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250 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.481 

(2) The most severe combination of 

loads that are likely to arise during a 
lateral drift landing must be taken 
into account. In absence of a more ra-
tional analysis of this condition, the 
following must be investigated: 

(i) A vertical load equal to 75% of the 

maximum ground reaction of § 25.473 
must be considered in combination 
with a drag and side load of 40% and 
25% respectively of that vertical load. 

(ii) The shock absorber and tire de-

flections must be assumed to be 75% of 
the deflection corresponding to the 
maximum ground reaction of 
§ 25.473(a)(2). This load case need not be 
considered in combination with flat 
tires. 

(3) The combination of vertical and 

drag components is considered to be 
acting at the wheel axle centerline. 

[Amdt. 25–91, 62 FR 40705, July 29, 1997; Amdt. 
25–91, 62 FR 45481, Aug. 27, 1997] 

§ 25.481

Tail-down landing conditions. 

(a) In the tail-down attitude, the air-

plane is assumed to contact the ground 
at forward velocity components, rang-
ing from V

L1

to V

L2

parallel to the 

ground under the conditions prescribed 
in § 25.473 with— 

(1) 

V

L1

equal to 

V

S0

(TAS) at the ap-

propriate landing weight and in stand-
ard sea level conditions; and 

(2) 

V

L2

equal to 

V

S0

(TAS) at the ap-

propriate landing weight and altitudes 
in a hot day temperature of 41 degrees 
F. above standard. 

(3) The combination of vertical and 

drag components considered to be act-
ing at the main wheel axle centerline. 

(b) For the tail-down landing condi-

tion for airplanes with tail wheels, the 
main and tail wheels are assumed to 
contact the ground simultaneously, in 
accordance with figure 3 of appendix A. 
Ground reaction conditions on the tail 
wheel are assumed to act— 

(1) Vertically; and 
(2) Up and aft through the axle at 45 

degrees to the ground line. 

(c) For the tail-down landing condi-

tion for airplanes with nose wheels, the 
airplane is assumed to be at an atti-
tude corresponding to either the stall-
ing angle or the maximum angle allow-
ing clearance with the ground by each 
part of the airplane other than the 

main wheels, in accordance with figure 
3 of appendix A, whichever is less. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–91, 62 FR 40705, July 29, 
1997; Amdt. 25–94, 63 FR 8848, Feb. 23, 1998] 

§ 25.483

One-gear landing conditions. 

For the one-gear landing conditions, 

the airplane is assumed to be in the 
level attitude and to contact the 
ground on one main landing gear, in 
accordance with Figure 4 of Appendix 
A of this part. In this attitude— 

(a) The ground reactions must be the 

same as those obtained on that side 
under § 25.479(d)(1), and 

(b) Each unbalanced external load 

must be reacted by airplane inertia in 
a rational or conservative manner. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–91, 62 FR 40705, July 29, 
1997] 

§ 25.485

Side load conditions. 

In addition to § 25.479(d)(2) the fol-

lowing conditions must be considered: 

(a) For the side load condition, the 

airplane is assumed to be in the level 
attitude with only the main wheels 
contacting the ground, in accordance 
with figure 5 of appendix A. 

(b) Side loads of 0.8 of the vertical re-

action (on one side) acting inward and 
0.6 of the vertical reaction (on the 
other side) acting outward must be 
combined with one-half of the max-
imum vertical ground reactions ob-
tained in the level landing conditions. 
These loads are assumed to be applied 
at the ground contact point and to be 
resisted by the inertia of the airplane. 
The drag loads may be assumed to be 
zero. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–91, 62 FR 40705, July 29, 
1997] 

§ 25.487

Rebound landing condition. 

(a) The landing gear and its sup-

porting structure must be investigated 
for the loads occurring during rebound 
of the airplane from the landing sur-
face. 

(b) With the landing gear fully ex-

tended and not in contact with the 
ground, a load factor of 20.0 must act 
on the unsprung weights of the landing 
gear. This load factor must act in the 

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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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