# Presentation: 334734

## AC 120.91: 

- Airport Obstacle Analysis

- Presented to: FLIGHT STANDARDS SERVICE
- By: AFS-400
- Date:  August 3, 2006

**Notes:**
Welcome/Intros...AFS-420
We are going to talk about AC 120.91...airport obstacle analysis
intent is not to make POIs TERPS experts or aircraft performance engineers
intent is to acquaint them with the methodologies and processes contained in the AC the Airlines have been using for years
The subject has resulted in much confusion for FS Inspectors and this briefing hopefully will clarify that
Ask that you hold questions till the end...
First lets look at the AC’s stated PURPOSE...>

## PURPOSE

**This AC Describes Acceptable Methods And Guidelines Re: Takeoff And Initial Climb-out Airport Obstacle Analysis **
**Complies With The Intent Of The Regulatory Requirements Of CFR Part 121, Part 135 **
**Two Methods For The Development Of Engine Out Procedures (EOPS). **

**Notes:**
This AC principally  does two things...
1st This AC Describes Acceptable Methods And Guidelines For Developing Takeoff And Initial Climb-out Airport Obstacle Analyses And In-flight Procedures considering engine out operations
2nd It describes the development of  Specific Engine Out Procedures or EOPs 
Complies With The Intent Of The Regulatory Requirements Of CFR Part 121, Part 135 And Other Associated One-engine-inoperative (OEI) Airplane Performance Requirements Relating To Turbine Engine Powered Airplanes and Prescribes Two Methods For The Development Of Engine Out Procedures (EOPS). 
This AC is really the “only game in town” that the airlines have...
And it provides very useful GUIDELINES...>

## EOP DEVELOPMENT GUIDELINES 

**Derived from Extensive FAA and Industry Experience **
**Been Used by the Industry for over 13 Years as a DRAFT Document**
**Signed by AFS-1 on May 5, 2006**
**Applies to Operations Conducted Under Part 121 and Operations of Large Transport and Commuter Category Airplanes Conducted Under Part 135 **

**Notes:**
Derived from Extensive FAA and Industry Experience 
Been Used by the Industry for over 13 Years as a DRAFT Document
Signed by AFS-1 on May 5, 2006
Applies to Operations Conducted Under Part 121 and Operations of Large Transport and Commuter Category Airplanes Conducted Under Part 135 
 To understand the intent of the AC We need to examine a few REGULATIONS..>

## APPLICABLE REGULATIONS

**Sections 121.177, 121.189, 135.367, 135.379, And 135.398**
**The Takeoff Flightpath Must Meet The Specified Obstacle Clearance Requirements In The Event Of An Engine Failure. **
**CFR Part 97 Applies To Standard Instrument Approach Procedures**

**Notes:**
These Regs... Specify Required Takeoff and Performance Operating Limitations for airplanes that experience an engine failure. 
They Include How to Determine That the Takeoff Flightpath meets Specified Obstacle Clearance Requirements in the Event of an Engine Failure
CFR Part 97 Applies To Standard Instrument Approach Procedures..It makes IAPs regulatory...
The criteria used to develop IAPs is called TERPS
The criteria used to develop EOPs is aircraft performance data found in the regulations
It’s Important We Understand what the Flight Standards Responsibilities are Regarding the development and use of  Standard IAPs and how they relate to engine out OPERATIONS...>

## INSTRUMENT PROCEDURES

**§ 97.20  Prescribes Standard Instrument Procedures And Weather Takeoff Minimums: **
**Based On The Criteria Contained In FAA Order 8260.3, U.S. Standard For Terminal Instrument Procedures (TERPS),**
**Other Related Orders In The 8260 Series**

**Notes:**
All together, Part 97 Prescribes Standard Instrument Approach Procedures For Instrument Letdown To Airports In The United States And The Weather Minimums That Apply To Takeoffs And Landings Under IFR At Those Airports.
This Subpart, 97.20 Prescribes Standard Instrument Procedures And Weather Takeoff Minimums Based On The Criteria Contained In FAA Order 8260.3, U.S. Standard For Terminal Instrument Procedures (Terps), And Other Related Orders In The 8260 Series That Also Address Instrument Procedure Design Criteria such as 8260.19C.
So what is Flight Standard’s role in the world of instrument PROCEDURES?>

## AFS-1 RESPONSIBILITY

**The **_**Use**_** Of Air Navigation Facilities, Appliances, And Systems By Aircraft Operating In Established Environments And The National Airspace System (NAS).**
_**Policy**_** And Oversight Of Manual And Automated Development And Maintenance Of Terminal And En Route Flight Procedures. **

**Notes:**
The Flight Standards Service is Responsible For The Use (Operative word) Of Air Navigation Facilities, Appliances, And Systems By Aircraft Operating In Established Environments And The National Airspace System (NAS).
Responsibility Includes Governing Policy (Operative word) And Oversight Of Manual And Automated Development And Maintenance Of Terminal And En Route Flight Procedures. AFS-400...>

## FLIGHT TECHNOLOGIES AND PROCEDURES DIVISION (AFS-400) RESPONSIBILITY.

**Policies, Criteria, And Standards For Establishing And Maintaining Terminal And En Route Flight Procedures**
**Final Authority To Issue, Amend And Appeal Standard Instrument Approach Procedures Under 14 CFR Part 97. **
**“****Special” Instrument Approach Procedures**
**Requests For Waivers Of Standards.**

**Notes:**
Is The Principal Element Of The Flight Standards Service Governing Policies, Criteria, And Standards For Establishing And Maintaining Terminal And En Route Flight Procedures
The Division Is Also Responsible For Approval/Disapproval Of Special Instrument Approach Procedures And Requests For Waivers Of Standards. AFS- 410, the Flight Operations BRANCH...>

## AFS-410 RESPONSIBILITIES

**Operational And Flight Technical Aspects Of All Weather Operations. **
**Develops Operational Mitigations for Waivers of Standards**
**Category I, II, And III Approach And Landing Operations Policy, As Well As Lower Than Standard Takeoff Minimums.**

**Notes:**
Is The Principal Element Of The Division With Respect To Concepts, Policies, Systems, And Programs Associated With The Operational And Flight Technical Aspects Of All Weather Operations. They do Operational “sanity” checks if you will on waiver requests and Special IAPs 
Also Develops Concepts For Design, Evaluation, And Approval Of Category I, II, And III Approach And Landing Operations, As Well As Lower Than Standard Takeoff Minimums. AFS-420, The Flight Procedures Standards BRANCH...>

## AFS-420,  RESPONSIBILITIES

**Rulemaking Process **
**Develops Criteria Pertinent To The Design Of Instrument Flight Procedures**
**Testing, Data Analysis, Verification, And Validation**
**The Technical Evaluation And Risk Assessment Of Proposed Instrument Operations Not Covered By Standard Criteria.**

**Notes:**
AFS-420, Is The Principal Element Within The Division, With Respect To The Rulemaking Process (i.e. Part 97) Of The Flight Procedures Program 
Responsible For The Development Of Criteria Pertinent To The Design Of Instrument Flight Procedures
It Also Provides For The Technical Evaluation And Risk Assessment Of Proposed Instrument Operations Not Covered By Standard Criteria.
AFS-420 is the primary interface between Flight Standards and what used to be AVN, Aviation System Standards 
AVN is now AJW...>

## TECHNICAL OPERATIONS AVIATION SYSTEM STANDARDS OFFICE (AJW-3).

**AJW (Formally AVN) Directly Responsible For:**
**AJW-32 (AVN-100) Development/ Maintenance Of Instrument Flight Procedures **
**AJW-33 (AVN-200) The In-flight Inspection Of Air Navigation Facilities**
**AJW-35 (AVN-500), Production/ Distribution Of Aeronautical Charts, Related Publications And Products **

**Notes:**
AJW Is The Principal Element Within Airway Facilities Service which falls under the Air Traffic Organization, Directly Responsible For The In-flight Inspection Of Air Navigation Facilities And For The Development And Maintenance Of Instrument Flight Procedures Throughout The United States And Its Territories.  Specifically:
AJW-32 (AVN-100) Development/ Maintenance Of Instrument Flight Procedures...these are the guys who build Instrument procedures 
AJW-33 (AVN-200) The In-flight Inspection Of Air Navigation Facilities
AJW-35 (AVN-500), Is The AVN Element Responsible For The Production And Distribution Of Aeronautical Charts And Related Publications And Products 
They are also referred to as the National Aeronautical Charting Office or NACO
So all these lines of business are involved in the development of instrument procedures, but it is important to understand that there are several different types of PROCEDURES...>

## TYPES OF PROCEDURES

**Public IAPs: CFR Part 97 (Regulatory), TERPS, Flight Checked>AFS-1**
**Special IAP’s: Order 8260.19C (Enabled), TERPS, Flight Checked>AFS-400**
**SIDs, STARs: TERPS, Flight Checked> National FLIGHT Data Digest (NFDD)**
**Charted Visual Flight Procedures (CVFPs): NFDD**
**Engine Out Procedures (EOPs): Developed By Operator, Accepted By POI**

**Notes:**
Public IAPs: CFR Part 97 (Regulatory-Incorporated by Reference), TERPS, Flight Checked>Approved by AFS-1
Special IAP’s: Order 8260.19C (Enabled-also regulatory), TERPS, Flight Checked>Approved by AFS-400
SIDS Developed by AJW STARS Developed by Air Traffic, Flight checked,  TERPS Criteria is used for obstacle assessment>Published in NFDD
Published in NATIONAL FLIGHT DATA DIGEST- A daily (except weekends and Federal holidays) publication of flight information appropriate to aeronautical charts, aeronautical publications, Notices to Airmen, or other media serving the purpose of providing operational flight data essential to safe and efficient aircraft operations
CVFPs: are not instrument approaches and do not have missed approach segments. Rwy 19 River approach at DCA...never flight checked, has no missed approach segment and would not meet TERPS criteria
ATC will not issue clearances for CVFPs when the weather is less than the published minimum. DCA is 2 miles. SFO Quiet Bridge is 5 miles
Engine Out Procedures (EOPs): Developed By Operator, Accepted By POI
So.....with all these the regulations in place.... why do we need an AC?...>

## WHY AC 120.91 WAS DEVELOPED

**CFR Part 25 Provides Requirements For Establishing The Airplane Flight Manual (AFM) Performance Data.**
**Provides Detailed Instructions for Determining ****Vertica****l Obstacle Clearance Requirements.**
**Offers ****Little**** Guidance On The ****Lateral ****Or Horizontal Clearance Requirements.**

**Notes:**
While The AFM Required by CFR Part 25, Provides Detailed Instructions For Determining The Vertical Clearance, It Offers Little Guidance On The Lateral Or Horizontal Obstacle Clearance Requirements.
  This AC Provides Information For Determining Safe Horizontal Clearance From Obstacles For The Actual Flightpath 
  It Also Provides Guidance And Acceptable Lateral Criteria To Assist An Operator In Developing EOPs 
So with this in mind...lets first look at the Regulatory Vertical Obstacle Clearance REQUIREMENTS...>

## FOR TWO ENGINE TURBOJET AIRCRAFT
CFR Part 25: Min Gross Flight Path: 2.4%
CFR Part 25: Min Net Flight Path: 
	2.4% - 0.8% = 1.6% (62.5:1 Slope)
CFR Part 121.189.D(2): Net Flight Path Must Clear All Obstacles By 35 Feet Vertically

**CFR Part 25: Min *****Gross***** Flight Path: 2.4%**
**CFR Part 25: Min *****Net***** Flight Path: **
**	****2.4% - 0.8% = 1.6% (62.5:1 Slope)**
**CFR Part 121.189.D(2): *****Net *****Flight Path Must Clear All Obstacles By 35 Feet Vertically**

**EOP CRITERIA: VERTICAL**

**Notes:**
CFR 25 talks about something called Gross and Net flight path
Its an Aircraft certification requirement
All this really means is the aircraft must have the performance to get up and go and clear obstacles
CFR Part 25: Prescribes a Min Gross Flight Path: 2.4%
CFR Part 25: Prescribes a Min Net Flight Path: which is the Gross Minus 0.8% to = 1.6% (62.5:1 Slope)
And the Net flight path must clear all obstacles by 35 feet
 What does this really mean? The FAA recognized long ago that A/C performance from the manufacturer was based on brand new aircraft , trimmed engines, company test pilots 
So it simply provides this 0.8%  safety “buffer”
these numbers happen to apply to two engine Part 25 turbojets...there are other values in Part 25 for 3 and 4 engine turbojets
But don’t worry about them because we have a PICTURE...>

## FAA OBSTACLE EVALUATION (OE)  CRITERIA

- 35’

- V2

- VR

- V1

**1****st**

**1500’ AGL**
**CFR Part 25.111.a**

**Gross Path (CFR**)

**Net Path (CFR) (Gross - 0.8%)**

**35’ min**

**35’ min**

**Accelerate-stop or**
**1 Engine take-off distance**

- Existing
- Man-made obstacle

- Existing
- Terrain obstacle

**Accelerate**

**Final Climb**

**Min 400’ AGL**

**CFR Take-off Flight Path**

**2nd**

**3rd**

**Notes:**
We start with the runway and continue through the three climb segments
... airplane accelerates through V1, rotates at VR and must reach V2 before it is 35 feet above the takeoff surface.
The point at 35’ is also called “reference zero” Because that is when Segment One begins. Segment One Begins at 35’ and The airplane should climb out at a speed as close as practical to, but not less than, V2 speed until the selected acceleration height is reached. 
The first segment climb ends at gear retraction with a positive climb established

2.In Segment  two...the Gear is up V2 speed constant with a 2.4% min climb gradient 
The acceleration height is chosen by the operator but may not be less than 400 feet. 

3. Segment three ... After the airplane reaches the acceleration
Height of 400’, the Third and Final climb segments begin with the transition to en
route climb configuration The operator has considerable
latitude in choosing the transition method. One extreme is to climb directly over the
obstacle at V2, with takeoff flaps and takeoff thrust. The
opposite extreme is to level off at the selected acceleration
height, accelerate in level flight to the flaps-up climb speed, and then continue
climbing and reducing thrust to MCT. An infinite
variety of flightpaths between these two extremes may
be used. In any event, the flightpath chosen to show
obstacle clearance must extend to the end of the takeoff
flightpath. The takeoff flightpath ends not lower than
1,500’for Part 25, and commuter category
airplanes.

Now we have covered the vertical...lets talk about horizontal obstacle CLEARANCE...>

## CFR Part 121.189 (Some Major US Carriers)

- 200’

- 200’

- 200’

- 220’

- 200’

- 300’

- 300’

- 300’

- 300’

**Net Takeoff Flight Path=212’**

**Notes:**
So what does Horizontal One Engine Inop Special Departure Criteria mean?
It means we shall ensure that there are no obstacles that will effect the aircraft Net Flight Path with an engine failure
Some US Carriers Use solely this CFR guidance of 200/300’ Obstacle Clearance
Part 121.189 requires a net takeoff flight path that clears all obstacles by at least 200’ horizontally within the airport boundaries and by at least 300 feet horizontally after passing the boundaries...
 The Flight Standards Interpretation and policy on this is that the net takeoff flight path includes the wingspan of the airplane
 So a B-747 with say a 212’ wingspan would have to clear obstacles after the airport boundaries by a minimum of 300’ laterally on either end
August, 1941..takeoff visibilities where so high pilots could visually maintain track...very tight...RNP Buffs...=.0494 
 Because of these issues, Most US Operators use a more conservative approach regarding obstacle clearance
This is what this AC is all ABOUT...>

## EOP CRITERIA: HORIZONTAL

**AC-120.91 (Most Major US Carriers)**
**Incorporates Best Industry Practices To Provide An Operationally Realistic Horizontal Clearance Plane**
**16:1 ‘Splay’ Reaching Maximum +/- 2000’ **
**ICAO (Some Major US Carriers And CFR 129)**
**8:1 ‘Splay’ Reaching Maximum +/- 3000’**

**Notes:**
This AC fills in the gaps...used by most US Carriers..
16:1 ‘Splay’ Reaching Maximum +/- 2000’
Incorporates Best Industry Practices To Provide An Operationally Realistic Horizontal Clearance Plane
Some US Carriers Use and Part 129 Foreign Carriers Use a more conservative 8:1 splay reaching a max of =/- 3000’
These are hard concepts...... I mean who invented the word “splay” anyway
But Don’t worry I have another PICTURE...

##  FAA OE CRITERIA

- ICAO splay

- AC splay

- 4800’

- 16:1

- 8:1

- 3000’

- 2000’

- Runway

- 300’ + wing span

- 32,000’

- 21,600’

**(FAR / AC / ICAO)**

- CFR

** ****FAA OE CRITERIA**

**Notes:**
CFR...200/300 CFR either side of the intended flight path...
AC 120.91 SPLAY...
ICAO SPLAY...
We have been talking about OEI EOPs...and Horizontal or Lateral Protection from obstacles 
There is a whole other animal in this business...called Obstruction Evaluation, done by the FAA
It is embodied in an entirely different process than we have been discussing...we have been discussing aircraft engine out performance requirements which are stand alone regulatory requirements...
Because it involves all engines operating...and is the normal way the FAA evaluates present and future obstacles in procedure design
We are talking about TERPS...>

## OBSTRUCTION EVALUATION CRITERIA

**FAA Order 8260.3b (TERPS)**
**Various Horizontal And Vertical Protection Surfaces **
** ****Vertical Surface: 200 Ft/Nm **
**	****>Obstacle Identification Surface (OIS, Net Surface) Of 40:1 **
**Horizontal Surface Typically ‘Splays’ At A 15 Deg Angle, Typical Maximum +/- 2 Nm**

**OBSTRUCTION EVALUATION CRITERIA**

**Notes:**
Order 8260.3b, Terps..is a standardized method for designing instrument flight procedures to avoid obstacles.  Briefly...TERPS describes...
 Various Horizontal And Vertical Protection Surfaces For All-engine Instrument Procedure Design
 The Vertical Surface Is Typically Represented By A Gross Climb Of 200 Ft/Nm And An Obstacle Identification Surface (OIS) or Net Surface) Of 40:1 
The 200 f//nm comes from adding the 152 f/nm (40:1) with the 48 ft/nm obstacle clearance safety factor.
The Horizontal Surface Typically ‘Splays’ At A 15 Deg Angle, Typical Maximum +/- 2 Nm
Reason we’ve briefly reviewed what TERPS criteria is important because of the differences
With CFR performance CRITERIA...>

## TERPS CRITERIA VERSUS ONE-ENGINE-INOPERATIVE (OEI) REQUIREMENTS

**Sids Or DPs: TERPS Or ICAO PANS-OPS As Normal (All Engines Operating) Operations **
_**Independent **_**and **_**Exclusive**_
**EOPs Do **_**Not**_** Need To Meet TERPS Requirements **
**Does Not Assure That OEI Obstacle Clearance Requirements Are Met. **

**Notes:**
Its easy to get confused by these differences...
Sids Or DPs Are Based On TERPS Or ICAO PANS-OPS) As Normal (All Engines Operating) Operations 
Thus, OEI Obstacle Clearance Requirements And The All-engines-operating TERPS Requirements Are Independent and Exclusive
EOPs Do Not Need To Meet TERPS Requirements 
Further, Compliance With TERPS All-engines-operating Climb Gradient Requirements Does Not Necessarily Assure That OEI Obstacle Clearance Requirements Are Met.
To  Continue...>

## TERPS CRITERIA VERSUS (OEI) REQUIREMENTS (CONT’D)

**TERPS: All-Engines-Operating Climb Gradients To An Altitude In A **_**Linear**_** Fashion**
**Engine Out Airplane Performance Requirements Are **_**Segmented**_
**TERPS: 200 F/NM**
**Operators **_**Must**_** Comply With 14 CFR Requirements **
**Differences Between TERPS And Engine Out Criteria**
***An Engine Failure During Takeoff Is A Non-normal Condition, And Therefore Takes Precedence Over Noise Abatement, Air Traffic, Sids, Dps, And Other Normal Operating Considerations.***
***  ***

**Notes:**
TERPS Typically Use Specified All-Engines-Operating Climb Gradients To An Altitude In A Linear Fashion
	Rather Than Certificated OEI Airplane Performance Requirements Which Are Segmented
	Operators Must Comply With 14 CFR Requirements For The Development Of Takeoff Performance Data And Procedures.
TERPS Typically Assume A Climb Gradient Of 200 F/NM Unless A Greater Gradient Is Specified.
Operators Must Comply With 14 CFR Requirements 
To Account for the Differences Between TERPS And Engine Out Criteria Including The Lateral And Vertical Obstacle Clearance Requirements. This is what we call in the business...”The Numbers”... 
The bottom line... Is that An Engine Failure During Takeoff Is A Non-normal Condition, And Therefore Takes Precedence Over Noise Abatement, Air Traffic, Sids, Dps, And Other Normal Operating Considerations.

With these concepts in mind let’s look at what EOPs are NOT

## WHAT EOPs ARE NOT

**EOPs are **_**NOT**_**  TERPS Or PANS-OPS Criteria**
**EOPs Do **_**Not **_**Provide Takeoff Data**
**EOPs Do **_**Not**_** Provide Standard ATC Departure **
**EOPs Are **_**Not**_** Developed or “Flight Checked” **
**EOPs Are **_**Not**_** Promulgated Under CFR Part 97**
**EOPs Are **_**Not**_** “Approved” By The FAA they Are “**_**Accepted”**_** **
**And... if the EOP is Associated With a “Special” IAP That Involves Unique Terrain or Pilot Flight Skills the Following Applies:**

**Notes:**

EOPS are Not Developed According To TERPS Or PANS-OPS Criteria
EOPs Do Not Provide Takeoff Data (Decision & Performance Airspeeds)...just Limiting Gross Weights
EOPs Do Not Provide Standard ATC Departure Routing...engine-out (Similar Degrade) Emergency Use Only
EOPs Are Not Developed or “Flight Checked” By AJW Using AFS-420 Criteria 
Are Not Promulgated Under CFR Part 97 (Not Incorporated by reference)
Therefore EOPs Are Not “Approved” By The FAA they Are “Accepted” By The FAA POI (Like Portions of the AFM) 
And... if the EOP is Associated With a “Special” IAP That Involves Unique Terrain or Pilot Flight Skills the Following APPLIES...>

## FAA FORM 8260-10

**AFS-410, FLIGHT OPERATIONS BRANCH, FAA FORM 8260-10**
- >>**The POI Shall Not Issue Ops Specs To An Operator Authorizing This Special IAP Until At Least The Following Two Conditions Are Met To The Satisfaction Of The AWOPM That Has Geographic Responsibility For This Special IAP:**
**The Operator Shall Develop An Engine-out Procedure (EOP) For This Special IAP, And;**
**The Operator Shall Have Fully Implemented The EOP For This Special IAP In The Operator’s Dispatch System, Flight Operations Manuals (As Appropriate) Training Program And Aircraft Maintenance Program (As Appropriate). **

**Notes:**
With the special procedure package will be AFS-410, FLIGHT OPERATIONS BRANCH, FAA FORM 8260-10 which states

>>The POI Shall Not Issue Ops Specs To An Operator Authorizing This Special IAP Until At Least The Following Two Conditions Are Met To The Satisfaction Of The AWOPM That Has Geographic Responsibility For This Special IAP:
1.	The Operator Shall Develop An Engine-out Procedure (EOP) For This Special IAP, And;
2.	The Operator Shall Have Fully Implemented The EOP For This Special IAP In The Operator’s Dispatch System, Flight Operations Manuals (As Appropriate) 	Training Program And Aircraft Maintenance Program (As Appropriate). 

We’ve seen what EOPs are not
Lets look at what they ARE...

## WHAT EOPs ARE

**Use CFR Performance Requirements And Concepts, **
**Can Increase Allowable Pax/Cargo Load And Safety Margins**
**Provide Escape Routing (When Necessary)**
**Developed By The Operator**

**Notes:**
Use CFR Performance Requirements And Concepts, 
AFM Information and Other Aircraft Performance Data
Can Increase Allowable Pax/Cargo Load And Safety Margins....the primary reason for developing these procedures is to maximize the takeoff weight...
Provide Escape Routing (When Necessary) From Normal ATC Departure Routing In The Event Of An Engine Loss Or Similar Performance Degrade
Developed By The Operator’s Performance Engineering Department Or External Source Contractors NOT the FAA
So lets see what goes in to EOP Development PROCESS...>

## ENGINE – OUT DEPARTURE PROCEDURE DEVELOPMENT

**Should Consider That An Engine Failure May Occur At **_**Any Point**_** On The Departure Flightpath.**
**Use An EOP Routing In The Event Of An Engine Failure On Takeoff.  **
**Obstacles Along This Track Are Used To Determine The Maximum Allowable Takeoff Weight For That Runway**.

**Notes:**
First,,, In Order For An Operator To Determine That A Departure Maintains The Necessary Obstacle Clearance With An Engine Failure, The Operator Should Consider That An Engine Failure May Occur At Any Point On The Departure Flightpath.
Second... The Most Common Procedure To Maximize Takeoff Weight When Significant Obstacles Are Present Along The Normal Departure Route Is To Use A EOP Routing In The Event Of An Engine Failure On Takeoff.  
Obstacles Along This Track Are Used To Determine The Maximum Allowable Takeoff Weight For That Runway
The most important consideration for an Operator developing these procedures is the determination of OBSTACLES

## OBSTACLE CONSIDERATIONS 

**Use The Best And Most Accurate Available Obstacle Data For A Particular Airport At The Time Of Analysis. **
**Frangible Structures **
**Indeterminate Objects (Objects Without Recorded Height; E.G. Trees) **
**Operators Shall Take Into Account Local Temporary Or Transient Obstacles**

**Notes:**
The AC provides this guidance when considering Obstacles...
-Frangible structures need not be considered in an obstacle analysis.
-Operators should use reasonable judgment to account for the height of indeterminate objects (objects without recorded height) 
-Operators shall take into account local temporary or transient obstacles such as ships, cranes, or trains. 
There are many sources of Obstacle DATA...>

## SOURCES OF OBSTACLE DATA

**NOS Airport Obstruction Chart (OC)**
**FAA Form 5010**
**Topographical Quadrangle Charts**
**Jeppesen/Lido Departure & Approach Charts**
**National Flight Data Digest**
**IFR Supplement (USAF)**
**Low Altitude Instrument Approach Charts (DoD)**
**Aeronautical Information Publication (AIP)**
**ICAO Type A/B/C Charts (TPC)**
**USGS 3 Arc Second Terrain Data**
**USGS 1 Arc Second Terrain Data**
**Digital Vertical Obstacle File (DVOF)**
**Digital Terrain Elevation Data (DTED)**
**National Geodetic Survey (NGS)**
**Area Navigation Approach Survey (ANA)**
**NOTAMs **

**Notes:**
These are sources of Obstacle Data...
Of primary importance in the EOP analysis is determining the end of  the takeoff SEGMENT..>.

## TERMINATION OF TAKEOFF SEGMENT 

**The End Of The Takeoff Flightpath Is Considered To Occur When:**
**Reached The MCA; Or**
**Able To Comply With En Route Obstacle Clearance Requirements; Or **
**Reached The MVA**
**When Determining The *****Limiting***** Takeoff Weight...**

**Notes:**
For The Purpose Of The Takeoff Obstacle Clearance Analysis, The End Of The Takeoff Flightpath Is Considered To Occur When:
-The Airplane Has Reached The MCA At A Fix Or MEA For A Route To The Intended Destination; Or
-The Airplane Is Able To Comply With En Route Obstacle Clearance Requirements; Or 
-The Airplane Has Reached The MVA, Or A Fix And Altitude From Which An Approach May Be Initiated. 
-When Determining The Limiting Takeoff Weight, The Obstacle Analysis Should Be Carried Out To The End Of The Takeoff 	Segment As Defined Above.

- One of the primary purposes of this AC is to provide clear methods of ANALYSIS...>

## METHODS OF ANALYSIS 

**The Net Takeoff Flightpath Must Clear All Obstacles By 35 Feet Vertically And 200/300 Feet Laterally **
**This AC Focuses On **_**Two**_** Methods That May Be Used To Identify And Ensure Clearance Of Critical Obstacles:  **
**The Area Analysis Method**
**The Flight Track Analysis Method. **

**Notes:**
Sections 121.189, 135.379, And 135.398 Require That The Net Takeoff Flightpath Clears All Obstacles By Either 35 Feet Vertically Or 200 Feet Laterally Inside The Airport Boundary, Or 300 Feet Laterally Outside The Airport Boundary. 
We’ve mentioned the CFR Net Takeoff VERTICAL Flight path requirements
This AC Focuses On Two Methods That May Be Used To Identify And Ensure Clearance Of Critical Obstacles:  
1. The Area Analysis Method 
2. The Flight Track Analysis Method.

Let’s first look at the Area Analysis METHOD...>

## THE AREA ANALYSIS METHOD 

**Defines An Obstacle Accountability Area (OAA) **
**The Minimum Width Of The OAA Is 200/300 Feet On Each Side Of The Intended Track **
**The Maximum Width Of The OAA Is 2,000 Feet On Each Side Of The Intended Track. **

**Notes:**
The Area Analysis Method Defines An Obstacle Accountability Area (OAA) Within Which All Obstacles Must Be Cleared Vertically. The OAA Is Centered On The Intended Flight Track with a min of 200/300 and a max of 2000’.
Lets try to picture THIS...

## OAA: STRAIGHT OUT DEPARTURES

**Notes:**
Starting at the runway...the 200’/300’ corridor is regulatory and controlling...Then at 4,800’ the 16:1 splay meets the 300’ edge of the corridor and begins to spread out.
The Width Of The OAA Is 0.0625D Feet On Each Side Of The Intended Track (Where D Is The Distance Along The Intended Flightpath From The End Of The Runway In Feet), Except When Limited By The Minimum And Maximum Widths of 200/300’ at the airport and 2000’ at 30,000’ from the runway where it parallels the flight track....
This is the Area Analysis method for a straight out departure
Lets look at the Area Analysis method when we are required to turn after DEPARTURE...>

## THE AREA ANALYSIS METHOD, CONT’D

**During ***Turns*** The Following Criteria Apply:**
**The Initial Straight Segment...**
**The Width Of The OAA At The Beginning Of The Turning Segment Is The Greater Of:**
**300 Feet On Each Side Of The Intended Track.**
**The Width Of The OAA At The End Of The Initial Straight Segment**
**The Maximum Width Of The OAA Is 3,000 Feet On Each Side Of The Intended Track.**

**Notes:**
During Departures Involving Turns Of The Intended Track Or When The Airplane Heading Is More Than 15 Degrees From The Extended Runway Centerline Heading, The Following Criteria Apply:
The initial straight segment, if any, has the same width as a straight-out departure.
The width of the OAA at the beginning of the turning segment is the greater of:
300 feet on each side of the intended track (regulatory requirement).
The width of the OAA at the end of the initial straight segment, if there is one.
The width of the end of the immediately preceding segment, if there is one, analyzed by the Flight Track Analysis Method ( which we will talk about in a second).

Lets look at a Picture of THIS...>

## OAA: TURNING DEPARTURES

**Notes:**
Starting from the runway...
same width as a straight-out departure
. at the beginning of the turning segment is the greater of:
-300 feet on each side of the intended track.
-The width of the OAA at the end of the initial straight segment, if there is one. You can hook ‘em together straight/turn or turn and straight
-Thereafter Turning Segments, The Width Of The OAA Increases By 0.125D Feet On Each Side Of The Intended Track (Where D Is The Distance Along The Intended Flightpath From The Beginning Of The First Turning Segment In Feet), Except When Limited By The Following Maximum Width: 
Which Is 3,000 Feet On Each Side Of The Intended Track
That was the area analysis method
Now lets look at an example of the area analysis METHOD...>

## AREA ANALYSIS METHOD

**Notes:**
 This is Colorado Springs...
Lets look at the Conventional missed approach...
the second analysis method called the flight track analysis METHOD..>. 

## FLIGHT TRACK ANALYSIS METHOD 

**The Flight Track Analysis Method Involves Analyzing The **_**Ground Track**_** Of The Flightpath.**
**Alternative Means Of Defining An OAA Based On The Navigational Capabilities Of The Aircraft. **

**Notes:**
The Flight Track Analysis Method Involves Analyzing The Ground Track Of The Flightpath

The Flight Track Analysis Method Is An Alternative Means Of Defining An OAA Based On The Navigational Capabilities Of The Aircraft.  This Methodology Requires The Operator To Evaluate The Effect Of Wind And Available Course Guidance On The Actual Ground Track. 

3. To CONTINUE...>

## FLIGHT TRACK ANALYSIS METHOD, CONT’D 

**Three Factors That The Operator Must Consider In Performing A Flight Track Analysis Are:**
**Pilotage In Turns  **
**Winds**
**Course Guidance**

**Notes:**
Three Factors That The Operator Must Consider In Performing A Flight Track Analysis Are:

Pilotage In Turns The Operator Should Consider The Ability Of A Pilot To Initiate And Maintain A Desired Speed And Bank Angle In A Turn. 

Winds. When Using The Flight Track Analysis Method While Course Guidance Is Not Available, Operators Should Take Into Account Winds That May Cause The Airplane To Drift Off The Intended Track. This method provides a tighter area of obstacle clearaance.  Wind factors are not required to be assessed in the area analysis method we previously looked at.
Course Guidance
One of the beautiful aspects of this method of analysis is you can utilize course GUIDANCE...

## COURSE GUIDANCE 

**Operators May Take Credit For Available Course Guidance**
**Allowance For Ground-based Course Guidance:**
**Localizer (Loc)—plus/Minus 1.25 Degree Splay **
**VOR—plus/Minus 3.5 Degree Splay **
**ADF—plus/Minus 5 Degree Splay **
**DME Fix—Plus/Minus 1 Minimum Instrument Display Increment But Not Less Than Plus/Minus 0.25 Nm.**

**Notes:**
Operators May Take Credit For Available Course Guidance When Calculating The Lateral Location Of The Actual Flight Track Relative To The Intended Track As Part Of A Flight Track Analysis.
The AC Provides this criteria...
DME fix...that one cracks me up...5 guys worked on this AC....

...but I like this next slide a lot...
To CONTINUE...>

## COURSE GUIDANCE, CONT’D

**Airplane Performance-based Area Navigation Capabilities.**
**Area Navigation Refers To A System That Permits Airplane Operations On Any Desired Course... **
**Minimum Allowance Is The System’s Demonstrated Accuracy**
_**Note:  Under No Circumstances Can The OAA Half-width Be Reduced To Less Than The Regulatory Minimums Of 200 Feet Within The Airport Boundaries And 300 Feet After Passing The Boundaries**_**. **

**Notes:**
- There Is Also Allowance For Airplane Performance-based Area Navigation Capabilities.
-Airplane-based Area Navigation Refers To A System (E.G., FMS, GPS, RNAV, RNP, IRS) That Permits Airplane Operations On Any Desired Course, Including A Turn Expansion For Flyby Or Flyover Waypoints, Without Direct Course Guidance From A Ground-Based NAVAID.
-The Minimum Allowance Is The Demonstrated Accuracy Of The Airplane-based Navigation Equipment

Note:  Under No Circumstances Can The OAA Half-width Be Reduced To Less Than The Regulatory Minimums Of 200 Feet Within The Airport Boundaries And 300 Feet After Passing The Boundaries. 

I love this analysis method. It is pilot friendly...
It lets me use my autopilot and makes my life easy...
Let’s take a look at an example of the Flight Track Analysis Method...>

## RENOILS or LOC RWY 16R

**Notes:**
This is the RENO ILS to 16R...this is a work in progress... 
Conventional ILS with a RNAV FMS Missed Approach
Lets Look at the Missed approach in greater detail..>

## RENO

**Notes:**

Lets look a video of this procedure...I consider this to be an elegant solution

## ALLOWANCE FOR VISUAL COURSE GUIDANCE 

**Visual Ground Reference Navigation Is Another Form Of Course Guidance. **
**To Laterally Avoid Obstacles By Visual Reference Can Be *****Very***** Precise**
**Must  Continuously Determine And Maintain The Correct Flightpath **
**Procedure Should Be Well Defined**

**Notes:**
Visual Ground Reference Navigation Is Another Form Of Course Guidance.  However, To Take Advantage Of Visual Course Guidance, A Flight Track Analysis Must Be Performed.
The Ability To Laterally Avoid Obstacles By Visual Reference Can Be Very Precise, because it is easy...Boston 9th Hole...If The Obstacles Can Be Seen And Are Apparent.  It Is The Operator’s Responsibility To Operate In Weather Conditions Consistent With The Use Of The Visual Ground Reference Points For The Navigation Upon Which The Obstacle Analysis Is Based.
To Take Advantage Of Visual Course Guidance, The Flightcrew Should Be Able To Continuously Determine And Maintain The Correct Flightpath With Respect To Ground Reference Points So As To Provide A Safe Clearance With Respect To Obstructions And Terrain.
The Procedure Should Be Well Defined With Respect To Ground Reference Points So That The Track To Be Flown Can Be Analyzed For Obstacle Clearance Requirements.
To CONTINUE...

##  VISUAL COURSE GUIDANCE, CONT’D 

**An Unambiguous Written And/Or Pictorial Description Of The Procedure Must Be Provided For Crew Use.**
**The Limiting Environmental Conditions Must Be Specified For The Use Of The Procedure**

**Notes:**
An Unambiguous Written And/Or Pictorial Description Of The Procedure Must Be Provided For Crew Use.
The Limiting Environmental Conditions (Wind, Ceiling, Visibility, Day/Night, Ambient Lighting, Obstruction Lighting, Etc.) Must Be Specified For The Use Of The Procedure So That The Flightcrew Is Able To Visually Acquire Ground Reference Navigation Points And Navigate With Respect To Those Points.
There are lots of other considerations, or I call “cats and dogs” when it comes to these procedures...

 Here are some additional CONSIDERATIONS...>

## ADDITIONAL CONSIDERATIONS 

**AFM Data Must Be Used For One-Engine-inoperative Takeoff Analysis. **
**Acceptable Data In Various Sources**
**Terrain And Obstacles At Certain Airports May Require A Higher-than-standard Cleanup Altitude To Be Used**

**Notes:**
Unless Otherwise Authorized, AFM Data Must Be Used For One-engine-inoperative Takeoff Analysis.  It Is Recognized That Many AFM’s Generally Contain Only The One-engine-inoperative  Performance For Loss Of An Engine At V1 On Takeoff To 1500’ AGL.
Operator’s May Find Appropriate Acceptable Data In Various Sources, Such As: Community Noise Documents, Performance Engineer’s Handbooks, Flight Characteristics Manuals, And Manufacturers’ Computer Programs.
The Terrain And Obstacles At Certain Airports May Require A Higher-than-standard Cleanup Altitude To Be Used And May Still Allow Acceleration And Cleanup To Be Accomplished Within The Takeoff Thrust Time Limit. 
Here’s some more CONSIDERATIONS...>

## ADDITIONAL CONSIDERATIONS, CONT’D

**Validation Flights:**
**Pre-Validation Flight Be Conducted In A Simulator **
**Acceptable Techniques Used For These Flights Include:**
**A Low Pass **
**Power Setting Representative Of One-Engine-Inoperative Conditions.**
**One Engine To Flight Idle**

**Notes:**
Consideration Should Be Given To Conducting A Validation Flight To Confirm Flightcrews’ Ability To Fly Actual, Special One-engine-inoperative Departures And To Uncover Any Potential Problems Associated With Those Procedures, Particularly If They Differ Significantly From The All-engines-operating Procedures, Or If Terrain Makes Course Guidance Questionable At The One-engine-inoperative  Altitudes.
If An Actual Validation Flight In An Airplane Is Required, It Is Recommended That A Pre-validation Flight Be Conducted In a Simulator To Simulate Actual Evaluation/Validation Conditions And ims are invaluable for these analysis.   Even if you don’t have the visual seen you have the aircraft performance capabilities...
Acceptable Techniques Used For These Flights Include:
Using A Power Setting On All Engines Calculated To Give A Thrust/Weight Ratio Representative Of One-engine-inoperative Conditions.
Setting One Engine To Flight Idle To Give A Thrust/Weight Ratio Representative Of One-engine-inoperative Conditions
Initiating The Procedure From A Low Pass Over The Runway At Configurations, Speeds, And Altitudes That Represent Takeoff Conditions.
Its extremely important to supply Flightcrews with clear unambiguous information on these EOPS...>

## FLIGHTCREW INFORMATION

**Flightcrew Instructions. **
**Flight Operations Bulletins, Revisions To Selected Flightcrew Manuals, Takeoff Charts, Notams, Or Special Ground Or Simulator Training.**
**Flightcrew Engine-out Briefings (Jepp 10-7)**
**EOP Routings **
**Transition From ATC IFR Departure To EOP Routing Is A Key Crew Coordination Item**

**Notes:**
Flightcrews Must Receive Instructions Through An Appropriate Means Regarding These Procedures. 
Based On The Complexity, This Instruction Could Be Done Through Flight Operations Bulletins, Revisions To Selected Flightcrew Manuals, Takeoff Charts, Notams, Or Special Ground Or Simulator Training.
EOPs Do Not Eliminate The Need For Flightcrew Engine-out Briefings (Jepp 10-7 Page)
How/When To Transition From ATC IFR Departure To SDP Routing Is A Key Crew Coordination Item
EOP Routings May Differ Significantly From ATC IFR Departure Routings For Terrain Considerations

To CONTINUE...>

## PILOT INFORMATION, CONT’D

**The Operator’s Instructions Should Advise Flightcrews Of at *****Least***** The Following:**
**Speeds And Bank Angles **
**Intended Track In Case Of Engine Failure. **
**When Flap Retraction And Thrust Reduction Are To Be Initiated.**
***[180kts(3 miles per min) x 500 F/Nm = 1500 fpm ]***

**Notes:**
The Operator’s Instructions Should Advise Flightcrews Of The Following (This May Be Accomplished As A General Policy For All Airports With Exceptions Stated As Applicable, Or Specified For Each Airport):
Speeds (Especially Relative To V2) And Bank Angles To Be Flown—all-engines-operating And One-engine-inoperative.
The Intended Track In Case Of An Engine Failure.  (Some Operators Have A Standard Policy Of Flying Runway Heading After An Engine Failure; Others Routinely Assume The All-engines-operating Ground Track Unless Specifically Stated Otherwise.)  In Any Case, The Intended Track Should Be Apparent To The Flightcrew, And Failure At Any Point Along The Track Should Be Taken Into Account.
The Points Along The Flightpath At Which The Flap Retraction Sequence And Thrust Reduction Are To Be Initiated.
NOTE:  Operators should incorporate procedures for converting required climb gradients to required climb rates in pilot and dispatcher airplane performance sections of their approved training programs. 

Now this AC addresses some very important concepts that significantly impact EOP procedure development
Namely that there is a difference in what a Missed approach is, what a rejected landing means, and what is a balked landing
Let’s take a LOOK...>

## MISSED APPROACHES, REJECTED LANDINGS, AND BALKED LANDINGS. 

**Parts 121 And 135 Do Not Address Missed Approaches Or Rejected Landings.**
**The *****Intent***** Is To Identify The Best Option For A Safe Lateral Ground Track And Flightpath To Follow**

**Notes:**

Parts 121 And 135 Do Not Specifically Require An Obstacle Clearance Analysis For One-engine-inoperative Missed Approaches Or Rejected Landings. The Missing Rule...Subpart I of 121 has rules for t/o, cruise and landing...
The Intent Is To Identify The Best Option Or Options For A Safe Lateral Ground Track And Flightpath To Follow In The Event That A Missed Approach, Balked Landing, Rejected Landing, Or Go-around Is Necessary.

To CONTINUE...>

## MISSED APPROACH VS REJECTED LANDING

**A One-Engine-Inoperative Missed Approach Can Frequently Be Flown Following The Published Missed Approach Procedure. **
** **
**Rejected Landing May Require Some Other Procedure**

**Notes:**
A One-engine-inoperative Missed Approach From The Minimum Descent Altitude (Height) (MDA (H)), Decision Altitude (Height) (DA (H)), Or Above Can Frequently Be Flown Following The Published Missed Approach Procedure.
A Rejected Landing From A Lower Altitude May Require Some Other Procedure (E.G., Following The Same One-engine-inoperative Procedure As Used For Takeoff). 

There is another animal called a balked landing...>

## ASSESSMENT CONDITIONS FOR BALKED LANDING 

**Starts At The End Of The Touchdown Zone (TDZ). **
**First One-third Of The Available Landing Distance Or 3,000 Feet, Whichever Is Less. **
**Operators May Propose To Use A Different Designation For A TDZ. **

**Notes:**
A “Balked Landing” Starts At The End Of The Touchdown Zone (TDZ). 
A TDZ Typically Is Considered To Be The First One-third Of The Available Landing Distance Or 3,000 Feet, Whichever Is Less. 
When Appropriate For The Purposes Of This Provision, Operators May Propose To Use A Different Designation For A TDZ. 

We’ve covered a lot of information in this IVT...and in SUMMARY...>

## SUMMARY

**AC-120.OBS is now AC-120.91**
**Takeoff and Initial Climb-Out Airport Obstacle Analyses and Engine Out Procedures.**
**Delineates Between TERPS And CFR Requirements **
_**Two**_** Methods That May Be Used To Identify And Ensure Clearance Of Critical Obstacles:  **
**The Area Analysis Method **
**The Flight Track Analysis Method. **

**Notes:**
AC-120.OBS is now AC-120.91
Describes Acceptable Methods and Guidelines for Developing Takeoff and Initial Climb-Out Airport Obstacle Analyses and Engine Out Procedures.
Delineates Between TERPS Criteria Versus One-Engine-Inoperative (OEI) CFR Requirements 
Focuses On Two Methods That May Be Used To Identify And Ensure Clearance Of Critical Obstacles:  
The Area Analysis Method 
The Flight Track Analysis Method. 
Now we will take your Questions or Comments?...>

## QUESTIONS AND COMMENTS

**Coby.Johnson@FAA.Gov**
- (202) 385-4670
- Phone Bridge Number for Questions and Answers:
- 	(202) 366-3920, passcode 4832.