Code of Federal Regulations - Title 14

397

Federal Aviation Administration, DOT

§ 25.255

(c)

Maximum speed for stability charac-

teristics in icing conditions. The max-
imum speed for stability characteris-
tics with the ice accretions defined in
appendix C, 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, 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]

§ 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
g.

(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),
need not be exceeded. In addition, the
entry speeds for flight test demonstra-
tions at normal acceleration values
less than 1 g must be limited to the ex-
tent necessary to accomplish a recov-
ery without exceeding V

DF.

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

fied in paragraph (a) of this section, it
must be possible from an overspeed
condition at V

to produce at

least 1.5 g for recovery by applying not
more than 125 pounds of longitudinal
control force using either the primary
longitudinal control alone or the pri-
mary longitudinal control and the lon-
gitudinal trim system. If the longitu-
dinal trim is used to assist in pro-
ducing the required load factor, it must
be shown at V

that the longitu-

dinal trim can be actuated in the air-
plane nose-up direction with the pri-
mary surface loaded to correspond to
the least of the following airplane
nose-up control forces:

(1) The maximum control forces ex-

pected in service as specified in §§ 25.301
and 25.397.

(2) The control force required to

produce 1.5 g.

(3) The control force corresponding to

buffeting or other phenomena of such

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