CS 25.729 Extending and retracting mechanisms

ED Decision 2016/010/R

(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 V_SR (with the flaps in takeoff position at design take-off weight), occurring during retraction and extension at any airspeed up to 1·5 V_SR1 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 V_C.

(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]