Section 25.255

14 CFR Ch. I (1-1-19 Edition)

condition must be available at any
speed up to VDF/MDF.
(5) With the airplane trimmed at
VMO/MMO, extension of the speedbrakes
over the available range of movements
of the pilot-s control, at all speeds
above VMO/MMO, but not so high that
VDF/MDF 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 characteristics, VFC/MFC. VFC/MFC is the maximum speed at which the requirements
of SectionSection 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 retracted. Except as noted in Section 25.253(c),
VFC/MFC may not be less than a speed
midway between VMO/MMO and VDF/MDF,
except that, for altitudes where Mach
number is the limiting factor, MFC need
not exceed the Mach number at which
effective speed warning occurs.
(c) Maximum speed for stability characteristics in icing conditions. The maximum speed for stability characteristics with the most critical of the ice
accretions defined in Appendices C and
O of this part, as applicable, in accordance with Section 25.21(g), at which the requirements of SectionSection 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) VFC; or
(3) A speed at which it is demonstrated that the airframe will be free
of ice accretion due to the effects of increased dynamic pressure.

spaschal on DSK3GDR082PROD with CFR

[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]

Section 25.255 Out-of-trim characteristics.
(a) From an initial condition with
the airplane trimmed at cruise speeds
up to VMO/MMO, the airplane must have
satisfactory maneuvering stability and

controllability with the degree of outof-trim in both the airplane nose-up
and nose-down directions, which results 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 equivalent degree of trim for airplanes that
do not have a power-operated trim system), except as limited by stops in the
trim system, including those required
by Section 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 specified 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 VFC/MFC; and
(2) At speeds between VFC/MFC and
VDF/MDF the direction of the primary
longitudinal control force may not reverse.
(c) Except as provided in paragraphs
(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) Section1 g to + 2.5 g; or
(2) 0 g to 2.0 g, and extrapolating by
an acceptable method to Section1 g and + 2.5
g.
(d) If the procedure set forth in paragraph (c)(2) of this section is used to
demonstrate compliance and marginal
conditions exist during flight test with
regard to reversal of primary longitudinal control force, flight tests must be
accomplished from the normal acceleration at which a marginal condition
is found to exist to the applicable limit
specified in paragraph (b)(1) of this section.
(e) During flight tests required by
paragraph (a) of this section, the limit
maneuvering load factors prescribed in
SectionSection 25.333(b) and 25.337, and the maneuvering load factors associated with
probable inadvertent excursions beyond the boundaries of the buffet onset
envelopes determined under Section 25.251(e),

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