U.S . Department of Transportation Federal Aviation Administration Advisory Circular Subject: Approval of Flight Systems Guidance Date: 5/24/16 Initiated by: AFS-400 AC No: 25.1329-1C 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) part 25, § 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. PRINCIPAL 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).
PAGE CONTROL CHART Remove Pages Dated Insert Pages Dated Page ii Page vi Pages viii and ix Page xii thru xiv Page xvi Page 7 Page 31 Page 43 Page 52 Page 63 Page 74 Page 80 Pages C-2 and C-3 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 10/27/14 Page ii Page vi Pages viii and ix Page xii thru xiv Page xvi Page 7 Page 31 Page 43 Page 52 Page 63 Page 74 Page 80 Pages C-2 and C-3 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 5/24/16 ORIGINAL SIGNED by /s/ John S. Duncan Director, Flight Standards Service
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 compliance with certain requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 25, § 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.
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CONTENTS Paragraph Page
INTRODUCTION1
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
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CONTENTS (CONTINUED) Paragraph Page
20. Compliance with § 25.13298
a. General8
b. Relevant paragraphs8
21—26 [RESERVED]13
CHAPTER 3. FLIGHT GUIDANCE SYSTEM ENGAGEMENT,
DISENGAGEMENT, INDICATIONS, AND OVERRIDE14
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 wind shear guidance system19
b. FD disengagement19
29. Autothrust Engagement, Disengagement, and Indications19
a. Autothrust engagement19
(1) Indication19
(2) Accessibility of controls19
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CONTENTS (CONTINUED) Paragraph 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 disengagement21
c. Autothrust override22
(1) Force required22
(2) Response to override22
(3) Engagement status with override22
31. FGS Engagement Mode Compatibility22
a. FGS mode engagement philosophy22
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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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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(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) Multicolor HUDs32
(4) Single HUD installation32
(5) Dual HUD installations32
(6) GPWS/TCAS on HUD32
e. Upset/unusual attitude recovery guidance32
(1) Guidance cues32
(2) Orientation cues33
47—51 [RESERVED]33
CHAPTER 5. PERFORMANCE OF FUNCTION34
52. General34
a. Intended function34
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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) FD36
(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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CONTENTS (CONTINUED) Paragraph Page
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) Wind shear 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 flightpath46
(2) Automatic mode transitions46
(3) TOGA46
64. Vertical Modes47
a. Target altitude selection47
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CONTENTS (CONTINUED) Paragraph Page
b. Vertical speed47
c. Flightpath angle47
d. Indicated airspeed/Mach hold (speed on elevator)47
e. Indicated airspeed/Mach select (speed on elevator)47
f. Flight level (FL) change (speed on elevator)47
g. Altitude capture47
(1) Mode transition47
(2) Guidelines for altitude capture mode48
h. Altitude hold49
(1) Entering mode49
(2) Mode transition annunciation49
(3) Barometric pressure adjustment49
i. VNAV49
(1) FMS path49
(2) Climb or descent49
65. Multiaxis Modes50
a. Takeoff mode50
(1) Vertical guidance50
(2) Lateral guidance50
(3) Rotation guidance50
(4) Autothrust50
(5) Operation and performance50
b. Go-around mode51
(1) Vertical elements51
(2) Speed51
(3) Autothrust51
(4) Engagement52
(5) All engine and engine-out capability52
c. Approach mode52
(1) Final approach path52
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CONTENTS (CONTINUED) Paragraph Page
(2) Mode annunciations52
(3) Submodes52
(4) Mode engagement sequence52
66. Autothrust Modes52
a. Thrust mode52
b. Speed mode53
c. Retard mode53
67. Special Considerations for VNAV Approach Operations Related to Selecting a
Target Altitude53
a. Approach operations53
b. VNAV path operations53
68. Control Wheel Steering (Control Steering through the Autopilot)53
a. General53
b. Design53
(1) Control forces53
(2) Bank and pitch attitudes53
(3) Control behavior54
(4) Stall and stall recovery54
(5) Adjustments to trim54
(6) Takeoff and landing54
(7) Automatic reversion to CWS mode54
c. Terminology and application of advisory material54
(1) Touch control steering (TCS)55
(2) Supervisory override55
69. Special Considerations for the Integration of Fly-by-Wire Flight Control Systems
and FGS55
a. Speed protection55
b. System degradation55
70—74 [RESERVED]55
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CHAPTER 7. FLIGHT GUIDANCE SYSTEM INTEGRATION56
75. General56
76. System Integration Issues56
a. Common and cascading failure modes56
b. Risk of error56
c. System safety analysis56
77. Functional Interfaces56
a. Interfacing sensors56
b. Potential inconsistencies between systems57
c. Function and performance57
78—82 [RESERVED]57
CHAPTER 8. SAFETY ASSESSMENT58
83. General58
a. Basic safety requirements58
b. Safety assessment58
c. Validation of safety assessment58
d. Coordination with the FAA58
84. FGS Failure Conditions58
a. Functionality58
b. Effect of failure condition59
85. Type and Severity of Failure Conditions59
a. Types of failure conditions59
(1) Loss of function59
(2) Malfunction59
b. Cause59
c. Severity60
d. Assessment of failure conditions60
(1) Functional failures60
(2) Airframe loads60
(3) Assessing total effect of failure60