273 

Federal Aviation Administration, DOT 

§ 25.729 

landing loads must be validated by en-
ergy absorption tests. A range of tests 
must be conducted to ensure that the 
analytical representation is valid for 
the design conditions specified in 
§ 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 appro-
priate drag loads during the test must 
simulate the airplane landing condi-
tions in a manner consistent with the 
development of rational or conserv-
ative limit loads. 

(b) The landing gear may not fail in 

a test, demonstrating its reserve en-
ergy absorption capacity, simulating a 
descent velocity of 12 f.p.s. at design 
landing weight, assuming airplane lift 
not greater than airplane weight act-
ing during the landing impact. 

(c) In lieu of the tests prescribed in 

this section, changes in previously ap-
proved 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] 

§§ 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 

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