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14 CFR Ch. I (1–1–19 Edition)

§ 25.255

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.

(c)

Maximum speed for stability charac-

teristics in icing conditions.

The max-

imum speed for stability characteris-
tics with the most critical of the ice
accretions defined in Appendices C and
O of this part, as applicable, in accord-
ance with § 25.21(g), at which the re-
quirements of §§ 25.143(g), 25.147(f),
25.175(b)(1), 25.177(a) through (c), and
25.181 must be met, is the lower of:

(1) 300 knots CAS;
(2) V

; or

(3) A speed at which it is dem-

onstrated that the airframe will be free
of ice accretion due to the effects of in-
creased dynamic pressure.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5671, Apr. 8,
1970; Amdt. 25–54, 45 FR 60172, Sept. 11, 1980;
Amdt. 25–72, 55 FR 29775, July 20, 1990; Amdt.
25–84, 60 FR 30750, June 9, 1995; Amdt. 25–121,
72 FR 44668, Aug. 8, 2007; Amdt. 25–135, 76 FR
74654, Dec. 1, 2011; Amdt. 25–140,79 FR 65525,
Nov. 4, 2014]

§ 25.255

Out-of-trim characteristics.

(a) From an initial condition with

the airplane trimmed at cruise speeds
up to V

MO,

the airplane must have

satisfactory maneuvering stability and

controllability with the degree of out-
of-trim in both the airplane nose-up
and nose-down directions, which re-
sults from the greater of—

(1) A three-second movement of the

longitudinal trim system at its normal
rate for the particular flight condition
with no aerodynamic load (or an equiv-
alent degree of trim for airplanes that
do not have a power-operated trim sys-
tem), except as limited by stops in the
trim system, including those required
by § 25.655(b) for adjustable stabilizers;
or

(2) The maximum mistrim that can

be sustained by the autopilot while
maintaining level flight in the high
speed cruising condition.

(b) In the out-of-trim condition speci-

fied in paragraph (a) of this section,
when the normal acceleration is varied
from + 1 g to the positive and negative
values specified in paragraph (c) of this
section—

(1) The stick force vs. g curve must

have a positive slope at any speed up to
and including V

; and

(2) At speeds between V

and

the direction of the primary

longitudinal control force may not re-
verse.

(d) and (e) of this section, compliance
with the provisions of paragraph (a) of
this section must be demonstrated in
flight over the acceleration range—

(1)

1 g to + 2.5 g; or

(2) 0 g to 2.0 g, and extrapolating by

an acceptable method to

1 g and + 2.5

(d) If the procedure set forth in para-

graph (c)(2) of this section is used to
demonstrate compliance and marginal
conditions exist during flight test with
regard to reversal of primary longitu-
dinal control force, flight tests must be
accomplished from the normal accel-
eration at which a marginal condition
is found to exist to the applicable limit
specified in paragraph (b)(1) of this sec-
tion.

(e) During flight tests required by

paragraph (a) of this section, the limit
maneuvering load factors prescribed in
§§ 25.333(b) and 25.337, and the maneu-
vering load factors associated with
probable inadvertent excursions be-
yond the boundaries of the buffet onset
envelopes determined under § 25.251(e),

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