Sec. 25.729 - Retracting mechanism.
(a) General. For airplanes with
retractable landing gear, the following apply:
(1) The landing gear retracting
mechanism, wheel well doors, and supporting structure, must be designed
(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 1.3 Vs
(with the flaps in takeoff position at design takeoff weight), occurring
during retraction and extension at any airspeed up to 1.6 Vs1
(with the flaps in the approach position at design landing weight), and
(iii) Any load factor up to those
specified in §25.345(a) for the flaps extended condition.
(2) Unless there are other means to
decelerate the airplane in flight at this speed, the landing gear, the
retracting mechanism, and the airplane 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
maneuvers prescribed for the airplane in addition to the conditions of
airspeed and load factor prescribed in paragraphs (a)(1) and (2) of this
(b) Landing gear lock. There must
be positive means to keep the landing gear extended, in flight and on the
(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 retraction system; or
(2) The failure of any single source of
hydraulic, electric, or equivalent energy supply.
(d) Operation test. The proper
functioning of the retracting mechanism 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 (as well as necessary switches to actuate the
indicator) or other means to inform the pilot that the gear is secured in
the extended (or retracted) position. This means must be designed as
(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
(2) The flightcrew 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 flightcrew for the warning required by
paragraph (e)(2) of this section 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 eliminate 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.
(f) Protection of equipment in wheel
wells. Equipment that is essential to safe operation of the airplane
and that is located in wheel wells must be protected from the damaging
effects of --
(1) A bursting tire, unless it is shown
that a tire cannot burst from overheat; and
(2) A loose tire tread, unless it is
shown that a loose tire tread cannot cause damage.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5676, Apr. 8, 1970; Amdt. 25-42, 43 FR 2323,
Jan. 16, 1978; Amdt. 25-72, 55 FR 29777, July 20, 1990; Amdt. 25-75, 56 FR
63762, Dec. 5, 1991]