AMC 25.729 Extending retracting mechanisms

ED Decision 2016/010/R

1.       PURPOSE. This Acceptable Means of Compliance (AMC) provides guidance material for use as an acceptable means of demonstrating compliance with the landing gear retracting mechanism requirements of the Certification Specification (CS) for large aeroplanes.

2.       RELATED DOCUMENTS.

a.       Related Certification Specifications. CS 25.729 and other paragraphs relating to landing gear extending and retracting mechanisms installations together with their applicable AMCs, if any. Paragraphs which prescribe requirements for the design, substantiation, and certification of landing gear extending and retracting mechanisms include:

CS 25.111    Take-off path

CS 25.301    Loads

CS25.303     Factor of safety

CS 25.305    Strength and deformation

CS 25.307    Proof of structure

CS 25.333    Flight envelope

CS 25.471    General [Ground loads]

CS 25.561    General [Emergency Landing Conditions]

CS 25.601    General [Design and Construction]

CS 25.603    Materials

CS 25.605    Fabrication methods

CS 25.607    Fasteners

CS 25.609    Protection of structure

CS 25.613    Material strength properties

CS 25.619    Special factors

CS 25.621    Casting factors

CS 25.623    Bearing factors

CS 25.625    Fitting factors

CS 25.729    Extending and retracting mechanisms

CS 25.777    Cockpit controls

CS 25.779    Motion and effect of cockpit controls

CS 25.781    Cockpit control knob shape

CS 25.863    Flammable fluid fire protection

CS 25.869    Fire protection: systems

CS 25.899    Electrical bonding, etc.

CS 25.1301  Function and installation

CS 25.1309  Equipment, systems and installations

CS 25.1315  Negative acceleration

CS 25.1316  System lightning protection

CS 25.1322  Warning, caution and advisory lights

CS 25.1353  Electrical equipment and installations

CS 25.1357  Circuit protective devices

CS 25.1360  Precautions against injury

CS 25.1435  Hydraulic systems

CS 25.1515  Landing gear speeds

CS 25.1555  Control markings  

CS 25.1583  Operating limitations

CS 25.1585  Operating procedures

b.       FAA Advisory Circulars (AC's).

AC 20-34D             Prevention of Retractable Landing Gear Failures

AC 23-17B             Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships

AC 25.1309-1A      System Design and Analysis

AC 25-7C               Flight Test Guide for Certification of Transport Category Airplanes

AC 25-22               Certification of Transport Airplane Mechanical Systems

AC 43.13-1B                   Acceptable Methods, Techniques and Practices - Aircraft Inspection and Repair.

c.       Federal Aviation Administration Orders.

Order 8110.4C       Type Certification Process

Advisory Circulars and FAA Orders can be obtained from the U.S. Department of Transportation, Subsequent Distribution Office, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, Landover, MD 20785.

d.       Society of Automotive Engineers (SAE) Documents.

SAE AIR-4566         Crashworthiness Landing Gear Design

SAE ARP-1311A     Landing Gear - Aircraft

ISO 7137                        Environmental Conditions and Test Procedures for Airborne Equipment (not an SAE document but is available from the SAE)

         These documents can be obtained from the Society of Automotive Engineers, Inc., 400 Commonwealth Drive, Warrendale, Pennsylvania, 15096.

e.       Industry Documents.

(1)     EUROCAE ED-14G/RTCA, Inc., Document No. DO-160G,

Environmental Conditions and Test Procedures for Airborne Equipment.

(2)     AMC 20-115, Software Considerations in Airborne Systems and Equipment Certification.

         These documents can be obtained from EUROCAE, 17 rue Hamelin, 75783 Paris Cedex 15, France

f.       Military Documents.

MIL-STD-810         Environmental Test Methods and Engineering Guidelines

This document can be obtained from the Department of Defence, DODSSP, Standardisation Document Order Desk, 700 Robbins Avenue, Building 4D, Philadelphia, PA 19111-5094.

4.       DISCUSSION.

a.       Intent of rule. (Reference CS 25.729 Extending and retracting mechanisms)

         This rule provides minimum design and certification requirements for landing gear actuation systems to address:

(1)     Structural integrity for the nose and main landing gear, extending and retracting mechanism(s), doors, gear supporting structure for loads imposed during flight;

(2)     Positive locking of the kinematic mechanisms;

(3)     Redundant means of extending the landing gear;

(4)     Demonstration of proper operation by test;

(5)     Gear up-and-locked and down-and-locked position indications and aural warning;

(6)     Equipment damage from tyre burst, loose tread, and wheel brake temperatures.

b.       Demonstration of extending and retracting mechanisms proper functioning. (Reference CS 25.729(d) Operation test)

         Guidance addressing flight testing used to demonstrate compliance with this paragraph may be found in FAA Advisory Circular (AC) 25-7C, Flight Test Guide for Transport Category Aeroplanes, Chapter 4, Section 4, paragraph 52, dated 16 October 2012.

c.       Extending and retracting mechanisms indication. (Reference CS 25.729(e) Position indicator and warning device)

(1)     When light indicators are used, they should be arranged so that-

(i)      A green light for each unit is illuminated only when the unit is secured in the correct landing position.

(ii)     A warning light consistent with CS 25.1322 is illuminated at all times except when the landing gear and its doors are secured in the landing or retracted position.

(2)     The warning required by CS 25.729(e)(2) should preferably operate whatever the position of wing leading- or trailing-edge devices or the number of engines operating.

(3)     The design should be such that nuisance activation of the warning is minimised, for example-

(i)      When the landing gear is retracted after a take-off following an engine failure, or during a take-off when a common flap setting is used for take-off and landing;

(ii)     When the throttles are closed in a normal descent; or

(iii)     When flying at low altitude in clean or low speed configuration (special operation).

(4)     Inhibition of the warning above a safe altitude out of final approach phase either automatically or by some other means to prevent these situations is acceptable, but it should automatically reset for a further approach.

(5)     Means to de-activate the warning required by CS 25.729(e) may be installed for use in abnormal or emergency conditions provided that it is not readily available to the flight crew, i.e. the control device is protected against inadvertent actuation by the flight crew and its de-activated state is obvious to the flight crew.

d.       Definitions. For definitions of V_SR and V_C, see CS-Definitions Chapter 2, entitled 'Abbreviations and symbols'.

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