251 

Federal Aviation Administration, DOT 

§ 25.493 

direction of motion of the unsprung 
weights as they reach their limiting 
positions in extending with relation to 
the sprung parts of the landing gear. 

§ 25.489

Ground handling conditions. 

Unless otherwise prescribed, the 

landing gear and airplane structure 
must be investigated for the conditions 
in §§ 25.491 through 25.509 with the air-
plane at the design ramp weight (the 
maximum weight for ground handling 
conditions). No wing lift may be con-
sidered. The shock absorbers and tires 
may be assumed to be in their static 
position. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5673, Apr. 8, 
1970] 

§ 25.491

Taxi, takeoff and landing roll. 

Within the range of appropriate 

ground speeds and approved weights, 
the airplane structure and landing gear 
are assumed to be subjected to loads 
not less than those obtained when the 
aircraft is operating over the roughest 
ground that may reasonably be ex-
pected in normal operation. 

[Amdt. 25–91, 62 FR 40705, July 29, 1997] 

§ 25.493

Braked roll conditions. 

(a) An airplane with a tail wheel is 

assumed to be in the level attitude 
with the load on the main wheels, in 
accordance with figure 6 of appendix A. 
The limit vertical load factor is 1.2 at 
the design landing weight and 1.0 at 
the design ramp weight. A drag reac-
tion equal to the vertical reaction mul-
tiplied by a coefficient of friction of 
0.8, must be combined with the vertical 
ground reaction and applied at the 
ground contact point. 

(b) For an airplane with a nose wheel 

the limit vertical load factor is 1.2 at 
the design landing weight, and 1.0 at 
the design ramp weight. A drag reac-
tion equal to the vertical reaction, 
multiplied by a coefficient of friction 
of 0.8, must be combined with the 
vertical reaction and applied at the 
ground contact point of each wheel 
with brakes. The following two atti-
tudes, in accordance with figure 6 of 
appendix A, must be considered: 

(1) The level attitude with the wheels 

contacting the ground and the loads 

distributed between the main and nose 
gear. Zero pitching acceleration is as-
sumed. 

(2) The level attitude with only the 

main gear contacting the ground and 
with the pitching moment resisted by 
angular acceleration. 

(c) A drag reaction lower than that 

prescribed in this section may be used 
if it is substantiated that an effective 
drag force of 0.8 times the vertical re-
action cannot be attained under any 
likely loading condition. 

(d) An airplane equipped with a nose 

gear must be designed to withstand the 
loads arising from the dynamic pitch-
ing motion of the airplane due to sud-
den application of maximum braking 
force. The airplane is considered to be 
at design takeoff weight with the nose 
and main gears in contact with the 
ground, and with a steady-state 
vertical load factor of 1.0. The steady- 
state nose gear reaction must be com-
bined with the maximum incremental 
nose gear vertical reaction caused by 
the sudden application of maximum 
braking force as described in para-
graphs (b) and (c) of this section. 

(e) In the absence of a more rational 

analysis, the nose gear vertical reac-
tion prescribed in paragraph (d) of this 
section must be calculated according 
to the following formula: 

V

W

A

B

B

f AE

A

B

E

N

T

=

+

+

+ +

⎡
⎣

⎢

⎤
⎦

⎥

μ

μ

Where: 

V

N

= Nose gear vertical reaction. 

W

T

= Design takeoff weight. 

A = Horizontal distance between the c.g. of 

the airplane and the nose wheel. 

B = Horizontal distance between the c.g. of 

the airplane and the line joining the cen-
ters of the main wheels. 

E = Vertical height of the c.g. of the airplane 

above the ground in the 1.0 g static con-
dition. 

μ 

= Coefficient of friction of 0.80. 

f = Dynamic response factor; 2.0 is to be used 

unless a lower factor is substantiated. In 
the absence of other information, the dy-
namic response factor f may be defined 
by the equation: 

f

= +

−

−

⎛

⎝

⎜⎜

⎞

⎠

⎟⎟

1

1

2

exp

πξ

ξ

Where: 

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