Chapter 8. Safety Assessment
Paragraph Page
83. General 75
a. Basic Safety Requirements 75
b. Safety Assessment 75
c. Validation of Safety Assessment 75
d. Coordination with the FAA 75
84. FGS Failure Conditions 75
a. Functionality 76
b. Effect of Failure Condition 76
85. Type and Severity of Failure Conditions 76
a. Types of Failure Conditions 76
(1) Loss of Function 76
(2) Malfunction 77
b. Cause 77
c. Severity 77
d. Assessment of Failure Conditions 77
(1) Functional Failures 77
(2) Airframe Loads 77
(3) Assessing Total Effect of Failure 78
86. Mitigation of Failure Conditions 78
a. General 78
b. Identification of Methods 78
c. FGS De-Selection 78
87. Validation of Failure Conditions 78
a. General 78
b. Validation Options 79
c. Validation Methodology 79
88. Specific Considerations 79
a. FGS Action During Ground Operations 79
b. FGS Operations in Close Proximity to the Ground 79
(1) Takeoff 80
(2) Approach 81
c. Cruise Operations 82
d. Asymmetric Thrust During Autothrust Operation 82
89. Failure to Disengage the FGS 83 90 – 97 [RESERVED] 83
Chapter 9. Compliance Demon stration Using Flight Test and Simulation
Paragraph Page
98. General 85
a. Methods of Compliance Demonstration 85
b. Criteria for Establishing Compliance 85
c. Elements of Certification Flight Test 85
d. Pilot–in–the–Loop Evaluation 85
e. Other Applicable Guidance Material for FGS Takeoff and/or Approach Modes 86
(1) Criteria to Consider 86
(2) Procedures to Show Compliance 86
f. Relation of AC Chapters 86 Figure 9-1, Relationship Between AC Chapters 87
99. Performance Demonstration (Fault Free): § 25.1301 88
a. General 88
(1) Certification Plan 88
(2) Evaluating Performance 88
(3) Evaluating Compatibility of Mode Controls, Indications, and Alerts 88
b. Normal Performance 88
(1) Demonstration 88
(2) Evaluation 88
(3) Expected Errors 89
c. Performance in “Other Than Normal” Conditions 89
(1) Test Program 89
(2) Evaluation of FGS 89
(3) Additional Guidance for Windshear 89
d. Specific Performance Conditions 89
(1) Icing Considerations 89
(2) Low-Speed Protection 90
(3) High-Speed Protection 91
(4) Go-Around 91
(5) Steep Approach [special authorization] 92
(6) Indication Of and Response To an Out Of Trim Condition 93
e. Flight Director (FD) /Head Up Display (HUD 93
(1) General 93
(2) Specific Demonstrations for HUD 94
(3) Simulator Demonstration for HUD 95
f. Flightcrew Override of the FGS 96
(1) Autopilot Override 96
(2) Autothrust Override 97
(3) Pitch Trim System Evaluation During Autopilot Override 97 9
10 Paragraph Page
100. Failure Conditions Requiring Validation: § 25.1309 97
a. General 97
(1) Safety Assessment 97
(2) Evaluation of Failure Conditions 97
b. Validation Elements 98
(1) Assessment 98
(2) Failure Condition 98
(3) Pilot Recognition 98
(4) Pilot Reaction Time 100
(5) Pilot Recovery 100
c. Takeoff 101
(1) Worst Case Failure Condition 101
(2) Failures to be Evaluated 101
(3) On Runway Guidance 101
d. Climb, Cruise, Descent, and Holding 101
e. Maneuvering 101
f. Approach 101
(1) Approach With Vertical Path Reference 101
(2) Approach Without Vertical Path Reference 103
(3) Steep Approach 103
g. Specific Conditions 103
(1) Failure Conditions to be Evaluated 103
(2) Failure to Disengage 103
101. Criteria Supporting Operational Use of Autopilot 103
a. Typical Flight Operations 103
b. Operations in Close Proximity to the Ground 104
(1) General 104
(2) Considerations 104
(3) Autopilot Engagement Altitude/Height After Takeoff 104
(4) Autopilot Engagement During Approach 105
(5) Circling Approach 107
c. Climb, Cruise, Descent, and Holding 107
d. Maneuvering 107
102. Automatic Disengagement of the Autopilot 108
103. Assessment of Human Factors 108
a. General 108
b. Flight Evaluations 108
(1) During Certification 108
(2) Prior to Certification 108
(3) Credit to Establish FGS Compliance 109
(4) Simulation Versus Flight Tests 109
c. Structured Subjective Evaluations 109
d. Pilot Training and Experience 110
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Paragraph Page
e. Evaluating New or Unique Design Features 110
f. Certification Planning Documentation 110 104 – 108 [RESERVED] 110
Chapter 10. Airplane Flight Manual
109. General 111
a. AFM Terminology 111
b. Low-Visibility Operations 111
110. Information Supporting Operational Use of Autopilot 111
a. General 111
b. Specifying a Minimum Use Height (MUH) 111
(1) Takeoff 111
(2) Cruise 111
(3) Approach 111
c. Maximum Displacement Deviation 112
111. Limitations 112
112. Non-Normal/Emergency Procedures 112
113. Normal Procedures 112
a. Documentation of Normal Procedures 112
b. Maximum Displacement Deviation 112
c. Procedures for Use of FGS in Icing Conditions 112
d. Aircraft With Published Flightcrew Operation Manuals (FCOM) 112
e. Aircraft Without Published FCOMs 113
Appendices
1 Safety Assessment A1-1
1. General A1-1
2. Identification of Failure Conditions A1-1
3. Considerations When Assessing The Severity of Failure Condition Effects A1-2
4. Failure Condition Classification A1-3 2 Definitions A2-1 3 Acronyms A3-1
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Tables
Number Page 2-1 Cross-References § 25.1329 Paragraphs to AC Chapters 17 5-1 Examples of Normal Conditions 48 5-2 Examples of Rare Normal Conditions 51 5-3 Examples of Non-Normal Conditions 54
Figures
Number Page 9-1 Relationship Between AC Chapters (Chapter 9) 87
1 — 10 [Reserved]
Chapter 1 Background
11. General.
a. Advisory Circular (AC) 25.1329-1B. This advisory material replaces material previously provided in AC 25.1329-1A for autopilots. The automatic control and guidance systems in current aircraft have evolved to a level that dictates a revision to current advisory material.
b. Scope. This advisory material provides information for flight guidance systems (FGS), which include any autopilot functions, flight director (FD) functions, and automatic thrust control functions as well as any interactions with stability augmentation and trim functions.
12. Evolution of FGSs.
a. Complexity. There have been dramatic changes in technology and system design, which have resulted in much higher levels of integration, automation, and complexity. These 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 introduction of fly–by–wire flight control systems has created new interface considerations for the FGS.
b. Guidance Considerations. These new systems are capable of providing better performance, increased safety, and decreased workload. But, if designed without consideration 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 on that experience.
13 — 16 [Reserved]
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15 Chapter 2 Overview of flight guidance systems (FGS)
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 relief 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. FGS Components.
a. Included in Definition. 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 Definition. 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 for such systems are applicable.
19. FGS functions.
a. Elements of FGS.
(1) Flight guidance and control (for exam ple, 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) Interactions with stability augmentation and trim systems.
(4) Alerting, status, mode annunciation, and situation information associated with flight guidance and control functions.
b. Approach and Landing System. The FGS includes those functions necessary to provide guidance and control in conjunction with an approach and landing system, such as the following:
(1) Instrument landing system (ILS)
(2) Microwave landing system (MLS)
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(3) Ground-Based Augm entation System (GBAS) Landing System (GLS.)
c. Flight Management System (FMS). The FGS also includes those functions necessary to provide guidance and control in conjunction with a FMS. The FGS does not include the flight planning and the generation of flight path and speed profiles tied to 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 commands.
d. Design Philosophy. The applicant should establish, document, and follow a design philosophy that supports the intended operational use regarding FGS behavior, modes of operation, the pilot interface with controls, indications, alerts, and mode functionality.
e. Description of FGS Behavior 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 part 25 rules to FGS
(e.g., §§ 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 used 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 § 25.1329 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 Paragraphs. The following table (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-Ref erences § 25.1329 Paragraphs to AC Chapters
Section/Paragraph AC Chapter Reference/Paragraph § 25.1329(a) Quick disengagement controls 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 control 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, and Override Paragraph 27, Autopilot Engagement, Disengagement, and Indications
Paragraph 29, Autothrust Engagement, Disengagement, Indications
§ 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 § 25.1309.
Chapter 3 FGS Engagement, Disengagement, Indications, and Override Paragraph 27, Autopilot Engagement, Disengagement, Indications
Paragraph 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, and Override
Chapter 8 Safety Assessment
Section/Paragraph AC Chapter Reference/Paragraph § 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 greater 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 Assessment
§ 25.1329(e) Under rare normal and non-normal conditions, disengagement of any automatic control function of a flight guidance system may not result in a transient any greater than a significant transient, as defined in paragraph (n)(2) of this section.
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 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 18
Section/Paragraph AC Chapter Reference/Paragraph § 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 and 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 Simulation
§ 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 errors 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