272 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.721 

(b) The warning required by para-

graph (a) of this section must continue 
until— 

(1) The configuration is changed to 

allow a safe takeoff; 

(2) Action is taken by the pilot to 

terminate the takeoff roll; 

(3) The airplane is rotated for take-

off; or 

(4) The warning is manually deacti-

vated by the pilot. 

(c) The means used to activate the 

system must function properly 
throughout the ranges of takeoff 
weights, altitudes, and temperatures 
for which certification is requested. 

[Amdt. 25–42, 43 FR 2323, Jan. 16, 1978] 

L

ANDING

G

EAR

 

§ 25.721

General. 

(a) The landing gear system must be 

designed so that when it fails due to 
overloads during takeoff and landing, 
the failure mode is not likely to cause 
spillage of enough fuel to constitute a 
fire hazard. The overloads must be as-
sumed to act in the upward and aft di-
rections in combination with side loads 
acting inboard and outboard. In the ab-
sence of a more rational analysis, the 
side loads must be assumed to be up to 
20 percent of the vertical load or 20 per-
cent of the drag load, whichever is 
greater. 

(b) The airplane must be designed to 

avoid any rupture leading to the spill-
age of enough fuel to constitute a fire 
hazard as a result of a wheels-up land-
ing on a paved runway, under the fol-
lowing minor crash landing conditions: 

(1) Impact at 5 feet-per-second 

vertical velocity, with the airplane 
under control, at Maximum Design 
Landing Weight— 

(i) With the landing gear fully re-

tracted; and 

(ii) With any one or more landing 

gear legs not extended. 

(2) Sliding on the ground, with— 
(i) The landing gear fully retracted 

and with up to a 20

° 

yaw angle; and 

(ii) Any one or more landing gear 

legs not extended and with 0

° 

yaw 

angle. 

(c) For configurations where the en-

gine nacelle is likely to come into con-
tact with the ground, the engine pylon 
or engine mounting must be designed 

so that when it fails due to overloads 
(assuming the overloads to act pre-
dominantly in the upward direction 
and separately, predominantly in the 
aft direction), the failure mode is not 
likely to cause the spillage of enough 
fuel to constitute a fire hazard. 

[Amdt. 25–139, 79 FR 59430, Oct. 2, 2014] 

§ 25.723

Shock absorption tests. 

(a) The analytical representation of 

the landing gear dynamic characteris-
tics that is used in determining the 
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: 

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