401 

Federal Aviation Administration, DOT 

§ 25.335 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–86, 61 FR 5220, Feb. 9, 1996] 

§ 25.335

Design airspeeds. 

The selected design airspeeds are 

equivalent airspeeds (EAS). Estimated 
values of 

V

S0

and 

V

S1

must be conserv-

ative. 

(a) 

Design cruising speed, V

C.

For 

V

C,

 

the following apply: 

(1) The minimum value of 

V

C

must be 

sufficiently greater than 

V

B

to provide 

for inadvertent speed increases likely 
to occur as a result of severe atmos-
pheric turbulence. 

(2) Except as provided in § 25.335(d)(2), 

V

C

may not be less than V

B

+ 1.32 U

REF

 

(with U

REF

as specified in 

§ 25.341(a)(5)(i)). However V

C

need not 

exceed the maximum speed in level 
flight at maximum continuous power 
for the corresponding altitude. 

(3) At altitudes where 

V

D

is limited 

by Mach number, 

V

C

may be limited to 

a selected Mach number. 

(b) 

Design dive speed, V

D.

V

D

must be 

selected so that 

V

C

/

M

C

is not greater 

than 0.8 

V

D

/

M

D,

or so that the minimum 

speed margin between 

V

C

/

M

C

and 

V

D

/

M

D

 

is the greater of the following values: 

(1) From an initial condition of sta-

bilized flight at 

V

C

/

M

C,

the airplane is 

upset, flown for 20 seconds along a 
flight path 7.5

° 

below the initial path, 

and then pulled up at a load factor of 
1.5

g  (0.5g  acceleration increment). The 

speed increase occurring in this maneu-
ver may be calculated if reliable or 
conservative aerodynamic data is used. 
Power as specified in § 25.175(b)(1)(iv) is 
assumed until the pullup is initiated, 
at which time power reduction and the 
use of pilot controlled drag devices 
may be assumed; 

(2) The minimum speed margin must 

be enough to provide for atmospheric 
variations (such as horizontal gusts, 
and penetration of jet streams and cold 
fronts) and for instrument errors and 
airframe production variations. These 
factors may be considered on a prob-
ability basis. The margin at altitude 
where M

C

is limited by compressibility 

effects must not less than 0.07M unless 
a lower margin is determined using a 
rational analysis that includes the ef-
fects of any automatic systems. In any 

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