue and land prior 

to the intersection. If the larger aircraft rotates prior 

to the intersection, avoid flight below its flight path. 

Abandon the approach unless a landing is ensured well 

before reaching the intersection. [Figure 14-47C] 

•	 Departing behind a large aircraft—rotate prior to the 

large aircraft’s rotation point and climb above its climb 

path until turning clear of the wake. 

•	 For intersection takeoffs on the same runway— 

be alert to adjacent larger aircraft operations, 

particularly upwind of the runway of intended use. 

If an intersection takeoff clearance is received, avoid 

headings that cross below the larger aircraft’s path. 

•	 If departing or landing after a large aircraft executing 

a low approach, missed approach, or touch-and-go 

landing (since vortices settle and move laterally 

near the ground, the vortex hazard may exist along 

the runway and in the flight path, particularly in a 

quartering tailwind), it is prudent to wait at least 2 

minutes prior to a takeoff or landing. 

•	 En route, it is advisable to avoid a path below and 

behind a large aircraft, and if a large aircraft is 

observed above on the same track, change the aircraft 

position laterally and preferably upwind. 

Collision Avoidance 

Title 14 of the CFR part 91 has established right-of-way 

rules, minimum safe altitudes, and VFR cruising altitudes 

to enhance flight safety. The pilot can contribute to collision 

avoidance by being alert and scanning for other aircraft. This 

is particularly important in the vicinity of an airport. 

Effective scanning is accomplished with a series of short, 

regularly spaced eye movements that bring successive areas of 

the sky into the central visual field. Each movement should not 

exceed 10°, and each should be observed for at least 1 second 

to enable detection. Although back and forth eye movements 

seem preferred by most pilots, each pilot should develop a 

scanning pattern that is most comfortable and then adhere to 

it to assure optimum scanning. Even if entitled to the right-ofway, a pilot should yield if another aircraft seems too close. 

Clearing Procedures 

The following procedures and considerations are in place to 

assist pilots in collision avoidance under various situations: 

•	 Before takeoff—prior to taxiing onto a runway or 

landing area in preparation for takeoff, pilots should 

scan the approach area for possible landing traffic, 

executing appropriate maneuvers to provide a clear 

view of the approach areas. 

•	 Climbs and descents—during climbs and descents in 

flight conditions that permit visual detection of other 

traffic, pilots should execute gentle banks left and right 

at a frequency that permits continuous visual scanning 

of the airspace. 

•	 Straight and level—during sustained periods of 

straight-and-level flight, a pilot should execute 

appropriate clearing procedures at periodic intervals. 

•	 Traffic patterns—entries into traffic patterns while 

descending should be avoided. 

•	 Traffic at VOR sites—due to converging traffic, 

sustained vigilance should be maintained in the 

vicinity of VORs and intersections. 

•	 Training operations—vigilance should be maintained 

and clearing turns should be made prior to a practice 

14-28 
Aircraft crossing over wake turbulence 

Aircraft altitude is above wake 

C 

Touchdown point 

Aircraft altitude is above wake 

Less than 2500 feet 

WIND 

Parallel Runway Situation 

B 

Touchdown point of larger aircraft 

WIND

A 

Side view 

Figure 14-47. Vortex avoidance procedures. 

14-29 
 

 

 

maneuver. During instruction, the pilot should be 

asked to verbalize the clearing procedures (call out 

“clear left, right, above, and below”). 

High-wing and low-wing aircraft have their respective blind 

spots. The pilot of a high-wing aircraft should momentarily 

raise the wing in the direction of the intended turn and look 

for traffic prior to commencing the turn. The pilot of a lowwing aircraft should momentarily lower the wing and look 

for traffic prior to commencing the turn. 

Pilot Deviations (PDs) 

A pilot deviation (PD) is an action of a pilot that violates any 

Federal Aviation Regulation. While PDs should be avoided, 

the regulations do authorize deviations from a clearance in 

response to a traffic alert and collision avoidance system 

resolution advisory. You must notify ATC as soon as possible 

following a deviation. 

Pilot deviations can occur in several different ways. 

Airborne deviations result when a pilot strays from 

an assigned heading or altitude or from an instrument 

procedure, or if the pilot penetrates controlled or restricted 

airspace without ATC clearance. 

To prevent airborne deviations, follow these steps: 

•	 Plan each flight—you may have flown the flight many 

times before but conditions and situations can change 

rapidly, such as in the case of a pop-up temporary 

flight restriction (TFR). Take a few minutes prior to 

each flight to plan accordingly. 

•	 Talk and squawk—Proper communication with ATC 

has its benefits. Flight following often makes the 

controller’s job easier because they can better integrate 

VFR and IFR traffic. 

•	 Give yourself some room—GPS is usually more 

precise than ATC radar. Using your GPS to fly up 

to and along the line of the airspace you are trying to 

avoid could result in a pilot deviation because ATC 

radar may show you within the restricted airspace. 

Ground deviations (also called surface deviations) include 

taxiing, taking off, or landing without clearance, deviating 

from an assigned taxi route, or failing to hold short of an 

assigned clearance limit. To prevent ground deviations, stay 

alert during ground operations. Pilot deviations can and 

frequently do occur on the ground. Many strategies and tactics 

pilots use to avoid airborne deviations also work on the ground. 

Pilots should also remain vigilant about vehicle/pedestrian 

deviations (V/PDs). A vehicle or pedestrian deviation 

includes pedestrians, vehicles or other objects interfering 

with aircraft operations by entering or moving on the runway 

movement area without authorization from air traffic control. 

In serious instances, any ground deviation (PD or VPD) can 

result in a runway incursion. Best practices in preventing 

ground deviations can be found in the following section 

under runway incursion avoidance. 

Runway Incursion Avoidance 

A runway incursion is “any occurrence in the airport runway 

environment involving an aircraft, vehicle, person, or object 

on the ground that creates a collision hazard or results in a loss 

of required separation with an aircraft taking off, intending 

to take off, landing, or intending to land.” It is important 

to give the same attention to operating on the surface as in 

other phases of flights. Proper planning can prevent runway 

incursions and the possibility of a ground collision. A pilot 

should always be aware of the aircraft’s position on the 

surface at all times and be aware of other aircraft and vehicle 

operations on the airport. At times, towered airports can be 

busy and taxi instructions complex. In this situation, it may 

be advisable to write down taxi instructions. The following 

are some practices to help prevent a runway incursion: 

•	 Read back all runway crossing and/or hold instructions. 

•	 Review airport layouts as part of preflight planning, 

before descending to land and while taxiing, as 

needed. 

•	 Know airport signage. 

•	 Review NOTAM for information on runway/taxiway 

closures and construction areas. 

•	 Request progressive taxi instructions from ATC when 

unsure of the taxi route. 

•	 Check for traffic before crossing any runway hold line 

and before entering a taxiway. 

•	 Turn on aircraft lights and the rotating beacon or strobe 

lights while taxing. 

•	 When landing, clear the active runway as soon as 

possible, then wait for taxi instructions before further 

movement. 

•	 Study and use proper phraseology in order to 

understand and respond to ground control instructions. 

•	 Write down complex taxi instructions at unfamiliar 

airports. 

Approximately three runway incursions occur each day at 

towered airports within the United States. The potential 

that these numbers present for a catastrophic accident is 

unacceptable. The following are examples of pilot deviations, 

operational incidents (OI), and vehicle (driver) deviations 

that may lead to runway incursions. 

14-30 
 

Pilot Deviations: 

•	 Crossing a runway hold marking without clearance 

from ATC 

•	 Taking off without clearance 

•	 Landing without clearance 

Operational Incidents (OI): 

•	 Clearing an aircraft onto a runway while another 

aircraft is landing on the same runway 

•	 Issuing a takeoff clearance while the runway is 

occupied by another aircraft or vehicle 

Vehicle (Driver) Deviations: 

•	 Crossing a runway hold marking without ATC 

clearance 

According to FAA data, approximately 65 percent of all 

runway incursions are caused by pilots. Of the pilot runway 

incursions, FAA data shows almost half of those incursions 

are caused by GA pilots. 

Causal Factors of Runway Incursions 

Detailed investigations of runway incursions over the past 

10 years have identified three major areas contributing to 

these events: 

•	 Failure to comply with ATC instructions 

•	 Lack of airport familiarity 

•	 Nonconformance with standard operating procedures 

Clear, concise, and effective pilot/controller communication is 

paramount to safe airport surface operations. You must fully 

understand and comply with all ATC instructions. It is mandatory 

to read back all runway “hold short” instructions verbatim. 

Taxiing on an unfamiliar airport can be very challenging, 

especially during hours of darkness or low visibility. A 

request may be made for progressive taxi instructions which 

include step by step taxi routing instructions. Ensure you 

have a current airport diagram, remain “heads-up” with eyes 

outside, and devote your entire attention to surface navigation 

per ATC clearance. All checklists should be completed while 

the aircraft is stopped. There is no place for non-essential 

chatter or other activities while maintaining vigilance during 

taxi. [Figure 14-48] 

Runway Confusion 

Runway confusion is a subset of runway incursions and 

often results in you unintentionally taking off or landing on 

a taxiway or wrong runway. Generally, you are unaware of 

the mistake until after it has occurred. 

Figure 14-48. Heads-up, eyes outside. 

In August 2006, the flight crew of a commercial regional jet 

was cleared for takeoff on Runway 22 but mistakenly lined 

up and departed on Runway 26, a much shorter runway. As 

a result, the aircraft crashed off the end of the runway. 

Causal Factors of Runway Confusion 

There are three major factors that increase the risk of runway 

confusion and can lead to a wrong runway departure: 

•	 Airport complexity 

•	 Close proximity of runway thresholds 

•	 Joint use of a runway as a taxiway 

Not only can airport complexity contribute to a runway 

incursion; it can also play a significant role in runway 

confusion. If you are operating at an unfamiliar airport and 

need assistance in executing the taxi clearance, do not hesitate 

to ask ATC for help. Always carry a current airport diagram 

and trace or highlight your taxi route to the departure runway 

prior to leaving the ramp. 

If you are operating from an airport with runway thresholds 

in close proximity to one another, exercise extreme caution 

when taxiing onto the runway. Figure 14-49 shows a perfect 

example of a taxiway leading to multiple runways that may 

cause confusion. If departing on Runway 36, ensure that you 

set your aircraft heading “bug” to 360°, and align your aircraft 

to the runway heading to avoid departing from the wrong 

runway. Before adding power, make one last instrument scan 

to ensure the aircraft heading and runway heading are aligned. 

Under certain circumstances, it may be necessary to 

use a runway as a taxiway. For example, during airport 

construction some taxiways may be closed requiring rerouting of traffic onto runways. In other cases, departing 

traffic may be required to back taxi on the runway in order 

to utilize the full runway length. 

14-31 
 

 

36

Figure 14-49. Confusing runway/runway intersection. 

Since inattention and confusion often are factors contributing to 

runway incursion, it is important to remain extremely cautious 

and maintain situational awareness (SA). When instructed to 

use a runway as a taxiway, do not become confused and take 

off on the runway you are using as a taxiway. 

ATC Instructions 

Title 14 of the Code of Federal Regulations (14 CFR) part 

91, section 91.123 requires you to follow all ATC clearances 

and instructions. Request clarification if you are unsure of the 

clearance or instruction to be followed. If you are unfamiliar 

with the airport or unsure of a taxi route, ask ATC for a 

“progressive taxi.” Progressive taxi requires the controller 

to provide step-by-step taxi instructions. 

The final decision to act on ATC’s instruction rests with you. 

If you cannot safely comply with any of ATC’s instructions, 

inform them immediately by using the word “UNABLE.” 

There is nothing wrong with telling a controller that you are 

unable to safely comply with the clearance. 

Another way to mitigate the risk of runway incursions is to 

write down all taxi instructions as soon as they are received 

from ATC. [Figure 14-50] It is also helpful to monitor ATC 

clearances and instructions that are issued to other aircraft. 

You should be especially vigilant if another aircraft has a 

similar sounding call sign so there is no mistake about who 

ATC is contacting or to whom they are giving instructions 

and clearances. 

Read back your complete ATC clearance with your aircraft 

call sign. This gives ATC the opportunity to clarify any 

misunderstandings and ensure that instructions were given to 

the correct aircraft. If, at any time, there is uncertainty about 

any ATC instructions or clearances, ask ATC to “say again” 

or ask for progressive taxi instructions. 

ATC Instructions—“Hold Short” 

The most important sign and marking on the airport is the 

hold sign and hold marking. These are located on a stub 

taxiway leading directly to a runway. They depict the holding 

position or the location where the aircraft is to stop so as not to 

enter the runway environment. [Figure 14-51] For example, 

Figure 14-52 shows the holding position sign and marking 

for Runway 13 and Runway 31. 

When ATC issues a “hold short” clearance, you are 

expected to taxi up to, but not cross any part of the runway 

holding marking. At a towered airport, runway hold 

markings should never be crossed without explicit ATC 

instructions. Do not enter a runway at a towered airport 

unless instructions are given from ATC to cross, takeoff 

from, or “line up and wait” on that specific runway. 

ATC is required to obtain a read-back from the pilot of 

all runway “hold short” instructions. Therefore, you 

must read back the entire clearance and “hold short” 

instruction, to include runway identifier and your call sign. 

Figure 14-50. A sound practice is to write down taxi instructions 

from ATC. 

14-32 
Figure 14-51. Do NOT cross a runway holding position marking 

without ATC clearance. If the tower is closed or you are operating 

from a non-towered airport, check both directions for conflicting 

traffic before crossing the hold position marking. 

Figure 14-53 shows an example of a controller’s taxi and “hold 

short” instructions and the reply from the pilot. 

ATC Instructions—Explicit Runway Crossing 

As of June 30, 2010, ATC is required to issue explicit 

instructions to “cross” or “hold short” of each runway. 

Instructions to “cross” a runway are normally issued one at a 

time, and an aircraft must have crossed the previous runway 

before another runway crossing is issued. Exceptions may 

apply for closely spaced runways that have less than 1,000 

feet between centerlines. This applies to all runways to include 

active, inactive, or closed. Figure 14-54 shows communication 

between ATC and a pilot who is requesting a taxi clearance. 

Extra caution should be used when directed by ATC to 

taxi onto or across a runway, especially at night and during 

reduced visibility conditions. Always comply with “hold 

November 477ZA, 

Runway four, taxi via 

Echo, hold short of 

Runway two five at 

Taxiway Delta. 

Controller 

November 477ZA, 

Runway four via Echo, 

hold short of Runway 

two five at Delta. 

Pilot 

Figure 14-53. Example of taxi and “hold short” instructions from 

ATC to a pilot. 

short” or crossing instructions when approaching an entrance 

to a runway. Scan the full length of the runway and the final 

approaches before entering or crossing any runway, even if 

ATC has issued a clearance. 

ATC Instructions—“Line Up and Wait” (LUAW) 

ATC now uses the “line up and wait” (LUAW) instruction 

when a takeoff clearance cannot be issued immediately due 

to traffic or other reasons. The words “line up and wait” have 

replaced “position and hold” in directing you to taxi onto a 

runway and await takeoff clearance. 

An ATC instruction to “line up and wait” is not a clearance 

for takeoff. It is only a clearance to enter the runway and 

hold in position for takeoff. Under LUAW phraseology, the 

controller states the aircraft call sign, departure runway, and 

“line up and wait.” Be aware that “traffic holding in position” 

will continue to be used to advise other aircraft that traffic 

has been authorized to line up and wait on an active runway. 

Pay close attention when instructed to “line up and wait,” 

especially at night or during periods of low visibility. Before 

Figure 14-52. Runway 13-31 holding position sign and marking 

located on Taxiway Charlie. 

“Ground, November 1234 

ready to taxi from the GA 

ramp with Bravo.” 

Pilot 

“November 1234, 

Runway two seven, taxi 

via Alpha, hold short 

of Runway three one.” 

ATC 

“November 1234, 

Runway two seven, taxi 

via Alpha, hold short 

Runway three one.” 

Pilot 

When able, tower will 

issue crossing clearance: 

“November 1234, cross 

Runway three one.” 

ATC 

Figure 14-54. Communication between ATC and a pilot who is 

requesting taxi procedures. 

14-33 
 

entering the runway, remember to scan the full length of the 

runway and its approach end for other aircraft. 

There have been collisions and incidents involving aircraft 

instructed to “line up and wait” while ATC waits for the 

necessary conditions to issue a takeoff clearance. An OI 

caused a 737 to land on a runway occupied by a twin-engine 

turboprop. The turboprop was holding in position awaiting 

takeoff clearance. Upon landing, the 737 collided with the 

twin-engine turboprop. 

When ATC instructs you to “line up and wait,” they should 

advise you of any anticipated delay in receiving your takeoff 

clearance. Possible reasons for ATC takeoff clearance delays 

may include other aircraft landing and/or departing, wake 

turbulence, or traffic crossing an intersecting runway. 

•	 If advised of a reason for the delay, or the reason is 

clearly visible, expect an imminent takeoff clearance 

once the reason is no longer an issue. 

•	 If a takeoff clearance is not received within 90 seconds 

after receiving the “line up and wait” instruction, 

contact ATC immediately. 

•	 When ATC issues “line up and wait” instructions 

and takeoff clearances from taxiway intersection, the 

taxiway designator is included. 

Example – “N123AG Runway One-Eight, at Charlie 

Three, line up and wait.” 

Example – “N123AG Runway One-Eight, at Charlie 

Three, cleared for takeoff.” 

If LUAW procedures are being used and landing traffic is a 

factor, ATC is required to: 

•	 Inform the aircraft in the LUAW position of the closest 

aircraft that is requesting a full-stop, touch-and-go, 

stop-and-go, option, or unrestricted low approach. 

Example – “N123AG, Runway One-Eight, line up 

and wait, traffic a Cessna 210 on a six-mile final.” 

•	 In some cases, where safety logic is being used, ATC 

is permitted to issue landing clearances with traffic in 

the LUAW position. Traffic information is issued to 

the landing traffic. 

Example – “N456HK, Runway One-Eight, cleared to 

land, traffic a DeHavilland Otter holding in position.” 

NOTE: ATC will/must issue a takeoff clearance to the 

traffic holding in position in sufficient time to ensure 

no conflict exists with landing aircraft. Prescribed 

runway separation must exist no later than when the 

landing aircraft crosses the threshold. 

•	 In cases where ATC is not permitted to issue landing 

clearances with traffic in the LUAW position, traffic 

information is issued to the closest aircraft that is 

requesting a full-stop, touch-and-go, stop-and-go, 

option, or unrestricted low approach. 

Example – “N456HK, Runway One-Eight, continue, 

traffic holding in position.” 

ATC Instructions—“Runway Shortened” 

You should review NOTAMs in your preflight planning to 

determine any airport changes that will affect your departure 

or arrival. When the available runway length has been 

temporarily or permanently shortened due to construction, 

the ATIS includes the words “warning” and “shortened” in 

the text of the message. For the duration of the construction 

when the runway is temporarily shortened, ATC will 

include the word “shortened” in their clearance instructions. 

Furthermore, the use of the term “full length” will not be used 

by ATC during this period of the construction. 

Some examples of ATC instructions are: 

•	 “Runway three six shortened, line up and wait.” 

•	 “Runway three six shortened, cleared for takeoff.” 

•	 “Runway three six shortened, cleared to land.” 

When an intersection departure is requested on a temporarily 

or permanently shortened runway during the construction, 

the remaining length of runway is included in the clearance. 

For example, “Runway three six at Echo, intersection 

departure, 5,600 feet available.” If following the construction, 

the runway is permanently shortened, ATC will include 

the word “shortened” until the Chart Supplement U.S. 

(formerly Airport/Facility Directory) is updated to include 

the permanent changes to the runway length. 

Pre-Landing, Landing, and After-Landing 

While en route and after receiving the destination airport 

ATIS/landing information, review the airport diagram and 

brief yourself as to your exit taxiway. Determine the following: 

•	 Are there any runway hold markings in close proximity 

to the exit taxiway? 

•	 Do not cross any hold markings or exit onto any 

runways without ATC clearance. 

After landing, use the utmost caution where the exit taxiways 

intersect another runway, and do not exit onto another runway 

without ATC authorization. Do not accept last minute 

turnoff instructions from the control tower unless you clearly 

understand the instructions and are at a speed that ensures you 

14-34 
 

can safely comply. Finally, after landing and upon exiting 

the runway, ensure your aircraft has completely crossed over 

the runway hold markings. Once all parts of the aircraft have 

crossed the runway holding position markings, you must hold 

unless further instructions have been issued by ATC. Do not 

initiate non-essential communications or actions until the 

aircraft has stopped and the brakes set. 

Engineered Materials Arresting Systems

(EMAS) 

Aircraft can and do overrun the ends of runways and 

sometimes with devastating results. An overrun occurs 

when an aircraft passes beyond the end of a runway during 

an aborted takeoff or on landing rollout. To minimize the 

hazards of overruns, the FAA incorporated the concept of 

a runway safety area (RSA) beyond the runway end into 

airport design standards. At most commercial airports, the 

RSA is 500 feet wide and extends 1,000 feet beyond each 

end of the runway. The FAA implemented this requirement 

in the event that an aircraft overruns, undershoots, or veers 

off the side of the runway. 

The most dangerous of these incidents are overruns, but 

since many airports were built before the 1,000-foot RSA 

length was adopted some 20 years ago, the area beyond the 

end of the runway is where many airports cannot achieve the 

full standard RSA. This is due to obstacles, such as bodies 

of water, highways, railroads, populated areas, or severe 

drop-off of terrain. Under these specific circumstances, the 

installation of an Engineered Materials Arresting System 

(EMAS) is an acceptable alternative to a RSA beyond the 

runway end. It provides a level of safety that is generally 

equivalent to a full RSA. [Figure 14-55] 

An EMAS uses materials of closely controlled strength and 

density placed at the end of a runway to stop or greatly slow 

an aircraft that overruns the runway. The best material found 

to date is a lightweight, crushable concrete. When an aircraft 

rolls into an EMAS arrestor bed, the tires of the aircraft sink 

into the lightweight concrete and the aircraft is decelerated 

by having to roll through the material. [Figure 14-56] 

Incidents 

To date, there have been several incidents listed below where 

the EMAS technology has worked successfully to arrest 

aircraft that overrun the runway. All cases have resulted in 

minimal to do damage to the aircraft. The only known injury 

was an ankle injury to a passenger during egress following 

the arrestment. [Figure 14-57] 

•	 May 1999—A Saab 340 commuter aircraft overran 

the runway at John F. Kennedy International Airport 

(JFK). 

Figure 14-55. Engineered material arresting system (EMAS) 

located at Yeager Airport, Charleston, West Virginia. 

• May 2003—A Cargo McDonnell Douglas (MD)-11 

overran the runway at JFK. 

• January 2005—A Boeing 747 overran the runway at 

JFK. 

•	 July 2006—A Mystere Falcon 900 overran the 

runway at Greenville Downtown Airport (KGMU) 

in Greenville, South Carolina. 

• July 2008—An Airbus A320 overran the runway at 

O’Hare International Airport (ORD). 

•	 January 2010—A Bombardier CRJ-200 regional jet 

overran the runway at Yeager Airport (KCRW) in 

Charleston, West Virginia (WV). [Figure 14-58] 

•	 October 2010—A G-4 Gulfstream overran the 

runway at Teterboro Airport (KTEB) in Teterboro, 

New Jersey (NJ). 

• November 2011—A Cessna Citation 550 overran the 

runway at Key West International Airport (KEYW) 

in Key West, Florida. 

EMAS Installations and Information 

Currently, EMAS is installed at 63 runway ends at 42 airports 

in the United States with plans to install more throughout the 

next few years. 

EMAS information is available in the Chart Supplement 

U.S. (formerly Airport/Facility Directory) under the specific 

airport information. Figure 14-59 shows airport information 

for Boston Logan International Airport. At the bottom of the 

page, it shows which runways are equipped with arresting 

systems and the type that they have. It is important for pilots 

to study airport information, become familiar with the details 

and limitations of the arresting system, and the runways that 

are equipped with them. [Figure 14-60] 

14-35 
ARRESTOR BED 

Runway Set back

Runway safety area length 

Side steps 

Runway width 

An EMASMAX bed is typically the full width of the runway and the arrestor bed is set-back from the end of the runway. 

Typical Plan View 

The front of an EMASMAX bed includes a lead-in ramp to transition the aircraft into the material. 

• Beyond the runway width, the sides of an EMASMAX bed are stepped to provide emergency vehicle access and passenger 

egress. 

• The length of the EMAS bed is dependent upon the space available in the existing RSA and the design aircraft for the EMAS. 

• As stated in FAA Advisory Circular 150/5220-22A, Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns, the 

EMAS is designed to arrest aircraft exiting the runway at speeds between 40 and 70 knots. 70 knots is the preferred EMAS 

design runway exit speed but in limited spaces, the EMAS may have design runway exit speeds as low as 40 knots. 

Typical Profile View 

Typical Section View 

Side steps 

Stepped sides provide arff 

access and passenger egress 

Arrestor bed 

Arrestor bed 

Debris deflector 

over concrete beam 

Lead in ramp 

Base surface 

Base surface 

Figure 14-56. Diagram of an EMASMAX system. 

Pilot Considerations 

Although engaging an EMAS should not be a desired 

outcome for the end of a flight, pilots need to know what 

EMAS is, how to identify it on the airfield diagram and 

on the airfield, as well as knowing what to do should they 

find themselves approaching an installation in an overrun 

situation. [Figure 14-59 and Figure 14-60] Pilots also need 

to know that an EMAS may not stop lightweight general 

aviation aircraft that are not heavy enough to sink into the 

crushable concrete. The time to discuss whether or not a 

runway has an EMAS at the end is during the pre-departure 

briefing prior to takeoff or during the approach briefing prior 

to commencing the approach. Following the guidance below 

ensures that the aircraft engages the EMAS according to the 

design entry parameters. 

During the takeoff or landing phase, if a pilot determines that 

the aircraft will exit the runway end and enter the EMAS, the 

following guidance should be adhered to: 

1.	 Continue deceleration - Regardless of aircraft speed 

upon exiting the runway, continue to follow Rejected/ 

Aborted Takeoff procedures, or if landing, Maximum 

Braking procedures outlined in the Flight Manual. 

14-36 
Figure 14-57. There have been several incidents where the EMAS 

has successfully arrested the aircraft. 

2.	 Maintain runway centerline - Not veering left or right 

of the bed and continuing straight ahead will maximize 

stopping capability of the EMAS bed. The quality of 

deceleration will be best within the confines of the bed. 

3.	 Maintain deceleration efforts - The arrestor bed is a 

passive system, so this is the only action required by 

the pilot. 

4.	 Once stopped, do not attempt to taxi or otherwise move 

the aircraft. 

Chapter Summary 

This chapter focused on airport operations both in the air and 

on the surface. For specific information about an unfamiliar 

airport, consult the Chart Supplement U.S. (formerly 

Airport/Facility Directory) and NOTAMS before flying. For 

further information regarding procedures discussed in this 

chapter, refer to 14 CFR part 91 and the AIM. By adhering 

to established procedures, both airport operations and safety 

are enhanced. 

This chapter is also designed to help you attain an 

understanding of the risks associated with surface navigation 

and is intended to provide you with basic information 

regarding the safe operation of aircraft at towered and 

nontowered airports. This chapter focuses on the following 

major areas: 

•	 Runway incursion overview 

•	 Taxi route planning 

•	 Taxi procedures 

•	 Communications 

•	 Airport signs, markings and lighting 

Figure 14-58. A Bombardier CRJ-200 regional jet overran the 

runway at Yeager Airport (KCRW) in Charleston, West Virginia. 

The chapter identifies best practices to help you avoid errors 

that may potentially lead to runway incursions. Although the 

chapter pertains mostly to surface movements for single-pilot 

operations, all of the information is relevant for flight crew 

operations as well. 

Additional information about surface operations is available 

through the following sources: 

•	 Federal Aviation Administration (FAA) Runway 

Safety website—www.faa.gov/go/runwaysafety 

•	 FAA National Aeronautical Navigation Services 

(AeroNav), formerly known as the National 

Aeronautical Charting Office (NACO)—www.faa. 

gov/air_traffic/flight_info/aeronav 

•	 Chart Supplement U.S. (formerly Airport/Facility 

Directory)—www.faa.gov/air_traffic/flight_info/ 

aeronav/digital_products/dafd/search/ 

•	 Automatic Terminal Information Service (ATIS) 

•	 Notice to Airmen (NOTAMs)—http://www.faa.gov/ 

pilots/flt_plan/notams 

•	 Advisory Circular (AC) 91-73, part 91 and part 135, 

Single-Pilot and Flight School Procedures During Taxi 

Operations 

•	 Aeronautical Information Manual (AIM)—www.faa. 

gov/air_traffic/publications/atpubs/aim/ 

•	 AC 120-74, parts 91, 121, 125, and 135, Flight Crew 

Procedures During Taxi Operations 

14-37 
Not to be used for navigation

Figure 14-59. EMAS information for Boston Logan International Airport located in the Chart Supplement U.S. (formerly Airport/ 

Facility Directory). 

14-38 
NE-1,

2

8

J

UL 2011 to 25 AU

G

2

011

N

E-1, 28 JUL 2011 to 25 AUG 2011 

Not to be used for navigation

Figure 14-60. An airport diagram with EMAS information. 

14-39 
14-40
 
 

15-1 

Introduction 

The two categories of airspace are: regulatory and 

nonregulatory. Within these two categories, there are four 

types: controlled, uncontrolled, special use, and other 

airspace. The categories and types of airspace are dictated 

by the complexity or density of aircraft movements, nature 

of the operations conducted within the airspace, the level of 

safety required, and national and public interest. Figure 15-1 

presents a profile view of the dimensions of various classes 

of airspace. Also, there are excerpts from sectional charts 

that are discussed in Chapter 16, Navigation, that are used 

to illustrate how airspace is depicted. 

Airspace 

Chapter 15 
 

 

14,500' MSL 

Nontowered 

airport with

instrument 

approach 

Nontowered 

airport with

no instrument 

approach 

700' 

AGL 700' 

AGL 

18,000' MSL 

FL 600 

1,200' 

AGL 

700' 

AGL 

1,200'

AGL 1,200'

AGL 

Class A 

Class B 

Class C 

Class D 

Class E 

Class G 

Class G Class G Class G 

Figure 15-1. Airspace profile. 

Controlled Airspace 

Controlled airspace is a generic term that covers the 

different classifications of airspace and defined dimensions 

within which air traffic control (ATC) service is provided 

in accordance with the airspace classification. Controlled 

airspace consists of: 

• Class A 

• Class B 

• Class C 

• Class D 

• Class E 

Class A Airspace 

Class A airspace is generally the airspace from 18,000 feet 

mean sea level (MSL) up to and including flight level (FL) 

600, including the airspace overlying the waters within 12 

nautical miles (NM) of the coast of the 48 contiguous states 

and Alaska. Unless otherwise authorized, all operation in Class 

A airspace is conducted under instrument flight rules (IFR). 

Class B Airspace 

Class B airspace is generally airspace from the surface to 

10,000 feet MSL surrounding the nation’s busiest airports in 

terms of airport operations or passenger enplanements. The 

configuration of each Class B airspace area is individually 

tailored, consists of a surface area and two or more layers 

(some Class B airspace areas resemble upside-down wedding 

cakes), and is designed to contain all published instrument 

procedures once an aircraft enters the airspace. ATC 

clearance is required for all aircraft to operate in the area, 

and all aircraft that are so cleared receive separation services 

within the airspace. 

Class C Airspace 

Class C airspace is generally airspace from the surface to 

4,000 feet above the airport elevation (charted in MSL) 

surrounding those airports that have an operational control 

tower, are serviced by a radar approach control, and have a 

certain number of IFR operations or passenger enplanements. 

Although the configuration of each Class C area is 

individually tailored, the airspace usually consists of a surface 

area with a five NM radius, an outer circle with a ten NM 

radius that extends from 1,200 feet to 4,000 feet above the 

airport elevation. Each aircraft must establish two-way radio 

communications with the ATC facility providing air traffic 

services prior to entering the airspace and thereafter must 

maintain those communications while within the airspace. 

Class D Airspace 

Class D airspace is generally airspace from the surface to 

2,500 feet above the airport elevation (charted in MSL) 

surrounding those airports that have an operational control 

tower. The configuration of each Class D airspace area is 

individually tailored and, when instrument procedures are 

published, the airspace is normally designed to contain the 

procedures. Arrival extensions for instrument approach 

procedures (IAPs) may be Class D or Class E airspace. Unless 

otherwise authorized, each aircraft must establish two-way 

radio communications with the ATC facility providing air 

traffic services prior to entering the airspace and thereafter 

maintain those communications while in the airspace. 

Class E Airspace 

Class E airspace is the controlled airspace not classified as 

Class A, B, C, or D airspace. A large amount of the airspace 

over the United States is designated as Class E airspace. 

15-2 
 

 

This provides sufficient airspace for the safe control and 

separation of aircraft during IFR operations. Chapter 3 of 

the Aeronautical Information Manual (AIM) explains the 

various types of Class E airspace. 

Sectional and other charts depict all locations of Class E 

airspace with bases below 14,500 feet MSL. In areas where 

charts do not depict a class E base, class E begins at 14,500 

feet MSL. 

In most areas, the Class E airspace base is 1,200 feet AGL. In 

many other areas, the Class E airspace base is either the surface 

or 700 feet AGL. Some Class E airspace begins at an MSL 

altitude depicted on the charts, instead of an AGL altitude. 

Class E airspace typically extends up to, but not including, 

18,000 feet MSL (the lower limit of Class A airspace). All 

airspace above FL 600 is Class E airspace. 

Uncontrolled Airspace 

Class G Airspace 

Uncontrolled airspace or Class G airspace is the portion of 

the airspace that has not been designated as Class A, B, C, 

D, or E. It is therefore designated uncontrolled airspace. 

Class G airspace extends from the surface to the base of the 

overlying Class E airspace. Although ATC has no authority 

or responsibility to control air traffic, pilots should remember 

there are visual flight rules (VFR) minimums that apply to 

Class G airspace. 

Special Use Airspace 

Special use airspace or special area of operation (SAO) 

is the designation for airspace in which certain activities 

must be confined, or where limitations may be imposed 

on aircraft operations that are not part of those activities. 

Certain special use airspace areas can create limitations on 

the mixed use of airspace. The special use airspace depicted 

on instrument charts includes the area name or number, 

effective altitude, time and weather conditions of operation, 

the controlling agency, and the chart panel location. On 

National Aeronautical Charting Group (NACG) en route 

charts, this information is available on one of the end panels. 

Special use airspace usually consists of: 

• Prohibited areas 

• Restricted areas 

• Warning areas 

• Military operation areas (MOAs) 

• Alert areas 

• Controlled firing areas (CFAs) 

Prohibited Areas 

Prohibited areas contain airspace of defined dimensions 

within which the flight of aircraft is prohibited. Such areas 

are established for security or other reasons associated with 

the national welfare. These areas are published in the Federal 

Register and are depicted on aeronautical charts. The area is 

charted as a “P” followed by a number (e.g., P-40). Examples 

of prohibited areas include Camp David and the National 

Mall in Washington, D.C., where the White House and the 

Congressional buildings are located. [Figure 15-2] 

Restricted Areas 

Restricted areas are areas where operations are hazardous to 

nonparticipating aircraft and contain airspace within which 

the flight of aircraft, while not wholly prohibited, is subject 

to restrictions. Activities within these areas must be confined 

because of their nature, or limitations may be imposed upon 

aircraft operations that are not a part of those activities, or 

both. Restricted areas denote the existence of unusual, often 

invisible, hazards to aircraft (e.g., artillery firing, aerial 

gunnery, or guided missiles). IFR flights may be authorized 

to transit the airspace and are routed accordingly. Penetration 

of restricted areas without authorization from the using 

or controlling agency may be extremely hazardous to the 

aircraft and its occupants. ATC facilities apply the following 

procedures when aircraft are operating on an IFR clearance 

(including those cleared by ATC to maintain VFR on top) via 

a route that lies within joint-use restricted airspace: 

1.	 If the restricted area is not active and has been released 

to the Federal Aviation Administration (FAA), the 

ATC facility allows the aircraft to operate in the 

restricted airspace without issuing specific clearance 

for it to do so. 

2.	 If the restricted area is active and has not been released 

to the FAA, the ATC facility issues a clearance that 

ensures the aircraft avoids the restricted airspace. 

Figure 15-2. An example of a prohibited area, P-40 around Camp 

David. 

15-3 
 

 

Restricted areas are charted with an “R” followed by a 

number (e.g., R-4401) and are depicted on the en route 

chart appropriate for use at the altitude or FL being flown. 

[Figure 15-3] Restricted area information can be obtained 

on the back of the chart. 

Warning Areas 

Warning areas are similar in nature to restricted areas; 

however, the United States government does not have sole 

jurisdiction over the airspace. A warning area is airspace of 

defined dimensions, extending from 3 NM outward from 

the coast of the United States, containing activity that may 

be hazardous to nonparticipating aircraft. The purpose of 

such areas is to warn nonparticipating pilots of the potential 

danger. A warning area may be located over domestic or 

international waters or both. The airspace is designated with 

a “W” followed by a number (e.g., W-237). [Figure 15-4] 

Military Operation Areas (MOAs) 

MOAs consist of airspace with defined vertical and lateral 

limits established for the purpose of separating certain 

military training activities from IFR traffic. Whenever an 

MOA is being used, nonparticipating IFR traffic may be 

cleared through an MOA if IFR separation can be provided by 

ATC. Otherwise, ATC reroutes or restricts nonparticipating 

IFR traffic. MOAs are depicted on sectional, VFR terminal 

area, and en route low altitude charts and are not numbered 

(e.g., “Camden Ridge MOA”). [Figure 15-5] However, the 

MOA is also further defined on the back of the sectional 

charts with times of operation, altitudes affected, and the 

controlling agency. 

Alert Areas 

Alert areas are depicted on aeronautical charts with an “A” 

followed by a number (e.g., A-211) to inform nonparticipating 

Figure 15-3. Restricted areas on a sectional chart. 

Figure 15-4. Requirements for airspace operations. 

pilots of areas that may contain a high volume of pilot training 

or an unusual type of aerial activity. Pilots should exercise 

caution in alert areas. All activity within an alert area shall 

be conducted in accordance with regulations, without waiver, 

and pilots of participating aircraft, as well as pilots transiting 

the area, shall be equally responsible for collision avoidance. 

[Figure 15-6] 

Controlled Firing Areas (CFAs) 

CFAs contain activities that, if not conducted in a controlled 

environment, could be hazardous to nonparticipating aircraft. 

The difference between CFAs and other special use airspace 

is that activities must be suspended when a spotter aircraft, 

radar, or ground lookout position indicates an aircraft might 

be approaching the area. There is no need to chart CFAs 

since they do not cause a nonparticipating aircraft to change 

its flight path. 

Other Airspace Areas 

“Other airspace areas” is a general term referring to the 

majority of the remaining airspace. It includes: 

• Local airport advisory (LAA) 

• Military training route (MTR) 

• Temporary flight restriction (TFR) 

• Parachute jump aircraft operations 

• Published VFR routes 

• Terminal radar service area (TRSA) 

• National security area (NSA) 

•	 Air Defense Identification Zones (ADIZ) land and 

water based and need for Defense VFR (DVFR) flight 

plan to operate VFR in this airspace 

•	 Intercept Procedures and use of 121.5 for 

communication if not on ATC already 

15-4 
Figure 15-5. Camden Ridge MOA is an example of a military operations area. 

Figure 15-6. Alert area (A-211). 

15-5 
 

 

 

 

 

 

 

 

• Flight Restricted Zones (FRZ) in vicinity of Capitol 

and White House 

•	 Special Awareness Training required by 

14 CFR 91.161 for pilots to operate VFR within 60 

NM of the Washington, DC VOR/DME 

• Wildlife Areas/Wilderness Areas/National Parks and 

request to operate above 2,000 AGL 

•	 National Oceanic and Atmospheric Administration 

(NOAA) Marine Areas off the coast with requirement 

to operate above 2,000 AGL 

•	 Tethered Balloons for observation and weather 

recordings that extend on cables up to 60,000 

Local Airport Advisory (LAA) 

An advisory service provided by Flight Service Station 

(FSS) facilities, which are located on the landing airport, 

using a discrete ground-to-air frequency or the tower 

frequency when the tower is closed. LAA services include 

local airport advisories, automated weather reporting with 

voice broadcasting, and a continuous Automated Surface 

Observing System (ASOS)/Automated Weather Observing 

Station (AWOS) data display, other continuous direct reading 

instruments, or manual observations available to the specialist. 

Military Training Routes (MTRs) 

MTRs are routes used by military aircraft to maintain 

proficiency in tactical flying. These routes are usually 

established below 10,000 feet MSL for operations at speeds 

in excess of 250 knots. Some route segments may be defined 

at higher altitudes for purposes of route continuity. Routes 

are identified as IFR (IR), and VFR (VR), followed by 

a number. [Figure 15-7] MTRs with no segment above 

1,500 feet AGL are identified by four number characters 

(e.g., IR1206, VR1207). MTRs that include one or more 

segments above 1,500 feet AGL are identified by three 

number characters (e.g., IR206, VR207). IFR low altitude 

en route charts depict all IR routes and all VR routes that 

Military Training 

Route (MTR) 

Figure 15-7. Military training route (MTR) chart symbols. 

accommodate operations above 1,500 feet AGL. IR routes 

are conducted in accordance with IFR regardless of weather 

conditions. VFR sectional charts depict military training 

activities, such as IR, VR, MOA, restricted area, warning 

area, and alert area information. 

Temporary Flight Restrictions (TFR) 

A flight data center (FDC) Notice to Airmen (NOTAM) 

is issued to designate a TFR. The NOTAM begins with 

the phrase “FLIGHT RESTRICTIONS” followed by the 

location of the temporary restriction, effective time period, 

area defined in statute miles, and altitudes affected. The 

NOTAM also contains the FAA coordination facility and 

telephone number, the reason for the restriction, and any other 

information deemed appropriate. The pilot should check the 

NOTAMs as part of flight planning. 

Some of the purposes for establishing a TFR are: 

•	 Protect persons and property in the air or on the surface 

from an existing or imminent hazard. 

•	 Provide a safe environment for the operation of 

disaster relief aircraft. 

• Prevent an unsafe congestion of sightseeing aircraft 

above an incident or event, that may generate a high 

degree of public interest. 

• Protect declared national disasters for humanitarian 

reasons in the State of Hawaii. 

• Protect the President, Vice President, or other public 

figures. 

•	 Provide a safe environment for space agency 

operations. 

Since the events of September 11, 2001, the use of TFRs has 

become much more common. There have been a number of 

incidents of aircraft incursions into TFRs that have resulted 

in pilots undergoing security investigations and certificate 

suspensions. It is a pilot’s responsibility to be aware of TFRs 

in their proposed area of flight. One way to check is to visit 

the FAA website, www.tfr.faa.gov, and verify that there is 

not a TFR in the area. 

Parachute Jump Aircraft Operations 

Parachute jump aircraft operations are published in the Chart 

Supplement U.S. (formerly Airport/Facility Directory). Sites 

that are used frequently are depicted on sectional charts. 

Published VFR Routes 

Published VFR routes are for transitioning around, under, or 

through some complex airspace. Terms such as VFR flyway, 

VFR corridor, Class B airspace VFR transition route, and 

terminal area VFR route have been applied to such routes. 

15-6 
 

 

 

These routes are generally found on VFR terminal area 

planning charts. 

Terminal Radar Service Areas (TRSAs) 

TRSAs are areas where participating pilots can receive 

additional radar services. The purpose of the service is 

to provide separation between all IFR operations and 

participating VFR aircraft. 

The primary airport(s) within the TRSA become(s) Class D 

airspace. The remaining portion of the TRSA overlies other 

controlled airspace, which is normally Class E airspace 

beginning at 700 or 1,200 feet and established to transition to/ 

from the en route/terminal environment. TRSAs are depicted 

on VFR sectional charts and terminal area charts with a solid 

black line and altitudes for each segment. The Class D portion 

is charted with a blue segmented line. Participation in TRSA 

services is voluntary; however, pilots operating under VFR 

are encouraged to contact the radar approach control and take 

advantage of TRSA service. 

National Security Areas (NSAs) 

NSAs consist of airspace of defined vertical and lateral 

dimensions established at locations where there is a 

requirement for increased security and safety of ground 

facilities. Flight in NSAs may be temporarily prohibited by 

regulation under the provisions of Title 14 of the Code of 

Federal Regulations (14 CFR) part 99, and prohibitions are 

disseminated via NOTAM. Pilots are requested to voluntarily 

avoid flying through these depicted areas. 

Air Traffic Control and the National 

Airspace System 

The primary purpose of the ATC system is to prevent a 

collision between aircraft operating in the system and to 

organize and expedite the flow of traffic. In addition to 

its primary function, the ATC system has the capability to 

provide (with certain limitations) additional services. The 

ability to provide additional services is limited by many 

factors, such as the volume of traffic, frequency congestion, 

quality of radar, controller workload, higher priority duties, 

and the pure physical inability to scan and detect those 

situations that fall in this category. It is recognized that these 

services cannot be provided in cases in which the provision 

of services is precluded by the above factors. 

Consistent with the aforementioned conditions, controllers 

shall provide additional service procedures to the extent 

permitted by higher priority duties and other circumstances. 

The provision of additional services is not optional on the 

part of the controller, but rather is required when the work 

situation permits. Provide ATC service in accordance with 

the procedures and minima in this order except when: 

1.	 A deviation is necessary to conform to ICAO 

Documents, National Rules of the Air, or special 

agreements where the United States provides ATC 

service in airspace outside the country and its 

possessions 

2. Other procedures/minima are prescribed in a letter of 

agreement, FAA directive, or a military document 

3. A deviation is necessary to assist an aircraft when an 

emergency has been declared 

Coordinating the Use of Airspace 

ATC is responsible for ensuring that the necessary 

coordination has been accomplished before allowing an 

aircraft under their control to enter another controller’s area 

of jurisdiction. 

Before issuing control instructions directly or relaying 

through another source to an aircraft that is within another 

controller’s area of jurisdiction that will change that 

aircraft’s heading, route, speed, or altitude, ATC ensures 

that coordination has been accomplished with each of the 

controllers listed below whose area of jurisdiction is affected 

by those instructions unless otherwise specified by a letter 

of agreement or a facility directive: 

1. The controller within whose area of jurisdiction the 

control instructions are issued 

2. The controller receiving the transfer of control 

3. Any intervening controller(s) through whose area of 

jurisdiction the aircraft will pass 

If ATC issues control instructions to an aircraft through a 

source other than another controller (e.g., Aeronautical Radio, 

Incorporated (ARINC), FSS, another pilot), they ensure that 

the necessary coordination has been accomplished with any 

controllers listed above, whose area of jurisdiction is affected 

by those instructions unless otherwise specified by a letter 

of agreement or a facility directive. 

Operating in the Various Types of Airspace 

It is important that pilots be familiar with the operational 

requirements for each of the various types or classes of 

airspace. Subsequent sections cover each class in sufficient 

detail to facilitate understanding regarding weather, type of 

pilot certificate held, and equipment required. 

Basic VFR Weather Minimums 

No pilot may operate an aircraft under basic VFR when the 

flight visibility is less, or at a distance from clouds that is 

less, than that prescribed for the corresponding altitude and 

class of airspace. [Figure 15-8] Except as provided in 14 CFR 

part 91, section 91.157, “Special VFR Weather Minimums,” 

15-7 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Basic VFR Weather Minimums 

Airspace Flight Visibility Distance from Clouds 

Class A Not applicable Not applicable 

Class B 3 statute miles Clear of clouds 

Class C 

3 statute miles 1,000 feet above 

500 feet below 

2,000 feet horizontal 

Class D 

3 statute miles 1,000 feet above 

500 feet below 

2,000 feet horizontal 

At or above 

10,000 feet MSL 

5 statute miles 1,000 feet above 

1,000 feet below 

1 statute mile horizontal 

Class E 

Less than 3 statute miles 1,000 feet above 

10,000 feet MSL 500 feet below 

2,000 feet horizontal 

Day, except as provided in section 91.155(b) 1,200 feet or less 1 statute mile Clear of clouds 

Night, except as provided in section 91.155(b) above the surface 

(regardless of 

MSL altitude). 

3 statute miles 1,000 feet above 

500 feet below 

2,000 feet horizontal 

Day 1 statute mile 1,000 feet above 

More than 1,200 500 feet below 

feet above the 2,000 feet horizontal 

Class G surface but less

than 10,000 feet Night 3 statute miles 1,000 feet above 

MSL. 500 feet below 

2,000 feet horizontal 

More than 1,200 5 statute miles 1,000 feet above 

feet above the 1,000 feet below 

surface and at or 1 statute mile horizontal 

above 10,000 feet 

MSL. 

Figure 15-8. Visual flight rule weather minimums. 

no person may operate an aircraft beneath the ceiling under 

VFR within the lateral boundaries of controlled airspace 

designated to the surface for an airport when the ceiling is 

less than 1,000 feet. Additional information can be found in 

14 CFR part 91, section 91.155(c). 

Operating Rules and Pilot/Equipment Requirements 

The safety of flight is a top priority of all pilots and the 

responsibilities associated with operating an aircraft 

should always be taken seriously. The air traffic system 

maintains a high degree of safety and efficiency with strict 

regulatory oversight of the FAA. Pilots fly in accordance 

with regulations that have served the United States well, as 

evidenced by the fact that the country has the safest aviation 

system in the world. 

All aircraft operating in today’s National Airspace System 

(NAS) has complied with the CFR governing its certification 

and maintenance; all pilots operating today have completed 

rigorous pilot certification training and testing. Of equal 

importance is the proper execution of preflight planning, 

aeronautical decision-making (ADM) and risk management. 

ADM involves a systematic approach to risk assessment 

and stress management in aviation, illustrates how personal 

attitudes can influence decision-making, and how those 

attitudes can be modified to enhance safety in the flight 

deck. More detailed information regarding ADM and 

risk mitigation can be found in Chapter 2, “Aeronautical 

Decision-Making.” 

15-8 
 

 

 

 

 

Pilots also comply with very strict FAA general operating 

and flight rules as outlined in the CFR, including the FAA’s 

important “see and avoid” mandate. These regulations provide 

the historical foundation of the FAA regulations governing 

the aviation system and the individual classes of airspace. 

Figure 15-9 lists the operational and equipment requirements 

for these various classes of airspace. It is helpful to refer to this 

figure as the specific classes are discussed in greater detail. 

Class A 

Pilots operating an aircraft in Class A airspace must conduct 

that operation under IFR and only under an ATC clearance 

received prior to entering the airspace. Unless otherwise 

authorized by ATC, each aircraft operating in Class A 

airspace must be equipped with a two-way radio capable of 

communicating with ATC on a frequency assigned by ATC. 

Unless otherwise authorized by ATC, all aircraft within 

Class A airspace must be equipped with the appropriate 

transponder equipment meeting all applicable specifications 

found in 14 CFR part 91, section 91.215. Additionally, 

beginning January 1, 2020, aircraft operating in the Class 

A airspace described in 14 CFR part 91, section 91.225, 

must have ADS-B Out equipment installed, which meets the 

performance requirements of 14 CFR part 91, section 91.227. 

Class B 

All pilots operating an aircraft within a Class B airspace area 

must receive an ATC clearance from the ATC facility having 

jurisdiction for that area. The pilot in command (PIC) may 

not take off or land an aircraft at an airport within a Class 

B airspace unless he or she has met one of the following 

requirements: 

1. A private pilot certificate 

2.	 A recreational pilot certificate and all requirements 

contained within 14 CFR part 61, section 61.101(d), or 

the requirements for a student pilot seeking a recreational 

pilot certificate in 14 CFR part 61, section 61.94. 

3.	 A sport pilot certificate and all requirements contained 

within 14 CFR part 61, section 61.325, or the 

requirements for a student pilot seeking a recreational 

pilot certificate in 14 CFR part 61, section 61.94, or 

the aircraft is operated by a student pilot who has met 

the requirements of 14 CFR part 61, sections 61.94 

and 61.95, as applicable. 

Unless otherwise authorized by ATC, all aircraft within Class 

B airspace must be equipped with the applicable operating 

transponder and automatic altitude reporting equipment 

specified in 14 CFR part 91, section 91.215(a) and an 

operable two-way radio capable of communications with 

ATC on appropriate frequencies for that Class B airspace 

area. Additionally, beginning January 1, 2020, aircraft 

operating in the Class B airspace described in 14 CFR part 91, 

section 91.225, must have ADS-B Out equipment installed, 

which meets the performance requirements of 14 CFR part 

91, section 91.227. 

Class C 

For the purpose of this section, the primary airport is the 

airport for which the Class C airspace area is designated. A 

satellite airport is any other airport within the Class C airspace 

area. No pilot may take off or land an aircraft at a satellite 

airport within a Class C airspace area except in compliance 

with FAA arrival and departure traffic patterns. 

Two-way radio communications must be established and 

maintained with the ATC facility providing air traffic services 

Class 

Airspace Entry Requirements Equipment* Minimum Pilot Certificate 

Class A ATC clearance IFR equipped Instrument rating 

Class B ATC clearance Two-way radio, transponder 

with altitude reporting capability 

Private—(However, a student or 

recreational pilot may operate at 

other than the primary airport if 

seeking private pilot certification and 

if regulatory requirements are met.) 

Class C Two-way radio communications 

prior to entry 

Two-way radio, transponder 

with altitude reporting capability 

No specific requirement 

Class D Two-way radio communications 

prior to entry 

Two-way radio No specific requirement 

Class E None for VFR No specific requirement No specific requirement 

Class G None No specific requirement No specific requirement 

*Beginning January 1, 2020, ADS-B Out equipment may be required in accordance with 14 CFR part 91, section 91.225. 

Figure 15-9. Requirements for airspace operations. 

15-9 
 

 

prior to entering the airspace and thereafter maintained while 

within the airspace. 

A pilot departing from the primary airport or satellite airport 

with an operating control tower must establish and maintain 

two-way radio communications with the control tower, 

and thereafter as instructed by ATC while operating in the 

Class C airspace area. If departing from a satellite airport 

without an operating control tower, the pilot must establish 

and maintain two-way radio communications with the ATC 

facility having jurisdiction over the Class C airspace area as 

soon as practicable after departing. 

Unless otherwise authorized by the ATC having jurisdiction 

over the Class C airspace area, all aircraft within Class C 

airspace must be equipped with the appropriate transponder 

equipment meeting all applicable specifications found in 14 

CFR part 91, section 91.215. Additionally, beginning January 

1, 2020, aircraft operating in the Class C airspace described 

in 14 CFR part 91, section 91.225, must have ADS-B 

Out equipment installed, which meets the performance 

requirements of 14 CFR part 91, section 91.227. 

Class D 

No pilot may take off or land an aircraft at a satellite airport 

within a Class D airspace area except in compliance with 

FAA arrival and departure traffic patterns. A pilot departing 

from the primary airport or satellite airport with an operating 

control tower must establish and maintain two-way radio 

communications with the control tower, and thereafter as 

instructed by ATC while operating in the Class D airspace 

area. If departing from a satellite airport without an operating 

control tower, the pilot must establish and maintain twoway radio communications with the ATC facility having 

jurisdiction over the Class D airspace area as soon as 

practicable after departing. 

Two-way radio communications must be established and 

maintained with the ATC facility providing air traffic services 

prior to entering the airspace and thereafter maintained while 

within the airspace. 

If the aircraft radio fails in flight under IFR, the pilot should 

continue the flight by the route assigned in the last ATC 

clearance received; or, if being radar vectored, by the direct 

route from the point of radio failure to the fix, route, or 

airway specified in the vector clearance. In the absence of 

an assigned route, the pilot should continue by the route 

that ATC advised may be expected in a further clearance; 

or, if a route had not been advised, by the route filed in the 

flight plan. 

If the aircraft radio fails in flight under VFR, the PIC may 

operate that aircraft and land if weather conditions are at or 

above basic VFR weather minimums, visual contact with 

the tower is maintained, and a clearance to land is received. 

Class E 

Unless otherwise required by 14 CFR part 93 or unless 

otherwise authorized or required by the ATC facility having 

jurisdiction over the Class E airspace area, each pilot 

operating an aircraft on or in the vicinity of an airport in a 

Class E airspace area must comply with the requirements 

of Class G airspace. Each pilot must also comply with any 

traffic patterns established for that airport in 14 CFR part 93. 

Unless otherwise authorized or required by ATC, no person 

may operate an aircraft to, from, through, or on an airport 

having an operational control tower unless two-way radio 

communications are maintained between that aircraft and the 

control tower. Communications must be established within 

four nautical miles from the airport, up to and including 2,500 

feet AGL. However, if the aircraft radio fails in flight, the PIC 

may operate that aircraft and land if weather conditions are at 

or above basic VFR weather minimums, visual contact with 

the tower is maintained, and a clearance to land is received. 

If the aircraft radio fails in flight under IFR, the pilot should 

continue the flight by the route assigned in the last ATC 

clearance received; or, if being radar vectored, by the direct 

route from the point of radio failure to the fix, route, or 

airway specified in the vector clearance. In the absence of 

an assigned route, the pilot should continue by the route 

that ATC advised may be expected in a further clearance; 

or, if a route had not been advised, by the route filed in the 

flight plan. Additionally, beginning January 1, 2020, aircraft 

operating in the Class E airspace described in 14 CFR part 91, 

section 91.225, must have ADS-B Out equipment installed, 

which meets the performance requirements of 14 CFR part 

91, section 91.227. 

Class G 

When approaching to land at an airport without an operating 

control tower in Class G airspace: 

1. Each pilot of an airplane must make all turns of that 

airplane to the left unless the airport displays approved 

light signals or visual markings indicating that turns 

should be made to the right, in which case the pilot 

must make all turns to the right. 

2.	 Each pilot of a helicopter or a powered parachute must 

avoid the flow of fixed-wing aircraft. 

15-10 
Unless otherwise authorized or required by ATC, no person 

may operate an aircraft to, from, through, or on an airport 

having an operational control tower unless two-way radio 

communications are maintained between that aircraft and the 

control tower. Communications must be established within 

four nautical miles from the airport, up to and including 2,500 

feet AGL. However, if the aircraft radio fails in flight, the PIC 

may operate that aircraft and land if weather conditions are at 

or above basic VFR weather minimums, visual contact with 

the tower is maintained, and a clearance to land is received. 

If the aircraft radio fails in flight under IFR, the pilot should 

continue the flight by the route assigned in the last ATC 

clearance received; or, if being radar vectored, by the direct 

route from the point of radio failure to the fix, route, or airway 

specified in the vector clearance. In the absence of an assigned 

route, the pilot should continue by the route that ATC advised 

may be expected in a further clearance; or, if a route had not 

been advised, by the route filed in the flight plan. 

Uncontrolled Airspace 

It is possible for some airports within Class G airspace to 

have a control tower (Lake City, FL, for example). Be sure to 

check the Chart Supplement U.S. (formerly Airport/Facility 

Directory) to be familiar with the airport and associated 

airspace prior to flight. 

Ultralight Vehicles 

No person may operate an ultralight vehicle within Class A, 

Class B, Class C, or Class D airspace or within the lateral 

boundaries of the surface area of Class E airspace designated 

for an airport unless that person has prior authorization from 

the ATC facility having jurisdiction over that airspace. (See 

14 CFR part 103.) 

Unmanned Free Balloons 

Unless otherwise authorized by ATC, no person may operate 

an unmanned free balloon below 2,000 feet above the surface 

within the lateral boundaries of Class B, Class C, Class D, 

or Class E airspace designated for an airport. (See 14 CFR 

part 101.) 

Unmanned Aircraft Systems 

Regulations regarding unmanned aircraft systems (UAS) are 

currently being developed and are expected to be published 

by summer 2016 as 14 CFR part 107. 

Parachute Jumps 

No person may make a parachute jump, and no PIC may 

allow a parachute jump to be made from an aircraft, in or 

into Class A, Class B, Class C, or Class D airspace without, 

or in violation of, the terms of an ATC authorization issued 

by the ATC facility having jurisdiction over the airspace. 

(See 14 CFR part 105.) 

Chapter Summary 

This chapter introduces the various classifications of airspace 

and provides information on the requirements to operate in 

such airspace. For further information, consult the AIM and 

14 CFR parts 71, 73, and 91. 

15-11 
15-12
 
16-1 

Navigation 

Chapter 16 

Introduction 

This chapter provides an introduction to cross-country 

flying under visual flight rules (VFR). It contains practical 

information for planning and executing cross-country flights 

for the beginning pilot. 

Air navigation is the process of piloting an aircraft from 

one geographic position to another while monitoring one’s 

position as the flight progresses. It introduces the need for 

planning, which includes plotting the course on an aeronautical 

chart, selecting checkpoints, measuring distances, obtaining 

pertinent weather information, and computing flight time, 

headings, and fuel requirements. The methods used in this 

chapter include pilotage—navigating by reference to visible 

landmarks, dead reckoning—computations of direction and 

distance from a known position, and radio navigation—by 

use of radio aids. 
Aeronautical Charts 

An aeronautical chart is the road map for a pilot flying under 

VFR. The chart provides information that allows pilots to track 

their position and provides available information that enhances 

safety. The three aeronautical charts used by VFR pilots are: 

• Sectional 

• VFR Terminal Area 

• World Aeronautical 

A free catalog listing aeronautical charts and related 

publications including prices and instructions for ordering is 

available at the Aeronautical Navigation Products website: 

www.aeronav.faa.gov. 

Sectional Charts 

Sectional charts are the most common charts used by pilots 

today. The charts have a scale of 1:500,000 (1 inch = 6.86 

nautical miles (NM) or approximately 8 statute miles (SM)), 

which allows for more detailed information to be included 

on the chart. 

The charts provide an abundance of information, including 

airport data, navigational aids, airspace, and topography. 

Figure 16-1 is an excerpt from the legend of a sectional 

chart. By referring to the chart legend, a pilot can interpret 

most of the information on the chart. A pilot should also 

check the chart for other legend information, which includes 

air traffic control (ATC) frequencies and information on 

airspace. These charts are revised semiannually except for 

some areas outside the conterminous United States where 

they are revised annually. 

VFR Terminal Area Charts 

VFR terminal area charts are helpful when flying in or near 

Class B airspace. They have a scale of 1:250,000 (1 inch 

= 3.43 NM or approximately 4 SM). These charts provide 

a more detailed display of topographical information and 

are revised semiannually, except for several Alaskan and 

Caribbean charts. [Figure 16-2] 

World Aeronautical Charts 

World aeronautical charts are designed to provide a standard 

series of aeronautical charts, covering land areas of the world, 

Figure 16-1. Sectional chart and legend. 

16-2 
Figure 16-2. VFR Terminal Area Chart and legend. 

at a size and scale convenient for navigation by moderate speed 

aircraft. They are produced at a scale of 1:1,000,000 (1 inch = 

13.7 NM or approximately 16 SM). These charts are similar to 

sectional charts, and the symbols are the same except there is 

less detail due to the smaller scale. [Figure 16-3] These charts 

are revised annually except several Alaskan charts and the 

Mexican/Caribbean charts, which are revised every 2 years. 

Latitude and Longitude (Meridians and 

Parallels) 

The equator is an imaginary circle equidistant from the poles 

of the Earth. Circles parallel to the equator (lines running east 

and west) are parallels of latitude. They are used to measure 

degrees of latitude north (N) or south (S) of the equator. The 

angular distance from the equator to the pole is one-fourth 

of a circle or 90°. The 48 conterminous states of the United 

States are located between 25° and 49° N latitude. The arrows 

in Figure 16-4 labeled “Latitude” point to lines of latitude. 

Meridians of longitude are drawn from the North Pole to the 

South Pole and are at right angles to the Equator. The “Prime 

Meridian,” which passes through Greenwich, England, is 

used as the zero line from which measurements are made in 

degrees east (E) and west (W) to 180°. The 48 conterminous 

states of the United States are between 67° and 125° W 

longitude. The arrows in Figure 16-4 labeled “Longitude” 

point to lines of longitude. 

Any specific geographical point can be located by reference 

to its longitude and latitude. Washington, D.C., for example, 

is approximately 39° N latitude, 77° W longitude. Chicago 

is approximately 42° N latitude, 88° W longitude. 

Time Zones 

The meridians are also useful for designating time zones. A 

day is defined as the time required for the Earth to make one 

complete rotation of 360°. Since the day is divided into 24 

hours, the Earth revolves at the rate of 15° an hour. Noon is 

the time when the sun is directly above a meridian; to the 

west of that meridian is morning, to the east is afternoon. 

16-3 
Longitude 

Latitu

d

e 

ator 

°N 

60°N 

4 N 

30

°N 

°S 

°S 

°S 

°°SS 

150°W

135°W 

120°W 

105°W 

90°W

60°W 

45°W 

30°W 

15°W 

Prime 

m

eridian 

The standard practice is to establish a time zone for each 90°N

°N 

Figure 16-4. Meridians and parallels—the basis of measuring time,

7

Figure 16-3. World aeronautical chart.

5°W

15° of longitude. This makes a difference of exactly 1 hour 75

between each zone. In the conterminous United States, 

there are four time zones. The time zones are Eastern (75°), 

Central (90°), Mountain (105°), and Pacific (120°). The 

dividing lines are somewhat irregular because communities 

near the boundaries often find it more convenient to use time 

5°

designations of neighboring communities or trade centers. 

15 Figure 16-5 shows the time zones in the conterminous United 

States. When the sun is directly above the 90th meridian, it 

is noon Central Standard Time. At the same time, it is 1 p.m. 

Eastern Standard Time, 11 a.m. Mountain Standard Time, 

Equ

15 and 10 a.m. Pacific Standard Time. When Daylight Saving 

Time is in effect, generally between the second Sunday in 30 March and the first Sunday in November, the sun is directly 

45 above the 75th meridian at noon, Central Daylight Time. 6600

These time zone differences must be taken into account 

during long flights eastward—especially if the flight must 

be completed before dark. Remember, an hour is lost when distance, and direction. 

16-4 
105° 

120° 

90° 

75° 

Pacific standard time Mountain standard time Central standard time Eastern standard time

Figure 16-5. Time zones in the conterminous United States. 

flying eastward from one time zone to another, or perhaps 

even when flying from the western edge to the eastern edge 

of the same time zone. Determine the time of sunset at the 

destination by consulting the flight service station (FSS) and 

take this into account when planning an eastbound flight. 

In most aviation operations, time is expressed in terms of 

the 24-hour clock. ATC instructions, weather reports and 

broadcasts, and estimated times of arrival are all based on 

this system. For example: 9 a.m. is expressed as 0900, 1 p.m. 

is 1300, and 10 p.m. is 2200. 

Because a pilot may cross several time zones during a flight, a 

standard time system has been adopted. It is called Universal 

Coordinated Time (UTC) and is often referred to as Zulu 

time. UTC is the time at the 0° line of longitude which passes 

through Greenwich, England. All of the time zones around 

the world are based on this reference. To convert to this time, 

a pilot should do the following: 

Eastern Standard Time ..........Add 5 hours
 

Central Standard Time ..........Add 6 hours
 

Mountain Standard Time.......Add 7 hours
 

Pacific Standard Time...........Add 8 hours
 

For Daylight Saving Time, 1 hour should be subtracted from 

the calculated times. 

Measurement of Direction 

By using the meridians, direction from one point to another 

can be measured in degrees, in a clockwise direction from 

true north. To indicate a course to be followed in flight, 

draw a line on the chart from the point of departure to the 

destination and measure the angle that this line forms with 

a meridian. Direction is expressed in degrees, as shown by 

the compass rose in Figure 16-6. 

Because meridians converge toward the poles, course 

measurement should be taken at a meridian near the midpoint 

of the course rather than at the point of departure. The course 

measured on the chart is known as the true course (TC). This 

is the direction measured by reference to a meridian or true 

north (TN). It is the direction of intended flight as measured 

in degrees clockwise from TN. 

As shown in Figure 16-7, the direction from A to B would be 

a TC of 065°, whereas the return trip (called the reciprocal) 

would be a TC of 245°. 

16-5 
065°

245°

36 

33 

30 

27 

24 

21 

18 

15 

12 

9 

6 

3 

NNW

NNE

NE

N

ESE

SS

WSS

E

WSW

WNW

NE

SE

SW

NW

The north magnetic pole is located close to 71° N latitude, 96° 

W longitude and is about 1,300 miles from the geographic 

or true north pole, as indicated in Figure 16-8. If the Earth 

were uniformly magnetized, the compass needle would point 

W

N

Figure 16-6. Compass rose. line.) An isogonic chart is shown in Figure 16-9. Minor 

bends and turns in the isogonic and agonic lines are caused 

The true heading (TH) is the direction in which the nose of by unusual geological conditions affecting magnetic forces 

the aircraft points during a flight when measured in degrees in these areas. 

clockwise from TN. Usually, it is necessary to head the 

aircraft in a direction slightly different from the TC to offset On the west coast of the United States, the compass needle 

E

the effect of wind. Consequently, numerical value of the TH points to the east of TN; on the east coast, the compass needle 

may not correspond with that of the TC. This is discussed points to the west of TN. 

more fully in subsequent sections in this chapter. For the 

purpose of this discussion, assume a no-wind condition exists 

under which heading and course would coincide. Thus, for 

a TC of 065°, the TH would be 065°. To use the compass 

accurately, however, corrections must be made for magnetic 

variation and compass deviation. 

Variation 

Variation is the angle between TN and magnetic north (MN). 

It is expressed as east variation or west variation depending 

upon whether MN is to the east or west of TN. TN 

Course A to B 065° MN 

toward the magnetic pole, in which case the variation between 

TN (as shown by the geographical meridians) and MN (as 

shown by the magnetic meridians) could be measured at any 

intersection of the meridians. 

Actually, the Earth is not uniformly magnetized. In the United 

States, the needle usually points in the general direction of 

the magnetic pole, but it may vary in certain geographical 

localities by many degrees. Consequently, the exact amount 

of variation at thousands of selected locations in the United 

States has been carefully determined. The amount and the 

direction of variation, which change slightly from time 

to time, are shown on most aeronautical charts as broken 

magenta lines called isogonic lines that connect points of 

equal magnetic variation. (The line connecting points at 

which there is no variation between TN and MN is the agonic 

S

B 

A Course B to A 245° Figure 16-8. Magnetic meridians are in red while the lines of 

longitude and latitude are in blue. From these lines of variation 

Figure 16-7. Courses are determined by reference to meridians on (magnetic meridians), one can determine the effect of local magnetic 

aeronautical charts. variations on a magnetic compass. 

16-6 
Figure 16-9. Note the agonic line where magnetic variation is zero. 

Easterly variation Westerly variation 

Agonic line 

Zero degree variation exists on the agonic line where 

MN and TN coincide. This line runs roughly west of the 

Great Lakes, south through Wisconsin, Illinois, western 

Tennessee, and along the border of Mississippi and Alabama. 

Compare Figures 16-9 and 16-10. 

Because courses are measured in reference to geographical 

meridians that point toward TN, and these courses are 

maintained by reference to the compass that points along a 

magnetic meridian in the general direction of MN, the true 

direction must be converted into magnetic direction for the 

purpose of flight. This conversion is made by adding or 

subtracting the variation indicated by the nearest isogonic 

line on the chart. 

For example, a line drawn between two points on a chart 

is called a TC as it is measured from TN. However, flying 

this course off the magnetic compass would not provide an 

accurate course between the two points due to three elements 

that must be considered. The first is magnetic variation, the 

second is compass deviation, and the third is wind correction. 

All three must be considered for accurate navigation. 

Magnetic Variation 

As mentioned in the paragraph discussing variation, the 

appropriate variation for the geographical location of 

the flight must be considered and added or subtracted as 

appropriate. If flying across an area where the variation 

changes, then the values must be applied along the route of 

flight appropriately. Once applied, this new course is called 

the magnetic course. 

Magnetic Deviation 

Because each aircraft has its own internal effect upon the 

onboard compass systems from its own localized magnetic 

influencers, the pilot must add or subtract these influencers 

based upon the direction he or she is flying. The application of 

deviation (taken from a compass deviation card) compensates 

the magnetic course unique to that aircraft’s compass system 

(as affected by localized magnetic influencers) and it now 

becomes the compass course. Therefore, the compass course, 

when followed (in a no wind condition), takes the aircraft 

from point A to point B even though the aircraft heading 

may not match the original course line drawn on the chart. 

If the variation is shown as “9° E,” this means that MN is 

9° east of TN. If a TC of 360° is to be flown, 9° must be 

subtracted from 360°, which results in a magnetic heading 

of 351°. To fly east, a magnetic course of 081° (090° – 9°) 

would be flown. To fly south, the magnetic course would be 

171° (180° – 9°). To fly west, it would be 261° (270° – 9°). 

To fly a TH of 060°, a magnetic course of 051° (060° – 9°) 

would be flown. 

Zero 

variation 

N 33 30 W 24 21 

S 15 12 E 

6 3 

N 33 30 W 24 21 

S 15 12 E 

6 3 

N 33 30 W 24 21 

S 15 12 E 

6 3 

West 

variation

East

variation 

NP 

MP 

SP SP

NP 

MP 

NP 

MP 

SP 

Figure 16-10. Effect of variation on the compass. 

16-7 
 

Remember, if variation is west, add; if east, subtract. One 

method for remembering whether to add or subtract variation 

is the phrase “east is least (subtract) and west is best (add).” 

Deviation 

Determining the magnetic heading is an intermediate step 

necessary to obtain the correct compass heading for the flight. 

To determine compass heading, a correction for deviation 

must be made. Because of magnetic influences within an 

aircraft, such as electrical circuits, radio, lights, tools, engine, 

and magnetized metal parts, the compass needle is frequently 

deflected from its normal reading. This deflection is called 

deviation. The deviation is different for each aircraft, and 

it also may vary for different headings in the same aircraft. 

For instance, if magnetism in the engine attracts the north 

end of the compass, there would be no effect when the plane 

is on a heading of MN. On easterly or westerly headings, 

however, the compass indications would be in error, as shown 

in Figure 16-11. Magnetic attraction can come from many 

other parts of the aircraft; the assumption of attraction in the 

engine is merely used for the purpose of illustration. 

Some adjustment of the compass, referred to as compensation, 

can be made to reduce this error, but the remaining correction 

must be applied by the pilot. 

Proper compensation of the compass is best performed by 

a competent technician. Since the magnetic forces within 

the aircraft change because of landing shocks, vibration, 

mechanical work, or changes in equipment, the pilot should 

occasionally have the deviation of the compass checked. The 

procedure used to check the deviation is called “swinging the 

compass” and is briefly outlined as follows. 

Figure 16-11. Magnetized portions of the airplane cause the 

compass to deviate from its normal indications. 

N 33 30 W 24 21 

S 15 12 E 

6 3 

N 33 30 W 24 21 

S 15 12

E 6 3

N 33 30 W 24 21 

S 15 12

E 6 3 

Magnetic North 

Magnetic North Magnetic North 

Magnetized engine 

The aircraft is placed on a magnetic compass rose, the engine 

started, and electrical devices normally used (such as radio) 

are turned on. Tailwheel-type aircraft should be jacked up into 

flying position. The aircraft is aligned with MN indicated on 

the compass rose and the reading shown on the compass is 

recorded on a deviation card. The aircraft is then aligned at 

30° intervals and each reading is recorded. If the aircraft is to 

be flown at night, the lights are turned on and any significant 

changes in the readings are noted. If so, additional entries 

are made for use at night. The accuracy of the compass can 

also be checked by comparing the compass reading with the 

known runway headings. 

A deviation card, similar to Figure 16-12, is mounted near 

the compass showing the addition or subtraction required to 

correct for deviation on various headings, usually at intervals 

of 30°. For intermediate readings, the pilot should be able to 

interpolate mentally with sufficient accuracy. For example, 

if the pilot needed the correction for 195° and noted the 

correction for 180° to be 0° and for 210° to be +2°, it could 

be assumed that the correction for 195° would be +1°. The 

magnetic heading, when corrected for deviation, is known 

as compass heading. 

Effect of Wind 

The preceding discussion explained how to measure a TC 

on the aeronautical chart and how to make corrections for 

variation and deviation, but one important factor has not 

been considered—wind. As discussed in the study of the 

atmosphere, wind is a mass of air moving over the surface of 

the Earth in a definite direction. When the wind is blowing 

from the north at 25 knots, it simply means that air is moving 

southward over the Earth’s surface at the rate of 25 NM in 

1 hour. 

Under these conditions, any inert object free from contact 

with the Earth is carried 25 NM southward in 1 hour. This 

effect becomes apparent when such things as clouds, dust, 

and toy balloons are observed being blown along by the wind. 

Obviously, an aircraft flying within the moving mass of air 

is similarly affected. Even though the aircraft does not float 

freely with the wind, it moves through the air at the same 

time the air is moving over the ground, and thus is affected 

by wind. Consequently, at the end of 1 hour of flight, the 

aircraft is in a position that results from a combination of 

the following two motions: 

For (Magnetic) N 30 60 E 120 150 

Steer (Compass) 0 28 57 86 117 148 

For (Magnetic S 210 240 W 300 330 

Steer (Compass) 180 212 243 274 303 332 

Figure 16-12. Compass deviation card. 

16-8 
 

 

• Movement of the air mass in reference to the ground 

• Forward movement of the aircraft through the air mass 

Actually, these two motions are independent. It makes no 

difference whether the mass of air through which the aircraft 

is flying is moving or is stationary. A pilot flying in a 70- 

knot gale would be totally unaware of any wind (except for 

possible turbulence) unless the ground were observed. In 

reference to the ground, however, the aircraft would appear 

to fly faster with a tailwind or slower with a headwind, or to 

drift right or left with a crosswind. 

As shown in Figure 16-13, an aircraft flying eastward at 

an airspeed of 120 knots in still air has a groundspeed (GS) 

exactly the same—120 knots. If the mass of air is moving 

eastward at 20 knots, the airspeed of the aircraft is not 

affected, but the progress of the aircraft over the ground is 

120 plus 20 or a GS of 140 knots. On the other hand, if the 

Figure 16-13. Motion of the air affects the speed with which aircraft 

move over the Earth’s surface. Airspeed, the rate at which an 

aircraft moves through the air, is not affected by air motion. 

090° 

Groundspeed 120 knots 

WINDS ARE CALM 

090° 

Groundspeed 140 knots 

WINDS 270° AT 20 KNOTS 

090° 

Groundspeed 100 knots 

WINDS 090° AT 20 KNOTS 

mass of air is moving westward at 20 knots, the airspeed of 

the aircraft remains the same, but GS becomes 120 minus 

20 or 100 knots. 

Assuming no correction is made for wind effect, if an aircraft 

is heading eastward at 120 knots and the air mass moving 

southward at 20 knots, the aircraft at the end of 1 hour is 

almost 120 miles east of its point of departure because of its 

progress through the air. It is 20 miles south because of the 

motion of the air. Under these circumstances, the airspeed 

remains 120 knots, but the GS is determined by combining 

the movement of the aircraft with that of the air mass. GS can 

be measured as the distance from the point of departure to 

the position of the aircraft at the end of 1 hour. The GS can 

be computed by the time required to fly between two points a 

known distance apart. It also can be determined before flight 

by constructing a wind triangle, which is explained later in 

this chapter. [Figure 16-14] 

The direction in which the aircraft is pointing as it flies is 

called heading. Its actual path over the ground, which is a 

combination of the motion of the aircraft and the motion of 

the air, is called track. The angle between the heading and 

the track is called drift angle. If the aircraft heading coincides 

with the TC and the wind is blowing from the left, the track 

does not coincide with the TC. The wind causes the aircraft 

to drift to the right, so the track falls to the right of the desired 

course or TC. [Figure 16-15] 

The following method is used by many pilots to determine 

compass heading: after the TC is measured, and wind 

correction applied resulting in a TH, the sequence TH ± 

variation (V) = magnetic heading (MH) ± deviation (D) 

= compass heading (CH) is followed to arrive at compass 

heading. [Figure 16-16] 

By determining the amount of drift, the pilot can counteract 

the effect of the wind and make the track of the aircraft 

coincide with the desired course. If the mass of air is moving 

across the course from the left, the aircraft drifts to the 

right, and a correction must be made by heading the aircraft 

sufficiently to the left to offset this drift. In other words, if 

the wind is from the left, the correction is made by pointing 

the aircraft to the left a certain number of degrees, therefore 

correcting for wind drift. This is the wind correction angle 

(WCA) and is expressed in terms of degrees right or left of 

the TC. [Figure 16-17] 

16-9 
 

Airspeed effect (1 hour) 

20 knots

Distance covered over ground (1 hour) 

Figure 16-14. Aircraft flight path resulting from its airspeed and direction and the wind speed and direction. 

Heading 

Wind 

Track 

Drift angle 

Desired course 

Figure 16-15. Effects of wind drift on maintaining desired course. 

Figure 16-16. Relationship between true, magnetic, and compass 

headings for a particular instance. 

Heading 

TN MN CN 

TH-088° 

MH­078° 

CH-074° 

VAR 10° E 

DEV 4° 

To summarize: 

•	 Course—intended path of an aircraft over the ground 

or the direction of a line drawn on a chart representing 

the intended aircraft path, expressed as the angle 

measured from a specific reference datum clockwise 

from 0° through 360° to the line. 

•	 Heading—direction in which the nose of the aircraft 

points during flight. 

•	 Track—actual path made over the ground in flight. (If 

proper correction has been made for the wind, track 

and course are identical.) 

•	 Drift angle—angle between heading and track. 

•	 WCA—correction applied to the course to establish 

a heading so that track coincides with course. 

•	 Airspeed—rate of the aircraft’s progress through 

the air. 

•	 GS—rate of the aircraft’s inflight progress over 

the ground. 

16-10 
 

 

Heading

Wind 

Track 

Wind 

correction 

angle 

Desired course 

090° 

075° 

Figure 16-17. Establishing a wind correction angle that counteracts wind drift and maintains the desired course. 

Basic Calculations 

Before a cross-country flight, a pilot should make common 

calculations for time, speed, and distance, and the amount 

of fuel required. 

Converting Minutes to Equivalent Hours 

Frequently, it is necessary to convert minutes into equivalent 

hours when solving speed, time, and distance problems. To 

convert minutes to hours, divide by 60 (60 minutes = 1 hour). 

Thus, 30 minutes is 30/60 = 0.5 hour. To convert hours to 

minutes, multiply by 60. Thus, 0.75 hour equals 0.75 × 60 

= 45 minutes. 

Time T = D/GS 

To find the time (T) in flight, divide the distance (D) by the 

GS. The time to fly 210 NM at a GS of 140 knots is 210 ÷ 

140 or 1.5 hours. (The 0.5 hour multiplied by 60 minutes 

equals 30 minutes.) Answer: 1:30. 

Distance D = GS X T 

To find the distance flown in a given time, multiply GS by 

time. The distance flown in 1 hour 45 minutes at a GS of 120 

knots is 120 × 1.75 or 210 NM. 

GS GS = D/T 

To find the GS, divide the distance flown by the time 

required. If an aircraft flies 270 NM in 3 hours, the GS is 

270 ÷ 3 = 90 knots. 

Converting Knots to Miles Per Hour 

Another conversion is that of changing knots to miles per hour 

(mph). The aviation industry is using knots more frequently 

than mph, but is important to understand the conversion for 

those that use mph when working with speed problems. The 

NWS reports both surface winds and winds aloft in knots. 

However, airspeed indicators in some aircraft are calibrated 

in mph (although many are now calibrated in both mph and 

knots). Pilots, therefore, should learn to convert wind speeds 

that are reported in knots to mph. 

A knot is 1 nautical mile per hour (NMPH). Because there are 

6,076.1 feet in 1 NM and 5,280 feet in 1 SM, the conversion 

factor is 1.15. To convert knots to mph, multiply speed in 

knots by 1.15. For example: a wind speed of 20 knots is 

equivalent to 23 mph. 

Most flight computers or electronic calculators have a 

means of making this conversion. Another quick method of 

conversion is to use the scales of NM and SM at the bottom 

of aeronautical charts. 

Fuel Consumption 

To ensure that sufficient fuel is available for your intended 

flight, you must be able to accurately compute aircraft fuel 

consumption during preflight planning. Typically, fuel 

consumption in gasoline-fueled aircraft is measured in 

gallons per hour. Since turbine engines consume much more 

fuel than reciprocating engines, turbine-powered aircraft 

require much more fuel, and thus much larger fuel tanks. 

When determining these large fuel quantities, using a volume 

measurement such as gallons presents a problem because 

the volume of fuel varies greatly in relation to temperature. 

In contrast, density (weight) is less affected by temperature 

and therefore, provides a more uniform and repeatable 

measurement. For this reason, jet fuel is generally quantified 

by its density and volume. 

This standard industry convention yields a pounds-of-fuelper-hour value which, when divided into the nautical miles 

(NM) per hour of travel (TAS ± winds) value, results in a 

specific range value. The typical label for specific range is 

NM per pound of fuel, or often NM per 1,000 pounds of fuel. 

Preflight planning should be supported by proper monitoring 

of past fuel consumption as well as use of specified fuel 

management and mixture adjustment procedures in flight. 

16-11 
 

 

For simple aircraft with reciprocating engines, the Aircraft 

Flight Manual/Pilot’s Operating Handbook (AFM/POH) 

supplied by the aircraft manufacturer provides gallons-perhour values to assist with preflight planning. 

When planning a flight, you must determine how much 

fuel is needed to reach your destination by calculating the 

distance the aircraft can travel (with winds considered) at 

a known rate of fuel consumption (gal/hr or lbs/hr) for the 

expected groundspeed (GS) and ensure this amount, plus an 

adequate reserve, is available on board. GS determines the 

time the flight will take. The amount of fuel needed for a 

given flight can be calculated by multiplying the estimated 

flight time by the rate of consumption. For example, a flight 

of 400 NM at 100 knots GS takes 4 hours to complete. If an 

aircraft consumes 5 gallons of fuel per hour, the total fuel 

consumption is 20 gallons (4 hours times 5 gallons). In this 

example, there is no wind; therefore, true airspeed (TAS) 

is also 100 knots, the same as GS. Since the rate of fuel 

consumption remains relatively constant at a given TAS, 

you must use GS to calculate fuel consumption when wind 

is present. Specific range (NM/lb or NM/gal) is also useful 

in calculating fuel consumption when wind is a factor. 

You should always plan to be on the surface before any of 

the following occur: 

•	 Your flight time exceeds the amount of flight time 

you calculated for the consumption of your preflight 

fuel amount 

•	 Your fuel gauge indicates low fuel level 

The rate of fuel consumption depends on many factors: 

condition of the engine, propeller/rotor pitch, propeller/ 

rotor revolutions per minute (rpm), richness of the mixture, 

and the percentage of horsepower used for flight at cruising 

speed. The pilot should know the approximate consumption 

rate from cruise performance charts or from experience. 

In addition to the amount of fuel required for the flight, 

there should be sufficient fuel for reserve. When estimating 

consumption you must plan for cruise flight as well as startup 

and taxi, and higher fuel burn during climb. Remember that 

ground speed during climb is less than during cruise flight 

at the same airspeed. Additional fuel for adequate reserve 

should also be added as a safety measure. 

Flight Computers 

Up to this point, only mathematical formulas have been used 

to determine such items as time, distance, speed, and fuel 

consumption. In reality, most pilots use a mechanical flight 

computer called an E6B or electronic flight calculator. These 

devices can compute numerous problems associated with 

flight planning and navigation. The mechanical or electronic 

computer has an instruction book that probably includes 

sample problems so the pilot can become familiar with its 

functions and operation. [Figure 16-18] 

Plotter 

Another aid in flight planning is a plotter, which is a protractor 

and ruler. The pilot can use this when determining TC and 

measuring distance. Most plotters have a ruler that measures 

in both NM and SM and has a scale for a sectional chart on one 

side and a world aeronautical chart on the other. [Figure 16-18] 

Pilotage 

Pilotage is navigation by reference to landmarks or 

checkpoints. It is a method of navigation that can be used 

on any course that has adequate checkpoints, but it is more 

commonly used in conjunction with dead reckoning and 

VFR radio navigation. 

The checkpoints selected should be prominent features 

common to the area of the flight. Choose checkpoints that can 

be readily identified by other features, such as roads, rivers, 

railroad tracks, lakes, and power lines. If possible, select 

features that make useful boundaries or brackets on each 

side of the course, such as highways, rivers, railroads, and 

mountains. A pilot can keep from drifting too far off course 

by referring to and not crossing the selected brackets. Never 

place complete reliance on any single checkpoint. Choose 

ample checkpoints. If one is missed, look for the next one while 

maintaining the heading. When determining position from 

checkpoints, remember that the scale of a sectional chart is 1 

inch = 8 SM or 6.86 NM. For example, if a checkpoint selected 

was approximately one-half inch from the course line on the 

chart, it is 4 SM or 3.43 NM from the course on the ground. 

In the more congested areas, some of the smaller features are 

not included on the chart. If confused, hold the heading. If a 

turn is made away from the heading, it is easy to become lost. 

Roads shown on the chart are primarily the well-traveled 

roads or those most apparent when viewed from the air. 

New roads and structures are constantly being built and 

may not be shown on the chart until the next chart is issued. 

Some structures, such as antennas, may be difficult to see. 

Sometimes TV antennas are grouped together in an area near 

a town. They are supported by almost invisible guy wires. 

Never approach an area of antennas less than 500 feet above 

the tallest one. Most of the taller structures are marked with 

strobe lights to make them more visible to pilots. However, 

some weather conditions or background lighting may make 

them difficult to see. Aeronautical charts display the best 

information available at the time of printing, but a pilot should 

be cautious for new structures or changes that have occurred 

since the chart was printed. 

16-12 
=

INSTRUCTIONS FOR USE 

1. Place hole over intersection of true course and true north line. 

2. Without changing position rotate plotter until edge is over true course line. 

3. From hole follow true north line to curved scale with arrow pointing in direction of flight. 

4. Read true course in degrees, on proper scale, over true north line. read scales counter-clockwise. 

SECTIONAL CHART SIDE - 1:500,000 NAVIGATIONAL FLIGHT PLOTTER 

0 

180 

270 

90 

10 

190

280 

100 

20 

200

290 

110 

30 

210 

330 

150 

340 

160 

350 

170

300 

120 

310 

130 

320 

140 

330

150 

340

160 

350

170

190

10 

200

20 

210

30

220 

230 

40 50

240 

60

250 

70 

260 

80 

NAUTICAL 5 MILES 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 NAUTICAL 85 MILES 

0 STATUTE 5 MILES 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

DEGREES 

Mode On/Off Clr

Dist Vol Wt Wx ÷ 

: 7 8 9 x 

Sto 4 5 6 −

Rcl 1 2 3 + 

Bksp 0 . +/­

C 

M 

P 

TSD Alt: As Wind Wt. Bal Timer

 Conv: Dist Vol Wt Wx 

A Plotter 

B Mechanical flight computer 

C Electronic flight computer 

Figure 16-18. A plotter (A), the computational and wind side of a mechanical flight computer (E6B) (B), and an electronic flight computer (C). 

Dead Reckoning 

Dead reckoning is navigation solely by means of computations 

based on time, airspeed, distance, and direction. The products 

derived from these variables, when adjusted by wind speed 

and velocity, are heading and GS. The predicted heading 

takes the aircraft along the intended path and the GS 

establishes the time to arrive at each checkpoint and the 

destination. Except for flights over water, dead reckoning 

is usually used with pilotage for cross-country flying. The 

heading and GS, as calculated, is constantly monitored and 

corrected by pilotage as observed from checkpoints. 

Wind Triangle or Vector Analysis 

If there is no wind, the aircraft’s ground track is the same as 

the heading and the GS is the same as the true airspeed. This 

condition rarely exists. A wind triangle, the pilot’s version 

of vector analysis, is the basis of dead reckoning. 

The wind triangle is a graphic explanation of the effect of 

wind upon flight. GS, heading, and time for any flight can be 

determined by using the wind triangle. It can be applied to 

the simplest kind of cross-country flight, as well as the most 

complicated instrument flight. The experienced pilot becomes 

16-13 
 

 

so familiar with the fundamental principles that estimates can 

be made that are adequate for visual flight without actually 

drawing the diagrams. The beginning student, however, needs 

to develop skill in constructing these diagrams as an aid to the 

complete understanding of wind effect. Either consciously or 

unconsciously, every good pilot thinks of the flight in terms 

of wind triangle. 

If flight is to be made on a course to the east, with a wind 

blowing from the northeast, the aircraft must be headed 

somewhat to the north of east to counteract drift. This can 

be represented by a diagram as shown in Figure 16-19. Each 

line represents direction and speed. The long blue and white 

hashed line shows the direction the aircraft is heading, and 

its length represents the distance traveled at the indicated 

airspeed for 1 hour. The short blue arrow at the right shows 

the wind direction, and its length represents the wind velocity 

for 1 hour. The solid yellow line shows the direction of the 

track or the path of the aircraft as measured over the earth, and 

its length represents the distance traveled in 1 hour or the GS. 

In actual practice, the triangle illustrated in Figure 16-19 is 

not drawn; instead, construct a similar triangle as shown by 

the blue, yellow, and black lines in Figure 16-20, which is 

explained in the following example. 

Suppose a flight is to be flown from E to P. Draw a line on 

the aeronautical chart connecting these two points; measure 

its direction with a protractor, or plotter, in reference to a 

meridian. This is the TC, which in this example is assumed 

to be 090° (east). From the NWS, it is learned that the wind 

at the altitude of the intended flight is 40 knots from the 

northeast (045°). Since the NWS reports the wind speed in 

knots, if the true airspeed of the aircraft is 120 knots, there is 

no need to convert speeds from knots to mph or vice versa. 

Now, on a plain sheet of paper draw a vertical line representing 

north to south. (The various steps are shown in Figure 16-21.) 

Step 1 

Place the protractor with the base resting on the vertical line 

and the curved edge facing east. At the center point of the 

base, make a dot labeled “E” (point of departure) and at the 

curved edge, make a dot at 90° (indicating the direction of the 

true course) and another at 45° (indicating wind direction). 

080° heading and 120 knots airspeed 

090° course and 110 knots groundspeed 

N 33 

30 W 

24 

21 

S 15 12 E 

6 3

Wind at 20°

 direction and 

35 knots velocity 

N 

S 

10°

Drift Angle 

8° left correction 

Figure 16-19. Principle of the wind triangle. 

Heading and airspeed 

Course and groundspeed 

N 33 30

W

24 21

S 15 12

E

6 3

P

W

E

Wind direction and velocity 

N

S

Figure 16-20. The wind triangle as is drawn in navigation practice. 

16-14 
90 80 

70 

60 

30 20 10 

170 160 

150 

140 

130 

120 

110 

100 

70 

60 

50 

 40 

30 20 10 

170 160 

150 

140 

130 

120 

110 

 

 

90 80 70 60 50 40 30 20 10 

170 160 150 140 130 120 110 100 

Airspeed 120 knots

TC 090° GS 88 

N 33 30 W 

24 21 

S 15 12 E 

6 3 

P 

W 

E 

N 

S 

50 

40 

90 

80 

100 

W 

E 

N 

S 

TC 090° 

Wind 

Mid point 

STEP 1 

STEP 4 

STEP 2 and 3 4 5 ° 

9 0 ° 

Figure 16-21. Steps in drawing the wind triangle. 

Step 2 

With the ruler, draw the true course line from E, extending it 

somewhat beyond the dot by 90°, and labeling it “TC 090°.” 

Step 3 

Next, align the ruler with E and the dot at 45°, and draw 

the wind arrow from E, not toward 045°, but downwind in 

the direction the wind is blowing making it 40 units long to 

correspond with the wind velocity of 40 knots. Identify this 

line as the wind line by placing the letter “W” at the end to 

show the wind direction. 

Step 4 

Finally, measure 120 units on the ruler to represent the 

airspeed, making a dot on the ruler at this point. The units 

used may be of any convenient scale or value (such as 1⁄4 

inch = 10 knots), but once selected, the same scale must 

be used for each of the linear movements involved. Then 

place the ruler so that the end is on the arrowhead (W) and 

the 120-knot dot intercepts the TC line. Draw the line and 

label it “AS 120.” The point “P” placed at the intersection 

represents the position of the aircraft at the end of 1 hour. 

The diagram is now complete. 

The distance flown in 1 hour (GS) is measured as the numbers 

of units on the TC line (88 NMPH or 88 knots). The TH 

necessary to offset drift is indicated by the direction of the 

airspeed line, which can be determined in one of two ways: 

•	 By placing the straight side of the protractor along 

the north-south line, with its center point at the 

intersection of the airspeed line and north-south line, 

read the TH directly in degrees (076°). [Figure 16-22] 

•	 By placing the straight side of the protractor along the 

TC line, with its center at P, read the angle between 

the TC and the airspeed line. This is the WCA, which 

must be applied to the TC to obtain the TH. If the wind 

blows from the right of TC, the angle is added; if from 

the left, it is subtracted. In the example given, the 

WCA is 14° and the wind is from the left; therefore, 

subtract 14° from TC of 090°, making the TH 076°. 

[Figure 16-23] 

After obtaining the TH, apply the correction for magnetic 

variation to obtain magnetic heading and the correction 

for compass deviation to obtain a compass heading. The 

compass heading can be used to fly to the destination by 

dead reckoning. 

To determine the time and fuel required for the flight, first 

find the distance to your destination by measuring the length 

of the course line drawn on the aeronautical chart (using the 

appropriate scale at the bottom of the chart). If the distance 

measures 220 NM, divide by the GS of 88 knots, which gives 

2.5 hours, or 2:30, as the time required. If fuel consumption 

is 8 gallons an hour, 8 × 2.5 or about 20 gallons is used. 

16-15 
90 80 70 

150 

140 

130 

120 

110 

100 

90 

60 

50 

 40 

30 

20 10 

130 

120 

110 

100 

90 80 70 60 50 40 30 20 10 

170 160 150 140 130 120 110 100 

TH 076° AS 120 

TC 090° GS 88 

P 

W 

E 

N 

S 

80 

70

7 6 ° 

Figure 16-22. Finding true heading by the wind correction angle. 

Briefly summarized, the steps in obtaining flight information 

are as follows: 

•	 TC—direction of the line connecting two desired 

points, drawn on the chart and measured clockwise 

in degrees from TN on the mid-meridian 

•	 WCA—determined from the wind triangle. (Added 

to TC if the wind is from the right; subtracted if wind 

is from the left) 

•	 TH—direction measured in degrees clockwise from 

TN, in which the nose of the plane should point to 

remain on the desired course 

Figure 16-23. Finding true heading by direct measurement. 

90 80 70 60 50 40 30 20 10

170 160 150 140 130 120 110 100 

TH 076° AS 120 

TC 090° GS 88 

P 

W 

E 

N 

S 

10 

20 

1 4 ° 

WCA =14° L 

•	 Variation—obtained from the isogonic line on the 

chart (added to TH if west; subtracted if east) 

•	 MH—an intermediate step in the conversion (obtained 

by applying variation to TH) 

•	 Deviation—obtained from the deviation card on the 

aircraft (added to or subtracted from MH, as indicated) 

•	 Compass heading—reading on the compass (found by 

applying deviation to MH) that is followed to remain 

on the desired course 

16-16 
 

•	 Total distance—obtained by measuring the length of 

the TC line on the chart (using the scale at the bottom 

of the chart) 

•	 GS—obtained by measuring the length of the TC line 

on the wind triangle (using the scale employed for 

drawing the diagram) 

•	 Estimated time en route (ETE)—total distance divided 

by GS 

•	 Fuel rate—predetermined gallons per hour used at 

cruising speed 

NOTE: Additional fuel for adequate reserve should be added 

as a safety measure. 

Flight Planning 

Title 14 of the Code of Federal Regulations (14 CFR) part 

91 states, in part, that before beginning a flight, the pilot in 

command (PIC) of an aircraft shall become familiar with all 

available information concerning that flight. For flights not 

in the vicinity of an airport, this must include information 

on available current weather reports and forecasts, fuel 

requirements, alternatives available if the planned flight 

cannot be completed, and any known traffic delays of which 

the PIC has been advised by ATC. 

Assembling Necessary Material 

The pilot should collect the necessary material well before 

beginning the flight. An appropriate current sectional chart 

and charts for areas adjoining the flight route should be among 

this material if the route of flight is near the border of a chart. 

Additional equipment should include a flight computer or 

electronic calculator, plotter, and any other item appropriate 

to the particular flight. For example, if a night flight is to 

be undertaken, carry a flashlight; if a flight is over desert 

country, carry a supply of water and other necessities. 

Weather Check 

It is wise to check the weather before continuing with other 

aspects of flight planning to see, first of all, if the flight is 

feasible and, if it is, which route is best. Chapter 12, “Aviation 

Weather Services,” discusses obtaining a weather briefing. 

Use of Chart Supplement U.S. (formerly Airport/ 

Facility Directory) 

Study available information about each airport at which a 

landing is intended. This should include a study of the Notices 

to Airmen (NOTAMs) and the Chart Supplement U.S. 

(formerly Airport/Facility Directory). [Figure 16-24] This 

includes location, elevation, runway and lighting facilities, 

available services, availability of aeronautical advisory 

station frequency (UNICOM), types of fuel available (use to 

Figure 16-24. Chart Supplement U.S. (formerly Airport/Facility 

Directory). 

decide on refueling stops), FSS located on the airport, control 

tower and ground control frequencies, traffic information, 

remarks, and other pertinent information. The NOTAMs, 

issued every 28 days, should be checked for additional 

information on hazardous conditions or changes that have 

been made since issuance of the Chart Supplement U.S. 

The sectional chart bulletin subsection should be checked for 

major changes that have occurred since the last publication date 

of each sectional chart being used. Remember, the chart may 

be up to 6 months old. The effective date of the chart appears 

at the top of the front of the chart. The Chart Supplement U.S. 

generally has the latest information pertaining to such matters 

and should be used in preference to the information on the 

back of the chart, if there are differences. 

Airplane Flight Manual or Pilot’s Operating 

Handbook (AFM/POH) 

The Aircraft Flight Manual or Pilot’s Operating Handbook 

(AFM/POH) should be checked to determine the proper 

loading of the aircraft (weight and balance data). The weight 

of the usable fuel and drainable oil aboard must be known. 

Also, check the weight of the passengers, the weight of all 

baggage to be carried, and the empty weight of the aircraft to 

be sure that the total weight does not exceed the maximum 

allowable weight. The distribution of the load must be known 

to tell if the resulting center of gravity (CG) is within limits. 

16-17 
 

Be sure to use the latest weight and balance information in 

the FAA-approved AFM or other permanent aircraft records, 

as appropriate, to obtain empty weight and empty weight 

CG information. 

Determine the takeoff and landing distances from the 

appropriate charts, based on the calculated load, elevation 

of the airport, and temperature; then compare these distances 

with the amount of runway available. Remember, the 

heavier the load and the higher the elevation, temperature, 

or humidity, the longer the takeoff roll and landing roll and 

the lower the rate of climb. 

Check the fuel consumption charts to determine the rate of 

fuel consumption at the estimated flight altitude and power 

settings. Calculate the rate of fuel consumption, and compare 

it with the estimated time for the flight so that refueling points 

along the route can be included in the plan. 

Charting the Course 

Once the weather has been checked and some preliminary 

planning completed, it is time to chart the course and 

determine the data needed to accomplish the flight. The 

following sections provide a logical sequence to follow in 

charting the course, complete a flight log, and filing a flight 

plan. In the following example, a trip is planned based on the 

following data and the sectional chart excerpt in Figure 16-25. 

Route of flight: Chickasha Airport direct to Guthrie Airport

 True airspeed (TAS)........................................115 knots

 Winds aloft...........................................360° at 10 knots

 Usable fuel.....................................................38 gallons

 Fuel rate...............................................................8 GPH

 Deviation..................................................................+2°
 

Steps in Charting the Course 

The following is a suggested sequence for arriving at the 

pertinent information for the trip. As information is determined, 

it may be noted as illustrated in the example of a flight log in 

Figure 16-26. Where calculations are required, the pilot may 

use a mathematical formula or a manual or electronic flight 

computer. If unfamiliar with the use of a manual or electronic 

computer, it would be advantageous to read the operation 

manual and work several practice problems at this point. 

First, draw a line from Chickasha Airport (point A) directly 

to Guthrie Airport (point F). The course line should begin at 

the center of the airport of departure and end at the center of 

the destination airport. If the route is direct, the course line 

consists of a single straight line. If the route is not direct, it 

consists of two or more straight line segments. For example, a 

VOR station that is off the direct route, but makes navigating 

easier, may be chosen (radio navigation is discussed later in 

this chapter). 

Appropriate checkpoints should be selected along the route 

and noted in some way. These should be easy-to-locate 

points, such as large towns, large lakes and rivers, or 

combinations of recognizable points, such as towns with 

an airport, towns with a network of highways, and railroads 

entering and departing. 

Normally, choose only towns indicated by splashes of yellow 

on the chart. Do not choose towns represented by a small 

circle—these may turn out to be only a half-dozen houses. (In 

isolated areas, however, towns represented by a small circle 

can be prominent checkpoints.) For this trip, four checkpoints 

have been selected. Checkpoint 1 consists of a tower located 

east of the course and can be further identified by the highway 

and railroad track, which almost parallels the course at this 

point. Checkpoint 2 is the obstruction just to the west of the 

course and can be further identified by Will Rogers World 

Airport, which is directly to the east. Checkpoint 3 is Wiley 

Post Airport, which the aircraft should fly directly over. 

Checkpoint 4 is a private, non-surfaced airport to the west of 

the course and can be further identified by the railroad track 

and highway to the east of the course. 

The course and areas on either side of the planned route 

should be checked to determine if there is any type of airspace 

with which the pilot should be concerned or which has 

special operational requirements. For this trip, it should be 

noted that the course passes through a segment of the Class 

C airspace surrounding Will Rogers World Airport where the 

floor of the airspace is 2,500 feet mean sea level (MSL) and 

the ceiling is 5,300 feet MSL (point B). Also, there is Class 

D airspace from the surface to 3,800 feet MSL surrounding 

Wiley Post Airport (point C) during the time the control 

tower is in operation. 

Study the terrain and obstructions along the route. This is 

necessary to determine the highest and lowest elevations, 

as well as the highest obstruction to be encountered so 

an appropriate altitude that conforms to 14 CFR part 91 

regulations can be selected. If the flight is to be flown 

at an altitude of more than 3,000 feet above the terrain, 

conformance to the cruising altitude appropriate to the 

direction of flight is required. Check the route for particularly 

rugged terrain so it can be avoided. Areas where a takeoff 

or landing is made should be carefully checked for tall 

obstructions. Television transmitting towers may extend to 

altitudes over 1,500 feet above the surrounding terrain. It is 

essential that pilots be aware of their presence and location. 

For this trip, it should be noted that the tallest obstruction is 

16-18 
Checkpoint 

Checkpoint 

Checkpoint 

Checkpoint 

A 

B Class C Airspace

C Class D Airspace

D Tallest obstruction

Highest elevation E 

F 

1 

2 

3 

4 

Route of flight: Chickasha Airport direct to Guthrie Airport 

True airspeed (TAS) . . . . . . . . . . . . . . . . . . . . 115 knots 

Winds aloft . . . . . . . . . . . . . . . . . . . . . . . 360° at 10 knots 

Usable fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 gallons 

Fuel rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 GPH 

Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +2° 

R 

Course line 

Figure 16-25. Sectional chart excerpt. 

16-19 
 

 

PILOT’S PLANNING SHEET 

COURSE TC TH MH DEV CH GS 

From 

To 

From 

To 

WIND 

Knots From 

WCA 

R+ LMAG VAR W+ ETOTAL MILES 

TOTAL 

TIME 

FUEL 

RATE 

TOTAL 

FUEL 

PLANE IDENTIFICATION DATE 

ALTITUDE

 Chickasha 

Guthrie 031° 10 360° 8000 3° L 28 7° E 21° +2° 23 53 106 kts 35 min 8 GPH 38 gal 

N123DB 

VISUAL FLIGHT LOG 

TIME OF 

DEPARTURE 

NAVIGATION 

AIDS COURSE ALTITUDE DISTANCE ELAPSED TIME GS CH REMARKS 

POINT OF 

DEPARTURE 

Chickasha Airport 

NAVAID 

IDENT. 

FREQ. 

TO 

FROM 

TO 

FROM POINT TO POINT

CUMULATIVE 

ACTUAL

ESTIMATED 

E 

ACTUAL

STIMATED 

E 

ACTUAL

STIMATED 

WEATHER 

AIRSPACE ETC. 

CHECKPOINT 

#1 

8000 

10000 

11 NM 6 min 

+5 

106 kts 023° 

CHECKPOINT 

#2 

8000 

10000 

10 NM 

21 NM 

6 min 106 kts 023° 

CHECKPOINT 

#3 

8000 

10000 

10.5 NM 

31.5 NM 

6 min 106 kts 023° 

CHECKPOINT 

#4 

8000 

10000 

13 NM 

44.5 NM 

7 min 106 kts 023° 

Guthrie Airport 

DESTINATION 8.5 NM 

53 NM 

5 min 

Figure 16-26. Pilot’s planning sheet and visual flight log. 

part of a series of antennas with a height of 2,749 feet MSL 

(point D). The highest elevation should be located in the 

northeast quadrant and is 2,900 feet MSL (point E). 

Since the wind is no factor and it is desirable and within the 

aircraft’s capability to fly above the Class C and D airspace 

to be encountered, an altitude of 5,500 feet MSL is chosen. 

This altitude also gives adequate clearance of all obstructions, 

as well as conforms to the 14 CFR part 91 requirement to 

fly at an altitude of odd thousand plus 500 feet when on a 

magnetic course between 0 and 179°. 

Next, the pilot should measure the total distance of the 

course, as well as the distance between checkpoints. The total 

distance is 53 NM, and the distance between checkpoints is 

as noted on the flight log in Figure 16-26. 

After determining the distance, the TC should be measured. 

If using a plotter, follow the directions on the plotter. The TC 

is 031°. Once the TH is established, the pilot can determine 

the compass heading. This is done by following the formula 

given earlier in this chapter. 

The formula is: 

TC ± WCA = TH ± V = MH ± D = CH 

The WCA can be determined by using a manual or electronic 

flight computer. Using a wind of 360° at 10 knots, it is 

determined the WCA is 3° left. This is subtracted from the 

TC making the TH 28°. Next, the pilot should locate the 

isogonic line closest to the route of the flight to determine 

variation. Figure 16-25 shows the variation to be 6.30° E 

(rounded to 7° E), which means it should be subtracted from 

the TH, giving an MH of 21°. Next, add 2° to the MH for 

the deviation correction. This gives the pilot the compass 

heading of 23°. 

Now, the GS can be determined. This is done using a manual 

or electronic calculator. The GS is determined to be 106 

knots. Based on this information, the total trip time, as well 

as time between checkpoints, and the fuel burned can be 

determined. These numbers can be calculated by using a 

manual or electronic calculator. 

16-20 
 

 

For this trip, the GS is 106 knots and the total time is 35 

minutes (30 minutes plus 5 minutes for climb) with a fuel 

burn of 4.7 gallons. Refer to the flight log in Figure 16-26 

for the time between checkpoints. 

As the trip progresses, the pilot can note headings and time 

and make adjustments in heading, GS, and time. 

Filing a VFR Flight Plan 

Filing a flight plan is not required by regulations; however, it 

is a good operating practice since the information contained 

in the flight plan can be used in search and rescue in the 

event of an emergency. 

Flight plans can be filed in the air by radio, but it is best to 

file a flight plan by phone just before departing. After takeoff, 

contact the FSS by radio and give them the takeoff time so 

the flight plan can be activated. 

When a VFR flight plan is filed, it is held by the FSS until 

1 hour after the proposed departure time and then canceled 

unless: the actual departure time is received; a revised 

proposed departure time is received; or at the time of filing, 

the FSS is informed that the proposed departure time is 

met, but actual time cannot be given because of inadequate 

communication. The FSS specialist who accepts the flight 

plan does not inform the pilot of this procedure, however. 

Figure 16-27 shows the flight plan form a pilot files with the 

FSS. When filing a flight plan by telephone or radio, give 

the information in the order of the numbered spaces. This 

enables the FSS specialist to copy the information more 

efficiently. Most of the fields are either self-explanatory 

or non-applicable to the VFR flight plan (such as item 13). 

However, some fields may need explanation. 

•	 Item 3 is the aircraft type and special equipment. An 

example would be C-150/X, which means the aircraft 

has no transponder. A listing of special equipment 

codes is found in the Aeronautical Information Manual 

(AIM). 

•	 Item 6 is the proposed departure time in UTC 

(indicated by the “Z”). 

•	 Item 7 is the cruising altitude. Normally, “VFR” can be 

entered in this block since the pilot chooses a cruising 

altitude to conform to FAA regulations. 

X 

N123DB C150/X 115 CHK, CHICKASHA 

AIRPORT 1400 5500 

Chickasha direct Guthrie 

GOK, Guthrie Airport 

Guthrie, OK 35 

4 45 1 

Jane Smith 

Aero Air, Oklahoma City, OK (405) 555-4149 

Red/White 

McAlester 

Figure 16-27. Domestic flight plan form. 

16-21 
 

 

•	 Item 8 is the route of flight. If the flight is to be direct, 

enter the word “direct;” if not, enter the actual route to 

be followed, such as via certain towns or navigation 

aids. 

•	 Item 10 is the estimated time en route. In the sample 

flight plan, 5 minutes was added to the total time to 

allow for the climb. 

•	 Item 12 is the fuel on board in hours and minutes. This 

is determined by dividing the total usable fuel aboard 

in gallons by the estimated rate of fuel consumption 

in gallons. 

Remember, there is every advantage in filing a flight plan; 

but do not forget to close the flight plan upon arrival. This 

should be done via telephone to avoid radio congestion. 

Ground-Based Navigation 

Advances in navigational radio receivers installed in aircraft, 

the development of aeronautical charts that show the exact 

location of ground transmitting stations and their frequencies, 

along with refined flight deck instrumentation make it 

possible for pilots to navigate with precision to almost any 

point desired. Although precision in navigation is obtainable 

through the proper use of this equipment, beginning pilots 

should use this equipment to supplement navigation by visual 

reference to the ground (pilotage). This method provides the 

pilot with an effective safeguard against disorientation in the 

event of radio malfunction. 

There are three radio navigation systems available for use 

for VFR navigation. These are: 

•	 VHF Omnidirectional Range (VOR) 

•	 Nondirectional Radio Beacon (NDB) 

•	 Global Positioning System (GPS) 

Very High Frequency (VHF) Omnidirectional 

Range (VOR) 

The VOR system is present in three slightly different 

navigation aids (NAVAIDs): VOR, VOR/distance measuring 

equipment (DME)(discussed in a later section), and 

VORTAC. By itself it is known as a VOR, and it provides 

magnetic bearing information to and from the station. When 

DME is also installed with a VOR, the NAVAID is referred 

to as a VOR/DME. When military tactical air navigation 

(TACAN) equipment is installed with a VOR, the NAVAID 

is known as a VORTAC. DME is always an integral part of 

a VORTAC. Regardless of the type of NAVAID utilized 

(VOR, VOR/DME, or VORTAC), the VOR indicator 

behaves the same. Unless otherwise noted in this section, 

VOR, VOR/DME, and VORTAC NAVAIDs are all referred 

to hereafter as VORs. 

The prefix “omni-” means all, and an omnidirectional range 

is a VHF radio transmitting ground station that projects 

straight line courses (radials) from the station in all directions. 

From a top view, it can be visualized as being similar to the 

spokes from the hub of a wheel. The distance VOR radials are 

projected depends upon the power output of the transmitter. 

The course or radials projected from the station are referenced 

to MN. Therefore, a radial is defined as a line of magnetic 

bearing extending outward from the VOR station. Radials are 

identified by numbers beginning with 001, which is 1° east 

of MN and progress in sequence through all the degrees of a 

circle until reaching 360. To aid in orientation, a compass rose 

reference to magnetic north is superimposed on aeronautical 

charts at the station location. 

VOR ground stations transmit within a VHF frequency band 

of 108.0–117.95 MHz. Because the equipment is VHF, the 

signals transmitted are subject to line-of-sight restrictions. 

Therefore, its range varies in direct proportion to the altitude 

of receiving equipment. Generally, the reception range of 

the signals at an altitude of 1,000 feet above ground level 

(AGL) is about 40 to 45 miles. This distance increases with 

altitude. [Figure 16-28] 

“A” and “B” signal 

received 

Only “A” signal received Only “B” signal received 

Neither “A” nor “B” 

signal received 

VOR VOR 

station station 

“A” “B” 

Figure 16-28. VHF transmissions follow a line-of-sight course. 

16-22 
 

 

 

 

 

 

 

 

 

 

VORs and VORTACs are classed according to operational 

use. There are three classes: 

•	 T (Terminal) 

•	 L (Low altitude) 

•	 H (High altitude) 

The normal useful range for the various classes is shown in 

the following table: 

VOR/VORTAC NAVAIDS 

Normal Usable Altitudes and Radius Distances

 Distance

 Class Altitudes ( M i l e s )

 T 12,000' and below 25

 L Below 18,000' 40

 H Below 14,500' 40

 H Within the conterminous 48 states 

only, between 14,500 and 17,999' 100

 H 18,000'—FL 450 130

 H FL 450—60,000' 100 

The useful range of certain facilities may be less than 50 

miles. For further information concerning these restrictions, 

refer to the Communication/NAVAID Remarks in the Chart 

Supplement U.S. 

The accuracy of course alignment of VOR radials is 

considered to be excellent. It is generally within plus or minus 

1°. However, certain parts of the VOR receiver equipment 

deteriorate, affecting its accuracy. This is particularly true 

at great distances from the VOR station. The best assurance 

of maintaining an accurate VOR receiver is periodic checks 

and calibrations. VOR accuracy checks are not a regulatory 

requirement for VFR flight. However, to assure accuracy of 

the equipment, these checks should be accomplished quite 

frequently and a complete calibration should be performed 

each year. The following means are provided for pilots to 

check VOR accuracy: 

•	 FAA VOR test facility (VOT) 

•	 Certified airborne checkpoints 

•	 Certified ground checkpoints located on airport 

surfaces 

If an aircraft has two VOR receivers installed, a dual VOR 

receiver check can be made. To accomplish the dual receiver 

check, a pilot must tune both VOR receivers to the same VOR 

ground facility. The maximum permissible variation between 

the two indicated bearings is 4°. A list of the airborne and 

ground checkpoints is published in the Chart Supplement U.S. 

Basically, these checks consist of verifying that the VOR 

radials the aircraft equipment receives are aligned with the 

radials the station transmits. There are not specific tolerances 

in VOR checks required for VFR flight. But as a guide to 

assure acceptable accuracy, the required IFR tolerances can 

be used—±4° for ground checks and ±6° for airborne checks. 

These checks can be performed by the pilot. 

The VOR transmitting station can be positively identified 

by its Morse code identification or by a recorded voice 

identification that states the name of the station followed by 

“VOR.” Many FSSs transmit voice messages on the same 

frequency that the VOR operates. Voice transmissions should 

not be relied upon to identify stations because many FSSs 

remotely transmit over several omniranges that have names 

different from that of the transmitting FSS. If the VOR is 

out of service for maintenance, the coded identification is 

removed and not transmitted. This serves to alert pilots that 

this station should not be used for navigation. VOR receivers 

are designed with an alarm flag to indicate when signal 

strength is inadequate to operate the navigational equipment. 

This happens if the aircraft is too far from the VOR or the 

aircraft is too low and, therefore, is out of the line of sight 

of the transmitting signals. 

Using the VOR 

In review, for VOR radio navigation, there are two 

components required: ground transmitter and aircraft 

receiving equipment. The ground transmitter is located at a 

specific position on the ground and transmits on an assigned 

frequency. The aircraft equipment includes a receiver with 

a tuning device and a VOR or omninavigation instrument. 

The navigation instrument could be a course deviation 

indicator (CDI), horizontal situation indicator (HSI), or a 

radio magnetic indicator (RMI). Each of these instruments 

indicates the course to the tuned VOR. 

Course Deviation Indicator (CDI) 

The CDI is found in most training aircraft. It consists of an 

omnibearing selector (OBS) sometimes referred to as the 

course selector, a CDI needle (left-right needle), and a TO/ 

FROM indicator. 

The course selector is an azimuth dial that can be rotated to 

select a desired radial or to determine the radial over which 

the aircraft is flying. In addition, the magnetic course “TO” 

or “FROM” the station can be determined. 

When the course selector is rotated, it moves the CDI or 

needle to indicate the position of the radial relative to the 

aircraft. If the course selector is rotated until the deviation 

16-23 
 

 

needle is centered, the radial (magnetic course “FROM” the 

station) or its reciprocal (magnetic course “TO” the station) 

can be determined. The course deviation needle also moves 

to the right or left if the aircraft is flown or drifting away 

from the radial which is set in the course selector. 

By centering the needle, the course selector indicates either 

the course “FROM” the station or the course “TO” the station. 

If the flag displays a “TO,” the course shown on the course 

selector must be flown to the station. [Figure 16-29] If 

“FROM” is displayed and the course shown is followed, the 

aircraft is flown away from the station. 

Horizontal Situation Indicator 

The HSI is a direction indicator that uses the output 

from a flux valve to drive the compass card. The HSI 

[Figure 16-30] combines the magnetic compass with 

navigation signals and a glideslope. The HSI gives the pilot 

an indication of the location of the aircraft in relation to the 

chosen course or radial. 

In Figure 16-30, the aircraft magnetic heading displayed 

on the compass card under the lubber line is 184°. The 

course select pointer shown is set to 295°; the tail of the 

pointer indicates the reciprocal, 115°. The course deviation 

bar operates with a VOR/Localizer (VOR/LOC) or GPS 

navigation receiver to indicate left or right deviations from 

the course selected with the course select pointer; operating 

in the same manner, the angular movement of a conventional 

VOR/LOC needle indicates deviation from course. 

The desired course is selected by rotating the course select 

pointer, in relation to the compass card, by means of the 

Figure 16-29. VOR indicator. 

OBS 

N 

E 

S 

W 

3

33 

24 

21

15 

12 

30

6 

TO N 

A 

V 

Unreliable signal flag 

TO/FROM indicator 

OBS knob 

Course index 

CDI needle 

Approximately 2 degrees 

in the VOR mode 

Figure 16-30. Horizontal situation indicator. 

33 

30 

24 

2I

I5 

I2 

6 

3 

GS GS 

DC 

NAV HDG 

Lubber line 

Compass warning flag 

Glideslope deviation scale 

NAV warning flag 

Course deviation bar 

Heading select knob 

Course select pointer 

Compass card 

Symbolic aircraft 

Heading select bug 

Course select knob 

To/From indicator Course deviation scale 

course select knob. The HSI has a fixed aircraft symbol 

and the course deviation bar displays the aircraft’s position 

relative to the selected course. The TO/FROM indicator is a 

triangular pointer. When the indicator points to the head of the 

course select pointer, the arrow shows the course selected. If 

properly intercepted and flown, the course takes the aircraft 

to the chosen facility. When the indicator points to the tail 

of the course, the arrow shows that the course selected, if 

properly intercepted and flown, takes the aircraft directly 

away from the chosen facility. 

When the NAV warning flag appears, it indicates no reliable 

signal is being received. The appearance of the HDG flag 

indicates the compass card is not functioning properly. 

Radio Magnetic Indicator (RMI) 

The RMI is a navigational aid providing aircraft magnetic 

or directional gyro heading and very high frequency 

omnidirectional range (VOR), GPS, and automatic direction 

16-24 
33 

30 

24 

21 

15 

12 

6 

3 

S 

W 

E 

N 

HDG 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33 30

24

2I

I5 I2 

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33 

30 

2I 24

I5 I2 

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

30 

33 

24 2I

I5 I2 

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33

30 

24 2I

I5 I2 

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33

30 

24 2I

I5 I2

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33

30 

24 2I

I5 I2

6 3 

N 

E 

S 

W 

3 

33 

24 21

15 12 

30

6 

O B S 

33

30 

24 2I

I5 I2

6 3 

N 

E 

W 

S 

3 

33 

24 21 

15 12 

30 

6 

O B S 

33

30 

24 2I 

I5 I2 

3 6 

3 

2 

1 

4 

5 

7 

8 

FROM 

A
 A
 D
 D
 F 6
 
 F
 FROM 

0 

27

6

NAV NAV
 18 FROM 

TO Figure 16-31. Radio magnetic indicator. 

finder (ADF) bearing information. [Figure 16-31] Remote 

indicating compasses were developed to compensate for 

errors in and limitations of older types of heading indicators. TO The remote compass transmitter is a separate unit usually WIND 

mounted in a wingtip to eliminate the possibility of magnetic 

interference. The RMI consists of a compass card, a heading 

index, two bearing pointers, and pointer function switches. 

The two pointers are driven by any two combinations of a 

GPS, an ADF, and/or a VOR. The pilot has the ability to select TO 

the navigation aid to be indicated. The pointer indicates the 

course to the selected NAVAID or waypoint. In Figure 16-31,

the green pointer is indicating the station tuned on the ADF. 

The yellow pointer is indicating the course to a VOR or GPS 

waypoint. Note that there is no requirement for a pilot to 

select a course with the RMI. Only the selected navigation 

source is pointed to by the needle(s). BRAVO
 

BRA 115.0
 

Tracking With VOR TO 

The following describes a step-by-step procedure for tracking 

to and from a VOR station using a CDI. Figure 16-32

illustrates the procedure. 

First, tune the VOR receiver to the frequency of the selected TO 

VOR station. For example, 115.0 to receive Bravo VOR. 

Next, check the identifiers to verify that the desired VOR 

is being received. As soon as the VOR is properly tuned, 

the course deviation needle deflects either left or right. 

Then, rotate the azimuth dial to the course selector until the 

course deviation needle centers and the TO-FROM indicator 

Figure 16-32. Tracking a radial in a crosswind. 

If a heading of 350° is maintained with a wind from the right indicates “TO.” If the needle centers with a “FROM” 

as shown, the aircraft drifts to the left of the intended track. indication, the azimuth should be rotated 180° because, in As the aircraft drifts off course, the VOR course deviation this case, it is desired to fly “TO” the station. Now, turn the needle gradually moves to the right of center or indicates the aircraft to the heading indicated on the VOR azimuth dial or direction of the desired radial or track. course selector, 350° in this example. 

16-25 
To return to the desired radial, the aircraft heading must be 

altered to the right. As the aircraft returns to the desired track, 

the deviation needle slowly returns to center. When centered, 

the aircraft is on the desired radial and a left turn must be 

made toward, but not to the original heading of 350° because 

a wind drift correction must be established. The amount of 

correction depends upon the strength of the wind. If the wind 

velocity is unknown, a trial-and-error method can be used 

to find the correct heading. Assume, for this example, a 10° 

correction for a heading of 360° is maintained. 

While maintaining a heading of 360°, assume that the course 

deviation begins to move to the left. This means that the wind 

correction of 10° is too great and the aircraft is flying to the 

right of course. A slight turn to the left should be made to 

permit the aircraft to return to the desired radial. 

When the deviation needle centers, a small wind drift 

correction of 5° or a heading correction of 355° should be 

flown. If this correction is adequate, the aircraft remains 

on the radial. If not, small variations in heading should be 

made to keep the needle centered and consequently keep the 

aircraft on the radial. 

As the VOR station is passed, the course deviation needle 

fluctuates, then settles down, and the “TO” indication 

changes to “FROM.” If the aircraft passes to one side of the 

station, the needle deflects in the direction of the station as 

the indicator changes to “FROM.” 

Generally, the same techniques apply when tracking 

outbound as those used for tracking inbound. If the intent is 

to fly over the station and track outbound on the reciprocal of 

the inbound radial, the course selector should not be changed. 

Corrections are made in the same manner to keep the needle 

centered. The only difference is that the omnidirectional 

range indicator indicates “FROM.” 

If tracking outbound on a course other than the reciprocal of 

the inbound radial, this new course or radial must be set in 

the course selector and a turn made to intercept this course. 

After this course is reached, tracking procedures are the same 

as previously discussed. 

Tips on Using the VOR 

•	 Positively identify the station by its code or voice 

identification. 

•	 Remember that VOR signals are “line-of-sight.” A 

weak signal or no signal at all is received if the aircraft 

is too low or too far from the station. 

•	 When navigating to a station, determine the inbound 

radial and use this radial. Fly a heading that will 

maintain the course. If the aircraft drifts, fly a heading 

to re-intercept the course then apply a correction to 

compensate for wind drift. 

•	 If minor needle fluctuations occur, avoid changing 

headings immediately. Wait a moment to see if the 

needle recenters; if it does not, then you must correctly 

recenter the course to the needle. 

•	 When flying “TO” a station, always fly the selected 

course with a “TO” indication. When flying “FROM” a 

station, always fly the selected course with a “FROM” 

indication. If this is not done, the action of the course 

deviation needle is reversed. To further explain this 

reverse action, if the aircraft is flown toward a station 

with a “FROM” indication or away from a station 

with a “TO” indication, the course deviation needle 

indicates in a direction opposite to that which it should 

indicate. For example, if the aircraft drifts to the right 

of a radial being flown, the needle moves to the right 

or points away from the radial. If the aircraft drifts to 

the left of the radial being flown, the needle moves 

left or in the direction opposite of the radial. 

•	 When navigating using the VOR, it is important to 

fly headings that maintain or re-intercept the course. 

Just turning toward the needle will cause overshooting 

the radial and flying an S turn to the left and right of 

course. 

Time and Distance Check From a Station Using a 

RMI 

To compute time and distance from a station, first turn the 

aircraft to place the RMI bearing pointer on the nearest 90° 

index. Note the time and maintain the heading. When the 

RMI bearing pointer has moved 10°, note the elapsed time 

in seconds and apply the formulas in the following example 

to determine the approximate time and distance from a given 

station. [Figure 16-33] 

The time from station may also be calculated by using a short 

method based on the above formula, if a 10° bearing change 

is flown. If the elapsed time for the bearing change is noted 

= Time in seconds between bearings 

Degrees of bearing change 

Minutes to station 

= 12 minutes to the station 

Time-Distance Check Example 

For example, if 2 minutes (120 seconds) is required to fly a 

bearing change of 10 degrees, the aircraft is— 

120 

10 

Figure 16-33. Time-distance check example. 

16-26 
 

 

 

in seconds and a 10° bearing change is made, the time from 

the station, in minutes, is determined by counting off one 

decimal point. Thus, if 75 seconds are required to fly a 10° 

bearing change, the aircraft is 7.5 minutes from the station. 

When the RMI bearing pointer is moving rapidly or when 

several corrections are required to place the pointer on the 

wingtip position, the aircraft is at station passage. 

The distance from the station is computed by multiplying TAS 

or GS (in miles per minute) by the previously determined time 

in minutes. For example, if the aircraft is 7.5 minutes from 

station, flying at a TAS of 120 knots or 2 NM per minute, 

the distance from station is 15 NM (7.5 × 2 = 15). 

The accuracy of time and distance checks is governed by 

existing wind, degree of bearing change, and accuracy of 

timing. The number of variables involved causes the result 

to be only an approximation. However, by flying an accurate 

heading and checking the time and bearing closely, the pilot 

can make a reasonable estimate of time and distance from 

the station. 

Time and Distance Check From a Station Using a 

CDI 

To compute time and distance from a station using a CDI, 

first tune and identify the VOR station and determine the 

radial on which you are located. Then turn inbound and 

re-center the needle if necessary. Turn 90° left or right, of 

the inbound course, rotating the OBS to the nearest 10° 

increment opposite the direction of turn. Maintain heading 

and when the CDI centers, note the time. Maintaining the 

same heading, rotate the OBS 10° in the same direction as 

was done previously and note the elapsed time when the 

CDI again centers. Time and distance from the station is 

determined from the formula shown in Figure 16-34. 

Course Intercept 

Course interceptions are performed in most phases of 

instrument navigation. The equipment used varies, but an 

intercept heading must be flown that results in an angle or 

rate of intercept sufficient for solving a particular problem. 

A = 60 x minutes flown between bearing change 

degrees of bearing change 

Time to 

station 

= TAS x minutes flown 

degrees of bearing change 

Distance to station 

Time-Distance Check Formula 

Figure 16-34. Time-distance check formula using a CDI. 

B 

Rate of Intercept 

Rate of intercept, seen by the aviator as bearing pointer or 

HSI movement, is a result of the following factors: 

•	 The angle at which the aircraft is flown toward a 

desired course (angle of intercept) 

•	 True airspeed and wind (GS) 

•	 Distance from the station 

Angle of Intercept 

The angle of intercept is the angle between the heading 

of the aircraft (intercept heading) and the desired course. 

Controlling this angle by selection/adjustment of the intercept 

heading is the easiest and most effective way to control 

course interceptions. Angle of intercept must be greater than 

the degrees from course, but should not exceed 90°. Within 

this limit, make adjustments as needed, to achieve the most 

desirable rate of intercept. 

When selecting an intercept heading, the key factor is the 

relationship between distance from the station and degrees 

from the course. Each degree, or radial, is 1 NM wide at 

a distance of 60 NM from the station. Width increases or 

decreases in proportion to the 60 NM distance. For example, 

1 degree is 2 NM wide at 120 NM—and 1⁄2 NM wide at 30 

NM. For a given GS and angle of intercept, the resultant rate 

of intercept varies according to the distance from the station. 

When selecting an intercept heading to form an angle of 

intercept, consider the following factors: 

•	 Degrees from course 

•	 Distance from the station 

•	 True airspeed and wind (GS) 

Distance Measuring Equipment (DME) 

Distance measuring equipment (DME) consists of an ultra 

high frequency (UHF) navigational aid with VOR/DMEs and 

VORTACs. It measures, in NM, the slant range distance of 

an aircraft from a VOR/DME or VORTAC (both hereafter 

referred to as a VORTAC). Although DME equipment is 

very popular, not all aircraft are DME equipped. 

To utilize DME, the pilot should select, tune, and identify 

a VORTAC, as previously described. The DME receiver, 

utilizing what is called a “paired frequency” concept, 

automatically selects and tunes the UHF DME frequency 

associated with the VHF VORTAC frequency selected by 

the pilot. This process is entirely transparent to the pilot. 

After a brief pause, the DME display shows the slant range 

distance to or from the VORTAC. Slant range distance is the 

direct distance between the aircraft and the VORTAC and 

is therefore affected by aircraft altitude. (Station passage 

directly over a VORTAC from an altitude of 6,076 feet AGL 

16-27 
 

 

would show approximately 1.0 NM on the DME.) DME is a 

very useful adjunct to VOR navigation. A VOR radial alone 

merely gives line of position information. With DME, a pilot 

may precisely locate the aircraft on a given line (radial). 

Most DME receivers also provide GS and time-to-station 

modes of operation. The GS is displayed in knots (NMPH). 

The time-to-station mode displays the minutes remaining to 

VORTAC station passage, predicated upon the present GS. 

GS and time-to-station information is only accurate when 

tracking directly to or from a VORTAC. DME receivers 

typically need a minute or two of stabilized flight directly 

to or from a VORTAC before displaying accurate GS or 

time-to-station information. 

Some DME installations have a hold feature that permits a 

DME signal to be retained from one VORTAC while the 

course indicator displays course deviation information from 

an ILS or another VORTAC. 

VOR/DME RNAV 

Area navigation (RNAV) permits electronic course guidance 

on any direct route between points established by the pilot. 

While RNAV is a generic term that applies to a variety 

of NAVAIDS, such as GPS and others, this section deals 

with VOR/DME-based RNAV. VOR/DME RNAV is not a 

separate ground-based NAVAID, but a method of navigation 

using VOR/DME and VORTAC signals specially processed 

by the aircraft’s RNAV computer. [Figure 16-35] 

NOTE: In this section, the term “VORTAC” also includes 

VOR/DME NAVAIDs. 

In its simplest form, VOR/DME RNAV allows the pilot to 

electronically move VORTACs around to more convenient 

locations. Once electronically relocated, they are referred 

to as waypoints. These waypoints are described as a 

combination of a selected radial and distance within the 

service volume of the VORTAC to be used. These waypoints 

allow a straight course to be flown between almost any 

origin and destination, without regard to the orientation of 

VORTACs or the existence of airways. 

While the capabilities and methods of operation of VOR/ 

DME RNAV units differ, there are basic principles of 

operation that are common to all. Pilots are urged to study 

the manufacturer’s operating guide and receive instruction 

prior to the use of VOR/DME RNAV or any unfamiliar 

navigational system. Operational information and limitations 

should also be sought from placards and the supplement 

section of the AFM/POH. 

VOR/DME-based RNAV units operate in at least three 

modes: VOR, en route, and approach. A fourth mode, VOR 

Parallel, may also be found on some models. The units need 

both VOR and DME signals to operate in any RNAV mode. 

If the NAVAID selected is a VOR without DME, RNAV 

mode will not function. 

In the VOR (or non-RNAV) mode, the unit simply functions 

as a VOR receiver with DME capability. [Figure 16-36] The 

unit’s display on the VOR indicator is conventional in all 

respects. For operation on established airways or any other 

ordinary VOR navigation, the VOR mode is used. 

To utilize the unit’s RNAV capability, the pilot selects and 

establishes a waypoint or a series of waypoints to define a 

course. A VORTAC (or VOR/DME) needs to be selected 

as a NAVAID, since both radial and distance signals are 

available from these stations. To establish a waypoint, a 

point somewhere within the service range of a VORTAC is 

defined on the basis of radial and distance. Once the waypoint 

is entered into the unit and the RNAV en route mode is 

selected, the CDI displays course guidance to the waypoint, 

not the original VORTAC. DME also displays distance to 

the waypoint. Many units have the capability to store several 

waypoints, allowing them to be programmed prior to flight, 

if desired, and called up in flight. 

RNAV waypoints are entered into the unit in magnetic 

bearings (radials) of degrees and tenths (i.e., 275.5°) and 

distances in NM and tenths (i.e., 25.2 NM). When plotting 

RNAV waypoints on an aeronautical chart, pilots find it 

Area Navigation Direct Route 

3 3 4 2 7 9

BEARING LOAD DISTANCE 

OFFSET EN ROUTE 

R 

N 

A 

V 

3 3 

4 4 

8 8 

12 12 

Figure 16-36. RNAV controls. 

Figure 16-35. Flying an RNAV course. 

16-28 
 

 

 

 

 

 

 

difficult to measure to that level of accuracy, and in practical 

application, it is rarely necessary. A number of flight planning 

publications publish airport coordinates and waypoints with 

this precision and the unit accepts those figures. There is a 

subtle but important difference in CDI operation and display 

in the RNAV modes. 

In the RNAV modes, course deviation is displayed in terms 

of linear deviation. In the RNAV en route mode, maximum 

deflection of the CDI typically represents 5 NM on either 

side of the selected course without regard to distance from the 

waypoint. In the RNAV approach mode, maximum deflection 

of the CDI typically represents 11⁄4 NM on either side of the 

selected course. There is no increase in CDI sensitivity as the 

aircraft approaches a waypoint in RNAV mode. 

The RNAV approach mode is used for instrument approaches. 

Its narrow scale width (1⁄4 of the en route mode) permits very 

precise tracking to or from the selected waypoint. In VFR 

cross-country navigation, tracking a course in the approach 

mode is not desirable because it requires a great deal of 

attention and soon becomes tedious. 

A fourth, lesser-used mode on some units is the VOR 

Parallel mode. This permits the CDI to display linear 

(not angular) deviation as the aircraft tracks to and from 

VORTACs. It derives its name from permitting the pilot 

to offset (or parallel) a selected course or airway at a fixed 

distance of the pilot’s choosing, if desired. The VOR parallel 

mode has the same effect as placing a waypoint directly 

over an existing VORTAC. Some pilots select the VOR 

parallel mode when utilizing the navigation (NAV) tracking 

function of their autopilot for smoother course following 

near the VORTAC. 

Navigating an aircraft with VOR/DME-based RNAV can be 

confusing, and it is essential that the pilot become familiar 

with the equipment installed. It is not unknown for pilots to 

operate inadvertently in one of the RNAV modes when the 

operation was not intended, by overlooking switch positions 

or annunciators. The reverse has also occurred with a pilot 

neglecting to place the unit into one of the RNAV modes by 

overlooking switch positions or annunciators. As always, the 

prudent pilot is not only familiar with the equipment used, 

but never places complete reliance in just one method of 

navigation when others are available for cross-check. 

Automatic Direction Finder (ADF) 

Many general aviation-type aircraft are equipped with ADF 

radio receiving equipment. To navigate using the ADF, 

the pilot tunes the receiving equipment to a ground station 

known as a nondirectional radio beacon (NDB). The NDB 

stations normally operate in a low or medium frequency band 

of 200 to 415 kHz. The frequencies are readily available on 

aeronautical charts or in the Chart Supplement U.S. 

All radio beacons, except compass locators, transmit 

a continuous three-letter identification in code, except 

during voice transmissions. A compass locator, which is 

associated with an instrument landing system, transmits a 

two-letter identification. 

Standard broadcast stations can also be used in conjunction 

with ADF. Positive identification of all radio stations is 

extremely important and this is particularly true when using 

standard broadcast stations for navigation. 

NDBs have one advantage over the VOR in that low or 

medium frequencies are not affected by line-of-sight. The 

signals follow the curvature of the Earth; therefore, if the 

aircraft is within the range of the station, the signals can be 

received regardless of altitude. 

The following table gives the class of NDB stations, their 

power, and their usable range: 

NONDIRECTIONAL RADIO BEACON (NDB) 

(Usable radius distances for all altitudes) 

Power Distance 

Class (Watts) (Miles) 

Compass Locator Under 25 15 

MH Under 50 2 5 

H 50–1999 * 5 0 

HH 2000 or more 75 

*Service range of individual facilities may be less than 

50 miles. 

One of the disadvantages that should be considered when 

using low frequency (LF) for navigation is that LF signals are 

very susceptible to electrical disturbances, such as lightning. 

These disturbances create excessive static, needle deviations, 

and signal fades. There may be interference from distant 

stations. Pilots should know the conditions under which these 

disturbances can occur so they can be more alert to possible 

interference when using the ADF. 

Basically, the ADF aircraft equipment consists of a tuner, 

which is used to set the desired station frequency, and the 

navigational display. 

The navigational display consists of a dial upon which the 

azimuth is printed and a needle which rotates around the 

dial and points to the station to which the receiver is tuned. 

16-29 
 

 

Some of the ADF dials can be rotated to align the 

azimuth with the aircraft heading; others are fixed with 0° 

representing the nose of the aircraft and 180° representing 

the tail. Only the fixed azimuth dial is discussed in this 

handbook. [Figure 16-37] 

Figure 16-38 illustrates terms that are used with the ADF 

and should be understood by the pilot. 

To determine the magnetic bearing “FROM” the station, 

180° is added to or subtracted from the magnetic bearing to 

the station. This is the reciprocal bearing and is used when 

plotting position fixes. 

Figure 16-37. ADF with fixed azimuth and magnetic compass. 

N-S E-W 

33 

30 

24

21 

15

12 

3 6

W

S 

E

N 

Figure 16-38. ADF terms. 

Radio station 

N-S E-W 

33

30 

24 

21 

15 12 

6 3 

W 

S

E 

N 

Magnetic bearing to station 

Relative

bearing 

Magnetic heading

Magnetic North 

Keep in mind that the needle of fixed azimuth points to the 

station in relation to the nose of the aircraft. If the needle 

is deflected 30° to the left for a relative bearing of 330°, 

this means that the station is located 30° left. If the aircraft 

is turned left 30°, the needle moves to the right 30° and 

indicates a relative bearing of 0° meaning that the aircraft 

is pointing toward the station. If the pilot continues flight 

toward the station keeping the needle on 0°, the procedure 

is called homing to the station. If a crosswind exists, the 

ADF needle continues to drift away from zero. To keep the 

needle on zero, the aircraft must be turned slightly resulting 

in a curved flight path to the station. Homing to the station 

is a common procedure but may result in drifting downwind, 

thus lengthening the distance to the station. 

Tracking to the station requires correcting for wind drift and 

results in maintaining flight along a straight track or bearing 

to the station. When the wind drift correction is established, 

the ADF needle indicates the amount of correction to the 

right or left. For instance, if the magnetic bearing to the 

station is 340°, a correction for a left crosswind would 

result in a magnetic heading of 330°, and the ADF needle 

would indicate 10° to the right or a relative bearing of 010°. 

[Figure 16-39] 

When tracking away from the station, wind corrections are 

made similar to tracking to the station, but the ADF needle 

points toward the tail of the aircraft or the 180° position on 

the azimuth dial. Attempting to keep the ADF needle on 

the 180° position during winds results in the aircraft flying 

a curved flight leading further and further from the desired 

track. When tracking outbound, corrections for wind should 

be made in the direction opposite of that in which the needle 

is pointing. 

Although the ADF is not as popular as the VOR for radio 

navigation, with proper precautions and intelligent use, the 

ADF can be a valuable aid to navigation. 

Global Positioning System 

The GPS is a satellite-based radio navigation system. 

Its RNAV guidance is worldwide in scope. There are no 

symbols for GPS on aeronautical charts as it is a space-based 

system with global coverage. Development of the system is 

underway so that GPS is capable of providing the primary 

means of electronic navigation. Portable and yoke-mounted 

units are proving to be very popular in addition to those 

permanently installed in the aircraft. Extensive navigation 

databases are common features in aircraft GPS receivers. 

16-30 
 

330° 33 30 

24

21 

15 12

6 3 

W 

S 

E 

N 

330° 33 30 

24

21 

15 12

6 3 

W 

S 

E 

N 

340° bearing to station 

Figure 16-39. ADF tracking. 

The GPS is a satellite radio navigation and time dissemination 

system developed and operated by the U.S. Department of 

Defense (DOD). Civilian interface and GPS system status 

is available from the U.S. Coast Guard. 

It is not necessary to understand the technical aspects of 

GPS operation to use it in VFR/IFR navigation. It does differ 

significantly from conventional, ground-based electronic 

navigation and awareness of those differences is important. 

Awareness of equipment approvals and limitations is critical 

to the safety of flight. 

The GPS navigation system broadcasts a signal that is used 

by receivers to determine precise position anywhere in the 

world. The receiver tracks multiple satellites and determines 

a pseudorange measurement to determine the user location. 

A minimum of four satellites is necessary to establish an 

accurate three-dimensional position. The Department of 

Defense (DOD) is responsible for operating the GPS satellite 

constellation and monitors the GPS satellites to ensure proper 

operation. 

The status of a GPS satellite is broadcast as part of the data 

message transmitted by the satellite. GPS status information 

is also available from the U.S. Coast Guard navigation 

information service at (703) 313-5907 or online at www. 

navcen.uscg.gov. Additionally, satellite status is available 

through the NOTAM system. 

The GPS receiver verifies the integrity (usability) of the 

signals received from the GPS constellation through receiver 

autonomous integrity monitoring (RAIM) to determine if 

a satellite is providing corrupted information. At least one 

satellite, in addition to those required for navigation, must 

be in view for the receiver to perform the RAIM function; 

thus, RAIM needs a minimum of five satellites in view or 

four satellites and a barometric altimeter (baro-aiding) to 

detect an integrity anomaly. For receivers capable of doing 

so, RAIM needs six satellites in view (or five satellites with 

baro-aiding) to isolate the corrupt satellite signal and remove 

it from the navigation solution. Baro-aiding is a method of 

augmenting the GPS integrity solution by using a nonsatellite 

input source. GPS derived altitude should not be relied upon 

to determine aircraft altitude since the vertical error can 

be quite large and no integrity is provided. To ensure that 

baro-aiding is available, the current altimeter setting must be 

entered into the receiver as described in the operating manual. 

RAIM messages vary somewhat between receivers; however, 

generally there are two types. One type indicates that there 

are not enough satellites available to provide RAIM integrity 

monitoring and another type indicates that the RAIM integrity 

monitor has detected a potential error that exceeds the limit 

for the current phase of flight. Without RAIM capability, the 

pilot has no assurance of the accuracy of the GPS position. 

Selective Availability 

Selective Availability (SA) is a method by which the accuracy 

of GPS is intentionally degraded. This feature is designed 

to deny hostile use of precise GPS positioning data. SA was 

discontinued on May 1, 2000, but many GPS receivers are 

designed to assume that SA is still active. 

The baseline GPS satellite constellation consists of 24 

satellites positioned in six earth-centered orbital planes 

with four operation satellites and a spare satellite slot in 

each orbital plane. The system can support a constellation 

of up to thirty satellites in orbit. The orbital period of a GPS 

satellite is one-half of a sidereal day or 11 hours 58 minutes. 

The orbits are nearly circular and equally spaced about the 

equator at a 60-degree separation with an inclination of 

16-31 
 

 

55 degrees relative to the equator. The orbital radius (i.e. 

distance from the center of mass of the earth to the satellite) 

is approximately 26,600 km. 

With the baseline satellite constellation, users with a clear 

view of the sky have a minimum of four satellites in view. 

It is more likely that a user would see six to eight satellites. 

The satellites broadcast ranging signals and navigation data 

allowing users to measure their pseudoranges in order to 

estimate their position, velocity and time, in a passive, listenonly mode. The receiver uses data from a minimum of four 

satellites above the mask angle (the lowest angle above the 

horizon at which a receiver can use a satellite). The exact 

number of satellites operating at any one particular time 

varies depending on the number of satellite outages and 

operational spares in orbit. For current status of the GPS 

constellation, please visit http://tycho.usno.navy.mil/gpscurr. 

html. [Figure 16-40] 

VFR Use of GPS 

GPS navigation has become a great asset to VFR pilots 

providing increased navigation capability and enhanced 

situational awareness while reducing operating costs due 

to greater ease in flying direct routes. While GPS has many 

benefits to the VFR pilot, care must be exercised to ensure 

that system capabilities are not exceeded. 

Types of receivers used for GPS navigation under VFR are 

varied from a full IFR installation being used to support a 

VFR flight to a VFR only installation (in either a VFR or IFR 

capable aircraft) to a hand-held receiver. The limitations of 

Figure 16-40. Satellite constellation. 

each type of receiver installation or use must be understood 

by the pilot to avoid misusing navigation information. In all 

cases, VFR pilots should never rely solely on one system 

of navigation. GPS navigation must be integrated with 

other forms of electronic navigation, as well as pilotage 

and dead reckoning. Only through the integration of these 

techniques can the VFR pilot ensure accuracy in navigation. 

Some critical concerns in VFR use of GPS include RAIM 

capability, database currency, and antenna location. 

RAIM Capability 

Many VFR GPS receivers and all hand-held units are not 

equipped with RAIM alerting capability. Loss of the required 

number of satellites in view, or the detection of a position 

error, cannot be displayed to the pilot by such receivers. 

In receivers with no RAIM capability, no alert would 

be provided to the pilot that the navigation solution had 

deteriorated and an undetected navigation error could occur. 

A systematic cross-check with other navigation techniques 

would identify this failure and prevent a serious deviation. 

In many receivers, an updatable database is used for 

navigation fixes, airports, and instrument procedures. 

These databases must be maintained to the current update 

for IFR operation, but no such requirement exists for VFR 

use. However, in many cases, the database drives a moving 

map display that indicates Special Use Airspace and the 

various classes of airspace in addition to other operational 

information. Without a current database, the moving map 

display may be outdated and offer erroneous information 

to VFR pilots wishing to fly around critical airspace areas, 

such as a Restricted Area or a Class B airspace segment. 

Numerous pilots have ventured into airspace they were trying 

to avoid by using an outdated database. If there is not a current 

database in the receiver, disregard the moving map display 

when making critical navigation decisions. 

In addition, waypoints are added, removed, relocated, or renamed as required to meet operational needs. When using 

GPS to navigate relative to a named fix, a current database 

must be used to properly locate a named waypoint. Without 

the update, it is the pilot’s responsibility to verify the 

waypoint location referencing to an official current source, 

such as the Chart Supplement U.S., sectional chart, or en 

route chart. 

In many VFR installations of GPS receivers, antenna location 

is more a matter of convenience than performance. In IFR 

installations, care is exercised to ensure that an adequate 

clear view is provided for the antenna to communicate with 

satellites. If an alternate location is used, some portion of 

the aircraft may block the view of the antenna increasing the 

possibility of losing navigation signal. 

16-32 
This is especially true in the case of hand-held receivers. The 

use of hand-held receivers for VFR operations is a growing 

trend, especially among rental pilots. Typically, suction cups 

are used to place the GPS antennas on the inside of aircraft 

windows. While this method has great utility, the antenna 

location is limited by aircraft structure for optimal reception 

of available satellites. Consequently, signal loss may occur 

in certain situations where aircraft-satellite geometry causes 

a loss of navigation signal. These losses, coupled with a lack 

of RAIM capability, could present erroneous position and 

navigation information with no warning to the pilot. 

While the use of hand-held GPS receivers for VFR operations 

is not limited by regulation, modification of the aircraft, such 

as installing a panel- or yoke-mounted holder, is governed by 

14 CFR part 43. Pilots should consult a mechanic to ensure 

compliance with the regulation and a safe installation. 

Tips for Using GPS for VFR Operations 

Always check to see if the unit has RAIM capability. If no 

RAIM capability exists, be suspicious of a GPS displayed 

position when any disagreement exists with the position 

derived from other radio navigation systems, pilotage, or 

dead reckoning. 

Check the currency of the database, if any. If expired, update 

the database using the current revision. If an update of an 

expired database is not possible, disregard any moving map 

display of airspace for critical navigation decisions. Be aware 

that named waypoints may no longer exist or may have been 

relocated since the database expired. At a minimum, the 

waypoints to be used should be verified against a current 

official source, such as the Chart Supplement U.S. or a 

Sectional Aeronautical Chart. 

While a hand-held GPS receiver can provide excellent 

navigation capability to VFR pilots, be prepared for 

intermittent loss of navigation signal, possibly with no RAIM 

warning to the pilot. If mounting the receiver in the aircraft, 

be sure to comply with 14 CFR part 43. 

Plan flights carefully before taking off. If navigating to userdefined waypoints, enter them prior to flight, not on the fly. 

Verify the planned flight against a current source, such as a 

current sectional chart. There have been cases in which one 

pilot used waypoints created by another pilot that were not 

where the pilot flying was expecting. This generally resulted 

in a navigation error. Minimize head-down time in the aircraft 

and maintain a sharp lookout for traffic, terrain, and obstacles. 

Just a few minutes of preparation and planning on the ground 

makes a great difference in the air. 

Another way to minimize head-down time is to become very 

familiar with the receiver’s operation. Most receivers are not 

intuitive. The pilot must take the time to learn the various 

keystrokes, knob functions, and displays that are used in 

the operation of the receiver. Some manufacturers provide 

computer-based tutorials or simulations of their receivers. 

Take the time to learn about the particular unit before using 

it in flight. 

In summary, be careful not to rely on GPS to solve all VFR 

navigational problems. Unless an IFR receiver is installed in 

accordance with IFR requirements, no standard of accuracy 

or integrity can be assured. While the practicality of GPS is 

compelling, the fact remains that only the pilot can navigate the 

aircraft, and GPS is just one of the pilot’s tools to do the job. 

VFR Waypoints 

VFR waypoints provide VFR pilots with a supplementary 

tool to assist with position awareness while navigating 

visually in aircraft equipped with area navigation receivers. 

VFR waypoints should be used as a tool to supplement current 

navigation procedures. The use of VFR waypoints include 

providing navigational aids for pilots unfamiliar with an area, 

waypoint definition of existing reporting points, enhanced 

navigation in and around Class B and Class C airspace, and 

enhanced navigation around Special Use Airspace. VFR 

pilots should rely on appropriate and current aeronautical 

charts published specifically for visual navigation. If 

operating in a terminal area, pilots should take advantage of 

the Terminal Area Chart available for the area, if published. 

The use of VFR waypoints does not relieve the pilot of any 

responsibility to comply with the operational requirements 

of 14 CFR part 91. 

VFR waypoint names (for computer entry and flight plans) 

consist of five letters beginning with the letters “VP” and are 

retrievable from navigation databases. The VFR waypoint 

names are not intended to be pronounceable, and they are not 

for use in ATC communications. On VFR charts, a standalone VFR waypoint is portrayed using the same four-point 

star symbol used for IFR waypoints. VFR waypoint collocated 

with a visual checkpoint on the chart is identified by a small 

magenta flag symbol. A VFR waypoint collocated with a 

visual checkpoint is pronounceable based on the name of the 

visual checkpoint and may be used for ATC communications. 

Each VFR waypoint name appears in parentheses adjacent 

to the geographic location on the chart. Latitude/longitude 

data for all established VFR waypoints may be found in the 

appropriate regional Chart Supplement U.S. 

16-33 
 

 

When filing VFR flight plans, use the five-letter identifier as 

a waypoint in the route of flight section if there is an intended 

course change at that point or if used to describe the planned 

route of flight. This VFR filing would be similar to VOR use 

in a route of flight. Pilots must use the VFR waypoints only 

when operating under VFR conditions. 

Any VFR waypoints intended for use during a flight should 

be loaded into the receiver while on the ground and prior to 

departure. Once airborne, pilots should avoid programming 

routes or VFR waypoint chains into their receivers. 

Pilots should be especially vigilant for other traffic while 

operating near VFR waypoints. The same effort to see and 

avoid other aircraft near VFR waypoints is necessary, as 

is the case when operating near VORs and NDBs. In fact, 

the increased accuracy of navigation through the use of 

GPS demands even greater vigilance as there are fewer 

off-course deviations among different pilots and receivers. 

When operating near a VFR waypoint, use all available 

ATC services, even if outside a class of airspace where 

communications are required. Regardless of the class of 

airspace, monitor the available ATC frequency closely for 

information on other aircraft operating in the vicinity. It is 

also a good idea to turn on landing light(s) when operating 

near a VFR waypoint to make the aircraft more conspicuous 

to other pilots, especially when visibility is reduced. 

Lost Procedures 

Getting lost in flight is a potentially dangerous situation, 

especially when low on fuel. If a pilot becomes lost, there 

are some good common sense procedures to follow. If a town 

or city cannot be seen, the first thing to do is climb, being 

mindful of traffic and weather conditions. An increase in 

altitude increases radio and navigation reception range and 

also increases radar coverage. If flying near a town or city, it 

may be possible to read the name of the town on a water tower. 

If the aircraft has a navigational radio, such as a VOR or ADF 

receiver, it can be possible to determine position by plotting 

an azimuth from two or more navigational facilities. If GPS 

is installed, or a pilot has a portable aviation GPS on board, 

it can be used to determine the position and the location of 

the nearest airport. 

Communicate with any available facility using frequencies 

shown on the sectional chart. If contact is made with a 

controller, radar vectors may be offered. Other facilities may 

offer direction finding (DF) assistance. To use this procedure, 

the controller requests the pilot to hold down the transmit 

button for a few seconds and then release it. The controller 

may ask the pilot to change directions a few times and repeat 

the transmit procedure. This gives the controller enough 

information to plot the aircraft position and then give vectors 

to a suitable landing site. If the situation becomes threatening, 

transmit the situation on the emergency frequency 121.5 MHz 

and set the transponder to 7700. Most facilities, and even 

airliners, monitor the emergency frequency. 

Flight Diversion 

There may come a time when a pilot is not able to make it to 

the planned destination. This can be the result of unpredicted 

weather conditions, a system malfunction, or poor preflight 

planning. In any case, the pilot needs to be able to safely 

and efficiently divert to an alternate destination. Risk 

management procedures become a priority during any type 

of flight diversion and should be used the pilot. For example, 

the hazards of inadvertent VFR into IMC involve a risk that 

the pilot can identify and assess and then mitigate through a 

pre-planned or in-flight diversion around hazardous weather. 

Before any cross-country flight, check the charts for airports 

or suitable landing areas along or near the route of flight. 

Also, check for navigational aids that can be used during a 

diversion. Risk management is explained in greater detail in 

Chapter 2, Aeronautical Decision-making. 

Computing course, time, speed, and distance information in 

flight requires the same computations used during preflight 

planning. However, because of the limited flight deck space 

and because attention must be divided between flying the 

aircraft, making calculations, and scanning for other aircraft, 

take advantage of all possible shortcuts and rule-of-thumb 

computations. 

When in flight, it is rarely practical to actually plot a course 

on a sectional chart and mark checkpoints and distances. 

Furthermore, because an alternate airport is usually not very far 

from your original course, actual plotting is seldom necessary. 

The course to an alternate destination can be measured 

accurately with a protractor or plotter but can also be 

measured with reasonable accuracy using a straightedge 

and the compass rose depicted around VOR stations. This 

approximation can be made on the basis of a radial from a 

nearby VOR or an airway that closely parallels the course 

to your alternate destination. However, remember that the 

magnetic heading associated with a VOR radial or printed 

airway is outbound from the station. To find the course to 

the station, it may be necessary to determine the reciprocal of 

that heading. It is typically easier to navigate to an alternate 

airport that has a VOR or NDB facility on the field. 

After selecting the most appropriate alternate destination, 

approximate the magnetic course to the alternate using a 

compass rose or airway on the sectional chart. If time permits, 

try to start the diversion over a prominent ground feature. 

16-34 
However, in an emergency, divert promptly toward your 

alternate destination. Attempting to complete all plotting, 

measuring, and computations involved before diverting to the 

alternate destination may only aggravate an actual emergency. 

Once established on course, note the time, and then use the 

winds aloft nearest to your diversion point to calculate a 

heading and GS. Once a GS has been calculated, determine a 

new arrival time and fuel consumption. Give priority to flying 

the aircraft while dividing attention between navigation and 

planning. When determining an altitude to use while diverting, 

consider cloud heights, winds, terrain, and radio reception. 

Chapter Summary 

This chapter has discussed the fundamentals of VFR 

navigation. Beginning with an introduction to the charts that 

can be used for navigation to the more technically advanced 

concept of GPS, there is one aspect of navigation that remains 

the same—the pilot is responsible for proper planning and 

the execution of that planning to ensure a safe flight. 

16-35 
16-36
 
17-1 

Introduction 

It is important for a pilot to be aware of the mental and 

physical standards required for the type of flying performed. 

This chapter provides information on medical certification and 

on a variety of aeromedical factors related to flight activities. 

Aeromedical 

Factors 

Chapter 17 
 

 

 

 

 

 

Obtaining a Medical Certificate 

Most pilots must have a valid medical certificate to exercise 

the privileges of their airman certificates. Glider and free 

balloon pilots are not required to hold a medical certificate. 

Sport pilots may hold either a medical certificate or a valid 

state driver’s license. Regardless of whether a medical 

certificate or drivers license is required, 14 CFR 61.53 

requires every pilot not to act as a crewmember if they know, 

or have reason to know, of any medical condition that would 

make them unable to operate the aircraft in a safe manner. 

Acquisition of a medical certificate requires an examination 

by an aviation medical examiner (AME), a physician 

with training in aviation medicine designated by the Civil 

Aerospace Medical Institute (CAMI). There are three classes 

of medical certificates. The class of certificate needed 

depends on the type of flying the pilot plans to perform. 

A third-class medical certificate is required for a private or 

recreational pilot certificate. It is valid for 5 years for those 

individuals who have not reached the age of 40; otherwise it 

is valid for 2 years. A commercial pilot certificate requires at 

least a second-class medical certificate, which is valid for 1 

year. First-class medical certificates are required for airline 

transport pilots and are valid for one year if the airman is 40 

or younger; 40 and older it is valid for 6 months. 

The standards are more rigorous for the higher classes of 

certificates. A pilot with a higher class medical certificate 

has met the requirements for the lower classes as well. Since 

the required medical class applies only when exercising the 

privileges of the pilot certificate for which it is required, a 

first-class medical certificate would be valid for 1 year if 

exercising the privileges of a commercial certificate and 2 or 5 

years, as appropriate, for exercising the privileges of a private 

or recreational certificate. The same applies for a second-class 

medical certificate. The standards for medical certification 

are contained in Title 14 of the Code of Federal Regulations 

(14 CFR) part 67 and the requirements for obtaining medical 

certificates can be found in 14 CFR part 61. 

Students who have physical limitations, such as impaired 

vision, loss of a limb, or hearing impairment may be issued 

a medical certificate valid for “student pilot privileges only” 

while learning to fly. Pilots with disabilities may require 

special equipment to be installed in the aircraft, such as 

hand controls for pilots with paraplegia. Some disabilities 

necessitate a limitation on the individual’s certificate; for 

example, impaired hearing would require the limitation 

“not valid for flight requiring the use of radio.” When all the 

knowledge, experience, and proficiency requirements have 

been met and a student can demonstrate the ability to operate 

the aircraft with the normal level of safety, a “statement of 

demonstrated ability” (SODA) can be issued. This waiver, 

or SODA, is valid as long as the physical impairment does 

not worsen. Contact the local Flight Standards District Office 

(FSDO) for more information on this subject. 

The FAA medical standards, 14 CFR part 67, specify fifteen 

medical conditions that are considered disqualifying by 

“history or clinical diagnosis.” Regardless of when one of 

these conditions was diagnosed and treated, an airman may 

not be issued a medical certificate except through a process 

called a “Special Issuance Authorization,” as explained 

in 14 CFR part 67, section 67.401. A special issuance is a 

discretionary issuance by the FAA Federal Air Surgeon and 

requires satisfactory completion of special testing determined 

by the FAA to demonstrate that an airman is safe to fly for 

the duration of the medical certificate issued. The specific 

disqualifying conditions include: 

•	 Diabetes mellitus requiring oral hypoglycemic 

medication or insulin 

• Angina pectoris 

•	 Coronary heart disease that has been treated or, if 

untreated, that has been symptomatic or clinically 

significant 

• Myocardial infarction 

• Cardiac valve replacement 

• Permanent cardiac pacemaker 

• Heart replacement 

• Psychosis 

• Bipolar disorder 

•	 Personality disorder that is severe enough to have 

repeatedly manifested itself by overt acts 

• Substance dependence (including alcohol) 

• Substance abuse 

• Epilepsy 

•	 Disturbance of consciousness and without satisfactory 

explanation of cause 

•	 Transient loss of control of nervous system function(s) 

without satisfactory explanation of cause 

However, this list includes only the mandatory disqualifying 

conditions. There are many other medical conditions that fall 

into the General Medical Condition section of the regulations 

that are considered by the FAA to be disqualifying even 

though they are not stated in the regulations. Conditions 

such as cancer, kidney stones, neurologic and neuromuscular 

conditions including Parkinson’s disease and multiple 

sclerosis, certain blood disorders, and other conditions that 

17-2 
 

 

 

 

may progress over time require review by the FAA before a 

medical certificate may be issued. 

The important thing to remember is that with very few 

exceptions, all disqualifying medical conditions may 

be considered for special issuance. If you can present 

satisfactory medical documentation to the FAA that your 

condition is stable, the chances are good that you will be 

able to qualify for an Authorization. 

Health and Physiological Factors

Affecting Pilot Performance 

A number of health factors and physiological effects can be 

linked to flying. Some are minor, while others are important 

enough to require special attention to ensure safety of flight. 

In some cases, physiological factors can lead to inflight 

emergencies. Some important medical factors that a pilot 

should be aware of include hypoxia, hyperventilation, 

middle ear and sinus problems, spatial disorientation, motion 

sickness, carbon monoxide (CO) poisoning, stress and 

fatigue, dehydration, and heatstroke. Other subjects include 

the effects of alcohol and drugs, anxiety, and excess nitrogen 

in the blood after scuba diving. 

Hypoxia 

Hypoxia means “reduced oxygen” or “not enough oxygen.” 

Although any tissue will die if deprived of oxygen long 

enough, the greatest concern regarding hypoxia during 

flight is lack of oxygen to the brain, since it is particularly 

vulnerable to oxygen deprivation. Any reduction in mental 

function while flying can result in life-threatening errors. 

Hypoxia can be caused by several factors, including an 

insufficient supply of oxygen, inadequate transportation of 

oxygen, or the inability of the body tissues to use oxygen. 

The forms of hypoxia are based on their causes: 

• Hypoxic hypoxia 

• Hypemic hypoxia 

• Stagnant hypoxia 

• Histotoxic hypoxia 

Hypoxic Hypoxia 

Hypoxic hypoxia is a result of insufficient oxygen available 

to the body as a whole. A blocked airway and drowning 

are obvious examples of how the lungs can be deprived of 

oxygen, but the reduction in partial pressure of oxygen at high 

altitude is an appropriate example for pilots. Although the 

percentage of oxygen in the atmosphere is constant, its partial 

pressure decreases proportionately as atmospheric pressure 

decreases. As an aircraft ascends during flight, the percentage 

of each gas in the atmosphere remains the same, but there are 

fewer molecules available at the pressure required for them 

to pass between the membranes in the respiratory system. 

This decrease in number of oxygen molecules at sufficient 

pressure can lead to hypoxic hypoxia. 

Dangers of Transporting Dry Ice 

Sublimation is a process in which a substance transitions 

from a solid to a gaseous state without passing through 

an intermediate liquid state. Dry ice sublimates into large 

quantities of CO2 gas, which can rapidly displace oxygencontaining air and potentially cause hypoxia via carbon 

dioxide intoxication. Case studies have shown that both illness 

and death can be caused by occupational and/or unintentional 

exposure when transporting dry ice in small, confined 

spaces such as a flightdeck or airplane. Exposure to high 

concentration of CO2 gas may lead to increased respiration, 

tachycardia, cardiac arrhythmia, and unconsciousness. 

Exposure to concentration of CO2 gas in excess of 10 percent 

may cause convulsions, coma, and/or death. 

The tendency of dry ice to rapidly sublimate also means that 

without proper ventilation, it can rapidly pressurize. For 

this reason, dry ice should never be placed inside a sealed 

transport container (i.e., leak-proof secondary container) 

and must be placed within an outer shipping container or 

storage container that allows adequate ventilation to release 

the CO2 gas and avoid pressurization. Sealing dry ice within a 

leak-proof container may result in explosion of the container 

potentially leading to serious physical injury or death. 

Hypemic Hypoxia 

Hypemic hypoxia occurs when the blood is not able to take 

up and transport a sufficient amount of oxygen to the cells 

in the body. Hypemic means “not enough blood.” This type 

of hypoxia is a result of oxygen deficiency in the blood, 

rather than a lack of inhaled oxygen, and can be caused by 

a variety of factors. It may be due to reduced blood volume 

(from severe bleeding), or it may result from certain blood 

diseases, such as anemia. More often, hypemic hypoxia 

occurs because hemoglobin, the actual blood molecule that 

transports oxygen, is chemically unable to bind oxygen 

molecules. The most common form of hypemic hypoxia is 

CO poisoning. This is explained in greater detail later in this 

chapter. Hypemic hypoxia can also be caused by the loss 

of blood due to blood donation. Blood volume can require 

several weeks to return to normal following a donation. 

Although the effects of the blood loss are slight at ground 

level, there are risks when flying during this time. 

Stagnant Hypoxia 

Stagnant means “not flowing,” and stagnant hypoxia or 

ischemia results when the oxygen-rich blood in the lungs 

is not moving, for one reason or another, to the tissues that 

17-3 
need it. An arm or leg “going to sleep” because the blood 

flow has accidentally been shut off is one form of stagnant 

hypoxia. This kind of hypoxia can also result from shock, 

the heart failing to pump blood effectively, or a constricted 

artery. During flight, stagnant hypoxia can occur with 

excessive acceleration of gravity (Gs). Cold temperatures 

can also reduce circulation and decrease the blood supplied 

to extremities. 

Histotoxic Hypoxia 

The inability of the cells to effectively use oxygen is defined 

as histotoxic hypoxia. “Histo” refers to tissues or cells, and 

“toxic” means poisonous. In this case, enough oxygen is being 

transported to the cells that need it, but they are unable to make 

use of it. This impairment of cellular respiration can be caused 

by alcohol and other drugs, such as narcotics and poisons. 

Research has shown that drinking one ounce of alcohol can 

equate to an additional 2,000 feet of physiological altitude. 

Symptoms of Hypoxia 

High-altitude flying can place a pilot in danger of becoming 

hypoxic. Oxygen starvation causes the brain and other vital 

organs to become impaired. The first symptoms of hypoxia 

can include euphoria and a carefree feeling. With increased 

oxygen starvation, the extremities become less responsive and 

flying becomes less coordinated. The symptoms of hypoxia 

vary with the individual, but common symptoms include: 

•	 Cyanosis (blue fingernails and lips) 

•	 Headache 

•	 Decreased response to stimuli and increased reaction 

time 

•	 Impaired judgment 

•	 Euphoria 

•	 Visual impairment 

•	 Drowsiness 

•	 Lightheaded or dizzy sensation 

•	 Tingling in fingers and toes 

•	 Numbness 

As hypoxia worsens, the field of vision begins to narrow and 

instrument interpretation can become difficult. Even with all 

these symptoms, the effects of hypoxia can cause a pilot to 

have a false sense of security and be deceived into believing 

everything is normal. 

Treatment of Hypoxia 

Treatment for hypoxia includes flying at lower altitudes and/ 

or using supplemental oxygen. All pilots are susceptible 

to the effects of oxygen starvation, regardless of physical 

endurance or acclimatization. When flying at high altitudes, 

it is paramount that oxygen be used to avoid the effects of 

hypoxia. The term “time of useful consciousness” describes 

the maximum time the pilot has to make rational, life-saving 

decisions and carry them out at a given altitude without 

supplemental oxygen. As altitude increases above 10,000 

feet, the symptoms of hypoxia increase in severity, and the 

time of useful consciousness rapidly decreases. [Figure 17-1] 

Since symptoms of hypoxia can be different for each 

individual, the ability to recognize hypoxia can be greatly 

improved by experiencing and witnessing the effects of it 

during an altitude chamber “flight.” The Federal Aviation 

Administration (FAA) provides this opportunity through 

aviation physiology training, which is conducted at the FAA 

CAMI in Oklahoma City, Oklahoma, and at many military 

facilities across the United States. For information about the 

FAA’s one-day physiological training course with altitude 

chamber and vertigo demonstrations, visit the FAA website 

at www.faa.gov. 

Hyperventilation 

Hyperventilation is the excessive rate and depth of respiration 

leading to abnormal loss of carbon dioxide from the blood. 

This condition occurs more often among pilots than is 

generally recognized. It seldom incapacitates completely, but 

it causes disturbing symptoms that can alarm the uninformed 

pilot. In such cases, increased breathing rate and anxiety 

further aggravate the problem. Hyperventilation can lead to 

unconsciousness due to the respiratory system’s overriding 

mechanism to regain control of breathing. 

Pilots encountering an unexpected stressful situation may 

subconsciously increase their breathing rate. If flying at 

higher altitudes, either with or without oxygen, a pilot may 

have a tendency to breathe more rapidly than normal, which 

often leads to hyperventilation. 

Since many of the symptoms of hyperventilation are similar 

to those of hypoxia, it is important to correctly diagnose and 

treat the proper condition. If using supplemental oxygen, 

check the equipment and flow rate to ensure the symptoms are 

Figure 17-1. Time of useful consciousness. 

Altitude Time of useful consciousness 

45,000 feet MSL 

40,000 feet MSL 

35,000 feet MSL 

30,000 feet MSL 

28,000 feet MSL 

25,000 feet MSL 

22,000 feet MSL 

20,000 feet MSL 

9 to 15 seconds 

15 to 20 seconds 

30 to 60 seconds 

1 to 2 minutes 

21⁄2 to 3 minutes 

3 to 5 minutes 

5 to 10 minutes 

30 minutes or more 

17-4 
 

 

 

not hypoxia related. Common symptoms of hyperventilation 

include: 

• Visual impairment 

• Unconsciousness 

• Lightheaded or dizzy sensation 

• Tingling sensations 

• Hot and cold sensations 

• Muscle spasms 

The treatment for hyperventilation involves restoring 

the proper carbon dioxide level in the body. Breathing 

normally is both the best prevention and the best cure 

for hyperventilation. In addition to slowing the breathing 

rate, breathing into a paper bag or talking aloud helps to 

overcome hyperventilation. Recovery is usually rapid once 

the breathing rate is returned to normal. 

Middle Ear and Sinus Problems 

During climbs and descents, the free gas formerly present in 

various body cavities expands due to a difference between 

the pressure of the air outside the body and that of the air 

inside the body. If the escape of the expanded gas is impeded, 

pressure builds up within the cavity and pain is experienced. 

Trapped gas expansion accounts for ear pain and sinus pain, 

as well as a temporary reduction in the ability to hear. 

The middle ear is a small cavity located in the bone of the 

skull. It is closed off from the external ear canal by the 

eardrum. Normally, pressure differences between the middle 

ear and the outside world are equalized by a tube leading 

from inside each ear to the back of the throat on each side 

called the Eustachian tube. These tubes are usually closed but 

open during chewing, yawning, or swallowing to equalize 

pressure. Even a slight difference between external pressure 

and middle ear pressure can cause discomfort. [Figure 17-2] 

During a climb, middle ear air pressure may exceed the 

pressure of the air in the external ear canal causing the 

eardrum to bulge outward. Pilots become aware of this 

pressure change when they experience alternate sensations 

of “fullness” and “clearing.” During descent, the reverse 

happens. While the pressure of the air in the external ear 

canal increases, the middle ear cavity, which equalized with 

the lower pressure at altitude, is at lower pressure than the 

external ear canal. This results in the higher outside pressure 

causing the eardrum to bulge inward. 

This condition can be more difficult to relieve due to the 

fact that the partial vacuum tends to constrict the walls of 

the Eustachian tube. To remedy this often painful condition, 

which also causes a temporary reduction in hearing 

Figure 17-2. The Eustachian tube allows air pressure to equalize 

in the middle ear. 

Opening to throat 

Middle ear 

Outer ear 

Auditory canal 

Eustachian tube 

Eardrum 

sensitivity, pinch the nostrils shut, close the mouth and lips, 

and blow slowly and gently into the mouth and nose. 

This procedure forces air through the Eustachian tube into the 

middle ear. It may not be possible to equalize the pressure in 

the ears if a pilot has a cold, an ear infection, or sore throat. 

A flight in this condition can be extremely painful, as well as 

damaging to the eardrums. If experiencing minor congestion, 

nose drops or nasal sprays may reduce the risk of a painful 

ear blockage. Before using any medication, check with an 

AME to ensure that it will not affect the ability to fly. 

In a similar way, air pressure in the sinuses equalizes with 

the pressure in the flight deck through small openings 

that connect the sinuses to the nasal passages. An upper 

respiratory infection, such as a cold or sinusitis, or a nasal 

allergic condition can produce enough congestion around an 

opening to slow equalization. As the difference in pressure 

between the sinuses and the flight deck increases, congestion 

may plug the opening. This “sinus block” occurs most 

frequently during descent. Slow descent rates can reduce the 

associated pain. A sinus block can occur in the frontal sinuses, 

located above each eyebrow, or in the maxillary sinuses, 

located in each upper cheek. It usually produces excruciating 

pain over the sinus area. A maxillary sinus block can also 

make the upper teeth ache. Bloody mucus may discharge 

from the nasal passages. 

Sinus block can be avoided by not flying with an upper 

respiratory infection or nasal allergic condition. Adequate 

protection is usually not provided by decongestant sprays 

or drops to reduce congestion around the sinus openings. 

Oral decongestants have side effects that can impair pilot 

performance. If a sinus block does not clear shortly after 

landing, a physician should be consulted. 

17-5 
 

 

 

Spatial Disorientation and Illusions 

Spatial disorientation specifically refers to the lack of 

orientation with regard to the position, attitude, or movement 

of the airplane in space. The body uses three integrated 

systems that work together to ascertain orientation and 

movement in space. 

•	 Vestibular system—organs found in the inner ear that 

sense position by the way we are balanced 

• Somatosensory system—nerves in the skin, muscles, 

and joints that, along with hearing, sense position 

based on gravity, feeling, and sound 

•	 Visual system—eyes, which sense position based on 

what is seen 

All this information comes together in the brain and, most 

of the time, the three streams of information agree, giving 

a clear idea of where and how the body is moving. Flying 

can sometimes cause these systems to supply conflicting 

information to the brain, which can lead to disorientation. 

During flight in visual meteorological conditions (VMC), 

the eyes are the major orientation source and usually prevail 

over false sensations from other sensory systems. When 

these visual cues are removed, as they are in instrument 

meteorological conditions (IMC), false sensations can cause 

a pilot to quickly become disoriented. 

The vestibular system in the inner ear allows the pilot to 

sense movement and determine orientation in the surrounding 

environment. In both the left and right inner ear, three 

semicircular canals are positioned at approximate right angles 

to each other. [Figure 17-3] Each canal is filled with fluid 

and has a section full of fine hairs. Acceleration of the inner 

ear in any direction causes the tiny hairs to deflect, which 

in turn stimulates nerve impulses, sending messages to the 

brain. The vestibular nerve transmits the impulses from 

the utricle, saccule, and semicircular canals to the brain to 

interpret motion. 

The somatosensory system sends signals from the skin, joints, 

and muscles to the brain that are interpreted in relation to the 

Earth’s gravitational pull. These signals determine posture. 

Inputs from each movement update the body’s position to the 

brain on a constant basis. “Seat of the pants” flying is largely 

dependent upon these signals. Used in conjunction with visual 

and vestibular clues, these sensations can be fairly reliable. 

However, the body cannot distinguish between acceleration 

forces due to gravity and those resulting from maneuvering 

the aircraft, which can lead to sensory illusions and false 

impressions of an aircraft’s orientation and movement. 

Under normal flight conditions, when there is a visual 

reference to the horizon and ground, the sensory system in the 

inner ear helps to identify the pitch, roll, and yaw movements 

of the aircraft. When visual contact with the horizon is lost, 

the vestibular system becomes unreliable. Without visual 

references outside the aircraft, there are many situations in 

which combinations of normal motions and forces create 

convincing illusions that are difficult to overcome. 

Prevention is usually the best remedy for spatial disorientation. 

Unless a pilot has many hours of training in instrument flight, 

flight should be avoided in reduced visibility or at night when 

the horizon is not visible. A pilot can reduce susceptibility 

to disorienting illusions through training and awareness and 

learning to rely totally on flight instruments. 

Figure 17-3. The semicircular canals lie in three planes and sense motions of roll, pitch, and yaw. 

YAW 

ROLL 

YAW 

PITCH 

PITCH ROLL 

The semicircular tubes are arranged 

at approximately, right angles to each 

other in the roll, pitch, and yaw axes. Vestibular nerve 

Endolymph fluid 

Ampulla of semicircular canal 

Hair cells 

Cupola 

Semicircular canals 

Otolith organ 

17-6 
Vestibular Illusions 

The Leans 

A condition called the leans, is the most common illusion 

during flight and is caused by a sudden return to level flight 

following a gradual and prolonged turn that went unnoticed by 

the pilot. The reason a pilot can be unaware of such a gradual 

turn is that human exposure to a rotational acceleration of 2 

degrees per second or lower is below the detection threshold 

of the semicircular canals. [Figure 17-4] Leveling the wings 

after such a turn may cause an illusion that the aircraft is 

banking in the opposite direction. In response to such an 

illusion, a pilot may lean in the direction of the original turn 

in a corrective attempt to regain the perception of a correct 

vertical posture. 

Coriolis Illusion 

The “coriolis illusion” occurs when a pilot has been in a turn 

long enough for the fluid in the ear canal to move at the same 

speed as the canal. A movement of the head in a different 

plane, such as looking at something in a different part of the 

flight deck, may set the fluid moving, creating the illusion 

of turning or accelerating on an entirely different axis. This 

action causes the pilot to think the aircraft is performing a 

maneuver it is not. The disoriented pilot may maneuver the 

aircraft into a dangerous attitude in an attempt to correct the 

aircraft’s perceived attitude. 

For this reason, it is important that pilots develop an 

instrument cross-check or scan that involves minimal head 

movement. Take care when retrieving charts and other objects 

in the flight deck—if something is dropped, retrieve it with 

minimal head movement and be alert for the coriolis illusion. 

Graveyard Spiral 

As in other illusions, a pilot in a prolonged coordinated, 

constant-rate turn may experience the illusion of not 

turning. During the recovery to level flight, the pilot will 

then experience the sensation of turning in the opposite 

direction causing the disoriented pilot to return the aircraft 

to its original turn. Because an aircraft tends to lose altitude 

in turns unless the pilot compensates for the loss in lift, 

the pilot may notice a loss of altitude. The absence of any 

sensation of turning creates the illusion of being in a level 

descent. The pilot may pull back on the controls in an attempt 

to climb or stop the descent. This action tightens the spiral 

and increases the loss of altitude; this illusion is referred to 

as a “graveyard spiral.” [Figure 17-5] This may lead to a 

loss of aircraft control. 

Somatogravic Illusion 

A rapid acceleration, such as experienced during takeoff, 

stimulates the otolith organs in the same way as tilting the 

head backwards. This action may create what is known as 

the “somatogravic illusion” of being in a nose-up attitude, 

especially in conditions with poor visual references. The 

disoriented pilot may push the aircraft into a nose-low or 

dive attitude. A rapid deceleration by quick reduction of the 

throttle(s) can have the opposite effect, with the disoriented 

pilot pulling the aircraft into a nose-up or stall attitude. 

Figure 17-5. Graveyard spiral. 

Graveyard spin 

Graveyard spiral 

No turning 

No sensation. 

Start of turn 

Sensation of turning 

as moving fluid deflects 

hairs. 

Constant rate turn 

No sensation after fluid 

accelerates to same 

speed as tube wall. 

Turn stopped 

Sensation of turning in 

opposite direction as moving 

fluid deflects hairs in opposite 

direction. 

Endolymph 

Cupola 

Tube 

Figure 17-4. Human sensation of angular acceleration. 

17-7 
 

Inversion Illusion Autokinesis 

An abrupt change from climb to straight-and-level flight can 

stimulate the otolith organs enough to create the illusion of 

tumbling backwards, known as “inversion illusion.” The 

disoriented pilot may push the aircraft abruptly into a noselow attitude, which may intensify this illusion. 

Elevator Illusion 

An abrupt upward vertical acceleration, as can occur in an 

updraft, can stimulate the otolith organs to create the illusion 

of being in a climb. This is known as “elevator illusion.” 

The disoriented pilot may push the aircraft into a nose-low 

attitude. An abrupt downward vertical acceleration, usually 

in a downdraft, has the opposite effect with the disoriented 

pilot pulling the aircraft into a nose-up attitude. 

Visual Illusions 

Visual illusions are especially hazardous because pilots rely 

on their eyes for correct information. Two illusions that lead 

to spatial disorientation, false horizon and autokinesis, affect 

the visual system only. 

False Horizon 

A sloping cloud formation, an obscured horizon, an aurora 

borealis, a dark scene spread with ground lights and stars, 

and certain geometric patterns of ground lights can provide 

inaccurate visual information, or “false horizon,” when 

attempting to align the aircraft with the actual horizon. 

The disoriented pilots as a result may place the aircraft in a 

dangerous attitude. 

When flying in the dark, a stationary light may appear to 

move if it is stared at for a prolonged period of time. As 

a result, a pilot may attempt to align the aircraft with the 

perceived moving light potentially causing him/her to lose 

control of the aircraft. This illusion is known as “autokinesis.” 

Postural Considerations 

The postural system sends signals from the skin, joints, and 

muscles to the brain that are interpreted in relation to the 

Earth’s gravitational pull. These signals determine posture. 

Inputs from each movement update the body’s position to 

the brain on a constant basis. “Seat of the pants” flying is 

largely dependent upon these signals. Used in conjunction 

with visual and vestibular clues, these sensations can be 

fairly reliable. However, because of the forces acting upon 

the body in certain flight situations, many false sensations 

can occur due to acceleration forces overpowering gravity. 

[Figure 17-6] These situations include uncoordinated turns, 

climbing turns, and turbulence. 

Demonstration of Spatial Disorientation 

There are a number of controlled aircraft maneuvers a pilot 

can perform to experiment with spatial disorientation. While 

each maneuver normally creates a specific illusion, any false 

sensation is an effective demonstration of disorientation. 

Thus, even if there is no sensation during any of these 

maneuvers, the absence of sensation is still an effective 

demonstration because it illustrates the inability to detect 

bank or roll. 

Skid, slip, and uncoordinated turns feel similar. 

Pilots feel they are being forced sideways in their seat. 

Level Coordinated turn Pull out 

Level skid Forward slip Uncoordinated turn 

Figure 17-6. Sensations from centrifugal force. 

17-8 
 

There are several objectives in demonstrating these various 

maneuvers. 

1.	 They teach pilots to understand the susceptibility of 

the human system to spatial disorientation. 

2.	 They demonstrate that judgments of aircraft attitude 

based on bodily sensations are frequently false. 

3.	 They help decrease the occurrence and degree 

of disorientation through a better understanding 

of the relationship between aircraft motion, head 

movements, and resulting disorientation. 

4.	 They help instill a greater confidence in relying on 

flight instruments for assessing true aircraft attitude. 

A pilot should not attempt any of these maneuvers at 

low altitudes or in the absence of an instructor pilot or an 

appropriate safety pilot. 

Climbing While Accelerating 

With the pilot’s eyes closed, the instructor pilot maintains 

approach airspeed in a straight-and-level attitude for several 

seconds, then accelerates while maintaining straight-andlevel attitude. The usual illusion during this maneuver, 

without visual references, is that the aircraft is climbing. 

Climbing While Turning 

With the pilot’s eyes still closed and the aircraft in a straightand-level attitude, the instructor pilot now executes, with a 

relatively slow entry, a well coordinated turn of about 1.5 

positive G (approximately 50° bank) for 90°. While in the 

turn, without outside visual references and under the effect of 

the slight positive G, the usual illusion produced is that of a 

climb. Upon sensing the climb, the pilot should immediately 

open the eyes to see that a slowly established, coordinated 

turn produces the same sensation as a climb. 

Diving While Turning 

Repeating the previous procedure, but with the pilot’s 

eyes should be kept closed until recovery from the turn is 

approximately one-half completed, can create the illusion of 

diving while turning. 

Tilting to Right or Left 

While in a straight-and-level attitude, with the pilot’s eyes 

closed, the instructor pilot executes a moderate or slight skid 

to the left with wings level. This creates the illusion of the 

body being tilted to the right. 

Reversal of Motion 

This illusion can be demonstrated in any of the three planes 

of motion. While straight and level, with the pilot’s eyes 

closed, the instructor pilot smoothly and positively rolls the 

aircraft to approximately 45° bank attitude while maintaining 

heading and pitch attitude. This creates the illusion of a strong 

sense of rotation in the opposite direction. After this illusion 

is noted, the pilot should open his or her eyes and observe 

that the aircraft is in a banked attitude. 

Diving or Rolling Beyond the Vertical Plane 

This maneuver may produce extreme disorientation. While 

in straight-and-level flight, the pilot should sit normally, 

either with eyes closed or gaze lowered to the floor. The 

instructor pilot starts a positive, coordinated roll toward a 

30° or 40° angle of bank. As this is in progress, the pilot 

tilts his or her head forward, looks to the right or left, then 

immediately returns his or her head to an upright position. 

The instructor pilot should time the maneuver so the roll is 

stopped as the pilot returns his or her head upright. An intense 

disorientation is usually produced by this maneuver, and the 

pilot experiences the sensation of falling downward into the 

direction of the roll. 

In the descriptions of these maneuvers, the instructor pilot is 

doing the flying, but having the pilot do the flying can also 

be a very effective demonstration. The pilot should close his 

or her eyes and tilt the head to one side. The instructor pilot 

tells the pilot what control inputs to perform. The pilot then 

attempts to establish the correct attitude or control input with 

eyes closed and head tilted. While it is clear the pilot has no 

idea of the actual attitude, he or she will react to what the 

senses are saying. After a short time, the pilot will become 

disoriented and the instructor pilot will tell the pilot to look 

up and recover. This exercise allows the pilot to experience 

the disorientation while flying the aircraft. 

Coping with Spatial Disorientation 

To prevent illusions and their potentially disastrous 

consequences, pilots can: 

1.	 Understand the causes of these illusions and remain 

constantly alert for them. Take the opportunity to 

experience spatial disorientation illusions in a device, 

such as a Barany chair, a Vertigon, or a Virtual Reality 

Spatial Disorientation Demonstrator. 

2.	 Always obtain and understand preflight weather 

briefings. 

3.	 Before flying in marginal visibility (less than 3 miles) 

or where a visible horizon is not evident, such as flight 

over open water during the night, obtain training and 

maintain proficiency in aircraft control by reference 

to instruments. 

4.	 Do not fly into adverse weather conditions or into 

dusk or darkness unless proficient in the use of flight 

instruments. If intending to fly at night, maintain 

17-9 
 

night-flight currency and proficiency. Include crosscountry and local operations at various airfields. 

5.	 Ensure that when outside visual references are used, 

they are reliable, fixed points on the Earth’s surface. 

6.	 Avoid sudden head movement, particularly during 

takeoffs, turns, and approaches to landing. 

7.	 Be physically tuned for flight into reduced visibility. 

Ensure proper rest, adequate diet, and, if flying at 

night, allow for night adaptation. Remember that 

illness, medication, alcohol, fatigue, sleep loss, and 

mild hypoxia are likely to increase susceptibility to 

spatial disorientation. 

8.	 Most importantly, become proficient in the use of 

flight instruments and rely upon them. Trust the 

instruments and disregard your sensory perceptions. 

The sensations that lead to illusions during instrument 

flight conditions are normal perceptions experienced by 

pilots. These undesirable sensations cannot be completely 

prevented, but through training and awareness, pilots can 

ignore or suppress them by developing absolute reliance 

on the flight instruments. As pilots gain proficiency in 

instrument flying, they become less susceptible to these 

illusions and their effects. 

Optical Illusions 

Of the senses, vision is the most important for safe flight. 

However, various terrain features and atmospheric conditions 

can create optical illusions. These illusions are primarily 

associated with landing. Since pilots must transition from 

reliance on instruments to visual cues outside the flight 

deck for landing at the end of an instrument approach, it 

is imperative that they be aware of the potential problems 

associated with these illusions and take appropriate corrective 

action. The major illusions leading to landing errors are 

described below. 

Runway Width Illusion 

A narrower-than-usual runway can create an illusion that the 

aircraft is at a higher altitude than it actually is, especially 

when runway length-to-width relationships are comparable. 

[Figure 17-7] The pilot who does not recognize this illusion 

will fly a lower approach, with the risk of striking objects 

along the approach path or landing short. A wider-thanusual runway can have the opposite effect with the risk of 

the pilot leveling out the aircraft high and landing hard or 

overshooting the runway. 

Runway and Terrain Slopes Illusion 

An upsloping runway, upsloping terrain, or both can create an 

illusion that the aircraft is at a higher altitude than it actually 

is. [Figure 17-7] The pilot who does not recognize this 

illusion will fly a lower approach. Downsloping runways and 

downsloping approach terrain can have the opposite effect. 

Featureless Terrain Illusion 

An absence of surrounding ground features, as in an 

overwater approach over darkened areas or terrain made 

featureless by snow, can create an illusion that the aircraft is 

at a higher altitude than it actually is. This illusion, sometimes 

referred to as the “black hole approach,” causes pilots to fly 

a lower approach than is desired. 

Water Refraction 

Rain on the windscreen can create an illusion of being at a 

higher altitude due to the horizon appearing lower than it is. 

This can result in the pilot flying a lower approach. 

Haze 

Atmospheric haze can create an illusion of being at a greater 

distance and height from the runway. As a result, the pilot 

has a tendency to be low on the approach. Conversely, 

extremely clear air (clear bright conditions of a high attitude 

airport) can give the pilot the illusion of being closer than 

he or she actually is, resulting in a high approach that may 

result in an overshoot or go around. The diffusion of light 

due to water particles on the windshield can adversely affect 

depth perception. The lights and terrain features normally 

used to gauge height during landing become less effective 

for the pilot. 

Fog 

Flying into fog can create an illusion of pitching up. Pilots 

who do not recognize this illusion often steepen the approach 

abruptly. 

Ground Lighting Illusions 

Lights along a straight path, such as a road or lights on moving 

trains, can be mistaken for runway and approach lights. Bright 

runway and approach lighting systems, especially where 

few lights illuminate the surrounding terrain, may create the 

illusion of less distance to the runway. The pilot who does 

not recognize this illusion will often fly a higher approach. 

How To Prevent Landing Errors Due to Optical 

Illusions 

To prevent these illusions and their potentially hazardous 

consequences, pilots can: 

1.	 Anticipate the possibility of visual illusions during 

approaches to unfamiliar airports, particularly at night 

or in adverse weather conditions. Consult airport 

17-10 
 

 

 

 

 

25 

25

N o rm a l A p p r o a c h

Normal Approach 

25 25

25 Normal Approach 

25 Normal Approach 

Downsloping runway Upsloping runway 

Downsloping runway Upsloping runway

Narrower runway Wider runway

Narrower runway Wider runway

Normal approach 

Approach due to illusion 

Runway width illusion 

• A narrower-than-usual runway can 

create an illusion that the aircraft 

is higher than it actually is, leading 

to a lower approach.

• A wider-than-usual runway can 

create an illusion that the aircraft is 

lower than it actually is, leading to 

a higher approach.

Runway slope illusion 

• A downsloping runway can create 

the illusion that the aircraft is lower 

than it actually is, leading to a 

higher approach.

• An upsloping runway can create 

the illusion that the aircraft is higher 

than it actually is, leading to a lower 

approach.

Figure 17-7. Runway illusions. 

diagrams and the Chart Supplement U.S. (formerly 4. Use Visual Approach Slope Indicator (VASI) or 

Airport/Facility Directory) for information on runway Precision Approach Path Indicator (PAPI) systems 

slope, terrain, and lighting. for a visual reference, or an electronic glideslope, 

whenever they are available. 2.	 Make frequent reference to the altimeter, especially 

during all approaches, day and night.	 5. Utilize the visual descent point (VDP) found on many 

nonprecision instrument approach procedure charts. 3.	 If possible, conduct an aerial visual inspection of
 

unfamiliar airports before landing.
 

17-11 
 

6.	 Recognize that the chances of being involved in an 

approach accident increase when an emergency or 

other activity distracts from usual procedures. 

7.	 Maintain optimum proficiency in landing procedures. 

In addition to the sensory illusions due to misleading inputs to 

the vestibular system, a pilot may also encounter various visual 

illusions during flight. Illusions rank among the most common 

factors cited as contributing to fatal aviation accidents. 

Sloping cloud formations, an obscured horizon, a dark scene 

spread with ground lights and stars, and certain geometric 

patterns of ground light can create illusions of not being 

aligned correctly with the actual horizon. Various surface 

features and atmospheric conditions encountered in landing 

can create illusions of being on the wrong approach path. 

Landing errors due to these illusions can be prevented by 

anticipating them during approaches, inspecting unfamiliar 

airports before landing, using electronic glideslope or VASI 

systems when available, and maintaining proficiency in 

landing procedures. 

Motion Sickness 

Motion sickness, or airsickness, is caused by the brain 

receiving conflicting messages about the state of the body. A 

pilot may experience motion sickness during initial flights, but 

it generally goes away within the first few lessons. Anxiety 

and stress, which may be experienced at the beginning of 

flight training, can contribute to motion sickness. Symptoms 

of motion sickness include general discomfort, nausea, 

dizziness, paleness, sweating, and vomiting. 

It is important to remember that experiencing airsickness is 

no reflection on one’s ability as a pilot. If prone to motion 

sickness, let the flight instructor know, there are techniques 

that can be used to overcome this problem. For example, 

avoid lessons in turbulent conditions until becoming more 

comfortable in the aircraft or start with shorter flights and 

graduate to longer instruction periods. If symptoms of motion 

sickness are experienced during a lesson, opening fresh air 

vents, focusing on objects outside the airplane, and avoiding 

unnecessary head movements may help alleviate some of the 

discomfort. Although medications like Dramamine can prevent 

airsickness in passengers, they are not recommended while 

flying since they can cause drowsiness and other problems. 

Carbon Monoxide (CO) Poisoning 

CO is a colorless and odorless gas produced by all internal 

combustion engines. Attaching itself to the hemoglobin in 

the blood about 200 times more easily than oxygen, CO 

prevents the hemoglobin from carrying oxygen to the cells, 

resulting in hypemic hypoxia. The body requires up to 48 

hours to dispose of CO. If severe enough, the CO poisoning 

can result in death. Aircraft heater vents and defrost vents 

may provide CO a passageway into the cabin, particularly if 

the engine exhaust system has a leak or is damaged. If a strong 

odor of exhaust gases is detected, assume that CO is present. 

However, CO may be present in dangerous amounts even 

if no exhaust odor is detected. Disposable, inexpensive CO 

detectors are widely available. In the presence of CO, these 

detectors change color to alert the pilot of the presence of CO. 

Some effects of CO poisoning are headache, blurred vision, 

dizziness, drowsiness, and/or loss of muscle power. Any time 

a pilot smells exhaust odor, or any time these symptoms are 

experienced, immediate corrective action should be taken 

including turning off the heater, opening fresh air vents and 

windows, and using supplemental oxygen, if available. 

Tobacco smoke also causes CO poisoning. Smoking at 

sea level can raise the CO concentration in the blood and 

result in physiological effects similar to flying at 8,000 feet. 

Besides hypoxia, tobacco causes diseases and physiological 

debilitation that can be medically disqualifying for pilots. 

Stress 

Stress is the body’s response to physical and psychological 

demands placed upon it. The body’s reaction to stress includes 

releasing chemical hormones (such as adrenaline) into the 

blood and increasing metabolism to provide more energy 

to the muscles. Blood sugar, heart rate, respiration, blood 

pressure, and perspiration all increase. The term “stressor” 

is used to describe an element that causes an individual to 

experience stress. Examples of stressors include physical 

stress (noise or vibration), physiological stress (fatigue), and 

psychological stress (difficult work or personal situations). 

Stress falls into two broad categories: acute (short term) and 

chronic (long term). Acute stress involves an immediate 

threat that is perceived as danger. This is the type of stress that 

triggers a “fight or flight” response in an individual, whether 

the threat is real or imagined. Normally, a healthy person can 

cope with acute stress and prevent stress overload. However, 

ongoing acute stress can develop into chronic stress. 

Chronic stress can be defined as a level of stress that presents 

an intolerable burden, exceeds the ability of an individual 

to cope, and causes individual performance to fall sharply. 

Unrelenting psychological pressures, such as loneliness, 

financial worries, and relationship or work problems can 

produce a cumulative level of stress that exceeds a person’s 

ability to cope with the situation. When stress reaches these 

levels, performance falls off rapidly. Pilots experiencing 

this level of stress are not safe and should not exercise their 

airman privileges. Pilots who suspect they are suffering from 

chronic stress should consult a physician. 

17-12 
 

 

Fatigue 

Fatigue is frequently associated with pilot error. Some of 

the effects of fatigue include degradation of attention and 

concentration, impaired coordination, and decreased ability 

to communicate. These factors seriously influence the 

ability to make effective decisions. Physical fatigue results 

from sleep loss, exercise, or physical work. Factors such as 

stress and prolonged performance of cognitive work result 

in mental fatigue. 

Like stress, fatigue falls into two broad categories: acute 

and chronic. Acute fatigue is short term and is a normal 

occurrence in everyday living. It is the kind of tiredness 

people feel after a period of strenuous effort, excitement, or 

lack of sleep. Rest after exertion and 8 hours of sound sleep 

ordinarily cures this condition. 

A special type of acute fatigue is skill fatigue. This type of 

fatigue has two main effects on performance: 

•	 Timing disruption—appearing to perform a task as 

usual, but the timing of each component is slightly off. 

This makes the pattern of the operation less smooth 

because the pilot performs each component as though it 

were separate, instead of part of an integrated activity. 

•	 Disruption of the perceptual field—concentrating 

attention upon movements or objects in the center of 

vision and neglecting those in the periphery. This is 

accompanied by loss of accuracy and smoothness in 

control movements. 

Acute fatigue has many causes, but the following are among 

the most important for the pilot: 

•	 Mild hypoxia (oxygen deficiency) 

•	 Physical stress 

•	 Psychological stress 

•	 Depletion of physical energy resulting from 

psychological stress 

•	 Sustained psychological stress 

Sustained psychological stress accelerates the glandular 

secretions that prepare the body for quick reactions during 

an emergency. These secretions make the circulatory and 

respiratory systems work harder, and the liver releases energy 

to provide the extra fuel needed for brain and muscle work. 

When this reserve energy supply is depleted, the body lapses 

into generalized and severe fatigue. 

Acute fatigue can be prevented by proper diet and adequate 

rest and sleep. A well-balanced diet prevents the body from 

needing to consume its own tissues as an energy source. 

Adequate rest maintains the body’s store of vital energy. 

Chronic fatigue, extending over a long period of time, usually 

has psychological roots, although an underlying disease is 

sometimes responsible. Continuous high-stress levels produce 

chronic fatigue. Chronic fatigue is not relieved by proper diet 

and adequate rest and sleep and usually requires treatment 

by a physician. An individual may experience this condition 

in the form of weakness, tiredness, palpitations of the heart, 

breathlessness, headaches, or irritability. Sometimes chronic 

fatigue even creates stomach or intestinal problems and 

generalized aches and pains throughout the body. When the 

condition becomes serious enough, it leads to emotional illness. 

If suffering from acute fatigue, stay on the ground. If fatigue 

occurs in the flight deck, no amount of training or experience 

can overcome the detrimental effects. Getting adequate rest 

is the only way to prevent fatigue from occurring. Avoid 

flying without a full night’s rest, after working excessive 

hours, or after an especially exhausting or stressful day. Pilots 

who suspect they are suffering from chronic fatigue should 

consult a physician. 

Exposure to Chemicals 

When conducting preflight and post-flight inspections, pilots 

must verify that the fluid levels in their aircraft meet the 

levels specified for safe operations as stated in the Pilot's 

Operating Handbook. These fluids include, but are not limited 

to hydraulic fluid, engine oil, and fuel. 

It is important that every pilot recognize the potential hazards 

of working with these fluids as well as the recommended first 

aid measures to follow should any of these fluids come in 

contact with their eyes, skin, and/or respiratory system. As 

the specific first aid measures for dealing with exposure to 

these chemicals can vary by chemical type, it is important that 

every pilot be familiar with the location and use of the Material 

Safety Data Sheet (MSDS) for each chemical they encounter. 

The procedures described in the following sections are 

minimum guideline for first aid for each of the indicated 

scenarios. Ultimately, the pilot should consult the MSDS 

for first aid procedures specific to the type of chemical and 

exposure scenario. 

Hydraulic Fluid 

•	 Eye Contact—immediately flush the eyes with clean 

water and seek medical attention if irritation occurs. 

•	 Skin Contact—remove all contaminated clothing and 

thoroughly cleanse the affected areas with mild soap 

and water or a waterless hand cleaner. If irritation or 

redness develops and persists, seek medical attention. 

Should the hydraulic fluid get into or under the skin, 

or into any other part of the body, regardless of the 

17-13 
 

appearance of the wound or its size, seek medical 

attention immediately. 

•	 Inhalation—if respiratory symptoms develop, move 

away from the source of exposure and into fresh air 

in a position comfortable for breathing. If symptoms 

persist, seek medical attention. 

•	 Ingestion—first aid is not normally required; however, 

if swallowed and symptoms develop, seek medical 

attention. 

Engine Oil 

•	 Eye Contact—immediately flush the eyes with clean 

water and seek medical attention if irritation occurs. 

•	 Skin Contact—remove all contaminated clothing and 

thoroughly cleanse the affected areas with soap and 

water. Launder contaminated clothing before reuse. 

•	 Inhalation—move away from the source of exposure 

and into fresh air. If respiratory irritation, dizziness, 

nausea, or unconsciousness occurs, seek immediate 

medical attention. If breathing stops, assisted 

ventilation is required via a bag-valve-mask or 

cardiopulmonary resuscitation (CPR). 

•	 Ingestion—seek immediate medical attention. If 

immediate medical attention is not available, contact 

a regional poison control center or emergency medical 

professional regarding the induction of vomiting or 

use of activated charcoal. Vomiting should never be 

induced to a person who is groggy or unconscious. 

Fuel 

•	 Eye Contact—immediately flush the eyes with 

clean water for at least 15 minutes and seek medical 

attention immediately. 

•	 Skin Contact—remove all contaminated clothing 

and thoroughly cleanse the affected areas with mild 

soap and water or a waterless hand cleaner. If skin 

surface is damaged, apply a clean dressing and seek 

medical attention. If irritation or redness develops, 

seek medical attention. Launder contaminated clothing 

before reuse. 

•	 Inhalation—move away from the source of exposure 

and into fresh air. If breathing stops, assisted 

ventilation is required via a bag-valve-mask or 

cardiopulmonary resuscitation (CPR). Once breathing 

is restored, the use of additional oxygen may be 

necessary. Seek medical attention immediately. 

•	 Ingestion—seek immediate medical attention. Do not 

induce vomiting or take anything by mouth as this may 

cause the material to enter the lungs and cause severe 

lung damage. Should vomiting occur, keep head below 

the hips to reduce the risks of aspiration. Monitor for 

breathing difficulties. Rinse out any material which 

enters the mouth until the taste is dissipated. 

Dehydration and Heatstroke 

Dehydration is the term given to a critical loss of water from 

the body. Causes of dehydration are hot flight decks and 

flight lines, wind, humidity, and diuretic drinks—coffee, tea, 

alcohol, and caffeinated soft drinks. Some common signs of 

dehydration are headache, fatigue, cramps, sleepiness, and 

dizziness. 

The first noticeable effect of dehydration is fatigue, which 

in turn makes top physical and mental performance difficult, 

if not impossible. Flying for long periods in hot summer 

temperatures or at high altitudes increases the susceptibility 

to dehydration because these conditions tend to increase the 

rate of water loss from the body. 

To help prevent dehydration, drink two to four quarts of 

water every 24 hours. Since each person is physiologically 

different, this is only a guide. Most people are aware of the 

eight-glasses-a-day guide: If each glass of water is eight 

ounces, this equates to 64 ounces, which is two quarts. If 

this fluid is not replaced, fatigue progresses to dizziness, 

weakness, nausea, tingling of hands and feet, abdominal 

cramps, and extreme thirst. 

The key for pilots is to be continually aware of their condition. 

Most people become thirsty with a 1.5 quart deficit or a loss 

of 2 percent of total body weight. This level of dehydration 

triggers the “thirst mechanism.” The problem is that the thirst 

mechanism arrives too late and is turned off too easily. A 

small amount of fluid in the mouth turns this mechanism off 

and the replacement of needed body fluid is delayed. 

Other steps to prevent dehydration include: 

•	 Carrying a container in order to measure daily water 

intake. 

•	 Staying ahead—not relying on the thirst sensation as 

an alarm. If plain water is not preferred, add some 

sport drink flavoring to make it more acceptable. 

•	 Limiting daily intake of caffeine and alcohol (both are 

diuretics and stimulate increased production of urine). 

Heatstroke is a condition caused by any inability of the body 

to control its temperature. Onset of this condition may be 

recognized by the symptoms of dehydration, but also has 

been known to be recognized only upon complete collapse. 

17-14 
 

 

 

 

 

 

 

 

 

 

 

 

To prevent these symptoms, it is recommended that an 

ample supply of water be carried and used at frequent 

intervals on any long flight, whether thirsty or not. The body 

normally absorbs water at a rate of 1.2 to 1.5 quarts per hour. 

Individuals should drink one quart per hour for severe heat 

stress conditions or one pint per hour for moderate stress 

conditions. If the aircraft has a canopy or roof window, 

wearing light-colored, porous clothing and a hat will help 

provide protection from the sun. Keeping the flight deck well 

ventilated aids in dissipating excess heat. 

Alcohol 

Alcohol impairs the efficiency of the human body. 

[Figure 17-8] Studies have shown that consuming alcohol 

is closely linked to performance deterioration. Pilots must 

make hundreds of decisions, some of them time-critical, 

during the course of a flight. The safe outcome of any flight 

depends on the ability to make the correct decisions and take 

Type Beverage Typical Serving Pure Alcohol 

(oz) Content (oz) 

Table wine 

Light beer 

Aperitif liquor 

Champagne 

Vodka 

Whiskey

 4.0

 12.0

 1.5

 4.0

 1.0

 1.25 

.48 

.48 

.38 

.48 

.50 

.50 

0.01–0.05% average individual appears normal 

(10–50 mg) 

0.03–0.12%* mild euphoria, talkativeness, decreased 

(30–120 mg) inhibitions, decreased attention, impaired 

judgment, increased reaction time 

0.09–0.25% emotional instability, loss of critical 

(90–250 mg) judgment, impairment of memory and 

comprehension, decreased sensory 

response, mild muscular incoordination 

0.18–0.30% confusion, dizziness, exaggerated 

(180–300 mg) emotions (anger, fear, grief), impaired 

visual perception, decreased pain 

sensation, impaired balance, staggering 

gait, slurred speech, moderate muscular 

incoordination 

0.27–0.40% apathy, impaired consciousness, stupor, 

(270–400 mg) significantly decreased response to 

stimulation, severe muscular 

incoordination, inability to stand or walk, 

vomiting, incontinence of urine and feces 

0.35–0.50% unconsciousness, depressed or 

(350–500 mg) abolished reflexes, abnormal body 

temperature, coma, possible death from 

respiratory paralysis (450 mg or above) 

* Legal limit for motor vehicle operation in most states is 0.08

 or 0.10% (80–100 mg of alcohol per dL of blood). 

Figure 17-8. Impairment scale with alcohol use. 

the appropriate actions during routine occurrences, as well 

as abnormal situations. The influence of alcohol drastically 

reduces the chances of completing a flight without incident. 

Even in small amounts, alcohol can impair judgment, 

decrease sense of responsibility, affect coordination, constrict 

visual field, diminish memory, reduce reasoning ability, and 

lower attention span. As little as one ounce of alcohol can 

decrease the speed and strength of muscular reflexes, lessen 

the efficiency of eye movements while reading, and increase 

the frequency at which errors are committed. Impairments 

in vision and hearing can occur from consuming as little as 

one drink. 

The alcohol consumed in beer and mixed drinks is ethyl 

alcohol, a central nervous system depressant. From a medical 

point of view, it acts on the body much like a general 

anesthetic. The “dose” is generally much lower and more 

slowly consumed in the case of alcohol, but the basic effects 

on the human body are similar. Alcohol is easily and quickly 

absorbed by the digestive tract. The bloodstream absorbs 

about 80 to 90 percent of the alcohol in a drink within 30 

minutes when ingested on an empty stomach. The body 

requires about 3 hours to rid itself of all the alcohol contained 

in one mixed drink or one beer. 

While experiencing a hangover, a pilot is still under the 

influence of alcohol. Although a pilot may think he or she is 

functioning normally, motor and mental response impairment 

is still present. Considerable amounts of alcohol can remain 

in the body for over 16 hours, so pilots should be cautious 

about flying too soon after drinking. 

Altitude multiplies the effects of alcohol on the brain. When 

combined with altitude, the alcohol from two drinks may have 

the same effect as three or four drinks. Alcohol interferes 

with the brain’s ability to utilize oxygen, producing a form 

of histotoxic hypoxia. The effects are rapid because alcohol 

passes quickly into the bloodstream. In addition, the brain 

is a highly vascular organ that is immediately sensitive to 

changes in the blood’s composition. For a pilot, the lower 

oxygen availability at altitude and the lower capability of 

the brain to use the oxygen that is available can add up to a 

deadly combination. 

Intoxication is determined by the amount of alcohol in the 

bloodstream. This is usually measured as a percentage by 

weight in the blood. 14 CFR part 91 requires that blood 

alcohol level be less than .04 percent and that 8 hours pass 

between drinking alcohol and piloting an aircraft. A pilot with 

a blood alcohol level of .04 percent or greater after 8 hours 

cannot fly until the blood alcohol falls below that amount. 

Even though blood alcohol may be well below .04 percent, 

a pilot cannot fly sooner than 8 hours after drinking alcohol. 

17-15 
 

 

 

Although the regulations are quite specific, it is a good idea 

to be more conservative than the regulations. 

Drugs 

The Federal Aviation Regulations include no specific 

references to medication usage. Two regulations, though, 

are important to keep in mind. Title 14 of the CFR part 61, 

section 61.53 prohibits acting as pilot-in-command or in any 

other capacity as a required pilot flight crewmember, while 

that person: 

1.	 Knows or has reason to know of any medical condition 

that would make the person unable to meet the 

requirement for the medical certificate necessary for 

the pilot operation, or 

2. Is taking medication or receiving other treatment for 

a medical condition that results in the person being 

unable to meet the requirements for the medical 

certificate necessary for the pilot operation. 

Further, 14 CFR part 91, section 91.17 prohibits the use 

of any drug that affects the person’s faculties in any way 

contrary to safety. 

There are several thousand medications currently approved 

by the U.S. Food and Drug Administration (FDA), not 

including OTC (over the counter) drugs. Virtually all 

medications have the potential for adverse side effects in 

some people. Additionally, herbal and dietary supplements, 

sport and energy boosters, and some other “natural” products 

are derived from substances often found in medications that 

could also have adverse side effects. While some individuals 

experience no side effects with a particular drug or product, 

others may be noticeably affected. The FAA regularly 

reviews FDA and other data to assure that medications found 

acceptable for aviation duties do not pose an adverse safety 

risk. Drugs that cause no apparent side effects on the ground 

can create serious problems at even relatively low altitudes. 

Even at typical general aviation altitudes, the changes in 

concentrations of atmospheric gases in the blood can enhance 

the effects of seemingly innocuous drugs that can result in 

impaired judgment, decision-making, and performance. In 

addition, fatigue, stress, dehydration, and inadequate nutrition 

can increase an airman’s susceptibility to adverse effects from 

various drugs, even if they appeared to tolerate them in the 

past. If multiple medications are being taken at the same time, 

the adverse effects can be even more pronounced. 

Another important consideration is that the medical 

condition for which a medication is prescribed may itself be 

disqualifying. The FAA will consider the condition in the 

context of risk for medical incapacitation, and the medication 

as well for cognitive impairment, and either or both could be 

found unacceptable for medical certification. 

Some of the most commonly used OTC drugs, antihistamines 

and decongestants, have the potential to cause noticeable 

adverse side effects, including drowsiness and cognitive 

deficits. The symptoms associated with common upper 

respiratory infections, including the common cold, often 

suppress a pilot’s desire to fly, and treating symptoms with 

a drug that causes adverse side effects only compounds 

the problem. Particularly, medications containing 

diphenhydramine (e.g., Benadryl) are known to cause 

drowsiness and have a prolonged half-life, meaning the drugs 

stay in one’s system for an extended time, which lengthens 

the time that side effects are present. 

Many medications, such as tranquilizers, sedatives, strong 

pain relievers, and cough suppressants, have primary 

effects that may impair judgment, memory, alertness, 

coordination, vision, and the ability to make calculations. 

[Figure 17-9] Others, such as antihistamines, blood pressure 

drugs, muscle relaxants, and agents to control diarrhea and 

motion sickness, have side effects that may impair the same 

critical functions. Any medication that depresses the nervous 

system, such as a sedative, tranquilizer, or antihistamine, can 

make a pilot more susceptible to hypoxia. 

Painkillers are grouped into two broad categories: analgesics 

and anesthetics. Analgesics are drugs that reduce pain, 

while anesthetics are drugs that deaden pain or cause loss 

of consciousness. 

Over-the-counter analgesics, such as acetylsalicylic acid 

(aspirin), acetaminophen (Tylenol), and ibuprofen (Advil), 

have few side effects when taken in the correct dosage. 

Although some people are allergic to certain analgesics or may 

suffer from stomach irritation, flying usually is not restricted 

when taking these drugs. However, flying is almost always 

precluded while using prescription analgesics, such as drugs 

containing propoxyphene (e.g., Darvon), oxycodone (e.g., 

Percodan), meperidine (e.g., Demerol), and codeine, since 

these drugs are known to cause side effects, such as mental 

confusion, dizziness, headaches, nausea, and vision problems. 

Anesthetic drugs are commonly used for dental and surgical 

procedures. Most local anesthetics used for minor dental and 

outpatient procedures wear off within a relatively short period 

of time. The anesthetic itself may not limit flying as much 

as the actual procedure and subsequent pain. 

17-16 
Stimulants are drugs that excite the central nervous 

system and produce an increase in alertness and activity. 

Amphetamines, caffeine, and nicotine are all forms of 

stimulants. Common uses of these drugs include appetite 

suppression, fatigue reduction, and mood elevation. Some 

of these drugs may cause a stimulant reaction, even though 

this reaction is not their primary function. In some cases, 

stimulants can produce anxiety and mood swings, both of 

which are dangerous when flying. 

Depressants are drugs that reduce the body’s functioning in 

many areas. These drugs lower blood pressure, reduce mental 

processing, and slow motor and reaction responses. There are 

several types of drugs that can cause a depressing effect on the 

body, including tranquilizers, motion sickness medication, 

some types of stomach medication, decongestants, and 

antihistamines. The most common depressant is alcohol. 

Substance Possible Side Effects Generic Or 

Brand Name 

Treatment 

for 

Alcohol 

Nicotine 

Amphetamines 

Caffeine 

Antacid 

Antihistamines 

Aspirin 

Beer 

Liquor 

Wine 

Cigars 

Cigarettes 

Pipe tobacco 

Chewing tobacco 

Snuff 

Ritalin 

Obetrol 

Eskatrol 

Coffee 

Tea 

Chocolate 

No-Doz 

Alka-2 

Di-Gel 

Maalox 

Coricidin 

Contac 

Dristan 

Dimetapp 

Omade 

Chlor-Trimeton 

Diphenhydramine 

Bayer 

Bufferin 

Alka-Seltzer 

N/A 

N/A 

Obesity (diet pills) 

Tiredness 

N/A 

Stomach acids 

Allergies 

Colds 

Headaches 

Fevers 

Aches 

Pains 

Impaired judgment and perception 

Impaired coordination and motor control 

Reduced reaction time 

Impaired sensory perception 

Reduced intellectual functions 

Reduced tolerance to G-forces 

Inner-ear disturbance and spatial disorientation (up to 48 hours) 

Central nervous system depression 

Sinus and respiratory system infection and irritation 

Impaired night vision 

Hypertension 

Carbon monoxide poisoning (from smoking) 

Prolonged wakefulness 

Nervousness 

Impaired vision 

Suppressed appetite 

Shakiness 

Excessive sweating 

Rapid heart rate 

Sleep disturbance 

Seriously impaired judgment 

Impaired judgment 

Reduced reaction time 

Sleep disturbance 

Increased motor activity and tremors 

Hypertension 

Irregular heart rate 

Rapid heart rate 

Body dehydration (through increased urine output) 

Headaches 

Liberations of carbon dioxide at altitude (distension may cause 

acute abdominal pain and may mask other medical problems) 

Drowsiness and dizziness (sometimes recurring) 

Visual disturbances (when medications also contain antispasmodic drugs) 

Irregular body temperature 

Variation in rate and depth of respiration 

Hypoxia and hyperventilation (two aspirin can contribute to) 

Nausea, ringing in ears, deafness, diarrhea, and hallucinations when taken in 

excessive dosages 

Corrosive action on the stomach lining 

Gastrointestinal problems 

Decreased clotting ability of the blood (clotting ability could be the difference 

between life and death in a survival situation) 

Figure 17-9. Adverse affects of various drugs. 

17-17 
 

 

 

 

 

 

Some drugs that are classified as neither stimulants nor 

depressants have adverse effects on flying. For example, 

some antibiotics can produce dangerous side effects, such 

as balance disorders, hearing loss, nausea, and vomiting. 

While many antibiotics are safe for use while flying, the 

infection requiring the antibiotic may prohibit flying. In 

addition, unless specifically prescribed by a physician, do 

not take more than one drug at a time, and never mix drugs 

with alcohol because the effects are often unpredictable. 

The dangers of illegal drugs also are well documented. 

Certain illegal drugs can have hallucinatory effects that occur 

days or weeks after the drug is taken. Obviously, these drugs 

have no place in the aviation community. 

14 CFR prohibits pilots from performing crewmember 

duties while using any medication that affects the body in 

any way contrary to safety. The safest rule is not to fly as a 

crewmember while taking any medication, unless approved to 

do so by the FAA. If there is any doubt regarding the effects 

of any medication, consult an AME before flying. 

Prior to each and every flight, all pilots must do a proper 

physical self-assessment to ensure safety. A great mnemonic, 

covered in Chapter 2 on Aeronautical Decision-Making, 

is IMSAFE, which stands for Illness, Medication, Stress, 

Alcohol, Fatigue, and Emotion. 

For the medication component of IMSAFE, pilots need to 

ask themselves, “Am I taking any medicines that might affect 

my judgment or make me drowsy? For any new medication, 

OTC or prescribed, you should wait at least 48 hours after 

the first dose before flying to determine you do not have any 

adverse side effects that would make it unsafe to operate an 

aircraft. In addition to medication questions, pilots should 

also consider the following – 

• Do not take any unnecessary or elective medications;

• Make sure you eat regular balanced meals;

• Bring a snack for both you and your passengers for

the flight;

• Maintain good hydration - bring plenty of water;

• Ensure adequate sleep the night prior to the flight; and 

• Stay physically fit.

Additionally, you should wait at least five maximal dosing 

intervals, the time between recommended or prescribed 

dosing, (e.g., a dosing interval of 5 to 6 hours would require 

you to wait 30 hours) before flying after taking any medication 

that has potentially adverse side effects (e.g., sedating or 

dizziness). Observing the recommended dosing interval 

doesn’t eliminate the risk for adverse side effects because 

everyone metabolizes medications differently. However, 

five times the dosing interval is a reasonable rule of thumb. 

Altitude-Induced Decompression Sickness (DCS) 

Decompression sickness (DCS) describes a condition 

characterized by a variety of symptoms resulting from 

exposure to low barometric pressures that cause inert gases 

(mainly nitrogen), normally dissolved in body fluids and 

tissues, to come out of physical solution and form bubbles. 

Nitrogen is an inert gas normally stored throughout the 

human body (tissues and fluids) in physical solution. When 

the body is exposed to decreased barometric pressures (as in 

flying an unpressurized aircraft to altitude or during a rapid 

decompression), the nitrogen dissolved in the body comes out 

of solution. If the nitrogen is forced to leave the solution too 

rapidly, bubbles form in different areas of the body causing a 

variety of signs and symptoms. The most common symptom 

is joint pain, which is known as “the bends.” [Figure 17-10] 

What to do when altitude-induced DCS occurs: 

• Put on oxygen mask immediately and switch the

regulator to 100 percent oxygen.

• Begin an emergency descent and land as soon as

possible. Even if the symptoms disappear during

descent, land and seek medical evaluation while

continuing to breathe oxygen.

• If one of the symptoms is joint pain, keep the affected 

area still; do not try to work pain out by moving the

joint around.

• Upon landing, seek medical assistance from an FAA

medical officer, AME, military flight surgeon, or

a hyperbaric medicine specialist. Be aware that a

physician not specialized in aviation or hypobaric

medicine may not be familiar with this type of medical 

problem.

• Definitive medical treatment may involve the use of

a hyperbaric chamber operated by specially-trained

personnel.

• Delayed signs and symptoms of altitude-induced DCS 

can occur after return to ground level regardless of

presence during flight.

DCS After Scuba Diving 

Scuba diving subjects the body to increased pressure, which 

allows more nitrogen to dissolve in body tissues and fluids. 

[Figure 17-11] The reduction of atmospheric pressure that 

accompanies flying can produce physical problems for scuba 

divers. A pilot or passenger who intends to fly after scuba 

diving should allow the body sufficient time to rid itself of 

excess nitrogen absorbed during diving. If not, DCS due to 

17-18 
DCS Type Bubble Location Signs and Symptoms (Clinical Manifestations) 

BENDS
 

NEUROLOGIC
 

Manifestations
 

CHOKES 

SKIN BENDS 

Mostly large joints 

of the body (elbows, 

shoulders, hip, wrists, 

knees, ankles) 

Brain 

Spinal cord 

Peripheral nerves 

Lungs 

Skin 

• Localized deep pain, ranging from mild (a “niggle”) to excruciating–sometimes a dull 

ache, but rarely a sharp pain 

• Active and passive motion of the joint aggravating the pain 

• Pain occurring at altitude, during the descent, or many hours later 

• Confusion or memory loss 

• Headache 

• Spots in visual field (scotoma), tunnel vision, double vision (diplopia), or blurry vision 

• Unexplained extreme fatigue or behavior changes 

• Seizures, dizziness, vertigo, nausea, vomiting, and unconsciousness 

• Abnormal sensations, such as burning, stinging, and tingling, around the lower chest 

and back 

• Symptoms spreading from the feet up and possibly accompanied by ascending 

weakness or paralysis 

• Girdling abdominal or chest pain 

• Urinary and rectal incontinence 

• Abnormal sensations, such as numbness, burning, stinging and tingling (paresthesia) 

• Muscle weakness or twitching 

• Burning deep chest pain (under the sternum) 

• Pain aggravated by breathing 

• Shortness of breath (dyspnea) 

• Dry constant cough 

• Itching usually around the ears, face, neck, arms, and upper torso 

• Sensation of tiny insects crawling over the skin 

• Mottled or marbled skin usually around the shoulders, upper chest, and abdomen 

accompanied by itching 

• Swelling of the skin, accompanied by tiny scar-like skin depressions (pitting edema) 

Figure 17-10. Signs and symptoms of altitude decompression sickness. 

evolved gas can occur during exposure to low altitude and 

create a serious inflight emergency. 

The recommended waiting time before going to flight 

altitudes of up to 8,000 feet is at least 12 hours after diving 

that does not require controlled ascent (nondecompression 

stop diving), and at least 24 hours after diving that does 

require controlled ascent (decompression stop diving). The 

waiting time before going to flight altitudes above 8,000 

feet should be at least 24 hours after any scuba dive. These 

recommended altitudes are actual flight altitudes above 

mean sea level (MSL) and not pressurized cabin altitudes. 

This takes into consideration the risk of decompression of 

the aircraft during flight. 

Vision in Flight 

Of all the senses, vision is the most important for safe flight. 

Most of the things perceived while flying are visual or heavily 

supplemented by vision. As remarkable and vital as it is, 

vision is subject to limitations, such as illusions and blind 

spots. The more a pilot understands about the eyes and how 

they function, the easier it is to use vision effectively and 

compensate for potential problems. 

The eye functions much like a camera. Its structure includes 

an aperture, a lens, a mechanism for focusing, and a surface 

for registering images. Light enters through the cornea at the 

front of the eyeball, travels through the lens, and falls on the 

retina. The retina contains light sensitive cells that convert 

Figure 17-11. To avoid the bends, scuba divers must not fly for 

specific time periods following dives. 

17-19 
The rods and 

cones (film) of 

the retina are 

the receptors 

which record 

the image and

transmit it 

through the 

optic nerve to

the brain for 

interpretation. 

Rods and 

cones 

Fovea 

(all cones) 

Lens 

Retina 

Optic nerve 

Optic disk 

(blind spot) 

Fovea centralis 

Iris 

The pupil (aperture) is the opening at 

the center of the iris. The size of the 

pupil is adjusted to control the amount 

of light entering the eye. 

PUPIL 

Light passes through the cornea (the 

transparent window on the front of the

eye) and then through the lens to 

focus on the retina. 

CORNEA 

Rod 

concentration 

Figure 17-12. The human eye. 

light energy into electrical impulses that travel through nerves 

to the brain. The brain interprets the electrical signals to form 

images. There are two kinds of light-sensitive cells in the 

eyes: rods and cones. [Figure 17-12] 

The cones are responsible for all color vision, from 

appreciating a glorious sunset to discerning the subtle shades 

in a fine painting. Cones are present throughout the retina, but 

are concentrated toward the center of the field of vision at the 

back of the retina. There is a small pit called the fovea where 

almost all the light sensing cells are cones. This is the area 

where most “looking” occurs (the center of the visual field 

where detail, color sensitivity, and resolution are highest). 

While the cones and their associated nerves are well suited 

to detecting fine detail and color in high light levels, the 

rods are better able to detect movement and provide vision 

in dim light. The rods are unable to discern color but are 

very sensitive at low-light levels. The trouble with rods is 

that a large amount of light overwhelms them, and they take 

longer to “reset” and adapt to the dark again. There are so 

many cones in the fovea that are at the very center of the 

visual field but virtually has no rods at all. So in low light, 

the middle of the visual field is not very sensitive, but farther 

from the fovea, the rods are more numerous and provide the 

major portion of night vision. 

Vision Types 

There are three types of vision: photopic, mesopic, and 

scotopic. Each type functions under different sensory stimuli 

or ambient light conditions. [Figure 17-13] 

Photopic Vision 

Photopic vision provides the capability for seeing color and 

resolving fine detail (20/20 or better), but it functions only 

in good illumination. Photopic vision is experienced during 

daylight or when a high level of artificial illumination exists. 

Types of Vision 

Types of vision used 

Photopic 

Mesopic 

Scotopic 

Light level 

High 

Medium/Low 

Low 

Technique of viewing 

Central 

Both 

Scanning 

Color perception 

Good 

Some 

None 

Receptors used 

Cones 

Cones/Rods 

Rods 

Acuity best 

20/20 

Varies 

20/200 

Blind spot 

Day 

Day/Night 

Day/Night 

Figure 17-13. Types of vision. 

17-20 
The cones concentrated in the fovea centralis of the eye are 

primarily responsible for vision in bright light. [Figure 17-12] 

Because of the high light level, rhodopsin, which is a 

biological pigment of the retina that is responsible for both 

the formation of the photoreceptor cells and the first events 

in the perception of light, is bleached out causing the rod 

cells to become less effective. 

Mesopic Vision 

Mesopic vision is achieved by a combination of rods and 

cones and is experienced at dawn, dusk, and during full 

moonlight. Visual acuity steadily decreases as available light 

decreases and color perception changes because the cones 

become less effective. Mesopic viewing period is considered 

the most dangerous period for viewing. As cone sensitivity 

decreases, pilots should use off-center vision and proper 

scanning techniques to detect objects during low-light levels. 

Scotopic Vision 

Scotopic vision is experienced under low-light levels and 

the cones become ineffective, resulting in poor resolution of 

detail. Visual acuity decreases to 20/200 or less and enables 

a person to see only objects the size of or larger than the 

big “E” on visual acuity testing charts from 20 feet away. 

In other words, a person must stand at 20 feet to see what 

can normally be seen at 200 feet under daylight conditions. 

When using scotopic vision, color perception is lost and a 

night blind spot in the central field of view appears at low 

light levels when the cone-cell sensitivity is lost. 

Central Blind Spot 

The area where the optic nerve connects to the retina in the 

back of each eye is known as the optic disk. There is a total 

absence of cones and rods in this area, and consequently, 

each eye is completely blind in this spot. [Figure 17-14] 

As a result, it is referred to as the blind spot that everyone 

Figure 17-14. Central blind spot. 

Pupil 

Blind spot 

Optic nerve 

Retina 

Center of vision 

LEFT Right

has in each eye. Under normal binocular vision conditions 

(both eyes are used together), this is not a problem because 

an object cannot be in the blind spot of both eyes at the same 

time. On the other hand, where the field of vision of one eye 

is obstructed by an object (windshield divider or another 

aircraft), a visual target could fall in the blind spot of the 

other eye and remain undetected. 

Figure 17-15 provides a dramatic example of the eye’s 

blind spot. 

1.	 Hold this page at an arm’s length. 

2.	 Completely cover your left eye (without closing or 

pressing on it) using your hand or other flat object. 

3.	 With your right eye, stare directly at the airplane on 

the left side of the picture page. In your periphery, you 

will notice the black X on the right side of the picture. 

4.	 Slowly move the page closer to you while continuing 

to stare at the airplane. 

Figure 17-15. The eye’s blind spot. 

17-21 
5.	 When the page is about 16–18 inches from you, the 

black X should disappear completely because it has 

been imaged onto the blind spot of your right eye. 

(Resist the temptation to move your right eye while 

the black X is gone or else it reappears. Keep staring 

at the airplane.) 

6.	 As you continue to look at the airplane, keep moving 

the page closer to you a few more inches, and the black 

X will come back into view. 

7.	 There is an interval where you are able to move the 

page a few inches backward and forward, and the black 

X will be gone. This demonstrates to you the extent 

of your blind spot. 

8.	 You can try the same thing again, except this time with 

your right eye covered stare at the black X with your 

left eye. Move the page in closer and the airplane will 

disappear. 

Another way to check your blind spot is to do a similar test 

outside at night when there is a full moon. Cover your left 

eye, looking at the full moon with your right eye. Gradually 

move your right eye to the left (and maybe slightly up or 

down). Before long, all you will be able to see is the large 

halo around the full moon; the entire moon itself will seem 

to have disappeared. 

Empty-Field Myopia 

Empty-field myopia is a condition that usually occurs when 

flying above the clouds or in a haze layer that provides 

nothing specific to focus on outside the aircraft. This causes 

the eyes to relax and seek a comfortable focal distance that 

may range from 10 to 30 feet. For the pilot, this means 

looking without seeing, which is dangerous. Searching out 

and focusing on distant light sources, no matter how dim, 

helps prevent the onset of empty-field myopia. 

Night Vision 

There are many good reasons to fly at night, but pilots must 

keep in mind that the risks of night flying are different than 

during the day and often times higher. [Figure 17-16] Pilots 

who are cautious and educated on night-flying techniques 

can mitigate those risks and become very comfortable and 

proficient in the task. 

Night Blind Spot 

It is estimated that once fully adapted to darkness, the rods are 

10,000 times more sensitive to light than the cones, making 

them the primary receptors for night vision. Since the cones 

are concentrated near the fovea, the rods are also responsible 

for much of the peripheral vision. The concentration of cones 

in the fovea can make a night blind spot in the center of the 

field of vision. To see an object clearly at night, the pilot must 

Figure 17-16. Night vision. 

expose the rods to the image. This can be done by looking 5° 

to 10° off center of the object to be seen. This can be tried in 

a dim light in a darkened room. When looking directly at the 

light, it dims or disappears altogether. When looking slightly 

off center, it becomes clearer and brighter. 

When looking directly at an object, the image is focused 

mainly on the fovea, where detail is best seen. At night, the 

ability to see an object in the center of the visual field is 

reduced as the cones lose much of their sensitivity and the 

rods become more sensitive. Looking off center can help 

compensate for this night blind spot. Along with the loss of 

Figure 17-17. Night blind spot. 

Cones active 

Rods active 

Night blind spot 

Pilots must look 5°–10° off center of the 

object in order for the object to be seen. 

17-22 
sharpness (acuity) and color at night, depth perception and 

judgment of size may be lost. [Figure 17-17] 

Dark Adaptation 

Dark adaptation is the adjustment of the human eye to a dark 

environment. That adjustment takes longer depending on the 

amount of light in the environment that a person has just left. 

Moving from a bright room into a dark one takes longer than 

moving from a dim room and going into a dark one. 

While the cones adapt rapidly to changes in light intensities, 

the rods take much longer. Walking from bright sunlight into 

a dark movie theater is an example of this dark adaptation 

period experience. The rods can take approximately 30 

minutes to fully adapt to darkness. A bright light, however, 

can completely destroy night adaptation, leaving night 

vision severely compromised while the adaptation process 

is repeated. 

Scanning Techniques 

Scanning techniques are very important in identifying objects 

at night. To scan effectively, pilots must look from right to 

left or left to right. They should begin scanning at the greatest 

distance an object can be perceived (top) and move inward 

toward the position of the aircraft (bottom). For each stop, an 

area approximately 30° wide should be scanned. The duration 

of each stop is based on the degree of detail that is required, 

but no stop should last longer than 2 to 3 seconds. When 

moving from one viewing point to the next, pilots should 

overlap the previous field of view by 10°. [Figure 17-18] 

Off-center viewing is another type of scan that pilots can use 

during night flying. It is a technique that requires an object be 

viewed by looking 10° above, below, or to either side of the 

object. [Figure 17-19] In this manner, the peripheral vision 

can maintain contact with an object. 

With off-center vision, the images of an object viewed longer 

than 2 to 3 seconds will disappear. This occurs because the 

rods reach a photochemical equilibrium that prevents any 

further response until the scene changes. This produces 

a potentially unsafe operating condition. To overcome 

this night vision limitation, pilots must be aware of the 

phenomenon and avoid viewing an object for longer than 2 

or 3 seconds. The peripheral field of vision will continue to 

pick up the object when the eyes are shifted from one offcenter point to another. 

Night Vision Protection 

Several things can be done to help with the dark adaptation 

process and to keep the eyes adapted to darkness. Some of 

the steps pilots and flight crews can take to protect their night 

vision are described in the following paragraphs. 

4 

2 

3 

1 

10° 

Figure 17-18. Scanning techniques. 

17-23 
°

Focal points 

X 

X X X

X 

Once an object is detected in the peripheral field of darkadapted vision, continued surveillance is maintained by 

use of “off-center” vision. Looking 10 right or left and 

above and below the object, viewing no longer than 2 to

3 seconds at each position. 

OBSERVER 

10 degrees 

10 degrees 10 degrees 

10 degrees 

Figure 17-19. Off-center viewing. 

Sunglasses 

If a night flight is scheduled, pilots and crew members should 

wear neutral density (N-15) sunglasses or equivalent filter 

lenses when exposed to bright sunlight. This precaution 

increases the rate of dark adaptation at night and improves 

night visual sensitivity. 

Oxygen Supply 

Unaided night vision depends on optimum function and 

sensitivity of the rods of the retina. Lack of oxygen to the rods 

(hypoxia) significantly reduces their sensitivity. Sharp clear 

vision (with the best being equal to 20–20 vision) requires 

significant oxygen especially at night. Without supplemental 

oxygen, an individual’s night vision declines measurably at 

pressure altitudes above 4,000 feet. As altitude increases, 

the available oxygen decreases, degrading night vision. 

Compounding the problem is fatigue, which minimizes 

physiological well being. Adding fatigue to high altitude 

exposure is a recipe for disaster. In fact, if flying at night at 

an altitude of 12,000 feet, the pilot may actually see elements 

of his or her normal vision missing or not in focus. Missing 

visual elements resemble the missing pixels in a digital image 

while unfocused vision is dim and washed out. 

For the pilot suffering the effects of hypoxic hypoxia, a simple 

descent to a lower altitude may not be sufficient to reestablish 

vision. For example, a climb from 8,000 feet to 12,000 feet for 

30 minutes does not mean a descent to 8,000 feet will rectify 

the problem. Visual acuity may not be regained for over an 

hour. Thus, it is important to remember, altitude and fatigue 

have a profound effect on a pilot’s ability to see. 

High Intensity Lighting 

If, during the flight, any high intensity lighting areas are 

encountered, attempt to turn the aircraft away and fly in the 

periphery of the lighted area. This will not expose the eyes to 

such a large amount of light all at once. If possible, plan your 

route to avoid direct over flight of built-up, brightly lit areas. 

Flightdeck Lighting 

Flightdeck lighting should be kept as low as possible so that 

the light does not monopolize night vision. After reaching 

the desired flight altitude, pilots should allow time to 

adjust to the flight conditions. This includes readjustment 

of instrument lights and orientation to outside references. 

During the adjustment period, night vision should continue 

to improve until optimum night adaptation is achieved. When 

it is necessary to read maps, charts, and checklists, use a dim 

white light flashlight and avoid shining it in your or any other 

crewmember’s eyes. 

Airfield Precautions 

Often time, pilots have no say in how airfield operations are 

handled, but listed below are some precautions that can be 

taken to make night flying safer and help protect night vision. 

•	 Airfield lighting should be reduced to the lowest 

usable intensity. 

•	 Maintenance personnel should practice light discipline 

with headlights and flashlights. 

•	 Position the aircraft at a part of the airfield where the 

least amount of lighting exists. 

17-24 
 

•	 Select approach and departure routes that avoid 

highways and residential areas where illumination 

can impair night vision. 

Self-Imposed Stress 

Night flight can be more fatiguing and stressful than day 

flight, and many self- imposed stressors can limit night vision. 

Pilots can control this type of stress by knowing the factors 

that can cause self-imposed stressors. Some of these factors 

are listed in the following paragraphs. [Figure 17-20] 

Drugs 

Drugs can seriously degrade visual acuity during the day and 

especially at night. Pilots who become ill should consult an 

aviation medical examiner (AME) or flight surgeon as to 

which drugs are appropriate to take while flying. 

Exhaustion 

Pilots who become fatigued during a night flight will not be 

mentally alert and will respond more slowly to situations 

requiring immediate action. Exhausted pilots tend to 

concentrate on one aspect of a situation without considering 

the total requirement. Their performance may become a 

safety hazard depending on the degree of fatigue and instead 

of using proper scanning techniques may get fixated on the 

instruments or stare off rather than multitask. 

Poor Physical Conditioning 

To overcome poor physical conditioning, pilots should 

participate in regular exercise programs. People who are 

physically fit become less fatigued during flight and have 

better night scanning efficiency. However, too much exercise 

in a given day may leave crew members too fatigued for 

night flying. 

Alcohol 

Alcohol is a sedative and its use impairs both coordination 

and judgment. As a result, pilots who are impaired by alcohol 

fail to apply the proper techniques of night vision. They are 

likely to stare at objects and to neglect scanning techniques. 

The amount of alcohol consumed determines the degree to 

which night vision is affected. The effects of alcohol are long 

lasting and the residual effects of alcohol can also impair 

visual scanning efficiency. 

Tobacco 

Of all the self-imposed stressors, cigarette smoking most 

decreases visual sensitivity at night. Smoking significantly 

increases the amount of carbon monoxide carried by the 

hemoglobin in red blood cells. This reduces the blood’s 

capacity to combine with oxygen, so less oxygen is carried 

in the blood. Hypoxia caused by carbon monoxide poisoning 

HYPOGLYCEMIA HYPOGLYCEMIA

HYPOGLYCEMIA HYPOGLYCEMIA

ALCOHOL ALCOHOL ALCOHOL ALCOHOL TOBACCO TOBACCO TOBACCO TOBACCO

POOR PHYSICAL 

POOR PHYSICAL 

POOL PHYSICAL 

CONDITION CONDITION

CONDITION

EXHAUSTION EXHAUSTION EXHAUSTION EXHAUSTION

DRUGS

DRUGS NUTRITIONAL 

DEFICIENCY

NUTRITIONAL 

DEFICIENCY

NUTRITIONAL 

DEFICIENCY

NUTRITIONAL 

DEFICIENCY

Figure 17-20. Self-imposed stress. 

affects peripheral vision and dark adaptation. The results 

are the same as those for hypoxia caused by high altitude. 

Smoking 3 cigarettes in rapid succession or 20 to 30 cigarettes 

within a 24-hour period may saturate from 8 to 10 percent 

of the capacity of hemoglobin. Smokers lose 20 percent of 

their night vision capability at sea level, which is equal to a 

physiological altitude of 5,000 feet. 

Hypoglycemia and Nutritional Deficiency 

Missing or postponing meals can cause low blood sugar, 

which impairs night flight performance. Low blood sugar 

levels may result in stomach contractions, distraction, 

breakdown in habit pattern, and a shortened attention span. 

Likewise, an insufficient consumption of vitamin A may 

also impair night vision. Foods high in vitamin A include 

eggs, butter, cheese, liver, apricots, peaches, carrots, squash, 

spinach, peas, and most types of greens. High quantities of 

vitamin A do not increase night vision but a lack of vitamin 

A certainly impairs it. 

Distance Estimation and Depth Perception 

Knowledge of the mechanisms and cues affecting distance 

estimation and depth perception assist pilots in judging 

distances at night. These cues may be monocular or binocular. 

The monocular cues that aid in distance estimation and depth 

perception include motion parallax, geometric perspective, 

retinal image size, and aerial perspective. 

Motion Parallax 

Motion parallax refers to the apparent motion of stationary 

objects as viewed by an observer moving across the 

landscape. When the pilot or crewmember looks outside the 

aircraft perpendicular to the direction of travel, near objects 

appear to move backward, past, or opposite the path of 

motion; far objects seem to move in the direction of motion 

or remain fixed. The rate of apparent movement depends on 

the distance the observer is from the object. 

17-25 
Geometric Perspective 

An object may appear to have a different shape when viewed 

at varying distances and from different angles. Geometric 

perspective cues include linear perspective, apparent 

foreshortening, and vertical position in the field. 

• Linear perspective—parallel lines, such as runway 

lights, power lines and railroad tracks, tend to 

converge as distance from the observer increases. 

[Figure 17-21A]

• Apparent foreshortening—the true shape of an object 

or a terrain feature appears elliptical when viewed 

from a distance. [Figure 17-21B]

• Vertical position in the field—objects or terrain 

features farther away from the observer appear higher 

on the horizon than those closer to the observer. 

[Figure 17-21C] 

Aerial Perspective 

The clarity of an object and the shadow cast by it are 

perceived by the brain and are cues for estimating distance. 

Subtle variations in color or shade are clearer the closer the 

observer is to an object. However, as distance increases, 

these distinctions may become blurry. The same applies to 

an object detail or texture. As a person gets farther from an 

object, its discrete details become less apparent. Another 

important fact to remember while flying at night is that every 

object casts a shadow from a light source. The direction in 

which the shadow is cast depends on the position of the light 

source. If the shadow of an object is cast toward the observer, 

the object is closer than the light source is to the observer. 

Binocular Cues 

Binocular cues of an object are dependent upon the slightly 

different viewing angle of each eye of an object. Binocular 

perception is useful only when the object is close enough to 

A B 

make an obvious difference in the viewing angle of both eyes. 

In the flight environment, most distances outside the cockpit 

are so great that binocular cues are of little, if any, value. In 

addition, binocular cues operate on a more subconscious 

level than monocular cues and are performed automatically. 

Night Vision Illusions 

There are many different types of visual illusions that 

commonly occur at night. Anticipating and maintaining 

awareness of them is usually the best way to avoid them. 

Autokinesis 

Autokinesis is caused by staring at a single point of light 

against a dark background for more than a few seconds. 

After a few moments, the light appears to move on its own. 

Apparent movement of the light source will begin in about 

8 to 10 seconds. To prevent this illusion, focus the eyes on 

objects at varying distances and avoid fixating on one source 

of light. This illusion can be eliminated or reduced by visual 

scanning, by increasing the number of lights, or by varying 

the light intensity. The most important of the three solutions 

is visual scanning. A light or lights should not be stared at 

for more than 10 seconds. 

False Horizon 

A false horizon can occur when the natural horizon is 

obscured or not readily apparent. It can be generated by 

confusing bright stars and city lights. It can also occur while 

flying toward the shore of an ocean or a large lake. Because 

of the relative darkness of the water, the lights along the 

shoreline can be mistaken for stars in the sky. [Figure 17-22] 

Reversible Perspective Illusion 

At night, an aircraft may appear to be moving away from 

a second aircraft when it is, in fact, approaching a second 

aircraft. This illusion often occurs when an aircraft is flying 

C 

Figure 17-21. Geometric perspective. 

17-26 
Apparent horizon Actual horizon 

Figure 17-22. At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground. 

parallel to another’s course. To determine the direction of 

flight, pilots should observe aircraft lights and their relative 

position to the horizon. If the intensity of the lights increases, 

the aircraft is approaching; if the lights dim, the aircraft is 

moving away. 

Size-Distance Illusion 

This illusion results from viewing a source of light that is 

increasing or decreasing in luminance (brightness). Pilots 

may interpret the light as approaching or retreating. 

Fascination (Fixation) 

This illusion occurs when pilots ignore orientation cues and 

fix their attention on a goal or an object. Student pilots tend to 

have this happen when they are concentrating on the aircraft 

instruments or attempting to land. They become fixated on 

one task and forget to look at what is going on around them. 

At night, this can be especially dangerous because aircraft 

ground-closure rates are difficult to determine, and there may 

be minimal time to correct the situation. 

Flicker Vertigo 

A light flickering at a rate between 4 and 20 cycles per 

second can produce unpleasant and dangerous reactions. Such 

conditions as nausea, vomiting, and vertigo may occur. On 

rare occasions, convulsions and unconsciousness may also 

occur. Proper scanning techniques at night can prevent pilots 

from getting flicker vertigo. 

Night Landing Illusions 

Landing illusions occur in many forms. Above featureless 

terrain at night, there is a natural tendency to fly a lowerthan-normal approach. Elements that cause any type of 

visual obscurities, such as rain, haze, or a dark runway 

environment, can also cause low approaches. Bright lights, 

steep surrounding terrain, and a wide runway can produce the 

illusion of being too low with a tendency to fly a higher-thannormal approach. A set of regularly spaced lights along a road 

or highway can appear to be runway lights. Pilots have even 

mistaken the lights on moving trains as runway or approach 

lights. Bright runway or approach lighting systems can create 

the illusion that the aircraft is closer to the runway, especially 

where few lights illuminate the surrounding terrain. 

Prior to flying at night, it is best to learn and know the 

challenges of the area in which you are flying in. Study the 

area and know how to navigate your way through areas that 

may pose a problem at night. For example, many areas near 

water may be obscured by low lying clouds or fog. To help 

deal with this type of situation, it is important to have a plan 

before you leave the ground. In the daytime, fly the routes 

and passes that you will be flying at night and determine the 

minimum altitude you are willing to use at night. If weather 

prevents you from maintaining the altitude that you planned, 

make a decision early to turn 180° and land at an alternate 

airport with better weather conditions. Always consider 

safer alternatives rather than hope things will work out by 

taking a chance. 

Pilots who fly at night should strongly consider oxygen 

supplementation at altitudes and times not required by the 

FAA, especially at night when critical judgment and hand-eye 

coordination is necessary (e.g., IFR) or if he/she is a smoker 

or not perfectly healthy. 

Enhanced Night Vision Systems 

Synthetic Vision Systems (SVS) and Enhanced Flight Vision 

Systems (EFVS) are two systems that can improve the safety 

of flight at night. The technology of both is evolving rapidly 

and being used more and more. [Figure 17-23] 

17-27 
 

Synthetic vision system Enhanced vision system 

Figure 17-23. Synthetic and enhanced vision systems. 

Synthetic Vision System 

A Synthetic Vision System (SVS) is an electronic means 

to display a synthetic vision image of the external scene 

topography to the flight crew. [Figure 17-24] It is not a 

real-time image like that produced by an EFVS. Unlike 

EFVS, SVS requires a terrain and obstacle database, a 

precise navigation solution, and a display. The terrain 

image is based on the use of data from a Digital Elevation 

Model (DEM) that is stored within the SVS. With SVS, the 

synthetic terrain/vision image is intended to enhance pilot 

awareness of spatial position relative to important features 

in all visibility conditions. This is particularly useful during 

critical phases of flight, such as takeoff, approach, and 

landing, where important features, such as terrain, obstacles, 

runways, and landmarks, may be depicted on the SVS 

display. [Figure 17-25] During approach operations, the 

obvious advantages of SVS are that the digital terrain image 

remains on the pilot’s display regardless of how poor the 

visibility is outside. 

An SVS image can be displayed on either a head-down 

display or head-up display (HUD); however, to date, SVS 

has only been certified on head-down displays. Development 

efforts to display a synthetic image on a HUD are currently 

underway as are efforts that would combine SVS with a realtime sensor image produced by an EFVS. These systems are 

known as Combined Vision Systems. While SVS is currently 

certified as an aid to situation awareness only, the FAA 

and aviation industry are working on defining operational 

concepts and airworthiness criteria that would enable SVS 

to be used for operational credit in certain low visibility 

conditions. Other future enhancements to SVS displays could 

include integrating ADS-B to display traffic information. 

Enhanced Flight Vision System 

Enhanced Vision (EV) or Enhanced Flight Vision System 

(EFVS) is an electronic means to provide a display of 

Figure 17-24. SVS system. Figure 17-25. Night time SVS system. 

17-28 
the external scene by use of an imaging sensor, such as 

a Forward-Looking InfraRed (FLIR) or millimeter wave 

radar (MMWR). In 2004, 14 CFR part 91, section 91.175 

was amended to reflect that operators conducting straightin instrument approach procedures (in other than Category 

II or Category III operations) may now operate below the 

published decision height (DH) or minimum descent altitude 

(MDA) when using an approved EFVS shown on the pilot’s 

HUD. This rule change provides “operational credit” for EV 

equipage. No such credit exists for SV. 

Chapter Summary 

This chapter provides an introduction to aeromedical factors 

relating to flight activities. More detailed information on 

the subjects discussed in this chapter is available in the 

Aeronautical Information Manual (AIM) and online at www. 

faa.gov. 

17-29 
17-30
 
A-1 

Short Field Takeoff Distance at 2,450 Pounds for a Cessna Model 172R 

Performance Data for Cessna 

Model 172R and Challenger 605 

Appendix A 
A-2 

Time, Fuel, and Distance to Climb at 2,450 Pounds for a Cessna Model 172R 
A-3 

Cruise Performance for a Cessna Model 172R 
A-4 

Short Field Landing Distance at 2,450 Pounds for a Cessna Model 172R 
 

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 

4,219 

3,600 

5,840 

4,940 

3,465 

3,401 

SL 

ISA 

6,432 

5,234 

9,400 

7,755 

4,804 

4,535 

5,000 ft 

ISA +20°C 

40,000 

35,000 

50,000 

46,000 

30,000 

2:00 4:00 6:00 8:00 9:50 

Conditions: 26,985 lb BOW, M 0.74 

cruise speed, ISA, zero wind, NBAA 

IFR reserves (200 NM) 

Note: Fuel burn figures provided on 

top of graph are based on 1,000 lb 

payload performance computations. 

Takeoff Field Length (feet) 3,190 6,570 10,230 14,200 18,105 Fuel 

Burn (lb) 

Time (hour) 

Gross 

Takeoff Weight (lb) 

Max 

Payload 

3,000 lb 

Payload 

1,000 lb 

Payload Zero Payload 

Challenger 605 Range/Payload Profile 

Range (NM) 

A-5 
A-6 

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 

500 

1,000 

2,000 

1,500 

2,500 

3,500 

3,000 

4,500 

4,000 

0 

Conditions: 26,985 lb BOW, 1,000 

lb payload, ISA, zero wind, NBAA 

IFR reserves (200 NM) 

M0.80 Cruise Speed 

M0.74 Cruise Speed 

Time (hour) 

Distance (NM) 

771 NM 

3,550 lb 

1,685 NM 

7,570 lb 

730 NM 

3,190 lb 

1,577 NM 

6,570 lb 

2,599 NM 

11,980 lb 

2,424 NM 

10,230 lb 

3,512 NM 

16,820 lb 

3,272 NM 

14,200 lb 

3,700 NM 

18,105 lb 

CHALLENGER 605 TIME AND FUEL VERSUS DISTANCE 

M0.80 Cruise Speed Time 0:00 2:00 4:00 6:00 8:00 8:25 

Distance (NM) 0 771 1,685 2,599 3,512 3,701 

Fuel (lb) 0 3,550 7,570 11,980 16,820 18,105 

M0.74 Cruise Speed Time 0:00 2:00 4:00 6:00 8:00 9:50 

Distance (NM) 0 730 1,577 2,424 3,272 4,045 

Fuel (lb) 0 3,190 6,570 10,230 14,200 18,105 

Conditions: 1,000 lb payload, ISA, zero wind, NBAA IFR reserves (200 NM alternate), 26,985 lb BOW 

Note: All Challenger 605 performance data are for discussion purposes only. By this document, Bombardier Inc., 

does not intend to make, and is not making, any offer, commitment, representation or warranty of any kind whatsoever. 

All data are subject to change without prior notice. 

4,045 NM 

18,105 lb 

Challenger 605 Time and Fuel Versus Distance 
Challenger 605 Time and Fuel Versus Distance 

CHALLENGER 605 SPECIFIC RANGE 

0.160 

0.150 

0.180 

0.170 

0.190 

0.210 

0.200 

0.230 

0.240 

0.220 

Conditions: 40,000 lb mid-cruise weight, zero wind, ISA 

Specific Range (NM/lb)

M 0.74 

Cruise Speed 

M 0.80 Cruise Speed 

M 0.82 Cruise Speed 

FL 390 

FL 370 

FL 350 

FL 330 

FL 310 

420 430 440 450 460 470 480 490
 

Speed (KTAS)
 

Note: All Challenger 605 performance data are for discussion purposes only. By this document, Bombardier Inc., 

does not intend to make, and is not making, any offer, commitment, representation or warranty of any kind whatsoever. 

All data are subject to change without prior notice. 

Plotting of constant FL lines 

Flight Level 

M0.82 M0.80 M0.74 

290 Speed 

Spc Range 

310 Speed 481 469 434 

Spc Range 0.165 0.178 0.199 

330 Speed 477 465 430 

Spc Range 0.174 0.188 0.208 

350 Speed 473 461 427 

Spc Range 0.181 0.197 0.216 

370 Speed 470 459 424 

Spc Range 0.185 0.204 0.222 

390 Speed 459 424 

Spc Range 0.205 0.223 

Plotting of Long Range Cruise and High Speed Cruise lines 

FL290 FL310 FL330 FL350 FL370 FL390 

M0.74 "X" 434 430 427 424 424 

M0.74 "Y" 0.199 0.208 0.216 0.222 0.223 

M0.80 "X" 469 465 461 459 459 

M0.80 "Y" 0.178 0.188 0.197 0.204 0.205 

M0.82 "X" 481 477 473 470 

M0.82 "Y" 0.165 0.174 0.181 0.185 

Note: Based on 40,000 lb mid-cruise weight, ISA Conditions, zero wind 

A-7 
A-8
 
Appendix B
 

Acronyms, Abbreviations, and 

NOTAM Contractions 

This is a list of common acronyms and abbreviations used in the aviation industry as well as NOTAM contractions. For 

a more complete list of contractions used in aviation, see FAA Order JO 7340.2 (as amended). Additional information 

regarding NOTAMs can be found at pilotweb.nas.faa.gov/PilotWeb/. 

A 

A/C—aircraft 

A/FD—airport/facility directory 

A/G—air to ground 

A/HA—altitude/height 

AAF—Army Air Field 

AAI —arrival aircraft interval 

AAP—advanced automation program 

AAR—airport acceptance rate 

ABDIS—Automated Data Interchange System Service B 

ABN—aerodrome beacon 

ABV—above 

ACAIS—air carrier activity information system 

ACAS—aircraft collision avoidance system 

ACC—area control center; Airports Consultants Council 

ACCT—accounting records 

ACCUM—accumulate 

ACD—Automatic Call Distributor 

ACDO—Air Carrier District Office 

ACF—Area Control Facility 

ACFO—Aircraft Certification Field Office 

ACFT—aircraft 

ACID—aircraft identification 

ACI-NA—Airports Council International-North America 

ACIP—airport capital improvement plan 

ACLS—automatic carrier landing system 

ACLT—actual landing time calculated 

ACO—Office of Airports Compliance and Field Operations; 

Aircraft Certification Office 

ACR—air carrier 

ACRP—Airport Cooperative Research Program 

ACS—Airman Certification Standard 

ACT—active, activated, or activity 

ADA—air defense area 

ADAP—Airport Development Aid Program 

ADAS—AWOS data acquisition system 

ADCCP—advanced data communications control procedure 

ADDA—administrative data 

ADF—automatic direction finding 

ADI—automatic de-ice and inhibitor 

ADIN—AUTODIN service 

ADIZ—air defense identification zone 

ADJ—adjacent 

ADL—aeronautical data-link 

ADLY—arrival delay 

ADO—airline dispatch office 

ADP—automated data processing 

ADS—automatic dependent surveillance 

ADSIM —airfield delay simulation model 

ADSY—administrative equipment systems 

ADTN—Administrative Data Transmission Network 

ADTN2000—Administrative Data Transmission Network 

2000 

ADVO—administrative voice 

ADZD—advised 

AEG—Aircraft Evaluation Group 

AERA—automated en route air traffic control 

AEX—automated execution 

AF—airway facilities 

AFB—Air Force Base 

AFIS—automated flight inspection system 

AFP—area flight plan 

AFRES—Air Force Reserve Station 

AFS—airways facilities sector 

AFSFO—AFS field office 

AFSFU—AFS field unit 

AFSOU—AFS field office unit (standard is AFSFOU) 

AFSS—automated flight service station 

AFTN—Automated Fixed Telecommunications Network 

AGIS—airports geographic information system 

AGL—above ground level 

AID—airport information desk 

AIG—Airbus Industries Group 

AIM—Airman’s Information Manual 

AlP—airport improvement plan 

AIRMET—Airmen’s Meteorological Information 

AIRNET—Airport Network Simulation Model 

AIS—aeronautical lnformation service 

AlT—automated information transfer 

ALP—airport layout plan 

B-1 
ALS—approach light system 

ALSFl—ALS with sequenced flashers I 

ALSF2—ALS with sequenced flashers II 

ALSIP—Approach Lighting System Improvement Plan 

ALSTG—altimeter setting 

ALT—altitude 

ALTM—altimeter 

ALTN—alternate 

ALTNLY—alternately 

ALTRV—altitude reservation 

AMASS—airport movement area safety system 

AMCC—ADF/ARTCC Maintenance Control Center 

AMDT—amendment 

AMGR—Airport Manager 

AMOS—Automatic meteorological observing system 

AMP—ARINC Message Processor; Airport Master Plan 

AMVER—automated mutual assistance vessel rescue system 

ANC—alternate network connectivity 

ANCA—Airport Noise and Capacity Act 

ANG—Air National Guard 

ANGB—Air National Guard Base 

ANMS—automated network monitoring system 

ANSI—American National Standards Group 

AOA—air operations area 

AP—airport; acquisition plan 

APCH—approach 

APL—airport lights 

APP—approach; approach control; Approach Control Office 

APS—airport planning standard 

AQAFO—Aeronautical Quality Assurance Field Office 

ARAC—Army Radar Approach Control (AAF); Aviation 

Rulemaking Advisory Committee 

ARCTR—FAA Aeronautical Center or Academy 

ARF—airport reservation function 

ARFF—aircraft rescue and fire fighting 

ARINC—Aeronautical Radio, Inc. 

ARLNO—Airline Office 

ARO—Airport Reservation Office 

ARP—airport reference point 

ARR—arrive; arrival 

ARRA—American Recovery and Reinvestment Act of 2009 

ARSA—airport service radar area 

ARSR—air route surveillance radar 

ARTCC—air route traffic control center 

ARTS—automated radar terminal system 

ASAS—aviation safety analysis system 

ASC—AUTODIN switching center 

ASCP—Aviation System Capacity Plan 

ASD—aircraft situation display 

ASDA—accelerate-stop distance available 

ASLAR—aircraft surge launch and recovery 

ASM—available seat mile 

ASOS—automated surface observing system 

ASP—arrival sequencing program 

ASPH—asphalt 

ASQP—airline service quality performance 

ASR—airport surveillance radar 

ASTA—airport surface traffic automation 

ASV—airline schedule vendor 

AT—air traffic 

ATA—Air Transport Association of America 

ATAS—airspace and traffic advisory service 

ATC—air traffic control 

ATCAA—air traffic control assigned airspace 

ATCBI—air traffic control beacon indicator 

ATCCC—Air Traffic Control Command Center 

ATCO—Air Taxi Commercial Operator 

ATCRB—air traffic control radar beacon 

ATCRBS—air traffic control radar beacon system 

ATCSCC—Air Traffic Control System Command Center 

ATCT—airport traffic control tower 

ATIS—automatic terminal information service 

ATISR—ATIS recorder 

ATM—air traffic management; asynchronous transfer mode 

ATMS—advanced traffic management system 

ATN—Aeronautical Telecommunications Network 

ATODN—AUTODIN terminal (FUS) 

ATOMS—air traffic operations management system 

ATOVN—AUOTVON (facility) 

ATS—air traffic service 

ATSCCP—ATS contingency command post 

AUTH—authority 

AUTOB—automatic weather reporting system 

AUTODIN—DoD Automatic Digital Network 

AUTOVON—DoD Automatic Voice Network 

AVBL—available 

AVN—Aviation Standards National Field Office, Oklahoma 

City 

AVON—AUTOVON service 

AWlS—airport weather information 

AWOS—automatic weather; observing/reporting system 

AWP—Aviation Weather Processor 

AWPG—aviation weather products generator 

AWS—air weather station 

AWY—airway 

AZM—azimuth 

B 

BA FAIR—braking action fair 

BA NIL—braking action nil 

BA POOR—braking action poor 

BANS—BRITE alphanumeric system 

BART—billing analysis reporting tool (GSA software tool) 

BASIC—basic contract observing station 

BASOP—military base operations 

B-2 
C 

BC—back course 

BCA—benefit/cost analysis 

BCN—beacon 

BCR—benefit/cost ratio 

BDAT—digitized beacon data 

BERM—snowbank(s) containing earth/gravel 

BLW—below 

BMP—best management practices 

BND—bound 

BOC—Bell Operating Company 

bps—bits per second 

BRG—bearing 

BRI—basic rate interface 

BRITE—bright radar indicator terminal equipment 

BRL—building restriction line 

BUEC—back-up emergency communications 

BUECE—back-up emergency communications equipment 

BYD—beyond 

C/S/S/N—capacity/safety/security/noise 

CAA—civil aviation authority; Clean Air Act 

CAAS—Class A Airspace 

CAB—civil aeronautics board 

CARF—Central Altitude Reservation Facility 

CASFO—Civil Aviation Security Office 

CAT—category; clear-air turbulence 

CAU—Crypto Ancillary Unit 

CBAS—Class B airspace 

CBI—computer based instruction 

CBSA—Class B surface area 

CC&O—customer cost and obligation 

CCAS—Class C Airspace 

CCC—Communications Command Center 

CCCC—staff communications 

CCCH—central computer complex host 

CCLKWS—counterclockwise 

CCS7-NI—Communication Channel Signal-7-Network 

Interconnect 

CCSA—Class C surface area 

CCSD—Command Communications Service Designator 

CCU—Central Control Unit 

CD—clearance delivery; common digitizer 

CDAS—Class D Airspace 

CDR—cost detail report 

CDSA—Class D surface area 

CDT—controlled departure time 

CDTI—cockpit display of traffic information 

CEAS—Class E Airspace 

CENTX—central telephone exchange 

CEP—capacity enhancement program 

CEQ—council on environmental quality 

CERAP—center radar approach control; combined center 

radar approach control 

CESA—Class E surface area 

CFC—central flow control 

CFCF—Central Flow Control Facility 

CFCS—central flow control service 

CFR—Code of Federal Regulations 

CFWP—central flow weather processor 

CFWU—central flow weather unit 

CGAS—Class G Airspace; Coast Guard Air Station 

CHG—change 

CIG—ceiling 

CK—check 

CL—centerline 

CLC—course line computer 

CLIN—contract line item 

CLKWS—clockwise 

CLR—clearance, clear(s), cleared to 

CLSD—closed 

CLT—calculated landing time 

CM—commercial service airport 

CMB—climb 

CMSND—commissioned 

CNL—cancel 

CNMPS—Canadian Minimum Navigation Performance 

Specification Airspace 

CNS—consolidated NOTAM system 

CNSP—consolidated NOTAM system processor 

CO—central office 

COE—U.S. Army Corps of Engineers 

COM—communications 

COMCO—command communications outlet 

CONC—concrete 

CONUS—Continental United States 

CORP—private corporation other than ARINC or MITRE 

CPD—coupled 

CPE—customer premise equipment 

CPMIS—consolidated personnel management information 

system 

CRA—conflict resolution advisory 

CRDA—converging runway display aid 

CRS—course 

CRT—cathode ray tube 

CSA—communications service authorization 

CSIS—centralized storm information system 

CSO—customer service office 

CSR—communications service request 

CSS—central site system 

CTA—controlled time of arrival; control area 

CTA/FIR—control area/flight information region 

CTAF—common traffic advisory frequency 

CTAS—center-TRACON automation system 

B-3 
 

CTC—contact 

CTL—control 

CTMA—Center Traffic Management Advisor 

CUPS—consolidated uniform payroll system 

CVFR—controlled visual flight rules 

CVTS—compressed video transmission service 

CW—continuous wave 

CWSU—Central Weather Service Unit 

CWY—clearway 

D 

DA—direct access; decision altitude/decision height; 

Descent Advisor 

DABBS—DITCO automated bulletin board system 

DAIR—direct altitude and identity readout 

DALGT—daylight 

DAR—Designated Agency Representative 

DARC—direct access radar channel 

dBA—decibels A-weighted 

DBCRC—Defense Base Closure and Realignment 

Commission 

DBE—disadvantaged business enterprise 

DBMS—database management system 

DBRITE—digital bright radar indicator tower equipment 

DCA—Defense Communications Agency 

DCAA—dual call, automatic answer device 

DCCU—Data Communications Control Unit 

DCE—data communications equipment 

DCMSND—decommissioned 

DCT—direct 

DDA—dedicated digital access 

DDD—direct distance dialing 

DDM—difference in depth of modulation 

DDS—Digital Data Service 

DEA—Drug Enforcement Agency 

DEDS—data entry and display system 

DEGS—degrees 

DEIS—Draft Environmental Impact Statement 

DEP—depart/departure 

DEPPROC—departure procedures 

DEWIZ—distance early warning identification zone 

DF—direction finder 

DFAX—digital facsimile 

DFI—direction finding indicator 

DGPS—Differential Global Positioning Satellite (System) 

DH—decision height 

DID—direct inward dial 

DIP—drop and insert point 

DIRF—direction finding 

DISABLD—disabled 

DIST—distance 

DITCO—Defense Information Technology Contracting 

Office Agency 

DLA—delay or delayed 

DLT—delete 

DLY—daily 

DME—distance measuring equipment 

DME/P—precision distance measuring equipment 

DMN—Data Multiplexing Network 

DMSTN—demonstration 

DNL—day-night equivalent sound level (also called Ldn) 

DOD—direct outward dial 

DoD—Department of Defense 

DOI—Department of Interior 

DOS—Department of State 

DOT—Department of Transportation 

DOTCC—Department of Transportation Computer Center 

DOTS—dynamic ocean tracking system 

DP—dew point temperature 

DRFT—snowbank(s) caused by wind action 

DSCS—digital satellite compression service 

DSPLCD—displaced 

DSUA—dynamic special use airspace 

DTS—dedicated transmission service 

DUAT—direct user access terminal 

DVFR—defense visual flight rules; day visual flight rules 

DVOR—doppler very high frequency omni-directional range 

DYSIM—dynamic simulator 

E 

E—east 

EA—environmental assessment 

EARTS—en route automated radar tracking system 

EB—eastbound 

ECOM—en route communications 

ECVFP—expanded charted visual flight procedures 

EDCT—expedite departure path 

EFC—expect further clearance 

EFIS—electronic flight information systems 

EIAF—expanded inward access features 

EIS—environmental impact statement 

ELEV—elevation 

ELT—emergency locator transmitter 

ELWRT—electrowriter 

EMAS—engineered materials arresting system 

EMPS—en route maintenance processor system 

EMS—environmental management system 

E-MSAW—en route automated minimum safe altitude 

warning 

ENAV—en route navigational aids 

ENG—engine 

ENRT—en route 

ENTR—entire 

EOF—emergency Operating Facility 

EPA—Environmental Protection Agency 

EPS—Engineered Performance Standards 

B-4 
EPSS—enhanced packet switched service 

ERAD—en route broadband radar 

ESEC—en route broadband secondary radar 

ESF—extended superframe format 

ESP—en route spacing program 

ESYS—en route equipment systems 

ETA—estimated time of arrival 

ETE—estimated time en route 

ETG—enhanced target generator 

ETMS—enhanced traffic management system 

ETN—Electronic Telecommunications Network 

EVAS—enhanced vortex advisory system 

EVCS—emergency voice communications system 

EXC—except 

F 

F&E—facility and equipment 

FAA—Federal Aviation Administration 

FAAAC—FAA aeronautical center 

FAACIS—FAA communications information system 

FAATC—FAA technical center 

FAATSAT—FAA telecommunications satellite 

FAC—facility/facilities 

FAF—final approach fix 

FAN—MKR fan marker 

FAP—final approach point 

FAPM—FTS2000 associate program manager 

FAR—Federal Aviation Regulation 

FAST—final approach spacing tool 

FAX—facsimile equipment 

FBO—fixed base operator 

FBS—fall back switch 

FCC—Federal Communications Commission 

FCLT—freeze calculated landing time 

FCOM—FSS radio voice communications 

FCPU—Facility Central Processing Unit 

FDAT—flight data entry and printout (FDEP) and flight 

data service 

FDC—flight data center 

FDE—flight data entry 

FDEP—flight data entry and printout 

FDIO—flight data input/output 

FDIOC—flight data input/output center 

FDIOR—flight data input/output remote 

FDM—frequency division multiplexing 

FDP—flight data processing 

FED—federal 

FEIS—Final Environmental Impact Statement 

FEP—front end processor 

FFAC—from facility 

FI/P—flight inspection permanent 

FI/T—flight inspection temporary 

FIFO—Flight Inspection Field Office 

FIG—flight inspection group 

FINO—Flight Inspection National Field Office 

FIPS—federal information publication standard 

FIR—flight information region 

FIRE—fire station 

FIRMR—Federal Information Resource Management 

Regulation 

FL—flight level 

FLOWSIM—traffic flow planning simulation 

FM—from 

FMA—final monitor aid 

FMF—facility master file 

FMIS—FTS2000 management information system 

FMS—flight management system 

FNA—final approach 

FNMS—FTS2000 network management system 

FOIA—Freedom Of Information Act 

FONSI—finding of no significant impact 

FP—flight plan 

FPM—feet per minute 

FRC—request full route clearance 

FREQ—frequency 

FRH—fly runway heading 

FRI—Friday 

FRZN—frozen 

FSAS—flight service automation system 

FSDO—Flight Standards District Office 

FSDPS—flight service data processing system 

FSEP—facility/service/equipment profile 

FSP—flight strip printer 

FSPD—freeze speed parameter 

FSS—flight service station 

FSSA—flight service station automated service 

FSTS—federal secure telephone service 

FSYS—flight service station equipment systems 

FTS—federal telecommunications system 

FT—feet/foot 

FTS2000—Federal Telecommunications System 2000 

FUS—functional units or systems 

FWCS—flight watch control station 

G 

GA—general aviation 

GAA—general aviation activity 

GAAA—general aviation activity and avionics 

GADO—General Aviation District Office 

GC—ground control 

GCA—ground control approach 

GIS—geographic information system 

GNAS—general national airspace system 

GNSS—global navigation satellite system 

GOES—Geostationary Operational Environmental Satellite 

GOESF—GOES feed point 

B-5 
I 

GOEST—GOES terminal equipment 

GOVT—government 

GP—glide path 

GPRA—Government Performance Results Act 

GPS—global positioning system 

GPWS—ground proximity warning system 

GRADE—graphical airspace design environment 

GRVL—gravel 

GS—glide slope indicator 

GSA—General Services Administration 

GSE—ground support equipment 

H 

H—non-directional radio homing beacon (NDB) 

HAA—height above airport 

HAL—height above landing 

HARS—high altitude route system 

HAT—height above touchdown 

HAZMAT—hazardous materials 

HCAP—high capacity carriers 

HDG—heading 

HDME—NDB with distance measuring equipment 

HDQ—FAA headquarters 

HEL—helicopter 

HELI—heliport 

HF—high frequency 

HH—NDB, 2kw or more 

HI-EFAS—high altitude EFAS 

HIRL—high intensity runway lights 

HIWAS—Hazardous lnflight Weather Advisory Service 

HLDC—high level data link control 

HLDG—holding 

HOL—holiday 

HOV—high occupancy vehicle 

HP—holding pattern 

HR—hour 

HSI—horizontal situation indicators 

HUD—housing and urban development 

HWAS—hazardous in-flight weather advisory 

Hz—Hertz 

I/AFSS—international AFSS 

IA—indirect access 

IAF—initial approach fix 

IAP—instrument approach procedures 

IAPA—instrument approach procedures automation 

IBM—International Business Machines 

IBP—international boundary point 

IBR—intermediate bit rate 

ICAO—International Civil Aviation Organization 

ICSS—international communications switching systems 

ID—identification 

IDAT—interfacility data 

IDENT—identify/identifier/identification 

IF—intermediate fix 

IFCP—interfacility communications processor 

IFDS—interfacility data system 

IFEA—in-flight emergency assistance 

IFO—International Field Office 

IFR—instrument flight rules 

IFSS—international flight service station 

ILS—instrument landing system 

IM—inner marker 

IMC—instrument meteorological conditions 

IN—inch/inches 

INBD—inbound 

INDEFLY—indefinitely 

INFO—information 

INM—integrated noise model 

INOP—inoperative 

INS—inertial navigation system 

INSTR—instrument 

INT—intersection 

INTL—international 

INTST—intensity 

IR—ice on runway(s) 

IRMP—information resources management plan 

ISDN—integrated services digital network 

ISMLS—interim standard microwave landing system 

ITI—interactive terminal interface 

IVRS—interim voice response system 

IW—inside wiring 

K 

Kbps—Kilobits per second 

Khz—Kilohertz 

KT—knots 

KVDT—keyboard video display terminal 

L 

L—left 

LAA—local airport advisory 

LAAS—low altitude alert system 

LABS—leased A B service 

LABSC—LABS GS-200 computer 

LABSR—LABS remote equipment 

LABSW—LABS switch system 

LAHSO—land and hold short operation 

LAN—local area network 

LAT—latitude 

LATA—local access and transport area 

LAWRS—limited aviation weather reporting station 

LB—pound/pounds 

B-6 
LC—local control 

LCF—local control facility 

LCN—local communications network 

LCTD—located 

LDA—localizer-type directional aid; landing directional aid 

LDG—landing 

LDIN—lead-in lights 

LEC—local exchange carrier 

LF—low frequency 

LGT—light or lighting 

LGTD—lighted 

LINCS—leased interfacility NAS C 

LIRL—low intensity runway lights 

LIS—logistics and inventory system 

LLWAS—low level wind shear alert system 

LLZ—localizer 

LM—compass locator at ILS middle marker 

LM/MS—low/medium frequency 

LMM—locator middle marker 

LO—compass locator at ILS outer marker 

LOC—local; locally; location; localizer 

LOCID—location identifier 

LOI—letter of intent 

LOM—compass locator at outer marker 

LONG—longitude 

LPV—lateral precision performance with vertical guidance 

LRCO—limited remote communications outlet 

LRNAV—long range navigation 

LRR—long range radar 

LSR—loose snow on runway(s) 

LT—left turn 

M 

MAA—maximum authorized altitude 

MAG—magnetic 

MAINT—maintain, maintenance 

MALS—medium intensity approach light system 

MALSF—medium intensity approach light system with 

sequenced flashers 

MALSR—medium intensity approach light system with 

runway alignment indicator lights 

MAP—maintenance automation program; military airport 

program; missed approach point; modified access pricing 

MAPT—missed approach point 

Mbps—megabits per second 

MCA—minimum crossing altitude 

MCAS—Marine Corps air station 

MCC—maintenance control center 

MCL—middle compass locater 

MCS—maintenance and control system 

MDA—minimum descent altitude 

MDT—maintenance data terminal 

MEA—minimum en route altitude 

MED—medium 

METI—meteorological information 

MF—middle frequency 

MFJ—modified final judgment 

MFT—meter fix crossing time/slot time 

MHA—minimum holding altitude 

Mhg—Meghertz 

MIA—minimum IFR altitudes 

MIDO—Manufacturing Inspection District Office 

MIN—minute 

MIRL—medium intensity runway lights 

MIS—Meteorological Impact Statement 

MISC—miscellaneous 

MISO—Manufacturing Inspection Satellite Office 

MIT—miles in trail 

MITRE—Mitre Corporation 

MLS—microwave landing system 

MM—middle marker 

MMAC—Mike Monroney Aeronautical Center 

MMC—maintenance monitoring console 

MMS—maintenance monitoring system 

MNM—minimum 

MNPS—minimum navigation performance specification 

MNPSA—minimum navigation performance specifications 

airspace 

MNT—monitor; monitoring; monitored 

MOA—memorandum of agreement; military operations area 

MOC—minimum obstruction clearance 

MOCA—minimum obstruction clearance altitude 

MODE C—altitude-encoded beacon reply; altitude reporting 

mode of secondary radar 

MODE S—mode select beacon system 

MON—Monday 

MOU—memorandum of understanding 

MPO—Metropolitan Planning Organization 

MPS—maintenance processor subsystem or master plan 

supplement 

MRA—minimum reception altitude 

MRC—monthly recurring charge 

MSA—minimum safe altitude; minimum sector altitude 

MSAW—minimum safe altitude warning 

MSG—message 

MSL—mean sea level 

MSN—message switching network 

MTCS—modular terminal communications system 

MTI—moving target indicator 

MU—mu meters 

MUD—mud 

MUNI—municipal 

MUX—multiplexor 

MVA—minimum vectoring altitude 

MVFR—marginal visual flight rules 

B-7 
N 

N—north 

NA—not authorized 

NAAQS—national ambient air quality standards 

NADA—ADIN concentrator 

NADIN—National Airspace Data Interchange Network 

NADSW—NADIN switches 

NAILS—National Airspace Integrated Logistics Support 

NAMS—NADIN IA 

NAPRS—National Airspace Performance Reporting System 

NAS—National Airspace System or Naval Air Station 

NASDC—National Aviation Safety Data 

NASP—National Airspace System Plan 

NASPAC—National Airspace System Performance Analysis 

Capability 

NATCO—National Communications Switching Center 

NAV—navigation 

NAVAID—navigation aid 

NAVMN—navigation monitor and control 

NAWAU—National Aviation Weather Advisory Unit 

NAWPF—National Aviation Weather Processing Facility 

NB—northbound 

NCAR—National Center for Atmospheric Research, 

Boulder, CO 

NCF—National Control Facility 

NCIU—NEXRAD Communications Interface Unit 

NCP—noise compatibility program 

NCS—national communications system 

NDB—non-directional radio beacon 

NDNB—NADIN II 

NE—northeast 

NEM—noise exposure map 

NEPA—National Environmental Policy Act 

NEXRAD—next generation weather radar 

NFAX—National Facsimile Service 

NFDC—National Flight Data Center 

NFIS—NAS Facilities Information System 

NGT—night 

NI—network interface 

NICS—national interfacility communications system 

NM—nautical mile(s) 

NMAC—near mid-air collision 

NMC—National Meteorological Center 

NMCE—network monitoring and control equipment 

NMCS—network monitoring and control system 

NMR—nautical mile radius 

NOAA—National Oceanic and Atmospheric Administration 

NOC—notice of completion 

NONSTD—nonstandard 

NOPT—no procedure turn required 

NOTAM—notice to airmen 

NPDES—National pollutant discharge elimination system 

NPE—non-primary airport entitlement 

NPIAS—national plan of integrated airport systems 

NR—number 

NRC—non-recurring charge 

NRCS—national radio communications systems 

NSAP—National Service Assurance Plan 

NSRCATN—National Strategy to Reduce Congestion on 

America’s Transportation Network 

NSSFC—National Severe Storms Forecast Center 

NSSL—National Severe Storms Laboratory, Norman, OK 

NSWRH—NWS Regional Headquarters 

NTAP—Notices To Airmen Publication 

NTP—National Transportation Policy 

NTSB—National Transportation Safety Board 

NTZ—no transgression zone 

NW—northwest 

NWS—National Weather Service 

NWSR—NWS weather excluding NXRD 

NXRD—advanced weather radar system 

O 

OAG—official airline guide 

OALT—operational acceptable level of traffic 

OAW—off-airway weather station 

OBSC—obscured 

OBST—obstruction 

ODAL—omnidirectional approach lighting system 

ODAPS—oceanic display and processing station 

OEP—operational evolution plan/partnership 

OFA—object free area 

OFDPS—offshore flight data processing system 

OFT—outer fix time 

OFZ—obstacle free zone 

OM—outer marker 

OMB—Office Of Management and Budget 

ONER—Oceanic Navigational Error Report 

OPLT—operational acceptable level of traffic 

OPR—operate 

OPS—operation 

OPSW—operational switch 

OPX—off premises exchange 

ORD—operational readiness demonstration 

ORIG—original 

OTR—oceanic transition route 

OTS—out of service; organized track system 

OVR—over 

P 

PABX—private automated branch exchange 

PAD—packet assembler/disassembler 

PAEW—personnel and equipment working 

PAM—peripheral adapter module 

PAPI—precision approach path indicator 

PAR—precision approach radar; preferential arrival route 

B-8 
 

PARL—parallel 

PAT—pattern 

PATWAS—Pilots Automatic Telephone Weather Answering 

Service 

PAX—passenger 

PBCT—proposed boundary crossing time 

PBRF—pilot briefing 

PBX—private branch exchange 

PCA—positive control airspace 

PCL—pilot controlled lighting 

PCM—pulse code modulation 

PD—Pilot Deviation 

PDAR—preferential arrival and departure route 

PDC—pre-departure clearance; program designator code 

PDN—Public Data Network 

PDR—preferential departure route 

PERM—permanent/permanently 

PFC—passenger facility charge 

PGP—planning grant program 

PIC—principal interexchange carrier 

PIDP—programmable indicator data processor 

PIREP—pilot weather report 

PJE—parachute jumping exercise 

PLA—practice low approach 

PLW—plow/plowed 

PMS—program management system 

PNR—prior notice required 

POLIC—police station 

POP—point of presence 

POT—point of termination 

PPIMS—personal property information management system 

PPR—prior permission required 

PR—primary commercial service airport 

PREV—previous 

PRI—primary rate interface 

PRM—precision runway monitor 

PRN—pseudo random noise 

PROC—procedure 

PROP—propeller 

PSDN—public switched data network 

PSN—packet switched network 

PSR —packed snow on runway(s) 

PSS—packet switched service 

PSTN—public switched telephone network 

PTC—presumed-to-conform 

PTCHY—patchy 

PTN—procedure turn 

PUB—publication 

PUP—principal user processor 

PVC—permanent virtual circuit 

PVD—plan view display 

PVT—private 

R 

RAIL—runway alignment indicator lights 

RAMOS—remote automatic meteorological observing 

system 

RAPCO—radar approach control (USAF) 

RAPCON—radar approach control (FAA) 

RATCC—Radar Air Traffic Control Center 

RATCF—Radar Air Traffic Control Facility (USN) 

RBC—rotating beam ceilometer 

RBDPE—radar beacon data processing equipment 

RBSS—Radar Bomb Scoring Squadron 

RCAG—remote communications air/ground facility 

RCC—Rescue Coordination Center 

RCCC—Regional Communications Control Centers 

RCF—Remote Communication Facility 

RCIU— Remote Control Interface Unit 

RCL— runway centerline; radio communications link 

RCLL—runway centerline light system 

RCLR—RCL repeater 

RCLT—RCL terminal 

RCO—remote communications outlet 

RCU—remote control unit 

RDAT—digitized radar data 

RDP—radar data processing 

RDSIM—runway delay simulation model 

REC—receive/receiver 

REIL—runway end identifier lights 

RELCTD—relocated 

REP—report 

RF—radio frequency 

RL—General Aviation Reliever Airport 

RLLS—runway lead-in lights system 

RMCC—Remote Monitor Control Center 

RMCF—Remote Monitor Control Facility 

RML—radio microwave link 

RMLR—RML repeater 

RMLT—RML terminal 

RMM—remote maintenance monitoring 

RMMS—remote maintenance monitoring system 

RMNDR—remainder 

RMS—remote monitoring subsystem 

RMSC—remote monitoring subsystem concentrator 

RNAV—area navigation 

RNP—required navigation performance 

ROD—record of decision 

ROSA—report of service activity 

ROT—runway occupancy time 

RP—restoration priority 

RPC—restoration priority code 

RPG—radar processing group 

RPLC—replace 

B-9 
RPZ—runway protection zone 

RQRD—required 

RRH—remote reading hygrothermometer 

RRHS—remote reading hydrometer 

RRL—runway remaining lights 

RRWDS—remote radar weather display 

RRWSS—RWDS sensor site 

RSA—runway safety area 

RSAT—runway safety action team 

RSR—en route surveillance radar 

RSS—remote speaking system 

RSVN—reservation 

RT—right turn; remote transmitter 

RT & BTL—radar tracking and beacon tracking level 

RTAD—remote tower alphanumerics display 

RTCA—Radio Technical Commission for Aeronautics 

RTE—route 

RTP—regional transportation plan 

RTR—remote transmitter/receiver 

RTRD—remote tower radar display 

RTS—return to service 

RUF—rough 

RVR—runway visual range 

RVRM—runway visual range midpoint 

RVRR—runway visual range rollout 

RVRT—runway visual range touchdown 

RW—runway 

RWDS—same as RRWDS 

RWP—real-time weather processor 

RWY—runway 

S 

S—south 

S/S—sector suite 

SA—sand, sanded 

SAC—Strategic Air Command 

SAFI—semi-automatic flight inspection 

SALS—short approach lighting system 

SAT—Saturday 

SATCOM—satellite communications 

SAWR—Supplementary Aviation Weather Reporting Station 

SAWRS—Supplementary Aviation Weather Reporting 

System 

SB—southbound 

SBGP—state block grant program 

SCC—System Command Center 

SCVTS—Switched Compressed Video Telecommunications 

Service 

SDF—simplified directional facility; simplified direction 

finding; software defined network 

SDIS—switched digital integrated service 

SDP—service delivery point 

SD-ROB—radar weather report 

SDS—switched data service 

SE—southeast 

SEL—single event level 

SELF—simplified short approach lighting system with 

sequenced flashing lights 

SFAR-38—Special Federal Aviation Regulation 38 

SFL—sequence flashing lights 

SHPO—State Historic Preservation Officer 

SIC—service initiation charge 

SID— standard instrument departure; station identifier 

SIGMET—significant meteorological information 

SIMMOD—airport and airspace simulation model 

SIMUL—simultaneous 

SIP—state implementation plan 

SIR—packed or compacted snow and ice on runway(s) 

SKED—scheduled 

SLR—slush on runway(s) 

SM—statute miles 

SMGC—surface movement guidance and control 

SMPS—sector maintenance processor subsystem 

SMS—safety management system; simulation modeling 

system 

SN—snow 

SNBNK—snowbank(s) caused by plowing 

SNGL—single 

SNR—signal-to-noise ratio, also: S/N 

SOAR—system of airports reporting 

SOC—service oversight center 

SOIR—simultaneous operations on intersecting runways 

SOIWR—simultaneous operations on intersecting wet 

runways 

SPD—speed 

SRAP—sensor receiver and processor 

SSALF—simplified short approach lighting system with 

sequenced flashers 

SSALR—simplified short approach lighting system with 

runway alignment indicator lights 

SSALS—simplified short approach lighting system 

SSB—single side band 

SSR—secondary surveillance radar 

STA—straight-in approach 

STAR—standard terminal arrival route 

STD—standard 

STMUX—statistical data multiplexer 

STOL—short takeoff and landing 

SUN—Sunday 

SURPIC—surface picture 

SVC—service 

SVCA—service A 

SVCB—service B 

SVCC—service C 

B-10 
SVCO—service O
 

SVFB—interphone service F (B)
 

SVFC—interphone service F (C)
 

SVFD—interphone service F (D)
 

SVFO—interphone service F (A)
 

SVFR—special visual flight rules
 

SW—southwest
 

SWEPT—swept or broom/broomed
 

T 

T—temperature 

T1MUX—T1 multiplexer 

TAA—terminal arrival area 

TAAS—terminal advance automation system 

TACAN—tactical air navigation 

TACR—TACAN at VOR, TACAN only 

TAF—terminal area forecast 

TAR—terminal area surveillance radar 

TARS—terminal automated radar service 

TAS—true air speed 

TATCA—terminal air traffic control automation 

TAVT—terminal airspace visualization tool 

TCA—traffic control airport or tower control airport; 

terminal control area 

TCACCIS—Transportation Coordinator Automated 

Command And Control Information System 

TCAS—Traffic Alert and Collision Avoidance System 

TCC—DOT Transportation Computer Center 

TCCC—Tower Control Computer Complex 

TCE—tone control equipment 

TCLT—tentative calculated landing time 

TCO—Telecommunications Certification Officer 

TCOM—Terminal Communications 

TCS—tower communications system 

TDLS—Tower Data-Link Services 

TDMUX—time division data multiplexer 

TDWR—terminal doppler weather radar 

TDZ—touchdown zone 

TDZ LG—touchdown zone lights 

TELCO—telephone company 

TELMS—telecommunications management system 

TEMPO—temporary 

TERPS—terminal instrument procedures 

TFAC—to facility 

TFC—traffic 

TFR—temporary flight restriction 

TGL—touch-and-go landings 

TH—threshold 

THN—thin 

THR—threshold 

THRU—through 

THU—Thursday 

TIL—until 

TIMS—telecommunications information management system 

TIPS—terminal information processing system 

TKOF—takeoff 

TL—taxilane 

TM—traffic management 

TM&O—telecommunications management and operations 

TMA—Traffic Management Advisor 

TMC—Traffic Management Coordinator 

TMC/MC—Traffic Management Coordinator/Military 

Coordinator 

TMCC—terminal information processing system; Traffic 

Management Computer Complex 

TMF—Traffic Management Facility 

TML—television microwave link 

TMLI—television microwave link indicator 

TMLR—television microwave link repeater 

TMLT—television microwave link terminal 

TMP—Traffic Management Processor 

TMPA—traffic management program alert 

TMS—traffic management system 

TMSPS—traffic management specialists 

TMU—traffic management unit 

TNAV—terminal navigational aids 

TODA—takeoff distance available 

TOF—time of flight 

TOFMS—time of flight mass spectrometer 

TOPS—Telecommunications Ordering And Pricing System 

(GSA software tool) 

TORA—take-off run available 

TR—telecommunications request 

TRACAB—terminal radar approach control in tower cab 

TRACON—Terminal Radar Approach Control Facility 

TRAD—terminal radar service 

TRB—Transportation Research Board 

TRML—terminal 

TRNG—training 

TRSN—transition 

TSA—taxiway safety area; Transportation Security 

Administration 

TSEC—terminal secondary radar service 

TSNT—transient 

TSP—telecommunications service priority 

TSR—telecommunications service request 

TSYS—terminal equipment systems 

TTMA—TRACON Traffic Management Advisor 

TTY—teletype 

TUE—Tuesday 

TVOR—terminal VHF omnidirectional range 

TW—taxiway 

TWEB—transcribed weather broadcast 

TWR—tower 

TWY—taxiway 

TY—type (FAACIS) 

B-11 
V 

U 

UAS—unmanned aircraft systems 

UFN—until further notice 

UHF—ultra high frequency 

UNAVBL—unavailable 

UNLGTD—unlighted 

UNMKD—unmarked 

UNMNT—unmonitored 

UNREL—unreliable 

UNUSBL—unusable 

URA—Uniform Relocation Assistance and Real Property 

Acquisition Policies Act of 1970 

USAF—United States Air Force 

USC—United States Code 

USOC—Uniform Service Order Code 

V/PD—Vehicle/pedestrian deviation 

VALE—voluntary airport low emission 

VASI—visual approach slope indicator 

VDME—VOR with distance measuring equipment 

VDP—visual descent point 

VF—voice frequency 

VFR—visual flight rules 

VGSI—visual glide slope indicator 

VHF—very high frequency 

VIA—by way of 

VICE—instead/versus 

VIS—visibility 

VLF—very low frequency 

VMC—visual meteorological conditions 

VNAV—visual navigational aids 

VNTSC—Volpe National Transportation System Center 

VOL—volume 

VON—virtual on-net 

VOR—VHF omnidirectional range 

VOR/DME—VHF omnidirectional range/distance 

measuring equipment 

VORTAC—VOR and TACAN (collocated) 

VOT—VOR Test Facility 

VP/D—vehicle/pedestrian deviation 

VRS—voice recording system 

VSCS—voice switching and control system 

VTA—vertex time of arrival 

VTAC—VOR and TACAN (collocated) 

VTOL—vertical takeoff and landing 

VTS—voice telecommunications system 

W 

W—west 

WAAS—Wide Area Augmentation System 

WAN—wide area network 

WB—westbound 

WC—work center 

WCP—Weather Communications Processor 

WECO—Western Electric Company 

WED—Wednesday 

WEF—with effect from; effective from 

WESCOM—Western Electric Satellite Communications 

WI—within 

WIE—with immediate effect, or effective immediately 

WKDAYS—Monday through Friday 

WKEND—Saturday and Sunday 

WMSC—Weather Message Switching Center 

WMSCR—Weather Message Switching Center Replacement 

WND—wind 

WPT—waypoint 

WSCMO—Weather Service Contract Meteorological 

Observatory 

WSFO—Weather Service Forecast Office 

WSMO—Weather Service Meteorological Observatory 

WSO—Weather Service Office 

WSR—wet snow on runway(s) 

WTHR—weather 

WTR—water on runway(s) 

WX—weather 

B-12 
 

Appendix C
 

Airport Signs 

Type of Sign Action or Purpose Type of Sign Action or Purpose

4 

B 

22 

A 4-22

B 8-APCH

C ILS

26-8 

J 

K 

22 

MIL 

A L G 

Taxiway/Runway Hold Position: 

Holding position for RWY 4-22 on TWY A. 

Runway Approach Hold Position: 

Runway approach holding position for 

RWY 8 on TWY B. 

ILS Critical Area Hold Position: 

Holding position for the ILS critical area 

on TWY C. 

No Entry: 

Identifies paved areas where aircraft entry is 

prohibited. 

Taxiway Location: 

Identifies taxiway on which aircraft is located. 

Runway Location: 

Identifies runway on which aircraft is located. 

Runway Distance Remaining: 

Provides remaining runway length in 1,000­

foot increments. 

Runway/Runway Intersection: 

Identifies intersecting runways or 

holding position for LAHSO operations. 

Runway Exit: 

Defines direction and designation of exit 

taxiway from runway. 

Taxiway Direction: 

Defines direction and designation of 

intersecting taxiway(s). 

Runway Safety Area Boundary: 

Identifies exit boundary of runway 

safety area. 

ILS Critical Area Boundary: 

Identifies exit boundary of ILS critical area. 

Outbound Destination: 

Defines directions to takeoff runway(s). 

Inbound Destination: 

Defines directions to destination for 

arriving aircraft. 

Taxiway Ending Marker: 

Indicates taxiway does not continue. 

Direction Sign Array: 

Identifies location in conjunction with 

multiple intersecting taxiways. 

Airport Signs and Markings 

Figure C-1. Samples and explanations of standard airport signs. 

C-1 
15 

15 15-33

15 

ILS 

15-APCH 

15-APCH 

A1 

A A D 15 

A1 

A2 

A2 

D 

D 

A1 

D 

D 

A

A 

15 

2 2a 

3 

5 

1 

8 

1 

12 

14 

1 

1 

7 

13 11 

1 

1 

1 1 

7 

9 

9 

10 

3 

4 

6 

9 

1 

9 

1 

8 

3a 

3a 

5 

8 

17 

Figure C-2. A sample runway with various possible markings and signs. 

C-2 
18 

15-33 

15-33 

33-15 

15-33 

33-15 

A2 

A 

A2 

18-36 A 

A2 

A

36-18 A 

1 

1 

1 

9 

3 

3 

4 2a 

2a 

6 

6 

6 

9 

1 

15 

16 

4 

4 

2a 

1 

1 

2 

2a 

3 

3a 

4 

5 

6 

7 

8 

Taxiway location sign 

Runway holding position sign at takeoff end 

Runway holding position sign at other than takeoff end 

Runway holding position marking 

Holding position marking for runway approach area 

Elevated runway guard lights 

Surface painted runway hold position sign 

Enhanced centerline marking (located 150' prior to 

runway hold position marking) 

Holding position sign for a runway approach area 

Runway safety area boundary sign (located on the 

backside of holding position sign) 

Taxiway direction sign 

Surface painted destination sign 

Holding position sign for ILS critical area 

Surface painted ILS critical area boundary marking 

ILS critical area boundary sign (located on backside of 

ILS hold sign) 

Blast pad 

Runway holding position sign and marking for Land and 

Hold Short Operations (LAHSO) 

Runway hold position sign for intersecting runways 

Outbound destination sign 

9 

10 

11 

12 

13 

14 

15 

16 

17 

C-3 
Airport Markings 

Type of Marking Action or Purpose

Holding Position: 

Denotes entrance to a runway from a 

taxiway, approach hold position on a 

taxiway, or LAHSO holding position 

on a runway. 

ILS Critical Area Boundary: 

Denotes entrance to an area to be 

protected for an ILS signal. 

Taxiway/Taxiway Holding Position: 

Denotes location on taxiway or apron 

where aircraft hold short of another 

taxiway. 

Non-Movement Area Boundary: 

Delineates movement area under 

control of ATC, from non-movement 

area. 

Surface Painted Holding Position: 

Denotes entrance to a runway from a 

taxiway. 

Enhanced Taxiway Centerline: 

Provides visual cue to help identify 

location of a runway holding position 

on a taxiway. These markings are 

installed 150 feet prior to the holding 

position markings. 

Surface Painted Taxiway Direction: 

Defines designation/direction of 

intersecting taxiway(s). 

Surface Painted Taxiway Location: 

Identifies taxiway on which the 

aircraft is located. 

Taxiway Edge: Solid Double Yellow Lines 

Defines edge of usable, full strength taxiway. Adjoining 

pavement IS NOT intended for use by aircraft. 

4-22 4-22 

T 

B 

Taxi direction Taxi direction 

Type of Marking 

NON-USEABLE

Action or Purpose 

Type of Marking 

Taxiway Edge: Dashed Double Yellow Lines 

Defines taxiway edge where adjoining pavement 

IS USABLE, such as along an apron or ramp. 

Action or Purpose 

NON-USEABLE 

USEABLE USEABLE

Figure C-3. Samples and explanations of standard airport markings. 

C-4 
G-1 

A 

14 CFR. See Title 14 of the Code of Federal Regulations. 

100-hour inspection. An inspection identical in scope to 

an annual inspection. Conducted every 100 hours of flight 

on aircraft of under 12,500 pounds that are used to carry 

passengers for hire. 

Absolute accuracy. The ability to determine present position 

in space independently, and is most often used by pilots. 

Absolute altitude. The actual distance between an aircraft 

and the terrain over which it is flying. 

Absolute pressure. Pressure measured from the reference 

of zero pressure, or a vacuum. 

A.C. Alternating current. 

Acceleration. Force involved in overcoming inertia, and 

which may be defined as a change in velocity per unit of time. 

Acceleration error. A magnetic compass error apparent when 

the aircraft accelerates while flying on an easterly or westerly 

heading, causing the compass card to rotate toward North. 

Accelerate-go distance. The distance required to accelerate 

to V1 with all engines at takeoff power, experience an engine 

failure at V1, and continue the takeoff on the remaining 

engine(s). The runway required includes the distance required 

to climb to 35 feet by which time V2 speed must be attained. 

Accelerate-stop distance. The distance required to accelerate 

to V1 with all engines at takeoff power, experience an engine 

failure at V1, and abort the takeoff and bring the airplane to 

a stop using braking action only (use of thrust reversing is 

not considered). 

Accelerometer. A part of an inertial navigation system 

(INS) that accurately measures the force of acceleration in 

one direction. 

Glossary 

ADC. See air data computer. 

ADF. See automatic direction finder. 

ADI. See attitude director indicator. 

Adiabatic cooling. A process of cooling the air through 

expansion. For example, as air moves up slope it expands with 

the reduction of atmospheric pressure and cools as it expands. 

Adiabatic heating. A process of heating dry air through 

compression. For example, as air moves down a slope it is 

compressed, which results in an increase in temperature. 

Adjustable-pitch propeller. A propeller with blades whose 

pitch can be adjusted on the ground with the engine not 

running, but which cannot be adjusted in flight. Also referred 

to as a ground adjustable propeller. Sometimes also used to 

refer to constant-speed propellers that are adjustable in flight. 

Adjustable stabilizer. A stabilizer that can be adjusted in 

flight to trim the airplane, thereby allowing the airplane to 

fly hands-off at any given airspeed. 

ADM. See aeronautical decision-making. 

ADS-B. See automatic dependent surveillance-broadcast. 

Advection fog. Fog resulting from the movement of warm, 

humid air over a cold surface. 

Adverse yaw. A condition of flight in which the nose of an 

airplane tends to yaw toward the outside of the turn. This is 

caused by the higher induced drag on the outside wing, which 

is also producing more lift. Induced drag is a by-product of 

the lift associated with the outside wing. 

Aerodynamics. The science of the action of air on an object, 

and with the motion of air on other gases. Aerodynamics 

deals with the production of lift by the aircraft, the relative 

wind, and the atmosphere. 
 

Aeronautical chart. A map used in air navigation containing 

all or part of the following: topographic features, hazards and 

obstructions, navigation aids, navigation routes, designated 

airspace, and airports. 

Aeronautical decision-making (ADM). A systematic 

approach to the mental process used by pilots to consistently 

determine the best course of action in response to a given 

set of circumstances. 

Agonic line. An irregular imaginary line across the surface of 

the Earth along which the magnetic and geographic poles are 

in alignment, and along which there is no magnetic variation. 

Ailerons. Primary flight control surfaces mounted on the 

trailing edge of an airplane wing, near the tip. Ailerons control 

roll about the longitudinal axis. 

Aircraft. A device that is used, or intended to be used, for 

flight. 

Aircraft altitude. The actual height above sea level at which 

the aircraft is flying. 

Aircraft approach category. A performance grouping of 

aircraft based on a speed of 1.3 times the stall speed in the 

landing configuration at maximum gross landing weight. 

Air data computer (ADC). An aircraft computer that 

receives and processes pitot pressure, static pressure, and 

temperature to calculate very precise altitude, indicated 

airspeed, true airspeed, and air temperature. 

Airfoil. Any surface, such as a wing, propeller, rudder, or 

even a trim tab, which provides aerodynamic force when it 

interacts with a moving stream of air. 

Air mass. An extensive body of air having fairly uniform 

properties of temperature and moisture. 

AIRMET. Inflight weather advisory issued as an amendment 

to the area forecast, concerning weather phenomena of 

operational interest to all aircraft and that is potentially 

hazardous to aircraft with limited capability due to lack of 

equipment, instrumentation, or pilot qualifications. 

Airplane. An engine-driven, fixed-wing aircraft heavier than 

air that is supported in flight by the dynamic reaction of air 

against its wings. 

Airplane Flight Manual (AFM). A document developed 

by the airplane manufacturer and approved by the Federal 

Aviation Administration (FAA). It is specific to a particular 

make and model airplane by serial number and it contains 

operating procedures and limitations. 

Airplane Owner/Information Manual. A document 

developed by the airplane manufacturer containing general 

information about the make and model of an airplane. The 

airplane owner’s manual is not FAA approved and is not 

specific to a particular serial numbered airplane. This manual 

is not kept current, and therefore cannot be substituted for 

the AFM/POH. 

Airport diagram. The section of an instrument approach 

procedure chart that shows a detailed diagram of the 

airport. This diagram includes surface features and airport 

configuration information. 

Airport/Facility Directory (A/FD). See Chart Supplement 

U.S. 

Airport surface detection equipment (ASDE). Radar 

equipment specifically designed to detect all principal 

features and traffic on the surface of an airport, presenting the 

entire image on the control tower console; used to augment 

visual observation by tower personnel of aircraft and/or 

vehicular movements on runways and taxiways. 

Airport surveillance radar (ASR). Approach control 

radar used to detect and display an aircraft’s position in the 

terminal area. 

Airport surveillance radar approach. An instrument 

approach in which ATC issues instructions for pilot 

compliance based on aircraft position in relation to the final 

approach course and the distance from the end of the runway 

as displayed on the controller’s radar scope. 

Air route surveillance radar (ARSR). Air route traffic 

control center (ARTCC) radar used primarily to detect 

and display an aircraft’s position while en route between 

terminal areas. 

Air route traffic control center (ARTCC). Provides ATC 

service to aircraft operating on IFR flight plans within 

controlled airspace and principally during the en route phase 

of flight. 

Airspeed. Rate of the aircraft’s progress through the air. 

G-2 
 

 

Airspeed indicator. A differential pressure gauge that 

measures the dynamic pressure of the air through which the 

aircraft is flying. Displays the craft’s airspeed, typically in 

knots, to the pilot. 

Air traffic control radar beacon system (ATCRBS). 

Sometimes called secondary surveillance radar (SSR), which 

utilizes a transponder in the aircraft. The ground equipment is 

an interrogating unit, in which the beacon antenna is mounted 

so it rotates with the surveillance antenna. The interrogating 

unit transmits a coded pulse sequence that actuates the aircraft 

transponder. The transponder answers the coded sequence 

by transmitting a preselected coded sequence back to the 

ground equipment, providing a strong return signal and 

positive aircraft identification, as well as other special data. 

Airway. An airway is based on a centerline that extends from 

one navigation aid or intersection to another navigation aid 

(or through several navigation aids or intersections); used 

to establish a known route for en route procedures between 

terminal areas. 

Airworthiness Certificate. A certificate issued by the FAA 

to all aircraft that have been proven to meet the minimum 

standards set down by the Code of Federal Regulations. 

Airworthiness Directive. A regulatory notice sent out by 

the FAA to the registered owner of an aircraft informing 

the owner of a condition that prevents the aircraft from 

continuing to meet its conditions for airworthiness. 

Airworthiness Directives (AD notes) are to be complied with 

within the required time limit, and the fact of compliance, 

the date of compliance, and the method of compliance are 

recorded in the aircraft’s maintenance records. 

Alert area. An area in which there is a high volume of pilot 

training or an unusual type of aeronautical activity. 

Almanac data. Information the global positioning system 

(GPS) receiver can obtain from one satellite which describes 

the approximate orbital positioning of all satellites in the 

constellation. This information is necessary for the GPS 

receiver to know what satellites to look for in the sky at a 

given time. 

ALS. See approach lighting system. 

Alternate airport. An airport designated in an IFR flight 

plan, providing a suitable destination if a landing at the 

intended airport becomes inadvisable. 

Alternate static source valve. A valve in the instrument static 

air system that supplies reference air pressure to the altimeter, 

airspeed indicator, and vertical speed indicator if the normal 

static pickup should become clogged or iced over. 

Altimeter. A flight instrument that indicates altitude by 

sensing pressure changes. 

Altimeter setting. Station pressure (the barometric pressure 

at the location the reading is taken) which has been corrected 

for the height of the station above sea level. 

Altitude engine. A reciprocating aircraft engine having a 

rated takeoff power that is producible from sea level to an 

established higher altitude. 

Ambient pressure. The pressure in the area immediately 

surrounding the aircraft. 

Ambient temperature. The temperature in the area 

immediately surrounding the aircraft. 

AME. See aviation medical examiner. 

Amendment status. The circulation date and revision 

number of an instrument approach procedure, printed above 

the procedure identification. 

Ammeter. An instrument installed in series with an electrical 

load used to measure the amount of current flowing through 

the load. 

Aneroid. The sensitive component in an altimeter or 

barometer that measures the absolute pressure of the air. 

It is a sealed, flat capsule made of thin disks of corrugated 

metal soldered together and evacuated by pumping all of 

the air out of it. 

Aneroid barometer. An instrument that measures the 

absolute pressure of the atmosphere by balancing the weight 

of the air above it against the spring action of the aneroid. 

Angle of attack. The angle of attack is the angle at which 

relative wind meets an airfoil. It is the angle that is formed 

by the chord of the airfoil and the direction of the relative 

wind or between the chord line and the flight path. The 

angle of attack changes during a flight as the pilot changes 

the direction of the aircraft and is related to the amount of 

lift being produced. 

G-3 
 

 

Angle of incidence. The acute angle formed between the 

chord line of an airfoil and the longitudinal axis of the aircraft 

on which it is mounted. 

Anhedral. A downward slant from root to tip of an aircraft’s 

wing or horizontal tail surface. 

Annual inspection. A complete inspection of an aircraft and 

engine, required by the Code of Federal Regulations, to be 

accomplished every 12 calendar months on all certificated 

aircraft. Only an A&P technician holding an Inspection 

Authorization can conduct an annual inspection. 

Anti-ice. Preventing the accumulation of ice on an aircraft 

structure via a system designed for that purpose. 

Antiservo tab. An adjustable tab attached to the trailing edge 

of a stabilator that moves in the same direction as the primary 

control. It is used to make the stabilator less sensitive. 

Approach lighting system (ALS). Provides lights that will 

penetrate the atmosphere far enough from touchdown to 

give directional, distance, and glidepath information for safe 

transition from instrument to visual flight. 

Area chart. Part of the low-altitude en route chart series, 

this chart furnishes terminal data at a larger scale for 

congested areas. 

Area forecast (FA). A report that gives a picture of clouds, 

general weather conditions, and visual meteorological 

conditions (VMC) expected over a large area encompassing 

several states. 

Area navigation (RNAV). Allows a pilot to fly a selected 

course to a predetermined point without the need to overfly 

ground-based navigation facilities, by using waypoints. 

Arm. See moment arm. 

ARSR. See air route surveillance radar. 

ARTCC. See air route traffic control center. 

ASDE. See airport surface detection equipment. 

ASOS. See Automated Surface Observing System. 

Aspect ratio. Span of a wing divided by its average chord. 

ASR. See airport surveillance radar. 

Asymmetric thrust. Also known as P-factor. A tendency for 

an aircraft to yaw to the left due to the descending propeller 

blade on the right producing more thrust than the ascending 

blade on the left. This occurs when the aircraft’s longitudinal 

axis is in a climbing attitude in relation to the relative wind. 

The P-factor would be to the right if the aircraft had a 

counterclockwise rotating propeller. 

ATC. Air Traffic Control. 

ATCRBS. See air traffic control radar beacon system. 

ATIS. See automatic terminal information service. 

Atmospheric propagation delay. A bending of the 

electromagnetic (EM) wave from the satellite that creates 

an error in the GPS system. 

Attitude. A personal motivational predisposition to respond 

to persons, situations, or events in a given manner that can, 

nevertheless, be changed or modified through training as sort 

of a mental shortcut to decision-making. 

Attitude and heading reference system (AHRS). A system 

composed of three-axis sensors that provide heading, attitude, 

and yaw information for aircraft. AHRS are designed to 

replace traditional mechanical gyroscopic flight instruments 

and provide superior reliability and accuracy. 

Attitude director indicator (ADI). An aircraft attitude 

indicator that incorporates flight command bars to provide 

pitch and roll commands. 

Attitude indicator. The foundation for all instrument flight, 

this instrument reflects the airplane’s attitude in relation to 

the horizon. 

Attitude instrument flying. Controlling the aircraft by 

reference to the instruments rather than by outside visual cues. 

Attitude management. The ability to recognize hazardous 

attitudes in oneself and the willingness to modify them as 

necessary through the application of an appropriate antidote 

thought. 

Autokinesis. Nighttime visual illusion that a stationary light 

is moving, which becomes apparent after several seconds of 

staring at the light. 

G-4 
Automated Surface Observing System (ASOS). Weather 

reporting system which provides surface observations every 

minute via digitized voice broadcasts and printed reports. 

Automated Weather Observing System (AWOS). 

Automated weather reporting system consisting of various 

sensors, a processor, a computer-generated voice subsystem, 

and a transmitter to broadcast weather data. 

Automatic dependent surveillance—broadcast (ADS–B). 

A function on an aircraft or vehicle that periodically 

broadcasts its state vector (i.e., horizontal and vertical 

position, horizontal and vertical velocity) and other 

information. 

Automatic direction finder (ADF). Electronic navigation 

equipment that operates in the low- and medium-frequency 

bands. Used in conjunction with the ground-based 

nondirectional beacon (NDB), the instrument displays the 

number of degrees clockwise from the nose of the aircraft 

to the station being received. 

Automatic terminal information service (ATIS). The 

continuous broadcast of recorded non-control information in 

selected terminal areas. Its purpose is to improve controller 

effectiveness and relieve frequency congestion by automating 

repetitive transmission of essential but routine information. 

Autopilot. An automatic flight control system which keeps 

an aircraft in level flight or on a set course. Automatic pilots 

can be directed by the pilot, or they may be coupled to a radio 

navigation signal. 

Aviation medical examiner (AME). A physician with 

training in aviation medicine designated by the Civil 

Aerospace Medical Institute (CAMI). 

Aviation Routine Weather Report (METAR). Observation 

of current surface weather reported in a standard international 

format. 

AWOS. See Automated Weather Observing System. 

Axes of an aircraft. Three imaginary lines that pass through 

an aircraft’s center of gravity. The axes can be considered 

as imaginary axles around which the aircraft rotates. The 

three axes pass through the center of gravity at 90° angles to 

each other. The axis from nose to tail is the longitudinal axis 

(pitch), the axis that passes from wingtip to wingtip is the 

lateral axis (roll), and the axis that passes vertically through 

the center of gravity is the vertical axis (yaw). 

Axial flow compressor. A type of compressor used in a 

turbine engine in which the airflow through the compressor 

is essentially linear. An axial-flow compressor is made up of 

several stages of alternate rotors and stators. The compressor 

ratio is determined by the decrease in area of the succeeding 

stages. 

Azimuth card. A card that may be set, gyroscopically 

controlled, or driven by a remote compass. 

B 

Back course (BC). The reciprocal of the localizer course 

for an ILS. When flying a back-course approach, an aircraft 

approaches the instrument runway from the end at which the 

localizer antennas are installed. 

Balance tab. An auxiliary control mounted on a primary 

control surface, which automatically moves in the direction 

opposite the primary control to provide an aerodynamic 

assist in the movement of the control. 

Baro-aiding. A method of augmenting the GPS integrity 

solution by using a nonsatellite input source. To ensure that 

baro-aiding is available, the current altimeter setting must 

be entered as described in the operating manual. 

Barometric scale. A scale on the dial of an altimeter to which 

the pilot sets the barometric pressure level from which the 

altitude shown by the pointers is measured. 

Basic empty weight (GAMA). Basic empty weight 

includes the standard empty weight plus optional and special 

equipment that has been installed. 

BC. See back course. 

Bernoulli’s Principle. A principle that explains how the 

pressure of a moving fluid varies with its speed of motion. 

An increase in the speed of movement causes a decrease in 

the fluid’s pressure. 

Biplanes. Airplanes with two sets of wings. 

Block altitude. A block of altitudes assigned by ATC to 

allow altitude deviations; for example, “Maintain block 

altitude 9 to 11 thousand.” 

Bypass ratio. The ratio of the mass airflow in pounds per 

second through the fan section of a turbofan engine to the 

mass airflow that passes through the gas generator portion 

of the engine. 

G-5 
C 

Cabin altitude. Cabin pressure in terms of equivalent altitude 

above sea level. 

Cage. The black markings on the ball instrument indicating 

its neutral position. 

Calibrated. The instrument indication compared with a 

standard value to determine the accuracy of the instrument. 

Calibrated orifice. A hole of specific diameter used to delay 

the pressure change in the case of a vertical speed indicator. 

Calibrated airspeed. The speed at which the aircraft 

is moving through the air, found by correcting IAS for 

instrument and position errors. 

Camber. The camber of an airfoil is the characteristic curve 

of its upper and lower surfaces. The upper camber is more 

pronounced, while the lower camber is comparatively flat. 

This causes the velocity of the airflow immediately above the 

wing to be much higher than that below the wing. 

Canard. A horizontal surface mounted ahead of the main 

wing to provide longitudinal stability and control. It may 

be a fixed, movable, or variable geometry surface, with or 

without control surfaces. 

Canard configuration. A configuration in which the span 

of the forward wings is substantially less than that of the 

main wing. 

Cantilever. A wing designed to carry loads without external 

struts. 

CAS. Calibrated airspeed. 

CDI. Course deviation indicator. 

Ceiling. The height above the earth’s surface of the lowest 

layer of clouds, which is reported as broken or overcast, or 

the vertical visibility into an obscuration. 

Center of gravity (CG). The point at which an airplane 

would balance if it were possible to suspend it at that point. 

It is the mass center of the airplane, or the theoretical point 

at which the entire weight of the airplane is assumed to 

be concentrated. It may be expressed in inches from the 

reference datum, or in percentage of mean aerodynamic 

chord (MAC). The location depends on the distribution of 

weight in the airplane. 

Center of gravity limits. The specified forward and aft 

points within which the CG must be located during flight. 

These limits are indicated on pertinent airplane specifications. 

Center of gravity range. The distance between the forward 

and aft CG limits indicated on pertinent airplane specifications. 

Center of pressure. A point along the wing chord line where 

lift is considered to be concentrated. For this reason, the center 

of pressure is commonly referred to as the center of lift. 

Centrifugal flow compressor. An impeller-shaped device 

that receives air at its center and slings the air outward at high 

velocity into a diffuser for increased pressure. Also referred 

to as a radial outflow compressor. 

Centrifugal force. An outward force that opposes centripetal 

force, resulting from the effect of inertia during a turn. 

Centripetal force. A center-seeking force directed inward 

toward the center of rotation created by the horizontal 

component of lift in turning flight. 

CG. See center of gravity. 

Changeover point (COP). A point along the route or 

airway segment between two adjacent navigation facilities 

or waypoints where changeover in navigation guidance 

should occur. 

Chart Supplement U.S. (formerly Airport/Facility 

Directory). An FAA publication containing information on 

all airports, communications, and NAVAIDs. 

Checklist. A tool that is used as a human factors aid in 

aviation safety. It is a systematic and sequential list of all 

operations that must be performed to properly accomplish 

a task. 

Chord line. An imaginary straight line drawn through an 

airfoil from the leading edge to the trailing edge. 

Circling approach. A maneuver initiated by the pilot to 

align the aircraft with a runway for landing when a straightin landing from an instrument approach is not possible or is 

not desirable. 

G-6 
 

Class A airspace. Airspace from 18,000 feet MSL up to and 

including FL 600, including the airspace overlying the waters 

within 12 NM of the coast of the 48 contiguous states and 

Alaska; and designated international airspace beyond 12 NM 

of the coast of the 48 contiguous states and Alaska within areas 

of domestic radio navigational signal or ATC radar coverage, 

and within which domestic procedures are applied. 

Class B airspace. Airspace from the surface to 10,000 feet 

MSL surrounding the nation’s busiest airports in terms of 

IFR operations or passenger numbers. The configuration of 

each Class B airspace is individually tailored and consists 

of a surface area and two or more layers, and is designed to 

contain all published instrument procedures once an aircraft 

enters the airspace. For all aircraft, an ATC clearance is 

required to operate in the area, and aircraft so cleared receive 

separation services within the airspace. 

Class C airspace. Airspace from the surface to 4,000 feet 

above the airport elevation (charted in MSL) surrounding 

those airports having an operational control tower, serviced 

by radar approach control, and having a certain number of IFR 

operations or passenger numbers. Although the configuration 

of each Class C airspace area is individually tailored, the 

airspace usually consists of a 5 NM radius core surface area 

that extends from the surface up to 4,000 feet above the airport 

elevation, and a 10 NM radius shelf area that extends from 

1,200 feet to 4,000 feet above the airport elevation. 

Class D airspace. Airspace from the surface to 2,500 feet 

above the airport elevation (charted in MSL) surrounding 

those airports that have an operational control tower. The 

configuration of each Class D airspace area is individually 

tailored, and when instrument procedures are published, the 

airspace is normally designed to contain the procedures. 

Class E airspace. Airspace that is not Class A, Class B, Class 

C, or Class D, and is controlled airspace. 

Class G airspace. Airspace that is uncontrolled, except 

when associated with a temporary control tower, and has 

not been designated as Class A, Class B, Class C, Class D, 

or Class E airspace. 

Clean configuration. A configuration in which all flight 

control surfaces have been placed to create minimum drag. 

In most aircraft this means flaps and gear retracted. 

Clearance. ATC permission for an aircraft to proceed under 

specified traffic conditions within controlled airspace, for 

the purpose of providing separation between known aircraft. 

Clearance delivery. Control tower position responsible for 

transmitting departure clearances to IFR flights. 

Clearance limit. The fix, point, or location to which an 

aircraft is cleared when issued an air traffic clearance. 

Clearance on request. An IFR clearance not yet received 

after filing a flight plan. 

Clearance void time. Used by ATC, the time at which the 

departure clearance is automatically canceled if takeoff has 

not been made. The pilot must obtain a new clearance or 

cancel the IFR flight plan if not off by the specified time. 

Clear ice. Glossy, clear, or translucent ice formed by the 

relatively slow freezing of large, supercooled water droplets. 

Coefficient of lift (CL). The ratio between lift pressure and 

dynamic pressure. 

Cold front. The boundary between two air masses where 

cold air is replacing warm air. 

Compass course. A true course corrected for variation and 

deviation errors. 

Compass locator. A low-power, low- or medium-frequency 

(L/MF) radio beacon installed at the site of the outer or middle 

marker of an ILS. 

Compass rose. A small circle graduated in 360° increments, 

to show direction expressed in degrees. 

Complex aircraft. An aircraft with retractable landing gear, 

flaps, and a controllable-pitch propeller. 

Compressor pressure ratio. The ratio of compressor 

discharge pressure to compressor inlet pressure. 

Compressor stall. In gas turbine engines, a condition in 

an axial-flow compressor in which one or more stages of 

rotor blades fail to pass air smoothly to the succeeding 

stages. A stall condition is caused by a pressure ratio that is 

incompatible with the engine rpm. Compressor stall will be 

indicated by a rise in exhaust temperature or rpm fluctuation, 

and if allowed to continue, may result in flameout and 

physical damage to the engine. 

Computer navigation fix. A point used to define a 

navigation track for an airborne computer system such as 

GPS or FMS. 

G-7 
 

 

Concentric rings. Dashed-line circles depicted in the plan 

view of IAP charts, outside of the reference circle, that show 

en route and feeder facilities. 

Condensation. A change of state of water from a gas (water 

vapor) to a liquid. 

Condensation nuclei. Small particles of solid matter in the 

air on which water vapor condenses. 

Cone of confusion. A cone-shaped volume of airspace 

directly above a VOR station where no signal is received, 

causing the CDI to fluctuate. 

Configuration. This is a general term, which normally refers 

to the position of the landing gear and flaps. 

Constant-speed propeller. A controllable-pitch propeller 

whose pitch is automatically varied in flight by a governor 

to maintain a constant rpm in spite of varying air loads. 

Continuous flow oxygen system. System that supplies 

a constant supply of pure oxygen to a rebreather bag that 

dilutes the pure oxygen with exhaled gases and thus supplies a 

healthy mix of oxygen and ambient air to the mask. Primarily 

used in passenger cabins of commercial airliners. 

Control and performance. A method of attitude instrument 

flying in which one instrument is used for making attitude 

changes, and the other instruments are used to monitor the 

progress of the change. 

Control display unit. A display interfaced with the master 

computer, providing the pilot with a single control point 

for all navigations systems, thereby reducing the number of 

required flight deck panels. 

Controllability. A measure of the response of an aircraft 

relative to the pilot’s flight control inputs. 

Controllable-pitch propeller (CPP). A type of propeller 

with blades that can be rotated around their long axis to 

change their pitch. If the pitch can be set to negative values, 

the reversible propeller can also create reverse thrust for 

braking or reversing without the need of changing the 

direction of shaft revolutions. 

Controlled airspace. An airspace of defined dimensions 

within which ATC service is provided to IFR and VFR flights 

in accordance with the airspace classification. It includes 

Class A, Class B, Class C, Class D, and Class E airspace. 

Control pressures. The amount of physical exertion on the 

control column necessary to achieve the desired attitude. 

Convective weather. Unstable, rising air found in 

cumiliform clouds. 

Convective SIGMET. Weather advisory concerning 

convective weather significant to the safety of all aircraft, 

including thunderstorms, hail, and tornadoes. 

Conventional landing gear. Landing gear employing a third 

rear-mounted wheel. These airplanes are also sometimes 

referred to as tailwheel airplanes. 

Coordinated flight. Flight with a minimum disturbance of 

the forces maintaining equilibrium, established via effective 

control use. 

COP. See changeover point. 

Coriolis illusion. The illusion of rotation or movement in an 

entirely different axis, caused by an abrupt head movement, 

while in a prolonged constant-rate turn that has ceased to 

stimulate the brain’s motion sensing system. 

Coupled ailerons and rudder. Rudder and ailerons are 

connected with interconnected springs in order to counteract 

adverse yaw. Can be overridden if it becomes necessary to 

slip the aircraft. 

Course. The intended direction of flight in the horizontal 

plane measured in degrees from north. 

Cowl flaps. Shutter-like devices arranged around certain 

air-cooled engine cowlings, which may be opened or closed 

to regulate the flow of air around the engine. 

Crew resource management (CRM). The application of 

team management concepts in the flight deck environment. 

It was initially known as cockpit resource management, 

but as CRM programs evolved to include cabin crews, 

maintenance personnel, and others, the phrase “crew 

resource management” was adopted. This includes single 

pilots, as in most general aviation aircraft. Pilots of small 

aircraft, as well as crews of larger aircraft, must make 

effective use of all available resources; human resources, 

hardware, and information. A current definition includes 

all groups routinely working with the flight crew who 

are involved in decisions required to operate a flight 

safely. These groups include, but are not limited to pilots, 

dispatchers, cabin crewmembers, maintenance personnel, 

and air traffic controllers. CRM is one way of addressing 

the challenge of optimizing the human/machine interface 

and accompanying interpersonal activities. 

G-8 
 

 

Critical altitude. The maximum altitude under standard 

atmospheric conditions at which a turbocharged engine can 

produce its rated horsepower. 

Critical angle of attack. The angle of attack at which a 

wing stalls regardless of airspeed, flight attitude, or weight. 

Critical areas. Areas where disturbances to the ILS localizer 

and glideslope courses may occur when surface vehicles or 

aircraft operate near the localizer or glideslope antennas. 

CRM. See crew resource management. 

Cross-check. The first fundamental skill of instrument flight, 

also known as “scan,” the continuous and logical observation 

of instruments for attitude and performance information. 

Cruise clearance. An ATC clearance issued to allow a 

pilot to conduct flight at any altitude from the minimum 

IFR altitude up to and including the altitude specified in the 

clearance. Also authorizes a pilot to proceed to and make an 

approach at the destination airport. 

Current induction. An electrical current being induced into, 

or generated in, any conductor that is crossed by lines of flux 

from any magnet. 

D 

DA. See decision altitude. 

Datum (Reference Datum). An imaginary vertical plane 

or line from which all measurements of arm are taken. The 

datum is established by the manufacturer. Once the datum 

has been selected, all moment arms and the location of CG 

range are measured from this point. 

D.C. Direct current. 

Dark adaptation. Physical and chemical adjustments of the 

eye that make vision possible in relative darkness. 

Dead reckoning. Navigation of an airplane solely by means 

of computations based on airspeed, course, heading, wind 

direction and speed, groundspeed, and elapsed time. 

Deceleration error. A magnetic compass error that occurs 

when the aircraft decelerates while flying on an easterly 

or westerly heading, causing the compass card to rotate 

toward South. 

Decision altitude (DA). A specified altitude in the precision 

approach, charted in feet MSL, at which a missed approach 

must be initiated if the required visual reference to continue 

the approach has not been established. 

Decision height (DH). A specified altitude in the precision 

approach, charted in height above threshold elevation, 

at which a decision must be made either to continue the 

approach or to execute a missed approach. 

Deice. The act of removing ice accumulation from an 

aircraft structure. 

Delta. A Greek letter expressed by the symbol Δ to indicate 

a change of values. As an example, ΔCG indicates a change 

(or movement) of the CG. 

Density altitude. Pressure altitude corrected for nonstandard 

temperature. Density altitude is used in computing the 

performance of an aircraft and its engines. 

Departure procedure (DP). Preplanned IFR ATC departure, 

published for pilot use, in textual and graphic format. 

Deposition. The direct transformation of a gas to a solid 

state, in which the liquid state is bypassed. Some sources use 

sublimation to describe this process instead of deposition. 

Detonation. The sudden release of heat energy from fuel in 

an aircraft engine caused by the fuel-air mixture reaching 

its critical pressure and temperature. Detonation occurs as 

a violent explosion rather than a smooth burning process. 

Deviation. A magnetic compass error caused by local 

magnetic fields within the aircraft. Deviation error is different 

on each heading. 

Dew. Moisture that has condensed from water vapor. Usually 

found on cooler objects near the ground, such as grass, as 

the near-surface layer of air cools faster than the layers of 

air above it. 

Dewpoint. The temperature at which air reaches a state where 

it can hold no more water. 

DGPS. Differential global positioning system. 

DH. See decision height. 

G-9 
 

Differential ailerons. Control surface rigged such that the 

aileron moving up moves a greater distance than the aileron 

moving down. The up aileron produces extra parasite drag 

to compensate for the additional induced drag caused by 

the down aileron. This balancing of the drag forces helps 

minimize adverse yaw. 

Differential Global Positioning System (DGPS). A system 

that improves the accuracy of Global Navigation Satellite 

Systems (GNSS) by measuring changes in variables to 

provide satellite positioning corrections. 

Differential pressure. A difference between two pressures. 

The measurement of airspeed is an example of the use of 

differential pressure. 

Dihedral. The positive acute angle between the lateral 

axis of an airplane and a line through the center of a wing 

or horizontal stabilizer. Dihedral contributes to the lateral 

stability of an airplane. 

Diluter-demand oxygen system. An oxygen system that 

delivers oxygen mixed or diluted with air in order to maintain 

a constant oxygen partial pressure as the altitude changes. 

Direct indication. The true and instantaneous reflection of 

aircraft pitch-and-bank attitude by the miniature aircraft, 

relative to the horizon bar of the attitude indicator. 

Direct User Access Terminal System (DUATS). A system 

that provides current FAA weather and flight plan filing 

services to certified civil pilots, via personal computer, 

modem, or telephone access to the system. Pilots can request 

specific types of weather briefings and other pertinent data 

for planned flights. 

Directional stability. Stability about the vertical axis of an 

aircraft, whereby an aircraft tends to return, on its own, to 

flight aligned with the relative wind when disturbed from that 

equilibrium state. The vertical tail is the primary contributor 

to directional stability, causing an airplane in flight to align 

with the relative wind. 

Distance circle. See reference circle. 

Distance measuring equipment (DME). A pulse-type 

electronic navigation system that shows the pilot, by an 

instrument-panel indication, the number of nautical miles 

between the aircraft and a ground station or waypoint. 

DME. See distance measuring equipment. 

DME arc. A flight track that is a constant distance from the 

station or waypoint. 

DOD. Department of Defense. 

Doghouse. A turn-and-slip indicator dial mark in the shape 

of a doghouse. 

Domestic Reduced Vertical Separation Minimum 

(DRVSM). Additional flight levels between FL 290 and FL 

410 to provide operational, traffic, and airspace efficiency. 

Double gimbal. A type of mount used for the gyro in an 

attitude instrument. The axes of the two gimbals are at right 

angles to the spin axis of the gyro, allowing free motion in 

two planes around the gyro. 

DP. See departure procedure. 

Drag. The net aerodynamic force parallel to the relative 

wind, usually the sum of two components: induced drag 

and parasite drag. 

Drag curve. The curve created when plotting induced drag 

and parasite drag. 

Drift angle. Angle between heading and track. 

DRVSM. See Domestic Reduced Vertical Separation 

Minimum. 

DUATS. See direct user access terminal system. 

Duplex. Transmitting on one frequency and receiving on a 

separate frequency. 

Dutch roll. A combination of rolling and yawing oscillations 

that normally occurs when the dihedral effects of an aircraft 

are more powerful than the directional stability. Usually 

dynamically stable but objectionable in an airplane because 

of the oscillatory nature. 

Dynamic hydroplaning. A condition that exists when 

landing on a surface with standing water deeper than the 

tread depth of the tires. When the brakes are applied, there is 

a possibility that the brake will lock up and the tire will ride 

on the surface of the water, much like a water ski. When the 

tires are hydroplaning, directional control and braking action 

are virtually impossible. An effective anti-skid system can 

minimize the effects of hydroplaning. 

G-10 
 

 

Dynamic stability. The property of an aircraft that causes 

it, when disturbed from straight-and-level flight, to develop 

forces or moments that restore the original condition of 

straight and level. 

E 

Eddy currents. Current induced in a metal cup or disc when 

it is crossed by lines of flux from a moving magnet. 

Eddy current damping. The decreased amplitude of 

oscillations by the interaction of magnetic fields. In the case 

of a vertical card magnetic compass, flux from the oscillating 

permanent magnet produces eddy currents in a damping disk 

or cup. The magnetic flux produced by the eddy currents 

opposes the flux from the permanent magnet and decreases 

the oscillations. 

EFC. See expect-further-clearance. 

EFD. See electronic flight display. 

EGT. See exhaust gas temperature. 

Electronic flight display (EFD). For the purpose of 

standardization, any flight instrument display that uses LCD or 

other image-producing system (cathode ray tube (CRT), etc.) 

Elevator. The horizontal, movable primary control surface in 

the tail section, or empennage, of an airplane. The elevator is 

hinged to the trailing edge of the fixed horizontal stabilizer. 

Elevator illusion. The sensation of being in a climb or 

descent, caused by the kind of abrupt vertical accelerations 

that result from up- or downdrafts. 

Emergency. A distress or urgent condition. 

Empennage. The section of the airplane that consists of the 

vertical stabilizer, the horizontal stabilizer, and the associated 

control surfaces. 

Emphasis error. The result of giving too much attention 

to a particular instrument during the cross-check, instead of 

relying on a combination of instruments necessary for attitude 

and performance information. 

Empty-field myopia. Induced nearsightedness that is 

associated with flying at night, in instrument meteorological 

conditions and/or reduced visibility. With nothing to focus 

on, the eyes automatically focus on a point just slightly ahead 

of the airplane. 

EM wave. Electromagnetic wave. 

Encoding altimeter. A special type of pressure altimeter 

used to send a signal to the air traffic controller on the ground, 

showing the pressure altitude the aircraft is flying. 

Engine pressure ratio (EPR). The ratio of turbine discharge 

pressure divided by compressor inlet pressure, which is used 

as an indication of the amount of thrust being developed by 

a turbine engine. 

En route facilities ring. Depicted in the plan view of IAP 

charts, a circle which designates NAVAIDs, fixes, and 

intersections that are part of the en route low altitude airway 

structure. 

En route high-altitude charts. Aeronautical charts for en 

route instrument navigation at or above 18,000 feet MSL. 

En route low-altitude charts. Aeronautical charts for en 

route IFR navigation below 18,000 feet MSL. 

EPR. See engine pressure ratio. 

Equilibrium. A condition that exists within a body when the 

sum of the moments of all of the forces acting on the body 

is equal to zero. In aerodynamics, equilibrium is when all 

opposing forces acting on an aircraft are balanced (steady, 

unaccelerated flight conditions). 

Equivalent airspeed. Airspeed equivalent to CAS in standard 

atmosphere at sea level. As the airspeed and pressure altitude 

increase, the CAS becomes higher than it should be, and a 

correction for compression must be subtracted from the CAS. 

Evaporation. The transformation of a liquid to a gaseous 

state, such as the change of water to water vapor. 

Exhaust gas temperature (EGT). The temperature of the 

exhaust gases as they leave the cylinders of a reciprocating 

engine or the turbine section of a turbine engine. 

Expect-further-clearance (EFC). The time a pilot can 

expect to receive clearance beyond a clearance limit. 

Explosive decompression. A change in cabin pressure faster 

than the lungs can decompress. Lung damage is possible. 

F 

FA. See area forecast. 

FAA. Federal Aviation Administration. 

FAF. See final approach fix. 

G-11 
False horizon. Inaccurate visual information for aligning the 

aircraft, caused by various natural and geometric formations 

that disorient the pilot from the actual horizon. 

FDI. See flight director indicator. 

Federal airways. Class E airspace areas that extend upward 

from 1,200 feet to, but not including, 18,000 feet MSL, unless 

otherwise specified. 

Feeder facilities. Used by ATC to direct aircraft to 

intervening fixes between the en route structure and the 

initial approach fix. 

Final approach. Part of an instrument approach procedure in 

which alignment and descent for landing are accomplished. 

Final approach fix (FAF). The fix from which the IFR 

final approach to an airport is executed, and which identifies 

the beginning of the final approach segment. An FAF is 

designated on government charts by a Maltese cross symbol 

for nonprecision approaches, and a lightning bolt symbol for 

precision approaches. 

Fixating. Staring at a single instrument, thereby interrupting 

the cross-check process. 

Fixed-pitch propellers. Propellers with fixed blade angles. 

Fixed-pitch propellers are designed as climb propellers, 

cruise propellers, or standard propellers. 

Fixed slot. A fixed, nozzle shaped opening near the leading 

edge of a wing that ducts air onto the top surface of the wing. 

Its purpose is to increase lift at higher angles of attack. 

FL. See flight level. 

Flameout. A condition in the operation of a gas turbine 

engine in which the fire in the engine goes out due to either 

too much or too little fuel sprayed into the combustors. 

Flaps. Hinged portion of the trailing edge between the 

ailerons and fuselage. In some aircraft ailerons and flaps are 

interconnected to produce full-span “flaperons.” In either 

case, flaps change the lift and drag on the wing. 

Floor load limit. The maximum weight the floor can sustain 

per square inch/foot as provided by the manufacturer. 

Flight configurations. Adjusting the aircraft control surfaces 

(including flaps and landing gear) in a manner that will 

achieve a specified attitude. 

Flight director indicator (FDI). One of the major 

components of a flight director system, it provides steering 

commands that the pilot (or the autopilot, if coupled) follows. 

Flight level (FL). A measure of altitude (in hundreds of feet) 

used by aircraft flying above 18,000 feet with the altimeter 

set at 29.92 "Hg. 

Flight management system (FMS). Provides pilot and crew 

with highly accurate and automatic long-range navigation 

capability, blending available inputs from long- and shortrange sensors. 

Flight path. The line, course, or track along which an aircraft 

is flying or is intended to be flown. 

Flight patterns. Basic maneuvers, flown by reference to the 

instruments rather than outside visual cues, for the purpose 

of practicing basic attitude flying. The patterns simulate 

maneuvers encountered on instrument flights such as holding 

patterns, procedure turns, and approaches. 

Flight strips. Paper strips containing instrument flight 

information, used by ATC when processing flight plans. 

FMS. See flight management system. 

FOD. See foreign object damage. 

Fog. Cloud consisting of numerous minute water droplets 

and based at the surface; droplets are small enough to be 

suspended in the earth’s atmosphere indefinitely. (Unlike 

drizzle, it does not fall to the surface. Fog differs from a 

cloud only in that a cloud is not based at the surface, and 

is distinguished from haze by its wetness and gray color.) 

Force (F). The energy applied to an object that attempts to 

cause the object to change its direction, speed, or motion. 

In aerodynamics, it is expressed as F, T (thrust), L (lift), W 

(weight), or D (drag), usually in pounds. 

Foreign object damage (FOD). Damage to a gas turbine 

engine caused by some object being sucked into the engine 

while it is running. Debris from runways or taxiways can 

cause foreign object damage during ground operations, and 

the ingestion of ice and birds can cause FOD in flight. 

Form drag. The drag created because of the shape of a 

component or the aircraft. 

G-12 
 

Frise-type aileron. Aileron having the nose portion 

projecting ahead of the hinge line. When the trailing edge 

of the aileron moves up, the nose projects below the wing’s 

lower surface and produces some parasite drag, decreasing 

the amount of adverse yaw. 

Front. The boundary between two different air masses. 

Frost. Ice crystal deposits formed by sublimation when 

temperature and dewpoint are below freezing. 

Fuel load. The expendable part of the load of the airplane. 

It includes only usable fuel, not fuel required to fill the lines 

or that which remains trapped in the tank sumps. 

Fundamental skills. Pilot skills of instrument cross-check, 

instrument interpretation, and aircraft control. 

Fuselage. The section of the airplane that consists of the 

cabin and/or cockpit, containing seats for the occupants and 

the controls for the airplane. 

G 

GAMA. General Aviation Manufacturers Association. 

Gimbal ring. A type of support that allows an object, such 

as a gyroscope, to remain in an upright condition when its 

base is tilted. 

Glideslope (GS). Part of the ILS that projects a radio beam 

upward at an angle of approximately 3° from the approach 

end of an instrument runway. The glideslope provides 

vertical guidance to aircraft on the final approach course for 

the aircraft to follow when making an ILS approach along 

the localizer path. 

Glideslope intercept altitude. The minimum altitude of an 

intermediate approach segment prescribed for a precision 

approach that ensures obstacle clearance. 

Global landing system (GLS). An instrument approach with 

lateral and vertical guidance with integrity limits (similar to 

barometric vertical navigation (BARO VNAV). 

Global navigation satellite system (GNSS). Satellite 

navigation system that provides autonomous geospatial 

positioning with global coverage. It allows small electronic 

receivers to determine their location (longitude, latitude, and 

altitude) to within a few meters using time signals transmitted 

along a line of sight by radio from satellites. 

Global positioning system (GPS). Navigation system 

that uses satellite rather than ground-based transmitters for 

location information. 

GLS. See global landing system. 

GNSS. See global navigation satellite system. 

Goniometer. As used in radio frequency (RF) antenna 

systems, a direction-sensing device consisting of two fixed 

loops of wire oriented 90° from each other, which separately 

sense received signal strength and send those signals to two 

rotors (also oriented 90°) in the sealed direction-indicating 

instrument. The rotors are attached to the direction-indicating 

needle of the instrument and rotated by a small motor until 

minimum magnetic field is sensed near the rotors. 

GPS. See global positioning system. 

GPS Approach Overlay Program. An authorization for 

pilots to use GPS avionics under IFR for flying designated 

existing nonprecision instrument approach procedures, with 

the exception of LOC, LDA, and SDF procedures. 

GPWS. See ground proximity warning system. 

Graveyard spiral. The illusion of the cessation of a turn while 

still in a prolonged, coordinated, constant rate turn, which 

can lead a disoriented pilot to a loss of control of the aircraft. 

Great circle route. The shortest distance across the surface 

of a sphere (the Earth) between two points on the surface. 

Ground adjustable trim tab. Non-movable metal trim tab 

on a control surface. Bent in one direction or another while 

on the ground to apply trim forces to the control surface. 

Ground effect. The condition of slightly increased air pressure 

below an airplane wing or helicopter rotor system that increases 

the amount of lift produced. It exists within approximately one 

wing span or one rotor diameter from the ground. It results 

from a reduction in upwash, downwash, and wingtip vortices, 

and provides a corresponding decrease in induced drag. 

Ground proximity warning system (GPWS). A system 

designed to determine an aircraft’s clearance above the Earth 

and provides limited predictability about aircraft position 

relative to rising terrain. 

G-13 
 

Groundspeed. Speed over the ground, either closing speed to 

the station or waypoint, or speed over the ground in whatever 

direction the aircraft is going at the moment, depending upon 

the navigation system used. 

GS. See glideslope. 

GWPS. See ground proximity warning system. 

Gyroscopic precession. An inherent quality of rotating bodies, 

which causes an applied force to be manifested 90° in the 

direction of rotation from the point where the force is applied. 

H 

HAA. See height above airport. 

HAL. See height above landing. 

HAT. See height above touchdown elevation. 

Hazardous attitudes. Five aeronautical decision-making 

attitudes that may contribute to poor pilot judgment: antiauthority, impulsivity, invulnerability, machismo, and 

resignation. 

Hazardous Inflight Weather Advisory Service (HIWAS). 

An en route FSS service providing continuously updated 

automated of hazardous weather within 150 nautical miles of 

selected VORs, available only in the conterminous 48 states. 

Head-up display (HUD). A special type of flight viewing 

screen that allows the pilot to watch the flight instruments 

and other data while looking through the windshield of the 

aircraft for other traffic, the approach lights, or the runway. 

Heading. The direction in which the nose of the aircraft is 

pointing during flight. 

Heading indicator. An instrument which senses airplane 

movement and displays heading based on a 360° azimuth, 

with the final zero omitted. The heading indicator, also called 

a directional gyro (DG), is fundamentally a mechanical 

instrument designed to facilitate the use of the magnetic 

compass. The heading indicator is not affected by the forces 

that make the magnetic compass difficult to interpret. 

Headwork. Required to accomplish a conscious, rational 

thought process when making decisions. Good decisionmaking involves risk identification and assessment, 

information processing, and problem solving. 

Height above airport (HAA). The height of the MDA above 

the published airport elevation. 

Height above landing (HAL). The height above a designated 

helicopter landing area used for helicopter instrument 

approach procedures. 

Height above touchdown elevation (HAT). The DA/DH or 

MDA above the highest runway elevation in the touchdown 

zone (first 3,000 feet of the runway). 

HF. High frequency. 

Hg. Abbreviation for mercury, from the Latin hydrargyrum. 

High performance aircraft. An aircraft with an engine of 

more than 200 horsepower. 

Histotoxic hypoxia. The inability of cells to effectively use 

oxygen. Plenty of oxygen is being transported to the cells 

that need it, but they are unable to use it. 

HIWAS. See Hazardous Inflight Weather Advisory Service. 

Holding. A predetermined maneuver that keeps aircraft 

within a specified airspace while awaiting further clearance 

from ATC. 

Holding pattern. A racetrack pattern, involving two turns 

and two legs, used to keep an aircraft within a prescribed 

airspace with respect to a geographic fix. A standard pattern 

uses right turns; nonstandard patterns use left turns. 

Homing. Flying the aircraft on any heading required to keep 

the needle pointing to the 0° relative bearing position. 

Horizontal situation indicator (HSI). A flight navigation 

instrument that combines the heading indicator with a CDI, 

in order to provide the pilot with better situational awareness 

of location with respect to the courseline. 

Horsepower. The term, originated by inventor James Watt, 

means the amount of work a horse could do in one second. 

One horsepower equals 550 foot-pounds per second, or 

33,000 foot-pounds per minute. 

Hot start. In gas turbine engines, a start which occurs with 

normal engine rotation, but exhaust temperature exceeds 

prescribed limits. This is usually caused by an excessively 

rich mixture in the combustor. The fuel to the engine must 

be terminated immediately to prevent engine damage. 

HSI. See horizontal situation indicator. 

HUD. See head-up display. 

G-14 
 

 

 

I 

Human factors. A multidisciplinary field encompassing the 

behavioral and social sciences, engineering, and physiology, 

to consider the variables that influence individual and 

crew performance for the purpose of optimizing human 

performance and reducing errors. 

Hung start. In gas turbine engines, a condition of normal 

light off but with rpm remaining at some low value rather than 

increasing to the normal idle rpm. This is often the result of 

insufficient power to the engine from the starter. In the event 

of a hung start, the engine should be shut down. 

Hydroplaning. A condition that exists when landing on a 

surface with standing water deeper than the tread depth of 

the tires. When the brakes are applied, there is a possibility 

that the brake will lock up and the tire will ride on the 

surface of the water, much like a water ski. When the tires 

are hydroplaning, directional control and braking action 

are virtually impossible. An effective anti-skid system can 

minimize the effects of hydroplaning. 

Hypemic hypoxia. A type of hypoxia that is a result of 

oxygen deficiency in the blood, rather than a lack of inhaled 

oxygen. It can be caused by a variety of factors. Hypemic 

means “not enough blood.” 

Hyperventilation. Occurs when an individual is experiencing 

emotional stress, fright, or pain, and the breathing rate and 

depth increase, although the carbon dioxide level in the 

blood is already at a reduced level. The result is an excessive 

loss of carbon dioxide from the body, which can lead to 

unconsciousness due to the respiratory system’s overriding 

mechanism to regain control of breathing. 

Hypoxia. A state of oxygen deficiency in the body sufficient 

to impair functions of the brain and other organs. 

Hypoxic hypoxia. This type of hypoxia is a result of 

insufficient oxygen available to the lungs. A decrease of 

oxygen molecules at sufficient pressure can lead to hypoxic 

hypoxia. 

IAF. See initial approach fix. 

IAP. See instrument approach procedures. 

IAS. See indicated airspeed. 

ICAO. See International Civil Aviation Organization. 

Ident. Air Traffic Control request for a pilot to push 

the button on the transponder to identify return on the 

controller’s scope. 

IFR. See instrument flight rules. 

ILS. See instrument landing system. 

ILS categories. Categories of instrument approach 

procedures allowed at airports equipped with the following 

types of instrument landing systems: 

ILS Category I: Provides for approach to a height 

above touchdown of not less than 200 feet, and with 

runway visual range of not less than 1,800 feet. 

ILS Category II: Provides for approach to a height 

above touchdown of not less than 100 feet and with 

runway visual range of not less than 1,200 feet. 

ILS Category IIIA: Provides for approach without 

a decision height minimum and with runway visual 

range of not less than 700 feet. 

ILS Category IIIB: Provides for approach without 

a decision height minimum and with runway visual 

range of not less than 150 feet. 

ILS Category IIIC: Provides for approach without a 

decision height minimum and without runway visual 

range minimum. 

IMC. See instrument meteorological conditions. 

Inclinometer. An instrument consisting of a curved glass 

tube, housing a glass ball, and damped with a fluid similar 

to kerosene. It may be used to indicate inclination, as a level, 

or, as used in the turn indicators, to show the relationship 

between gravity and centrifugal force in a turn. 

Indicated airspeed (IAS). Shown on the dial of the 

instrument airspeed indicator on an aircraft. Indicated 

airspeed (IAS) is the airspeed indicator reading uncorrected 

for instrument, position, and other errors. Indicated airspeed 

means the speed of an aircraft as shown on its pitot static 

airspeed indicator calibrated to reflect standard atmosphere 

adiabatic compressible flow at sea level uncorrected for 

airspeed system errors. Calibrated airspeed (CAS) is IAS 

corrected for instrument errors, position error (due to 

incorrect pressure at the static port) and installation errors. 

Indicated altitude. The altitude read directly from the 

altimeter (uncorrected) when it is set to the current altimeter 

setting. 

G-15 
 

 

 

Indirect indication. A reflection of aircraft pitch-and-bank 

attitude by instruments other than the attitude indicator. 

Induced drag. Drag caused by the same factors that produce 

lift; its amount varies inversely with airspeed. As airspeed 

decreases, the angle of attack must increase, in turn increasing 

induced drag. 

Induction icing. A type of ice in the induction system that 

reduces the amount of air available for combustion. The most 

commonly found induction icing is carburetor icing. 

Inertial navigation system (INS). A computer-based 

navigation system that tracks the movement of an aircraft 

via signals produced by onboard accelerometers. The initial 

location of the aircraft is entered into the computer, and all 

subsequent movement of the aircraft is sensed and used to 

keep the position updated. An INS does not require any inputs 

from outside signals. 

Initial approach fix (IAF). The fix depicted on IAP charts 

where the instrument approach procedure (IAP) begins unless 

otherwise authorized by ATC. 

Inoperative components. Higher minimums are prescribed 

when the specified visual aids are not functioning; this 

information is listed in the Inoperative Components Table 

found in the United States Terminal Procedures Publications. 

INS. See inertial navigation system. 

Instantaneous vertical speed indicator (IVSI). Assists in 

interpretation by instantaneously indicating the rate of climb 

or descent at a given moment with little or no lag as displayed 

in a vertical speed indicator (VSI). 

Instrument approach procedures (IAP). A series of 

predetermined maneuvers for the orderly transfer of an 

aircraft under IFR from the beginning of the initial approach 

to a landing or to a point from which a landing may be 

made visually. 

Instrument flight rules (IFR). Rules and regulations 

established by the Federal Aviation Administration to govern 

flight under conditions in which flight by outside visual 

reference is not safe. IFR flight depends upon flying by 

reference to instruments in the flight deck, and navigation is 

accomplished by reference to electronic signals. 

Instrument landing system (ILS). An electronic system 

that provides both horizontal and vertical guidance to a 

specific runway, used to execute a precision instrument 

approach procedure. 

Instrument meteorological conditions (IMC). 

Meteorological conditions expressed in terms of visibility, 

distance from clouds, and ceiling less than the minimums 

specified for visual meteorological conditions, requiring 

operations to be conducted under IFR. 

Instrument takeoff. Using the instruments rather than 

outside visual cues to maintain runway heading and execute 

a safe takeoff. 

Intercooler. A device used to reduce the temperatures of the 

compressed air before it enters the fuel metering device. The 

resulting cooler air has a higher density, which permits the 

engine to be operated with a higher power setting. 

Interference drag. Drag generated by the collision of 

airstreams creating eddy currents, turbulence, or restrictions 

to smooth flow. 

International Civil Aviation Organization (ICAO). The 

United Nations agency for developing the principles and 

techniques of international air navigation, and fostering 

planning and development of international civil air transport. 

International standard atmosphere (IAS). A model of 

standard variation of pressure and temperature. 

Interpolation. The estimation of an intermediate value 

of a quantity that falls between marked values in a series. 

Example: In a measurement of length, with a rule that is 

marked in eighths of an inch, the value falls between 3/8 

inch and 1/2 inch. The estimated (interpolated) value might 

then be said to be 7/16 inch. 

Inversion. An increase in temperature with altitude. 

Inversion illusion. The feeling that the aircraft is tumbling 

backwards, caused by an abrupt change from climb to straightand-level flight while in situations lacking visual reference. 

Inverter. A solid-state electronic device that converts D.C. 

into A.C. current of the proper voltage and frequency to 

operate A.C. gyro instruments. 

Isobars. Lines which connect points of equal barometric 

pressure. 

Isogonic lines. Lines drawn across aeronautical charts to 

connect points having the same magnetic variation. 

IVSI. See instantaneous vertical speed indicator. 

G-16 
 

 

L 

J 

Jet route. A route designated to serve flight operations from 

18,000 feet MSL up to and including FL 450. 

Jet stream. A high-velocity narrow stream of winds, usually 

found near the upper limit of the troposphere, which flows 

generally from west to east. 

Judgment. The mental process of recognizing and analyzing 

all pertinent information in a particular situation, a rational 

evaluation of alternative actions in response to it, and a timely 

decision on which action to take. 

K 

KIAS. Knots indicated airspeed. 

Knot. The knot is a unit of speed equal to one nautical mile 

(1.852 km) per hour, approximately 1.151 mph. 

Kollsman window. A barometric scale window of a 

sensitive altimeter used to adjust the altitude for the 

altimeter setting. 

LAAS. See local area augmentation system. 

Lag. The delay that occurs before an instrument needle attains 

a stable indication. 

Land breeze. A coastal breeze flowing from land to sea 

caused by temperature differences when the sea surface is 

warmer than the adjacent land. The land breeze usually occurs 

at night and alternates with the sea breeze that blows in the 

opposite direction by day. 

Land as soon as possible. Land without delay at the nearest 

suitable area, such as an open field, at which a safe approach 

and landing is assured. 

Land as soon as practical. The landing site and duration of 

flight are at the discretion of the pilot. Extended flight beyond 

the nearest approved landing area is not recommended. 

Land immediately. The urgency of the landing is paramount. 

The primary consideration is to ensure the survival of the 

occupants. Landing in trees, water, or other unsafe areas 

should be considered only as a last resort. 

Lateral axis. An imaginary line passing through the center 

of gravity of an airplane and extending across the airplane 

from wingtip to wingtip. 

Lateral stability (rolling). The stability about the 

longitudinal axis of an aircraft. Rolling stability or the ability 

of an airplane to return to level flight due to a disturbance 

that causes one of the wings to drop. 

Latitude. Measurement north or south of the equator in 

degrees, minutes, and seconds. Lines of latitude are also 

referred to as parallels. 

LDA. See localizer-type directional aid. 

Lead radial. The radial at which the turn from the DME arc 

to the inbound course is started. 

Leading edge. The part of an airfoil that meets the airflow first. 

Leading edge devices. High lift devices which are found 

on the leading edge of the airfoil. The most common types 

are fixed slots, movable slats, and leading edge flaps. 

Leading-edge flap. A portion of the leading edge of an 

airplane wing that folds downward to increase the camber, 

lift, and drag of the wing. The leading-edge flaps are 

extended for takeoffs and landings to increase the amount 

of aerodynamic lift that is produced at any given airspeed. 

Leans, the. A physical sensation caused by an abrupt correction 

of a banked attitude entered too slowly to stimulate the motion 

sensing system in the inner ear. The abrupt correction can 

create the illusion of banking in the opposite direction. 

Licensed empty weight. The empty weight that consists 

of the airframe, engine(s), unusable fuel, and undrainable 

oil plus standard and optional equipment as specified in the 

equipment list. Some manufacturers used this term prior to 

GAMA standardization. 

Lift. A component of the total aerodynamic force on an airfoil 

and acts perpendicular to the relative wind. 

Limit load factor. Amount of stress, or load factor, that an 

aircraft can withstand before structural damage or failure 

occurs. 

Lines of flux. Invisible lines of magnetic force passing 

between the poles of a magnet. 

L/MF. See low or medium frequency. 

LMM. See locator middle marker. 

G-17 
Load factor. The ratio of a specified load to the total weight 

of the aircraft. The specified load is expressed in terms of 

any of the following: aerodynamic forces, inertial forces, or 

ground or water reactions. 

Loadmeter. A type of ammeter installed between the generator 

output and the main bus in an aircraft electrical system. 

LOC. See localizer. 

Local area augmentation system (LAAS). A differential 

global positioning system (DGPS) that improves the accuracy 

of the system by determining position error from the GPS 

satellites, then transmitting the error, or corrective factors, 

to the airborne GPS receiver. 

Localizer (LOC). The portion of an ILS that gives left/right 

guidance information down the centerline of the instrument 

runway for final approach. 

Localizer-type directional aid (LDA). A NAVAID used 

for nonprecision instrument approaches with utility and 

accuracy comparable to a localizer but which is not a part 

of a complete ILS and is not aligned with the runway. Some 

LDAs are equipped with a glideslope. 

Locator middle marker (LMM). Nondirectional radio 

beacon (NDB) compass locator, collocated with a middle 

marker (MM). 

Locator outer marker (LOM). NDB compass locator, 

collocated with an outer marker (OM). 

LOM. See locator outer marker. 

Longitude. Measurement east or west of the Prime Meridian 

in degrees, minutes, and seconds. The Prime Meridian is 0° 

longitude and runs through Greenwich, England. Lines of 

longitude are also referred to as meridians. 

Longitudinal axis. An imaginary line through an aircraft 

from nose to tail, passing through its center of gravity. The 

longitudinal axis is also called the roll axis of the aircraft. 

Movement of the ailerons rotates an airplane about its 

longitudinal axis. 

Longitudinal stability (pitching). Stability about the lateral 

axis. A desirable characteristic of an airplane whereby it tends 

to return to its trimmed angle of attack after displacement. 

Low or medium frequency. A frequency range between 

190 and 535 kHz with the medium frequency above 300 

kHz. Generally associated with nondirectional beacons 

transmitting a continuous carrier with either a 400 or 1,020 

Hz modulation. 

Lubber line. The reference line used in a magnetic compass 

or heading indicator. 

M 

MAA. See maximum authorized altitude. 

MAC. See mean aerodynamic chord. 

Mach number. The ratio of the true airspeed of the aircraft 

to the speed of sound in the same atmospheric conditions, 

named in honor of Ernst Mach, late 19th century physicist. 

Mach meter. The instrument that displays the ratio of the 

speed of sound to the true airspeed an aircraft is flying. 

Magnetic bearing (MB). The direction to or from a radio 

transmitting station measured relative to magnetic north. 

Magnetic compass. A device for determining direction 

measured from magnetic north. 

Magnetic dip. A vertical attraction between a compass 

needle and the magnetic poles. The closer the aircraft is to a 

pole, the more severe the effect. 

Magnetic heading (MH). The direction an aircraft is pointed 

with respect to magnetic north. 

Magneto. A self-contained, engine-driven unit that supplies 

electrical current to the spark plugs; completely independent 

of the airplane’s electrical system. Normally there are two 

magnetos per engine. 

Magnus effect. Lifting force produced when a rotating 

cylinder produces a pressure differential. This is the same 

effect that makes a baseball curve or a golf ball slice. 

Mandatory altitude. An altitude depicted on an instrument 

approach chart with the altitude value both underscored and 

overscored. Aircraft are required to maintain altitude at the 

depicted value. 

Mandatory block altitude. An altitude depicted on an 

instrument approach chart with two underscored and 

overscored altitude values between which aircraft are 

required to maintain altitude. 

G-18 
 

Maneuverability. Ability of an aircraft to change directions 

along a flight path and withstand the stresses imposed upon it. 

Maneuvering speed (VA). The design maneuvering speed. 

Operating at or below design maneuvering speed does not 

provide structural protection against multiple full control 

inputs in one axis or full control inputs in more than one 

axis at the same time. 

Manifold absolute pressure. The absolute pressure of the 

fuel/air mixture within the intake manifold, usually indicated 

in inches of mercury. 

MAP. See missed approach point. 

Margin identification. The top and bottom areas on an 

instrument approach chart that depict information about 

the procedure, including airport location and procedure 

identification. 

Marker beacon. A low-powered transmitter that directs its 

signal upward in a small, fan-shaped pattern. Used along the 

flight path when approaching an airport for landing, marker 

beacons indicate both aurally and visually when the aircraft 

is directly over the facility. 

Mass. The amount of matter in a body. 

Maximum altitude. An altitude depicted on an instrument 

approach chart with overscored altitude value at which or 

below aircraft are required to maintain altitude. 

Maximum authorized altitude (MAA). A published altitude 

representing the maximum usable altitude or flight level for 

an airspace structure or route segment. 

Maximum landing weight. The greatest weight that an 

airplane normally is allowed to have at landing. 

Maximum ramp weight. The total weight of a loaded aircraft, 

including all fuel. It is greater than the takeoff weight due to the 

fuel that will be burned during the taxi and runup operations. 

Ramp weight may also be referred to as taxi weight. 

Maximum takeoff weight. The maximum allowable weight 

for takeoff. 

Maximum weight. The maximum authorized weight of 

the aircraft and all of its equipment as specified in the Type 

Certificate Data Sheets (TCDS) for the aircraft. 

Maximum zero fuel weight (GAMA). The maximum 

weight, exclusive of usable fuel. 

MB. See magnetic bearing. 

MCA. See minimum crossing altitude. 

MDA. See minimum descent altitude. 

MEA. See minimum en route altitude. 

Mean aerodynamic chord (MAC). The average distance 

from the leading edge to the trailing edge of the wing. 

Mean sea level. The average height of the surface of the 

sea at a particular location for all stages of the tide over a 

19-year period. 

MEL. See minimum equipment list. 

Meridians. Lines of longitude. 

Mesophere. A layer of the atmosphere directly above the 

stratosphere. 

METAR. See Aviation Routine Weather Report. 

MFD. See multi-function display. 

MH. See magnetic heading. 

MHz. Megahertz. 

Microburts. A strong downdraft which normally occurs 

over horizontal distances of 1 NM or less and vertical 

distances of less than 1,000 feet. In spite of its small 

horizontal scale, an intense microburst could induce 

windspeeds greater than 100 knots and downdrafts as strong 

as 6,000 feet per minute. 

Microwave landing system (MLS). A precision instrument 

approach system operating in the microwave spectrum which 

normally consists of an azimuth station, elevation station, 

and precision distance measuring equipment. 

Mileage breakdown. A fix indicating a course change 

that appears on the chart as an “x” at a break between two 

segments of a federal airway. 

Military operations area (MOA). Airspace established for 

the purpose of separating certain military training activities 

from IFR traffic. 

G-19 
 

 

Military training route (MTR). Airspace of defined vertical 

and lateral dimensions established for the conduct of military 

training at airspeeds in excess of 250 knots indicated airspeed 

(KIAS). 

Minimum altitude. An altitude depicted on an instrument 

approach chart with the altitude value underscored. Aircraft 

are required to maintain altitude at or above the depicted value. 

Minimum crossing altitude (MCA). The lowest allowed 

altitude at certain fixes an aircraft must cross when proceeding 

in the direction of a higher minimum en route altitude (MEA). 

Minimum descent altitude (MDA). The lowest altitude (in 

feet MSL) to which descent is authorized on final approach, 

or during circle-to-land maneuvering in execution of a 

nonprecision approach. 

Minimum drag. The point on the total drag curve where 

the lift-to-drag ratio is the greatest. At this speed, total drag 

is minimized. 

Minimum en route altitude (MEA). The lowest published 

altitude between radio fixes that ensures acceptable 

navigational signal coverage and meets obstacle clearance 

requirements between those fixes. 

Minimum equipment list (MEL). A list developed for larger 

aircraft that outlines equipment that can be inoperative for 

various types of flight including IFR and icing conditions. This 

list is based on the master minimum equipment list (MMEL) 

developed by the FAA and must be approved by the FAA for 

use. It is specific to an individual aircraft make and model. 

Minimum obstruction clearance altitude (MOCA). The 

lowest published altitude in effect between radio fixes on VOR 

airways, off-airway routes, or route segments, which meets 

obstacle clearance requirements for the entire route segment 

and which ensures acceptable navigational signal coverage 

only within 25 statute (22 nautical) miles of a VOR. 

Minimum reception altitude (MRA). The lowest altitude 

at which an airway intersection can be determined. 

Minimum safe altitude (MSA). The minimum altitude 

depicted on approach charts which provides at least 1,000 feet 

of obstacle clearance for emergency use within a specified 

distance from the listed navigation facility. 

Minimum vectoring altitude (MVA). An IFR altitude lower 

than the minimum en route altitude (MEA) that provides 

terrain and obstacle clearance. 

Minimums section. The area on an IAP chart that displays the 

lowest altitude and visibility requirements for the approach. 

Missed approach. A maneuver conducted by a pilot when 

an instrument approach cannot be completed to a landing. 

Missed approach point (MAP). A point prescribed in each 

instrument approach at which a missed approach procedure 

shall be executed if the required visual reference has not 

been established. 

Mixed ice. A mixture of clear ice and rime ice. 

MLS. See microwave landing system. 

MM. Middle marker. 

MOA. See military operations area. 

MOCA. See minimum obstruction clearance altitude. 

Mode C. Altitude reporting transponder mode. 

Moment. The product of the weight of an item multiplied 

by its arm. Moments are expressed in pound-inches (lb-in). 

Total moment is the weight of the airplane multiplied by the 

distance between the datum and the CG. 

Moment arm. The distance from a datum to the applied force. 

Moment index (or index). A moment divided by a constant 

such as 100, 1,000, or 10,000. The purpose of using a moment 

index is to simplify weight and balance computations of 

airplanes where heavy items and long arms result in large, 

unmanageable numbers. 

Monocoque. A shell-like fuselage design in which the 

stressed outer skin is used to support the majority of imposed 

stresses. Monocoque fuselage design may include bulkheads 

but not stringers. 

Monoplanes. Airplanes with a single set of wings. 

Movable slat. A movable auxiliary airfoil on the leading edge 

of a wing. It is closed in normal flight but extends at high 

angles of attack. This allows air to continue flowing over the 

top of the wing and delays airflow separation. 

MRA. See minimum reception altitude. 

MSA. See minimum safe altitude. 

MSL. See mean sea level. 

G-20 
 

MTR. See military training route. 

Multi-function display (MFD). Small screen (CRT or LCD)
 

in an aircraft that can be used to display information to the 

pilot in numerous configurable ways. Often an MFD will be 

used in concert with a primary flight display.
 

MVA. See minimum vectoring altitude.
 

N 

N1. Rotational speed of the low pressure compressor in a 

turbine engine. 

N2. Rotational speed of the high pressure compressor in a 

turbine engine. 

Nacelle. A streamlined enclosure on an aircraft in which 

an engine is mounted. On multiengine propeller-driven 

airplanes, the nacelle is normally mounted on the leading 

edge of the wing. 

NACG. See National Aeronautical Charting Group. 

NAS. See National Airspace System. 

National Airspace System (NAS). The common network of 

United States airspace—air navigation facilities, equipment 

and services, airports or landing areas; aeronautical charts, 

information and services; rules, regulations and procedures, 

technical information; and manpower and material. 

National Aeronautical Charting Group (NACG). A 

Federal agency operating under the FAA, responsible for 

publishing charts such as the terminal procedures and en 

route charts. 

National Route Program (NRP). A set of rules and 

procedures designed to increase the flexibility of user flight 

planning within published guidelines. 

National Security Area (NSA). Areas consisting of airspace of 

defined vertical and lateral dimensions established at locations 

where there is a requirement for increased security and safety 

of ground facilities. Pilots are requested to voluntarily avoid 

flying through the depicted NSA. When it is necessary to 

provide a greater level of security and safety, flight in NSAs 

may be temporarily prohibited. Regulatory prohibitions are 

disseminated via NOTAMs. 

National Transportation Safety Board (NTSB). A United 

States Government independent organization responsible for 

investigations of accidents involving aviation, highways, 

waterways, pipelines, and railroads in the United States. 

NTSB is charged by congress to investigate every civil 

aviation accident in the United States. 

NAVAID. Navigational aid. 

NAV/COM. Navigation and communication radio. 

NDB. See nondirectional radio beacon. 

Negative static stability. The initial tendency of an aircraft 

to continue away from the original state of equilibrium after 

being disturbed. 

Neutral static stability. The initial tendency of an aircraft 

to remain in a new condition after its equilibrium has been 

disturbed. 

NM. Nautical mile. 

NOAA. National Oceanic and Atmospheric Administration. 

No-gyro approach. A radar approach that may be used in 

case of a malfunctioning gyro-compass or directional gyro. 

Instead of providing the pilot with headings to be flown, 

the controller observes the radar track and issues control 

instructions “turn right/left” or “stop turn,” as appropriate. 

Nondirectional radio beacon (NDB). A ground-based radio 

transmitter that transmits radio energy in all directions. 

Nonprecision approach. A standard instrument approach 

procedure in which only horizontal guidance is provided. 

No procedure turn (NoPT). Term used with the appropriate 

course and altitude to denote that the procedure turn is not 

required. 

NoPT. See no procedure turn. 

NOTAM. See Notice to Airmen. 

Notice to Airmen (NOTAM). A notice filed with an aviation 

authority to alert aircraft pilots of any hazards en route or at 

a specific location. The authority in turn provides means of 

disseminating relevant NOTAMs to pilots. 

G-21 
 

 

NRP. See National Route Program. 

NSA. See National Security Area. 

NTSB. See National Transportation Safety Board. 

NWS. National Weather Service. 

O 

Obstacle departure procedures (ODP). A preplanned 

instrument flight rule (IFR) departure procedure printed for 

pilot use in textual or graphic form to provide obstruction 

clearance via the least onerous route from the terminal area 

to the appropriate en route structure. ODPs are recommended 

for obstruction clearance and may be flown without ATC 

clearance unless an alternate departure procedure (SID or 

radar vector) has been specifically assigned by ATC. 

Obstruction lights. Lights that can be found both on and off 

an airport to identify obstructions. 

Occluded front. A frontal occlusion occurs when a fastmoving cold front catches up with a slow moving warm front. 

The difference in temperature within each frontal system is 

a major factor in determining whether a cold or warm front 

occlusion occurs. 

ODP. See obstacle departure procedures. 

OM. Outer marker. 

Omission error. The failure to anticipate significant 

instrument indications following attitude changes; for 

example, concentrating on pitch control while forgetting 

about heading or roll information, resulting in erratic control 

of heading and bank. 

Optical illusion. A misleading visual image. For the 

purpose of this handbook, the term refers to the brain’s 

misinterpretation of features on the ground associated 

with landing, which causes a pilot to misread the spatial 

relationships between the aircraft and the runway. 

Orientation. Awareness of the position of the aircraft and of 

oneself in relation to a specific reference point. 

Otolith organ. An inner ear organ that detects linear 

acceleration and gravity orientation. 

Outer marker. A marker beacon at or near the glideslope 

intercept altitude of an ILS approach. It is normally located 

four to seven miles from the runway threshold on the 

extended centerline of the runway. 

Outside air temperature (OAT). The measured or indicated 

air temperature (IAT) corrected for compression and friction 

heating. Also referred to as true air temperature. 

Overcontrolling. Using more movement in the control 

column than is necessary to achieve the desired pitch-andbank condition. 

Overboost. A condition in which a reciprocating engine 

has exceeded the maximum manifold pressure allowed by 

the manufacturer. Can cause damage to engine components. 

Overpower. To use more power than required for the purpose 

of achieving a faster rate of airspeed change. 

P 

P-static. See precipitation static. 

PAPI. See precision approach path indicator. 

PAR. See precision approach radar. 

Parallels. Lines of latitude. 

Parasite drag. Drag caused by the friction of air moving 

over the aircraft structure; its amount varies directly with 

the airspeed. 

Payload (GAMA). The weight of occupants, cargo, and 

baggage. 

Personality. The embodiment of personal traits and 

characteristics of an individual that are set at a very early 

age and extremely resistant to change. 

P-factor. A tendency for an aircraft to yaw to the left due to 

the descending propeller blade on the right producing more 

thrust than the ascending blade on the left. This occurs when 

the aircraft’s longitudinal axis is in a climbing attitude in 

relation to the relative wind. The P-factor would be to the 

right if the aircraft had a counterclockwise rotating propeller. 

PFD. See primary flight display. 

Phugoid oscillations. Long-period oscillations of an 

aircraft around its lateral axis. It is a slow change in pitch 

accompanied by equally slow changes in airspeed. Angle 

of attack remains constant, and the pilot often corrects for 

phugoid oscillations without even being aware of them. 

PIC. See pilot in command. 

Pilotage. Navigation by visual reference to landmarks. 

G-22 
Pilot in command (PIC). The pilot responsible for the 

operation and safety of an aircraft. 

Pilot report (PIREP). Report of meteorological phenomena 

encountered by aircraft. 

Pilot’s Operating Handbook/Airplane Flight Manual 

(POH/AFM). FAA-approved documents published by the 

airframe manufacturer that list the operating conditions for 

a particular model of aircraft. 

PIREP. See pilot report. 

Pitot pressure. Ram air pressure used to measure airspeed. 

Pitot-static head. A combination pickup used to sample pitot 

pressure and static air pressure. 

Plan view. The overhead view of an approach procedure on 

an instrument approach chart. The plan view depicts the routes 

that guide the pilot from the en route segments to the IAF. 

Planform. The shape or form of a wing as viewed from 

above. It may be long and tapered, short and rectangular, or 

various other shapes. 

Pneumatic. Operation by the use of compressed air. 

POH/AFM. See Pilot’s Operating Handbook/Airplane 

Flight Manual. 

Point-in-space approach. A type of helicopter instrument 

approach procedure to a missed approach point more than 

2,600 feet from an associated helicopter landing area. 

Poor judgment chain. A series of mistakes that may lead 

to an accident or incident. Two basic principles generally 

associated with the creation of a poor judgment chain are: 

(1) one bad decision often leads to another; and (2) as a 

string of bad decisions grows, it reduces the number of 

subsequent alternatives for continued safe flight. ADM is 

intended to break the poor judgment chain before it can 

cause an accident or incident. 

Position error. Error in the indication of the altimeter, ASI, 

and VSI caused by the air at the static system entrance not 

being absolutely still. 

Position report. A report over a known location as 

transmitted by an aircraft to ATC. 

Positive static stability. The initial tendency to return to a 

state of equilibrium when disturbed from that state. 

Power. Implies work rate or units of work per unit of time, 

and as such, it is a function of the speed at which the force is 

developed. The term “power required” is generally associated 

with reciprocating engines. 

Powerplant. A complete engine and propeller combination 

with accessories. 

Precession. The characteristic of a gyroscope that causes an 

applied force to be felt, not at the point of application, but 

90° from that point in the direction of rotation. 

Precipitation. Any or all forms of water particles (rain, 

sleet, hail, or snow) that fall from the atmosphere and reach 

the surface. 

Precipitation static (P-static). A form of radio interference 

caused by rain, snow, or dust particles hitting the antenna and 

inducing a small radio-frequency voltage into it. 

Precision approach. A standard instrument approach 

procedure in which both vertical and horizontal guidance 

is provided. 

Precision approach path indicator (PAPI). A system of 

lights similar to the VASI, but consisting of one row of lights 

in two- or four-light systems. A pilot on the correct glideslope 

will see two white lights and two red lights. See VASI. 

Precision approach radar (PAR). A type of radar used 

at an airport to guide an aircraft through the final stages of 

landing, providing horizontal and vertical guidance. The 

radar operator directs the pilot to change heading or adjust 

the descent rate to keep the aircraft on a path that allows it 

to touch down at the correct spot on the runway. 

Precision runway monitor (PRM). System allows 

simultaneous, independent instrument flight rules (IFR) 

approaches at airports with closely spaced parallel runways. 

Preferred IFR routes. Routes established in the major 

terminal and en route environments to increase system 

efficiency and capacity. IFR clearances are issued based 

on these routes, listed in the Chart Supplement U.S. except 

when severe weather avoidance procedures or other factors 

dictate otherwise. 

Preignition. Ignition occurring in the cylinder before the time 

of normal ignition. Preignition is often caused by a local hot 

spot in the combustion chamber igniting the fuel-air mixture. 

Pressure altitude. Altitude above the standard 29.92 "Hg 

plane. 

G-23 
 

Pressure demand oxygen system. A demand oxygen system 

that supplies 100 percent oxygen at sufficient pressure above 

the altitude where normal breathing is adequate. Also referred 

to as a pressure breathing system. 

Prevailing visibility. The greatest horizontal visibility 

equaled or exceeded throughout at least half the horizon 

circle (which is not necessarily continuous). 

Preventive maintenance. Simple or minor preservative 

operations and the replacement of small standard parts 

not involving complex assembly operation as listed in 14 

CFR part 43, appendix A. Certificated pilots may perform 

preventive maintenance on any aircraft that is owned or 

operated by them provided that the aircraft is not used in air 

carrier service. 

Primary and supporting. A method of attitude instrument 

flying using the instrument that provides the most direct 

indication of attitude and performance. 

Primary flight display (PFD). A display that provides 

increased situational awareness to the pilot by replacing the 

traditional six instruments used for instrument flight with 

an easy-to-scan display that provides the horizon, airspeed, 

altitude, vertical speed, trend, trim, and rate of turn among 

other key relevant indications. 

PRM. See precision runway monitor. 

Procedure turn. A maneuver prescribed when it is necessary 

to reverse direction to establish an aircraft on the intermediate 

approach segment or final approach course. 

Profile view. Side view of an IAP chart illustrating the vertical 

approach path altitudes, headings, distances, and fixes. 

Prohibited area. Designated airspace within which flight 

of aircraft is prohibited. 

Propeller. A device for propelling an aircraft that, when 

rotated, produces by its action on the air, a thrust approximately 

perpendicular to its plane of rotation. It includes the control 

components normally supplied by its manufacturer. 

Propeller/rotor modulation error. Certain propeller 

rpm settings or helicopter rotor speeds can cause the VOR 

course deviation indicator (CDI) to fluctuate as much as 

±6°. Slight changes to the rpm setting will normally smooth 

out this roughness. 

R 

Rabbit, the. High-intensity flasher system installed at many 

large airports. The flashers consist of a series of brilliant 

blue-white bursts of light flashing in sequence along the 

approach lights, giving the effect of a ball of light traveling 

toward the runway. 

Radar. A system that uses electromagnetic waves to identify 

the range, altitude, direction, or speed of both moving and 

fixed objects such as aircraft, weather formations, and terrain. 

The term RADAR was coined in 1941 as an acronym for 

Radio Detection and Ranging. The term has since entered 

the English language as a standard word, radar, losing the 

capitalization in the process. 

Radar approach. The controller provides vectors while 

monitoring the progress of the flight with radar, guiding 

the pilot through the descent to the airport/heliport or to a 

specific runway. 

Radar services. Radar is a method whereby radio waves are 

transmitted into the air and are then received when they have 

been reflected by an object in the path of the beam. Range is 

determined by measuring the time it takes (at the speed of light) 

for the radio wave to go out to the object and then return to the 

receiving antenna. The direction of a detected object from a 

radar site is determined by the position of the rotating antenna 

when the reflected portion of the radio wave is received. 

Radar summary chart. A weather product derived from the 

national radar network that graphically displays a summary 

of radar weather reports. 

Radar weather report (SD). A report issued by radar 

stations at 35 minutes after the hour, and special reports 

as needed. Provides information on the type, intensity, and 

location of the echo tops of the precipitation. 

Radials. The courses oriented from a station. 

Radio or radar altimeter. An electronic altimeter that 

determines the height of an aircraft above the terrain by 

measuring the time needed for a pulse of radio-frequency 

energy to travel from the aircraft to the ground and return. 

Radio frequency (RF). A term that refers to alternating 

current (AC) having characteristics such that, if the current is 

input to antenna, an electromagnetic (EM) field is generated 

suitable for wireless broadcasting and/or communications. 

G-24 
Radio magnetic indicator (RMI). An electronic navigation 

instrument that combines a magnetic compass with an ADF or 

VOR. The card of the RMI acts as a gyro-stabilized magnetic 

compass, and shows the magnetic heading the aircraft is flying. 

Radiosonde. A weather instrument that observes and reports 

meteorological conditions from the upper atmosphere. This 

instrument is typically carried into the atmosphere by some 

form of weather balloon. 

Radio wave. An electromagnetic (EM) wave with frequency 

characteristics useful for radio transmission. 

RAIM. See receiver autonomous integrity monitoring. 

RAM recovery. The increase in thrust as a result of ram air 

pressures and density on the front of the engine caused by 

air velocity. 

Random RNAV routes. Direct routes, based on area 

navigation capability, between waypoints defined in terms 

of latitude/longitude coordinates, degree-distance fixes, or 

offsets from established routes/airways at a specified distance 

and direction. 

Ranging signals. Transmitted from the GPS satellite, signals 

allowing the aircraft’s receiver to determine range (distance) 

from each satellite. 

Rapid decompression. The almost instantaneous loss of 

cabin pressure in aircraft with a pressurized cockpit or cabin. 

RB. See relative bearing. 

RBI. See relative bearing indicator. 

RCO. See remote communications outlet. 

Receiver autonomous integrity monitoring (RAIM). A 

system used to verify the usability of the received GPS signals 

and warns the pilot of any malfunction in the navigation 

system. This system is required for IFR-certified GPS units. 

Recommended altitude. An altitude depicted on an instrument 

approach chart with the altitude value neither underscored nor 

overscored. The depicted value is an advisory value. 

Receiver-transmitter (RT). A system that receives and 

transmits a signal and an indicator. 

Reduced vertical separation minimum (RVSM). Reduces 

the vertical separation between flight levels (FL) 290 and 410 

from 2,000 feet to 1,000 feet, and makes six additional FLs 

available for operation. Also see DRVSM. 

Reference circle (also, distance circle). The circle depicted 

in the plan view of an IAP chart that typically has a 10 NM 

radius, within which chart the elements are drawn to scale. 

Regions of command. The “regions of normal and reversed 

command” refers to the relationship between speed and the 

power required to maintain or change that speed in flight. 

Region of reverse command. Flight regime in which flight 

at a higher airspeed requires a lower power setting and a 

lower airspeed requires a higher power setting in order to 

maintain altitude. 

REIL. See runway end identifier lights. 

Relative bearing (RB). The angular difference between the 

aircraft heading and the direction to the station, measured 

clockwise from the nose of the aircraft. 

Relative bearing indicator (RBI). Also known as the fixedcard ADF, zero is always indicated at the top of the instrument 

and the needle indicates the relative bearing to the station. 

Relative humidity. The ratio of the existing amount of 

water vapor in the air at a given temperature to the maximum 

amount that could exist at that temperature; usually expressed 

in percent. 

Relative wind. Direction of the airflow produced by an object 

moving through the air. The relative wind for an airplane in 

flight flows in a direction parallel with and opposite to the 

direction of flight; therefore, the actual flight path of the 

airplane determines the direction of the relative wind. 

Remote communications outlet (RCO). An unmanned 

communications facility that is remotely controlled by air 

traffic personnel. 

Required navigation performance (RNP). A specified level 

of accuracy defined by a lateral area of confined airspace in 

which an RNP-certified aircraft operates. 

Restricted area. Airspace designated under 14 CFR part 

73 within which the flight of aircraft, while not wholly 

prohibited, is subject to restriction. 

Reverse sensing. The VOR needle appearing to indicate the 

reverse of normal operation. 

G-25 
RF. Radio frequency. 

Rhodopsin. The photosensitive pigments that initiate the 

visual response in the rods of the eye. 

Rigging. The final adjustment and alignment of an aircraft 

and its flight control system that provides the proper 

aerodynamic characteristics. 

Rigidity. The characteristic of a gyroscope that prevents its 

axis of rotation tilting as the Earth rotates. 

Rigidity in space. The principle that a wheel with a heavily 

weighted rim spinning rapidly will remain in a fixed position 

in the plane in which it is spinning. 

Rime ice. Rough, milky, opaque ice formed by the 

instantaneous freezing of small supercooled water droplets. 

Risk. The future impact of a hazard that is not eliminated 

or controlled. 

Risk elements. There are four fundamental risk elements 

in aviation: the pilot, the aircraft, the environment, and the 

type of operation that comprise any given aviation situation. 

Risk management. The part of the decision-making 

process which relies on situational awareness, problem 

recognition, and good judgment to reduce risks associated 

with each flight. 

RMI. See radio magnetic indicator. 

RNAV. See area navigation. 

RNP. See required navigation performance. 

RT. See receiver-transmitter. 

Rudder. The movable primary control surface mounted on 

the trailing edge of the vertical fin of an airplane. Movement 

of the rudder rotates the airplane about its vertical axis. 

Ruddervator. A pair of control surfaces on the tail of an 

aircraft arranged in the form of a V. These surfaces, when 

moved together by the control wheel, serve as elevators, 

and when moved differentially by the rudder pedals, serve 

as a rudder. 

Runway centerline lights. Runway lighting which consists 

of flush centerline lights spaced at 50-foot intervals beginning 

75 feet from the landing threshold. 

Runway edge lights. A component of the runway lighting 

system that is used to outline the edges of runways at night 

or during low visibility conditions. These lights are classified 

according to the intensity they are capable of producing. 

Runway end identifier lights (REIL). A pair of synchronized 

flashing lights, located laterally on each side of the runway 

threshold, providing rapid and positive identification of the 

approach end of a runway. 

Runway visibility value (RVV). The visibility determined 

for a particular runway by a transmissometer. 

Runway visual range (RVR). The instrumentally derived 

horizontal distance a pilot should be able to see down the 

runway from the approach end, based on either the sighting 

of high-intensity runway lights, or the visual contrast of 

other objects. 

RVR. See runway visual range. 

RVV. See runway visibility value. 

S 

SA. See selective availability. 

St. Elmo’s Fire. A corona discharge which lights up the 

aircraft surface areas where maximum static discharge occurs. 

Satellite ephemeris data. Data broadcast by the GPS 

satellite containing very accurate orbital data for that satellite, 

atmospheric propagation data, and satellite clock error data. 

Sea breeze. A coastal breeze blowing from sea to land 

caused by the temperature difference when the land surface 

is warmer than the sea surface. The sea breeze usually occurs 

during the day and alternates with the land breeze that blows 

in the opposite direction at night. 

Sea level engine. A reciprocating aircraft engine having a 

rated takeoff power that is producible only at sea level. 

Scan. The first fundamental skill of instrument flight, 

also known as “cross-check;” the continuous and logical 

observation of instruments for attitude and performance 

information. 

Sectional aeronautical charts. Designed for visual 

navigation of slow- or medium-speed aircraft. Topographic 

information on these charts features the portrayal of relief, 

and a judicious selection of visual check points for VFR 

flight. Aeronautical information includes visual and radio 

aids to navigation, airports, controlled airspace, restricted 

areas, obstructions and related data. 

G-26 
 

 

 

 

SDF. See simplified directional facility. 

Selective availability (SA). A satellite technology permitting 

the Department of Defense (DOD) to create, in the interest 

of national security, a significant clock and ephemeris error 

in the satellites, resulting in a navigation error. 

Semicircular canal. An inner ear organ that detects angular 

acceleration of the body. 

Semimonocoque. A fuselage design that includes a 

substructure of bulkheads and/or formers, along with stringers, 

to support flight loads and stresses imposed on the fuselage. 

Sensitive altimeter. A form of multipointer pneumatic 

altimeter with an adjustable barometric scale that allows the 

reference pressure to be set to any desired level. 

Service ceiling. The maximum density altitude where the best 

rate-of-climb airspeed will produce a 100-feet-per-minute 

climb at maximum weight while in a clean configuration 

with maximum continuous power. 

Servo. A motor or other form of actuator which receives a 

small signal from the control device and exerts a large force 

to accomplish the desired work. 

Servo tab. An auxiliary control mounted on a primary control 

surface, which automatically moves in the direction opposite 

the primary control to provide an aerodynamic assist in the 

movement of the control. 

SIDS. See standard instrument departure procedures. 

SIGMET. The acronym for Significant Meteorological 

information. A weather advisory in abbreviated plain 

language concerning the occurrence or expected occurrence 

of potentially hazardous en route weather phenomena that may 

affect the safety of aircraft operations. SIGMET is warning 

information, hence it is of highest priority among other types 

of meteorological information provided to the aviation users. 

Signal-to-noise ratio. An indication of signal strength 

received compared to background noise, which is a measure 

of the adequacy of the received signal. 

Significant weather prognostic. Presents four panels 

showing forecast significant weather. 

Simplex. Transmission and reception on the same frequency. 

Simplified directional facility (SDF). A NAVAID used 

for nonprecision instrument approaches. The final approach 

course is similar to that of an ILS localizer; however, the 

SDF course may be offset from the runway, generally not 

more than 3°, and the course may be wider than the localizer, 

resulting in a lower degree of accuracy. 

Single-pilot resource management (SRM). The ability 

for a pilot to manage all resources effectively to ensure the 

outcome of the flight is successful. 

Situational awareness. Pilot knowledge of where the aircraft 

is in regard to location, air traffic control, weather, regulations, 

aircraft status, and other factors that may affect flight. 

Skidding turn. An uncoordinated turn in which the rate of 

turn is too great for the angle of bank, pulling the aircraft to 

the outside of the turn. 

Skills and procedures. The procedural, psychomotor, and 

perceptual skills used to control a specific aircraft or its 

systems. They are the airmanship abilities that are gained 

through conventional training, are perfected, and become 

almost automatic through experience. 

Skin friction drag. Drag generated between air molecules 

and the solid surface of the aircraft. 

Slant range. The horizontal distance from the aircraft antenna 

to the ground station, due to line-of-sight transmission of the 

DME signal. 

Slaved compass. A system whereby the heading gyro is 

“slaved to,” or continuously corrected to bring its direction 

readings into agreement with a remotely located magnetic 

direction sensing device (usually a flux valve or flux gate 

compass). 

Slipping turn. An uncoordinated turn in which the aircraft 

is banked too much for the rate of turn, so the horizontal lift 

component is greater than the centrifugal force, pulling the 

aircraft toward the inside of the turn. 

Small airplane. An airplane of 12,500 pounds or less 

maximum certificated takeoff weight. 

Somatogravic illusion. The misperception of being 

in a nose-up or nose-down attitude, caused by a rapid 

acceleration or deceleration while in flight situations that 

lack visual reference. 

G-27 
Spatial disorientation. The state of confusion due to 

misleading information being sent to the brain from various 

sensory organs, resulting in a lack of awareness of the aircraft 

position in relation to a specific reference point. 

Special flight permit. A flight permit issued to an aircraft 

that does not meet airworthiness requirements but is capable 

of safe flight. A special flight permit can be issued to move 

an aircraft for the purposes of maintenance or repair, buyer 

delivery, manufacturer flight tests, evacuation from danger, 

or customer demonstration. Also referred to as a ferry permit. 

Special use airspace. Airspace in which flight activities are 

subject to restrictions that can create limitations on the mixed 

use of airspace. Consists of prohibited, restricted, warning, 

military operations, and alert areas. 

Special fuel consumption. The amount of fuel in pounds 

per hour consumed or required by an engine per brake 

horsepower or per pound of thrust. 

Speed. The distance traveled in a given time. 

Spin. An aggravated stall that results in an airplane 

descending in a helical, or corkscrew path. 

Spiral instability. A condition that exists when the static 

directional stability of the airplane is very strong as compared 

to the effect of its dihedral in maintaining lateral equilibrium. 

Spiraling slipstream. The slipstream of a propeller-driven 

airplane rotates around the airplane. This slipstream strikes 

the left side of the vertical fin, causing the aircraft to yaw 

slightly. Rudder offset is sometimes used by aircraft designers 

to counteract this tendency. 

Spoilers. High-drag devices that can be raised into the air 

flowing over an airfoil, reducing lift and increasing drag. 

Spoilers are used for roll control on some aircraft. Deploying 

spoilers on both wings at the same time allows the aircraft 

to descend without gaining speed. Spoilers are also used to 

shorten the ground roll after landing. 

SRM. See single-pilot resource management. 

SSR. See secondary surveillance radar. 

SSV. See standard service volume. 

Stabilator. A single-piece horizontal tail surface on an 

airplane that pivots around a central hinge point. A stabilator 

serves the purposes of both the horizontal stabilizer and the 

elevators. 

Stability. The inherent quality of an airplane to correct for 

conditions that may disturb its equilibrium, and to return 

or to continue on the original flight path. It is primarily an 

airplane design characteristic. 

Stagnant hypoxia. A type of hypoxia that results when the 

oxygen-rich blood in the lungs is not moving to the tissues 

that need it. 

Stall. A rapid decrease in lift caused by the separation of 

airflow from the wing’s surface, brought on by exceeding 

the critical angle of attack. A stall can occur at any pitch 

attitude or airspeed. 

Standard atmosphere. At sea level, the standard atmosphere 

consists of a barometric pressure of 29.92 inches of mercury 

("Hg) or 1013.2 millibars, and a temperature of 15 °C (59 

°F). Pressure and temperature normally decrease as altitude 

increases. The standard lapse rate in the lower atmosphere for 

each 1,000 feet of altitude is approximately 1 "Hg and 2 °C 

(3.5 °F). For example, the standard pressure and temperature 

at 3,000 feet mean sea level (MSL) are 26.92 "Hg (29.92 

"Hg – 3 "Hg) and 9 °C (15 °C – 6 °C). 

Standard empty weight (GAMA). This weight consists of 

the airframe, engines, and all items of operating equipment 

that have fixed locations and are permanently installed in the 

airplane including fixed ballast, hydraulic fluid, unusable 

fuel, and full engine oil. 

Standard holding pattern. A holding pattern in which all 

turns are made to the right. 

Standard instrument departure procedures (SIDS). 

Published procedures to expedite clearance delivery and to 

facilitate transition between takeoff and en route operations. 

Standard rate turn. A turn in which an aircraft changes its 

direction at a rate of 3° per second (360° in 2 minutes) for 

low- or medium-speed aircraft. For high-speed aircraft, the 

standard rate turn is 11⁄2° per second (360° in 4 minutes). 

Standard service volume (SSV). Defines the limits of the 

volume of airspace which the VOR serves. 

Standard terminal arrival route (STAR). A preplanned 

IFR ATC arrival procedure published for pilot use in graphic 

and/or textual form. 

Standard weights. Weights established for numerous items 

involved in weight and balance computations. These weights 

should not be used if actual weights are available. 

G-28 
STAR. See standard terminal arrival route. 

Static longitudinal stability. The aerodynamic pitching 

moments required to return the aircraft to the equilibrium 

angle of attack. 

Static pressure. Pressure of air that is still or not moving, 

measured perpendicular to the surface of the aircraft. 

Static stability. The initial tendency an aircraft displays 

when disturbed from a state of equilibrium. 

Station. A location in the airplane that is identified by a 

number designating its distance in inches from the datum. 

The datum is, therefore, identified as station zero. An item 

located at station +50 would have an arm of 50 inches. 

Stationary front. A front that is moving at a speed of less 

than 5 knots. 

Steep turns. In instrument flight, any turn greater than standard 

rate; in visual flight, anything greater than a 45° bank. 

Stepdown fix. The point after which additional descent is 

permitted within a segment of an IAP. 

Strapdown system. An INS in which the accelerometers 

and gyros are permanently “strapped down” or aligned with 

the three axes of the aircraft. 

Stratoshere. A layer of the atmosphere above the tropopause 

extending to a height of approximately 160,000 feet. 

Stress. The body’s response to demands placed upon it. 

Stress management. The personal analysis of the kinds of 

stress experienced while flying, the application of appropriate 

stress assessment tools, and other coping mechanisms. 

Structural icing. The accumulation of ice on the exterior 

of the aircraft. 

Sublimation. Process by which a solid is changed to a gas 

without going through the liquid state. 

Suction relief valve. A relief valve in an instrument vacuum 

system required to maintain the correct low pressure inside 

the instrument case for the proper operation of the gyros. 

Supercharger. An engine- or exhaust-driven air compressor 

used to provide additional pressure to the induction air so the 

engine can produce additional power. 

Supercooled water droplets. Water droplets that have been 

cooled below the freezing point, but are still in a liquid state. 

Surface analysis chart. A report that depicts an analysis of 

the current surface weather. Shows the areas of high and low 

pressure, fronts, temperatures, dewpoints, wind directions 

and speeds, local weather, and visual obstructions. 

Synchro. A device used to transmit indications of angular 

movement or position from one location to another. 

Synthetic vision. A realistic display depiction of the aircraft 

in relation to terrain and flight path. 

T 

TAA. See terminal arrival area. 

TACAN. See tactical air navigation. 

Tactical air navigation (TACAN). An electronic navigation 

system used by military aircraft, providing both distance and 

direction information. 

Takeoff decision speed (V1). Per 14 CFR section 23.51: 

“the calibrated airspeed on the ground at which, as a result 

of engine failure or other reasons, the pilot assumed to have 

made a decision to continue or discontinue the takeoff.” 

Takeoff distance. The distance required to complete an 

all-engines operative takeoff to the 35-foot height. It must 

be at least 15 percent less than the distance required for a 

one-engine inoperative engine takeoff. This distance is not 

normally a limiting factor as it is usually less than the oneengine inoperative takeoff distance. 

Takeoff safety speed (V2). Per 14 CFR part 1: “A referenced 

airspeed obtained after lift-off at which the required oneengine-inoperative climb performance can be achieved.” 

TAWS. See terrain awareness and warning system. 

Taxiway lights. Omnidirectional lights that outline the edges 

of the taxiway and are blue in color. 

Taxiway turnoff lights. Lights that are flush with the runway 

which emit a steady green color. 

TCAS. See traffic alert collision avoidance system. 

TCH. See threshold crossing height. 

TDZE. See touchdown zone elevation. 

G-29 
TEC. See Tower En Route Control. 

Technique. The manner in which procedures are executed. 

Telephone information briefing service (TIBS). An FSS 

service providing continuously updated automated telephone 

recordings of area and/or route weather, airspace procedures, 

and special aviation-oriented announcements. 

Temporary flight restriction (TFR). Restriction to flight 

imposed in order to: 

1.	 Protect persons and property in the air or on the surface 

from an existing or imminent flight associated hazard; 

2.	 Provide a safe environment for the operation of 

disaster relief aircraft; 

3.	 Prevent an unsafe congestion of sightseeing aircraft 

above an incident; 

4.	 Protect the President, Vice President, or other public 

figures; and, 

5.	 Provide a safe environment for space agency 

operations. 

Pilots are expected to check appropriate NOTAMs during 

flight planning when conducting flight in an area where a 

temporary flight restriction is in effect. 

Tension. Maintaining an excessively strong grip on the control 

column, usually resulting in an overcontrolled situation. 

Terminal aerodrome forecast (TAF). A report established 

for the 5 statute mile radius around an airport. Utilizes the 

same descriptors and abbreviations as the METAR report. 

Terminal arrival area (TAA). A procedure to provide a 

new transition method for arriving aircraft equipped with 

FMS and/or GPS navigational equipment. The TAA contains 

a “T” structure that normally provides a NoPT for aircraft 

using the approach. 

Terminal instrument approach procedure (TERP). 

Prescribes standardized methods for use in designing 

instrument flight procedures. 

TERP. See terminal instrument approach procedure. 

Terminal radar service areas (TRSA). Areas where 

participating pilots can receive additional radar services. The 

purpose of the service is to provide separation between all 

IFR operations and participating VFR aircraft. 

Terrain awareness and warning system (TAWS). A 

timed-based system that provides information concerning 

potential hazards with fixed objects by using GPS positioning 

and a database of terrain and obstructions to provide true 

predictability of the upcoming terrain and obstacles. 

TFR. See temporary flight restriction. 

Thermosphere. The last layer of the atmosphere that begins 

above the mesosphere and gradually fades away into space. 

Threshold crossing height (TCH). The theoretical height 

above the runway threshold at which the aircraft’s glideslope 

antenna would be if the aircraft maintained the trajectory 

established by the mean ILS glideslope or MLS glidepath. 

Thrust. The force which imparts a change in the velocity of a 

mass. This force is measured in pounds but has no element of 

time or rate. The term “thrust required” is generally associated 

with jet engines. A forward force which propels the airplane 

through the air. 

Thrust (aerodynamic force). The forward aerodynamic 

force produced by a propeller, fan, or turbojet engine as it 

forces a mass of air to the rear, behind the aircraft. 

Thrust line. An imaginary line passing through the center of 

the propeller hub, perpendicular to the plane of the propeller 

rotation. 

Time and speed table. A table depicted on an instrument 

approach procedure chart that identifies the distance from the 

FAF to the MAP, and provides the time required to transit 

that distance based on various groundspeeds. 

Timed turn. A turn in which the clock and the turn 

coordinator are used to change heading a definite number 

of degrees in a given time. 

TIS. See traffic information service. 

Title 14 of the Code of Federal Regulations (14 CFR). 

Includes the federal aviation regulations governing the 

operation of aircraft, airways, and airmen. 

Torque. (1) A resistance to turning or twisting. (2) Forces that 

produce a twisting or rotating motion. (3) In an airplane, the 

tendency of the aircraft to turn (roll) in the opposite direction 

of rotation of the engine and propeller. (4) In helicopters with 

a single, main rotor system, the tendency of the helicopter 

to turn in the opposite direction of the main rotor rotation. 

G-30 
 

 

Torquemeter. An instrument used with some of the larger 

reciprocating engines and turboprop or turboshaft engines to 

measure the reaction between the propeller reduction gears 

and the engine case. 

Total drag. The sum of the parasite drag and induced drag. 

Touchdown zone elevation (TDZE). The highest elevation 

in the first 3,000 feet of the landing surface, TDZE is 

indicated on the instrument approach procedure chart when 

straight-in landing minimums are authorized. 

Touchdown zone lights. Two rows of transverse light bars 

disposed symmetrically about the runway centerline in the 

runway touchdown zone. 

Tower En Route Control (TEC). The control of IFR 

en route traffic within delegated airspace between two 

or more adjacent approach control facilities, designed to 

expedite traffic and reduce control and pilot communication 

requirements. 

TPP. See United States Terminal Procedures Publication. 

Track. The actual path made over the ground in flight. 

Tracking. Flying a heading that will maintain the desired 

track to or from the station regardless of crosswind conditions. 

Traffic Alert Collision Avoidance System (TCAS). 

An airborne system developed by the FAA that operates 

independently from the ground-based Air Traffic Control 

system. Designed to increase flight deck awareness of 

proximate aircraft and to serve as a “last line of defense” for 

the prevention of midair collisions. 

Traffic information service (TIS). A ground-based service 

providing information to the flight deck via data link using 

the S-mode transponder and altitude encoder to improve the 

safety and efficiency of “see and avoid” flight through an 

automatic display that informs the pilot of nearby traffic. 

Trailing edge. The portion of the airfoil where the airflow 

over the upper surface rejoins the lower surface airflow. 

Transcribed Weather Broadcast (TWEB). An FSS service, 

available in Alaska only, providing continuously updated 

automated broadcast of meteorological and aeronautical data 

over selected L/MF and VOR NAVAIDs. 

Transponder. The airborne portion of the ATC radar 

beacon system. 

Transponder code. One of 4,096 four-digit discrete codes 

ATC assigns to distinguish between aircraft. 

Trend. Immediate indication of the direction of aircraft 

movement, as shown on instruments. 

Tricycle gear. Landing gear employing a third wheel located 

on the nose of the aircraft. 

Trim. To adjust the aerodynamic forces on the control 

surfaces so that the aircraft maintains the set attitude without 

any control input. 

Trim tab. A small auxiliary hinged portion of a movable 

control surface that can be adjusted during flight to a position 

resulting in a balance of control forces. 

Tropopause. The boundary layer between the troposphere 

and the stratosphere which acts as a lid to confine most of the 

water vapor, and the associated weather, to the troposphere. 

Troposphere. The layer of the atmosphere extending from 

the surface to a height of 20,000 to 60,000 feet, depending 

on latitude. 

True airspeed. Actual airspeed, determined by applying a 

correction for pressure altitude and temperature to the CAS. 

True altitude. The vertical distance of the airplane above 

sea level—the actual altitude. It is often expressed as feet 

above mean sea level (MSL). Airport, terrain, and obstacle 

elevations on aeronautical charts are true altitudes. 

Truss. A fuselage design made up of supporting structural 

members that resist deformation by applied loads. The trusstype fuselage is constructed of steel or aluminum tubing. 

Strength and rigidity is achieved by welding the tubing 

together into a series of triangular shapes, called trusses. 

T-tail. An aircraft with the horizontal stabilizer mounted on 

the top of the vertical stabilizer, forming a T. 

Turbine discharge pressure. The total pressure at the 

discharge of the low-pressure turbine in a dual-turbine axialflow engine. 

Turbine engine. An aircraft engine which consists of an 

air compressor, a combustion section, and a turbine. Thrust 

is produced by increasing the velocity of the air flowing 

through the engine. 

G-31 
 

Turbocharger. An air compressor driven by exhaust gases, 

which increases the pressure of the air going into the engine 

through the carburetor or fuel injection system. 

Turbofan engine. A fanlike turbojet engine designed to 

create additional thrust by diverting a secondary airflow 

around the combustion chamber. 

Turbojet engine. A turbine engine which produces its thrust 

entirely by accelerating the air through the engine. 

Turboprop engine. A turbine engine which drives a 

propeller through a reduction gearing arrangement. Most of 

the energy in the exhaust gases is converted into torque, rather 

than using its acceleration to drive the aircraft. 

Turboshaft engine. A gas turbine engine that delivers power 

through a shaft to operate something other than a propeller. 

Turn-and-slip indicator. A flight instrument consisting 

of a rate gyro to indicate the rate of yaw and a curved glass 

inclinometer to indicate the relationship between gravity and 

centrifugal force. The turn-and-slip indicator indicates the 

relationship between angle of bank and rate of yaw. Also 

called a turn-and-bank indicator. 

Turn coordinator. A rate gyro that senses both roll and 

yaw due to the gimbal being canted. Has largely replaced 

the turn-and-slip indicator in modern aircraft. 

TWEB. See Transcribed Weather Broadcast. 

U 

UHF. See ultra-high frequency. 

Ultra-high frequency (UHF). The range of electromagnetic 

frequencies between 300 MHz and 3,000 MHz. 

Ulitimate load factor. In stress analysis, the load that 

causes physical breakdown in an aircraft or aircraft 

component during a strength test, or the load that according 

to computations, should cause such a breakdown. 

Uncaging. Unlocking the gimbals of a gyroscopic instrument, 

making it susceptible to damage by abrupt flight maneuvers 

or rough handling. 

Uncontrolled airspace. Class G airspace that has not been 

designated as Class A, B, C, D, or E. It is airspace in which 

air traffic control has no authority or responsibility to control 

air traffic; however, pilots should remember there are VFR 

minimums which apply to this airspace. 

Underpower. Using less power than required for the purpose 

of achieving a faster rate of airspeed change. 

United States Terminal Procedures Publication (TPP). 

Booklets published in regional format by FAA Aeronautical 

Navigation Products (AeroNav Products) that include DPs, 

STARs, IAPs, and other information pertinent to IFR flight. 

Unusual attitude. An unintentional, unanticipated, or 

extreme aircraft attitude. 

Useful load. The weight of the pilot, copilot, passengers, 

baggage, usable fuel, and drainable oil. It is the basic empty 

weight subtracted from the maximum allowable gross weight. 

This term applies to general aviation aircraft only. 

User-defined waypoints. Waypoint location and other data 

which may be input by the user, this is the only GPS database 

information that may be altered (edited) by the user. 

V 

V1. See takeoff decision speed. 

V2. See takeoff safety speed. 

VA. See maneuvering speed. 

Vapor lock. A problem that mostly affects gasoline-fuelled 

internal combustion engines. It occurs when the liquid fuel 

changes state from liquid to gas while still in the fuel delivery 

system. This disrupts the operation of the fuel pump, causing 

loss of feed pressure to the carburetor or fuel injection system, 

resulting in transient loss of power or complete stalling. 

Restarting the engine from this state may be difficult. The 

fuel can vaporize due to being heated by the engine, by the 

local climate or due to a lower boiling point at high altitude. 

Variation. Compass error caused by the difference in 

the physical locations of the magnetic north pole and the 

geographic north pole. 

VASI. See visual approach slope indicator. 

VDP. See visual descent point. 

Vector. A force vector is a graphic representation of a force 

and shows both the magnitude and direction of the force. 

Vectoring. Navigational guidance by assigning headings. 

VEF. Calibrated airspeed at which the critical engine of a 

multi-engine aircraft is assumed to fail. 

G-32 
 

Velocity. The speed or rate of movement in a certain 

direction. 

Venturi tube. A specially shaped tube attached to the outside 

of an aircraft to produce suction to allow proper operation 

of gyro instruments. 

Vertical axis. An imaginary line passing vertically through 

the center of gravity of an aircraft. The vertical axis is called 

the z-axis or the yaw axis. 

Vertical card compass. A magnetic compass that consists of 

an azimuth on a vertical card, resembling a heading indicator 

with a fixed miniature airplane to accurately present the 

heading of the aircraft. The design uses eddy current damping 

to minimize lead and lag during turns. 

Vertical speed indicator (VSI). A rate-of-pressure change 

instrument that gives an indication of any deviation from a 

constant pressure level. 

Vertical stability. Stability about an aircraft’s vertical axis. 

Also called yawing or directional stability. 

Very-high frequency (VHF). A band of radio frequencies 

falling between 30 and 300 MHz. 

Very-high frequency omnidirectional range (VOR). 

Electronic navigation equipment in which the flight deck 

instrument identifies the radial or line from the VOR station, 

measured in degrees clockwise from magnetic north, along 

which the aircraft is located. 

Vestibule. The central cavity of the bony labyrinth of the 

ear, or the parts of the membranous labyrinth that it contains. 

VFE. The maximum speed with the flaps extended. The upper 

limit of the white arc. 

VFR. See visual flight rules. 

VFR on top. ATC authorization for an IFR aircraft to operate 

in VFR conditions at any appropriate VFR altitude. 

VFR over the top. A VFR operation in which an aircraft 

operates in VFR conditions on top of an undercast. 

VFR terminal area chart. At a scale of 1:250,000, a chart 

that depicts Class B airspace, which provides for the control 

or segregation of all the aircraft within the Class B airspace. 

The chart depicts topographic information and aeronautical 

information including visual and radio aids to navigation, 

airports, controlled airspace, restricted areas, obstructions, 

and related data. 

V-G diagram. A chart that relates velocity to load factor. It 

is valid only for a specific weight, configuration and altitude 

and shows the maximum amount of positive or negative lift 

the airplane is capable of generating at a given speed. Also 

shows the safe load factor limits and the load factor that the 

aircraft can sustain at various speeds. 

Victor airways. Airways based on a centerline that extends 

from one VOR or VORTAC navigation aid or intersection, 

to another navigation aid (or through several navigation aids 

or intersections); used to establish a known route for en route 

procedures between terminal areas. 

Visual approach slope indicator (VASI). A visual aid of 

lights arranged to provide descent guidance information 

during the approach to the runway. A pilot on the correct 

glideslope will see red lights over white lights. 

Visual descent point (VDP). A defined point on the final 

approach course of a nonprecision straight-in approach 

procedure from which normal descent from the MDA to the 

runway touchdown point may be commenced, provided the 

runway environment is clearly visible to the pilot. 

Visual flight rules (VFR). Flight rules adopted by the 

FAA governing aircraft flight using visual references. VFR 

operations specify the amount of ceiling and the visibility the 

pilot must have in order to operate according to these rules. 

When the weather conditions are such that the pilot cannot 

operate according to VFR, he or she must use instrument 

flight rules (IFR). 

Visual meteorological conditions (VMC). Meteorological 

conditions expressed in terms of visibility, distance from 

cloud, and ceiling meeting or exceeding the minimums 

specified for VFR. 

VLE. Landing gear extended speed. The maximum speed at 

which an airplane can be safely flown with the landing gear 

extended. 

VLO. Landing gear operating speed. The maximum speed for 

extending or retracting the landing gear if using an airplane 

equipped with retractable landing gear. 

VMC. Minimum control airspeed. This is the minimum 

flight speed at which a light, twin-engine airplane can be 

satisfactorily controlled when an engine suddenly becomes 

inoperative and the remaining engine is at takeoff power. 

VMC. See visual meteorological conditions. 

G-33 
 

VNE. The never-exceed speed. Operating above this speed is 

prohibited since it may result in damage or structural failure. 

The red line on the airspeed indicator. 

VNO. The maximum structural cruising speed. Do not 

exceed this speed except in smooth air. The upper limit of 

the green arc. 

VOR. See very-high frequency omnidirectional range. 

VORTAC. A facility consisting of two components, VOR 

and TACAN, which provides three individual services: VOR 

azimuth, TACAN azimuth, and TACAN distance (DME) 

at one site. 

VOR test facility (VOT). A ground facility which emits a 

test signal to check VOR receiver accuracy. Some VOTs are 

available to the user while airborne, while others are limited 

to ground use only. 

VOT. See VOR test facility. 

VSI. See vertical speed indicator. 

VS0. The stalling speed or the minimum steady flight speed 

in the landing configuration. In small airplanes, this is the 

power-off stall speed at the maximum landing weight in the 

landing configuration (gear and flaps down). The lower limit 

of the white arc. 

VS1. The stalling speed or the minimum steady flight speed 

obtained in a specified configuration. For most airplanes, this 

is the power-off stall speed at the maximum takeoff weight 

in the clean configuration (gear up, if retractable, and flaps 

up). The lower limit of the green arc. 

V-tail. A design which utilizes two slanted tail surfaces to 

perform the same functions as the surfaces of a conventional 

elevator and rudder configuration. The fixed surfaces act as 

both horizontal and vertical stabilizers. 

VX. Best angle-of-climb speed. The airspeed at which an 

airplane gains the greatest amount of altitude in a given 

distance. It is used during a short-field takeoff to clear an 

obstacle. 

VY. Best rate-of-climb speed. This airspeed provides the 

most altitude gain in a given period of time. 

VYSE. Best rate-of-climb speed with one engine inoperative. 

This airspeed provides the most altitude gain in a given 

period of time in a light, twin-engine airplane following an 

engine failure. 

W 

WAAS. See wide area augmentation system. 

Wake turbulence. Wingtip vortices that are created when 

an airplane generates lift. When an airplane generates lift, 

air spills over the wingtips from the high pressure areas 

below the wings to the low pressure areas above them. This 

flow causes rapidly rotating whirlpools of air called wingtip 

vortices or wake turbulence. 

Warm front. The boundary area formed when a warm air 

mass contacts and flows over a colder air mass. Warm fronts 

cause low ceilings and rain. 

Warning area. An area containing hazards to any aircraft 

not participating in the activities being conducted in the 

area. Warning areas may contain intensive military training, 

gunnery exercises, or special weapons testing. 

WARP. See weather and radar processing. 

Waste gate. A controllable valve in the tailpipe of an aircraft 

reciprocating engine equipped with a turbocharger. The valve 

is controlled to vary the amount of exhaust gases forced 

through the turbocharger turbine. 

Waypoint. A designated geographical location used for route 

definition or progress-reporting purposes and is defined in 

terms of latitude/longitude coordinates. 

WCA. See wind correction angle. 

Weather and radar processor (WARP). A device that 

provides real-time, accurate, predictive, and strategic weather 

information presented in an integrated manner in the National 

Airspace System (NAS). 

Weather depiction chart. Details surface conditions as 

derived from METAR and other surface observations. 

Weight. The force exerted by an aircraft from the pull of 

gravity. 

Wide area augmentation system (WAAS). A differential 

global positioning system (DGPS) that improves the accuracy 

of the system by determining position error from the GPS 

satellites, then transmitting the error, or corrective factors, 

to the airborne GPS receiver. 

Wind correction angle (WCA). The angle between the 

desired track and the heading of the aircraft necessary to 

keep the aircraft tracking over the desired track. 

G-34 
 

Wind direction indicators. Indicators that include a 

wind sock, wind tee, or tetrahedron. Visual reference will 

determine wind direction and runway in use. 

Wind shear. A sudden, drastic shift in windspeed, direction, 

or both that may occur in the horizontal or vertical plane. 

Winds and temperature aloft forecast (FB). A twice daily 

forecast that provides wind and temperature forecasts for 

specific locations in the contiguous United States. 

Wing area. The total surface of the wing (in square feet), 

which includes control surfaces and may include wing area 

covered by the fuselage (main body of the airplane), and 

engine nacelles. 

Wings. Airfoils attached to each side of the fuselage and are 

the main lifting surfaces that support the airplane in flight. 

Wing root. The wing root is the part of the wing on a fixedwing aircraft that is closest to the fuselage. Wing roots 

usually bear the highest bending forces in flight and during 

landing, and they often have fairings to reduce interference 

drag between the wing and the fuselage. The opposite end 

of a wing from the wing root is the wing tip. 

Wing span. The maximum distance from wingtip to wingtip. 

Wingtip vortices. The rapidly rotating air that spills over an 

airplane’s wings during flight. The intensity of the turbulence 

depends on the airplane’s weight, speed, and configuration. 

Also referred to as wake turbulence. Vortices from heavy 

aircraft may be extremely hazardous to small aircraft. 

Wing twist. A design feature incorporated into some wings 

to improve aileron control effectiveness at high angles of 

attack during an approach to a stall. 

Work. A measurement of force used to produce movement. 

World Aeronautical Charts (WAC). A standard series 

of aeronautical charts covering land areas of the world at a 

size and scale convenient for navigation (1:1,000,000) by 

moderate speed aircraft. Topographic information includes 

cities and towns, principal roads, railroads, distinctive 

landmarks, drainage, and relief. Aeronautical information 

includes visual and radio aids to navigation, airports, airways, 

restricted areas, obstructions and other pertinent data. 

Z 

Zone of confusion. Volume of space above the station where 

a lack of adequate navigation signal directly above the VOR 

station causes the needle to deviate. 

Zulu time. A term used in aviation for coordinated universal 

time (UTC) which places the entire world on one time standard. 

G-35 
G-36
 
Index 

A 

Adjustable stabilizer.....................................................6-12
 

Adverse balance ...........................................................10-3
 

Adverse conditions.......................................................13-5
 

Adverse yaw...................................................................6-3
 

Advisory circular (AC) ................................................1-10
 

Aeromedical factors.....................................................17-1
 

Aeronautical charts ............................................ 14-3, 16-2
 

Aeronautical decision-making .......................................2-1
 

History of ADM .........................................................2-2
 

Aeronautical Information Manual (AIM)......................1-9
 

After-landing..............................................................14-34
 

Ailerons..........................................................................6-3
 

Coupled ailerons.........................................................6-4
 

Differential ailerons....................................................6-4
 

Frise-type ailerons......................................................6-4
 

Airborne radar..............................................................13-4
 

Aircraft documents.........................................................9-6
 

Aircraft engine ...............................................................7-1
 

Aircraft inspections........................................................9-8
 

100-hour Inspection....................................................9-8
 

Altimeter system inspection .......................................9-9
 

Annual inspection.......................................................9-8
 

Preflight inspections...................................................9-9
 

Transponder inspection ..............................................9-9
 

Aircraft maintenance......................................................9-8
 

Aircraft owner/operator responsibilities ......................9-13
 

Aircraft Owners and Pilots Association (AOPA) ........3-13
 

Aircraft types and categories .......................................1-15
 

Air data computer (ADC) ............................................8-14
 

Airfoil..................................................................... 4-6, 4-7
 

Leading edge ..............................................................4-6
 

Trailing edge...............................................................4-6
 

Airframe systems .........................................................7-25
 

Airline Deregulation Act of 1978 ..................................1-7
 

Air masses..................................................................12-17
 

Air navigation ..............................................................16-1
 

Airplane........................................................................1-15
 

Airplane flight manuals (AFM) ......................... 9-1, 16-17
 

Airport beacon ...........................................................14-16
 

Airport lighting ..........................................................14-18
 

Airport markings..........................................................14-5
 

Other markings.......................................................14-15
 

Runway markings.....................................................14-5
 

Taxiway markings..................................................14-11
 

Airports ........................................................................14-2
 

Civil airports.............................................................14-2
 

Military/federal government airports .......................14-2
 

Private airports .........................................................14-2
 

Towered....................................................................14-2
 

Nontowered ..............................................................14-2
 

Airport signs...............................................................14-15
 

Destination signs ........................................ 14-12, 14-16
 

Direction signs........................................................14-16
 

Information signs....................................................14-16
 

Location signs ........................................................14-15
 

Mandatory instruction signs ...................................14-15
 

Runway distance remaining signs ..........................14-16
 

Airport surveillance radar ............................................13-4
 

Air Route surveillance radar (ARSR)..........................13-2
 

Air Route traffic control center (ARTCC)...................13-2
 

Airship..........................................................................1-15
 

Airspace .......................................................................15-1
 

Airspeed ............................................................. 9-2, 16-10
 

Airspeed indicator (ASI)..............................................11-2
 

Airspeed indicator markings..........................................8-9
 

Airspeed limitations.......................................................8-9
 

Airspeed tape ...............................................................8-12
 

Air traffic control (ATC) ................................. 14-24, 15-7
 

Airworthiness certificate................................................9-7
 

Airworthiness directives (ADs) ...................................9-12
 

Alcohol.......................................................................17-15
 

Alert areas ....................................................................15-4
 

Alternator .....................................................................7-30
 

Altimeter .............................................................. 8-3, 8-13
 

Setting the altimeter....................................................8-5
 

Altimeter operation ........................................................8-6
 

Altitude ................................................................ 8-6, 12-6
 

Absolute altitude.........................................................8-7
 

Density altitude...........................................................8-7
 

Indicated altitude ........................................................8-6
 

Pressure altitude .........................................................8-7
 

True altitude ...............................................................8-6
 

Altitude-induced decompression sickness (DCS)......17-18
 

I-1 
Ammeter ......................................................................7-31
 

Aneroid barometer .......................................................12-5
 

Aneroid wafer ................................................................8-3
 

Angle of attack (AOA)...................................................6-4
 

Anti-ice ........................................................................7-40
 

Antiservo tab........................................................ 3-6, 6-11
 

Approach light systems..............................................14-16
 

Arm ..............................................................................10-4
 

Assembling necessary material..................................16-17
 

ATC Automation ...........................................................1-6
 

ATC delays ..................................................................13-5
 

ATC radar beacon system (ATCRBS).......................14-24
 

ATC radar weather displays.......................................13-16
 

Atmosphere ................................................. 4-1, 11-2, 12-2
 

Atmospheric circulation...............................................12-3
 

Atmospheric pressure........................................... 4-3, 11-2
 

Atmospheric stability.................................................12-12
 

Attitude indicator ............................................... 8-13, 8-18
 

Autokinesis ................................................................17-26
 

Automatic decision-making.........................................2-21
 

Operational pitfalls...................................................2-21
 

Automatic direction finder (ADF) .............................16-29
 

Automation ..................................................................2-25
 

Automation management.............................................2-31
 

Autopilot ......................................................................6-12
 

Autopilot systems.........................................................2-27
 

Aviation forecasts ........................................................13-9
 

Area forecasts (FA) ...................................... 13-9, 13-10
 

Terminal aerodrome forecasts (TAF).......................13-9
 

Forecast change group.........................................13-9
 

Forecast significant weather ................................13-9
 

Forecast sky condition..........................................13-9
 

Forecast visibility .................................................13-9
 

Forecast wind .......................................................13-9
 

ICAO station identifier .........................................13-9
 

Probability forecast ..............................................13-9
 

Type of report .......................................................13-9
 

Aviation medical examiner (AME) .............................17-2
 

Aviation routine weather report (METAR) ...............12-17
 

Aviation safety inspector (ASI) .....................................1-9
 

Aviation weather reports..............................................13-5
 

Aviation routine weather report (METAR) 

Altimeter setting....................................................13-7
 

Modifier ................................................................13-6
 

Remarks ................................................................13-7
 

Sky condition.........................................................13-7
 

Station identifier ...................................................13-6
 

Temperature and dew point..................................13-7
 

Type of report .......................................................13-6
 

Visibility................................................................13-6
 

Weather.................................................................13-6
 

Wind......................................................................13-6
 

Zulu time ...............................................................13-7
 

Pilot weather reports (PIREPs).................................13-8
 

Axes of an aircraft........................................................5-12
 

Axes of rotation..............................................................6-3
 

B 

Balance.........................................................................10-2
 

Balance tabs .................................................................6-11
 

Balloon.........................................................................1-15
 

Barbs ..........................................................................12-12
 

Basic aerodynamics .......................................................3-2
 

Drag............................................................................3-2
 

Lift..............................................................................3-2
 

Thrust .........................................................................3-2
 

Weight ........................................................................3-2
 

Basic empty weight......................................................10-4
 

Bernoulli, Daniel............................................................4-6
 

Bernoulli’s Principle of Differential Pressure................4-6
 

Best angle-of-climb speed (VX) ...................................8-10
 

Best rate-of-climb speed (VY)......................................8-10
 

Binocular cues............................................................17-26
 

Blade angle...................................................................5-28
 

Bleed air heating systems.............................................7-30
 

Blocked pitot system....................................................8-10
 

Blocked static system...................................................8-11
 

Boundary layer..................................................... 5-6, 5-46
 

Brake horsepower (BHP)..................................... 7-6, 7-24
 

Brakes ..........................................................................7-34
 

Bus bar .........................................................................7-31
 

C 

Cabin pressure control system .....................................7-35
 

Cabin pressurization system ........................................7-35
 

Calibrated airspeed (CAS) ................................. 8-9, 11-18
 

Canard............................................................................6-7
 

Carbon monoxide (CO) poisoning.............................17-12
 

Carburetor air temperature gauge ................................7-11
 

Carburetor heat.............................................................7-10
 

Carburetor icing .............................................................7-9
 

Carburetor systems.........................................................7-8
 

Float-type carburetor..................................................7-8
 

Pressure-type carburetor.............................................7-9
 

Ceiling........................................................................12-17
 

Center of gravity (CG)....................................... 10-2, 10-4
 

CG limits ..................................................................10-5
 

CG range...................................................................10-5
 

Central blind spot.......................................................17-21
 

Certificated flight instructor (CFI)..................... 1-19, 1-23
 

Certificate of aircraft registration...................................9-6
 

I-2 
Chandelles....................................................................5-36
 

Chart Supplement U.S. ..............................................16-17
 

Clearing procedures...................................................14-28
 

Before takeoff.........................................................14-28
 

Climbs and descents...............................................14-28
 

Straight and Level ..................................................14-28
 

Traffic at VOR sites ...............................................14-28
 

Traffic patterns.......................................................14-28
 

Training operations.................................................14-28
 

Climb performance ......................................................11-6
 

Angle of climb (AOC)..............................................11-7
 

Climb Performance Factors......................................11-8
 

Rate of climb (ROC) ................................................11-7
 

Clouds ........................................................................12-15
 

Cloud classification ................................................12-17
 

Alto......................................................................12-17
 

Castellanus .........................................................12-17
 

Cirrus..................................................................12-17
 

Cumulus ..............................................................12-17
 

Fracto .................................................................12-17
 

Lenticularus ........................................................12-17
 

Nimbus ................................................................12-17
 

Stratus.................................................................12-17
 

Code of Federal Regulations (CFR) ..............................1-7
 

Collision avoidance....................................................14-28
 

Combustion..................................................................7-18
 

Combustion heater systems..........................................7-29
 

Compass heading .......................................................16-16
 

Composite materials in aircraft......................................3-9
 

Composites.....................................................................3-9
 

Compressor stalls.........................................................7-23
 

Control .........................................................................10-3
 

Control instruments......................................................3-13
 

Controllability.................................................... 5-15, 5-42
 

Controlled airport.........................................................14-2
 

Controlled airspace ......................................................15-2
 

Class A airspace .......................................................15-2
 

Class B airspace........................................................15-2
 

Class C airspace........................................................15-2
 

Class D airspace .......................................................15-2
 

Class E airspace........................................................15-2
 

Controlled firing areas (CFAs) ....................................15-4
 

Convective currents .....................................................12-7
 

Convective significant meteorological
 

information (WST).....................................................13-12
 

Converting KTS to MPH ...........................................16-11
 

Converting minutes to equivalent hours....................16-11
 

Cooling...........................................................................7-1
 

Coriolis force ...............................................................12-3
 

Corkscrew effect ..........................................................5-31
 

Course ........................................................................16-10
 

Course deviation indicator (CDI)...............................16-23
 

Course intercept .........................................................16-27
 

Angle of intercept...................................................16-27
 

Rate of intercept .....................................................16-27
 

Cross-country flying ....................................................16-1
 

Crosswind and headwind component chart ...............11-25
 

Current conditions........................................................13-5
 

D 

Dark adaptation..........................................................17-23
 

Datum...........................................................................10-5
 

Data link weather.......................................................13-21
 

Data link weather products ........................................13-23
 

Flight information service-broadcast (FIS-B)........13-23
 

Daylight saving time ....................................................16-5
 

Dead reckoning ..........................................................16-13
 

DECIDE model............................................................2-18
 

Choose (a course of action)......................................2-20
 

Detect (the problem).................................................2-20
 

Do (the necessary actions)........................................2-20
 

Estimate (the need to react)......................................2-20
 

Evaluate (the effect of the action) ............................2-20
 

Identify (solutions) ...................................................2-20
 

Decision-making in a dynamic environment ...............2-21
 

Use of resources .......................................................2-21
 

External resources................................................2-23
 

Internal resources.................................................2-23
 

Decision-making process.............................................2-12
 

Dehydration................................................................17-14
 

Deice system ................................................................7-40
 

Delta.............................................................................10-5
 

Density altitude ..............................................................4-4
 

Density altitude charts................................................11-20
 

Density altitude (DA)...................................................12-5
 

Department of transportation (DOT) .............................1-6
 

Deposition..................................................................12-15
 

Designated pilot examiner ...........................................1-24
 

Design maneuvering speed (VA)..................................8-10
 

Destination forecast .....................................................13-5
 

Determining loaded weight and CG ............................10-7
 

Deviation.......................................................... 16-8, 16-16
 

Dew point....................................................... 12-13, 13-13
 

Distance measuring equipment (DME) .....................16-27
 

Doppler radar ...............................................................13-3
 

Drag........................................................................ 5-1, 5-6
 

Form drag ...................................................................5-6
 

Induced drag....................................................... 5-6, 5-7
 

Interference drag.........................................................5-6
 

Parasite drag ...............................................................5-6
 

Skin friction drag........................................................5-6
 

I-3 
Drift angle ..................................................................16-10
 

Drugs..........................................................................17-16
 

Dutch roll .....................................................................5-20
 

Dynamic hydroplaning...............................................11-13
 

E 

Eddy current damping..................................................8-27
 

Electrical ........................................................................7-1
 

Electrical system ..........................................................7-30
 

Electronic flight display (EFD)............... 3-12, 8-12, 13-18
 

Elevator.................................................................. 3-6, 6-5
 

Emergency locator transmitter (ELT)............................9-9
 

Empennage............................................................. 3-3, 3-6
 

Empty-field myopia ...................................................17-22
 

Engine ............................................................................7-1
 

Engine cooling systems................................................7-17
 

Engineered materials arresting systems (EMAS) ......14-35
 

Engine pressure ratio (EPR).........................................7-22
 

Engine temperature limitations....................................7-23
 

Enhanced flight vision system ...................................17-28
 

Enhanced night vision systems..................................17-27
 

Enhanced situational awareness...................................2-30
 

Enhanced taxiway centerline markings .....................14-12
 

En route forecast ..........................................................13-5
 

Environmental control systems......................................7-1
 

Equipment use..............................................................2-27
 

Equivalent airspeed (EAS).........................................11-18
 

Equivalent shaft horsepower (ESHP) ..........................7-24
 

Estimated time en route (ETE) ..................................16-17
 

Exhaust gas temperature (EGT)...................................7-22
 

Exhaust gas temperature (EGT) gauge ..........................7-9
 

Exhaust heating systems ..............................................7-29
 

Exhaust systems...........................................................7-18
 

Explosive decompression.............................................7-36
 

Exposure to chemicals ...............................................17-13
 

Engine oil ...............................................................17-14
 

Fuel.........................................................................17-14
 

Hydraulic fluid .......................................................17-13
 

F 

Fairings ..........................................................................5-6
 

False horizon..............................................................17-26
 

Fascination (fixation).................................................17-27
 

Fatigue........................................................................17-13
 

FDC NOTAMs.............................................................1-13
 

Featureless terrain illusion .........................................17-10
 

Federal Aviation Administration (FAA)........................1-3
 

Federal certification of pilots and mechanics ................1-4
 

Federal Communications Commission (FCC). 9-13, 14-22
 

Field offices ...................................................................1-8
 

Filing a VFR flight plan.............................................16-21
 

Flameout ......................................................................7-24
 

Flaperons........................................................................6-5
 

Flaps...............................................................................6-8
 

Fowler flaps................................................................6-9
 

Plain flap ....................................................................6-8
 

Split flap .....................................................................6-8
 

Flicker vertigo............................................................17-27
 

Flight..............................................................................1-2
 

Flight computers ........................................................16-12
 

Flight controls................................................................6-2
 

Flight control systems....................................................6-1
 

Flight diversion ..........................................................16-34
 

Flight limits....................................................................9-4
 

Flight maneuvers..........................................................5-36
 

Flight planning...........................................................16-17
 

Flight school.................................................................1-18
 

Flight service station....................................................13-4
 

Flight Standards District Office (FSDO).......................1-9
 

Flight Standards Service (AFS) .....................................1-8
 

Floor load limit ............................................................10-5
 

Flux gate compass system............................................8-20
 

Fog ................................................................. 12-15, 17-10
 

Advection fog.........................................................12-15
 

Ice fog.....................................................................12-15
 

Radiation fog ..........................................................12-15
 

Sea smoke...............................................................12-15
 

Steam fog................................................................12-15
 

Upslope fog ............................................................12-15
 

Forces in climbs ...........................................................5-23
 

Forces in descents ........................................................5-24
 

Forces in turns..............................................................5-22
 

Foreign object damage (FOD) .....................................7-23
 

Free directional oscillations .........................................5-20
 

Free-stream velocity.......................................................5-6
 

Friction...........................................................................4-2
 

Fronts .........................................................................12-18
 

Cold front ...............................................................12-20
 

Fast-moving cold front .......................................12-20
 

Occluded front........................................................12-21
 

Warm front .............................................................12-18
 

Fuel ................................................................................7-1
 

Fuel consumption.......................................................16-11
 

Fuel contamination.......................................................7-27
 

Fuel fired geaters..........................................................7-29
 

Fuel gauges ..................................................................7-26
 

Fuel grades...................................................................7-27
 

Aviation gasoline (AVGAS) ....................................7-27
 

Supplemental type certificate (STC) ........................7-27
 

Fuel injection system ...................................................7-11
 

Fuel load.......................................................................10-5
 

I-4 
Fuel primer...................................................................7-25
 

Fuel rate .....................................................................16-17
 

Fuel selectors ...............................................................7-26
 

Fuel systems.................................................................7-25
 

Fuel-pump system ....................................................7-25
 

Gravity-feed system .................................................7-25
 

Fuel tanks.....................................................................7-25
 

Full authority digital engine control (FADEC)............7-20
 

Fuselage .........................................................................3-3
 

G 

General Aviation Manufacturers
 

Association (GAMA).....................................................9-2
 

Generator......................................................................7-30
 

Glider ...........................................................................1-15
 

Global positioning system (GPS)..................... 3-13, 16-30
 

RAIM capability.....................................................16-32
 

Selective availability ..............................................16-31
 

VFR use of GPS .....................................................16-32
 

Graphical METARs...................................................13-21
 

Ground adjustable tabs.................................................6-11
 

Ground lighting illusions ...........................................17-10
 

Ground power unit (GPU) ...........................................7-30
 

Groundspeed (GS) .................................. 8-9, 16-10, 16-17
 

Gyroscopic action ..................................... 5-31, 5-32, 8-15
 

Precession.................................................................8-15
 

Rigidity in space.......................................................8-15
 

Gyroscopic attitude indicators .....................................6-12
 

Gyroscopic flight instruments......................................8-15
 

Gyroscopic principles ..................................................8-15
 

H 

Hazard............................................................................2-4
 

Hazardous attitudes........................................................2-5
 

Hazardous in-flight weather advisory (HIWAS) .........13-4
 

Haze ...........................................................................17-10
 

Heading......................................................................16-10
 

Heading indicator............................................... 8-13, 8-19
 

Heatstroke ..................................................................17-14
 

High speed flight..........................................................5-44
 

Hypersonic................................................................5-45
 

Subsonic flow................................................. 5-44, 5-45
 

Supersonic flow........................................................5-44
 

Transonic..................................................................5-45
 

High speed flight controls............................................5-49
 

High speed stalls ..........................................................5-36
 

Horizontal situation indicator ....................................16-24
 

Human behavior...........................................................2-11
 

Humidity ............................................................ 4-5, 12-13
 

Relative humidity ...................................................12-13
 

Hydraulic systems........................................................7-31
 

Hydromechanical ...........................................................6-2
 

Hyperventilation ..........................................................17-4
 

Hypoxia........................................................................17-3
 

Histotoxic hypoxia ...................................................17-4
 

Hypemic hypoxia .....................................................17-3
 

Hypoxic hypoxia ......................................................17-3
 

Stagnant hypoxia ......................................................17-3
 

I
 

Ice.................................................................................5-26
 

Icing ...........................................................................12-24
 

Ignition...........................................................................7-1
 

Ignition system.............................................................7-15
 

Illusions........................................................................17-6
 

Impact pressure chamber and lines................................8-2
 

Inches of mercury ........................................................12-4
 

Inclinometer .................................................................8-18
 

Indicated airspeed (IAS) .................................... 8-8, 11-18
 

Induction ........................................................................7-1
 

Induction system............................................................7-7
 

In-flight weather advisories .......................................13-11
 

AIRMET.................................................................13-11
 

SIGMET .................................................................13-12
 

In-runway lighting .....................................................14-18
 

Instrument landing system (ILS) .................................3-13
 

Intelligent flight control systems (IFCS) .......................6-2
 

International Civil Aviation Organization
 

(ICAO) ............................................................... 4-3, 14-22
 

International Standard Atmosphere (ISA) .. 4-3, 11-2, 12-5
 

Inversion ....................................................................12-13
 

Isobars........................................................................12-12
 

J 

Jet-fueled piston engine .................................................7-4
 

K 

Knowledge examination ..............................................1-21
 

L 

Lags..............................................................................8-27
 

Land and hold short lights..........................................14-18
 

Landing ......................................................................14-34
 

Landing charts............................................................11-26
 

Landing gear ..........................................3-3, 3-7, 7-1, 7-33
 

Landing gear extended speed (VLE) .............................8-10
 

Landing gear operating speed (VLO) ............................8-10
 

Landing performance .................................................11-16
 

Landing strip indicators .............................................14-20
 

I-5 
Lattitude .......................................................................16-3
 

Lazy eights...................................................................5-36
 

Leading edge device ......................................................6-9
 

Leading edge cuffs ...................................................6-10
 

Leading edge flaps....................................................6-10
 

Leads............................................................................8-27
 

Licensed empty weight ................................................10-5
 

Lift..................................................................................5-1
 

Lift/drag ratio.................................................................5-5
 

Lighter-than-air aircraft ...............................................1-15
 

Lightning....................................................................12-25
 

Lightning strike protection...........................................3-11
 

Likelihood of an event ...................................................2-6
 

Improbable..................................................................2-6
 

Occasional ..................................................................2-6
 

Probable......................................................................2-6
 

Remote .......................................................................2-6
 

Load distribution..........................................................5-43
 

Loadmeter ....................................................................7-31
 

Local airport advisory..................................................15-6
 

Longitude .....................................................................16-3
 

Lost procedures..........................................................16-34
 

Lubrication.....................................................................7-1
 

M 

Mach buffet..................................................................5-49
 

Mach number ...............................................................5-45
 

Magnetic compass........................................................8-23
 

Induced errors...........................................................8-24
 

Acceleration error ................................................8-26
 

Deviation...............................................................8-24
 

Dip errors .............................................................8-25
 

Northerly turning errors.......................................8-26
 

Oscillation error ...................................................8-27
 

Southerly turning errors .......................................8-26
 

Variation...............................................................8-24
 

Magnetic compasses ....................................................6-12
 

Magnetic heading.......................................................16-16
 

Magnus effect.................................................................4-6
 

Maintenance entries .....................................................9-10
 

Managing aircraft automation......................................2-29
 

Maneuverability ...........................................................5-15
 

Manifold absolute pressure (MAP)................................7-6
 

Maximum landing weight............................................10-5
 

Maximum ramp weight................................................10-5
 

Maximum takeoff weight.............................................10-5
 

Maximum weight.........................................................10-5
 

Maximum zero fuel weight..........................................10-5
 

Mean aerodynamic chord (MAC)...................... 5-13, 10-5
 

Measurement of direction ............................................16-5
 

Medical certificate .......................................................17-2
 

Medical certification requirements ..............................1-20
 

Motion sickness .........................................................17-12
 

Multi-function display (MFD) ......................... 3-12, 13-18
 

Meridians .....................................................................16-3
 

Mesopic vision...........................................................17-21
 

Mesosphere ..................................................................12-3
 

Meteorologists..............................................................13-1
 

Microjets ......................................................................7-20
 

Middle ear ....................................................................17-5
 

Military operation areas (MOAs).................................15-4
 

Military training routes (MTRs) ..................................15-6
 

Minimum control speed (VMC) ..................................8-10
 

Minimum equipment lists (MEL)..................................9-9
 

Mixture control ..............................................................7-9
 

Moisture .....................................................................12-13
 

Moment........................................................................10-5
 

Moment arm....................................................... 10-4, 5-13
 

Moment index ..............................................................10-5
 

Monocoque ............................................................ 3-3, 3-8
 

N 

N1 indicator ..................................................................7-23
 

N2 indicator ..................................................................7-23
 

National Aeronautics and Space Administration
 

(NASA)................................................................ 6-2, 3-13
 

National airspace system..............................................15-7
 

National Oceanic and Atmospheric Administration 

(NOAA) .........................................................................4-5
 

National security areas (NSAs)....................................15-7
 

National weather service (NWS) .................................13-1
 

Navigation instruments ................................................3-13
 

Negative arm..............................................................10-10
 

Negative dynamic stability ..........................................5-15
 

Negative static stability................................................5-14
 

Net thrust......................................................................7-24
 

Neutral dynamic stability.............................................5-15
 

Neutral static stability ..................................................5-14
 

Newton’s Basic Laws of Motion ...................................4-5
 

Newton’s First Law........................................................4-5
 

Newton’s First Law of Motion ....................................5-22
 

Newton’s Second Law...................................................4-5
 

Newton’s Third Law......................................................4-6
 

Newton’s Third Law of Physics ..................................5-31
 

Next generation weather radar system
 

(NEXRAD) ................................................................13-18
 

Abnormalities.........................................................13-21
 

Limitations .............................................................13-21
 

Night blind spot..........................................................17-22
 

Night landing illusions...............................................17-27
 

Night vision................................................................17-22
 

Night vision illusions.................................................17-26
 

I-6 
Night vision protection ..............................................17-23
 

Nondirectional beacon (NDB) .....................................3-13
 

Notices to Airmen (NOTAM)......................................13-5
 

FDC NOTAMs.........................................................1-12
 

NOTAM composition ..............................................1-13
 

NOTAM (D) information.........................................1-12
 

O 

Obstruction lights.......................................................14-19
 

Dual lighting...........................................................14-19
 

High intensity white obstruction lights ..................14-19
 

Red obstruction lights.............................................14-19
 

Obstructions on wind ...................................................12-8
 

Oil Systems ..................................................................7-16
 

Operational incidents (OI) .........................................14-31
 

Optical illusions.........................................................17-10
 

Original equipment manufacturer (OEM) .....................7-4
 

Outside air temperature (OAT) gauge ............... 7-11, 8-28
 

Oxygen masks..............................................................7-38
 

Oxygen systems ...........................................................7-37
 

Continuous-flow oxygen system..............................7-38
 

Diluter-demand oxygen systems ..............................7-38
 

Electrical pulse-demand oxygen system ..................7-38
 

Pressure-demand oxygen systems............................7-38
 

P 

Parachute jump aircraft operations ..............................15-6
 

Parachute jumps.........................................................15-11
 

Parallels........................................................................16-3
 

PAVE checklist..............................................................2-8
 

Payload.........................................................................10-5
 

Pennants .....................................................................12-12
 

Perceive, Process, Perform (3P)...................................2-15
 

Forming good safety habits ......................................2-18
 

Performance .................................................................11-5
 

Performance charts.....................................................11-19
 

Performance data .........................................................11-1
 

Performance instruments .............................................3-12
 

P factor............................................................... 5-30, 5-32
 

Photopic vision...........................................................17-20
 

Pilotage ......................................................................16-12
 

Pilot certifications ........................................................1-16
 

Airline transport pilot...............................................1-18
 

Commercial pilot......................................................1-18
 

Private pilot ..............................................................1-17
 

Recreational pilot .....................................................1-17
 

Sport pilot.................................................................1-16
 

Pilot deviations...........................................................14-31
 

Pilot’s operating handbook (POH)..................... 9-1, 16-17
 

Pitch .............................................................................5-13
 

Pitching ........................................................................5-15
 

Pitot-static flight instruments.........................................8-1
 

Placards..........................................................................9-4
 

Plotter.........................................................................16-12
 

Positive dynamic stability............................................5-15
 

Positive static stability .................................................5-14
 

Postural considerations ................................................17-8
 

Powered-lift..................................................................1-15
 

Powered parachute .......................................................1-15
 

Powerplant ...............................................3-3, 3-7, 7-1, 9-3
 

Practical test.................................................................1-22
 

Precipitation ...............................................................12-17
 

Precision approach path indicator (PAPI)..................14-16
 

Pre-landing.................................................................14-34
 

Pressure ..........................................................................4-3
 

Pressure altimeter...........................................................8-3
 

Pressure altitude ................................................... 4-4, 11-3
 

Pressurized aircraft.......................................................7-34
 

Preventive maintenance ...............................................9-10
 

Primary flight controls...................................................6-2
 

Primary flight display ..................................................3-12
 

Primary locations of the FAA
 

Field offices 

Flight Standards District Office (FSDO) ...............1-9
 

Flight Standards Service (AFS)..............................1-8
 

Primary radar .............................................................14-24
 

Procedures, vortex avoidance ....................................14-28
 

Professional Air Traffic Controllers Organization 

(PATCO) strike..............................................................1-6
 

Prohibited areas............................................................15-3
 

Propeller.......................................................... 3-7, 7-1, 7-4
 

Adjustable-pitch propeller..........................................7-6
 

Fixed-pitch propeller..................................................7-5
 

Propeller anti-ice..........................................................7-41
 

Propeller blade .............................................................5-28
 

Propeller principles ......................................................5-28
 

Published VFR routes ..................................................15-6
 

Pulse oximeters ............................................................7-39
 

R 

Radar observations.......................................................13-3
 

Radar traffic advisories..............................................14-26
 

Radio communications...............................................14-22
 

Radio equipment........................................................14-22
 

Radio magnetic indicator (RMI)................................16-24
 

Radio navigation ........................................................16-22
 

Radius of turn...............................................................5-39
 

Range performance ......................................................11-9
 

I-7 
Rapid decompression...................................................7-36
 

Reciprocating engines....................................................7-2
 

Four-stroke engines....................................................7-3
 

Horizontally-opposed engine .....................................7-2
 

In-line engines............................................................7-2
 

Radial engines............................................................7-2
 

Two-stroke engine......................................................7-3
 

Reference datum ..........................................................10-5
 

Refueling procedures ...................................................7-29
 

Region of reversed command ....................................11-11
 

Repairs and alterations.................................................9-12
 

Respect for onboard systems .......................................2-29
 

Restricted areas ............................................................15-3
 

Retractable landing gear ..............................................7-34
 

Reversible perspective illusion ..................................17-26
 

Risk ........................................................................ 2-4, 2-6
 

Mitigating risk ............................................................2-8
 

Risk management...........................................................2-3
 

Rocket ..........................................................................1-15
 

Roll...............................................................................5-13
 

Rolling..........................................................................5-17
 

Rotorcraft .....................................................................1-15
 

Gyroplane .................................................................1-15
 

Helicopter.................................................................1-15
 

Runway and terrain slopes illusion............................17-10
 

Runway approach area holding position signs and 

markings.....................................................................14-14
 

Runway centerline lighting system (RCLS) ..............14-18
 

Runway confusion .....................................................14-31
 

Runway end identifier lights (REIL) .........................14-17
 

Rough air......................................................................5-37
 

Rudder.................................................................... 3-6, 6-4
 

Ruddervators..................................................................6-8
 

Runway holding position marking...............................14-8
 

Runway holding position sign .....................................14-6
 

Runway incursion avoidance .....................................14-30
 

Runway lighting.........................................................14-17
 

Runway surface and gradient.....................................11-12
 

Runway width illusion ...............................................17-10
 

S 

Safety program airmen notification system
 

(SPANS) ......................................................................1-14
 

Satellite ........................................................................13-4
 

Scanning techniques...................................................17-23
 

Scotopic vision...........................................................17-21
 

Sectional charts ............................................................16-2
 

Segmented circle visual indicator system..................14-20
 

Self-Imposed stress....................................................17-25
 

Semimonocoque..................................................... 3-3, 3-8
 

Servicing of oxygen systems .......................................7-39
 

Severity of an event .......................................................2-6
 

Catastrophic................................................................2-6
 

Critical........................................................................2-6
 

Marginal .....................................................................2-6
 

Negligible ...................................................................2-6
 

Shock waves.................................................................5-46
 

Significant Meteorological Information (SIGMET)..13-12
 

Single-engine best rate-of-climb (VYSE).......................8-10
 

Single-pilot resource management.................................2-4
 

Sinus problems.............................................................17-5
 

Situational awareness...................................................2-24
 

Obstacles to maintaining situational awareness .......2-24
 

Size-distance illusion .................................................17-27
 

Skidding turn................................................................5-23
 

Slipping turn.................................................................5-23
 

Slip/skid indicator ........................................................8-13
 

Slotted flap.....................................................................6-8
 

Spatial disorientation ...................................................17-6
 

Special airworthiness certificate ....................................9-8
 

Special flight permits ...................................................9-12
 

Special use airspace .....................................................15-3
 

Spins.............................................................................5-36
 

Spiral instability...........................................................5-20
 

Spoilers ........................................................................6-10
 

Squall line ..................................................................12-23
 

SRM and the 5P check.................................................2-13
 

Passengers ................................................................2-14
 

Pilot ..........................................................................2-14
 

Plan...........................................................................2-14
 

Plane .........................................................................2-14
 

Programming............................................................2-15
 

Stabilator........................................................................6-7
 

Stability............................................5-14, 5-42, 10-2, 10-3
 

Dynamic stability .....................................................5-14
 

Lateral stability.........................................................5-17
 

Dihedral................................................................5-18
 

Sweepback and wing location...............................5-18
 

Keel effect and weight distribution.......................5-18
 

Longitudinal stability ...............................................5-15
 

Static stability...........................................................5-14
 

Vertical stability .......................................................5-19
 

Stalls................................................................... 5-25, 5-36
 

Stall speed performance charts ..................................11-27
 

Standard airworthiness certificate..................................9-7
 

Standard datum plane (SDP)........................................11-3
 

Standard empty weight ................................................10-5
 

Standard temperature lapse rate ...................................11-2
 

Standard weights..........................................................10-5
 

Starting system.............................................................7-18
 

Static pressure chamber and lines..................................8-2
 

Station ..........................................................................10-5
 

I-8 
Straight and Level............................................ 11-5, 14-28
 

Stratosphere..................................................................12-3
 

Stress..........................................................................17-12
 

Stress management.......................................................2-21
 

Student pilot.................................................................1-20
 

Student pilot solo requirements ...................................1-21
 

Subcomponents of an airplane .......................................3-8
 

Airframe .....................................................................3-8
 

Brakes.........................................................................3-8
 

Electrical system.........................................................3-8
 

Flight controls ............................................................3-8
 

Sublimation................................................................12-15
 

Sumps...........................................................................7-27
 

Superchargers...............................................................7-12
 

Surface aviation weather observations (METARs) .....13-2
 

Sweepback ...................................................................5-48
 

Synopsis .......................................................................13-5
 

Synthetic vision system..............................................17-28
 

T 

Tachometer ..................................................................8-13
 

Tailwheel landing gear airplanes .................................7-33
 

Takeoff charts ............................................................11-20
 

Takeoff performance..................................................11-14
 

Taxiway centerline lead-on lights..............................14-18
 

Taxiways, marking and lighting of permanently
 

Closed runways..........................................................14-14
 

Temperature ................................................... 12-13, 13-13
 

Temporary flight restrictions (TFR) ............................15-6
 

Terminal doppler weather radar (TDWR) ...................13-4
 

Terminal radar service area (TRSA)................ 14-26, 15-7
 

Tetrahedron................................................................14-20
 

Thermosphere ..............................................................12-3
 

Thielert, Frank................................................................7-4
 

Three-color visual approach path...............................14-17
 

Thrust ..................................................................... 5-1, 5-2
 

Thrust horsepower (THP) .................................... 7-6, 7-24
 

Thunderstorms ...........................................................12-22
 

Time and distance check from a station.....................16-26
 

Time Zones ..................................................................16-3
 

Central standard time................................................16-5
 

Eastern standard time ...............................................16-5
 

Mountain standard time............................................16-5
 

Pacific standard time ................................................16-5
 

Tornadoes...................................................................12-23
 

Torque ..........................................................................5-30
 

Torquemeter.................................................................7-22
 

Total distance .............................................................16-17
 

Touchdown zone lights (TDZL)................................14-18
 

Track ..........................................................................16-10
 

Transcontinental air mail route ......................................1-4
 

Transcribed weather broadcast (TWEB)
 

(Alaska only)................................................................13-4
 

Transponder ...............................................................14-25
 

Trend vectors ...............................................................8-14
 

Tricycle landing gear airplanes....................................7-33
 

Trim systems................................................................6-10
 

Trim tabs .............................................................. 3-6, 6-10
 

Tropopause...................................................................12-3
 

Troposphere .................................................................12-2
 

True airspeed (TAS) .......................................... 8-9, 11-18
 

True course.................................................................16-16
 

True heading ..............................................................16-16
 

Truss structure................................................................3-8
 

T-tail configuration ........................................................6-6
 

Turbine engines............................................................7-20
 

Turbofan ...................................................................7-21
 

Turbojet ....................................................................7-20
 

Turboprop.................................................................7-21
 

Turboshaft ................................................................7-21
 

Turbosuperchargers............................................ 7-12, 7-13
 

Turbulence .................................................................12-24
 

Turn indicators................................................... 8-13, 8-16
 

Turn-and-slip indicator.............................................8-16
 

Turn rate indicator........................................................8-13
 

U 

Ultralight vehicle .........................................................1-14
 

Uncontrolled airspace ..................................................15-3
 

Class G airspace .......................................................15-3
 

Universal coordinated time (UTC) ..............................16-5
 

Unmanned free balloons............................................15-11
 

Upper air observations .................................................13-2
 

Useful load...................................................................10-5
 

V
 

VA ...............................................................................11-18
 

Variable inlet guide vane (VIGV)................................7-24
 

Variation .......................................................... 16-6, 16-16
 

Vector analysis...........................................................16-13
 

Vehicle (driver) deviations ........................................14-31
 

Vertical card magnetic compass ..................................8-27
 

Vertical speed indicator (VSI) ............................. 8-7, 8-13
 

Very high frequency (VHF).......................................16-22
 

Very high frequency (VHF) omni-directional
 

radio range (VOR) ........................................... 3-13, 16-22
 

Very light jets (VLJs)...................................................7-20
 

Vestibular illusions
 

Coriolis illusion ........................................................17-7
 

Elevator illusion .......................................................17-8
 

Graveyard spiral .......................................................17-7
 

I-9 
Somatogravic illusion...............................................17-7
 

The leans...................................................................17-7
 

vestibular system..........................................................17-6
 

VFE ..............................................................................11-18
 

VFR terminal area charts .............................................16-2
 

VFR waypoints ..........................................................16-33
 

Vg diagram...................................................................5-37
 

Viscosity ........................................................................4-2
 

Visibility ....................................................................12-17
 

Vision in flight...........................................................17-19
 

Visual approach slope indicator (VASI)....................14-16
 

visual flight rules (VFR) ..............................................16-1
 

Visual glide slope indicators......................................14-16
 

Visual illusions.............................................................17-8
 

Autokinesis...............................................................17-8
 

False horizon ............................................................17-8
 

VLE..............................................................................11-18
 

VLO..............................................................................11-18
 

VNE..............................................................................11-19
 

VNO .............................................................................11-19
 

VOR/DME RNAV.....................................................16-28
 

Vortex avoidance procedures.....................................14-28
 

Vortex behavior .........................................................14-27
 

Vortex generation.......................................................14-26
 

Vortex strength...........................................................14-27
 

VS0 ..............................................................................11-18
 

VS1 ..............................................................................11-18
 

V-Tail.............................................................................6-8
 

VX ...............................................................................11-18
 

VY ...............................................................................11-18
 

W 

Wake turbulence ................................................ 5-9, 14-26
 

Warning areas ..............................................................15-4
 

Water refraction .........................................................17-10
 

WCA ..........................................................................16-10
 

Weather........................................................................12-1
 

Weather avoidance assistance....................................13-18
 

Weather briefings.........................................................13-5
 

Abbreviated briefing.................................................13-5
 

Outlook briefing .......................................................13-5
 

Standard briefing ......................................................13-5
 

Weather charts ...........................................................13-13
 

Significant weather prognostic charts....................13-15
 

Surface analysis chart.............................................13-13
 

Dew point............................................................13-13
 

Present weather..................................................13-13
 

Pressure change/tendency ..................................13-13
 

Sea level pressure ...............................................13-13
 

Sky cover.............................................................13-13
 

Temperature........................................................13-13
 

Wind....................................................................13-13
 

Weather depiction chart..........................................13-15
 

Weather check............................................................16-17
 

Weather products age and expiration.........................13-18
 

Weight.......................................... 5-1, 5-2, 5-8, 5-40, 10-2
 

Weight and balance............................................ 5-40, 10-4
 

Weight and balance computations............................10-5
 

Weight and balance restrictions ...............................10-6
 

Weight and loading distribution.....................................9-3
 

Weight control .............................................................10-1
 

Weight-shift-control.....................................................1-15
 

Wind correction angle (WCA)...................................16-16
 

Wind direction indicators...........................................14-20
 

Wind patterns...............................................................12-7
 

Winds and temperature aloft forecast (FB)................13-13
 

Winds and temperatures aloft ......................................13-5
 

Wind shear
 

Low-level wind shear.............................................12-11
 

Wind shifts.................................................................12-21
 

Wind sock ..................................................................14-20
 

Wind triangle .............................................................16-13
 

Winglets .........................................................................4-9
 

Wings .............................................................................3-3
 

Wingtip vortices.............................................................5-8
 

World aeronautical charts ............................................16-2
 

WSR-88D NEXRAD radar..........................................13-3
 

Y 

Yaw..............................................................................5-13
 

Yawing.........................................................................5-19
 

Yaw String ...................................................................8-18
 

Z 

Zero fuel weight.........................................................10-10
 

I-10