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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) 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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CONTENTS (CONTINUED) Paragraph Page
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
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CONTENTS (CONTINUED) Paragraph Page
86. Mitigation of Failure Conditions60
a. General60
b. Identification of methods61
c. FGS deselection61
87. Validation of Failure Conditions61
a. General61
b. Validation options61
c. Validation methodology61
88. Specific Considerations62
a. FGS action during ground operations62
b. FGS operations in close proximity to the ground62
(1) Takeoff62
(2) Approach63
c. Cruise operations64
d. Asymmetric thrust during autothrust operation64
89. Failure to Disengage the FGS65
90—97 [RESERVED]65
CHAPTER 9. COMPLIANCE DEMONSTRATION USING FLIGHT TEST AND
SIMULATION66
98. General66
a. Methods of compliance demonstration66
b. Criteria for establishing compliance66
c. Elements of certification flight test66
d. Pilot-in-the-loop evaluation66
e. Other applicable guidance material for FGS takeoff and/or approach modes66
(1) Criteria to consider66
(2) Procedures to show compliance67
f. Relationship of AC chapters67
99. Performance Demonstration (Fault Free): § 25.130167
a. General67
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(1) Certification plan67
(2) Evaluating performance68
(3) Evaluating compatibility of mode controls, indications, and alerts68
b. Normal performance68
(1) Demonstration68
(2) Evaluation68
(3) Expected errors68
c. Performance in “other than normal” conditions68
(1) Test program68
(2) Evaluation of FGS69
(3) Additional guidance for wind shear69
d. Specific performance conditions69
(1) Icing considerations69
(2) Low-speed protection70
(3) High-speed protection70
(4) Go-around70
(5) Steep approach (special authorization)71
(6) Indication of and response to an out-of-trim condition72
e. FD/HUD72
(1) General72
(2) Specific demonstrations for HUD73
(3) Simulator demonstration for HUD74
f. Flightcrew override of the FGS75
(1) Autopilot override75
(2) Autothrust override75
(3) Pitch trim system evaluation during autopilot override75
100. Failure Conditions Requiring Validation: § 25.130976
a. General76
(1) Safety assessment76
(2) Evaluation of failure conditions76
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CONTENTS (CONTINUED) Paragraph Page
b. Validation elements76
(1) Assessment76
(2) Failure condition76
(3) Pilot recognition77
(4) Pilot reaction time78
(5) Pilot recovery79
c. Takeoff79
(1) Worst-case failure condition79
(2) Failures to be evaluated79
(3) On runway guidance79
d. Climb, cruise, descent, and holding79
e. Maneuvering79
f. Approach79
(1) Approach with vertical path reference80
(2) Approach without vertical path reference81
(3) Steep approach81
g. Specific conditions81
(1) Failure conditions to be evaluated81
(2) Failure to disengage81
101. Criteria Supporting Operational Use of Autopilot81
a. Typical flight operations81
b. Operations in close proximity to the ground82
(1) General82
(2) Considerations82
(3) Autopilot engagement altitude/height after takeoff82
(4) Autopilot engagement during approach83
(5) Circling approach85
c. Climb, cruise, descent, and holding85
d. Maneuvering85
102. Automatic Disengagement of the Autopilot85
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CONTENTS (CONTINUED) Paragraph Page
103. Assessment of Human Factors85
a. General85
b. Flight evaluations86
(1) During certification86
(2) Prior to certification86
(3) Credit to establish FGS compliance86
(4) Simulation versus flight tests86
c. Structured subjective evaluations87
d. Pilot training and experience87
e. Evaluating new or unique design features87
f. Certification planning documentation87
104—108 [RESERVED]87
CHAPTER 10. AIRPLANE FLIGHT MANUAL88
109. General88
a. AFM terminology88
b. Low-visibility operations88
110. Information Supporting Operational Use of Autopilot88
a. General88
b. Specifying a MUH88
c. Maximum displacement deviation88
111. Limitations89
112. Non-Normal/Emergency Procedures89
113. Normal Procedures89
a. Documentation of normal procedures89
b. Maximum displacement deviation89
c. Procedures for use of FGS in icing conditions89
d. Aircraft with published FCOMs89
e. Aircraft without published FCOMs89
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CONTENTS (CONTINUED)
APPENDICES Number Page
A Safety AssessmentA-1
1. GeneralA-1
2. Identification of Failure ConditionsA-1
3. Considerations when Assessing the Severity of Failure Condition EffectsA-2
4. Failure Condition ClassificationA-3
B DefinitionsB-1
C AcronymsC-1
TABLES Number Page
1 Related 14 CFR Sections2
2 Related Advisory Circulars3
3 Related SAE Documents4
4 Related RTCA Documents4
2-1 Cross-References for § 25.1329 Paragraphs to AC Chapters8
5-1 Examples of Normal Conditions35
5-2 Examples of Rare Normal Conditions38
5-3 Examples of Non-Normal Conditions40
B-1 Terms and DefinitionsB-1
C-1 Acronyms and DefinitionsC-1
FIGURES Number Page
9-1 Relationship between AC Chapters67
INTRODUCTION
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 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 (FD), 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, operators of certain transport category airplanes, foreign regulatory authorities, and Federal Aviation Administration (FAA) transport airplane type certificate (TC) engineers and their designees.
b. The guidance in this AC is neither mandatory nor regulatory in nature and 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 these 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 compliance 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 regulatory 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, ACs, 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 regulations can be downloaded from the U.S. Government Publishing Office e-CFR. A paper copy may be ordered from the U.S. Government Publishing Office, Superintendent of Documents, Attn: New Orders, PO Box 371954, Pittsburgh, PA, 15250-7954.
2 Table 1. Related 14 CFR sections Section Title § 25.143 Controllability and Maneuverability—General § 25.301 Loads § 25.671 Control Systems—General § 25.672 Stability augmentation and automatic and power-operated systems § 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 instruments § 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 Flight Manual—Operating procedures
b. Advisory Circulars. 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 publication of this AC, you should refer to the latest version for guidance. You can find the latest version at the FAA Web site.
3 Table 2. Related Advisory Circulars Number Title Date AC 20-115C Airborne Software Assurance July 19, 2013 AC 20-138D Airworthiness Approval of Positioning and October 10, 2014 Change 1 Navigation Systems AC 20-152 RTCA, Inc., Document RTCA/DO-254, July 5, 2005 Design Assurance Guidance for Airborne Electronic Hardware AC 20-174 Development of Civil Aircraft and Systems September 30, 2011 AC 25-7C Flight Test Guide for Certification of Transport October 16, 2012 Category Airplanes AC 25-11B Electronic Flight Displays October 7, 2014 AC 25-12 Airworthiness Criteria for the Approval of Airborne Windshear Warning Systems in November 2, 1987 Transport Category Airplanes 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 October 27, 2009
(h) AC 25.1581-1 Airplane Flight Manual July 14, 1997 Change 1 AC 120-28D Criteria for Approval of Category III Weather July 13, 1999 Minima for Takeoff, Landing, and Rollout AC 120-29A Criteria for Approving Category I and August 12, 2002 Category II Weather Minima for Approach AC 120-41 Criteria for Operational Approval of Airborne November 11, 1983 Wind Shear Alerting and Flight Guidance Systems 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.