U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Approval of Flight Guidance Systems Date: AC No: 25.1329-1C Initiated By: AIR-626 Change: 2
1. PURPOSE. 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 system. 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 (FDs), and automatic thrust control as well as any interactions with stability augmentation and trim functions .
2. PRINCIPAL CHANGES. Change 2 provides clarification on the autopilot disengagement aural alert. Change 2 also provides clarification about potential hazards for systems without automatic disengagement to address the automatic trim response to an override of the autopilot.
Change 2 also provides clarification about potential hazards caused by incompatible mode engagement. Change 2 updates references to related ACs and industry documents.
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AC 25.1329-1C CHG 2
AC 25.1329-1C CHG 2
3. WEBSITE AVAILABILITY. To access this AC electronically, you can go to either of the following sites:
a. http://www.faa.gov/regulations_policies/advisory_circulars/
b. https://drs.faa.gov/browse Daniel J. Elgas Aviation Safety Director, Policy and Standards Division, Aircraft Certification Service
U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Approval of Flight Guidance Date: 5/24/16 AC No: 25.1329-1C Systems Initiated By: AFS-400 Change: 1
1. PURPOSE. This advisory circular (AC) describes an acceptable means for showing compliance with certain requirements of title 14 of the Code of Federal Regulations (14 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.
2. PRINCIPLE CHANGES. Microwave landing systems (MLS) are no longer used in the U.S. National Airspace System. This change removes the terms “MLS” and “microwave landing system” from the AC. This change replaces pilot -not-flying (PNF) with pilot monitoring (PM).
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U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Approval of Flight Guidance Systems Date: 10/27/14 AC No: 25.1329-1C Initiated By: ANM-110 This advisory circular (AC) describes an acceptable means for showing complianc e with certain requirements of title 14, Code of Federal Regulations ( 14 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 of this AC.
/s/ Michael Kaszycki Acting Manager, Transport Airplane Directorate Aircraft Certification Service
AC 25.1329-1C CHG 2 Paragraph Page INT
RODUCTION1
1. Purpose1
2. Applicability1
3. Cancellation1
4. Related Regulations, ACs, and Industry Documents1
a. Regulations1
b. Advisory Circulars2
c. Related Industry Standards4
d. Other FAA documents4
5—10 [RESERVED]5
CHAPTER 1. BACKGROUND6
11. General6
a. AC 25.1329-1C6
b. Scope6
12. Evolution of FGS6
a. Complexity6
b. Guidance considerations6
13—16 [RESERVED]6
CHAPTER 2. OVERVIEW OF FLIGHT GUIDANCE SYSTEMS7
17. Purpose of FGS7
18. Components7
a. Included in definition7
b. Excluded from definition7
19. FGS Functions7
a. Elements of FGS7
b. Approach and landing system7
c. Flight management system (FMS)7
d. Design philosophy8
e. Description of FGS behavior and operation8
ii
CONTENTS
CONTENTS (CONTINUED) Paragraph Page
20. Compliance with § 25.13298
a. General8
b. Relevant paragraphs8
21—26 [RESERVED]8
CHAPTER 3. FGS ENGAGEMENT, DISENGAGEMENT, INDICATIONS, AND OVERRIDE .. 14
27. Autopilot Engagement, Disengagement, and Indications14
a. Autopilot engagement14
(1) Single switch action14
(2) Engagement status of autopilot14
(3) Multiple autopilots14
(4) Acceptable transients14
(5) FD not engaged14
(6) FD engaged14
b. Autopilot disengagement15
(1) General15
(2) Autopilot disengagement alerts16
(3) Quick disengagement control16
(4) Alternative means of autopilot disengagement17
(5) Flightcrew pitch trim input17
28. FD Engagement, Disengagement, and Indications18
a. FD engagement18
(1) General18
(2) Guidance cue(s)19
(3) Reactive windshear guidance system19
b. FD disengagement19
29. Autothrust Engagement, Disengagement, and Indications19
a. Autothrust engagement19
(1) Indication19
(2) Accessibility of controls19
AC 25.1329-1C CHG 2 iii
AC 25.1329-1C CHG 2
CONTENTS (CONTINUED) Paragr aph Page
(3) Inadvertent engagement/disengagement19
(4) Automatic engagement19
b. Autothrust disengagement20
(1) Indication of disengagement20
(2) Inadvertent disengagement20
(3) Consequence of disengagement20
(4) Autothrust quick disengagement control20
30. Override of the FGS21
a. General21
b. Autopilot override21
(1) With automatic disengagement21
(2) Without automatic disengagement22
c. Autothrust override22
(1) Force required22
(2) Response to override22
(3) Engagement status with override23
31. FGS Engagement Mode Compatibility23
a. FGS mode engagement philosophy23
b. Engagement mode compatibility23
32—41 [RESERVED]23
CHAPTER 4. CONTROLS, INDICATIONS, AND ALERTS24
42. General24
a. Human-machine interface (HMI)24
b. Design of controls, indications, and alerts24
c. Evaluation of information provided by FGS24
43. FGS Controls24
a. General24
b. Design considerations24
(1) Differentiation of knob shape and position24
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AC 25.1329-1C CHG 2
CONTENTS (CONTINUED) Paragraph Page
(2) Design to support correct selection of target values24
(3) Commonality across aircraft types25
(4) Positioning of controls and related indications25
(5) Inadvertent operation25
44. FGS Mode Selection, Annunciation, and Indication25
a. Annunciation of engagement of the FGS25
b. Description of FGS modes25
c. FGS mode annunciations25
(1) Active and armed modes25
(2) Location25
(3) Discriminators26
(4) Color26
d. Mode changes26
(1) Operationally relevant mode changes26
(2) Attention-getting features26
(3) Use of alerts26
e. Failure to engage or arm26
f. FGS mode display and indications26
45. FGS Alerting, Warning, Caution, Advisory, and Status27
a. General27
(1) Alerting provisions27
(2) Determination of FGS capability27
b. Speed protection alerts27
(1) Alerts to crew27
(2) Alert specifications27
(3) Consistency27
(4) Nuisance alerts27
c. Loss of autopilot approach mode27
d. Awareness of potential significant transient condition (“bark before bite”)28
(1) General28
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CONTENTS (CONTINUED) Paragraph Page
(2) Flightcrew alert(s)28
(3) Situations to consider for an alert28
46. FGS Considerations for HUDs29
a. General29
b. Characteristics of HUD guidance29
(1) Supplemental use display system29
(2) External visual references29
(3) Interference and occlusion30
(4) Display criteria30
(5) Conformal symbology30
(6) Low-visibility approach30
(7) Clutter30
c. HUD/HDD compatibility30
(1) General30
(2) Consistency and compatibility30
d. Alerting issues31
(1) Alerts displayed on HUDs31
(2) Monochrome HUDs32
(3) Multi-color HUDs32
(4) Single HUD installation32
(5) Dual HUD installations32
(6) GPWS/TCAS on HUD32
e. Upset/unusual attitude recovery guidance33
(1) Guidance cues33
(2) Orientation cues33
47—51 [RESERVED]33
CHAPTER 5. PERFORMANCE OF FUNCTION34
52. General34
a. Intended function34
AC 25.1329-1C CHG 2 vi
AC 25.1329-1C CHG 2
CONTENTS (CONTINUED) Paragraph Page
b. Effect of system tolerances34
53. Normal Performance34
a. General34
b. Conditions to consider34
c. Level of performance36
(1) Significant characteristics36
(2) Configuration changes36
(3) Compliance evaluation36
(4) Prescribed levels of performance36
(5) Equivalence of performance36
(6) Autopilot36
(7) Flight director36
(8) Autothrust36
(9) Automatic trim36
54. Performance in Rare Normal Conditions37
a. General37
(1) Range of conditions37
(2) Effect on performance37
b. Conditions to consider37
c. Level of performance38
(1) Performance standard38
(2) Autopilot authority limit39
(3) Masking of potential hazard39
55. Icing Considerations in Normal and Rare Normal Conditions39
a. Effect on performance39
b. Alerts39
c. Effect on speed protection39
56. Performance in Non-Normal Conditions39
a. General39
b. Conditions to consider39
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c. Level of performance40
(1) Performance standard40
(2) Autopilot authority limit40
(3) Masking of potential hazard41
57. Speed Protection41
a. General41
(1) Speed excursions41
(2) Compliance with § 25.1329(h)41
(3) Design standard42
b. Low-speed protection42
(1) General42
(2) Factors to consider42
(3) Low-speed protection during approach operations43
(4) Windshear recovery guidance44
c. High-speed protection44
(1) General44
(2) Factors to consider44
58—61 [RESERVED]45
CHAPTER 6. CHARACTERISTICS OF SPECIFIC MODES46
62. General46
63. Lateral Modes46
a. Heading or track hold46
b. Heading or track select46
c. LNAV mode46
(1) Lateral flight path46
(2) Automatic mode transitions46
(3) Takeoff or go-around (TOGA)46
64. Vertical Modes47
a. Target altitude selection47
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