AC 25.1329-1C CHG 2
CONTENTS (CONTINUED)
APPENDI CES 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
D Advisory Circular FeedbackD-1
TABLES Number Page
1-1-1 Related 14 CFR Sections2
1-1-2 Related Advisory Circulars3
1-1-3 Related SAE Documents4
1-1-4 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
xvi
AC 25.1329-1C CHG 2
INTRODUCTION
1. Purpose. This AC describes an acceptable means for showing compliance with certain requirements of 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 (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, operators of certain transport category airplanes, foreign regulatory authorities, Federal Aviation Administration (FAA) transport airplane type certificate engineers , and FAA designees.
b. This is a guidance document. Its content is not legally binding in its own right and will not be relied upon by the Department as a separate basis for affirmative enforcement action or other administrative penalty. Conformance with this guidance document is voluntary only.
Nonconformity will not affect rights and obligations under existing statutes and regulations. This document is intended only to provide information to the public regarding existing requirements under the law or agency policies. The guidan ce 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 . If the FAA becomes aware of circumstances in which following this AC would not result in compliance with the applicable regulations, the FAA may require additional substantiation or design changes as a basis for finding compliance.
3. Cancellation. This AC cancels AC 25.1329-1C Change 1, d ated May 24, 2016.
4. Related Regulations, ACs, a nd Industry Documents. The following related documents are provided for information purposes and are not necessarily directly referenced in this AC.
a. Regulations. Table 1-1 i dentifies 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 Bookstore website.
AC 25.1329-1C CHG 2 Table 1-1. Related 14 CFR Sections Controllability and Maneuverability —General Control Systems—General Trim systems Motion and effect of cockpit controls Installation Function and installation Equipment, systems, and installations Supercooled large drop icing conditions Airplane Flight Manual—Operating limitations Title Section Loads Stability augmentation and automatic and power -operated systems § 25.143 § 25.301 § 25.671 § 25.672 § 25.677 § 25.777 § 25.779 § 25.781 § 25.901 § 25.903 § 25.1301 § 25.1303 § 25.1309 § 25.1322 § 25.1420 § 25.1581 § 25.1583 § 25.1585 Cockpit controls Cockpit control knob shape Engines Flight and navigations instruments Flightcrew alerting Airplane Flight Manual—General Airplane Flight Manual—Operating procedures
b. Ad visory Circulars. Table 1-2 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 website.
AC 25.1329-1C CHG 2 Table 1-2. Related Advisory Circulars AC 20-115D Airborne Software Development Assurance Using July 21, 2017 EUROCAE ED-12( ) and RTCA DO-178( ) AC 20-152A RTCA, Inc., Document RTCA/DO-254, Design October 7, 2022 Assurance Guidance for Airborne Electronic Hardware AC 20-191 Airworthiness Approval of Airborne Systems used TBD for Takeoff, Precision Approach, Landing, and Rollout in Low-Visibility Conditions AC 25-7D Flight Test Guide for Certification of Transport May 4, 2018 Category Airplanes AC 25-12 Airworthiness Criteria for the Approval of Airborne November 2, 1987 Windshear Warning Systems in Transport Category Airplanes AC 25.1322-1 Flightcrew Alerting December 13, 2010 AC 120-118 Criteria for Approval/Authorization of All Weather July 2, 2018 Operations (AWO) for Takeoff, Landing, and Rollout Number Title Date AC 20-138D Airworthiness Approval of Positioning and April 7, 2016 Change 2 Navigation Systems AC 20-174 Development of Civil Aircraft and Systems September 30, 2011 AC 21-16G RTCA Document DO-160 versions D, E, F, and G, June 22, 2011 “Environmental Conditions and Test Procedures for Airborne Equipment” AC 25-11B Electronic Flight Displays October 7, 2014 AC 25.1309-1B System Design and Analysis August 30, 2024 AC 25.1581-1 Airplane Flight Manual July 14, 1997 Change 1 AC 120-41 Criteria for Operational Approval of Airborne Wind November 11, 1983 Shear Alerting and Flight Guidance Systems (cancelled) 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.
AC 25.1329-1C CHG 2
c. Related Industry Standards.
(1) The following documents are available from the Society of Automotive Engineers (SAE). You can pur chase 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 1-3. Related SAE Documents SAE ARP4761A Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment SAE ARP5366 Autopilot, Flight Director, and Autothrust Systems Number Title SAE ARP5288 Transport Category Airplane Head Up Display (HUD) Systems SAE AS8055A Minimum Performance Standard for Airborne Head Up Display (HUD)
(2) The following documents are available from RTCA, Inc. (formerly the Radio Technical Commission for Aeronautics) . You can purchase these documents from the RTCA website.
Table 1-4. Related RTCA Documents RTCA DO-178C/ Software Considerations in Airborne Systems and EUROCAE ED-12C Equipment Certification RTCA DO-254/ Design Assurance Guidance for Airborne Electronic EUROCAE ED-80 Hardware Number Title RTCA DO-160G/ Environmental Conditions and Test Procedures for EUROCAE ED-14G Airborne Equipment
d. Other FAA Documents.
(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.
AC 25.1329-1C CHG 2
(2) FAA Order 8260.3D, United States Standard for Terminal Instrument Procedures (TERPS), dated February 16, 2018, is available at the FAA website.
5—10 [RESERVED] 5
AC 25.1329-1C CHG 2 CHAPTER 1. BACKGROUND
11. General.
a. AC 25.1329-1C. 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). Specifically, in this AC, the FAA added a reference to § 25.1420, Supercooled large drop icing conditions , in table 1-1; 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 FGS.
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 t he 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.
13—16 [RESERVED] 6
CHG 1 CHAPTER 2. OVERVIEW OF FLIGHT GUIDANCE 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 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. 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 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) 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) Ground-based augmentation system (GBA S) landing system (GLS).
c. Flight management system (FMS). The FGS also includes those functions necessary to provide guidance and control in conjunction with an FMS. The FGS does not include the flight planning and the generation of flight path and speed profiles tied to 7
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, and the pilot interface with controls, indications, alerts, and mode functionality.
e. Description of FGS behavior and operation. 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 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. 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 for § 25.1329 Paragraphs to AC Chapters 14 CFR Section § 25.1329(a) Chapter 3 Quick disengagement controls for the autopilot FGS Engagement, Disengagement, and autothrust functions must be provided for Indications, and Override each pilot. The autopilot quick disengagement Paragraph 27, controls must be located on both control wheels Autopilot Engagement, (or equivalent). The autothrust quick Disengagement, and Indications disengagement controls must be located on the thrust control levers. Quick disengagement Paragraph 29, controls must be readily accessible to each pilot Autothrust Engagement, while operating the control wheel (or Disengagement, and Indications equivalent) and thrust control levers.
AC Chapter/Paragraph Reference 8
§ 25.1329(b) Chapter 3 The effects of a failure of the system to FGS Engagement, Disengagement, disengage the autopilot or autothrust functions Indications, and Override when manually commanded by the pilot must Paragraph 27, be assessed in accordance with the requirements Autopilot Engagement, of § 25.1309. Disengagement, and 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) Chapter 3 Engagement or switching of the flight guidance FGS Engagement, Disengagement, system, a mode, or a sensor may not cause a Indications, and Override transient response of the airplane’s flight path Chapter 8 any greater than a minor transient, as defined in paragraph (n)(1) of this section. Safety Assessment § 25.1329(d) Chapter 3 Under normal conditions, the disengagement of FGS Engagement, Disengagement, any automatic control function of a flight Indications, and Override guidance system may not cause a transient Chapter 4 response of the airplane’s flight path any greater than a minor transient. Controls, Indications, and Alerts Paragraph 45, FGS Alerting, Warning, Caution, Advisory, and Status Chapter 8 Safety Assessment 14 CFR Section AC Chapter/Paragraph Reference 9
§ 25.1329(e) Chapter 3 Under rare normal and non-normal conditions, FGS Engagement, Disengagement, disengagement of any automatic control Indications, and Override function of a flight guidance system may not Chapter 4 result in a transient any greater than a significant transient, as defined in Controls, Indications, and Alerts paragraph (n)(2) of this section. Paragraph 45, FGS Alerting, Warning, Caution, Advisory, and Status Chapter 8 Safety Assessment § 25.1329(f) Chapter 4 The function and direction of motion of each Controls, Indications, and Alerts command reference control, such as heading Paragraph 43, select or vertical speed, must be plainly FGS Controls indicated on, or adjacent to, each control if necessary to prevent inappropriate use or confusion.
§ 25.1329(g) Chapter 4 Under any condition of flight appropriate to its Controls, Indications, and Alerts use, the flight guidance system may not produce Paragraph 45, hazardous loads on the airplane, nor create FGS Alerting, Warning, Caution, hazardous deviations in the flight path . This Advisory, and Status applies to both fault-free operation and in the event of a malfunction, and assumes that the Chapter 5 pilot begins corrective action within a Performance of Function reasonable period of time.
Chapter 8 Safety Assessment Chapter 9 Compliance Demonstration Using Flight Test and Simulation 14 CFR Section AC Chapter/Paragraph Reference 10
§ 25.1329(h) Chapter 5 When the flight guidance system is in use, a Performance of Function means must be provided to avoid excursions Paragraph 57, beyond an acceptable margin from the speed Speed Protection 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.
§ 25.1329(i) Chapter 4 The flight guidance system functions, controls, Controls, Indications, and Alerts 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.
§ 25.1329(j) Chapter 3 Following disengagement of the autopilot, a FGS Engagement, Disengagement, warning (visual and auditory) must be provided Indications, and Override to each pilot and be timely and distinct from all Paragraph 27, other cockpit warnings. Autopilot Engagement, Disengagement, and Indications Chapter 8 Safety Assessment 14 CFR Section AC Chapter/Paragraph Reference 11