# 0

U

. S. Department of Transportation Federal Aviation Administration 

# Advisory Circular

Subject: Approval of Flight Guidance Systems Date: I 0 /2 7/14 AC No: 25

. 1329-IC Initiated By: ANM-11 0

This advisory circular (AC) describes an acceptable means for showing compliance with certain requirements of Title 14, Code of Federal Regulations (CFR) 25.1329, Flight guidance systems. While part 25 contains the airworthiness standards applicable to transport category airplanes, the guidance in this AC pertains to the functions of autopilots , flight directors, and automatic thrust control as well as any interactions with stability augmentation and trim functions. This revision incorporates minor changes associated with issuance of the final rule for Airplane and Engine Certification Requirements in Supercooled Large Drop , Mixed Phase , and Ice Crystal Icing Conditions.

If you have suggestions for improving this AC , you may use the feedback form at the end ofthis AC.

Michael Kaszycki Acting Manager, Transport Airplane Directorate Aircraft Certification Service10/27/14 AC 25.1329

- 1C

CONTENTS Paragraph Page

ii INTRODUCTION

................................ ................................ ................................ ....................... 1 1. Purpose

................................ ................................ ................................ ............................. 1 2. Applicability

................................ ................................ ................................ .................... 1 3. Cancellation

................................ ................................ ................................ ..................... 1 4. Related Regulations, ACs, and Industry Documents

................................ ....................... 1

a. Regulations

................................ ................................ ................................ ................ 1 b. Advisory Circulars

................................ ................................ ................................ ..... 2

c. Related Industry Standards

................................ ................................ ........................ 4 d. Other FAA documents

................................ ................................ ............................... 4 5

— 10 [RESERVED]

................................ ................................ ................................ ............ 5
CHAPTER 1

. BACKGROUND

................................ ................................ ................................ ... 6 11. General

................................ ................................ ................................ ............................. 6

a. AC 25.1329

- 1C

................................ ................................ ................................ .......... 6 b. Scope

................................ ................................ ................................ .......................... 6 12. Evolution of FGS

................................ ................................ ................................ ............. 6

a. Complexity

................................ ................................ ................................ ................. 6 b. Guidance considerations

................................ ................................ ............................ 6 13

— 16 [RESERVED]

................................ ................................ ................................ ............ 6
CHAPTER 2

. OVERVIEW OF FLIGHT G UIDANCE SYSTEMS

................................ ................ 7 17. Purpose of FGS

................................ ................................ ................................ ................ 7 18. Components

................................ ................................ ................................ ..................... 7

a. Included in definition

................................ ................................ ................................ . 7 b. Excluded from definition

................................ ................................ ........................... 7 19. FGS Functions

................................ ................................ ................................ ................. 7

a. Elements of FGS

................................ ................................ ................................ ........ 7 b. Approach and landing system

................................ ................................ .................... 7

c. Flight management system

................................ ................................ ........................ 7 d. De sign philosophy

................................ ................................ ................................ ..... 8

e. Description of FGS behavior and operation

................................ .............................. 810/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

iii 20. Compliance with § 25.1329

................................ ................................ ............................. 8

a. General

................................ ................................ ................................ ....................... 8 b. Relevant paragraphs

................................ ................................ ................................ ... 8 21

— 26 [RESERVED]

................................ ................................ ................................ .......... 13
CHAPTER 3

. FGS ENGAGEMENT, DISE NGAGEMENT, INDICATIO NS, AND OVERRIDE

.. 14 27. Autopilot Engagement, Disengagement, and Indications

................................ .............. 14

a. Autopilot engagement

................................ ................................ .............................. 14 (1) Single switch action

................................ ................................ ........................ 14 (2) Engagement status of autopilot

................................ ................................ ....... 14 (3) Multiple autopilots

................................ ................................ .......................... 14 (4) Acceptable transients

................................ ................................ ...................... 14 (5) FD not en gaged

................................ ................................ ............................... 14 (6) FD engaged

................................ ................................ ................................ ..... 14 b. Autopilot disengagement

................................ ................................ ......................... 15 (1) Gen eral

................................ ................................ ................................ ............ 15 (2) Autopilot disengagement alerts

................................ ................................ ....... 16 (3) Quick disengagement control

................................ ................................ ......... 16 (4) Alternative means of autopilot disengagement

................................ ............... 17 (5) Flightcrew pitch trim input

................................ ................................ ............. 17 28. FD Engagement, Disen gagement, and Indications

................................ ........................ 18

a. FD engagement

................................ ................................ ................................ ........ 18 (1) General

................................ ................................ ................................ ............ 18 (2) Guidance cue(s)

................................ ................................ .............................. 19 (3) Reactive windshear guidance system

................................ .............................. 19 b. FD disengagement

................................ ................................ ................................ ... 19 29. Autothrust Engagement, Disengagement, and Indications

................................ ............ 19

a. Autothrust engagement

................................ ................................ ............................ 19 (1) Indication

................................ ................................ ................................ ........ 19 (2) Accessibility of controls

................................ ................................ ................. 1910/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

iv (3) Inadvertent engagement/disengagement

................................ ......................... 19 (4) Automatic engagement

................................ ................................ ................... 19 b. Autothrust disengagement

................................ ................................ ....................... 20 (1) Indication of disengagement

................................ ................................ ........... 20 (2) Inadvertent disengagement

................................ ................................ ............. 20 (3) Consequence of disengagement

................................ ................................ ...... 20 (4) Autothrus t quick disengagement control

................................ ........................ 20 30. Override of the FGS

................................ ................................ ................................ ....... 21

a. General

................................ ................................ ................................ ..................... 21 b. Autopilot override

................................ ................................ ................................ .... 21 (1) With automatic disengagement

................................ ................................ ....... 21 (2) Without automatic disengagement

................................ ................................ .. 21

c. Autothrust override

................................ ................................ ................................ .. 22 (1) Force required

................................ ................................ ................................ . 22 (2) Response to override

................................ ................................ ....................... 22 (3) Engagement status with override

................................ ................................ .... 22 31. FGS Engagement Mode Compatibility

................................ ................................ .......... 22

a. FGS mode engagement philosophy

................................ ................................ ......... 22 b. Engagement mode compatibility

................................ ................................ ............. 23 32

— 41 [RESERVED]

................................ ................................ ................................ .......... 2 3
CHAPTER 4

. CONTROLS, INDICATION S, AND ALERTS

................................ ..................... 24 42. General

................................ ................................ ................................ ........................... 24

a. Human

- machine interface

................................ ................................ ........................ 24 b. Design of controls, indications, and alerts

................................ ............................... 24

c. Evaluation of information provided by FGS

................................ ........................... 24 43. FGS Controls

................................ ................................ ................................ ................. 24

a. General

................................ ................................ ................................ ..................... 24 b. Design considerations

................................ ................................ .............................. 24 (1) Differentiation of knob shape and position

................................ ..................... 2410/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

v (2) Design to support correct selection of target values

................................ ....... 24 (3) Commonality across aircraft types

................................ ................................ .. 25 (4) Positioning of controls and related indications

................................ ............... 25 (5) Inadverten t operation

................................ ................................ ...................... 25 44. FGS Mode Selection, Annunciation, and Indication

................................ ..................... 25

a. Annunciation of engagement of the FGS

................................ ................................ . 25 b. Description of FGS modes

................................ ................................ ....................... 25

c. FGS mode annunciations

................................ ................................ ......................... 25 (1) Active and ar med modes

................................ ................................ ................. 25 (2) Location

................................ ................................ ................................ .......... 25 (3) Discriminators

................................ ................................ ................................ . 26 (4) Color

................................ ................................ ................................ ............... 26 d. Mode changes

................................ ................................ ................................ .......... 26 (1) Operationally relevant mode changes

................................ ............................. 26 (2 ) Attention

- getting features

................................ ................................ ............... 26 (3) Use of alerts

................................ ................................ ................................ .... 26

e. Failure to engage or arm

................................ ................................ .......................... 26 f. FGS mode display and indications

................................ ................................ .......... 26 45. FGS Alerting, Warning, Caution, Advisory, and Status

................................ ................ 27

a. Genera l

................................ ................................ ................................ ..................... 27 (1) Alerting provisions

................................ ................................ .......................... 27 (2) Determination of FGS capability

................................ ................................ .... 27 b. Speed protection alerts

................................ ................................ ............................. 27 (1) Alerts to crew

................................ ................................ ................................ .. 27 (2) Alert specifications

................................ ................................ ......................... 27 (3) Consistency

................................ ................................ ................................ ..... 27 (4) Nuisance alerts

................................ ................................ ................................ 27

c. Loss of autopilot approach mode

................................ ................................ ............. 27 d. Awareness of potential significant transient condition (“bark before bite”)

........... 28 (1) General

................................ ................................ ................................ ............ 2810/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

vi (2) Flightcrew alert(s)

................................ ................................ ........................... 28 (3) Situations to consider for an alert

................................ ................................ ... 28 46. FGS Considerations for HUDs

................................ ................................ ...................... 29

a. General

................................ ................................ ................................ ..................... 29 b. Characteristics of HUD guidance

................................ ................................ ............ 29 (1) Supplemental use displa y system

................................ ................................ .... 29 (2) External visual references

................................ ................................ ............... 29 (3) Interference and occlusion

................................ ................................ .............. 30 (4) Display criteria

................................ ................................ ................................ 30 (5) Conformal symbology

................................ ................................ .................... 30 (6) Low visibility approach

................................ ................................ .................. 30 (7) Clutter

................................ ................................ ................................ ............. 30

c. HUD/HDD compatibility

................................ ................................ ......................... 30 (1) General

................................ ................................ ................................ ............ 30 (2) Consistency and compatibility

................................ ................................ ........ 30 d. Alerting issues

................................ ................................ ................................ .......... 31 (1) Alerts displayed on HUDs

................................ ................................ .............. 31 (2) Monochrome HUDs

................................ ................................ ........................ 32 (3) Multi

- color HUDs

................................ ................................ ........................... 32 (4) Single HUD installatio n

................................ ................................ .................. 32 (5) Dual HUD installations

................................ ................................ ................... 32 (6) GPWS/TCAS on HUD

................................ ................................ ................... 32

e. Up set/unusual attitude recovery guidance

................................ ............................... 32 (1) Guidance cues

................................ ................................ ................................ . 32 (2) Orientation cues

................................ ................................ .............................. 33 47

— 51 [RESERVED]

................................ ................................ ................................ .......... 33
CHAPTER 5

. PERFORMANCE OF FUNCT ION

................................ ................................ ...... 34 52. General

................................ ................................ ................................ ........................... 34

a. Intended function

................................ ................................ ................................ ..... 3410/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

vii b. Effect of system tolerances

................................ ................................ ...................... 34 53. Normal Performance

................................ ................................ ................................ ...... 34

a. General

................................ ................................ ................................ ..................... 34 b. Conditions to consider

................................ ................................ ............................. 34

c. Level of performance

................................ ................................ ............................... 36 (1) Significant characteristics

................................ ................................ ............... 36 (2) Configuration changes

................................ ................................ .................... 36 (3) Co mpliance evaluation

................................ ................................ .................... 36 (4) Prescribed levels of performance

................................ ................................ .... 36 (5) Equivalence of performance

................................ ................................ ........... 36 (6) Autopilot

................................ ................................ ................................ ......... 36 (7) Flight director

................................ ................................ ................................ .. 36 (8) Autothrust

................................ ................................ ................................ ....... 36 (9) Automatic trim

................................ ................................ ................................ 36 54. Performance in Rare Normal Conditions

................................ ................................ ....... 37

a. General

................................ ................................ ................................ ..................... 37 (1) Range of conditions

................................ ................................ ........................ 37 (2) Effect on performance

................................ ................................ ..................... 37 b. Conditions to consider

................................ ................................ ............................. 37

c. Level of performance

................................ ................................ ............................... 38 (1) Performance standard

................................ ................................ ...................... 38 (2) Auto pilot authority limit

................................ ................................ ................. 39 (3) Masking of potential hazard

................................ ................................ ............ 39 55. Icing Considerations in Normal and Rare Normal Conditions

................................ ...... 39

a. Effect on performance

................................ ................................ .............................. 39 b. Alerts

................................ ................................ ................................ ........................ 39

c. Effect on speed protect ion

................................ ................................ ....................... 39 56. Performance in Non

- Normal Conditions

................................ ................................ ....... 39

a. General

................................ ................................ ................................ ..................... 39 b. Conditions to consider

................................ ................................ ............................. 3910/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

viii c. Level of performance

................................ ................................ ............................... 40 (1) Performance standard

................................ ................................ ...................... 40 (2) Autopilot authority limit

................................ ................................ ................. 40 (3) Masking of potential hazard

................................ ................................ ............ 41 57. Speed Protection

................................ ................................ ................................ ............ 41

a. General

................................ ................................ ................................ ..................... 41 (1) Speed excursions

................................ ................................ ............................. 41 (2) Compliance with § 25.1329(h)

................................ ................................ ....... 41 (3) Design standard

................................ ................................ ............................... 42 b. Low

- speed protection

................................ ................................ ............................... 42 (1) General

................................ ................................ ................................ ............ 42 (2) Factors to consider

................................ ................................ .......................... 42 (3) Low

- speed protection during approach operations

................................ ......... 43 (4) Windshear recovery guidance

................................ ................................ ......... 44

c. High

- speed protection

................................ ................................ .............................. 44 (1) General

................................ ................................ ................................ ............ 44 (2) Factors to consider

................................ ................................ .......................... 44 58

— 61 [RESERVED]

................................ ................................ ................................ .......... 45
CHAPTER 6

. CHARACTERISTICS OF S PECIFIC MODES

................................ .................... 46 62. General

................................ ................................ ................................ ........................... 46 63. Lateral Modes

................................ ................................ ................................ ................ 46

a. Heading or track hold

................................ ................................ ............................... 46 b. Heading or track select

................................ ................................ ............................. 46

c. LNAV mode

................................ ................................ ................................ ............. 46 (1) Lateral flight path

................................ ................................ ............................ 46 (2) Automatic mode transitions

................................ ................................ ............ 46 (3) Takeoff or go

- around

................................ ................................ ...................... 46 64. Vertical Modes

................................ ................................ ................................ ............... 47

a. Target altitude selection

................................ ................................ ........................... 4710/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

ix b. Vertical speed

................................ ................................ ................................ ........... 4 7

c. Flight path angle

................................ ................................ ................................ ...... 47 d. Indicated airspeed/Mach hold (speed on elevator)

................................ .................. 47

e. Indicated airspeed/Mach select (s peed on elevator)

................................ ................ 47 f. Flight level change (speed on elevator)

................................ ................................ ... 47
g. Altitude capture

................................ ................................ ................................ ........ 47 (1) Mode transition

................................ ................................ ............................... 47 (2) Guidelines for altitude capture mode

................................ .............................. 48 h. Altitude hold

................................ ................................ ................................ ............ 49 (1) Entering mode

................................ ................................ ................................ . 49 (2) Mode transition annunciation

................................ ................................ ......... 49 (3) Barometric pressur e adjustment

................................ ................................ ...... 49 i. VNAV

................................ ................................ ................................ ...................... 49 (1) FMS path

................................ ................................ ................................ ......... 49 (2) Climb or descent

................................ ................................ ............................. 49 65. Multi

- Axis Modes

................................ ................................ ................................ .......... 50

a. Takeoff mode

................................ ................................ ................................ ........... 50 (1) Vertical guida nce

................................ ................................ ............................ 50 (2) Lateral guidance

................................ ................................ .............................. 50 (3) Rotation guidance

................................ ................................ ........................... 50 (4) Auto thrust

................................ ................................ ................................ ....... 50 (5) Operation and performance

................................ ................................ ............. 50 b. Go

- around mode

................................ ................................ ................................ ...... 51 (1) Vertical elements

................................ ................................ ............................ 51 (2) Speed

................................ ................................ ................................ ............... 51 (3) Autothrust

................................ ................................ ................................ ....... 51 (4) Enga gement

................................ ................................ ................................ ..... 52 (5) All engine and engine out capability

................................ .............................. 52

c. Approach mode

................................ ................................ ................................ ........ 52 (1) Final approach path

................................ ................................ ......................... 5210/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

x (2) Mode annunciations

................................ ................................ ........................ 52 (3) Sub

- modes

................................ ................................ ................................ ....... 52 (4) Mode engagement sequence

................................ ................................ ........... 52 66. Autothrust Modes

................................ ................................ ................................ ........... 52

a. Thrust mode

................................ ................................ ................................ ............. 52 b. Speed mode

................................ ................................ ................................ .............. 53

c. Retard mode

................................ ................................ ................................ ............. 53 67. Special Considerations for VNAV Approach Operations Related to Selecting a Target Altitude

................................ ................................ ................................ .......................... 53

a. Approach operations

................................ ................................ ................................ 53 b. VNAV path operations

................................ ................................ ............................ 53 68. Control Wheel Steering (Control Steering through the Autopilot)

................................ 53

a. General

................................ ................................ ................................ ..................... 53 b. Design

................................ ................................ ................................ ...................... 53 (1) Control forces

................................ ................................ ................................ .. 53 (2) Bank and pitch attitudes

................................ ................................ .................. 53 (3) Control behavior

................................ ................................ ............................. 54 (4) Stall and stall recovery

................................ ................................ .................... 54 (5) Adjustments to trim

................................ ................................ ......................... 54 ( 6) Takeoff and landing

................................ ................................ ........................ 54 (7) Automatic reversion to CWS mode

................................ ................................ 54

c. Terminology and application of advisory material

................................ .................. 54 (1) Touch control steering

................................ ................................ .................... 55 (2) Supervisory override

................................ ................................ ....................... 55 69. Special Co nsiderations for the Integration of Fly

- by

- Wire Flight Control Systems and FGS

................................ ................................ ................................ ......................... 55

a. Speed protection

................................ ................................ ................................ ....... 55 b. System degradation

................................ ................................ ................................ .. 55 70

— 74 [RESERVED]

................................ ................................ ................................ .......... 5510/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

xi CHAPTER 7

. FGS INTEGRATION

................................ ................................ .......................... 56 75. General

................................ ................................ ................................ ........................... 56 76. System Integration Issues

................................ ................................ .............................. 56

a. Common and cascading failure modes

................................ ................................ .... 56 b. Risk of error

................................ ................................ ................................ ............. 56

c. System safety analysis

................................ ................................ ............................. 56 77. Functional Interfaces

................................ ................................ ................................ ...... 56

a. Interfacing sensors

................................ ................................ ................................ ... 56 b. Potential inconsistencies between systems

................................ .............................. 57

c. Function and performance

................................ ................................ ....................... 57 78

— 82 [RESERVED]

................................ ................................ ................................ .......... 57
CHAPTER 8

. SAFETY ASSESSMENT

................................ ................................ ................... 58 83. Gene ral

................................ ................................ ................................ ........................... 58

a. Basic safety requirements

................................ ................................ ........................ 58 b. Safety assessment

................................ ................................ ................................ ..... 58

c

. Validation of safety assessment

................................ ................................ ............... 58 d. Coordination with the FAA

................................ ................................ ..................... 58 84. FGS Failure Conditions

................................ ................................ ................................ . 58

a. Functionality

................................ ................................ ................................ ............ 58 b. Effect of failure condition

................................ ................................ ........................ 59 85. Type and Severity of Failure Condit ions

................................ ................................ ....... 59

a. Types of failure conditions

................................ ................................ ...................... 59 (1) Loss of function

................................ ................................ .............................. 59 (2) Malfunction

................................ ................................ ................................ ..... 59 b. Cause

................................ ................................ ................................ ........................ 59

c. Severity

................................ ................................ ................................ .................... 60 d. Assessment of failure conditions

................................ ................................ ............. 60 (1) Functional failures

................................ ................................ .......................... 60 (2) Airframe loads

................................ ................................ ................................ 60 (3) Assessing total effect of failure

................................ ................................ ....... 6010/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

xii 86. Mitigation of Failure Conditions

................................ ................................ ................... 60

a. General

................................ ................................ ................................ ..................... 60 b. Identification of methods

................................ ................................ ......................... 61

c. FGS de

- selection

................................ ................................ ................................ ...... 61 87. Validation of Failure Conditio ns

................................ ................................ ................... 61

a. General

................................ ................................ ................................ ..................... 61 b. Validation options

................................ ................................ ................................ .... 61

c. Validation metho dology

................................ ................................ ........................... 61 88. Specific Considerations

................................ ................................ ................................ . 62

a. FGS action during ground operations

................................ ................................ ...... 62 b. FGS operations in close proximity to the ground

................................ .................... 62 (1) Takeoff

................................ ................................ ................................ ............ 62 (2) Approach

................................ ................................ ................................ ......... 63

c. Cruise operations

................................ ................................ ................................ ..... 64 d. Asymmetric thrust during autothrust operation

................................ ....................... 64 89. Failure to Disengage the FGS

................................ ................................ ........................ 65 90

— 97 [RESERVED]

................................ ................................ ................................ .......... 65
CHAPTER 9

. COMPLIANCE DEMONSTRA TION USING FLIGHT TE ST AND SIMULATION

................................ ................................ ................................ .................. 66 98. General

................................ ................................ ................................ ........................... 66

a. Methods of compliance demonstration

................................ ................................ .... 66 b. Criteria for es tablishing compliance

................................ ................................ ........ 66

c. Elements of certification flight test

................................ ................................ .......... 66 d. Pilot

- in

- the

- loop evaluation

................................ ................................ ..................... 66

e. Other applicable guidance material for FGS takeoff and/or approach modes

......... 66 (1) Criteria to consider

................................ ................................ .......................... 66 (2) Procedures to show compliance

................................ ................................ ...... 67 f. Relationship of AC chapters

................................ ................................ .................... 67 99. Performance Demonstration (Fault F ree): § 25.1301

................................ ................... 67

a. General

................................ ................................ ................................ ..................... 6710/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

xiii (1) Certification plan

................................ ................................ ............................ 67 (2) Evaluating performance

................................ ................................ .................. 68 (3) Evaluating compatibility of mode controls, indications, and alerts

................ 68 b. Normal performance

................................ ................................ ................................ 68 (1) Demonstration

................................ ................................ ................................ . 68 (2) Evaluation

................................ ................................ ................................ ....... 68 (3) Expected errors

................................ ................................ ............................... 68

c. Performance in “other than normal” conditions

................................ ...................... 68 (1) Test program

................................ ................................ ................................ ... 68 (2) Evaluation of FGS

................................ ................................ ........................... 69 (3) Additional guidance for windshear

................................ ................................ . 69 d. Specific performance conditions

................................ ................................ .............. 69 (1) Icing considerations

................................ ................................ ........................ 6 9 (2) Low

- speed protection

................................ ................................ ...................... 70 (3) High

- speed protection

................................ ................................ ..................... 70 (4) Go

- around

................................ ................................ ................................ ....... 70 (5) Steep approach (special authorization)

................................ ........................... 71 ( 6) Indication of and response to an out

- of

- trim condition

................................ .. 72

e. Flight director/head up display

................................ ................................ ................ 72 (1) General

................................ ................................ ................................ ............ 72 (2) Specific demonstrations for HUD

................................ ................................ ... 73 (3) Simulator demonstration for HUD

................................ ................................ .. 74 f. Flightcrew override of the FGS

................................ ................................ ............... 75 (1) Autopilot override

................................ ................................ ........................... 75 (2) Autothrust override

................................ ................................ ......................... 75 (3) Pitch trim system evaluation during autopilot override

................................ .. 75 100. Failure Conditions Requiring Validation: § 25.1309

................................ .................... 76

a. General

................................ ................................ ................................ ..................... 76 (1) Safety assessment

................................ ................................ ............................ 76 (2) Evaluation of failure conditions

................................ ................................ ...... 7610/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

xiv b. Validation elements

................................ ................................ ................................ . 76 (1) Assessment

................................ ................................ ................................ ...... 76 (2) Failure condition

................................ ................................ ............................. 76 (3) Pilot recognition

................................ ................................ .............................. 77 (4) Pilot reaction time

................................ ................................ ........................... 78 (5) Pilot recovery

................................ ................................ ................................ .. 79

c. Takeoff

................................ ................................ ................................ ..................... 79 (1) Worst

- case failure condition

................................ ................................ ........... 79 (2) Failures to be evaluated

................................ ................................ .................. 79 (3) On runway guidance

................................ ................................ ....................... 79 d. Climb, cruise, descent, and holding

................................ ................................ ......... 79

e. Maneuvering

................................ ................................ ................................ ............ 79 f. Approach

................................ ................................ ................................ .................. 79 (1) Approach with vertical path reference

................................ ............................ 80 (2) Approach without vertical path reference

................................ ....................... 81 (3) Steep approach

................................ ................................ ................................ 81
g. Specific conditions

................................ ................................ ................................ ... 81 (1) Failure conditions to be evaluated

................................ ................................ .. 81 (2) Failure to disengage

................................ ................................ ........................ 81 101. Criteria Supporting Operational Use of Autopilot

................................ ......................... 81

a. Typical flight operations

................................ ................................ .......................... 81 b. Operations in close proximity to the gro und

................................ ............................ 82 (1) General

................................ ................................ ................................ ............ 82 (2) Considerations

................................ ................................ ................................ . 82 (3) Autopilot engage ment altitude/height after takeoff

................................ ........ 82 (4) Autopilot engagement during approach

................................ .......................... 83 (5) Circling approach

................................ ................................ ............................ 85

c. Climb, cruise, descent, and holding

................................ ................................ ......... 85 d. Maneuvering

................................ ................................ ................................ ............ 85 102. Automatic Disengagem ent of the Autopilot

................................ ................................ .. 8510/27/14 AC 25.1329

- 1C

C ONTENTS (CONTINUED) Paragraph Page

xv 103. Assessment of Human Factors

................................ ................................ ....................... 85

a. General

................................ ................................ ................................ ..................... 85 b. Flight evaluations

................................ ................................ ................................ ..... 86 (1) During certification

................................ ................................ ......................... 86 (2) Prior to certification

................................ ................................ ........................ 86 (3) Credit to establish FGS compliance

................................ ................................ 86 (4) Simulation versus flight tests

................................ ................................ .......... 86

c. Structured subje ctive evaluations

................................ ................................ ............ 87 d. Pilot training and experience

................................ ................................ ................... 87

e. Evaluating new or unique design features

................................ ............................... 87 f. Certification planning documentation

................................ ................................ ...... 87 104

— 108 [RESERVED]

................................ ................................ ................................ . 87
CHAPTER 10

. AIRPLANE FL IGHT MANUAL

................................ ................................ ......... 88 109. General

................................ ................................ ................................ ........................... 88

a. AFM terminology

................................ ................................ ................................ .... 88 b. Low

- visi bility operations

................................ ................................ ......................... 88 110. Information Supporting Operational Use of Autopilot

................................ .................. 88

a. General

................................ ................................ ................................ ..................... 88 b. Specifying a MUH

................................ ................................ ................................ ... 88

c. Maximum displacement deviation

................................ ................................ ........... 88 111. Limitations

................................ ................................ ................................ ..................... 89 112. Non

- Normal/Emergency Procedures

................................ ................................ ............. 89 113. Normal Procedures

................................ ................................ ................................ ......... 89

a. Documentatio n of normal procedures

................................ ................................ ...... 89 b. Maximum displacement deviation

................................ ................................ ........... 89

c. Procedures for use of FGS in icing conditions

................................ ........................ 89 d. Aircraft with published FCOMs

................................ ................................ .............. 89

e. Aircraft without published FCOMs

................................ ................................ ......... 8910/27/14 AC 25.1329

- 1C

CONTENTS (CONTINUED)

APPENDICES
Number Page A S afety Assessment

................................ ................................ .............................. A

- 1 1

. General

................................ ................................ ................................ ............ A

- 1 2

. Identification of Failure Conditions

................................ ................................ A

- 1 3

. Considerations when Assessing the Severity of Failure Condition Effects

.... A

- 2 4

. Failure Condition Classification

................................ ................................ ..... A

- 3 B D efinitions

................................ ................................ ................................ ........... B

- 1 C A cronyms

................................ ................................ ................................ ............ C

- 1

TABLES
Number Page 1 Related 14 CFR Sections

................................ ................................ ........................ 2 2 Related Advisory Circ ulars

................................ ................................ ..................... 3 3 Related SAE Documents

................................ ................................ ......................... 4 4 Related RTCA Documents

................................ ................................ ..................... 4 2

- 1 Cross

- References for § 25.1329 Paragraphs to AC Chapters

................................ . 8 5

- 1 Examples of Normal Conditions

................................ ................................ ........... 35 5

- 2 Examples of Rare Normal Conditions

................................ ................................ .. 38 5

- 3 Examples of Non

- Normal Conditions

................................ ................................ .. 40 B

- 1 Terms and Definitions

................................ ................................ ......................... B

- 1 C

- 1 Acronyms and Definitions

................................ ................................ .................. C

- 1

FIGURES
Number Page 9

- 1 Relationship between AC Chapters

................................ ................................ ...... 6710/27/14 AC 25.1329

- 1C

1 INTRODUCTION

1. Purpose
. This AC describes an acceptable means for showing complia nce with certain requirements of 14 CFR 25.1329, Flight guidance systems

. While p art 25 contains the airworthiness standards applicable to transport category airplanes, the guidance in this AC pertains to the functions of autopilots, flight directors (FD s ), and automatic thrust control as well as any interactions with stability augmentation and trim functions.
2. Applicability
.

a. The guidance provided in this document is directed to airplane manufacturers, modifiers, operator s of certain transport category airplanes , foreign regulatory authorities, and Federal Aviation Administration (FAA) transport airplane type certificate engineers and their designees

. b. The guidance in this AC is neither mandatory nor regulatory in nature an d does not constitute a regulation

. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations

. We will consider other methods of showing compliance that an applicant may elect to present

. While thes e guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations

. If, however, we become aware of circumstances that convince us that following this AC would not result in c ompliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation or design changes as a basis for finding compliance.

c. The material in this AC does not change or create any additional regu latory requirements, nor does it authorize changes in, or permit deviations from, regulatory requirements.
3. Cancellation
. This AC cancels AC 25.1329

- 1B Change 1 , dated October 16, 2012

. 4. Related Regulations, AC s , and Industry Documents
. The following related documents are provided for information purposes and are not necessarily directly referenced in this AC.

a. Regulations
. Table 1 identifies the related 14 CFR regulations that are referenced in this AC. The full text of these regulat ions can be downloaded from the U.S. Government Printing Office e

- CFR . A paper copy may be ordered from the Government Printing Office , Superintendent of Documents, Attn: New Orders, PO Box 371954, Pittsburgh, PA , 1525 0

- 7954.10/27/14 AC 25.1329

- 1C

2 Table 1
. Related 14 CFR Sections

Section Title § 25.143 Controllability and Maneuverability

— General § 25.301 Loads § 25.671 Control S ystems

— General § 25.672 Stability augmentation and automatic and power

- operated system s § 25.677 Trim systems § 25.777 Cockpit controls § 25.779 Motion and effect of cockpit controls § 25.781 Cockpit control knob shape § 25.901 Installation § 25.903 Engines § 25.1301 Function and installation § 25.1303 Flight and navigations instrum ents § 25.1309 Equipment, systems, and installations § 25.1322 Flightcrew Alerting § 25.1420 Supercooled large drop icing conditions § 25.1581 Airplane Flight Manual

— General § 25.1583 Airplane Flight Manual

— Operating limitations § 25.1585 Airplane Fl ight Manual

— Operating procedures

b. A dvisory C ircular s . Table 2 identifies the ACs that are related to the guidance in this AC. The table lists the latest version of each AC at the time of publication. If any AC is revised after pub lication of this AC, you should refer to the latest version for guidance. You can find the latest version at the FAA website

.10/27/14 AC 25.1329

- 1C

3 Table 2
. Related Advisory Circ ulars

Number Title Date
AC 20

- 115 C A irborne Software Assurance July 19, 2013
AC 20

- 138 D Change 1 Airworthiness Approval of Positioning and Navigation Systems O ctober 10, 2014

AC 20

- 152 RTCA, Inc., Document RTCA/DO

- 254, Design Assurance Guidance for Airborne Electronic Hardware July 5, 2005

AC 20

- 174 Dev elopment of Civil Aircraft and Systems September 30, 2011
AC 25

- 7C Flight Test Guide for Certification of Transport Category Airplanes October 16, 2012

AC 25

- 11 B Electronic Flight Displays October 7, 2014
AC 25

- 12 Airworthiness Criteria for the Approval of Airborne Windshear Warning Systems in Trans port Category Airplanes November 2, 1987

AC 25.672

- 1 Active Flight Controls November 15, 1983
AC 25.1309

- 1A System Design and Analysis October 3, 2011
AC 25.1419

- 2 Compliance with the Ice Protection Requirements of §§ 25.1419(e), (f), (g), and (h) October 2 7 , 20 09

AC 25.1581

- 1 Change 1 Airplane Flight Manual July 14, 1997

A C 120

- 28 D Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout July 13, 1999

AC 120

- 29A Criteria for Approving Category I and Category II Weather Minima for Approach August 12, 2002

AC 120

- 41 Criteria for Operational Approval of Airborne Wind S hear Alerting and Flight Guidance Systems November 11, 1983

Note: This table identifies the latest version of each AC at the time of publication

. If any AC is revised after publication of this AC , you should refer to the latest version for guidance.10/27/14 AC 25.1329

- 1C

4 c. Related Industry Standards
. (1) The following d ocuments are available from the Society of Automotive Engineers (SAE)

. You can purchase these documents by mail from SAE Customer Service , 400 Commonwealth Drive, Warrendale, PA , 15096 ; by faxing your order information to (724) 776

- 0790; or from the SAE website

. Table 3
. Related SAE Documents

Number Title
SAE ARP4754 A Guidelines for Development of Civil Aircraft and Systems
SAE ARP4761 Guidelines and Methods for Conducting the Safety Assessment P rocess on Civil Airborne Systems and Equipment
SAE ARP5288 Transport Category Airplane Head Up Display (HUD) Systems
SAE ARP5366 Autopilot, Flight Director , and Autothrust Systems
SAE AS8055 Minimum Performance Standard for Airborne Head Up Display (HUD )
(2) The following documents are available from RTCA, Inc

. (formerly the Radio Techni cal Commission for Aeronautics)

. You can purchase these documents by mail from RTCA Inc., 1150 18th Street NW

. , Suite 910, Washington, DC 20036 ; by fax ing the Document Order Form to (202) 833

- 9434; or from the RTCA website

. Table 4
. Related RTCA Documents

Number Title
RTCA DO

- 178B/ EUROCAE ED

- 12B Software Consid erations in Airborne Systems and Equipment Certification
RTCA DO

- 160E/ EUROCAE ED

- 14D Environmental Conditions and Test Procedures for Airborne Equipment
RTCA DO

- 254/ EUROCAE ED

- 80 Design Assurance Guidance for Airborne Electronic Hardware

d. Other FAA doc uments
. (1) Federal Aviation Administration Human Factors Team Report on: The Interfaces Between Flightcrews and Modern Flight Deck Systems , dated June 18, 1996 , is available at the FAA website

.10/27/14 AC 25.1329

- 1C

5 (2) FAA Order 8260.3 B , United States Standard for Terminal Instrument Procedures (TERPS) , Changes 1

– 19 , is available at FAA website

. 5

— 10 [RESERVED]10/27/14 AC 25.1329

- 1C

6 CHAPTER 1

. BACKGROUND

11. General
.

a. AC 2 5.1329

- 1C
. This revision incorporates minor changes associated with issuance of the final rule for Airplane and Engine Certification Requirements in Supercooled Large Drop, Mixed Phase, and Ice Crystal Icing Conditions ( 79 FR 65508 , November 4, 2014 )

. Spec ifically, in this AC, we added a reference to § 25.1420, Supercooled large drop icing conditions , in table 1 ; excepted “large drop icing” as an icing normal condition in table 5

- 1 ; and added “large drop icing” as a rare normal condition in table 5

- 2

. b. Scope
. This advisory material provides information for flight guidance systems (FGS), which include any autopilot functions, FD functions, and automatic thrust control functions as well as any interactions with stability augmentation and trim functions.
12. Evolution of FG S

.

a. Complexity
. There have been dramatic changes in technology and system design, which have resulted in much higher levels of integration, automation, and complexity

. T hese changes have also redefined the allocation of functions and interfaces between systems

. Relatively simple, dedicated systems have been replaced with digital multi

- function systems with more modes and automatic changes in modes of operation

. The introd uction of fly

- by

- wire flight control systems has created new interfa ce considerations for the FGS.
b. Guidance c onsiderations
. These new systems are capable of providing better performance, increased safety, and decreased workload

. But, if designed without co nsideration for the criteria in this AC, these systems could also be confusing and not immediately intuitive for the flightcrew

. Significant operational experience has been gained on new generation systems, and this guidance material is provided based o n t hat experience.
13

— 16 [RESERVED]10/27/14 AC 25.1329

- 1C

7 CHAPTER 2

. OVERVIEW OF FLIGHT G UIDANCE SYSTEMS

17. Purpose of FGS
. The FGS is primarily intended to assist the flightcrew in the basic control and tactical guidance of the airplane

. The system may also provide workload reli ef to the pilots and provide a means to fly a flight path more accurately to support specific operational requirements, such as reduced vertical separation minimum (RVSM) or required navigation performance (RNP).
18. Components
.

a. Included in d efinition
. For the purpose of this AC, the term “FGS” includes all the equipment necessary to accomplish the FGS function, including the sensors, computers, power supplies, servo

- motors/actuators, and associated wiring

. It includes any indications and controllers necessary for the pilot to manage and supervise the system.
b. Excluded from d efinition
. Any equipment or component that remains mechanically connected to the primary flight controls or propulsion controls when the FGS is not in use is regarded as a part of the primary flight controls and propulsion system, and the provisions fo r such systems are applicable.
19. FGS Functions
.

a. Elements of FGS
. (1) Flight guidance and control (for example, autopilot, FD displayed head down or head up). (2) Autothrottle/autothrust systems

. The term “ autothrust” is generic in nature and includes power control systems for propeller driven airplanes. (3) I nteractions with stability augmentation and trim systems. (4) Alerting, status, mode annunciation, and situation information associated with flight guidance an d control functions.
b. Approach and landing s ystem
. The FGS includes those functions necessary to provide guidance and control in conjunction with an approach and landing s ystem, such as the following: (1) Instrument landing system (ILS)

. (2) Microwave landing syste m (MLS)

. (3) Ground

- based augmentation system (GBA S ) landing system (GLS)

.

c. Flight management s ystem
. The FGS also includes those functions necessary to provide guidance and control in conjunction with a flight management system ( FMS )

. The FGS does not include the flight planning and the generation of flight path and speed profiles tied to10/27/14 AC 25.1329

- 1C

8 waypoints and other flight planning aspects of the FMS

. However, it does include the interface between the FMS and FGS necessary for the execution of flight path and speed com mands.
d. Design p hilosophy
. The applicant should establish, document, and follow a design philosophy that supports the intended operational use regarding FGS behavior, modes of operation, and the pilot interface with controls, indications, alerts, and mode f unctionality.

e. Description of FGS b eh avior and o peration
. A description of the FGS behavior and operation should be addressed from flightcrew and maintenance perspectives in appropriate documentation and training material.
20. Compliance with § 25.1329
.

a. General
. Subsequent chapters of this advisory material provide acceptable means of compliance with § 25.1329 and the applicability of other p art 25 rules to FGS ( for example , §§ 25.1301 and 25.1309)

. The demonstrated means of compliance may include a combination of analysis, laboratory testing, flight testing, and simulator testing

. The applicant should coordinate with the FAA early in the certification program via a certification plan to reach agreement on the methods to be u sed to demonstrate compliance.
Note 1: This AC uses the terminology “should” and “should not” when discussing compliance to the AC itself, as the AC represents one, but not the only, method of complying with § 25.1329.
Note 2: This AC uses the terminology “must” and “may not” when discussing compliance to § 2 5.1329 and other specific rules, as compliance to a rule is not optional

. In these cases, the AC text supplies a reference to the specific rule being discussed.
b. Relevant p aragraphs
. Table 2

- 1 lists the relevant paragraphs of § 25.1329 and indicates where acceptable means of compliance with each paragraph can be found within this AC.
Table 2

- 1
. Cross

- References for § 25.1329 Paragraphs to AC Chapters

14 CFR Section AC Chapter/Paragraph Reference § 25.1329(a) Quick disengagement control s for the autopilot and autothrust functions must be provided for each pilot

. The autopilot quick disengagement controls must be located on both control wheels (or equivalent)

. The autothrust quick disengagement controls must be located on the thrust contr ol levers

. Quick disengagement controls must be readily accessible to each pilot while operating the control wheel (or equivalent) and thrust control levers. Chapter 3 FGS Engagement, Disengagement, Indications, a nd Override Paragraph 27 , Autopilot Engagement, Disengagement, and Indications Paragraph 29 , Aut othrust Engagement, Disengagement, and Indications10/27/14 AC 25.1329

- 1C

9 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(b) The effects of a failure of the system to disengage the autopilot or autothrust functions when manually commanded by the pilot must be assessed in accordance with the requirements of § 25.13 09. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 27 , Autopilot Engagement, Disengagement, and Indications Pa ragraph 29 , Autothrust Engagement, Disengagement, and Indications Paragraph 30 , Override of the FGS Chapter 8 Safety Assessment Paragraph 89 , Failure to Disengage the FGS § 25.1329(c) Engagement or switching of the flight guidance system, a mode, or a sensor may not cause a transient response of the airplane’s flight path any greater than a minor transient, as defined in paragraph (n)(1) of this section. Chapter 3 FGS Engagement, Disengagement, Indications, an d Override Chapter 8 Safety Assessment
§ 25.1329(d) Under normal conditions, the disengagement of any automatic control function of a flight guidance system may not cause a transient response of the airplane’s flight path any g reater than a minor transient. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Chapter 4 Controls, Indications, and Alerts Paragraph 45 , FGS Alerting, Warning, Caution, Advisory, and Status Chapter 8 Safety Assessment10/27/14 AC 25.1329

- 1C

10 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(e) Under rare normal and non

- normal conditi ons, disengagement of any automatic control function of a flight guidance system may not result in a transient any greater than a significant tra nsient, as defined in paragraph (n)(2) of this section. Chapter 3 FG S Engagement, Disengagement, Indications, and Override Chapter 4 Controls, Indications, and Alerts Paragraph 45 , FGS Alerting, Warning, Caut ion, Advisory, and Status Chapter 8 Safety Assessment § 25.1329(f) The function and direction of motion of each command reference control, such as heading select or vertical speed, must be plainly indicated on, or adjacent to, each control if necessary to prevent inappropriate use or confusion. Chapter 4 Controls, Indications, and Alerts Paragraph 43 , FGS Controls

§ 25.1329(g) Under any condition of flight appropriate to its use, the flight guidance system may not produce hazardous loads on the airplane, nor create hazardous deviations in the flight path

. This applies to both fault

- free operation a nd in the event of a malfunction, and assumes that the pilot begins corrective action within a reasonable period of time. Chapter 4 Controls, Indications, and Alerts Paragraph 45 , FGS Alerting, Warning, Caution, Advisory, and Status Chapter 5 Performance of Function Chapter 8 Safety Assessment Chapter 9 Compliance Demonstration Using Flight Test and Simulation10/27/14 AC 25.1329

- 1C

11 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(h) When the flight guidance system is in use, a means must be provided to avoid excursions beyond an acceptable margin from the speed range of the normal flight envelope

. If the airplane experiences an excursion outside this range, a means must be provided to prevent the flight guidance system from providing guidance or control to an unsafe speed. Chapter 5 Performance of Function Paragraph 57 , Speed Protection

§ 25.1329(i) The flight guidance system functions, controls, indications, and alerts must be designed to minimize flightcrew e rrors and confusion concerning the behavior and operation of the flight guidance system

. Means must be provided to indicate the current mode of operation, including any armed modes, transitions, and reversions

. Selector switch position is not an acceptable means of indication

. The controls and indications must be grouped and presented in a logical and consistent manner

. The indications must be visible to each pilot under all expected lighting conditions. Chapter 4 Controls, Indications, and Alerts

§ 25.1329(j) Following disengagement of the autopilot, a warning (visual and auditory) must be provided to each pilot and be timely and distinct from all other cockpit warnings. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 27 , Autopilot Engagement, Disengagement, and Indications Chapter 8 Safety Assessment10/27/14 AC 25.1329

- 1C

12 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(k) Following disengagement of the autothrust function, a caution must be provided to each pilot. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 27 , Autopilot Engagement, Disengagement, and Indications Chapter 8 Safety Assessment § 25.1329(l) The autopilot may not create a potential haz ard when the flightcrew applies an override force to the flight controls. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 30 , Override of the FGS Chapter 4 Controls, Indications, and Alerts Paragraph 45 , FGS Alerting, Warning, Caution, Advisory, and St atus Chapter 8 Safety Assessment § 25.1329(m) During autothrust operation, it must be possible for the flightcrew to move the thrust levers without requiring excessive force

. The autothrust may not create a pot ential hazard when the flightcrew applies an override force to the thrust levers. Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 30 , Override of the FGS Chapter 8 Safety Assessment10/27/14 AC 25.1329

- 1C

13 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(n) For purposes of this section, a transient is a disturbance in the control or flight path of the airplane that is not consistent with response to flightcrew inputs or environmental conditions. (1) A minor transient would not significantly reduce safety margins and would involve flightcrew actions that are well within their capabilities

. A minor transient may involve a slight increa se in flightcrew workload or some physical discomfort to passengers or cabin
crew. (2) A significant transient may lead to a significant reduction in safety margins, an increase in flightcrew workload, discomfort to the flightcrew, or physical distress to the passengers or cabin crew, possibly including
non
- fatal injuries

. Significant transients do not require, in order to remain within or recover to the normal flight envelope, any of the following: (i) Exceptional piloting skill, alertness, or strength. (i i) Forces applied by the pilot which are greater than those specified in § 25.143(c ). (iii) Accelerations or attitudes in the airplane that might result in further hazard to secured or
non
- secured occupants. Appendix B

— D efinitions

Note: The text for each paragraph in § 25.1329 is included in this AC for reference only

. Please refer to the actual text in 14 CFR part 25.
2 1

— 26 [RESERVED]10/27/14 AC 25.1329

- 1C

14 CHAPTER 3

. FGS ENGAGEMENT, DISE NGAGEMENT, INDIC ATIONS, AND OVERRIDE

27. Autopilot Engagement, Disengagement, and Indications
. Autopilot engagement and disengagement should be accomplished in a manner consistent with other flightcrew procedures and tasks and should not require und ue attention.

a. Autopilot e ng agement
. (1) Single switch a ction
. Each pilot should be able to select the autopilot function of the FGS with a single switch action

. The single switch action should engage b oth the pitch and roll axes. (2) Engagement status of a utopilot
. The autopilot system shou ld provide positive indication to the flightcrew that the system has been engaged

. The selector switch position is not acceptable as a means of indication

. See § 25.1329(i)

. Regardless of the method used, the engagement status (and changes in status) of th e autopilot(s) should be clearly indicated and should not require undue attention or recall.
Note: If an operational need is identified for split

- axis engagement, then annunciation or indication should be provided for each axis. (3) Multiple a utopilots
. If a single autopilot within a multiple autopilot installation can be individually selected by the flightcrew, the engagement annunciation should reflect the flightcrew selection

. It should not be possible for multiple autopilots to be engaged in different modes

. For modes that use multiple autopilots, the additional autopilots may engage automatically at selection of the mode or after arming the mode

. A means should be provided to determine that adequate autopilot capability exists to support the in tended operation (f or example, “Land 2” and “ Land 3” are used in some aircraft). (4) Acceptable t ransients
. The engagement of the autopilot should be free of perceptible transients

. Under dynamic conditions, including maneuvering flight, minor transients are acceptable

. However, with normal operating conditions, significant transients may not occur

. See § 25.1329(d)

. (5) FD n ot e ngaged
. Without a FD engaged, the initial lateral and vertical modes should be consistent with minimal disturbance from the flight path

. For example, the lat eral mode at engagement may roll the airplane to wings level , and then hold the airplane heading/track or maintain the existing bank angle (if in a norm al range)

. A heading/track pre
- select at engagement function may be provided, if precautions are taken t o ensure that selection reflects the current intent of the flightcrew

. The modes at engagement should be annunciated , and any associated selected targ et values should be displayed. (6) FD e ngaged
. With a FD engaged, the autopilot should engage in a mode consis tent with (that is, the same as, or if that is not possible, then compatible with) the active FD mode of operation

. Consideration should be given to the mode in which the autopilot will engage when large commands are present on either or both FDs

. The foll owing examples list some of these considerations:10/27/14 AC 25.1329

- 1C

15 (a) Should the autopilot retain the active FD mode or should it engage in the basic default mode? (b) Are there any implications for current flight path references and targets? (c) Is there any potential for flightcrew confusion and unintended changes in flight path or modes?
Note: The design should consider the possibility that the pilot may attempt to engage the autopilot outside of the normal flight envelope

. It is not required that the autopilot compensate for unusual att itudes or other situations outside the normal flight envelope, unless that is part of the autopilot’s intended function.
b. Autopilot d isengagement
. (1) General
. (a) Normal c onditions

. Under normal conditions, automatic or manual disengagement of the autopilot should be free o f perceptible transients or out

- of

- trim forces that are not consistent with the maneuvers being conducted by the airplane at the time of disengagement

. A disengagement in normal conditions may not result in a transient any greater than a minor tr ansient

. If multiple autopilots are engaged, any disengagement of an individual autopilot may not result in a transient any greater than a minor transient

. See § 25.1329(d)

. The disengagement of an individual autopilot should not adversely affect the opera tion of the
r emaining engaged autopilot(s). (b) Other than n ormal c onditions

. Under other t han normal conditions (that is, rare normal or non
- normal conditions), disengagement of the autopilot may not result in a transient any greater than a significant transi ent

. See § 25.1329(e)

. ( For a discussion of rare normal and
non
- normal conditions , s ee Chapter 5 , Performance of Function , paragraph 54 , Performance in Rare Normal Conditions , and paragraph 56 , Performance in Non

- Normal Conditions , of this AC

. ) The flightcrew should be able to respond to a significant transi ent with out using any of the following:
1 E xceptional piloting skill, alertness, or strength,
2 F orces greate r than those given in § 25.143(d ) , or
3 A ccelerations or attitudes in the airplane that might result in a hazard to
sec ured or non

- secured occupants. (c) Pot ential for s ignificant t ransient

. The flightcrew should be made aware (via a suitable alerting or other indication) of conditions or situations (for example, continued out

- of

- trim) that could result in a significant transient at disengagement

. ( See Chapter 4 , Controls, Indications, and Alerts , paragraph 45.d , Awareness of Potential Significant Transient Condition (“Bark before Bite”)

. )10/27/14 AC 25.1329

- 1C

16 Note: See appendix B for definitions of significant transient and minor transient

. F or a discussion of normal conditions, rare normal conditi ons, and
non
- normal conditions , s ee Chapter 5 , paragraphs 5 3 , 54 , and 56 , respectively, of this AC

. (2) A utopilot d isengagement a lerts
. (a) Alert t ype

. Since it is necessary for a pilot to immediately assume manual control following disengagement (manual or automa tic) of the autopilot, a warning (both visual and aural) mus t be given

. See § 25.1329(j)

. (b) Aural w arning s pecifications

. A timely aural warning must be provided and must be distinct from all other cockpit warnings

. See § 25.1329(j)

. It should sound long eno ugh to ensure that it is heard and recognized by the pilot and other flightcrew members, but not so long that it adversely affects communication between crewmembers or is a distraction

. The aural warning should continue until silenced by one of the followi ng means:
1 Activation of the autopi lot quick disengagement control

. 2 Re

- engagement of the autopilot

. 3 Another acceptable means. (c) Multiple a utopilot s ystem

. 1 Disengagement of an autopilot channel within a multiple

- channel autopilot system, downgraded system capa bility, or a reduction in the level of system redundancy that requires immediate flightcrew awareness and possible timely action should cause a caution level alert to be issued to the flightcrew.
2 Disengagement of an autopilot channel within a multiple

- chan nel autopilot system that requires only flightcrew awareness should cause a suitable advisory level alert to be issued to the flightcrew. (3) Quick d isengagement c ontrol
. (a) Purpose

. The purpose of the quick disengagement control is to ensure the capability for e ach pilot to manually disengage the autopilot quickly with a minim um of pilot hand/limb movement. (b) Location

. The quick disengagement control must be located on each control wheel or equivalent

. See § 25.1329(a)

. It should be within easy reach of one or more fingers/thumb of the pilot’s hand when the hand is in a position for normal use on th e control wheel or equivalent. (c) Criteria

. T he quick disengagement control:10/27/14 AC 25.1329

- 1C

17 1 Must be operable with one hand on the control wheel or equivalent and the other hand on the thru st levers

. See § 25.1329(a)

. 2 Should be accessible and operable from a normal hands

- on position without requiring a shift in hand position or grip on the control wheel or equivalent.
3 Should be easily locatable by the pilot without having to first locate the control visually.
4 Should be designed so that any action to operate the quick disengagement control should not cause an unintended input to the control wheel (or equivalent).
5 Should be designed to minimize inadvertent operation and interference from other nearby control wheel (or equivalent) switches/devices, such as radio control or trim.
Note: When establishing location of the quick disengagement control, consideration should be given to its accessibility with large displacements of or forces on the control whe el (or equivalent) and the possible need to operate the quick disengagement control with the other hand. (4) Alternative m eans of a utopilot d isengagement
. (a) Factors to c onsider

. When a § 25.1309 assessment shows a need for an alternative means of disengagement, the following factors should be addressed:
1 Independence from primary quick dis engagement control.
2 Whether alternative means are re adily accessible to each pilot.
3 Reliability and the possibility of latent failu re of those alternative means. (b) Acceptable m eans

. The following means of providing an alternative disengagement have been found to be acceptable:
1 Selecting the engagement control to the “off” position.
2 Disengaging the bar on mode select panel (MSP).
3 Activating the trim switch on the yoke.
Note: Use of circuit breakers as a means of disengagement is not considered acceptable. (5) Flightcrew p itch t rim i nput
. If the autopilot is engaged and the pilot applies manual pitch trim input, and the autopilot is designed to d isengage because of that flight crew action, the au topilot must disengage with no more than a minor transient

. See § 25.1329(c)

. Alternatively, pitch trim changes may be inhibited, such that the potential for a transient is removed.10/27/14 AC 25.1329

- 1C

18 28. FD E ngagement, Disengagement, and Indications
. Engagement and disengagemen t of the FD should be accomplished consistent with other flightcrew procedures and tasks and shoul d not require undue attention.

a. FD e ngagement
. (1) General
. (a) Selection

. A means may be provided for each pilot to select (that is, turn on) and de

- select (that is, turn off) the FD for display on his or her primary flight display (PFD). (b) Engagement

. A FD is considered “engaged” if it is selected and displaying guidance cues.
Note: The distinction is made between “engaged” and “selected ” because the FD might be selected but not displaying guidance cue(s) (for example, the c ue(s) are biased out of view). (c) Engagement s tatus of FD

. The selection status of the FD and the source of FD guidance should be clear and unambiguous

. Failure of a selected FD should be clearly annunciated. (d) Multiple FDs

. If there are multiple FDs and if necessary for crew awareness, indications should be provided to denote which FD is engaged (for example, FD1, FD2, HUD)

. For airplanes with multiple FDs installed, all engaged FDs should always be in the same armed and active FGS modes

. The selection status of each FD should be clear and unambiguous for each pilot

. In addition, indications should be provided to denote loss of FD independence (for example, first offic er selection of captain’s FD). (e) Autopilot e nga ged

. A FD should engage into the current modes and targets of an already engaged autopilot or FD, if any

. With no autopilot engaged, the basic modes at engagement of the FD functions should be established consistent w ith typical flight operations.
Note: The enga gement of the pitch axis in Vertical Speed or Flight Path Angle and engagement of the lateral axis in Heading Hold, Heading Select, or Bank Angle Hold have been found to be acceptable. (f) HUD

. Since the HUD can display flight guidance, the HUD guidance mode
s hould be indicated to both pilots and should be compatible with the active hea d down FD mode. (g) Maneuvering f light

. Engagement during maneuvering flight should be considered.
Note: The design should consider the safety consequences if it is possible for the FD to engage outside of the normal flight envelope

. It is not required that the FD should compensate for unusual attitudes or other situations outside the normal flight envelope, unless that is part of the FD’s intended function.10/27/14 AC 25.1329

- 1C

19 (2) Guidance c ue(s)
. (a) Display

. The FD command guidance cue(s) will typically be displayed u nder the following conditions:
1 When the FD is selected and valid co mmand guidance is available, or
2 When the FD is automatically providing guidanc e

. (See paragraph 28.a(3) be low. ) (b) Engagement i ndication

. The display of guidance cue(s) (for example, FD bars) is sufficient ind ication that the FD is engaged. (c) Invalid g uidance

. The FD guidance cue(s) should be removed when guidance is determined to be invalid. (3) Reactive w indshear g ui dance s ystem
. For airplanes equipped with a FD windshear guidance system, FD engagement should be provided consistent with the criteria in AC 25

- 12 and AC 120

- 41

. b. FD d isengagement
. There should be a means for each pilot to readily de

- select his or her on

- side FD function

. Flightcrew awareness of disengagement and de

- selection is important

. Removal of guidance cue(s) alone is not sufficient indication of de

- selection because the guidance cue(s) may be removed from view fo r a number of reasons, including invalid guidance or autopilot engagement

. Therefore, the FD function should provide clear and unambiguous indication to the flightcrew that the function has been de

- selected.
29. A utothrust Engagement, Disengagement, and Indica tions
. Engagement and disengagement should be accomplished in a manner consistent with other flightcrew procedures and tasks and should not require undue attention.

a. Autothrust e ngagement
. (1) Indication
. The autothrust function must provide the flightcrew posi tive indication tha t the system has been engaged

. See § 25.1329(i)

. (2) Accessibility of c ontrols
. The autothrust engagement controls shoul d be accessible to each pilot. (3) Inadvertent e ngagement/ d isengagement
. The autothrust function should normally be designed to prevent inadvertent engagement and inadvertent ap plication of thrust for both on

- ground and in

- air operations

. For example, separate arm and eng age functions may be provided. (4) Automatic e ngagement
. Intended automatic engagement, such as a “wake up” mode to protect for unsafe speeds, may be acceptable

. (See Chapter 5 , paragraph 57.b , Low

- Speed Protection , of this AC .) If such automatic engagement occurs, it should be clear to the flightcrew that automatic engagement has occurred

. The automatic engagement may not10/27/14 AC 25.1329

- 1C

20 cause a transient larger than a minor transient

. See § 25.1329(c)

. The transition to the engaged state should be smooth, and should not cause large, unexpected changes in pitch attitudes or pitching moments

. The reason for automatic engagement should be clear and obvious to the flightcrew.
Note: The design should consider the possibility that the pilot may attempt to engage the autothrust function outside of the normal flight envelope or at excessive or too low engine thrust

. It is not expected that the autothrust feature should compensate for situations outside the normal flight envelope or normal engine operation range, unless that is part of the intended f un ction of the autothrust system.
b. Autothrust d isengagement
. (1) Indication of d isengagement
. Positive indication of disengagement of the autothrust function must result in a caution level alert to the flightcrew

. See § 25.1329(k)

. The autothrust “engage” statu s a nnunciations should be deleted. (a) Visual i ndication

. 1 Foll owing automatic disengagement: Visual indication of disengagement should persist until canceled by flightcrew action.
2 F ollowing manual disengagement: If an aural alert is provided, visual indication of disengagement should persist for some minimum period

. If an aural alert is not provided, visual indication of disengagement should persist until canceled by flightcrew action. (b) Aural alert

. If provided, the aural disengagement alert should be of suffici ent duration and volume to assure that the flightcrew has been alerted that disengagement has occurred

. However, an extended cycle of an aural alert is not acceptable following disengagement, if such an alert can significantly interfere with flightcrew coo rdin ation or radio communication. (2) Inadvertent d isengagement
. The autothrust normally should be designed to preclude inadvertent disengagement during activation of a utothrust modes of operation. (3) Consequence of d isengagement
. Under normal conditions, autothr ust disengagement may not cause a transient any greater than a minor transient

. See § 25.1329(d)

. The transition to the disengaged state should be smooth and not cause unexpected changes in pitch attitude or pitching moment or a significant thrust transien t

. The disengagement should not preclude, inhibit, or interfere with timely thrust changes for go

- around, landing, or other maneuvers req uiring manual thrust changes. (4) Autothrust q uick d isengagement c ontrol
. Autothrust quick disengagement controls must be p rovided for each pilot on the respective thrust control (thrust lever or equivalent)

. A single

- action, quick disengagement switch must be incorporated on the thrust control, so that switch activation can be executed when the pilot’s other hand is on the co ntrol wheel (or equivalent)

. See § 25.1329(a)

. The disengagement control should be positioned such10/27/14 AC 25.1329

- 1C

21 that inadvertent disengagement of the autothrust function is unlikely

. Positioning the control on the outboard side has been s hown to be acceptable for multi

- engine aircraft

. Thrust lever knob, end

- mounted disengagement controls available on both sides to facilitate use by either pilot have been shown to be preferable to those positioned to be ac cessible by the pilot’s palm.
30. O verride of the FGS
.

a. General
. An ov erride of an engaged FGS function is defined as an action taken by the flightcrew intended to prevent, oppose, or alter an operation being conducted by the FGS function without first disengaging that function.
b. Autopilot o verride
. (1) With a utomatic d isengageme nt
. (a) Override f orce

. The autopilot should disengage when the flightcrew applies a significant override force to the controls

. The applicant should interpret “significant” as a force that is consistent with an intention to overpower the autopilot by either o r both pilots

. The autopilot should not disengage by minor application of force to the controls, such as a pilot gently bumping the control column while entering or exitin g a pilot seat during cruise.
Note: Twenty

- five pounds (25 lbs) of force at the control col umn or wheel has been determined to be a significant override force level for other than approach operations on some aircraft types

. To reduce nuisance disengagement, higher forces have been found acceptable for certain approach, landing, and go

- around ope rations on some aircraft

. The force to disengage an autopilot is not necessarily the force required at the column to oppose autopilot control, that is, to cause elevator movement

. The corresponding forces for a sidestick controller may be diff erent. (b) Transi ents r esulting from o verride

. In normal operating conditions, a transient larger than a minor transient may not result from autopilot disengagement when the flightcrew applies an override force to the controls

. See § 25.1329(d)

. Mitigation may be accomplis hed through provision of an appropriate alert and flightcrew procedure. (c) Sustained o verride f orce below level required for automatic d isconnect

. Sustained application of force below the disengagement threshold may not result in a potential hazard

. See § 25. 1329(l)

. For example, the automatic trim should not run to oppose the override of the autopilot by the flightcrew that would result in unacceptable airplane motion, if the autopilot were to automatically disengage or be manually disengaged. (2) Without a utomat ic d isengagement
. (a) Potential h azard

. If the FGS is not designed to disengage in response to any override force, then the response to an override may not result in a potential hazard

. Sustained application of an override force may not result in a potential h azard, such as when the flightcrew abruptly releases the force o n the controls

. See § 25.1329(l )

. Mitigation may be accomplished through provision of an appropriate alert and flightcrew p rocedure.10/27/14 AC 25.1329

- 1C

22 Note: The term “sustained application of override force” is inten ded to describe a force that is applied to the controls , which may be small, slow, and sustained for some period of time

. This may be due to an inadvertent crew action or may be an intentional crew action meant to “assist” the autopilot in a par ticular man euver

. (See Chapter 9 , Compliance Demonstration Using Flight Test and Simulation , paragraph 99.f , Flightcrew Override of the FGS , of this AC for more information.) (b) Tr ansients r esulting from o verride

. In normal operating conditions, a transient larger than a minor transient may not result from manual autopilot disengagement after the flightcrew has applied an override force to the controls

. See § 25.1329(d)

. Mitigation may be accomplished through provision of an appropriate alert and flightcrew procedure.
Note 1: The term “override force” is intended to describe a pilot action that is intended to prevent, oppose , or alter an operation being conducted by a flight guidance functio n without first disengaging that function

. One possible reason for this action could be an avoidance maneuver, such as responding to a traffic alert and collision avoidance system (TCAS) resolution advisory that requires immediate action by the flightcrew and would typically involve a rapid and force ful input from the flightcrew.
Note 2: For control wheel steering considerations, see Chapter 6 , Characteristics of Specific Modes , paragraph 68 , Control Wheel Steering (Control Steering through the Autopilot) , of this AC

.

c. Autothrust o verride
. (1) Force r equired
. It should be possible for the pilot to readily override the autothrust function and set thrust by moving the thrust levers ( or equivalent) with one hand. (2) Response t o o verride
. The autothrust response to a flightcrew override may not create a potential hazard

. See § 25.1329(m)

. The autothrust response to the flightcrew override should not result in an abrupt change of pitch attitude, an abrupt pitching moment, or an uncontrolled cha nge of thrust. (3) Engagement s tatus w ith o verride
. Autothrust functions may be designed to remain safely engaged during pilot override

. Alternatively, autothrust fu nctions may disengage as a result of pilot override, provided that the design prevents unintentional autothrust disengagement and adequately alerts the flightcrew to ensure pilot awareness.
31. FGS E ngagement Mode Compatibility
.

a. FGS m ode e ngagement p hilosophy
. A description of the philosophy used for the mode at engagement of the autopilot, FD, and autothrust functions should be provided in flightcrew training material.10/27/14 AC 25.1329

- 1C

23 b. Engagement m ode c ompatibility
. It should not be possible to select incompatible FGS command or guidance functions, such as commanding speed through elevator an d autothrust at the same time.
32

— 41 [RESERVED]10/27/14 AC 25.1329

- 1C

24 CHAPTER 4

. CONTROLS, INDICATION S, AND ALERTS

42. General
.

a. Human

- m achine i nterface
. The human

- machine interface with the FGS is crucial to ensuring safe, effective, and consistent FGS operation

. The manner in which FGS information is depicted to the flightcrew is vital to flightcrew awareness and, therefore, to safe operation of the FGS.
b. Design of c ontrols, i ndications, and a lerts
. These f eatures must be designed to minimize flightcrew errors and confusion

. See § 25.1329(i)

. Indications and alerts should be presented in a manner compatible with the procedures and assigned tasks of the flightcrew and provide the necessary information to perf orm those tasks

. The indications must be grouped and presented in a logical and consistent manner and must be visible from each pilot’s station under all expected lighting conditions

. See § 25.1329(i)

. The choice of colors, fonts, font size, location, orie ntation, movement, graphical layout, and other characteristics

— such as steady or flashing

— should all contribute to the effectiveness of the system

. Controls, indications, and alerts should be implemented in a consisten t manner.

c. Evaluation of i nformation p r ovided by FGS
. It is recommended that the applicant evaluate the adequacy and effectiveness of the information provided by the FGS interface

— that is the controls, indications, alerts, and displays

— to ensure flightcrew awareness of F GS behavior and operatio n

. See Chapter 9 of this AC for more discussion of appropriate analyses , which may include, for example, cognitive task analy sis as a basis for evaluation.
43. FGS C ontrols
.

a. General
. The FGS controls must be designed and located to prevent c rew errors, confusion, and inadvertent operation

. See § 25.1329(i)

. They should be designed to provide convenience of operation to each crewmember

. The function and direction of motion of each control must be readily apparent or plainly indicated on or adj acent to each control, if needed to prevent inappropriate use or confusion

. See § 25.1329(f)

. Sections 25.777(b) and 25.779(a) provide requirements regarding direction of motion of flight deck controls

. These requirements apply for FGS command reference co ntrols that select target values, such as heading select or vertical speed

. Section 25.781 also provides requirement s for the shapes of the knobs.
b. Design c onsiderations
. The design of the FGS should address the fol lowing specific considerations: (1) Differenti ation of k nob s hape and p osition
. Errors by the flightcrew have included confusing spee d and heading knobs on the MSP. (2) Design to s upport c orrect s election of t arget v alues
. Use of a single control, such as concentric controls, for selecting multiple comman d reference targets has resulted in
err oneous target value selection.10/27/14 AC 25.1329

- 1C

25 (3) Commonality a cross a ircraft t ypes . Use of uniform control design in different aircraft prevents negative transfer of learning with respect to operation of the controls

. Using knowledge a bout the operation of the controls on one type of airplane has resulted in activation of the incorrect control when pilots move from that type of airplane to another type of airplane

. An example of this is confusion between the takeoff/go

- around button and the autothrust disengagement button when transitioning between aircraft types with differing designs and locations for these controls. (4) Positioning of c ontrols and r elated i ndications
. Individual FGS controls, flight mode annunciator (FMA), and related PFD information should be positioned so that, as much as reasonably practical, items of related function have similarly related positions

. Misinterpretation and confusion have occurred due to the inconsistent arrangement of FGS controls wit h the annunciations on the FMA. (5) Inadvertent o peration
. The FGS controls must be located to discourage or avoid inadvertent operation, such as inadvertent engagement or disengagement

. See § 25.777(a)

. Further design aspects of the FGS controls, other than location of th e cont rols, should also be used to discourage or avoid inadvertent operation

. Examples include the shape of the control and the force required for operation.
44. FGS M ode Selection, Annunciation, and Indication
.

a. Annunc iation of e ngagement of the FGS
. Engagement of t he FGS functions must be suitably annunciated to each pilot

. See § 25.1329(i)

. Guidance is provided in Chapter 3 , FGS Engagement, Disengagement, Indications, and Override , of this AC

. b. Description of FGS m odes
. The operator should be provided with appropriate descriptions of the FGS modes and their behaviors.

c. FGS m ode a nnunciations
. Mode annunciation must indicate the state of the system

. See § 25.1329(i)

. Mode annunciation should be presented in a manner compatible with flightcrew procedures/tasks and be consistent with the mode annunciation design for the specific aircraft type

. That is, the mode annunciation should be compatible with other flight deck systems mode annunciations

. Mode selector swi tch position or status is not acceptable as the sole means of mode annunciation

. See § 25.1329(i)

. Modes and mode changes should be depicted in a manner that achieves fligh tcrew attention and awareness. (1) Active and a rmed m odes
. The FGS mode annunciations mu st effectively and unambiguously indicate the active and armed modes of operation

. See § 25.1329(i)

. The mode annunciation should convey explicitly, and as simply as possible, what the FGS is doing (for active modes), what it will be doing (for armed modes ), and target information (such as selected speed, heading, and altitude) for satisfactory flightcrew a wareness. (2) Location
. Mode annunciations should be located in the forward field of view

. For example, a suitable location is on the PFD

. Engaged modes shou ld be annunciated at different locations than armed modes to assist in mode recognition.10/27/14 AC 25.1329

- 1C

26 (3) Discriminators
. Color, font type, font size, location, highlighting, and symbol flashing have historical precedent as good discriminators, when implemented appropriate ly

. The fonts and font size should be chosen so that annunciation of FGS mode and status information is readable and understandable without eyestrain when viewed by the pilot seated at the design eye position

. The use of graphical or symbolic (that is, non

- textual) indications is acceptable

. Implementation of such discriminators should follow accepted guidelines, as described in applicable interna tional standards (such as AC 25

- 11 A , Flight Test Guide for Certification of Transport Category Airplanes ), and should be evaluated for their consistency and integration with the flight deck design. (4) Color
. Color should be used in a consistent manner and assure compatibility with the overall use of color on the flight deck

. S pecific colors should be used such that the FGS displays are consistent with other flight deck systems, such as a FMS

. The use of monochrome displays is not precluded, provided that the aspects of flightcrew attention and awareness are satisfied

. Engaged m odes should be annunciated with different colors than armed modes to assist in mode rec ognition.
d. Mode c hanges
. (1) Operationally r elevant m ode c hanges
. Mode changes that are operationally relevant

— especially mode reversions and sustained speed protection

— shoul d be clearly and positively annunciated to ensure flightcrew awareness

. Altitude Capture is an example of an operationally relevant mode that should be annunciated because pilot actions during that brief time the mode is operational may have different effe cts on the airplane

. Annunciation of sustained speed protection should be clear and distinct to ensure flightcrew awareness

. The FGS sub

- modes that are not operationally relevant (for example, sub

- modes as the FGS transitions from instrument landing syste m Localizer (LOC) Capture to Localizer Track) need not be annunciate d. (2) Attention

- g etting f eatures
. The transition from an armed mode to an engaged mode should provide an additional attention

- getting feature, such as boxing and flashing on an electronic dis play (see AC 25

- 11A ) for a suitable, but brief, period (for example, ten seconds) to assist in flightcrew awareness

. Aural notification of mode changes should be limi ted to special considerations. (3) Use o f a lerts
. In

- service experience has shown that mode an nunciation alone may be insufficient

— unclear or not compelling enough

— to communicate mode changes to the flightcrew, especially in high workload situations

. Therefore, the safety consequences of the flightcrew not recognizing mode changes should be conside red

. If necessary, an appropriate alert shou ld be used.

e. Failure to e ngage or a rm . The failure of a mode to engage or arm when selected by t he pilot should be apparent.
f. F GS m ode d isplay and i ndications
. Mode information provided to the flightcrew should be sufficiently detailed, so that the consequences of the interaction between the FGS and the flightcrew can be determined unambiguously

. The FGS interface should provide timely and10/27/14 AC 25.1329

- 1C

27 positive indication when the FGS deviates from the pilot’ s direct commands (f or example, a target altitude or s peed setting) or from the pilot’ s pre
- programmed set of commands (for example, waypoint crossing)

. The interface should also provide clear indication when there is a difference or conflict between pilot

- initiated commands

. An example would be when a pilot engages positive vertical speed and then selects an altitude that is lower than the aircraft altitude

. The default action taken by t he FGS should be made apparent.
45. FGS A lerting, Warning, Caution, Advisory, and Status
.

a. Gene ral
. (1) Alerting p rovisions
. Alerting information must follow the provisions of § 25.1322

. The advisory material associated with § 25.1322 should be consulted

. Alerts for FGS engagement and disenga gement are described in Chapter 3 of this A C

. (2) Determination of FGS c apability
. There should be some method for the flightcrew to determine and monitor the availability or capability of the FGS (for example, prior to dispatch), where the intended operation is predicated on the use of the FGS

. The me thod of monitoring provided should take account of the hazard resulting from the loss of the autopilot function for the intended operation.
b. Speed p rotection a lerts
. (1) Alerts to c rew . To assure crew awareness, an alert should be provided when a sustained spee d protection condition is detected

. This is in addition to any annunciations associated with mode reversions that occur as a consequence of invoking speed protection

. (See Chapter 5 , pa ragraph 57 , Speed Protection , of this AC ). (2) Alert s pecifications
. (a) Low

- s peed p rotection

. Low

- speed protection alerts should include both an aural and a visual component. (b) High

- s peed p rotection

. High

- speed protection alerts need include only a visual alert component because of existing high

- speed aural alert requirements

. However, giving an alert prior to that required aural alert is not precluded

. See § 25.1303(c)(1) for o verspeed alerting regulations. (3) Consistency
. Alerts for speed protectio n should be consistent with the protection provided and with the oth er alerts in the flight deck. (4) Nuisance a lerts
. Care should be taken to set appropriate values for indicating speed protection that would not be considered a nuisance for the flightcrew.

c. Lo ss of a utopilot a pproach m ode
. The loss of the Approach mode requires immediate flightcrew awareness

. This may be accomplished through autopilot di sengagement described in AC 120

- 28D

. If the autopilot remains engaged and reverts to a non

- approach mode, an appropriate aural warning and/or visual alert should be provided.10/27/14 AC 25.1329

- 1C

28 d. Awareness of potential significant transient condition (“b ark b efore b ite”)
. (1) General
. There have been situations where an autopilot was engaged, operating normally , and controlling up to the limit of its authority for an extended period of time, and the flightcrew was unaware of the potential hazard

. This service experience has shown that, without timely flightcrew awareness and action, such a situation can progress to a loss of control after autopilot disengagement, particularly in rare normal or non

- normal conditions

. However, with adequate flightcrew awareness and pilot action, lo ss of control may be prevented. (2) Flightcrew a lert(s)
. To help ensure flightcrew awareness and timely action, appropriate alert(s)

— normally a caution or warning

— should be provided to the flightcrew for conditions that could require except ional piloting skill or alertness for manual control following autopilot disengagement (for example, significantly out

- of

- trim conditions)

. The number and type of alerts required should be determined by the unique situations that are being detected and by the crew procedures required to address those situations

. Any alert should be clear and unambiguous and should be consistent and compatible with other flight deck alerts

. Care should be taken to set appropriate thresholds for these alerts so that they are not considered a nuisance for the flightcrew. (3) Situations to c onsider for an a lert
. (a) Sustained l ateral c ontrol c ommand

. If the autopilot is holding a sustained lateral control command, it could be indicative of an unusual operating condition for which the
au topilot is compensating

. Examples of such unusual operating conditions are asymmetric lift and/or drag due to asymmetric icing, fuel imbalance, or asymmetric thrust

. In the worst case, the autopilot may be operating at or near its full authority in one dir ection

. If the autopilot were to disengage while holding this lateral trim, the result would be that the airplane could undergo a rolling moment that could possibly take the pilot by surprise

. Therefore, a timely alert should be considered to permit the cr ew to manually disengage the autopilot and take control prior to any automatic disengagement that might result from the condition. (b) Sustained p itch c ommand

. If the autopilot is holding sustained pitch command, it could be indicative of an unusual operating condition (for example, inoperative automatic horizontal trim) for which the autopilot is compensating

. If the autopilot were to disengage while holding this pitch command, the result would be that the airplane could undergo an abrupt change in pitch that could possibly take the pilot by surprise

. Therefore, a timely alert should be considered to permit the crew to manually disengage the autopilot and take control prior to any automatic disengagement that might result from the condition. (c) Bank and p itch a ngl es

. Most autopilots are designed with operational limits in both the pitch and roll axes, such that those predetermined limits will not be purposely exceeded

. If the airplane exceeds those limits, it could be indicative of a situation that requires the pil ot to intervene

. Such a situation may not be covered by paragraphs 45.d(3)(a) or 45.d(3)(b) above

. Therefore, a timely alert should bring this condition to the attention of the flightcrew and permit the crew to manually disengage the autopilot and take control prior to any automatic d isengagement that might result.10/27/14 AC 25.1329

- 1C

29 (4) Automatic d isengagement

. It is preferable that the autopilot remains engaged during out

- of

- trim conditions

. However, if there is an autom atic disengagement feature due to excessive out

- of

- trim, an alert should be generated and should precede any automatic disengagement with sufficient margin to permit timely flightcrew recognition and manual disengagement

. See also Chapter 3 , paragraph 30 , Override of the FGS , of this AC for related material.
Note 1: This paragraph is not intended to require alerting for all instances of automatic autopilot disengagement

. It is intended only for conditions that would, if not addressed, lead to disengagement that could result in a significant transient (or greater) for which the pilot may be unprepared

. The intent is to provide crew awareness that would allow the flightcrew to be prepared with hands on controls and take appropriate corrective action before the condition results in a potentially hazardous airplane configuration or state.
Note 2: This paragraph describes alerting requirements for conditions resulting in unintended out

- of

- tr im operation

. There are FGS functions that can intentionally produce out

- of

- trim conditions

. Examples would be parallel rudder operation in align or engine failure compensation modes, pitch trim operation during the approach/landing to provide trim up/flar e spring bias, and pitch trim operation for certain types of speed/Mach trim systems

. It is not the intent of this paragraph to require alerts for functions producing intentional out

- of

- trim conditions

. Other system indications (for example, mode and statu s annunciations) should be provided to make the crew aware of the operation of thes e functions, where appropriate.
46. FGS C onsiderations for HUD s .

a. General
. HUDs have unique characteristics compared to flight displays installed on the instrument panel

. Most of these HUD differences are addressed during HUD certification whether or not the HUD provides flight guidance functions

. The intent of this chapter is to address how such HUD differences may affect FGS functions

. (See SAE ARP5288 for further information on this subject

. See paragraph 4.c of this AC for information on how to obtain SAE docu ments .)
b. Characteristics of HUD g uidance
. (1) Supplemental u se d isplay s ystem
. If the H UD is designed as a supplemental use display system, it does not replace the requirement for standard head down display (HDD) of flight instrument data

. The HUD is intended for use during takeoff, climb, cruise, descent, approach, and landing under day, ni ght, visual meteorological conditions (VMC), and instrument meteorological conditions (IMC) conditions

. When it can be reasonably expected that the pilot will operate primarily by reference to the HUD, it should be shown that the HUD is satisfactory for ma nually controlling the airplane and for monitor ing the performance of the FGS. (2) External v isual r eferences
. During takeoff and landing in certain light and visibility conditions, HUD symbology can be extremely dominant in comparison to external10/27/14 AC 25.1329

- 1C

30 visual refer ences

. When visual references are relatively dim, extremely active symbology dynamics and guidance cue gains can lead the pilot to make excessively strong corrections

. It should be shown that

— if HUD guidance cues are followed regardless of the appearance o f external visual references

— they do not cause the pilot to take unsafe actions. (3) Interference and o cclusion
. It should be shown that there is no interference between the indications of primary flight information and the flight guidance cues

. In takeoff, ap proach, and landing FGS modes, the flight guidance symbology should have occlusion priority

. That is, the flight guidance symbology should not be obscured or covered by the primary flight information

. The HUD guidance symbology should not excessively inter fere with pilots’ forward view, ability to visually maneuver the airplane, acquire opposing traffic, and see the runway environment. (4) Display c riteria
. Generally, the criteria for the mechanization of guidance displayed on the HUD should be no different tha n for guidance dis played on the HDD

. See Chapter 5 of this AC

. (5) Conformal s y mbology
. Unlike HDDs, HUDs are capable of displaying certain symbology conformal to the outside scene, including guidance cues

. Consequently, the range of motion of this conformal symbology, including the guidance cues, can present certain challenges in rapidly changing and high crosswind conditions

. In certain cases, the motion of the guidance and the primary reference cue may be limited by the field of view

. It s hould be shown that, in such cases, the guidance remains usable and that there is a positive indication that it is no longer
con formal with the outside scene. (6) Low v isibility a pproach
. The HUD guidance is often used in cases, like the low visibility approac h, where the pilot will need to reference both the information displayed on the HUD and outside references

. Consequently, it should be shown that the location and presentation of the HUD information does not distract the pilot or obscure the pilot’s outsid e view

. For example, it would be necessary for the pilot to track the guidance to the runway without having the view of runway references or hazards along the flight path obscured by the HUD symbology. (7) Clutter
. The HUD display should present flight guidanc e information in a clear and unambiguous manner

. Display clutter should be minimized

. Some flight guidance data elements are essential or critical and should not be remo ved by any de

- clutter function.

c. HUD/HDD c ompatibility
. (1) General
. The HUD FGS symbology s hould be compatible and consistent with symbology on other FGS displays such as head down electron ic flight instruments

. The FGS

- related display parameters should be consistent to avoid misinterpretation of similar information, but the display presentation s need not be identical

. The HUD and head down PFD formats and data sources need to be compatible to ensure that the same FGS

- related information presented on both displays h ave the same intended meaning. (2) Consistency and c ompatibility
. While not all inform ation displayed on the HUD is directly related to the FGS, the pilot is likely to use most of the displayed information while using the HUD

- displayed guidance and FGS annunciations

. Therefore, when applicable, the10/27/14 AC 25.1329

- 1C

31 guidelines below for the presentation of F GS

- related display information should be followed as much as possible

. Certain deviations from these guidelines may be appropriate due to conflict with other information display characteristics or requirements unique to HUDs

. These may include minimization of display clutter, minimization of excessive symbol flashing, and the presentation of certain information c onformal to the outside scene. (a) Symbology

. Symbols should be the same f ormat

. For example, a triangle

- shaped pointer head down should appear as a tr iangle pointer head up

. However, some differences in HUD symbology, such as the FD “circle” versus head down FD “bars” or “wedge ,” have been found acceptable. (b) Location

. Information (symbols) should appear in the same general location relative to other info rmation. (c) Alphanumeric d ata

. Alphanumeric readouts should have the same resolution, units, and labeling

. For example, the command reference indication for “vertical speed” should be displayed in the same foot

- per
- minute increments and be labeled with th e sa me characters as the HDDs. (d) Analog s cales

. Analog scales or dials should have the same range and dynamic operation

. For example, a glideslope deviation scale displayed head up should have the same displayed range as the glideslope deviation scale displayed head down, and the direction of movement should be consistent. (e) Display of FGS m odes

. The FGS modes and status state transitions should be displayed on the HUD using consistent methods, except for the use of color

. That is, the method used head down to indi cate a FD mode transitioning from armed to capture d should also be used head up. (f) Information s ources

. Information sources should be consistent between the HUDs and th e HDDs used by the same pilot. (g) Display of FGS c ommand i nformation

. When FGS command inform ation (for example, a FD command) is displayed on the HUD in addition to the HDDs, the HUD depiction and guidance cue deviation “scaling” needs to be consistent with that used on the HDDs

. This is intended to provide comparable pilot performance and worklo ad when using either HUDs or HDDs. (h) Display for p ilot n ot f lying

. The same information concerning current HUD system mode, reference data, status state transitions, and alert information that is displayed to the pilot flying (PF) on the HUD should also be d isplayed to the pilot not flying (PNF) on the HDDs

. Consistent nomenclature should be used to ensure unambiguous awareness of the HUD operation.
d. Alerting i ssues . (1) Alerts d isplayed on HUDs
. Although HUDs are typically not intended to be classified as integra ted caution and warning systems, they may display cautions, warnings, and10/27/14 AC 25.1329

- 1C

32 advisories as part of their FGS function

. In this regard, HUDs should provide the equivalent alerting functionality as the head down PFD(s)

. Warnings that require continued flightcre w attention on the PFD also should be presented on the HUD (for example, TCAS, windshear, and ground proximity warning (GPWS) annunciations)

. If master alerting indications are not provided within the peripheral field of view of the pilot while using the H UD, the HUD should provide annunciations that inform the pilot of cautio n and/or warning conditions. (2) Monochrome HUDs
. For monochrome HUD s, appropriate use of attention

- getting properties, such as flashing, outline boxes, brightness, size, and/or location a re necessary to adequately compensate for the lack of color normally assigned to distinguish and call attention to
cau tions and warnings. (3) Multi

- c olor HUDs
. For multi

- color HUDs, the use of red, amber, or yellow for symbols not related to caution and warnin g functions should be avoided, so that the effectiveness of distinguishing characteristics of true cautions and warnings is not reduced. (4) Single HUD i nstallation
. Single HUD installations rely on the fact that the pilot not flying will monitor the head down instruments and alerting systems for failures of systems, modes, and functions not associ ated with PFDs. (5) Dual HUD i nstallations

. Dual HUD installations require special consideration for alerting systems

. It should be assumed that both pilots will be head up simultaneously (full or part

- time), especially when the HUD is being used as the primary flight reference or when the HUD is required equipment for the operation being conducted

. If master alerting indications are not provided within the peripheral fiel d of view of each pilot while using the HUD, then each HUD should provide annunciations that direct the pilot’s attention to head down alerting displays

. The types of information that should trigger the HUD master alerting display are any cautions or warni ngs not already duplicated on the HUD from head down primary display as well as any caution level or warning level engine indications or system alerts.
Note: The objective is to avoid redirecting attention of the pilot flying to an other display when an immediate maneuver is required (for example, TCAS resolution advisory, w indshear). (6) GPWS/ TCAS on HUD
. If a GPWS, windshear detection system, windshear escape guidance system, or a TCAS is installed, then the guidance, warnings , and annunciations required to be a par t of these systems and normally required to be in the pilot’s primary field of view should be displayed on the HUD.

e. Upset/ u nusual a ttitude r ecovery g uidance
. (1) Guidance c ues . Upsets due to wake turbulence or other environmental conditions may result in near instantaneous excursions in pitch and bank angles and a subsequent unusual attitude

. If the HUD is designed to provide guidance for recovery from upsets or unusual attitudes, recovery steering guidance commands should be distinct from and not confused with orientation symbolo gy such as horizon “pointers.” For example, a cue for left control wheel/stick input should not be confused with a cue indicating direction to the nearest horizon

. Guidance should be removed if cues become invalid at extreme attitudes, such as zenith, nadir, overbanked10/27/14 AC 25.1329

- 1C

33 (for example, greater than 90 degrees bank angle), or inverted

. For extreme attitudes, it is acceptable for the pilot to transition to the HDD, provided that the cues to transition from the HUD are clear and unambiguous. (2) O rientation c ues . If the HUD is designed to provide only orientation during upsets or unusual attitudes (that is, no guidance cues are provided), those orientation cues should be designed to prevent them from being mistaken as flight control input commands.
47

— 51 [RESERVE D]10/27/14 AC 25.1329

- 1C

34 CHAPTER 5

. PERFORMANCE OF FUNCT ION

52. General
.

a. Intended f unction
. The FGS should provide guidance or control, as appropriate, for the intended function of the active mode(s) in a safe and predictable manner within the airplane’s normal flight envelope

. There are special considerations when the FGS is operating at the limits of its performance capabilities or under significant environmental conditions

. The following paragraphs provide criteria for acceptable means of compliance and interp retive material pertaining to these considerations.
b. Effect of s ystem t olerances
. Where system tolerances have a significant effect on autopilot authority limits, consideration should be given to the effect on autopilot performance

. Factors to be considered include, but are not limited to, tolerances of servo authority, servo clutch setting, “cam

- out” settings, control friction, and sensor tolerances.
53. Normal P erformance
.

a. General
. The FGS should be designed to provide guidance or control, as appropriate, for the intended function of the active mode(s) in a safe and predictable manner within the airp lane’s normal flight envelope.
b. Conditions to c onsider
. The design of the FGS should consider the normal conditions listed in table 5

- 1 of this AC

. This table does not fully define every condition that may be encountered during an airplane’s life and unequivocally categorize what can be conside red to be a “normal condition.” Rather, the table is intended to give examples to be used during system development and testing

. By the very nature of the phenomena involved, there will always be some subjectivity to these categorizations

. Also, the same conditions may affect different airplane models in very different ways

. These differences should be consi dered in determining how to characterize the severity of the conditions discussed in the table.10/27/14 AC 25.1329

- 1C

35 Table 5

- 1
. Examples of Normal Conditions

Condition Example
No failure conditions All airplane systems that are associated with airplane performance are fully o perational

. Failures of those systems could im pair the FGS ’s ability to perform its functions. Light to moderate winds Constant wind in a specific direction that may cause a slight deviation in intended flight path or a small difference between airspeed a nd groundspeed. Light to moderate wind gradients Variation in wind velocity

— as a function of altitude, position, or time

— that may cause slight erratic or unpredictable changes in intended flight path. Light to moderate gusts Non

- repetitive momentary chan ges in wind velocity that can cause changes in altitude and/or attitude to occur, but the aircraft remains in positive control at all times. Light turbulence Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, ro ll, or yaw).
Moderate turbulence Similar to light turbulence but of greater intensity

. Changes in altitude and/or attitude occur, but the aircraft remains in positive control at all times

. Light chop Turbulence that causes slight, rapid, and somewhat rh ythmic bumpiness without appreciable changes in altitude or attitude. Moderate chop Similar to light chop but of greater intensity

. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude. Icing All icing conditions co vered by 14 CFR p art 25, Appendix C, with the exception of “asymmetric icing” and “large drop icing” discussed under “Rar e Normal Conditions” in table 5

- 2 of this AC

. Note: Representative levels of the environmental effects should be established consistent with the airplane’s intended operation.10/27/14 AC 25.1329

- 1C

36 c. Level of p erformance
. (1) Significant c haracteristics
. Any performance characteristics that are operationally significant or operationally limiting must be identified with an appropriate statement or limitation in the airplane flight manual (AFM)

. See § 25.1581

. (2) Configuration c hanges
. The FGS should perform its intended function during routine airplane configuration or power changes, including the operation of secondary flight controls an d landing gear. (3) Compliance e valuation
. Evaluation of FGS performance for compliance should be based on the minimum level of performance needed for its intended functions

. Subjective judgment may be applied to account for experience acquired from similar eq uipment and levels that have been established as operationally acceptable by the end

- user. (4) P rescribed l evels of p erformance
. There are certain operations that dictate a prescribed level of performance

. When the FGS is intended for operations that require s pecific levels of performance, the use of FGS should be shown to meet those specific levels of performance (for example, low visibility operations

— Category II and III operations, RVSM, RNP). (5) Equivalence of p erformance
. The FGS performance of intended funct ions should at least be equivalent to that expected of a pilot for a similar task

. AC 25

- 7C and SAE ARP5366, Autopilot, Flight Director, and Autothrust Systems , may prove useful for establishing the general behavior of the FGS

. When integrated with navigation (NAV) sensors or the FMS, the FGS should satisfy the flight technical error tolerances expected for th e use of those systems in performing their intended functions. (6) Autopilot
. The autopilot should provide smooth and accurate control without divergent or perceptible sustained nuisance oscillation. (7) Flight d irector
. The FD, in each available display presentat ion (for example, single cue, cross

- pointer, flight path director) should provide smooth and accurate guidance and be appropriately damped, to achieve satisfactory control task performance without pilot compensation or excessive workload. (8) Autothru st
. The a utothrust function should provide smooth and accurate control of thrust without significant or sustained oscillatory power changes or excessive overshoot of the required power setting. (9) Automatic t rim
. The automatic pitch trim function should operate at a r ate sufficient to mitigate excessive control surface deflections or limitations of control authority without introducing adverse interactions with automatic control of the aircraft

. Automatic roll and yaw trim functions, if installed, should operate withou t introducing adverse interactions with auto matic control of the aircraft.10/27/14 AC 25.1329

- 1C

37 54. P erformance in Rare Normal Conditions
.

a. General
. (1) Range of c onditions
. The FGS will encounter a wide range of conditions in normal operations, some of which may be infrequent but levy a greater than average demand on the FGS capabilities

. Certain environmental conditions, as discussed in paragraph 54.b below, are prime examples

. The FGS performance during such rare normal conditions should be assessed. (2) Effe ct on p erformance
. Rare normal conditions may degrade the performance of the FGS but should be safe for operation of the FGS

. The relative infrequency of such conditions may also be a factor in the flightcrew’s ability to detect and mitigate in a timely ma nner any limited capability of the FGS to cope with them.
b. Conditions to c onsider
. The design of the FGS should consider the rare normal conditions listed in the table 5

- 2 of this AC

. This table does not fully define every condition th at may be encountered during an airplane’s life and unequivocally categorize what can be considered t o be a “rare normal condition.” Rather, the table is intended to give examples to be used during system development and testing

. By the very nature of the phenomena involved, there will always be some subjectivity to these categorizations

. Also, the same conditions may affect different airplane models in very different ways

. These differences should be considered in determining how to characterize the severi ty of the conditions discussed in the table.10/27/14 AC 25.1329

- 1C

38 Table 5

- 2
. Examples of Rare Normal Conditions

Condition Example Significant winds Constant wind in a specific direction that may cause a large change in intended flight path or groundspeed or cause a large diff erence between airspeed and groundspeed. Significant wind gradients Variation in wind velocity

— as a function of altitude, position, or time

— that may cause large changes in intended flight path.
Windshear/ microburst A wind gradient of such magnitude that it may cause damage to the aircraft. Large gusts Non

- repetitive momentary changes in wind velocity that can cause large changes in altitude and/or attitude to occur

. Aircraft may be momentarily out of control.
Severe turbulence Turbulence that causes la rge, abrupt changes in altitude or attitude

. It usually causes large variations in indicated airspeed

. Aircraft may be momentarily out of control. Large drop icing Applicable icing co nditions covered by 14 CFR part 25, Appendix O. Asymmetric icing Icing conditions that result in ice accumulations that causes the FGS, if engaged, to counter the aerodynamic effect of the icing conditions with a sustained pitch, roll, or yaw command that approaches its maximum authority.
Note: Airplanes intended to meet § 121.35 8 for windshear warning and guidance need FD windshear guidance

. The FGS may also provide suitable autopilot control during windshear

. See AC 25

- 12 and AC 120

- 41 for windshear guidance system requirements.

c. Level of p erformance
. (1) Performance s tandard
. For ra re normal conditions, the FGS should be designed to provide guidance or control, as appropriate, for the intended function of the active mode(s) in a safe and predictable manner, both within the normal flight envelope and for momentary excursions outside t he normal flight envelope

. If a determination is made that there are environmental conditions in which the FGS cannot be safely operated, appropriate operational limitations should be placed in the AFM.10/27/14 AC 25.1329

- 1C

39 (2) Autopilot a uthority l imit
. Operations in rare normal conditions may result in automatic or pilot

- initiated autopilot disengagement close to the limit of autopilot authority

. Autopilot disengagement in rare normal conditions should meet the safety criteria for autopilot disengagement found in Chapter 3 , paragraph 27.b , Autopilot Disengagement , and the criteria for flig ht guidance alerting in Chapter 4 , paragraph 45. d of this AC

. (3) Masking of p otential h azard
. It is not necessary that the FGS always be disengaged when rare normal conditions that may degrade its performance or capability are encountered

. The FGS may significantly help the flightcrew during such conditio ns

. However, the design should address the potential for the FGS to mask a condition from the flightcrew or otherwise delay appropriate flightcrew action

. F or discussion of alerting under such conditions , s ee Chapter 4 , paragraph 45 , FGS Alerting, Warning, Caution, Advisory, and Status , of this AC

. 55. Icing Considerations in Normal and Rare Normal Conditions
.

a. Effect on p erformance
. The FGS typically will be designed t o provide acceptable performance in all standard airplane configurations

. Operating an airplane in icing conditions can have significant implications on the aerodynamic characteristics of the airplane (for example, ice accretion on wings, tail, and engines ) and, consequently, on FGS performance

. Ice accretion may be slow, rapid, symmetric, or asymmetric

. During autopilot operation, the flightcrew may not be aware of the gradual onset of icing conditions or the effect that the accumulation of ice is having
o n the handling qualities of the airplane.
b. Alerts
. Means should be provided to alert the flightcrew when icing conditions begin to have an effect upon FGS perfo rmance, as described in Chapter 4 , paragraph 4 5 of this AC

.

c. Effect o n s peed p rotection
. The implication of icing conditions on speed protection should be assessed

. If the threshold of the stall warning system is adjusted due to icing conditions, appropriate adjustments should als o be made to the FGS low

- speed protection threshold, which is discussed in paragraph 57.b of this chapter.
56. P erformance in Non

- Normal Conditions
.

a. General
. The FGS will occasionally be operating when the airplane transitions outside of its normal fli ght envelope, due to failures or non

- standard ferry configurations

. Under such circumstances, the FGS characteristics and flightcrew interaction with the FGS should be shown to be safe.
b. Conditions to c onsider
. Table 5

- 3 of this AC sho ws examples of non

- normal conditions

. The table does not fully define every condition that may be encountered during an airplane’s life and unequivocally categorize what can be considered to be a “non

- normal condition.” Rather, the table is intended to giv e examples to be used during system development and testing

. By the very nature of the phenomena involved, there will always be some subjectivity to these categorizations

. Also, the same conditions may affect different airplane models in very different way s

. These differences should be considered in determining how to characterize the severity of the conditions discussed in the following table.10/27/14 AC 25.1329

- 1C

40 Table 5

- 3
. Examples of Non

- Normal Conditions

c. Level of p erformance
. (1) Performance s tandard
. For non

- normal conditions, the FGS should be designed to provide guidance or control, as appropriate, for the intended function of the active mode(s) in a safe and predictable manner, both within the normal flight envelope and for momentary excursions outside the normal flight envelope

. If a determination is made that there are
non
- normal conditions in which the FGS cannot be safely operated, appropriate operational limitations should be placed in the AFM. (2) Autopilot a uthority l imit
. Operations in non

- normal conditions may result in automatic or pilot

- initiated autopilot disengagement close to the limit of autopilot authority

. Autopilot disengagement in non

- normal conditions should meet the safety criteria for autopilot disengagement found in Chapter 3 , paragraph 27.b and th e criteria for flig ht guidance alerting in Chapter 4 , paragraph 45.d of this AC

. Condition Term Significant fuel imbalance Large variation of the amo unt of fuel between the two wing tanks (and center and tail tanks, if so equipped) that causes the FGS, if engaged, to counter the aerodynamic effect of the fuel imbalance with a pitch, roll, or yaw command that is approaching maximum system authority.
No n
- standard ferry flight configurations Possible aerodynamic drag (both symmetrical and unsymmetrical) caused by non

- standard airplane ferry flight conditions such as locked high lift devices, landing gear locked in the deployed position, or an extra engine carried underneath one wing in an inoperative position. Inoperative engine(s) Loss of one or more engines that causes the FGS, if engaged, to counter the aerodynamic effect of the difference in thrust with a pitch, roll, or yaw command that is approachin g maximum system authority.
Loss of one or more hydraulic systems Loss of one or more hydraulic systems down to the minimum amount of remaining operational systems that the FGS is certified to operate. Inoperative Ice Detection/Protection System Loss of ice detection/protection system on an airplane so equipped where the FGS is certified for operation in icing conditions with that failure present.10/27/14 AC 25.1329

- 1C

41 (3) Masking of p o tential h azard
. It is not necessary that the FGS always be disengaged when non

- normal conditions that may degrade its performance or capability are encountered

. The FGS may significantly help the flightcrew during such conditions

. However, the design should address the potential for the FGS to mask a condition from the flightcrew or otherwise delay appropriate flightc rew action

. F or discussion of alerting under such conditions , s ee Chapter 4 , paragraph 45 of this AC

. 57. S peed Protection
.

a. General
. (1) Speed e xcursions
. The requirement for speed protection is based on the prem ise that reliance on flightcrew attentiveness to airspeed indications alone during FGS operation is not adequate to avoid unacceptable speed excursions outside the speed range of the normal flight envelope

. Many existing FGS systems have no provisions to a void speed excursions outside the normal flight envelope

. Some FGSs will remain engaged until the aircraft slows to stall conditions and also to speeds well above maximum operating limit speed/maximum operating limit Mach (V MO /M MO ). (2) Compliance with § 25.13 29(h)
. Standard stall warning and high

- speed alerts are not always timely enough for the flightcrew to intervene to prevent unacceptable speed excursions during FGS operation

. The intent of § 25.1329(h) is for the FGS to provide a speed protection function for all operating modes, so that the airspeed can be safely maintained within an acceptable margin of the speed range of the normal flight envelope

. The FGS design may use any of the following ways or a combination of ways to provide acceptable speed prot ection: (a) The FGS provides speed p rotection

. In this case, the following are acceptable means to comply with this rule:
1 The FGS may detect the speed protection condition, alert the flightcrew, and provide speed protection control or guidance.
2 The FGS may det ect the speed protection condition, alert the flightcrew, and then disengage the FGS.
3 The FGS may detect the speed protection condition, alert the flightcrew, and remain engaged in the active mode without providing speed protection control or guidance. (b) Oth er systems provide speed p rotection

. Other systems, such as the primary flight control system or the FMS (when in a vertical navigation (VNAV) mode) may be used to provide equivalent speed protection.
Note: If compliance with this requirement is based on use of alerting alone, the alerts should be shown to be appropriate and timely to ensure flightcrew awareness and enable the pilot to keep the airplane within an acceptable margin from the speed range of the normal flight envelope

. F or additional discussion of sp eed protection alerting , s ee Chapter 4 , paragraph 45.b , Speed Protection Alerts

.10/27/14 AC 25.1329

- 1C

42 (3) Design s tandard
. (a) Interaction of FGS e lements

. The design should consider ho w and when the speed protection is provided for combinations of autopilot, FDs, and autothrust operation

. Care should be taken to set appropriate values for transitioning into and out of speed protection such that the flightcrew does not consider the trans itions a nuisance. (b) Integration of p itch and t hrust c ontrol

. The speed protection function should integrate pitch and thrust control

. Consideration should be given to automatically activating the autothrust function when speed protection is invoked

. If an a utothrust function is either not provided or is unavailable, speed protection should be provided through pitch control alone. (c) Interaction of s ystems

. The role and interaction of autothrust with elements of the FMS, the primary flight control system, and th e propulsion system, as applicable, should be accounted for in the design for speed protection. (d) Engine i noperative

. Consideration should be given to the effects of an engine inoperative condition on the performance of speed protection.
b. Low

- s peed p rotection
. (1) General
. When the FGS is engaged in any mode (with the possible exception of Appr oach, as discussed in paragraph 57.b(3) below) for which the available thrust is insufficient to maintain a safe operating speed, the low

- speed protection function should be invoked to avoid unsafe speed excursions. (2) Factors to c onsider
. Activation of speed protection should take into account such factors as the phase of flight, turbulence and gusty wind conditions, and compatibility with the speed schedules

. The low

- speed protection function should activate at a suitable margin to stall warning that will not result in nuisance alerts

. Consider the operational speeds, as specified in the AFM, for all

- engine and engine

- inoperative cases during the fo llowing phases of flight: (a) Takeoff

. (b) Departure, climb, cruise, descent, and terminal area operations

. During these flight phases, airplanes are normally operated at or above the minimum maneuvering speed for the given flap configuration.
Note: For high altitude op erations, it may be desirable to incorporate low

- speed protection at the appropriate engine out drift

- down speed schedule, if the FGS (or other integrated sensors/systems) can determine that the thrust deficiency is due to an engine failure. (c) Approach

. (d) Tran sition from approach t o go
- around and go

- around climb

.10/27/14 AC 25.1329

- 1C

43 Note: A low

- speed alert and a transition to the Speed Protection mode at approximately 1.13 V SR (reference stall speed) for the landing flap configuration ha s been found to be acceptable. (3) Low

- s peed p rotectio n d uring a pproach o perations
. (a) Non

- i nterference

. Speed protection should not interfere with the approach and landing phases of flight. (b) Autothrust o peration

. It is assumed that with autothrust operating normally, the combination of thrust control and pitch c ontrol during the approach will be sufficient to maintain speed and desired vertical flight path

. In cases where it is not sufficient, an alert should be provided in time for the flightcrew to take appropriate corrective action. (c) Defined v ertical p ath

. For approach operations with a defined vertical path (for example, ILS, MLS, GLS, Lateral Navigation (LNAV) mode, VNAV mode), if the thrust is insufficient to maintain both the desired flight path and the desired approach speed, there are several ways to meet the intent of low

- speed protection:
1 The FGS may maintain the defined vertical path as the airplane decelerates below the desired approach speed unt il the airspeed reaches the low

- speed protection value

. At that time, the FGS would provide guidance to maint ain the low

- speed protection value as the airplane departs the defined vertical path

. The FGS mode reversion and low

- speed alert should be activa ted to ensure pilot awareness.
Note: The pilot is expected to take corrective action to add thrust and return the airplane to the defined vertical path or go

- around, as necessa ry.
2 The FGS may maintain the defined vertical path as the airplane decelerates below the desired approach speed to the low

- speed protection value

. The FGS will then provide a low

- speed alert while remaining in the existing FGS approach mode.
Note: The pilot is expected to take corrective action to add thrust to cause the airplane to accelerate back to the desired approach speed while maintaining the defined vertical path or go

- around, as necessary.
3 The FG S may maintain the defined vertical path as the airplane decelerates below the desired approach speed until the airspeed reaches the low

- speed protection value

. The FGS will then provide a low

- speed alert and disengage.
Note: The pilot is expected to take correc tive act ion when alerted to the low

- speed condition and the disengagement of the autopilot, to add thrust, and to manually return the airplane to the desired vertical path or go
- around. (d) Vertical f light p ath n ot p rotected

. If the speed protection is invoked during approach such that vertical flight path is not protected, the subsequent behavior of the FGS after speed protection should be carefully considered

. Activating low

- speed protection during the10/27/14 AC 25.1329

- 1C

44 approach, resuming the Approach mode, and re

- acquiring th e defined vertical path may be an acceptable response, if the activation is sufficiently brief and not accompanied by large speed or path deviations

. This response is considered consistent with criteria for Category III auto matic landing systems in AC 120

- 28D, appendix 3, section 8.1, Automatic Flight Control Systems , which states that it should not be possible to change the flight path of the airplane with the autopilot(s) engaged, except by initiating an automatic go

- around. (4) Windshear r ecovery g uidance
. T he i nteraction between low

- speed protection and windshear recovery guidance is a special case

. Windshear recovery guidance that meets the criteria found in AC 25

- 12 and AC 120

- 41 provides the necessary low

- speed protection when it is activated and is consi dered acceptable for compliance with § 25.1329(h)

. The autopilot should be disengaged when the windshear recovery guidance activates, unless autopilot operation has been shown to be safe in these conditions and provides effective automatic windshear recove ry that meets the criteria found in the ACs referenced above.

c. High

- s peed p rotection
. (1) General
. Section 25.1329(h) states that means must be provided to avoid excursions beyond an acceptable margin from the speed range of the normal flight envelope

. V MO and M MO mark the upper speed/Mach limit of the normal flight envelope

. This is not inten ded to require or preclude high

- speed protection based on airplane configurations (for example, flaps extended). (2) Factors to c onsider
. (a) Duration of a irspeed e xcursions, r ate of a irspeed c hange, t urbulence, and g ust
c haracteristics :
1 Operations at or near V MO /M MO in routine atmospheric conditions (for example, light turbulence) are safe

. Small, brief excursions above V MO /M MO by themselves are not unsafe.
2 The FGS design should st rive to strike a balance between providing adequate speed protection margin and avoiding nuisance activation of high

- speed protection.
Note: The following factors apply on ly to designs that provide high

- speed protection through FGS control of airspeed. (b) High

- s pee d p rotection w hile in a ltitude h old m ode :
1 Climbing to control airspeed is not desirable because departing an assigned altitude can be disruptive to air traffic control (ATC) and potentially hazardous (for example, in RVSM airspace)

. As long as the speed do es not exceed a certain margin beyond V MO /M MO (for example, six knots), it is better that the FGS remain in Altitude Hold mode.
2 The autothrust function, if operating normally, should effect high

- speed protection by limiting its speed reference to the norma l speed envelope (that is, at or below V MO /M MO ).10/27/14 AC 25.1329

- 1C

45 3 The basic airplane high

- speed alert should be sufficient for the pilot to recognize the overspeed condition and take corrective action to reduce thrust

. However, if the airspeed exceeds a margin beyond V MO /M MO (for example, six knots), the FGS may transition from Altitude Hold to the Overspeed Protection mode and depart (that is, climb above) the selected altitude. (c) High

- s peed p rotection d uring c limbs and d escents :
1 When the elevator channel of the FGS is not c ontrolling airspeed, the autothrust function, if engaged, should reduce thrust, as needed , to prevent sustained airspeed excursions beyond V MO /M MO (for example, six knots) down to the minimum appropriate value.
2 When thrust is already the minimum appropriat e value or the autothrust function is not operating, the FGS should begin using pit ch control, as needed, for high

- speed protection.
3 If conditions are encountered that result in airspeed excursions above V MO /M MO , it is preferable for the FGS to smoothly an d positively guide or control the airplane back to within the speed range of the normal flight envelope.
58

— 61 [RESERVED]10/27/14 AC 25.1329

- 1C

46 CHAPTER 6

. CHARACTERISTICS OF S PECIFIC MODES

62. General
. There are certain operational modes of the FGS that have been implemented in different ways in different airplanes and systems

. The following paragraphs provide guidance and interpretative material that clarifies the operational intent of these modes, and criteria shown to be acceptable in current operations

. The guidance in this chapter does not preclude other mode implementations

. Pilot understanding of the mode behavior is especially important to avoid confusion

. Therefore, mode behavior should be clearly annunciated, as described in Chapter 4 , paragraph 44 , FGS Mode Selection, Annunciation, and Indication , of this AC

. 63. L ateral Modes
. This paragraph discusses modes that are implemented in many FGSs that
are used primarily for lateral/directional control of the airplane

. The criteria below identify acceptable mode operation, based on past operational experience gained from the use of these modes.

a. Heading or t rack h old
. In the Heading or Track Hold mode, the F GS should maintain the airplane heading or track

. When the airplane is in a bank when the Heading or Track Hold mode is engaged, the FGS should roll the airplane to a wings

- level condition and maintain the heading or track when wings

- level is achieved (typ ically less than five degrees of bank angle).
b. Heading or t rack s elect
. In the Heading or Track Select mode, the FGS should expeditiously acquire and maintain a “selected” heading or track value consistent with occupant comfort

. When the mode is initially e ngaged, the FGS should turn the airplane in a direction that is the shortest heading (or track) change to acquire the new heading (or track)

. Once the Heading/Track Select mode is active, changes in the selected value should result in changes in heading/tr ack

. The FGS must turn the airplane in the same direction as the sense of the selected heading change

. See § 25.779(a)(1)

. That is, if the pilot turns the heading select knob clockwise, the airplane must turn to the right, even if the shortest heading (or track) change is in the opposite direction

. The target heading or track value should be presented to the flightcrew.

c. LNAV m ode
. (1) Lateral f light p ath
. In the LNAV mode, the FGS should acquire and maintain the lateral flight path commanded by a flight managem ent function (that is, FMS or equivalent). (2) Automatic m ode t ransitions
. If the airplane is not on the desired lateral path or within the designed path capture criteria when LNAV is selected, the FGS LNAV mode should enter an armed state

. The FGS should tran sition from the armed state to an engaged state at a point where the lateral flight path can be smoothly acquired and tracked. (3) Takeoff or g o - a round
. For an FGS incorporating the LNAV mode during the takeoff or go

- around ( TOGA ) phase, the design should spec ify maneuvering capability immediately after takeoff and any limits that may exist

. After TOGA, maneuvering should be based upon aircraft performance with the objective to prevent excessive roll attitudes where wingtip impact with the runway becomes probab le, yet satisfy operational requirements where terrain and/or thrust limitations exist.10/27/14 AC 25.1329

- 1C

47 64. V ertical M odes
. This paragraph discusses modes that are implemented in many FGSs that are used primarily for pitch control of the airplane

. The criteria identified refl ect operational experience gained from the use of these modes.

a. Target a ltitude s election
. To avoid unconstrained climbs or descents for any altitude transitions when using applicable vertical modes, the altitude select controller should be set to a new tar get altitude before the vertical mode can be selected

. If the design allows the vertical mode to be selected before setting the target altitude, then consideration should be given to the potential vulnerability of unconstrained climb or descent leading to an altitude violation or controlled flight into terrain

. Consideration should also be given to appropriate annunciation of the deviation from previously selected altitude and/or subsequent required pilot action to reset the selected altitude.
b. Vertical s pee d
. In the Vertical Speed mode, the FGS should smoothly acquire and maintain a selected vertical speed

. Consideration should be given to the situation where the selected value is outside the performance capability of the airplane

. Another situation to consi der is use of Vertical Speed mode without autothrust

. These situations could potentially lead to a low

- speed or high

- speed condition and corresponding pilot awareness vulnerabilities

. F or discussion of acceptable means of compliance for these situations , s ee Chapter 5 , paragraph 57 of this AC

.

c. Flight p ath a ngle
. In the Flight Path Angle mode, the FGS should smoothly acquire and maintain the selected flight path angle

. Consideration should be given to the s ituation where the selected value is outside the performance capability of the airplane

. The use of Flight Path Angle mode without autothru st

— potentially leading to a low

- speed or high

- speed condition and corresponding pilot awareness vulnerabilities

— shoul d also be considered

. Acceptable means of compliance have included a reversion to an envelope protection mode or a timely annunciation of the situation.
d. Indicated a irspeed/ Mach h old ( speed on elevator )
. In the Airspeed/Mach Hold mode, the FGS should mainta in the airspeed or Mach at the time of engagement.

e. Indicated a irspeed/ Mach s elect ( speed on elevator )
. In the Airspeed/Mach Select mode, the FGS should acquire and maintain a selected airspeed or Mach

. The selected airspeed or Mach may be either pre

- select ed or synchronized to the airspeed or Mach at the time of engagement.
f. Flight level c hange ( speed on elevator )
. In the flight level ( FL ) Change mode, the FGS should change altitude in a coordinated way with thrust control on the airplane

. The autopilot/FD
w ill typically maintain speed control through the elevator

. The autothrust function, if engaged, should control the thrust to the appropriate value for climb or descent.

g. Altitude c apture
. (1) Mode t ransition
. The Altitude Capture mode should command the FGS to transition from a vertical mode to smoothly capture and maintain the selected target altitude with consideration of the rates of climb and descent experienced in service.10/27/14 AC 25.1329

- 1C

48 (2) Guidelines for a ltitude c apture m ode
. In

- service experience has shown that certain im plementations have the potential to cause pilot confusion that may lead to altitude violations

. Accordingly, the following are guidelines for the Altitude Capture mode. (a) Automatic a rming of m ode

. The Altitude Capture mode should be automatically armed to en sure capture of the selected altitude

. Annunciation of the armed status is not required if the Altitude Capture mode is armed at all times

. If the FGS is in the Altitude Capture mode, it should be annunciated. (b) Engagement f rom a ny v ertical m ode

. The Altitud e Capture mode should engage from any vertical mode if the computed flight path will intercept the selected altitude and the altitude capture criteria are satisfied, except as specified during an approach (for example, when the glidepath for Approach mode is active). (c) Changing c limb/ d escent c ommand r eferences

. Changes in the climb/descent command references (for example, the vertical speed command reference), with the exception of those made by the flightcrew using the altitude select controller, should not prevent c apture of the target altitude. (d) Capturing s elected a ltitude

. The Altitude Capture mode should smoothly capture the selected altitude, using an acceptable acceleration limit and pitch attitude with consi deration for occupant comfort. (e) Minimizing a cce leration o vershoot

. The acceleration limit may, under certain conditions, result in an overshoot

. To minimize the altitude overshoot, the normal acceleration limit may be increased, consistent with occupant safety. (f) Selecting other v ertical m odes

. Pilot sel ection of other vertical modes at the time of altitude capture should not prevent or adversely affect the level off at the target altitude

. One means of compliance is to inhibit transition to other pilot

- selectable vertical modes (except Altitude Hold, Go

- Around, and Approach modes) during altitude capture, unless the target altitude is changed

. If glidepath capture criteria are satisfied during altitude capture, then the FGS should transition to glidepath capture. (g) Changing t arget a ltitude

. The FGS must be designed to minimize flightcrew confusion concerning the FGS operation when the target altitude is changed during altitude capture

. See § 25.1329(i)

. It should be suitably annunciated and appropriate for the phase of flight. (h) Barometric p ressure a djustment

. Adjusting the datum pressure at any time during altitude capture should not result in loss of the capture mode

. The transition to the pressure altitude s hould be accomplished smoothly. (i) Maintaining r eference a irspeed

. If the autothrust function is active d uring altitude capture, the autopilot and autothrust functions should be designed such that the FGS maintains the reference airspeed during the level

- off maneuver

. For example, if the autopilot changes from a speed mode to an altitude capture or control mo de, then the autothrust should transition to a speed mode to maintain the reference airspeed.10/27/14 AC 25.1329

- 1C

49 h. Altitude h old
. (1) Entering m ode
. The Altitude Hold mode may be entered either by flightcrew selection or by transit ion from another vertical mode. (a) Pilot s election

. 1 L evel flight

. When initiated by pilot action in level flight, the Altitude Hold mode should provide guidance or control to maintain altitude at the time the mode is selected.
2 Climbing or descending

. When initiated by pilot action when the airplane is either climbing or descending, the FGS should immediately initiate a pitch change to arrest the climb or descent and maintain the altitude when level flight (for example, less than 200 feet per minute) is reached

. The intensity of the leveling maneuver should be consistent with occupant comfort and safety. (b) Automatic t ransition

. When initiated by an automatic transition from Altitude Capture, the Altitude Hold mode should provide guidance or contr ol to the selected altitude. (2) Mode t ransition a nnunciation
. Automatic transition into the Altitude Hold mode from another vertical mode should be clearly annunciated for flightcrew awareness. (3) Barometric p ressure a djustment
. Any airplane response due to an adjustment of the d atum pressure should be smooth.
i. VNAV
. (1) FMS p ath
. (a) Ac quire v ertical p ath

. In the VNAV mode, the FGS should acquire and maintain the vertical flight path commanded by a flight management function (that is, FMS or equivalent)

. If the airplane is not on the desired FMS path when the VNAV mode is selected, the F GS VNAV mode should go into an armed state or provide guidance to smoothly acquire the FMS path

. The flightcrew should establish the airplane on a flight profile to intercept the desired FMS path

. The FGS should transition from the armed state to an engage d state at a point where the FGS can smoothly acquire and track the FMS path. (b) Deviation from v ertical p ath

. If the aircraft is flying a vertical path (for example, VNAV path), then the deviation from that path should be displayed in the primary field of vi ew, such as the PFD, navigation display (ND), or other acceptable display. (2) Climb or d escent
. (a) Autothrust f unction

. When VNAV is selected for climb or descent, the autothrust function (if installed and engaged) should maintain the appropriate thrust setting

. When leveling after a VNAV climb or descent, the autothrust function should maintain the target speed.10/27/14 AC 25.1329

- 1C

50 (b) Preclude VNAV c limb

. The FGS should preclude a VNAV climb, unless the MSP altitude window is set to an altitude above th e current altitude. (c) Preclude VNA V d escent

. The FGS should preclude a VNAV descent, unless the MSP altitude window is set to an altitude below the current altitude, except when on a final approach to a runway. (d) Preclude MSP a ltitude f ly

- t hrough

. The FGS should not allow the VNAV climb or d escent to pass through a MSP altitude, except when on a final approach to a runway.
Note: See paragraph 67 , Special Considerations for VNAV Approach Operations Related to Selecting a Targe t Altitude , of this AC

. 65. M ulti

- Axis Modes
. This paragraph discusses modes that are implemented in many FGSs that are used in an integrated manner for pitch, lateral/directional control, and thrust management of the airplane

. The criteria identified reflect operational experience gained from the use of these modes.

a. Takeoff m ode
. (1) Vertical g uidance
. In the Takeoff mode, the vertical element of the FGS should provide vertical guidance to acquire and maintain a safe climb out speed after initial rotation for tak eoff. (2) Lateral g uidance
. In the Takeoff mode, the lateral element of the FGS, if implemented, should maintain runway heading/track or wings level after liftoff

. A separate lateral mode annunciation should be provided. (3) Rotation g uidance
. If rotation guidance is provided, the use of the guidance should not result in a tail strike

. It should be consistent with takeoff methods necessary to meet takeoff performance requirements up to 35 feet above ground level (AGL)

. If no rotation guidance is provided, the pitch command bars may be displayed during takeoff roll but should not be considered as providing rotation guidance, unless it is part of the intended function. (4) Autothrust
. The autothrust function should increase and maintain engine thrust to the selected thrus t limits (for example, full takeoff thrust, de

- rate). (5) Operation and p erformance
. The FGS design should address all engine and engine

- inoperative conditions consistent with the following takeoff system performance characteristics after liftoff. (a) Transitions b etween f light p hases

. Takeoff system operation should be continuous and smooth through transition from the runway portion of the takeoff to the airborne por tion and reconfiguration for en route climb

. The pilot should be able to continue the use of the
sa me primary display(s) for the airborne portion as for the runway portion

. Changes in guidance modes and display formats should be automatic.10/27/14 AC 25.1329

- 1C

51 (b) Pitch a ttitude and c limb s peed/ n ormal o peration

. The vertical axis guidance of the takeoff system during normal ope ration should result in the appropriate pitch attitude and climb speed for the airplane considering the following factors:
1 Normal rate rotation of the airplane to the commanded pitch attitude at V R (takeoff rotation speed)

- 10 knots for all engines operat ive and V R - 5 knots for engine out should not result in a tail

- strike.
2 The system should provide commands that lead the airplane to smoothly acquire a pitch attitude that results in capture and tracking of the all

- engine takeoff climb speed, V 2 (takeoff s afety speed) + X

. X is the all

- engine speed add itive from the AFM (normally 10 knots or higher)

. If pitch limited conditions are encountered, a higher climb airspeed may be used to achieve the required takeoff path without exceeding the pitch limit. (c) Engine

- o ut o peration

. For engine

- out operation, the system should provide commands that lead the airplane to smoothly acquire a pitch attitude that results in capture and tracking of the following reference speeds:
1 V 2 , for engine failure at or below V 2 . This spe ed should be attained by the time the airplane has reached 35 feet altitude.
2 Airspeed at engine failure for failures between V 2 and V 2 + X.
3 V 2 + X, for failures at or above V 2 + X

. Alternatively, the airspeed at engine failure may be used, provided it has been shown that the minimum takeoff climb gradient can still be achieved at that speed. (d) Lateral c ommands d uring t akeoff m ode

. If implemented, the lateral element of the Takeoff mode should maintain runway heading/track or wings level after liftoff and a
se parate lateral mode annunciation should be provided.
b. Go

- around m ode
. Characteristics of the Go

- Around mode and resulting flight path should be consistent with a manually flown go

- around. (1) Vertical e lements
. The vertical element of the FGS Go

- Around mode sho uld initially rotate the airplane or provide guidance to rotate the airplane to arrest the rate of descent. (2) Speed
. The FGS should acquire and maintain a safe speed during climbout and airplane configuration changes

. Typically, a safe speed for go

- around cl imb is V 2 , but a different speed may be found safe for windshear recoveries

. See AC 25

- 12. (3) Autothrust
. (a) Thrust d uring c limb

. The autothrust function, if installed, should increase thrust and either maintain thrust to specific thrust limits or maintain thrus t for an adequate, safe climb

. The autothrust function should not exceed thrust limits (for example, full go

- around thrust or de

- rated go

- around thrust limits)

. Furthermore, the autothrust function should not reduce10/27/14 AC 25.1329

- 1C

52 thrust for wind below the minimum value required for an adequate, safe climb or reduce the thrust lever position below a point that would cause a warning system to activate. (b) Pitch a ttitude d uring g o
- a round

. The initial go

- around maneuver may require a significant change in pitch attitude

. It is acceptable to reduce thrust to lower the pitch attitude for comfort of the occupants when a safe climb gradient has been established

. It should be possible for the pilot to re

- select the full thrust value, if needed. (4) Engagement
. The Go

- Around mode should e ngage when go

- around is selected by the pilot, even if the MSP selected altitude is at or below the go

- around initiation point

. The airplane should climb until another vertical mode is selected or the MSP altitude is adjusted to an altitude above the prese nt aircraft altitude. (5) All e ngine and e ngine o ut c apability
. The FGS design of the Go

- Around mode should address all engine and engine

- out operation

. The design should consider an engine failure resulting in a go

- around and the engine failure occurring duri ng an all engine go

- around.

c. Approach m ode
. (1) Final a pproach p ath
. In the Approach mode, the FGS should capture and track a final approach lateral and vertical path, if applicable, from a NAV or landing system, for example, ILS, MLS, GLS, RNP, area navigation (RNAV)

. See AC 120

- 28D and AC 120

- 29A

. (2) Mode a nnunciations
. The FGS should annunciate all operationally relevant approach modes

. Mode s that are armed and waiting for capture criteria to be satisfied should be indicated in additi on to the active pre

- capture mode

. A positive indication of the capture of the previously armed mode should be provided. (3) Sub

- m odes
. The FGS may have sub

- modes th at become active without additional crew selection

. An assessment of the significance of these sub

- mode transitions to the flightcrew should be made

. If assessed to be significant (for example, flare), positive annunciation of the transition should be prov ided. (4) Mode engagement s equence . Glideslope capture mode engagement may occur prior to localizer capture

. However, it is the flightcrew’s responsibility to ensure proper safe obstacle/terrain clearance when following vertical guidance when the airplane is n ot established on the final lateral path.
Note: Additional guidance and criteria are con tained in AC 120

- 29A and AC 120

- 28D.
66. Autothrust Modes
. This paragraph discusses modes that are implemented in many FGSs that are used primarily for controlling the engines on the airplane

. The criteria identified reflect operational experience gained from the use of these modes.

a. Thrust m ode
. In the Thrust mode, the FGS should command the autothrust function to achieve a selected target thrust value.10/27/14 AC 25.1329

- 1C

53 b. Speed m ode
. In the Speed mo de, the FGS should command the autothrust function to acquire and maintain the selected target speed value, assuming that the selected speed is within the speed range of the normal flight envelope

. The autothrust system may fly a higher airspeed than the s elected target speed during an approach when operating in winds or turbulent conditions.

c. Retard m ode
. If a Retard mode is implemented in the FGS, it should work in the same manner for both automatic and manual landings when the autothrust function is engag ed.
67. Special Considerations for VNAV Approach Operations Related to Selecting a Target Altitude
.

a. Approach o perations
. The FGS vertical modes should allow the pilot to set the target altitude to a missed approach value prior to capturing the final approach s egment

. This should be possible for capturing from both above and below the final approach segment.
b. VNAV p ath o perations
. It should be possible to define a descent path to the final approach fix and another path from the final approach fix to the runway wi th the target altitude set for the missed approach altitude

. Appropriate targets and descent points should be identified by the FMS.
68. Control Wheel Steering ( Control Steering through the A utopilot )
.

a. General
. In the control wheel steering ( CWS ) mode, the FGS allows the flightcrew to maneuver the airplane manually through the autopilot control path

. CWS is considered an FGS mode, as it is a specific function of the FGS

. However, during CWS operation, the pilot is in control of the aircraft, rather than the FGS

. Operationally, CWS is identical to the pilot flying the airplane during manual flight

. In both cases, the pilot is in control of the flight path and speed of the airplane

. The only difference is the mechanization of how the actual flight control surfaces are moved

. No automatic FGS commands are involved during CWS operation, with the possible exception of automatic aircraft trim function(s)

. Therefore, paragraphs in this AC, such as those that discuss speed protection and performance objectives, should be applied only to those autopilot modes with which the FGS is in control of the flight path of the airplane

. Such paragraphs in this AC should not be applied to CWS, unless such features are specifically provided while the FGS is in the CWS mode.
b. Design
. If provided, a CWS mode should meet the following: (1) Control f orces . It should be possible for the pilot to maneuver the airplane using the normal flight controls with the CWS mode engaged and to achieve the maximum available control surface deflection without using forces so high that the controllability requirements of § 25.143(d ) are not met

. Excessive discontinuities in control force that might adversely affect the flight path should not be encountered. (2) Bank and p itch a ttitudes
. The maximum bank and pitch a ttitudes that can be achieved during CWS operations should be limited to those necessary for the normal operation of the airplane.10/27/14 AC 25.1329

- 1C

54 Note 1: Normal operational limits are typically 35 degrees in roll and +20 degrees to

– 10 degrees in pitch.
Note 2: Limits that can be physic ally overcome with forceful control commands by the pilot are sometimes referred to as “soft limits.” (3) Control b ehavior
. It should be possible to perform all normal maneuvers smoothly and accurately without nuisance oscillation

. It should also be possible t o counter all normal changes of trim due to change of configuration or power, within the range of flight conditions in which CWS may be used. (4) Stall and s tall r ecovery . The stall and stall recovery characteristics of the airplane should remain acceptable

. I t should be assumed that recovery from such a stall is made with CWS in use, unless automatic disengagement of the autopilot is provided. (5) Adjustments to t rim
. In showing compliance with § 25.143(f), consideration should be given to adjustments to trim that may be made by the autopilot in the course of maneuvers that can reasonably be expected

. Some alleviation may be acceptable in the case of unusually prolonged maneuvers, provided that the reduced control forces would not be potentially hazardous. (6) Takeoff and l anding
. If the use of CWS for takeoff and landing is to be per mitted, it should be shown that

— (a) Sufficient control, in both amplitude and rate, is available without encountering force discontinuities. (b) Reasonable mishandling is not hazardous (for exampl e, engaging the autopilot while the elevators or ailerons are held in an out

- of

- trim position). (c) Runaway rates and control forces are such that the pilot can readily overpower the autopilot with no significant deviation in flight path. (d) Any lag in aircraft r esponse induced by the CWS mode is acceptable for the intended maneuver. (7) Automatic r eversion to CWS m ode
. The autopilot, when engaged, should not automatically revert to the CWS mode by applying an input to the control column or wheel, unless the autopilot is in a capture mode (for example, Altitude Capture or Localizer Capture)

. When the force is released, the autopilot should return to the previously engaged capture mode or to the Track/Heading Hold mode.

c. Terminology and a pplication of a dvisory m aterial
. The term “CWS” is currently used by industry to refer to several different types of systems

. Several other types of systems that are similar in nature to CWS, but functionally different from it, are described below

. Paragraph 68 .b , Design , of this AC applies to systems as described in paragraph 68.a , General , of this AC

. It does not apply to those systems described in paragraphs 68.c(1) and 68.c(2) below

.10/27/14 AC 25.1329

- 1C

55 These descriptions are intended to be generic

. Implementation may vary from airplane to airplane. (1) Touch c ontrol s teering
. A touch control steering ( TCS ) syst em is available on many business and commuter aircraft

. With a TCS system, a pilot is able to physically disengage the autopilot servos from the flight control system, usually by pushing and holding a button on the control wheel, without causing the autopi lot system itself to disengage or lose its currently selected modes

. The pilot may then maneuver the airplane as desired using the aircraft’s flight control system (that is, the autopilot servos are not part of the control loop)

. The pilot is then able to reconnect the autopilot servos to the flight control system by releasing the TCS button

. Using the new orientation of the aircraft as a basis, the autopilot will then reassume control of the airplane using the same mode selections as were present before th e selection of TCS

. This type of system on some aircraft is also sometimes referred to as CWS. (2) Supervisory o verride
. A function available on some aircraft is referred to as a “supervisory override” of an engaged autopilot

. With this function, a pilot is ab le to physically overpower an engaged autopilot servo by applying force to the flight deck controls

. With a supervisory override, the autopilot does not automatically disengage due to the pilot input

. This allows the pilot to position the airplane as desir ed using the flight deck controls without first disengaging the autopilot

. When the pilot releases the controls, the autopilot reassumes control of the airplane using the same mode selections as were present before the supervisory override.
69. Special Conside rations for the Integration of Fly

- by

- Wire Flight Control Systems and FGS
.

a. Speed p rotection
. Speed protection features may be implemented in the fly

- by

- wire flight control system

. However, if speed protection is also implemented within the FGS, it should b e compatible with the envelope protection features of the fly

- by

- wire flight control system

. The FGS speed protection (normal flight envelope) should operate to or within the limits of the flight control system (limit flight envelope).
b. Syst em d egradation
. Information should be provided to the flightcrew about the impact on the FGS following degradation of the fly

- by

- wire flight control systems.
70

— 74 [RESERVED]10/27/14 AC 25.1329

- 1C

56 CHAPTER 7

. FGS INTEGRATION

75. General
. Throughout the preceding chapters of the document, FGSs and functions have been considered as being separate and distinct from other systems and functions on the aircraft

. It is recognized that in complex aircraft designs, the flight guidance functions are closely integrated with other avionics functions and th at the physical integration of these systems may have a bearing on how airplane level safety is assessed

. The following paragraphs provide guidance on the likely FGS system integration issues found in more complex aircraft system designs and the interfaces that should be considered within the bounds of demonstrating the intended function, performance, and safety of the FGS.
76. System Integration Issues
.

a. Com mon and c ascading f ailure m odes
. Integration of other aircraft systems with the FGS has the potential of reducing the independence of failure effects and partitioning between functions

. This is particularly the case where hardware and software resources are shared by different systems and functions (for example, aircraft data network and integrated modular
av ionics (IMA) architectures)

. In addition to considering the reliability and integrity aspects of the FGS as a separate system, it may be necessary to address the effects of FGS failures with respect to fault propagation, detection, and isolation within oth er systems

. The overall effect on the aircraft of a combination of individual system failure conditions occurring as a result of a common or cascade failure, may be more severe than the individual system effect

. For example, failure conditions classified u nder § 25.1309 as “ minor” or “ major” by themselves may have hazardous effects at the aircraft level when considered in combination

. With regard to isolation of failures and particularly combination of failures, the ability of the alerting system to provide clear and unambiguous information to the flightcrew becomes of significant importance

. (See also Chapter 8 , Safety Assessment , of this AC .)
b. Risk of e rror . Complex and highly integrated avionics s ystems present greater risk for development error

. With non

- traditional human

- machine interfaces, there is also the potential for operational flightcrew errors

. Moreover, integration of systems may result in a greater likelihood of undesirable and unintend ed effects.

c. System s afety a nalysis
. When credit is taken for shared resources or partitioning schemes, these should be justified and documented within the system safety analysis

. When considering the functional failures of the system, where such partitioni ng schemes cannot be shown to provide the necessary isolation, possible combination failure modes should be taken into account

. An example of this type of failure would be multi

- axis active failures, where the control algorithms for more than one axis are hosted on a single processing element

. Further, the functional integration of control functions such as control surface trimming, yaw channel, and stability augmentation, while not strictly FGS, should be considered.
77. Functional Interfaces
.

a. Interfacing s ens ors . In its simplest form, the FGS may be considered as interfacing with sensors that provide the necessary inputs to enable computation of its various functions

. Typically, these sensors will include air and inertial data, engine control, and NAV sensors such10/27/14 AC 25.1329

- 1C

57 as ILS, very high frequency omnirange (VOR), and distance measuring equipment (DME)

. In the case of engine control, a feedback loop may also be provided

. The FGS may also be considered as providing inner loop closure to outer loop commands

. The most c ommon interface is with the FMS, which provides targets for LNAV and VNAV in the form of steering orders.
b. Potential i nconsistencies b etween s ystems
. In demonstrating the intended function and performance of both the FGS and systems providing outer loop com mands, the applicant needs to address potential inconsistencies between limits provided by the two different systems

. One example of this is possible conflicts between FMS steering commands with basic FGS pitch and bank angle limits

. Failure to address the se points can result in discontinuities, mode switching, and reversions, leading to erroneous NAV and other possible safety issues (for example, buffet margin at high altitude)

. Similar issues arise in the inner loop, across the functional interface betwee n FGS and flight controls

. In fly

- by

- wire aircraft, the loss of synchronization between the two can result in mode anomalies and autopilot disengagement.

c. Function and p erformance
. The applicant should demonstrate the intended function and performance of th e FGS across all possible functional interfaces

. The alerting system should also be assessed to ensure that accurate and adequate information is provided to the flightcrew when dealing with failures across functional interfaces.
78

— 82 [RESERVED]10/27/14 AC 25.1329

- 1C

58 CHAPT ER 8

. SAFETY ASSESSMENT

83. General
.

a. Basic s afety r equirements
. Section 25.1309 defines the basic safety requirements for airworthiness approval of airplane systems and AC 25.1309

- 1A, System Design and Analysis , provides an acceptable means of demonstrating compliance with this rule

. This chapter provides additional guidance and interpretive material for the application of § 25.1309 to the approval of FGS.
b. Safety a ssessment
. A safety assessment should be performed to identify the failure conditions, classify their hazard level according to the guidance of AC 25.1309

- 1A, and establish that the failure conditions occur with a probability corresponding to the hazard classification or are mitigated as intended

. The saf ety assessment should include the rationale and coverage of the FGS protection and monitoring philosophies employed

. The safety assessment should include an appropriate evaluation of each of the identified FGS failure conditions and an analysis of the expo sure to common mode/cause or cascade failure in accordance with AC 25.1309

- 1A

. Additionally, the safety assessment should include justification and description of any functional partitioning schemes employed to reduce the effect/likelihood of failures of i ntegrated components or functions.

c. Validation of s afety a ss essment
. There may be situations where the severity of the effect of a failure condition identified in the safety analysis needs to be validated

. Laboratory, simulator, or flight test may accomplis h the validation of the assessment

. The test facility for each validation test should be chosen based on specific criteria, such as the difficulty of setting up the test conditions, potential hazard to an airplane and the test crew, and the validity of tha t validation test in that specific facility.
d. Coordinatio n with the FAA
. It is recommended that the safety analysis plan and the functional hazard assessment be coordinated with the FAA early in the certification program.
84. FGS F ailure C onditions
. One of the initial steps in establishing compliance with § 25.1309 for a system is to identify the failure conditions that are associated with that system

. The failure conditions are typically characterized by an undesired change in the intended function of the syste m

. The failure condition should identify the functionality affected and the effect on the airplane and/or its occupants, specify any considerations relating to phase of flight, and identify any flightcrew action or other means of mitigation that are releva nt.

a. Functionality
. The primary functions of a FGS may include the following: (1) Automatic control of the airplane’s flight path utilizing the airplane’s aerodynamic control surfaces. (2) Guidance provided to the flightcrew to achieve a particular desired flight p ath or maneuver via information presented on a HUD or HDD system. (3) Control of the thrust applied to the airplane.10/27/14 AC 25.1329

- 1C

59 b. Effect of f ailure c ondition
. Dependent upon the functionality provided in a specific FGS, the failure conditions could potentially impact the f ollowing: (1) Control of the airplane in the pitch, roll, and directional axes. (2) Control of thrust. (3) Integrity and availability of guidance and system annunciations/alerts provided to the flightcrew. (4) Structural integrity of the airplane. (5) Ability of the flightcre w to cope with adverse operating conditions. (6) Flightcrew performance and workload. (7) Safety of the occupants of the airplane.
Note: The safety assessment of a FGS for use in supporting takeoff, approach , and landing operations in low visibility conditions is furthe r addressed in AC 120

- 29A and AC 120

- 28D.
85. T ype and Severity of Failure Conditions
.

a. Types of f ailure c onditions
. The type of the FGS failure conditions will depend, to a large extent, upon the architecture, design philosophy, and implementation of the syste m

. Types of failure conditions can include the following: (1) Loss of f unction
. A control or display element no longer provides control, guidance, or system annunciation/alerting. (2) Malfunction
. A control or display element performs in an inappropriate manner, i ncluding the following sub

- types: (a) Hardover

. The control or display goes to full displacement in a brief period of time

. The resultant effect on the flight path and occupants of the airplane and possible adverse structural effects are the primary concerns. (b) Slowover

. The control or display moves away from the correct control or display value over a relatively long period of time

. The potential delay in recognizing the situation and the effect on the flight path are the primary concerns. (c) Oscillatory

. The contr ol or display is replaced or augmented by an oscillatory element

. In addition to difficulty controlling the aircraft flight path, there may be effects on structu ral integrity and occupant well

- being.
b. Cause
. Failure conditions are a manifestation of malfunc tions in

— (1) Primary FGS elements, such as autopilot, FD, or HUD.10/27/14 AC 25.1329

- 1C

60 (2) Interfacing sensors to the FGS, such as inertial or air data. (3) Control and display elements, such as servos or PFDs. (4) Interfacing systems, such as the FMS or primary flight controls. (5) Basic aircra ft services, such as electrical or hydraulic power.

c. Severity
. The severity of the FGS failure conditions and their associated classifications will frequently depend on the phase of flight, airplane configuration, and the type of operation being conducted

. The effect of any control system variability (for example, tolerances and rigging) on the failure conditions should be considered

. The severity of the failure conditions can be mitigated by various design strategies

. (See paragraph 86 , Mitigation of Failure Conditions

. )
d. A ssessment of f ailure c onditions
. (1) Functional f ailures
. Appendix A , Safety As sessment , of this AC presents some considerations for use when assessing the type and severity of condition that results from functional failures

. The classifications of failure conditions that have been identified on previous airplane certification progr ams are identified

. The classifications of failure conditions should be agreed with the FAA during the § 25.1309 safety assessment process. (2) Airframe l oads
. With the exception of the catastrophic failure condition, the classification of failure conditions l eading to the imposition of airframe loads should be assessed in accordance with 14 CFR p art 25, Subpart C, Structure, and § 25.1309, Equipment, systems, and installations

. The assessment needs to account for loads occurring during the active malfunction, recovery, or continuation of the flight with the system in the failed state. (3) As sessing t otal e ffect of f ailure
. Complex integrated systems may require that the total effect resulting from single failure be assessed

. For example, some failures may result in a number of failure conditions that, if assessed individually, may be considered major effects but when considered in combination may be hazardous

. Special consideration concerning complex integration of systems can be found in Chapter 7 , FGS Integration , paragraph 76 , System Integration Issues , of this AC

. 86. M itigation of Failure Conditions
.

a. General
. The propagation of potential failure conditions to their full effect may be nullified or mitigated by a number of methods

. These methods could include, but are not limited to, the following: (1) Failure d etection and m onitoring. (2) Fault i solation and r econfiguration. (3) Redundancy. (4) Authority l imiting.10/27/14 AC 25.1329

- 1C

61 (5) Flightcrew a ction to i ntervene.
b. Identification of m ethods
. Means to assure continued performance of any system design mitigation methods should be identified

. The mitigation methods should be described in the safety analysis/assessment document o r be available by reference to another document (for example, a system description document).

c. FGS de

- s election
. The design of typical FGS allows for the de

- selection of control and guidance elements

. The long

- term effects on occupants and any structural im plication of oscillatory failures can be mitigated by de

- selection of the FGS.
87. V alidation of Failure Conditions
.

a. General
. The method of validation of failure conditions will depend on the effect of the condition, any assumptions made, and any associated ri sk

. The severity of some failure conditions may be obvious, and other conditions may be somewhat subjective

. If flightcrew action is used to mitigate the propagation of the effect of a failure condition, the information available to the flightcrew to initi ate appropriate action (for example, motion, alerts, and displays) and the assumed flightcrew response should be identified

. It is recommended that there be early coordination with the FAA to identify any program necessary to validate any of these assumpti ons.
b. Validation o ptions
. The validation options for failure conditions include the following: (1) Analysis. (2) Laboratory Testing. (3) Simulation. (4) Flight Test.

c. Validation m eth odology
. The validation testing and analysis should take account of architectural strategies (for example, redundant channels, high integrity components, rate limit/magnitude limiting, etc.)

. It is anticipated that the majority of failure condition s can be validated by analysis to support the probability aspect of the § 25.1309 assessment

. It may be necessary to substantiate the severity of a failure condition effect by ground simulation or flight test

. This is particularly true where pilot recognition of the failure condition requires justification, or if there is some variability in the response of the airplane

. Failure conditions that are projec ted to be less probable than 10 - 7 per flight hour, independent of effect severity, need not be demonstrated with a flight test

. Guidance on the assessment of traditional failure conditions is provided in Chapter 9 of this AC

. New and novel functionality may require additional assessment methods to be agreed to with the authority.10/27/14 AC 25.1329

- 1C

62 88. S pecific Considerations
. The following paragraphs identify specific considerations that should be given to po tential failure conditions for various phases of flight.

a. FGS a ction d uring g round o perations
. The potential hazard that may result due to inappropriate autopilot, autothrust, or other system control action during maintenance operations should be assessed

. This includes while the airplane is parked at the gate and during taxi operations

. System interlocks or crew or maintenance procedures and placards may mitigate these hazards.
b. FGS o perations in c lose p roximity to the g round
. The response of the airplane to failures in the FGS could have implications for the safety of operations when the airplane is close to the ground

. For the purpose of this AC, close to the ground can be assumed to be less than 500 feet above the liftoff point or touchdown zone or a runwa y
. A specific safety assessment should be performed if approval for operations where the autopilot is engaged or remains engaged in close proximity to the ground.
Note: AC 120

- 29A and AC 120

- 28D identify additional considerations and criteria for operating the a irplane in low visibility conditions. (1) Takeoff
. If approval is sought for engagement of the autopilot below 5 00 feet after liftoff, an assessment of the effect of any significant FGS failure conditions on the net vertical flight path, the speed control, and the bank angle of the airplane should be conducted

. An autopilot minimum engage height

- takeoff will be established based, in part, on the characteristics of the airplane in response to the failures and the acceptability of flightcrew recognition of the condition

. A pilot assessment of certain failure conditions may be required

. (See Chapter 9 of this AC. ) The minimum engage height

- takeoff based upon this assessment should be provided in the AFM. (a) Vertical a xis a ssessment

. 1 The operatio nal objective during the initial climb is to maintain an appropriate climb profile to assure obstacle clearance and to maintain an appropriate speed profile during climbout

. ( See Chapter 6 of this AC ).
2 The FGS failure conditions should b e assessed for the potential for a significant reduction in the net takeoff flight path below 500 feet and a significant increase in pitch attitude that results in the airplane speed dropping to unacceptable values.
3 For failure conditions that are likely t o oc cur more frequently than 1 x 10 - 7 per flight hour or would have hazardous or catastrophic effects without pilot intervention, the ability of pilots to adequately perform the intervention should be evaluated and documented in AFM limitations or procedur es, if those failure conditions require operational limitations or flightcrew procedures. (b) Lateral a xis a ssessment

. 1 The operational objective during the initial climb is to maintain an appropriate heading or track to provide separation from potential adjace nt runway operations.10/27/14 AC 25.1329

- 1C

63 2 The FGS failure conditions should be assessed for the potential for producing a bank angle that results in significant deviation from the runway track or intended track.
3 For failure conditions that are likely to occur more frequently than 1 x 10 - 7 per flight hour or would have hazardous or catastrophic effects without pilot intervention, the ability of pilots to adequately perform the intervention should be evaluated and, as necessary, documented in AFM limitations or procedures. (2) Appro ach
. (a) Assessment of f ailure c onditions

. I f the autopilot is to remain engaged below 500 feet above the touchdown zone during approach, an assessment of the effect of any significant FGS failure conditions on the net vertical flight path, the speed control, and the bank angle of the airplane should be conducted

. The lowest point on the approach appropriate for the use of the autopilot will be established based on the characteristics of the airplane in response to the failure conditions and the acceptability o f flightcrew recognition of the condition

. See Chapter 9 of this AC for details regarding how these failure conditions on approach should be assessed. (b) Approach Operations

. 1 A number of approach operations may be conducted using automatic flight control

. These can include, but are not limited to, the following:

• ILS, MLS, and GLS

.

• RNAV ( for example , LNAV and VNAV)

.

• NAV (for example, VOR, LOC, and Backcourse)

.

• Open loop flight path management (for example, vertical speed, flight path angle, track or heading select).
2 Some operations may be conducted with a single autopilot channel engaged, and some operations may be conducted with multiple autopilots engaged

. The engagement of multiple autopilots may have the effect of mitig ating the effect of certain failure conditions

. The effectiveness of these mitigation methods should be established.
3 The type of operation and the prevailing visibility conditions will determine the decision altitude ( height ) ( DA( H) ) or minimum descent alt itude ( height ) ( MDA(H) ) for a particular flight operation

. The operation may continue using automatic flight control if the visual requirements are met.
4 The lowest altitude at which the autopilot should remain engaged may vary with the type of operation be ing conducted

. The resultant flight path deviation from any significant failure condition would impact the autopilot minimum operational use height

. The minimum use height (MUH) for approach should be provided in the AFM.10/27/14 AC 25.1329

- 1C

64 (c) Vertical a xis a ssessment

. 1 The oper ational objective during the approach is to maintain an appropriate descent profile to assure obstacle clearance and to maintain an appropriate speed profile.
2 FGS failure conditions should be assessed for the potential for a significant reduction in the ap proach flight path when below 500 feet above touchdown and for a significant increase in pitch attitude that results in the airplane speed dropping to unacceptable values.
3 For failure conditions that are likely to oc cur more frequently than 1 x 10 - 7 per fl ight hour or would have hazardous or catastrophic effects without pilot intervention, the ability of pilots to adequately perform the intervention should be evaluated and documented in AFM limitations or procedures, if those failure conditions require oper ational limitations or flightcrew procedures. (d) Lateral a xis a ssessment

. 1 The operational objective during the approach is to maintain an appropriate track to provide alignment with the runway centerline or intended flight path to support the landing.
2 The FGS failure conditions should be assessed for the potential for producing a bank angle that results in significant deviation from the runway track or intended track.
3 For failure conditions that are likely to oc cur more frequently than 1 x 10 - 7 per flight hour or would have hazardous or catastrophic effects without pilot intervention, the ability of pilots to adequately perform the intervention should be evaluated and, as necessary, documented in AFM limitations or procedures.

c. Cruise o perations
. The primary con cerns during cruise operations are adverse effects that the airplane response to failure conditions may have on the structure of the airplane and to the occupants

. At a minimum, the accelerations and attitude resulting from any failure condition should be assessed

. The mitigation of the effect of a failure condition by the flightcrew may not be as immediate as during takeoff a nd landing operations

. Chapter 9 of this AC provides guidance and considerations for this phase of flight.
d. Asymmet ric t hrust d uring a utothrust o peration
. During autothrust operation, it is possible that a failure (for example, engine failure, throttle lever jam, or thrust control cable jam) could result in a significant asymmetric thrust failure condition that may be aggravated by the continued use of the autothrust system

. Because the FGS could potentially compensate for the asymmetric condition with roll (and possibly yaw) control, the pilot may not immediately be aware of the developing situation

. Therefore, an aler t should be considered as a means of mitigation to draw the pilot’s attention to an asymmetric thrust condition during FGS operation.10/27/14 AC 25.1329

- 1C

65 89. F ailure to Disengage the FGS
. The requirement for quick disengagement for the autopilot and autothrust functions is intend ed to provide a routine and intuitive means for the flightcrew to quickly disengage those functions

. The implication of failures that preclude the quick disengagement from functioning should be assessed consi stent with the guidelines of AC 25.1309

- 1A

. See § 25.1329(b)

. This assessment should consider the effects of failure to disengage the autopilot and/or autothrust functions during the approach using the quick disengagement controls

. The feasibility of the use of the alternative means of d isengagement def ined in Chapter 3 , paragraph 27.b(4) , Al t ernative Means of Autopilot Disengagement , of this AC should be assessed

. If the assessment indicates the aircraft can be landed manually with the autopilot and/or aut othrust engaged, this should be demonstrated in flight test.
90

— 97 [RESERVED]10/27/14 AC 25.1329

- 1C

66 CHAPTER 9

. COMPLIANCE DEMONSTRA TION USING FLIGHT TEST AND SIMU LATION

98. G eneral
.

a. Meth ods of c ompliance d emonstration
. Validation of the performance and integrity of FGS oper ation will typically be accomplished by a combination of analysis, laboratory test, simulation, and flight test

. This chapter focuses on compliance demonstration by flight test or simulation with flightcrew participation

. The chapter includes the evaluatio n necessary to confirm acceptable performance of intended functions, including the human

- machine interface and the acceptability of failure scenarios

. The specific requirements for flight or simulator evaluation will consider the specifics of the applicant ’s design, the supporting engineering analysis, and the scope and depth of the applicant’s laboratory testing

. The type and extent of the various validation methods may vary, depending upon the FGS functionality, certification considerations, the applicant ’s facilities, and other practical and economic constraints.
b. Crite ria for e stablishing c ompliance
. The criteria to be used for establishing compliance with §§ 25.1301, 25.1309, and 25.1329 may be found in Chapters 3 through 8 of this AC

.

c. Elemen ts of c ertif ication f light t est
. The certification flight test program should investigate representative phases of flight and aircraft configurations used by the FGS

. The program should evaluate all of the FGS modes through appropriate maneuvers and representative
env ironmental conditions, including turbulence

. Combinations of FGS elements (for example, autopilot engaged and autothrust disengaged) should be considered

. Certain failure scenarios may require flight or simulator demonstration

. The airplane should be equip ped with sufficient instrumentation to record the parameters appropriate to the test

. Examples of parameters that could be recorded include normal acceleration, airspeed, height, pitch and roll angles, and autopilot engagement state

. The flight test instru mentation should not affect the behavior of the FGS or any other system.
d. Pilot

- in

- the

- l oop e valuatio n . An important part of the pilot

- in

- the

- loop evaluation is validation of human factors

. A thorough evaluation of the human

- machine interface is required to ensure safe, effective, and consistent FGS operation

. Portions of this evaluation will be conducted during flight test

. Representative simulators can be used to accomplish the evaluation of human factors and workload studies

. The level and fidelity of the simulator used should be commensurate with the certification credit being sought, and its use should be agreed upon with the FAA.

e. Other a pplicable g uidance m aterial for FG S t akeoff and/or a pproach m odes
. (1) Criteria to c onsider
. The following criteria should be considered for applicability in developing the overall and integrated flight test and simulation requirements: (a) AC 120

- 29A, Criteria for Approving Category I and II Weather Minima for Approach

.10/27/ 14 AC 25.1329

- 1C

67 (b) AC 120

- 28D, Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout

. The criteria need to be included in the requirements to be tested. (2) Procedures to s how c ompliance
. Procedures that may be used to show
c ompliance are provided in AC 25

- 7 C

. (See paragraph 181, Flight Guidance System

- § 25.1329

. )
f. Relationship of AC c hap ters
. Figure 9

- 1 depicts the relationship between this chapter and the other chap ters contained within this AC. Figure 9

- 1
. Rela tionship between AC Chapters

99. P erforman ce Demonstration (Fault Free): § 25.1301
.

a. General
. (1) Certification p lan
. The certification plan should identify the specific functionality provided by the FGS

. The flight test and/or simulator program will typically assess this functionality under representa tive operational conditions, including applicable airplane10/27/14 AC 25.1329

- 1C

68 configurations and a representative range of airplane weight, center of gravity (CG), and operational envelope. (2) Evaluating p erforman ce . The performance of the FGS in each of its guidance and control modes should be evaluated

. The acceptability of the performance of the FGS may be based on test pilot assessment, taking into account the experience acquired from similar equipment capabili ties and the general behavior of the airplane

. The FGS should be evaluated for its low and high maneuvering capability

. AC 25

- 7C provide s additional information on FGS test procedures. (3) Evaluating c ompatibility of m ode c ontrols, i ndications, and a lerts
. The acceptability of mode controls and annunciations, any associated alerts, and general compatibility with cockpit displays should be evaluated

. The FGS should be free from unexpected disengagement, and no confusion should result from FGS mode changes

. Addit ional considerations relating to the assessment of human factors is provided in Chapter 9 , paragraph 103 , Assessment of Human Factors , of this AC

. b. Normal p erform ance . (1) Demonstration
. Normal performance is considered to be performance during operations well within the airplane’s flight envelope and with routine atmospheric and environmental conditions

. Normal performance should be demonstrated over a range of condit ions that represent typical conditions experienced in operational use. (2) Evaluation
. The FGS should be evaluated to determine the acceptability of the following characteristics: (a) Stability and tracking of automatic control elements. (b) Controllability and tracki ng of guidance elements. (c) Acquisition of flight paths for capture modes. (d) Consistency of integration of modes (of this chapter). (3) Expected e rrors . Performance should be assessed in the presence of errors that can reasonably be expected in operation (for examp le, the incorrect selection of approach speed).

c. Performance in “ o ther t han n ormal” c onditions
. Other than normal conditions are the combination of “rare normal” and “non

- normal” conditions

. Performance in “other than normal conditions” is considered to be performance of the system under conditions that are experienced infrequently by the airplane during operational use

. Examples of rare normal and
non
- normal conditions are given in Chapter 5 , paragraph 54 and paragraph 56 of this AC. (1) Test p rogram . The test program should assess the FGS performance in more challenging environmental conditions (for example, winds, wind gradients, and various levels of turbulence) as the opport unity presents itself

. Rare environmental conditions may require the FGS to operate at the limits of its capabilities

. The intent of the evaluation is to assess the10/27/14 AC 25.1329

- 1C

69 performance of the FGS under more demanding conditions that may be experienced infrequently in

- service

. Due to the severity of some environmental conditions, such as severe and extreme turbulence or flights into severe windshear, it is neither recommended nor required that the FGS flight evaluations include demonstration under those conditions

. Those conditions are more appropriately addressed by simulator evaluation. (2) Evaluation of FGS
. The FGS should be evaluated to determine the acceptability of the following characteristics: (a) Stability of automatic control elements and ability to resume trackin g following any upset. (b) Controllability of guidance elements and ability to resume tracking following any upset. (c) Acceptability of mode transitions and overall cockpit system integration. (3) Additional g uidance for w indshear
. If the FGS provides windshear escap e guidance, performance demonstration requirements should be conducted consistent with AC 25

- 12.
d. Specific p erformance c onditions
. The following paragraphs identify specific performance conditions requiring evaluation by flight test and/or simulation. (1) Icing c onsiderations
. The FGS performance and safety in icing conditions should be demonstrated by flight test and/or simulation tests and be supported by analysis where necessary

. The implications of continued use of the automatic flight control elements of th e FGS in icing conditions should be assessed

. Ice accumulation on the airplane wings and surfaces can progressively change the aerodynamic characteristics and stability of the airplane

. Even though the FGS may perform safely under these conditions, its con tinued use may mask this change, which, in turn, can lead to pilot handling difficulties and potential loss of control, should the autopilot become disengaged (either automatically or manually). (a) Test p rogram

. A test program should assess the potential vuln erability of the FGS to icing conditions by evaluating autopilot performance during artificial ice shape tests or during natural icing tests.
1 Sufficient autopilot testing and analysis should be conduct ed to ensure that the autopilot’ s performance is accept able

. This testing and analysis shoul d include evaluation of the low

- speed protection threshold in the event that stall warning parameters are adjusted to account for icing condition s

. For more information, s ee Chapter 5 , paragraph 55 , Icing Considerations in Normal and Rare Normal Conditions , of this AC

. 2 In general, it is not necessary to conduct an autopilot evaluation that encompasses all weights , CG positions (including lateral asymmetry), altitudes, and deceleration device configurations

. However, if the autopilot performance with ice accretion shows a significant difference from the non

- contaminated airplane or testing indicates marginal perfor mance, additional tests may be necessary.10/27/14 AC 25.1329

- 1C

70 3 If significant autopilot inputs are required to compensate for the icing conditions, then the acceptability of the indication of a significant out

- of

- trim condition should be assessed, and the subsequent response o f the airplane when the autopilot disengages (manual or automatic) should be determined

. For more information, see Chapter 3 , paragraph 27.b and Chapter 4 , paragraph 45.d of this AC

. (b) De

- icing

. If the airplane is configured with a de

- icing system, the autopilot should demonstrate satisfactory performance during the shedding of ice from the airplane. (c) AFM l imitations

. Where degradation is noted that is not significa nt enough to require changes to the autopilot system or to de

- icing or anti

- icing systems, appropriate limitations and procedures should be established and presented in the AFM. (2) Low

- s peed p rotection
. The FGS should be assessed f or the acceptability of the low

- speed protection performance under the following conditions: (a) High altitude cruise with a simulated engine failure. (b) Climb to altitude capture at low altitude with a simulated engine failure during capture. (c) Vertical speed with insufficient climb power. (d) A pproach with speed abuse. (3) High

- s peed p rotection
. The FGS should be assessed fo r the acceptability of the high

- speed protection performance under the following conditions: (a) High altitude level flight with autothrust function. (b) High altitude level flight witho ut autothrust function. (c) High altitude descending flight with autothrust function. (4) Go

- a round
. (a) Mode a ssessment

. The objective of the Go

- Around mode (s ee Chapter 6 , paragraph 65.b , Go

- Around Mode , of this AC ) is to quickly change the flight path of the airplane from approach to landing to a safe climbout trajectory

. The mode has specific utility in low visibility conditions when operations are predicated on a DA ( H ) , and a go

- around is necessary if visual references are not acquired at the DA ( H )

. Therefore, the assessment of the Go

- Around mode may be conducted in conjunction with the evaluation of the FGS to support low visibility operations, using additional crit eria contained in AC 120

- 28D and AC 120

- 29A. (b) Flight e valuation

. The flight evaluation should be conducted to assess the rotation characteristics of the airplane and the performance of the airplane in acquiring and maintaining a safe flight path

. The accept ability of the operation if contact is made with the runway during the missed approach or balked landing should be established.10/27/14 AC 25.1329

- 1C

71 1 Factors to be considered

. A demonstration program should be established that confirms acceptable operation when the following fa ctors are considered: (aa) Airplane weight and CG. (bb) Various landing configurations. (cc) Use of manual thrust or autothrust. (dd) Consequences of thrust de

- rates with selection of Go

- Around mode. (ee) An engine failure at the initiation of go

- around. ( ff) An engine failure during go

- around after go

- around power is reached. (gg) Initiation altitude (for example, in ground effect, not in ground effect during flare).
2 Characteristics to be evaluated: (aa) The pitch response of the airplane during the initia l transition. (bb) Speed performance during airplane reconfiguration and climbout. (cc) Integrated autopilot and autothrust operation. (dd) Transition to missed approach altitude. (ee) Lateral performance during an engine failure.
3 Go

- around initiation h eig hts

. Where height loss during a go

- around maneuver is significant or is required to support specific operational approval, demonstrated values for various initiation heights should be included in the AFM. (5) Steep a pproach ( special authorization )
. (a) Flight test /s imulator d emonstration

. Typical approach operations include glidepath angles betwee n 2.75 and 3.77 degrees

. Application for approval to conduct operations on glide path angles of greater than 3.77 degrees requires add itional evaluation

. See AC 120

- 29A,
se ction 4.3, Landing , for further discussion

. For such an approval, the FGS flight test and simulator demonstration should include the following:
1 Approach path capture, tracking, and speed control.
2 Recovery of the system from abuse cases (for example, glidep ath angle and speed).
3 Assessment of autopilot disengagement transient.10/27/14 AC 25.1329

- 1C

72 4 Demonstration of Go

- Around mode from a steep approach. (b) Autopilot u se on s teep a pproaches

. For autopilot use at approach angles greater than 4.5 degrees, the criteria of AC 25

- 7C , Chapte r 8, Airwort hiness : Miscellaneous Items , should be satisfied

. This advisory material contains airworthiness and transition criteria for steep approaches

. In a ddition, the criteria of AC 120

- 29A, paragraph 6.2.8, Approach Ban Applicability , should be assess ed depending on the operational and low visibility requirements. (6) Indication of and r esponse to an o ut
- of

- trim c ondition
. An assessment should be performed to determine the acceptability of the out

- of

- trim annunciation and subsequent response to disengageme nt

. (See Chapter 4 , paragraph 45.d of this AC .)

e. Flight d ire ctor/head up d isplay
. (1) General
. The guidance aspect of an FGS may be provided by a head down FD or a HUD

. HDD s normally use FD guidance cues that prov ide steering commands

— such as a cross pointer or single “V”

— for the pilot to follow

. HUDs normally display a flight path vector that represents the instantaneous flight path

. The vector is based on the aircraft energy state and directional vectors

. Various new display media are evolving (for example, enhanced vision system (EVS) and simulated vision system) that may integrate guidance elements with situational elements. (a) Flight t est or s imulator p rogram

. The flight test or simulator program should demonstrat e that the FD or HUD guidance elements provide smooth, accurate, and damped guidance in all applicable modes to achieve satisfactory control task performance without pilot compensation or excessive workload. (b) Performance

. The FD guidance should provide adeq uate performance for operations under the conditions listed below

. Some pilot compensation may be acceptable for these conditions:
1 Stability augmentation off.
2 Alternate fly

- by

- wire control modes (for example, direct law), if any.
3 An engine inoperative. (c) Non

- s tationary t racking r eference

. FDs designed to work with a non

- stationary tracking reference (such as a flight path angle or flight path vector , which are commonly used with HUD guidance) should be evaluated in conditions , which bring these guidance symbo ls to the field of view limits of the display

. Crosswinds and certain combinations of airspeed, gross weight, CG, and flap/slat/gear configurations might cause such conditions

. At these limits , the dynamics of the guidance response to pilot control inputs can differ, with potentially adverse effects on tracking performance, pilot compensation, and workload. (d) Primary i nstrument r eferences

. It should be demonstrated that movement of the FD and its tracking reference do not interfere with primary instrument ref erences throughout10/27/14 AC 25.1329

- 1C

73 their range of motion

. The pilot’s ability to interpret the guidance and essential flight information should not be adversely affected by the movement dynamics or range of motion. (2) Specific d emonstrations f or HUD
. (a) Compliance

. These demons trations are intended to show compliance with the following paragraphs of this AC:
1 Chapter 2 , paragraph 28 , FD Engagement, Disengagement, and Indications

. 2 Chapter 3 , paragraph 44 , FGS Mode Selection, Annunciation, and Indication

. 3 Chapter 4 , paragraph 46 , FGS Considerations for HUDs

. 4 Chapter 4 , paragraph 53 , Normal Performance (specifically, criteria for FD guidance)

. (b) Demonstrations r equire d

. When the PF is using the HUD, the HUD is where the pilot is looking for the basic flight information, and the pilot is less likely to be scanning the head down instruments

. Therefore, the following should be demonstrated:
1 The location and presentation o f the HUD information (for example, guidance, flight information, and alerts/annunciations) does not distract the pilot or obscure the pilot’s outside view

. For example, the pilot should be able to track the guidance to the runway without having the view o f runway references or hazards along the flight path obscured by the HUD symbology.
2 Pilot awareness of primary flight information, annunciations, and alerts is satisfactory when using any HUD display mode

. Some display modes that are designed to minimize “ clutter” could degrade pilot awareness of essential information

. For example, a “digital

- only” display mode may not provide sufficient speed and altitude awareness during high

- speed descents.
3 It should be demonstrated that the pilot can positively detect c ases when conformal symbology is field of view limited.
4 Approach mode guidance, if provided, should be satisfactory throughout the intended range of conditions, including at the minimum approach speed and maximum crosswind with expected gust components, fo r which approval is sought.
5 Visual cautions and warnings associated with the FGS can be immediately detected by the PF while using the HUD.

6 The PF can immediately respond to windshear warnings, ground proximity warnings, TCAS warnings, and other warnings r equiring immediate flight control10/27/14 AC 25.1329

- 1C

74 action, such as a go

- around, while using the HUD without having to revert to a head down flight display. (c) Pilot not f lying

. In certain phases of flight, it is important that the PNF and the flightcrew be aware of problems w ith the HUD used by the PF

. Therefore, it should also be demonstrated that the PNF can immediately be made aware of any visual cautions and warnings associated with the HUD for applicable phases of flight. (d) Approach m ode

. If Approach mode guidance is provid ed, satisfactory performance should be demonstrated throughout the intended range of operating conditions for which approval is sought

. For example, performance should be demonstrated at the minimum approach speed and maximum crosswind with expected gust c omponents. (e) Recovery g uidance

. If recovery guidance is provided, it should be demonstrated that the pilot can immediately detect and recover from unusual attitudes when using the HUD

. Specialized unusual attitude recovery symbology, if provided, should be s hown to provide unequivocal indications of the attitude condition (for example, sky/ground, pitch, roll, and horizon) and to correctly guide the pilot to the nearest horizon

. The stroke presentation of flight information on a HUD may not be as inherently i ntuitive for recognition and recovery as the conventional HDD (for example, contrasting color, area fill, shading vs. line strokes)

. The HUD display design needs to be able to compensate for these differences to provide adequate pilot recognition and recov ery cues. (3) Simulator d emonstration for HUD
. If a pilot

- in

- the

- loop flight simulation is used for some demonstrations, then a high fidelity, engineering quality facility is typically required

. The level of simulator may vary with the functionality being prov ided and the types of operation being conducted

. Factors for validation of the simulation for demonstration purposes include the following: (a) Guidance and control system interfaces. (b) Motion base suitability. (c) Adequacy of stability derivative estimates used. (d) Ad equacy of any simplification assumptions used for the equations of motion. (e) Fidelity of flight controls and consequent simulated aircraft response to control inputs

. (A correlation of the simulator performance to flight test results should be made.) (f) Fidelit y of the simulation of aircraft performance

. (A correlation of the simulator performance to flight test results should be made.) (g) Adequacy of flight deck instruments and displays. (h) Adequacy of simulator and display transient response to disturbances or failu res (for example, engine failure, auto

- feather, electrical bus switching).10/27/14 AC 25.1329

- 1C

75 (i) Visual reference availability, fidelity, and delays. (j) Suitability of visibility restriction models, such as appropriate calibration of visual references for the tests to be performed for day, night, and dusk conditions. (k) Fidelity of any other significant factor or limitation relevant to the validity of the simulation.
f. Flightcrew o verride of the FGS
. A flight evaluation should be conducted to demonstrate compl iance with Chapter 3 , paragraph 30 of this AC

. The flight evaluation should consider the implication of system configuration for various flight phases and operations. (1) Autopilot o verride
. (a) Assessing e ffect

. The effect of flightcrew o verride should be assessed by applying an input on the cockpit controller (for example, the control column or equivalent) to each axis for which the FGS is designed to disengage

. The evaluation should be repeated with progressively increasing rate of force application to assess FGS behavior

. This assessment should include the initial application of force on the cockpit controller as well as when the force is removed from the controllers

. The effects of speed and altitude should be considered when conducting the evaluation. (b) No a utomatic d isengagement

. If the autopilot is designed such that it does not automatically disengage due to a pilot override, verify that no potential hazards are generated due to the override per Chapter 3 , paragraph 30 of this AC

. (c) Multiple c hannel e ngagement

. If the design of the autopilot provides for multiple channel engagement for some phases of flight that results in a higher override force, these conditions should be evaluated.
Note: AC 120

- 28D, a ppendix 3, Airworthiness Approval for Airborne Systems Used to Land and Rollout in Low Visibility Conditions , s ection 8, Airborne Systems , contains guidance for evaluating autopilot override for systems supporting low visibility operations. (2) Auto thrust o verride
. The capability of the flightcrew to override the autothrust system should be conducted at various flight phases

. The evaluation should include an override of the autothrust system with a single hand on the thrust levers while maintaining c ontrol of the airplane using the opposite hand on the control wheel (o r equivalent)

. This action may not result in a po tential hazard per § 25.1329(m) , either during the override or after the pilot releases the thrust levers

. See Chapter 3 , paragraph 30 of this AC for additional guidance

. If the autothrust system automatically disengages due to the override, the alerts that accompany the disengagement should be assessed to ensure flightcrew awareness. (3) Pitc h t rim s ystem e valuation d uring a utopilot o verride
. (a) Effect of o verride

. The effect of flightcrew override during automatic control on the automatic trim systems should be conducted

. The pilot should also apply an input to the10/27/14 AC 25.1329

- 1C

76 pitch cockpit controller below that which would cause the autopilot to disengage and verify that the automatic pitch trim sys tem meets the intent in Chapter 3 , paragraph 30 of this AC

. (b) No a utomatic d isengagement

. If the system design is such that the autopilot does not have an automatic disengagement on override feature, the pilot should initiate an intentional override for an extended period of time

. The autopilot should then be disengaged with the quick disconnect button and any tran sient response asse ssed in compliance with Chapter 3 , paragraph 30 of this AC

. The effectiveness and timeliness of any alerts used to mitigate the effects of the override condition should be assessed duri ng this eval uation.
100. Failure C onditions Requiring Validation: § 25.1309
.

a. General
. (1) Safety a ssessment
. The safety assessment process identified in Chapter 8 of this AC should identify any failure condition responses that would require pilot evaluation to assess the severity of the effect, and the validity of any assumptions used for pilot recognition and mitigation

. The classification of a failure condition can vary according to flight condition and may need to be confirmed by simulator or f light test. (2) Evaluation of f ailure c onditions
. This chapter provides guidance on the test criteria, including recognition considerations, for flight evaluation of these failure conditions

. In addition, certain probable failures should be demonstrated to ass ess the performance of the FGS and the adequacy of any applicable flightcrew procedures

. AC 25

- 7C, paragraph 181b(9) provides guidance on test methods for particular types of failure condition s that have been identified by the safety assessment.
b. Validation e lements
. (1) Assessment
. The safety assessment described in Chapter 8 of this AC establishes the FGS failure condition for which appropriate testing should be undertaken

. Assessment of failure conditions has the following elements: (a) Failure condition insertion. (b) Pilot recognition of the effects of the failure condition. (c) Pilot reaction time

. That is, the time between pilot recognition of the failure condition and initiation of the recovery. (d) Pilot recovery. (2) Failure c ondition
. (a) Autopilot

. Failure conditions of the autopilot should be simulated such that overall response is representative of how that failure condition would affect the airplane and its systems

. Failure conditions should include multi

- axis failures and automatic trim failures, if10/27/14 AC 25.1329

- 1C

77 tho se failure conditions exist (given the architecture of a specific FGS) and are relevant to the safety assessment. (b) Flight d irector

. FD failure conditions should be validated, if those failure conditions are relevant to the safety assessment. (c) Most c ritical c onditions

. The flight conditions under which the failure condition is inserted should be the most critical

. Examples of these flight conditions are CG, weight, flap setting, altitude, speed, power, and thrust

. If an autothrust system is installed, the test s should be performed with the autothrust system engaged or disengaged, whichever is the more adverse case. (3) Pilot r ecognition
. (a) General

. The pilot may detect a failure condition through airplane motion cues or by cockpit flight instruments and alerts

. The s pecific recognition cues will vary with flight condition, phase of flight, and crew duties. (b) Hardover

. The recognition point should be that at which a pilot operating in
non
- visual conditions may be expected to recognize the need to take action

. Recognition of the effect of the failure may be through the behavior of the airplane (for example, in the pitch axis by aircraft motion and associated normal acceleration cues and in the roll axis by excessive bank angle) or an appropriate alerting system

. Control co lumn or wheel movements alone should not be used for recognition

. The recognition time should not normally be less than 1 second

. If a recognition time of less than 1 second is asserted, specific justification will be required

. For example, additional test s may be required to ensure that the recognition time is representative in light of the cues available to the pilot. (c) Slowover

. This type of failure condition is typically recognized by a path deviation indicated on primary flight instruments (for example, course deviation indicator (CDI), altimeter, or vertical speed indicator)

. It is important that the recognition criteria are agreed upon with the FAA

. The following identify examples of recognition criteria as a function of flight phase:
1 En route cruise

. R ecognition through the altitude alerting system can be assumed for vertical path deviation

. The lateral motion of the airplane may go unrecognized for a significant period of time, unless a bank angle alerting system is installed and the slowover results i n a bank angle in excess of the limit allowed by the alerting system.
2 Climb and descent

. Recognition through increasing/decreasing vertical speed, pitch attitude, roll attitude, or heading can be assumed.
3 On an approach with vertical path reference

. A disp lacement recognition threshold should be identified and selected for testing that is appropriate for the display(s) and failure condition(s) to be assessed.
Note 1: For an ILS or GLS approach in a significant wind gradient, a value of 1 dot on the displayed ILS/GL S deviation scale is considered a10/27/14 AC 25.1329

- 1C

78 reasonable value for crew recognition

. In smooth atmospheric conditions with steady state tracking with the vertical flight path typically maintained at less than a fraction of a needle width, a detection and recognition t hreshold even below 1/2 dot may be suitable.
Note 2: For RNAV systems that do not use dots, some multiple of needle width related to an established crew monitoring tolerance of normal performance may be appropriate (for example, three needle widths of deviation on the VNAV scale).
Note 3: Credit may be taken for excessive deviation alerts, if available.
4 On an approach without vertical path reference, criteria similar to the climb/descent condition can be assumed. (d) Oscillatory

. It is assumed that oscillatory failures that ha ve structural implications are addressed under 14 CFR p art 25, Subpart C, and § 25.1309

. It can be assumed that the flightcrew will disengage the automatic control elements of the FGS that have any adverse oscillatory effect and will not follow any adverse oscillatory guidance

. However, if there are any elements of the FGS that cannot be disconnected in the presence of an oscillatory failure condition, the long

- term effects on crew workload and the occupants will need to be evaluated. (4) Pilot reaction t ime
. T he pilot reaction time is considered dependent upon the pilot attentiveness, based upon the phase of flight and associated duties

. The following assumptions are considered acceptable: (a) Climb, c ruise, d escent , and h olding

. Recovery action should not be initi ated until three seconds after the recognition point. (b) Maneuvering f light

. Recovery action should not be initiated until one second after the recognition point. (c) Approach

. The demonstration of malfunctions should be consistent with operation in non

- visual co nditions

. The pilot can be assumed to be carefully monitoring the airplane performance and will respond rapidly once the malfunction has been recognized

. A reaction time of one second between recognition point and initiation of recovery is appropriate for this phase of flight.
Note 1: For the final phase of landing (for example, below 80 feet), the pilot can be assumed to react upon recognition without delay.
Note 2: For phases of flight where the pilot is exercising manual control using CWS, if implemented, the pilot can be assumed to commence recovery action at the recognition point.10/27/14 AC 25.1329

- 1C

79 (5) Pilot r ecovery . (a) Pilot r ecovery a ction

. The recovery action should be commenced after the reaction time

. Following such delay, the pilot should be able to return the airplane to its normal fli ght attitude under full manual control without engaging in any dangerous maneuvers during recovery and without control forces exceedi ng the values given in § 25.143(d )

. During the recovery, the pilot may overpower the autopilot or disengage it. (b) Minimum a ut opilot u se h eight

. For the purpose of determining the minimum height at which the autopilot may be used during an approach or for height loss assessments, a representative pilot recovery maneuver appropriate to the airplane type and flight condition should be performed

. This maneuver should not lead to an unsafe speed excursion to resume a normal flight path

. An incremental normal acceleration in the order of 0.5 g is considered the maximum for this type of maneuver.

c. Takeoff
. (1) Worst

- c ase f ailure c ondition
. T he primary concern for the takeoff phase of fl ight is the effect of the worst

- case failure condition identified by the safety assessment on the following: (a) The net effect on the flight path of the airplane after takeoff, and (b) The airplane’s attitude and spee d during climbout. (2) Failures to be e valuated
. Failures that would cause the airplane to pitch up, pitch down, and bank during the takeoff should be evaluated, if those failure conditions exist (given the architecture of a specific FGS) and are relevant to t he safety assessment. (3) On r unway g uidance
. If the FGS provides on runway guidance for takeoff, the effect of any failures of that takeoff guidance should be assessed

. See AC 120

- 28D for additional information.
d. Clim b, c ruise, d escent, and h olding
. Where the safety analysis identifies a failure condition requiring flight/simulator evaluation with pilot assessment, the height loss should be established in accordance with the method described in AC 25

- 7C, paragraph 181b(9)(e) 4 , Assessment of Approach w ithout Ver tical Path Reference

.

e. Maneuvering
. Where the safety analysis identifies a failure condition that has a dynamic effect on the roll control of the airplane, the failure condition should be introduced at the bank angle for normal operation

. The bank angle sho uld not exceed 60 degrees when the pilot recognition and the recovery times identified above are applied.
f. Approach
. A discussion of the operational considerations for approach opera tions is contained in paragraph 101 , Criteria Supporting Operational Use of Autopilot

. This chapter identifies test criteria to support those considerations

. The safety assessment process should identify the demonstration of specific failure conditions du ring the approach

. The fault demonstration process during approach should include the four phases identified in10/27/14 AC 25.1329

- 1C

80 paragraph 100.b , Validation Elements , of this AC

. The failure condition should be inserted at a safe but representative height

. The deviation profile should be identified and applied as indicated in AC 25

- 7C, paragraph 181b(9)(e) , Approach

. (1) Approach w ith v ertical p ath r eference
. (a) xLS (that is, ILS, MLS, or GLS)

. 1 ILS a nd MLS operations are typically conducted on instrument approach procedures designed in accordance with United States Standard for Terminal Instrument Procedures (TERPS)

. See FAA Order 8260.3 B , or the International Civil Aviation Organization (ICAO) Procedures for Air Navigat ion Services

– Aircraft Operations (PANS

- OPS) criteria or equivalent

. These criteria together with ICAO Annex 14 are generally intended to take into account obstacles be neath a reference obstacle identification surface.
Note: The FAA may establish operational criteria for GLS at a later time.
2 In assessing the implication of the effect of failures during autopilot operations, a reference 1:29 slope penetration boundary has been applied against the deviation profile to identify an appropriate altitude for continued autopilot operation

. The 1:29 slope has been found to provide an acceptable margin above obstacles on an approach.
3 The worst

- case failure condition identified by the sa fety assessment ( s ee Chapter 8 , paragraph 87 , Validation of Failure Conditions ) should be demonstrated against the deviation profile criteria and a MUH established

. ( See A C 25

- 7C , paragraph 181b(9)(e) 3 , Assessment of Approach w ith Vertical Path Reference

. ) (b) Area n avigation

. 1 For RNAV coupled approach operations, a vertical flight path similar to an xLS flight path will be used (for example, 3 degree path starting 50 feet above the threshold)

. However, due to sensor characteristics it is assumed that RNAV operations will be conducted with a DA(H) or MDA(H) that is higher than an equivalent MUH on an xLS approach to the same runway

. Further, for this type of operation, it s hould be noted that the MUH is always in the visual segment of the approach, as the failure recognition and recovery maneuver are assumed to be conducted with the pilot having established outside visual reference.
2 In order to derive only one MUH value for simplicity of use, it is assumed that the effects of failure on the autopilot in RNAV operation are no worse than for the xLS operation

. No further determination or demonstration is required

. However, the applicant should show that due account has been tak en in the safety assessment of the differences between the RNAV and xLS inputs to the autopilot (for example, barometric altitude input, FMS position and guidance commands, and their failure effects)

. If these effects can be bounded or otherwise reconciled , then the xLS demonstrated MUH may also be considered applicable to RNAV operations.10/27/14 AC 25.1329

- 1C

81 3 If these effects cannot be bounded or accounted for within those for the xLS operation, the MUH should be determined in accordance with an Approach w ithout Vertical Path Reference below. (2) Approach w ithout v ertical p ath r eference
. For an approach without vertical path reference (for example, VOR, Non Directional Beacon ( NDB ), localizer only) the FGS mode of operation is typically vertical speed/flight path angle (that is, a cruise mode)

. The worst

- case failure condition for this type of mode should be demonstrated in the approach configuration

. An appropriate height loss should then be established in accordance with the method described in AC 25

- 7C , paragraph 181b(9)(e) 4

. (3) Ste ep a pproach
. In support of an approval to use the FGS on glide path angles of greater than 3.77 degrees (see Chapter 9 , paragraph 99.d(5) , Steep Approach (Sp ecial Authorization) of this AC ), an assessment should be made of the effects of failure conditions for this type of operation

. For use of autopilot, an appropriate MUH should be established in accordance with the deviation profile method described in thi s chapter

. For this assessment, the obstacle plane associated with a nominal 3 degree glidepath angle (1:29 slope) should be adjusted according to the maximum approach angle for which approval is sought.

g. Specific c onditions
. (1) Failure c onditions to be e valua ted
. The following are failure conditions that should be considered as part of the FGS evaluation program: (a) Engine failure during approach; continue approach to decision altitude/minimum descent altitude (DA/MDA). (b) Potential fuel imbalance. (c) Airplane system f ailures that affect FGS operational capabilities

. Examples include failures of hydraulic systems, electrical systems, flight controls, and FGS related sensors

. When possible, these failure conditions should be evaluated with a flight test

. However, some fa ilure conditions, due to their potential hazards, may best be evaluated via a high fidelity flight simulation. (2) Failure to d isengage
. The probability of failure of an FGS element to disengage when the quick disengagement control is operated should be shown to be acceptable by the safety analysis process

. If credit is to be taken for acceptable continued manual operation with the FGS elements remaining engaged, that is, without operating any of the other disengagement controls, then a flight demonstration sho uld be conducted though approach, landing , and rollout.
101. Criteria Supporting Operational Use of Autopilot
.

a. Typical f light o perations
. The criteria contained in this paragraph are intended to identify how the functional capability of the FGS, established dur ing the certification, can be used to support typical flight operations

. The criteria are based on experience gained from certification programs and functionality provided by traditional systems

. A FGS providing10/27/14 AC 25.1329

- 1C

82 non
- traditional functionality

— using new or n ovel technology and/or implementation techniques

— may require additional criteria to be established.
b. Operations i n c lose p roximity to the g round
. (1) General
. During low visibility operations, multiple redundant autopilot channels may be used, and the effect of any autopilot failures on the flight path may be eliminated or substantially minimized by the protection provided by that redundancy

. The considerations in the following paragraphs apply primarily to single channel operations where performance or integrit y aspects may require further considera tion

. F or specific considerations relating to autopilot operations close to the groun d in the presence of failures, s ee Chapter 8 , paragraph 88.b , FGS Operations in Clos e Proximity to the Ground , of this AC

. (2) Considerations
. The minimum engagement point for the autopilot after takeoff and the minimum use of the autopilot during approach should take into consideratio n the effect of the following: (a) Failures and their effects (that is, failure conditions). (b) Fault

- free performance. (c) Any specific operational considerations and/or mitigation. (3) Autopilot e ngagement a ltitude/ h eight after t akeoff
. (a) Deviation from f light p ath

. The potential deviation of the airplane from the desired fligh t path due to the effect of a failure condition may necessitate delaying the engagement of an autopilot to an acceptable height above the departure runway. (b) Worst

- case d eviation p rofile

. To support the determination of the minimum engagement height, if auto pilot failure condition(s) are identified that will cause a significant deviation below the intended vertical flight path, the worst

- case deviation profile should be identified

. This profile and the recovery of the airplane should not result in penetration of the net flight path as defined in § 25.115. (c) Other e ffects

. If the failure condition(s) have a neutral effect on the flight path but has implications for speed control during takeoff, the acceptability of cues for the flightcrew detection of the conditi on should be made

. The effect of any failure condition relating to the bank angle of the airplane should also be assessed

. In all of the above, account should be taken of operating the airplane at the weight/al titude/temperature (WAT) limit. (d) Minimum e ngage ment h eight

. The minimum engagement height will typically be established, based on the greatest of the following factors:
1 The lowest altitude or height where the flightcrew could reasonably be assumed to engage the autopilot

. Consideration should be given to normal flightcrew tasks during rotation and liftoff (typically 100 feet or greater).10/27/14 AC 25.1329

- 1C

83 2 Any allowance for the acceptability of the performance of the autopilot during the basic engagement/mode transition.
3 The lowest altitude or height consistent with the r esponse of the airplane to any identified autopilot failure condition(s).
4 Activation of an armed stall identification system, such as a stick pusher (if installed). (e) Deviation i nformation

. If the response to the worst

- case failure condition causes a signifi cant transition below the intended vertical flight path, the deviation information should be provided in the AFM. (4) Autopilot e ngagement d uring a pproach
. (a) Deviation from f light p ath

. The potential deviation of the airplane from the desired flight path due to the effect of a failure condition may necessitate the disengagement of an autopilot at an appropriate height on the approach to landing. (b) MUH

- a pproach

. The operational MUH for approach will be established, based on the following considerations:
1 The altitude or height at which the performance of the automatic control is no longer acceptable.
2 The lowest altitude or height consistent with the response of the airplane to a subsequent autopilot failure.
3 Any specific operational consideration. (c) Approach with v ertic al p ath r eference

. 1 Approaches with vertical path reference can include xLS or RNAV

. Operations using xLS can be assumed to be conducted with respect to a flight path prescribed or established as an integral part of navigation service provided by the State

. RNAV approach operations will be conducted using an onboard database that provides a navigation flight path to the runway.
2 The operational consideration for this type of operation relates to an assessment of the adequacy of continued use of the autopilot in maintaining the desired vertical flight path

. Considerations include the lowest altitude consistent with the response of the airplane to an autopilot failure.
3 To support this determination, if one or more autopilot failure condition(s) is identified tha t causes a significant transition below the intended vertical flight path, the worst

- case deviation profile should be identified using the method identified in Chapter 9 , paragraph 100.f(1) , Approach with Ver tical Path Reference , of this AC

. If the failure condition(s) has a neutral effect on the flight path, the acceptability of cues for the flightcrew10/27/14 AC 25.1329

- 1C

84 detection of the condition should be made

. The effect of any failure condition relating to the bank angle of the airplane should be assessed.
4 For the purpose of the airworthiness assessment, the vertical flight path an xLS and RNAV approach can be assumed to be a flight path of 3 degrees that passes through the runway threshold at an altitude of 50 feet

. Conside rations for steep approaches are provided in Chapter 9 , paragraph 99.d(5) of this AC

. 5 The vertical flight path control for an xLS approach will be made with reference to the path defined by the navigation ser vice

. The RNAV vertical flight path will typically be conducted with reference to barometric altitude

. An appropriate adjustment to the MUH may be necessary to take into account the vertical accuracy of RNAV operations.
Note: Temperature effect compensation shou ld be considered as part of the operational authorization.

6 The MUH

- Approach is the value identified using the method identified in AC 25

- 7C, paragraph 181b(9)(e)

. (d) Approach w ithout v ertical p ath r eference

. 1 Flight operations with no vertical path reference a re conducted with an appropriate visual segment for final approach path

. In the interest of providing appropriate automatic control to assist in a stabilized approach, the minimum use of the autopilot should be consistent with the performance needed for th e descent (for example, vertical speed/flight path angle) and the pilot detection and recovery from an autopilot failure.
2 To support this determination, if one or more autopilot failure conditions is identified that causes a significant transition below th e intended vertical flight path, the worst

- case deviation profile should be identified

. If the failure condition has a neutral effect on the flight path but has implications for speed control during takeoff, the acceptability of cues for the flightcrew det ection of the condition should be made

. The effect of any failure condition relating to the bank angle of the airplane should be assessed.
3 For FGS that are failure protected (that is, fail

- passive), the MUH will typically be no lower than 50 feet above run way elevation

. However, when determining this limitation, account should be taken of the handling task presented to the pilot when regaining manual control, especially in limiting crosswind conditions.
4 For FGS that are not failure protected (that is, not f ail

- passive), the demonstrated MUH

- Approach will typically be established based on the greater of the following considerations: (aa) 50 feet above runway elevation. (bb) Two times the height loss for the airplane as a result of any identified autopilot fai lure condition, using the method identified in AC 25

- 7C, paragraph 181b(9)(e)

.10/27/14 AC 25.1329

- 1C

85 (5) Circling a pproach
. (a) For the purpose of th is AC, circling approaches may be considered to have the following visual segments associated with the approach:
1 A segment at or above th e minimums prescribed by the procedure that parallel the runway in the opposite direction of the landing runway,
2 A turning segment to align with the runway that can be level or partially descending, and
3 A final descending segment to landing. (b) Operationally, the autopilot may remain engaged even after leaving the MDA(H) for reasons related to safety and flightcrew workload relief

. This operational procedure should be balanced against unacceptable performance or failure characteristics

. As this procedure is in the visual segment, no specific constraints for the use of the autopilot are considered necessary for this phase of flight, unless specific unacceptable performance or failure characteristics related to circling approach are identified during the certific ation program.

c. Clim b, c ruise, d escent, and h olding
. The value of the use of the autopilot in providing flightcrew workload relief in climb, cruise, descent, and holding phases of flight should be balanced against the failure characteristics of the autopilo t

. No specific constraints for the use of the autopilot are considered necessary for these phases of flight, unless specific unacceptable performance or failure characteristics related to climb, cruise, or descent are identified during the certification pr ogram.
d. Mane uvering
. No specific constraints for the use of the autopilot are considered necessary for maneuvering flight, unless unacceptable performance or failure characteristics are identified during the certification program

. Chapter 9 , paragraph 100.e , Maneuvering , of this AC provides assessment criteria for maneuvering flight for autopilot failures.
102. A utomatic Disengagement of the Autopilot
. The automatic diseng agement of the FGS will occur for several reasons, such as system failures, sensor failures, or unusual accelerations

. The automatic disengagement characteristics of the FGS should be investigated throughout the flight envelope

. These disengagement cases s hould be analyzed to determine the ones that can be demonstrated during the test program

. For each disengagement case, the transients, warnings, and pilot workload for recovery should be e valuated, and compliance with § 25.1329(d) and (e) must be verified

. The use of simulation is recommended for all conditions that are expected to result in significant transients.
103. A ssessment of Human Factors
.

a. General
. The evaluation, demonstration , and testing should assess the acceptability of the human

- machine interface with the FGS and the potential for flightcrew errors and confusion concerning the behavior and operation of the FGS, when used by a representative range of pilots

. The evaluation of normal and non

- normal FGS operations should include the representative
ran ge of conditions in terms of crew mental or physical workload, required crew response10/27/14 AC 25.1329

- 1C

86 timeliness, and potential for confusion or indecision

. The set of test cases should represent operationally relevant scenarios and the assumptions about pilot training an d skill level should be documented.
b. Flight e valuations
. (1) During c ertification
. Flight evaluation during certification is a final assessment and is intended to validate the design. (2) Prior to c ertification
. Evaluations prior to certification are typically cond ucted in a variety of ways and at different levels of fidelity in order to finalize the design

. These may include the following: (a) Engineering evaluations and task analyses, including cognitive and physical tasks. (b) Mock

- up evaluations and demonstrations. (c) Part

- task evaluations and demonstrations. (d) Simulator evaluations, demonstrations, and tests. (e) Engineering flight evaluations, demonstrations, and tests. (3) Credit to e stablish FGS c ompliance
. The data and experiences from these evaluations may be useful for credit to establish FGS compliance with regulations having human factors considerations

. In addition, applicants have successfully used comparisons to previously certificated designs to obtain such credit (although such credit is not assured)

. Additional testing may be necessary for new FGS flightcrew interface designs or functions. (4) Simulation versus flight t ests
. In some cases, the FAA may consider that less flight testing may be required to show compliance, if the simulation evaluations have added confidence wit h respect to the reduced potential for crew error and confusion and other human factors attributes of the pilot/FGS interface. (a) Selecting m ethodology

. In many cases , the evaluation, demonstration, and test scenarios, including failures and environmental eve nts, will determine whether the data should be obtained in simulation or in flight because of safety considerations or unavailability of the necessary environmental conditions. (b) High f idelity s imulation

. In some test scenarios, a very high fidelity simulati on will be needed

. In addition to the simulation validation considerations ide ntified in Chapter 9 , paragraph 99.e(3)(b) , Motion Base Suitability , of this AC, the simulation used may need to include the following features, depending on the functionality of the FGS:
1 Physical implementation of flight deck controls, displays, indicators, and annunciators for all flightcrew positions that are relevant to the ob jectives of the evaluation.10/27/14 AC 25.1329

- 1C

87 2 Adequate emulations of relevant equipment (hardware and software function), including capability to introduce failures.
3 Weather simulation, including gusts, turbulence, windshear, and visibility.
4 Representation of the operationa l environments, including interaction with air traffic services, day/night operations, etc., as relevant to the functions and pilot tasks being evaluated.
5 Data collection capabilities. (c) Simulation c onformity

. In some cases, certification credit or demonstra tion of compliance using simulations may not be granted due to inability to find simulation conformity

. Conformity should be accounted for when seeking certification testing credit using a simulator.

c. Structured s ubjective e valuations
. Simulator evaluations and tests are intended to generate objective and/or subjective data

. It may not always be possible or necessary to obtain quantifiable measurements of flightcrew performance, even with high fidelity flight or simulation evaluation, demonstration, or test scenarios

. In these cases, evaluation procedures should be based on the use of structured subjective methods, such as rating scales, questionnaires, and/or interviews

. When there is dependence on this type of data, evaluations should consider multiple data collection techniques with an appropriate number of pilot evaluators.
d. Pilot t raining a nd e xperience
. In order to provide sound evaluations, pilots should be trained appropriately on the FGS operation and procedures

. They should have experience in the kind s of operation and aircraft types for which the FGS is intended

. Finally, they should be familiar with the intended function of the FGS, its operational and design philosophy, and the way that this philosophy fits with the overall flight deck and its opera tional and design philosophy.

e. Evaluatin g n ew or u nique d esign f eatures
. Rationale should be provided for decisions regarding new or unique features in a design

. It should be confirmed that the data resulting from the evaluations support acceptability of an y new or unique features.
f. Certi fication p lanning d ocumentation
. The certification planning documentation should describe the means to show compliance with the human factors related considerations of the FGS with this AC.
104

— 108 [RESERVED]10/27/14 AC 25.1329

- 1C

88 CHAPTER 10

. AIRPLANE FLIGHT MANU AL

109. General
. The following paragraphs provide guidance on material to be provided in the AFM to ensure that the appropriate information related to FGS operation is translated into air carrier operations

. For additional guidance, note th at AC 25.1581

- 1 Change 1 , addresses requirements of the AFM for transport category aircraft and distinguishes between those aircraft that are used in air carrier operations and those n ot in air carrier service.

a. AFM t erminology
. The terminology used in the AFM should be consistent with the intended operational use.
b. Low

- v isibility o perations
. Appropriate AFM information related to low

- visibility operations are addressed in AC 120

- 28D and AC 120

- 29A.
110. I nformation Supporting Operational Use of Autopilot
.

a. General

. The airworthiness certification process will assess the effect of autopilot Failure Conditions as identified in Chapters 8 and 9 of this AC

. If a specific MUH is necessary, then the height should be provided in the AFM limitations section

. If the design is such that the effects of one or more failure conditions do not require establishment of a MUH, then the pertinent deviation profile or height loss information should b e provided in the normal or
non
- normal section of the AFM, as applicable.
b. Specif ying a MUH
. If a MUH or a height loss value is applicable, it should be specified as follows: (1) Takeoff

— a utopilot engagement altitude or height. (2) Cruise

— height loss. (3) Approach

— MUH or height loss

. (a) Approach with vertical path r eference

. The MUH should be determined based on clearance above a 1:29 plane using the deviation profile method, as discussed in AC 25

- 7C, paragraph 181b(9)(e) , and shown in f igure 181

- 2 , Deviation Profile Method , of that AC

. (b) Approach without vertical path r eference

. The height loss should be determined using the height loss method, as discussed in AC 25

- 7C, paragraph 181b(9)(e) , and shown in f igure 181

- 3 , Height Loss Method , of that AC

. (c) Assessment of approach with vertical pa th r eference

. As shown in AC 25

- 7C, f igure 181

- 2, Deviation Profile Method

.

c. Maximum displacement d eviation
. If minimum engagement altitude(s) or height(s) are not specified, then “maximum displacement deviation” information from a pertinent takeoff flight path and approach profile should be provided in the AFM normal procedures section, or in the associated flightcrew operation manual (FCOM).10/27/14 AC 25.1329

- 1C

89 111. L imitations
. The AFM limitations section presents those FGS operating limitations appropriate to the airplane model as established in the course of the type certification process

. The FGS operational limitations listed in the AFM (should any exist) must specify any configuration/envelope restrictions

. See §§ 25.1581(a)(1) and 25.1583

. 112. N on - N ormal/Emergency Procedures
. Th e AFM must include non

- normal or emergency procedures appropriate to the FGS identified during the certification program

. See § 25.1581(a)(1) and § 25.1585(a)(2) and (a)(3)

. 113. N ormal Procedures
.

a. Documentation of normal p rocedures
. The normal procedures for u se of the FGS must be documented in the AFM

. See §§25.1581(a)(1) and 25.1585(a)(1)

. These procedures should be demonstrated during the type certification process.
b. Maximum d isplacement d eviation
. In lieu of specification of minimum engagement altitude (s) or height(s) (see paragraph 110 of this AC ), the AFM may alternately specify “maximum displacement deviations” from a specified takeoff flight path or from a specified approach profile

. This information may be based on typica l departure or approach flight paths suited for the aircraft type and for failure conditions that are determined applicable to the type of FGS and modes suitable for use.

c. Procedures for use of FGS in icing c onditions
. The flight manual should include any
n ecessary procedures for the use of the FGS in icing conditions (including moderate and heavy icing conditions)

. In particular, the procedures should include any necessary changes in operating speeds, required either operationally or as a result of relevant design features of the speed protection function of the FGS

. For example, variations in minimum speeds as a function of de/anti

- icing system selection, speed increments during approach, and landing in turbulence should be part of the documented procedures

. d. Aircraft with p ublished FCOM s . The AFMs for aircraft for which the manufacturer has published a FCOM must contain essential information on normal operating procedures that are considered unique to the operation of the FGS for the aircraft type or are oth erwise necessary for safe operation

. See § 25.1581(a)(2)

. FGS description and integration with the overall flight deck design philosophy, specification, and operational procedures that are normally associated with FGSs should be included in the FCOM

. If ap plicable, a FCOM may contain the “maximum displacement deviation” inform ation described in paragraph 110 of this AC in either numeric or graphic form.

e. A ircraft without p ublished FCOMs
. For aircraft that rely on the AFM as t he sole operating manual, the AFM must contain operating information sufficient for flightcrew reference

. See § 25.1581(a)(2)

. The FGS description and integration with the overall flight deck design philosophy, specification and operational procedures norm ally associated with FGSs, should be made available so that an appropriately trained flightcrew may operate the FGS under normal conditions.10/27/14 AC 25.1329

- 1C Appendix A

A

- 1 APPENDIX A. S AFETY ASSESSMENT

1. General
. This appendix provides material that may be useful in supporting the safety assessment a ctivities identified in Chapter 8 of this AC

. 2. Identification of Failure Conditions.

a. The following cases should be considered for applicability when establishing failure conditi ons, as indicated in Chapter 8 of this AC

. (1) Loss of autopilot in single or multiple axes. (2) Loss of guidance in single or multiple axes. (3) Loss of thrust control. (4) Partial loss or degradation of autopilot function. (5) Unintended autopilot commands in a single axis or multiple axes simultaneously (for examp le, hardover, slowover, and oscillatory failure modes). (6) Unintended guidance commands in a single axis or multiple axes. (7) Unintended thrust control. (8) A sustained out

- of

- trim condition with the autopilot engaged without an alert. (9) Autopilot disengagement in an out

- of

- trim condition. (10) Autopilot disengagement without a warning. (11) Inability to disengage the autopilot or autothrust function. (12) Uncommanded engagement of an autopilot or autothrust. (13) Jamming or loading of primary flight controls. (14) Unintended thrust asymmetry.
b. A typical failure conditio n statement may be of the form: ‘[Failure]’ during ‘[Phase of Flight]’ that ‘[Effect]’ when ‘[Mitigation Consideration]’

c. Failure conditions may result from failures within the FGS or from failure associated with aircraft interfac ing systems or components (for example, NAV receivers, attitude heading reference systems, FMS, hydraul ics, electrical systems, etc.).10/27/14 AC 25.1329

- 1C Appendix A

A

- 2 3. Considerations when Assessing the Severity of Failure Condition Effects.

a. Complete definition of failure c ondition
. The “f ailure condition” definition is
com plete (as defined in AC 25.1309

- 1A) when the effects resulting from the failure are identified

. The complete definition of the “failure condition” and its effect will then support the subsequent failure condition hazard c lassification.
b. Factors t o c onsider
. When assessing the effect that results from a failure, the following factors should be considered for various phases of flight: (1) The impact of the loss of control or unintended control on the structural integrity of the a irplane as a result of simple loading or as a result of excitation of aerodynamic or structural modes

— both at the time of occurrence a nd while the flight continues. (2) Implications of the airplane response in terms of attitude, speed, accelerations, flight pa th, and the impact on the occupants and on flightcrew performance. (3) Degradation in the stability or other fly ing qualities of the airplane. (4) The duration of the condition. (5) The aircraft configuration. (6) The aircraft motion cues that will be used by t he flightcr ew for recognition. (7) Availability, level, and type of alerti ng provided to the flightcrew. (8) Expected flightcrew corrective actio n on detection of the failure.

c. Possible c haract eristics of failure c onditions
. Failure conditions may include the following charac teristics: (1) “Hardover” effects
. T ypically , these are considered significant and are readily detectable by the flightcrew, based on the resulting aircraft motion or guidance cues. (2) “Slowover” effects
. T ypically , these are not readily detected by the flightcre w
. The effect may involve departures from intended flight path that are not initially detectable by aircraft motion alone and may be detectable only by motion cues when a significant flight path deviation has occurred or by an appropriate flightcrew alert. (3) “Oscillatory” effects
. T ypically , these are repetitive motions or guidance conditions not related to intended guidance or control

. The magnitude, period, and duration of the condition and any mitigation considerations will determine the final effect. (4) “Los s of” effects
. T ypically , this is the removal of control, guidance , or functionality that may have an immediate effect or may not be immediately apparent to the flightcrew.10/27/14 AC 25.1329

- 1C Appendix A

A

- 3 Note: Chapter 9 of this AC provides guidance on crew recognition consi derations.
4. Failure Condition Classification
. The following are examples of the type of failure condition effects that have been identified in previous airplane certification programs

. The specific number and type of failure condition may vary with airplane type, airplane system architecture, and FGS design philosophy (for example, failure detection, redundancy management, failure annunciation, etc.).

a. Catastrophic failure c onditions
. The following effects have been assessed catastrophic in previous a irplane certification programs: (1) A load on any part of the primary structure sufficient to cause a structural failure preventing safe flight and landing. (2) Unrecoverab le loss of flight path control. (3) Exceedance of V DF /M DF (demonstrated flight dive speed/demonstrated flight dive Mach). (4) Flutter or vibration that causes a structural failure preventing safe flight and landing. (5) A temporary loss of control (for example, stall) where the flightcrew is unable to prevent con tact with obstacles or terrain. (6) Deviations in flight path from which the flightcrew are unable to prevent contact with obstacl es, terrain, or other aircraft.
b. Hazardous failure c onditions
. The following effects have been assessed hazardous in previous a irplane certification programs: (1) Exceedance of an airspeed halfway between V MO (maximum operating limit speed) and V DF or a Mach number halfway between M MO (maximum operating limit Mach) and M DF . (2) A stall, even if the flightcrew is able to recover safe flight path control. (3) A load factor less than zero. (4) Bank an gles of more than 60 degrees en route or more than 30 degrees below a height of 1000 ft. (304.8 m above an applicable airport elevation). (5) Degradation of the flying qualities of the airplane that excessively increases flightcrew workload. (6) Failure that could res ult in a rejected takeoff (RTO) and high speed overrun (for example, 60 knots).10/27/14 AC 25.1329

- 1C Appendix A

A

- 4 (7) A flight path deviation that requires a severe maneuver to prevent contact with obstacle, terrain , or other aircraft.
Note: Severe maneuver includes risk of serious injury or death o f a small number of occupants.

c. Major failure c onditions
. The following effects have been assessed “major” in previous a irplane certification programs: (1) A flight path deviation, including the required recovery maneuver, which may result in passenger injuries

. Consideration should be given to phases of flight where the occupants may reasonably be moving about the airplane or be serving or cons uming hot drinks

. See appendix B for the definition of significant tra nsient. (2) Degradation of the flying qualities of the airplane that significantly increase flightcrew workload.10/27/14 AC 25.1329

- 1C Appendix B

B

- 1 APPENDIX B. D EFINITIONS

The following definitions apply to the requirements of § 25.1329 and the guidance material provided in this AC

. You should not assume t hat these definitions apply to the same or similar terms used in other regulations or ACs

. Terms for which standard dictionary definitions apply are not defined in this AC.
Table B

- 1 . Terms and Definitions

Term Definition
Abnormal Condition See N on
- Normal C ondition. Advisory Crew awareness is required and subsequent crew action may be required.
Alert A generic term used to describe a flight deck indication meant to attract the attention of the flightcrew to a non

- normal operational or airplane system condition without implying the degree or level of urgency for recognition and corrective action by the crew

. Warnings, cautions, and advisories are considered alerts. Analysis The terms “analysis” and “asses sment” are used throughout

. Each has a broad definition and the two terms are to some extent interchangeable

. However, the term analysis generally implies a more specific, more detailed evaluation, while the term assessment may be a more general or broader evaluation but may include one or more types of analysis.
Arm A condition where the intent to transition to a new mode or state has been established but the criteria necessary to make that transition has not been satisfied.
Assessment See the definition of analysis above.
Autopilot The autopilot function provides automatic control of the airplane, typically in pitch, roll, and yaw

. The term includes the sensors, computers, power supplies, servo

- motors/actuators and associated wiring, necessary for its f unction

. It includes any indications and controllers necessary for the pilot to manage and supervise the system

. Any part of the autopilot system that remains connected to the primary flight controls when the autopilot is not in use is regarded as a part o f the primary flight controls.10/27/14 AC 25.1329

- 1C Appendix B

B

- 2 Term Definition
Autothrust The autothrust function provides automatic control of the thrust of the airplane

. The term includes the sensors, c omputers, power supplies, servo

- motors/actuators and associated wiring, necessary for its function

. It includes any indications and controllers necessary for the pilot to manage and supervise the system

. Any part of the autothrust that remains connected to the engine controls when the autothrust is not in use is regarded as a part of the engine control system.
Caution A flight deck indication that alerts the flightcrew to a
non
- normal operational or airplane system condition that requires immediate crew awareness

. Subsequent pilot corrective compensatory action will be required. Cognitive Task Analysi s An analysis that focuses on the mental processes, skills, strategies, and use of information required for task performance. Complex A system is complex when its operation, failure modes, or failure effects are difficult to comprehend without the aid of analytical methods.
Conformal Positioned and scaled with respect to the outside view. Control Wheel Steering (CWS) A flight guidance system (FGS) function which, when engaged, enables the pilot/first officer to manually fly the airplane by positioning th e flight control surfaces using the autopilot servos

. The positions of the flight deck controls (for example, control column, control wheel) are determined by the FGS, which converts them into autopilot servo commands

. The autopilot servos, in turn, drive the appropriate flight control surfaces.
Conventional A system is considered to be conventional if its functionality, the technological means used to implement its functionality, and its intended usage are all the same as, or closely similar to, that of p reviously approved systems that are commonly used. Engage A steady state that exists when a flightcrew request for mode or system functionality has been satisfied.

Error An omission or incorrect action by a crewmember or maintenance personnel, or a mista ke in requirements, design, or implementation.10/27/14 AC 25.1329

- 1C Appendix B

B

- 3 Term Definition
Failure An occurrence that affects the operation of a component, part, or element such that it can no longer function as intended (this includes both loss of function and malfunction). Note: Errors may cause failures, but are not considered to be failures.
Failure Condition A condition having an effect on the airplane and/or its occupants, either direct or consequential, which is caused or contributed to by one or more failures or errors, considering flight p hase and relevant adverse operational or environmental conditions, or external events. Fail Operational System A system capable of completing an operation, following the failure of any single element or component of that system, without pilot action.
Fai l Passive System A system which, in the event of a failure, results in: (a) N o significant deviation in the aircraft flight path or attitude, and (b) N o out

- of

- trim condition at disengagement that is not easily controlled by the pilot. Flight Director (FD ) A visual cue or set of cues that are used during manual control of the airplane as command information to direct the pilot how to maneuver the airplane, usually in pitch, roll and/or yaw, to track a desired flight path

. The FD, displayed on the pilot’ s p rimary head down attitude indicator (ADI) or head up display (HUD), is a component of the FGS and is integrated with airborne attitude, air data, and NAV systems. Flight Guidance System (FGS) A system consisting of one or more of the following elements:

• A utopilot

• F light director, and

• A utomatic thrust control. A flight guidance system (FGS) also includes any interactions with stability augmentation and trim systems.10/27/14 AC 25.1329

- 1C Appendix B

B

- 4 Term Definition Flight Management System (FMS) An aircraft area navigation (RNAV) system and associated dis plays and input/output devices(s) having complex multi

- waypoint lateral (LNAV) and vertical (VNAV) capability (or equivalent), data entry capability, database memory to store route and instrument flight procedure information, and display readout of NAV par ameters

. The FMS provides guidance commands to the FGS for the purpose of automatic navigation and speed control when the FGS is engaged in an appropriate mode or modes (for example, VNAV, LNAV, RNAV). Head Up Display (HUD) A transparent optical display s ystem located level with and between the pilot and the forward windscreen

. The HUD displays a combination of control, performance, NAV, and command information superimposed on the external field of view

. It includes the display element, sensors, computers and power supplies, indications and controls

. It is integrated with airborne attitude, air data and navigation NAV systems, and as a display of command information is considered a component of the FGS.
Inadvertent A condition or action that was not planne d or intended.
Latent Failure A failure is latent until it is made known to the flightcrew or maintenance personnel

. A significant latent failure is one that would, in combination with one or more specific failures or events, result in a hazardous or cata strophic failure condition. Limit Flight Envelope The outermost flight envelope of the airplane normally associated with the limit loads of the airplane structure. Minimum Engage Height The minimum height after takeoff at which the flightcrew is permitte d to engage the autopilot

. Also referred to as minimum use height takeoff

. See “minimum use height.” Minimum Use Height (MUH) A height specified during airworthiness demonstration or review above which, under standard or specified conditions, a probable f ailure of a system is not likely to cause a significant path displacement unacceptably reducing flight path clearance from specified reference surfaces (for example, airport elevation) or specified obstacle clearance surfaces.
Minor Transient See “Transie nt.”10/27/14 AC 25.1329

- 1C Appendix B

B

- 5 Term Definition
Mode A mode is system configuration that corresponds to a single (or set of) FGS behavior(s).
Mode Reversion An automatic mode change that returns the FGS to a previously engaged mode or to a pre

- determined “default” mode for that condition

. This ma y occur due to several reasons, such as specific criteria becoming satisfied or because the FGS cannot perform the currently selected operation

. This type of mode change is not requested by the flightcrew and therefore may be unexpected.
Non

- Normal Condit ion A condition or configuration of the airplane that would not normally be experienced during routine flight operations

— usually due to failures

. Also includes unusual airplane ferry configurations, such as transporting a spare engine or landing gear locke d down ferry flight.
Normal Condition Any fault

- free condition typically experienced in normal flight operations

. Operations typically well within the aircraft flight envelope, and with routine atmospheric and environmental conditions. Normal Flight Enve lope The range of altitude and operating speeds that are defined by the airplane manufacturer as consistent with conducting flight operations for which the airplane is designed

. This envelope is generally associated with practical, routine operation and/or prescribed conditions, whether all

- engine or engine inoperative.
Other t han Normal Condition The summation of rare normal and non

- normal conditions.

Override (of engaged FGS functions) An action taken by the flightcrew intended to prevent, oppose, or al ter an operation being conducted by a flight guidance function, without first disengaging that function.
Rare Normal Condition A fault

- free condition that is experienced infrequently by the airplane due to severe environmental conditions (for example, sig nificant wind, turbulence, or asymmetric icing). Redundancy The presence of more than one independent means for accomplishing a given function or flight operation.
Select The flightcrew action of requesting functionality or an end state condition.10/27/14 AC 25.1329

- 1C Appendix B

B

- 6 Term Definition Signi ficant Transient See “Transient.” Stability Augmentation System Automatic systems that provide or enhance stability for specific aerodynamic characteristics of an airplane (for example, yaw damper, longitudinal stability augmentation system, Mach trim). System A combination of components, parts, and elements that are i nter

- connected to perform one or more specific functions.
Transient A disturbance in the control or flight path of the airplane that is not consistent with response to flightcrew inputs or environmental conditions.
Minor Transient: A transient that would not significantly reduce safety margins and which involves flightcrew actions that are well within their capabilities involving a slight increase in flightcrew workload or some physical dis comfort to passengers or cabin crew

. Significant Transient: A transient that would lead to a significant reduction in safety margins, an increase in flightcrew workload, discomfort to the flightcrew, or physical distress to passengers or cabin crew, possi bly including non

- fatal injuries

. Note: The flightcrew should be able to respond to any significant transient without:

• Exceptional piloting skill, alertness, or strength,

• Forces greater than those given in § 25.143(c), and

• Accelerations or attitudes in th e airplane that might result in further hazard to secured or non

- secured occupants. Warning A flight deck indication that alerts the flightcrew to a
non
- normal operational or airplane system requiring immediate recognition

. Immediate corrective or compens atory action by the flightcrew is required.10/27/14 AC 25.1329

- 1C Appendix C

C

- 1 APPENDIX C. A CRONYMS

Table C

- 1 . Acronyms and Definitions
Acronym Definition
AC Advisory Circular
ADI Attitude Director Indicator
AFM Airplane Flight Manual
AGL Above Ground Level
ARP Aerospace Recommended Practice
ATC Air Traffic Control
CDI Course Deviation Indicator
CFR Code of Federal Regulations
CG Center of Gravity
CWS Control Wheel Steering
DA Decision Altitude DA(H) Decision Altitude (Height)

DME Distance Measuring Equi pment
EVS Enhanced Vision System
FAA Federal Aviation Administration
FCOM Flightcrew Operations Manual

FD F light Director
FGS Flight Guidance System

FL Flight Level
FMA Flight Mode Annunciator10/27/14 AC 25.1329

- 1C Appendix C

C

- 2 Acronym Definition
FMS Flight Management System
GBAS Ground

- Based Augment ation System
GLS GBAS Landing System
GPWS Ground Proximity Warning System

HDD Head Down Display
HUD Head Up Display
ICAO International Civil Aviation Organization
ILS Instrument Landing System
IMA Integrated Modular Avionics
IMC Instrument Meteorol ogical Conditions
LNAV Lateral Navigation
LOC Instrument Landing System Localizer MDA(H) Minimum Descent Altitude (Height)
MLS Microwave Landing System
MSL Mean Sea Level
MSP Mode Select Panel
MUH Minimum Use Height ( autopilot )
NAV Navigation
ND N avigation Display
N DB Non Directional Beacon
PAN

- OPS Procedures for Air Navigation

– Aircraft Operations

PF Pilot Flying

PFD Primary Flight Display
PNF Pilot Not Flying10/27/14 AC 25.1329

- 1C Appendix C

C

- 3 Acronym Definition
RNAV Area Navigation
RNP Required Navigation Performance
RTO Rejected Takeoff
RVSM Reduced Vertical Separation Minimum
SAE Society of Automotive Engineers
TCAS Traffic Alert and Collision Avoidance System
TCS Touch Control Steering
TERPS Terminal Instrument Procedures
TOGA Takeoff or Go

- Around
V DF / M DF Demonstrated Flight Div e Speed/Demonstrated Flight Dive Mach
V MO /M MO Maximum Operating Limit Speed/Maximum Operating Limit Mach
V R Rotation Speed
V SR Reference Stall Speed ( s ee § 25.103)
V 2 Takeoff Safety Speed
VMC Visual Meteorological Conditions
VNAV Vertical Navigation
VOR Very High Frequency Omnirange Station
WAT Weight Altitude Temperature
xLS ILS, MLS, or GLSAdvisory Circular Feedback

If you find an error in this AC , have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by (1) emailing this form to 9 -AWA- AVS

AIR500-Coord@faa.gov or (2) faxing it to the attention of the Aircraft Certification Service Di rectives Management Officer at (202) 267-3983.

Subject: Date:
Please check all appropriate line items:
☐ An error (procedural or typographical) has been noted in paragraph on page

.
☐ Recommend paragraph on pa ge be changed as follows:

☐ In a future change to this AC, please cover the following subject: ( Briefly describe what you want added.)

☐ Other comments:

☐ I would like to discuss the above. Please contact me.

Submitted by: Date: