239 

Federal Aviation Administration, DOT 

§ 25.341 

(1) May not be less than 

¥

1.0 at 

speeds up to 

V

C

; and 

(2) Must vary linearly with speed 

from the value at 

V

C

to zero at 

V

D

. 

(d) Maneuvering load factors lower 

than those specified in this section 
may be used if the airplane has design 
features that make it impossible to ex-
ceed these values in flight. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5672, Apr. 8, 
1970] 

§ 25.341

Gust and turbulence loads. 

(a) 

Discrete Gust Design Criteria. 

The 

airplane is assumed to be subjected to 
symmetrical vertical and lateral gusts 
in level flight. Limit gust loads must 
be determined in accordance with the 
provisions: 

(1) Loads on each part of the struc-

ture must be determined by dynamic 
analysis. The analysis must take into 
account unsteady aerodynamic charac-
teristics and all significant structural 
degrees of freedom including rigid body 
motions. 

(2) The shape of the gust must be: 

U

U

ds

=

⎛
⎝⎜

⎞
⎠⎟

⎡

⎣

⎢

⎤

⎦

⎥

2

1- Cos

s

H

π

for 0 

≤

s 

≤

2H 

where— 
s = distance penetrated into the gust (feet); 
U

ds

= the design gust velocity in equivalent 
airspeed specified in paragraph (a)(4) of 
this section; and 

H = the gust gradient which is the distance 

(feet) parallel to the airplane’s flight 
path for the gust to reach its peak veloc-
ity. 

(3) A sufficient number of gust gra-

dient distances in the range 30 feet to 
350 feet must be investigated to find 
the critical response for each load 
quantity. 

(4) The design gust velocity must be: 

U

U

F H

ds

ref

g

=

(

)

350

1 6

where— 

U

ref

= the reference gust velocity in equiva-

lent airspeed defined in paragraph (a)(5) 
of this section. 

F

g

= the flight profile alleviation factor de-

fined in paragraph (a)(6) of this section. 

(5) The following reference gust ve-

locities apply: 

(i) At airplane speeds between V

B

and 

V

C

: Positive and negative gusts with 

reference gust velocities of 56.0 ft/sec 
EAS must be considered at sea level. 
The reference gust velocity may be re-
duced linearly from 56.0 ft/sec EAS at 
sea level to 44.0 ft/sec EAS at 15,000 
feet. The reference gust velocity may 
be further reduced linearly from 44.0 ft/ 
sec EAS at 15,000 feet to 20.86 ft/sec 
EAS at 60,000 feet. 

(ii) At the airplane design speed V

D

: 

The reference gust velocity must be 0.5 
times the value obtained under 
§ 25.341(a)(5)(i). 

(6) The flight profile alleviation fac-

tor, F

g

, must be increased linearly from 

the sea level value to a value of 1.0 at 
the maximum operating altitude de-
fined in § 25.1527. At sea level, the flight 
profile alleviation factor is determined 
by the following equation: 

F

F

F

Where

F

Z

F

R Tan

R

R

Maximum Landing Weight

Maximum Take off Weight

R

Maximum Zero Fuel Weight

Maximum Take off Weight

g

gz

gm

gz

mo

gm

=

+

(

)

= −

=

⎛

⎝

⎞

⎠

=

=

0 5

1

250000

4

2

1

1

2

.

:

;

;

;

;

π

-

-

Z

mo

= Maximum operating altitude defined in 

§ 25.1527 (feet). 

(7) When a stability augmentation 

system is included in the analysis, the 
effect of any significant system non-
linearities should be accounted for 
when deriving limit loads from limit 
gust conditions. 

(b) 

Continuous turbulence design cri-

teria. 

The dynamic response of the air-

plane to vertical and lateral contin-
uous turbulence must be taken into ac-
count. The dynamic analysis must take 
into account unsteady aerodynamic 
characteristics and all significant 
structural degrees of freedom including 

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spaschal on DSK3GDR082PROD with CFR