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CS 25.729 Extending and retracting mechanisms

Large Aeroplanes (CS-25) · CS-25 · EAR revision 26 Jan 2023

IRImplementing rule

CS 25.729Extending and retracting mechanisms

(See AMC 25.729)

(a)General. For aeroplanes with retractable landing gear, the following apply:

(1)The landing gear extending and retracting mechanisms, wheel well doors, and supporting structure, must be designed for –:

(i)the loads occurring in the flight conditions when the gear is in the retracted position;

(ii)the combination of friction loads, inertia loads, brake torque loads, air loads, and gyroscopic loads resulting from the wheels rotating at a peripheral speed equal to 1·23 VSR (with the flaps in takeoff position at design take-off weight), occurring during retraction and extension at any airspeed up to 1·5 VSR1 with the wing-flaps in the approach position at design landing weight, and

(iii)any load factor up to those specified in CS 25.345(a) for the wing-flaps extended condition.

(2)Unless there are other means to decelerate the aeroplane in flight at this speed, the landing gear, the extending and retracting mechanisms, and the aeroplane structure (including wheel well doors) must be designed to withstand the flight loads occurring with the landing gear in the extended position at any speed up to 0·67 VC.

(3)Landing gear doors, their operating mechanism, and their supporting structures must be designed for the yawing manoeuvres prescribed for the aeroplane in addition to the conditions of airspeed and load factor prescribed in sub-paragraphs (a)(1) and (2) of this paragraph.

(b)Landing gear lock. There must be positive means to keep the landing gear extended in flight and on the ground. There must be positive means to keep the landing gear and doors in the correct retracted position in flight, unless it can be shown that lowering of the landing gear or doors, or flight with the landing gear or doors extended, at any speed, is not hazardous.

(c)Emergency operation. There must be an emergency means for extending the landing gear in the event of –

(1)any reasonably probable failure in the normal extension and retraction systems; or

(2)the failure of any single source of hydraulic, electric, or equivalent energy supply.

(d)Operation test. The proper functioning of the extending and retracting mechanisms must be shown by operation tests.

(e)Position indicator and warning device. If a retractable landing gear is used, there must be a landing gear position indicator easily visible to the pilot or to the appropriate crew members (as well as necessary devices to actuate the indicator) to indicate without ambiguity that the retractable units and their associated doors are secured in the extended (or retracted) position. The means must be designed as follows:

(1)If switches are used, they must be located and coupled to the landing gear mechanical systems in a manner that prevents an erroneous indication of ‘down and locked’ if the landing gear is not in a fully extended position, or of ‘up and locked’ if the landing gear is not in the fully retracted position. The switches may be located where they are operated by the actual landing gear locking latch or device.

(2)The flight crew must be given an aural warning that functions continuously, or is periodically repeated, if a landing is attempted when the landing gear is not locked down.

(3)The warning must be given in sufficient time to allow the landing gear to be locked down or a go-around to be made.

(4)There must not be a manual shut-off means readily available to the flight crew for the warning required by sub-paragraph (e)(2) of this paragraph such that it could be operated instinctively, inadvertently or by habitual reflexive action.

(5)The system used to generate the aural warning must be designed to minimise false or inappropriate alerts.

(6)Failures of systems used to inhibit the landing gear aural warning, that would prevent the warning system from operating, must be improbable.

(7)A clear indication or warning must be provided whenever the landing gear position is not consistent with the landing gear selector lever position.

[Amdt 25/4]

[Amdt 25/14]

[Amdt 25/18]

IR · CS 25.729 — CS-25 · ED Decision 2016/010/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

AMCAcceptable means of compliance

AMC 25.729Extending retracting mechanisms

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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 VSR and VC, see CS-Definitions Chapter 2, entitled 'Abbreviations and symbols'.

[Amdt 25/4]

[Amdt 25/12]

[Amdt 25/14]

[Amdt 25/18]

AMC · AMC 25.729 — CS-25 · ED Decision 2016/010/R · CS-25 Easy Access Rules · EAR revision 26 Jan 2023

All rules in SUBPART D – DESIGN AND CONSTRUCTION

Consolidated from the EASA Easy Access Rules (revision 26 Jan 2023, extracted 17 Aug 2026) for convenience. Not the official publication — verify against the Official Journal of the European Union and the EASA publications before operational use.

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