434 

14 CFR Ch. I (1–1–14 Edition) 

§§ 25.725–25.727 

gear system that has similar energy 
absorption characteristics. 

[Doc. No. 1999–5835, 66 FR 27394, May 16, 2001] 

§§ 25.725–25.727

[Reserved] 

§ 25.729

Retracting mechanism. 

(a) 

General.  For airplanes with re-

tractable landing gear, the following 
apply: 

(1) The landing gear retracting mech-

anism, wheel well doors, and sup-
porting structure, must be designed 
for— 

(i) The loads occurring in the flight 

conditions when the gear is in the re-
tracted position, 

(ii) The combination of friction 

loads, inertia loads, brake torque loads, 
air loads, and gyroscopic loads result-
ing from the wheels rotating at a pe-
ripheral speed equal to 1.23V

SR

(with 

the wing-flaps in take-off position at 
design take-off weight), occurring dur-
ing 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 spec-

ified in § 25.345(a) for the wing-flaps ex-
tended 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 

V

C.

 

(3) Landing gear doors, their oper-

ating 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 sec-
tion. 

(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 ex-
tended, 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 en-
ergy supply. 

(d) 

Operation test. The proper func-

tioning of the retracting mechanism 
must be shown by operation tests. 

(e) 

Position indicator and warning de-

vice.  If a retractable landing gear is 
used, there must be a landing gear po-
sition indicator easily visible to the 
pilot or to the appropriate crew mem-
bers (as well as necessary devices to ac-
tuate the indicator) to indicate with-
out ambiguity that the retractable 
units and their associated doors are se-
cured in the extended (or retracted) po-
sition. 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 flightcrew must be given an 

aural warning that functions continu-
ously, or is periodically repeated, if a 
landing is attempted when the landing 
gear is not locked down. 

(3) The warning must be given in suf-

ficient 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 
minimize false or inappropriate alerts. 

(6) Failures of systems used to in-

hibit the landing gear aural warning, 
that would prevent the warning system 
from operating, must be improbable. 

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