208
14 CFR Ch. I (1–1–14 Edition)
§ 23.253
up to V
MO
/M
MO
, except stall buffeting,
which is allowable.
(c) For airplanes with M
D
greater
than M 0.6 or a maximum operating al-
titude greater than 25,000 feet, the posi-
tive maneuvering load factors at which
the onset of perceptible buffeting oc-
curs must be determined with the air-
plane in the cruise configuration for
the ranges of airspeed or Mach number,
weight, and altitude for which the air-
plane is to be certificated. The enve-
lopes of load factor, speed, altitude,
and weight must provide a sufficient
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.
[Amdt. 23–62, 76 FR 75755, Dec. 2, 2011]
§ 23.253
High speed characteristics.
If a maximum operating speed V
MO
/
M
MO
is established under § 23.1505(c),
the following speed increase and recov-
ery characteristics must be met:
(a) 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
speed up to V
MO
/M
MO
. These conditions
and characteristics include gust upsets,
inadvertent control movements, low
stick force gradients in relation to con-
trol friction, passenger movement, lev-
eling off from climb, and descent from
Mach to airspeed limit altitude.
(b) Allowing for pilot reaction time
after occurrence of the effective inher-
ent or artificial speed warning speci-
fied in § 23.1303, it must be shown that
the airplane can be recovered to a nor-
mal attitude and its speed reduced to
V
MO
/M
MO
, without—
(1) Exceptional piloting strength or
skill;
(2) Exceeding V
D
/M
D
, or V
DF
/M
DF
for
turbojets, the maximum speed shown
under § 23.251, or the structural limita-
tions; and
(3) Buffeting that would impair the
pilot’s ability to read the instruments
or to control the airplane for recovery.
(c) There may be no control reversal
about any axis at any speed up to the
maximum speed shown under § 23.251.
Any reversal of elevator control force
or tendency of the airplane to pitch,
roll, or yaw must be mild and readily
controllable, using normal piloting
techniques.
(d)
Maximum speed for stability charac-
teristics, V
FC
/M
FC.
V
FC
/M
FC
may not be
less than a speed midway between V
MO
/
M
MO
and V
DF
/M
DF
except that, for alti-
tudes where Mach number is the lim-
iting factor, M
FC
need not exceed the
Mach number at which effective speed
warning occurs.
[Amdt. 23–7, 34 FR 13087, Aug. 13, 1969; as
amended by Amdt. 23–26, 45 FR 60170, Sept.
11, 1980; Amdt. 23–45, 58 FR 42160, Aug. 6, 1993;
Amdt. 23–50, 61 FR 5192, Feb. 9, 1996; Amdt.
23–62, 76 FR 75755, Dec. 2, 2011]
§ 23.255
Out of trim characteristics.
For airplanes with an M
D
greater
than M 0.6 and that incorporate a
trimmable horizontal stabilizer, the
following requirements for out-of-trim
characteristics apply:
(a) From an initial condition with
the airplane trimmed at cruise speeds
up to V
MO
/M
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 the following:
(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 § 23.655(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 +l g to the positive and negative
values specified in paragraph (c) of this
section, the following apply:
(1) The stick force versus g curve
must have a positive slope at any speed
up to and including V
FC
/M
FC
; and
(2) At speeds between V
FC
/M
FC
and
V
DF
/M
DF,
the direction of the primary
longitudinal control force may not re-
verse.
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