231 

Federal Aviation Administration, DOT 

§ 25.253 

(3) At speeds that may reasonably be 

expected in operation on water; 

(4) With sudden failure of the critical 

engine at any time while on water; and 

(5) At each weight and center of grav-

ity position, relevant to each operating 
condition, within the range of loading 
conditions for which certification is re-
quested. 

(c) In the water conditions of para-

graph (b) of this section, and in the 
corresponding wind conditions, the sea-
plane or amphibian must be able to 
drift for five minutes with engines in-
operative, aided, if necessary, by a sea 
anchor. 

M

ISCELLANEOUS

F

LIGHT

R

EQUIREMENTS

 

§ 25.251

Vibration and buffeting. 

(a) The airplane must be dem-

onstrated in flight to be free from any 
vibration and buffeting that would pre-
vent continued safe flight in any likely 
operating condition. 

(b) Each part of the airplane must be 

demonstrated in flight to be free from 
excessive vibration under any appro-
priate speed and power conditions up to 
V

DF

/M

DF

. The maximum speeds shown 

must be used in establishing the oper-
ating limitations of the airplane in ac-
cordance with § 25.1505. 

(c) Except as provided in paragraph 

(d) of this section, there may be no buf-
feting condition, in normal flight, in-
cluding configuration changes during 
cruise, severe enough to interfere with 
the control of the airplane, to cause ex-
cessive fatigue to the crew, or to cause 
structural damage. Stall warning buf-
feting within these limits is allowable. 

(d) There may be no perceptible buf-

feting condition in the cruise configu-
ration in straight flight at any speed 
up to 

V

MO

/

M

MO,

except that stall warn-

ing buffeting is allowable. 

(e) For an airplane with M

D

greater 

than .6 or with a maximum operating 
altitude greater than 25,000 feet, the 
positive maneuvering load factors at 
which the onset of perceptible buf-
feting occurs must be determined with 
the airplane in the cruise configuration 
for the ranges of airspeed or Mach 
number, weight, and altitude for which 
the airplane is to be certificated. The 
envelopes of load factor, speed, alti-
tude, and weight must provide a suffi-

cient range of speeds and load factors 
for normal operations. Probable inad-
vertent excursions beyond the bound-
aries of the buffet onset envelopes may 
not result in unsafe conditions. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5671, Apr. 8, 
1970; Amdt. 25–72, 55 FR 29775, July 20, 1990; 
Amdt. 25–77, 57 FR 28949, June 29, 1992] 

§ 25.253

High-speed characteristics. 

(a) 

Speed increase and recovery charac-

teristics. 

The following speed increase 

and recovery characteristics must be 
met: 

(1) Operating conditions and charac-

teristics likely to cause inadvertent 
speed increases (including upsets in 
pitch and roll) must be simulated with 
the airplane trimmed at any likely 
cruise speed up to 

V

MO

/

M

MO

. These con-

ditions and characteristics include gust 
upsets, inadvertent control move-
ments, low stick force gradient in rela-
tion to control friction, passenger 
movement, leveling off from climb, and 
descent from Mach to airspeed limit al-
titudes. 

(2) Allowing for pilot reaction time 

after effective inherent or artificial 
speed warning occurs, it must be shown 
that the airplane can be recovered to a 
normal attitude and its speed reduced 
to 

V

MO

/

M

MO,

without— 

(i) Exceptional piloting strength or 

skill; 

(ii) Exceeding 

V

D

/

M

D,

V

DF

/

M

DF,

or the 

structural limitations; and 

(iii) Buffeting that would impair the 

pilot’s ability to read the instruments 
or control the airplane for recovery. 

(3) With the airplane trimmed at any 

speed up to V

MO

/M

MO

, there must be no 

reversal of the response to control 
input about any axis at any speed up to 
V

DF

/M

DF

. Any tendency to pitch, roll, or 

yaw must be mild and readily control-
lable, using normal piloting tech-
niques. When the airplane is trimmed 
at V

MO

/M

MO

, the slope of the elevator 

control force versus speed curve need 
not be stable at speeds greater than 
V

FC

/M

FC

, but there must be a push force 

at all speeds up to V

DF

/M

DF

and there 

must be no sudden or excessive reduc-
tion of elevator control force as V

DF

/ 

M

DF

is reached. 

(4) Adequate roll capability to assure 

a prompt recovery from a lateral upset 

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