U.S. Department of Transportation

Federal Aviation

Administration 

# Advisory Circular

Subject: APPROVAL OF FLIGHT
GUIDANCE SYSTEMS Date : DRAFT
Initiated by: ANM

- 1 1 0 AC No: 25.1329

- 1 B
Change : 1

1. PURPOSE.

a. This change update s Advisory Circular ( AC ) 25.1329

- 1B, Approval of Flight Guidance Systems , dated July 16, 2006.

b. The change number and the date o f the changed material are shown at the top of each page with the change number and date.

2. PRINCIPAL CHANGES

.

a. Minor revisions were made to reflect gui d ance changes associated with the issuance of

the final rule for Airplane and Engine Certific ation Requirements in Supercooled Large Drop, Mixed Phase, and Ice Crystal Icing Conditions

, published XXXXXXX , 200 X (7 X FR XXXXX ).

The se changes include a reference to the icing considerations of § 25.1420. G rammatical and typographical errors were also corrected.

b. Paragraph 4a is revised to include § 25.1420 in the table.

c. Paragraph 4b is revised to include AC 25

- 7A, Flight Test Guide for Certification of Transport Category Airplanes in the table.

d. Paragraph 4d is revised to provide an Internet address and change a reference to an FAA

document.

e. Paragraph 18b is revised to change “ part of the F GS ” to “ equipment or component

. ”

f. Paragraph 19b(3) is revised to add the words “landing system (GLS).”

g. Paragraph 19b(4) was dele ted.

h. Paragraph 28b is revised to change “may” to “should.”Draft AC 25.1329

- 1B Change 1

2 i. Paragraph 29a(1) is revised to change “should” to “must” and add “(See § 25.1329(i)).”

j. Paragraph 42b is revised to change “should” to “must.”

k. Table 5

- 1 is revised to add “ an d applicable icing conditions covered by 14 CFR

p art 25, Appendix X ”

l. Paragraph 99d(5)(a) is revised to change “ 2.77 ” to “ 2.75 ” and “ 3.75 ” to “ 3.77. ”

m. Paragraph 99f(2) is revised to change “must” to “may.”

n. Paragraph 100f(3) is revised to c hange “ 3.75 ” to “ 3.77. ”

3. W EBSITE AVAILABILITY

. To access AC 25.1329

- 1B electronically, log on to the Regulatory Guidance Library (RGL) website: http://rgl.faa.gov.

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16 7/17/06 16 XX/XX/XX

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103 7/17/06 103 XX/XX/XX

(Signature B lock)Draft AC 25.1329

- 1B Change 1

i i 4. RELATED REGULATIONS, ACs, AND INDUSTRY DOCUMENTS.

a. Regulations

. The following related documents are provided for information purposes and are not necessarily directly referenced in this AC. The full text of 14 CFR can be

downloaded from th e Internet at http://www.gpoaccess.gov/nara. A paper copy may be ordered from the Government Printing Office (GPO), Superintendent of Documents, Attn: New Orders, PO Box 371954, Pittsburgh, PA 15250

- 7954.

Section Title

§ 25.143 Controllability and M aneuverability, 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 Warning, caution, and advisory lights

§ 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 proceduresDraft AC 25.1329

- 1B Change 1

i i i b. ACs. An electronic copy of the following AC s can be downloaded from the Internet at http:// rgl .faa.gov. A paper copy may be ordered from the U.S. Department of Transportation, Subsequent Distribution Office, M

- 30, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20795.

Number Titl e

AC 20

- 115B RTCA, Inc., Document RTCA/DO 178B [Radio Technical Commission for Aeronautics]

AC 20

- 129 Airworthiness Approval of Vertical Navigation (VNAV) Systems for use in the U.S. National Airspace System (NAS)

and Alaska

AC 20

- 152 Design Assurance Guidance for Airborne Electronic Hardware

RTCA/DO 254

AC 25

- 7A Flight Test Guide for Certification of Transport Category Airplanes

AC 25

- 11 Transport Category Airplane Electronic Display Systems

AC 25

- 12 Airworthiness Criteria for the Approval of Airbo rne Windshear Warning Systems in Transport Category Airplanes

AC 25.672

- 1 Active Flight Controls

AC 25.1309

- 1A System Design and Analysis

AC 25.1419

- 1 Certification of Transport Category Airplanes for Flight in Icing

Conditions

AC 25.1581

- 1 Airplane F light Manual

AC 120

- 28D Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout

AC 120

- 29A Criteria for Approving Category 1 and Category II Landing Minima for FAR 121 Operators

AC 120

- 41 Criteria for Operational Approval of Airborne Windshear Alerting and Flight Guidance Systems

NOTE: This table represents the latest version of each AC at the time of publication. These individual ACs may be updated in the future, such that this table may reference a specific version of an AC that has been superseded. The latest version of each AC should always be used, even though this document may reference a previous version of an AC.Draft AC 25.1329

- 1B Change 1

v d. FAA Documents. An electronic copy of the following FAA document can be

downloaded from the In ternet at http://www.faa.gov/aircraft/air_cert/design_approvals/csta/publications /

.

Title

Federal Aviation Administration Human Factors Team Report on: The Interfaces Between Flight Crews and Modern Flight Deck Systems

– Jun e 18, 1996

An elect ronic copy of the following FAA Order can be downloaded from the Internet at http://www.airweb.faa.gov/rgl. A paper copy may be ordered from the U.S. Department of Transportation, Subsequent Distribution Office, M

- 30, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20795.

Number Title

FAA Order

8260.3 United States Standard for Terminal Instrument Procedures

Ali Bahrami Manager, Transport Airplane Directorate

Aircraft Certification ServiceDraft AC 25.1329

- 1B Change 1

15 CHAPTER 2 OVERVIEW OF FLIGHT GUIDANC E 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 m ore 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” i ncludes 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 supervis e 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 propulsi on 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 t erm “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 wi th 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 landin g system (ILS)

(2) Microwave landing system (MLS)Draft AC 25.1329

- 1B Change 1

16 (3) Global navigation satellite system (GNSS) landing system (GLS)

c. Flight Management System (FMS). The FGS also includes those functions necessary to provide guidance and control in conjun ction 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 f or 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 interf ace 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 (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 ag reement on the methods to be used to demonstrate compliance.

N OTE: 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.

N OTE: This AC uses the terminology “must” and “may not” when discussing compliance to § 25.1329 and other specific rule s , as compliance to a rule is not optional. In these cases,

t he 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.Draft AC 25.1329

- 1B Change 1

29 criteria in AC 25

– 12, Airworthiness Criteria for the Approval of Airborne Windshear Warning Systems in Transport Category Airplanes; and AC 120

– 41, Criteria for Operational Approval of Airborne Windshear Alerting and Flight Guidance.

b. FD Disengagement. There should be a means for each pilot to readil y de

- select his or

her on

– side FD function. Flightcrew awareness of disengagement and de

- selection is important. Removal of guidance cue(s) alone is not sufficient indication of de

- selection, because the guidance cue(s) may be removed from view for a num ber of reasons, including invalid guidance or autopilot engagement. Therefore, the FD function should provide clear and unambiguous indication to the flightcrew that the function has been deselected.

29. AUTOTHRUST ENGAGEMENT, DISENGAGEMENT, AND INDIC ATIONS. Engagement and disengagement should be accomplished in a manner consistent with other flightcrew procedures and tasks and should not require undue attention.

a. Autothrust Engagement.

(1) Indication. The autothrust function must provi de the flightcrew positive indication that the system has been engaged. ( See § 25.1329(i) )

(2) Accessibility of Controls. The autothrust engagement controls should be accessible to each pilot.

(3) Inadvertent Engagement/Disengagement. The aut othrust function should normally be designed to prevent inadvertent engagement and inadvertent application of thrust for both on

– ground and in

– air operations. For example, separate arm and engage functions may be provided.

(4) Automatic Engagement. Intended automatic engagement, such as a “wake up” mode to protect for unsafe speeds, may be acceptable. (See Chapter 5, paragraph 57b, Low Speed Protection.) If such automatic engagement occurs, it should be clear to the flightcrew that automatic engag ement has occurred. The automatic engagement may not cause a transient larger

than a minor transient

. [See § 25.1329(c)] The transition to the engaged state should be smooth, and should not cause large, unexpected changes in pitch attitudes or pitching moments. The reason for automatic engagement should be clear and obvious to the flightcrew.

NOTE: The design should consider the possibility that the pilot may attempt to engage the autothrust function outside of the normal flight envelope or at

excessi ve or too low engine thrust. It is not expected that the autothrust feature should compensate for situations outside the normal flight envelope or normal engine operation range, unless that is part of the intended function of the autothrust system.Draft AC 25.1329

- 1B Change 1

35 CHAP TER 4 CONTROLS, INDICATIONS, AND ALERTS

42. GENERAL.

a. Human

- Machine Interface. The human

- machine interface with the FGS is crucial to ensuring safe, effective, and consistent FGS operation. The manner in which FGS information is depicted to the flightcrew is vital to flightcrew awareness and, therefore, to safe operation of the

FGS.

b. Design of Controls, Indications, and Alerts. These features must be designed to minimize flightcrew errors and confusion. ( See § 25.1329(i )) Indications an d alerts should be presented in a manner compatible with the procedures and assigned tasks of the flightcrew and provide the necessary information to perform those tasks. The indications must be grouped and presented in a logical and consistent manner and must be visible from each pilot’s station under all expected lighting conditions. ( See § 25.1329(i ) ) The choice of colors, fonts , font size, location, orientation, movement, graphical layout, and other characteristics

— such as steady or flashing

— should a ll contribute to the effectiveness of the system. Controls, indications, and alerts should be implemented in a consistent manner.

c. Evaluation of Information Provided by FGS. It is recommended that the applicant evaluate the adequacy and effectivene ss of the information provided by the FGS interface, that is the controls, indications, alerts, and displays, to ensure flightcrew awareness of FGS behavior and operation. See Chapter 9, Compliance Demonstration Using Flight Test and Simulation, for

more discussion of appropriate analyses which may include, for example, cognitive task analysis

as a basis for evaluation.

43. FGS CONTROLS.

a. General. The FGS controls must be designed and located to prevent crew errors, confusion, and inadvertent o peration. ( See § 25.1329(i) ) They should be designed to provide convenience of operation to each crewmember. The function and direction of motion of each control must be readily apparent or plainly indicated on or adjacent to each control, if needed to prevent inappropriate use or confusion. ( See § 25.1329(f )) Sections 25.777(b) and 25.779(a) provide requirements regarding direction of motion of flight deck controls. These requirements apply for FGS command reference controls which select target value s, such as heading select or vertical speed. Section 25.781 also provides requirements for the shapes of the knobs.

b. Design Considerations. The design of the FGS should address the following specific

considerations:

(1) Differentiation of Kno b Shape and Position. Errors by the flightcrew have included confusing speed and heading knobs on the MSP.Draft AC 25.1329

- 1B Change 1

4 8 Table 5

- 1
Examples of Normal Conditions

No failure conditions All airplane systems that are associated with airplane performance are fully operat ional. Failures of those systems could impair the flight guidance system's (FGS) ability to perform its functions.

Light to moderate

winds Constant wind in a specific direction that may cause a slight deviation in intended flight path or a small differ ence between airspeed and groundspeed.

Light to moderate wind gradients Variation in wind velocity

— as a function of altitude, position,

or time

— which may cause slight erratic or unpredictable changes in intended flight path.

Light to moderate

gusts Non

– r epetitive momentary changes in wind velocity that can cause changes in altitude and/or attitude to occur, but the aircraft remains in positive control at all times.

Light turbulence Turbulence that momentarily causes slight, erratic changes in

altitude an d/or attitude (pitch, roll, or yaw).

Moderate turbulence Similar to light turbulence but of greater intensity. Changes in altitude and/or attitude occur, but the aircraft remains in positive

control at all times.

Light chop Turbulence that causes slig ht, rapid, and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude.

Moderate chop Similar to light chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or

attitude.

Icing All icing conditions covered by 14 CFR part 25, Appendix C and applicable icing conditions covered by 14 CFR p art 25, Appendix X

, with the exception of “asymmetric icing”

discussed under “Rare Normal Conditions” in Table 5

- 2.

NOTE: Representativ e levels of the environmental effects should be established consistent with the airplane’s intended operation.Draft AC 25.1329

- 1B Change 1

92 (ff) An engine failure during go

– around after go

– around power is

reached.

(gg) Initiation altitude (for example, in ground effect , not in ground effect during flare).

2 Characteristics to be evaluated:

(aa) The pitch response of the airplane during the initial transition.

(bb) Speed performance during airplane reconfiguration and climbout.

(cc) Integrated autopilot and autothrust operation.

(dd) Transition to missed approach altitude.

(ee) Lateral performance during an engine failure.

3 Go

- Around Initiation Heights. Where height loss during a go

– around maneuver is significant or is req uired to support specific operational approval, demonstrated values for various initiation heights should be included in the AFM.

(5) Steep Approach [special authorization].

(a) Flight Test/Simulator Demonstration. Typical approach operations in clude glidepath angles between 2.7 5 and 3.7 7 degrees. Application for approval to conduct operations on glidepath angles of greater than 3.7 7 degrees requires additional evaluation. See AC 120

- 29A, section 4.3, Landing, for further discussion. For such an approval, the FGS flight test and simulator demonstration should include the following:

1 Approach path capture, tracking, and speed control.

2 Recovery of the system from abuse cases (for example, glidepath angle and speed).

3 Assessm ent of autopilot disengagement transient.

4 Demonstration of Go

– Around mode from a steep approach.

(b) Autopilot Use on Steep Approaches. For autopilot use at approach angles greater than 4.5 degrees, the criteria of AC 25

- 7A, Flight Test Guide for Certification of Transport Category Airplanes, Chapter 8, Airworthiness

- Miscellaneous Items, should be satisfied. This advisory material contains airworthiness and transition criteria for steep approaches. In addition, the criteria of AC 120

- 29A, Cr iteria for Approval of Category I and II Weather Minima for Approach, paragraph 6.2.8, Approach Ban Applicability, should be assessed depending on the operational and low visibility requirements.Draft AC 25.1329

- 1B Change 1

97 NOTE: AC 120

- 28D, Appendix 3, Airworthiness Approval for A irborne Systems Used to Land and Rollout in Low Visibility Conditions, Section 8, Airborne Systems, contains guidance for evaluating autopilot override for systems supporting low visibility operations.

(2) Autothrust Override. The capability of the fl ightcrew to override the autothrust system should be demonstrated at various flight phases. The evaluation should include an override of the autothrust system with a single hand on the thrust levers while maintaining control of the airplane using the oppo site hand on the control wheel (or equivalent). This action

may not result in a potential hazard per § 25.1329(m), either during the override or after the pilot releases the thrust levers. Refer to Chapter 3, paragraph 30 of this AC for additional guidan ce. If the autothrust system automatically disengages due to the override, the alerts that accompany the disengagement should be assessed to ensure flightcrew awareness.

(3) Pitch Trim System Evaluation During Autopilot Override.

(a) Effect of Ov erride. The effect of flightcrew override during automatic control on the automatic trim systems should be conducted. The pilot should also apply an input to the pitch cockpit controller below that which would cause the autopilot to disengage and verify that the automatic pitch trim system meets the intent in Chapter 3, paragraph 30.

(b) No Automatic Disengagement. If the system design is such that the autopilot does not have an automatic disengagement on override feature, the pilot should initiat e an intentional override for an extended period of time. The autopilot should then be disengaged with the quick disconnect button and any transient response assessed in compliance with Chapter 3, paragraph 30. The effectiveness and timeliness of any ale rts used to mitigate the effects of the override condition should be assessed during this evaluation.

100. FAILURE CONDITIONS REQUIRING VALIDATION: § 25.1309.

a. General.

(1) Safety Assessment. The safety assessment process identified in Chap ter 8 should identify any failure condition responses that would require pilot evaluation to assess the severity of the effect, and the validity of any assumptions used for pilot recognition and mitigation. The

classification of a failure condition can va ry according to flight condition and may need to be confirmed by simulator or flight test.

(2) Evaluation of Failure Conditions. This chapter provides guidance on the test criteria, including recognition considerations, for flight evaluation of these failure conditions. In addition, certain probable failures should be demonstrated to assess the performance of the FGS and the adequacy of any applicable flightcrew procedures.Draft AC 25.1329

- 1B Change 1

103 (2) Approach Without Vertical Path Reference. For an approach without vertical path reference (for example, VOR, Non Directional Beacon (NBD), localizer only) the FGS mode of operation is typically vertical speed/flight path angle (that is, a cruise mode). The worst case failure condition for this type of mode should be dem onstrated in the approach configuration. An appropriate height loss should then be established in accordance with the method described in Appendix 2, Flight Test Procedures, paragraph 5c(4)(c).

(3) Steep Approach. In support of an approval to use the FGS on glidepath angles of greater than 3. 7 7 degrees (see Chapter 9, paragraph 99d(5), Steep Approach ( special

authorization ) ), an assessment should be made of the effects of failure conditions for this type of operation. For use of autopilot, an appr opriate MUH should be established in accordance with the deviation profile method described in this chapter. For this assessment, the obstacle plane

associated with a nominal 3 degree glidepath angle (1:29 slope) should be adjusted, according to

the maxim um approach angle for which approval is sought.

g. Specific Conditions.

(1) Failure Conditions to be Evaluated. The following are failure conditions that should be considered as part of the FGS evaluation program:

(a) Engine failure during app roach; continue approach to decision altitude/minimum descent altitude (DA/MDA).

(b) Potential fuel imbalance.

(c) Airplane system failures that affect FGS operational capabilities. Examples include failures of hydraulic systems, electrical sy stems, flight controls, and FGS related sensors. When possible, these failure conditions should be evaluated with a flight test. However, some failure conditions, due to their potential hazards, may best be evaluated via a high fidelity flight

simulation

.

(2) Failure to Disengage. The probability of failure of an FGS element to disengage when the quick disengagement control is operated should be shown to be acceptable by the safety analysis process. If credit is to be taken for acceptable continued manual operation with the FGS elements remaining engaged, that is, without operating any of the other disengagement controls, then a flight demonstration should be conducted though approach, landing and rollout.

101. CRITERIA SUPPORTING OPERATIONAL USE OF AUTOPILOT.

a. Typical Flight Operations. The criteria contained in this paragraph are intended to identify how the functional capability of the FGS, established during the certification, can be utilized to support typical flight operations. The cr iteria are based on experience