Code of Federal Regulations - Title 14

396

14 CFR Ch. I (1–1–14 Edition)

§ 25.253

(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

MO,

except that stall warn-

ing buffeting is allowable.

(e) For an airplane with M

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

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

MO,

without—

(i) Exceptional piloting strength or

skill;

(ii) Exceeding

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

, there must be no

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

. 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

, the slope of the elevator

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

, but there must be a push force

at all speeds up to V

and there

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

is reached.

(4) Adequate roll capability to assure

a prompt recovery from a lateral upset
condition must be available at any
speed up to V

(5) With the airplane trimmed at

, extension of the speedbrakes

over the available range of movements
of the pilot’s control, at all speeds
above V

, but not so high that

would be exceeded during the

maneuver, must not result in:

(i) An excessive positive load factor

when the pilot does not take action to
counteract the effects of extension;

(ii) Buffeting that would impair the

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

(iii) A nose down pitching moment,

unless it is small.

(b)

Maximum speed for stability charac-

teristics, V

. V

is the max-

imum speed at which the requirements
of §§ 25.143(g), 25.147(f), 25.175(b)(1),
25.177(a) through (c), and 25.181 must be
met with flaps and landing gear re-
tracted. Except as noted in § 25.253(c),
V

may not be less than a speed

midway between V

and V

except that, for altitudes where Mach
number is the limiting factor, M

need

not exceed the Mach number at which
effective speed warning occurs.

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