Federal Aviation Administration, DOT

Section 25.729

landing loads must be validated by energy absorption tests. A range of tests
must be conducted to ensure that the
analytical representation is valid for
the design conditions specified in
Section 25.473.
(1) The configurations subjected to
energy absorption tests at limit design
conditions must include at least the
design landing weight or the design
takeoff weight, whichever produces the
greater value of landing impact energy.
(2) The test attitude of the landing
gear unit and the application of appropriate drag loads during the test must
simulate the airplane landing conditions in a manner consistent with the
development of rational or conservative limit loads.
(b) The landing gear may not fail in
a test, demonstrating its reserve energy absorption capacity, simulating a
descent velocity of 12 f.p.s. at design
landing weight, assuming airplane lift
not greater than airplane weight acting during the landing impact.
(c) In lieu of the tests prescribed in
this section, changes in previously approved design weights and minor
changes in design may be substantiated
by analyses based on previous tests
conducted on the same basic landing
gear system that has similar energy
absorption characteristics.
[Doc. No. 1999-5835, 66 FR 27394, May 16, 2001]

SectionSection 25.725-25.727

spaschal on DSK3GDR082PROD with CFR

Section 25.729

[Reserved]

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
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 1.23VSR (with
the wing-flaps in take-off 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 Section 25.345(a) for the wing-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 section.
(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 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 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

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