c. Related Industry Standards.
(1) The following documents are available from the Society of Automotive Engineers (SAE). You can purchase 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 Web site.
Table 3. Related SAE Documents Number Title SAE ARP4754A Guidelines for Development of Civil Aircraft and Systems SAE ARP4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment SAE ARP5288 Transport Category Airplane Head-Up Display (HUD) Systems SAE ARP5366 Autopilot, Flight Director, and Autothrust Systems SAE AS8055 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 by mail from RTCA Inc., 1150 18th Street NW, Suite 910, Washington, DC 20036; by faxing the Document Order Form to (202) 833-9434; or from the RTCA Web site.
Table 4. Related RTCA Documents Number Title RTCA DO-178B/ EUROCAE ED-12B Software Considerations in Airborne Systems and Equipment Certification RTCA DO-160E/ EUROCAE ED-14D Environmental Conditions and Test Procedures for Airborne Equipment RTCA DO-254/ EUROCAE ED-80 Design Assurance Guidance for Airborne Electronic Hardware
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 Web site.
(2) FAA Order 8260.3, United States Standard for Terminal Instrument Procedures (TERPS), Changes 1 – 19, is available at the FAA Web site.
5—10 [RESERVED]
6 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 Federal Register (FR) 65508, November 4, 2014). Specifically, in this AC, we added a reference to § 25.1420, Supercooled large drop icing conditions, in Table 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 multifunction 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]
7 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 flightpath 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 (GBAS) 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 flightpath and speed profiles tied to
8 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 flightpath 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 part 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-References for § 25.1329 Paragraphs to AC Chapters 14 CFR Section AC Chapter/Paragraph Reference § 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 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 27, Autopilot Engagement, Disengagement, and Indications Paragraph 29, Autothrust Engagement, Disengagement, and Indications
9 14 CFR Section AC Chapter/Paragraph Reference § 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 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 27, Autopilot Engagement, 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) 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 Flight Guidance System Engagement, Disengagement, Indications, and Override Chapter 8 Safety Assessment § 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 Flight Guidance System Engagement, Disengagement, Indications, and Override Chapter 4 Controls, Indications, and Alerts Paragraph 45, FGS Alerting, Warning, Caution, Advisory, and Status Chapter 8 Safety Assessment
10 14 CFR Section AC Chapter/Paragraph Reference § 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 Flight Guidance System 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 § 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
11 14 CFR Section AC Chapter/Paragraph Reference § 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 § 25.1329(j) Following disengagement of the autopilot, a warning (visual and auditory) must be provided to each pilot and be timely and distinct from all other cockpit warnings.
Chapter 3 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 27, Autopilot Engagement, Disengagement, and Indications Chapter 8 Safety Assessment
12 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(k) Following disengagement of the autothrust function, a caution must be provided to each pilot.
Chapter 3 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 27, Autopilot Engagement, Disengagement, and Indications Chapter 8 Safety Assessment § 25.1329(l) The autopilot may not create a potential hazard when the flightcrew applies an override force to the flight controls.
Chapter 3 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 30, Override of the FGS Chapter 4 Controls, Indications, and Alerts Paragraph 45, FGS Alerting, Warning, Caution, Advisory, and Status Chapter 8 Safety Assessment § 25.1329(m) During autothrust operation, it must be possible for the flightcrew to move the thrust levers without requiring excessive force. The autothrust may not create a potential hazard when the flightcrew applies an override force to the thrust levers.
Chapter 3 Flight Guidance System Engagement, Disengagement, Indications, and Override Paragraph 30, Override of the FGS Chapter 8 Safety Assessment
13 14 CFR Section AC Chapter/Paragraph Reference § 25.1329(n) For purposes of this section, a transient is a disturbance in the control or flight path of the airplane that is not consistent with response to flightcrew inputs or environmental conditions.
(1) A minor transient would not significantly reduce safety margins and would involve flightcrew actions that are well within their capabilities. A minor transient may involve a slight increase in flightcrew workload or some physical discomfort to passengers or cabin crew.
(2) A significant transient may lead to a significant reduction in safety margins, an increase in flightcrew workload, discomfort to the flightcrew, or physical distress to the passengers or cabin crew, possibly including non-fatal injuries. Significant transients do not require, in order to remain within or recover to the normal flight envelope, any of the following:
(i) Exceptional piloting skill, alertness, or strength.
(ii) Forces applied by the pilot which are greater than those specified in § 25.143(c).
(iii) Accelerations or attitudes in the airplane that might result in further hazard to secured or non-secured occupants.
Appendix B—Definitions Note: The text for each paragraph in § 25.1329 is included in this AC for reference only. Please refer to the actual text in part 25.
21—26 [RESERVED]
14 CHAPTER 3. FLIGHT GUIDANCE SYSTEM ENGAGEMENT, DISENGAGEMENT,
INDICATIONS, AND OVERRIDE
27. Autopilot Engagement, Disengagement, and Indications. Autopilot engagement and disengagement should be accomplished in a manner consistent with other flightcrew procedures and tasks and should not require undue attention.
a. Autopilot engagement.
(1) Single-switch action. Each pilot should be able to select the autopilot function of the FGS with a single-switch action. The single-switch action should engage both the pitch and roll axes.
(2) Engagement status of autopilot. The autopilot system should provide positive indication to the flightcrew that the system has been engaged. The selector switch position is not acceptable as a means of indication. See § 25.1329(i). Regardless of the method used, the engagement status (and changes in status) of the autopilot(s) should be clearly indicated and should not require undue attention or recall.
Note: If an operational need is identified for split-axis engagement, then annunciation or indication should be provided for each axis.
(3) Multiple autopilots. If a single autopilot within a multiple autopilot installation can be individually selected by the flightcrew, the engagement annunciation should reflect the flightcrew selection. It should not be possible for multiple autopilots to be engaged in different modes. For modes that use multiple autopilots, the additional autopilots may engage automatically at selection of the mode or after arming the mode. A means should be provided to determine that adequate autopilot capability exists to support the intended operation (for example, “Land 2” and “Land 3” are used in some aircraft).
(4) Acceptable transients. The engagement of the autopilot should be free of perceptible transients. Under dynamic conditions, including maneuvering flight, minor transients are acceptable. However, with normal operating conditions, significant transients may not occur.
See § 25.1329(d).
(5) FD not engaged. Without a FD engaged, the initial lateral and vertical modes should be consistent with minimal disturbance from the flightpath. For example, the lateral mode at engagement may roll the airplane to wings level, and then hold the airplane heading/track or maintain the existing bank angle (if in a normal range). A heading/track preselect at engagement function may be provided, if precautions are taken to ensure that selection reflects the current intent of the flightcrew. The modes at engagement should be annunciated, and any associated selected target values should be displayed.
(6) FD engaged. With a FD engaged, the autopilot should engage in a mode consistent with (that is, the same as, or if that is not possible, then compatible with) the active FD mode of operation. Consideration should be given to the mode in which the autopilot will engage when large commands are present on either or both FDs. The following examples list some of these considerations:
(a) Should the autopilot retain the active FD mode or should it engage in the basic default mode?
(b) Are there any implications for current flight path references and targets?
(c) Is there any potential for flightcrew confusion and unintended changes in flightpath or modes?
Note: The design should consider the possibility that the pilot may attempt to engage the autopilot outside of the normal flight envelope. It is not required that the autopilot compensate for unusual attitudes or other situations outside the normal flight envelope, unless that is part of the autopilot’s intended function.
b. Autopilot disengagement.
(1) General.
(a) Normal conditions. Under normal conditions, automatic or manual disengagement of the autopilot should be free of perceptible transients or out-of-trim forces that are not consistent with the maneuvers being conducted by the airplane at the time of disengagement. A disengagement in normal conditions may not result in a transient any greater than a minor transient. If multiple autopilots are engaged, any disengagement of an individual autopilot may not result in a transient any greater than a minor transient. See § 25.1329(d). The disengagement of an individual autopilot should not adversely affect the operation of the remaining engaged autopilot(s).
(b) Other than normal conditions. Under other than normal conditions (that is, rare normal or non-normal conditions), disengagement of the autopilot may not result in a transient any greater than a significant transient. See § 25.1329(e). (For a discussion of rare normal and non-normal conditions, see Chapter 5, Performance of Function, paragraph 54, Performance in Rare Normal Conditions, and paragraph 56, Performance in Non-Normal Conditions, of this AC.) The flightcrew should be able to respond to a significant transient without using any of the following:
1 Exceptional piloting skill, alertness, or strength;
2 Forces greater than those given in § 25.143(d); or 3 Accelerations or attitudes in the airplane that might result in a hazard to secured or nonsecured occupants.
(c) Potential for significant transient. The flightcrew should be made aware (via a suitable alerting or other indication) of conditions or situations (for example, continued out-of-trim) that could result in a significant transient at disengagement. (See Chapter 4, Controls, Indications, and Alerts, paragraph 45.d, Awareness of Potential Significant Transient Condition (“Bark before Bite”).)