223
Federal Aviation Administration, DOT
§ 25.161
of bank of not more than 5 degrees.
V
MCL-2
must be established with—
(1) The airplane in the most critical
configuration (or, at the option of the
applicant, each configuration) for ap-
proach and landing with one critical
engine inoperative;
(2) The most unfavorable center of
gravity;
(3) The airplane trimmed for ap-
proach with one critical engine inoper-
ative;
(4) The most unfavorable weight, or,
at the option of the applicant, as a
function of weight;
(5) For propeller airplanes, the pro-
peller of the more critical inoperative
engine in the position it achieves with-
out pilot action, assuming the engine
fails while at the power or thrust nec-
essary to maintain a three degree ap-
proach path angle, and the propeller of
the other inoperative engine feathered;
(6) The power or thrust on the oper-
ating engine(s) necessary to maintain
an approach path angle of three de-
grees when one critical engine is inop-
erative; and
(7) The power or thrust on the oper-
ating engine(s) rapidly changed, imme-
diately after the second critical engine
is made inoperative, from the power or
thrust prescribed in paragraph (g)(6) of
this section to—
(i) Minimum power or thrust; and
(ii) Go-around power or thrust set-
ting.
(h) In demonstrations of V
MCL
and
V
MCL-2
—
(1) The rudder force may not exceed
150 pounds;
(2) The airplane may not exhibit haz-
ardous flight characteristics or require
exceptional piloting skill, alertness, or
strength;
(3) Lateral control must be sufficient
to roll the airplane, from an initial
condition of steady flight, through an
angle of 20 degrees in the direction nec-
essary to initiate a turn away from the
inoperative engine(s), in not more than
5 seconds; and
(4) For propeller airplanes, hazardous
flight characteristics must not be ex-
hibited due to any propeller position
achieved when the engine fails or dur-
ing any likely subsequent movements
of the engine or propeller controls.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–42, 43 FR 2321, Jan. 16,
1978; Amdt. 25–72, 55 FR 29774, July 20, 1990; 55
FR 37607, Sept. 12, 1990; Amdt. 25–84, 60 FR
30749, June 9, 1995; Amdt. 25–108, 67 FR 70827,
Nov. 26, 2002]
T
RIM
§ 25.161
Trim.
(a)
General. Each airplane must meet
the trim requirements of this section
after being trimmed, and without fur-
ther pressure upon, or movement of, ei-
ther the primary controls or their cor-
responding trim controls by the pilot
or the automatic pilot.
(b)
Lateral and directional trim. The
airplane must maintain lateral and di-
rectional trim with the most adverse
lateral displacement of the center of
gravity within the relevant operating
limitations, during normally expected
conditions of operation (including op-
eration at any speed from 1.3
V
SR1
to
V
MO
/M
MO
).
(c)
Longitudinal trim. The airplane
must maintain longitudinal trim dur-
ing—
(1) A climb with maximum contin-
uous power at a speed not more than
1.3
V
SR1
, with the landing gear re-
tracted, and the flaps (i) retracted and
(ii) in the takeoff position;
(2) Either a glide with power off at a
speed not more than 1.3 V
SR1
, or an ap-
proach within the normal range of ap-
proach speeds appropriate to the
weight and configuration with power
settings corresponding to a 3 degree
glidepath, whichever is the most se-
vere, with the landing gear extended,
the wing flaps (i) retracted and (ii) ex-
tended, and with the most unfavorable
combination of center of gravity posi-
tion and weight approved for landing;
and
(3) Level flight at any speed from 1.3
V
SR1
, to
V
MO
/M
MO,
with the landing gear
and flaps retracted, and from 1.3
V
SR1
to
V
LE
with the landing gear extended.
(d)
Longitudinal, directional, and lat-
eral trim. The airplane must maintain
longitudinal, directional, and lateral
trim (and for the lateral trim, the
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14 CFR Ch. I (1–1–24 Edition)
§ 25.171
angle of bank may not exceed five de-
grees) at 1.3
V
SR1
during climbing flight
with—
(1) The critical engine inoperative;
(2) The remaining engines at max-
imum continuous power; and
(3) The landing gear and flaps re-
tracted.
(e) Airplanes with four or more en-
gines. Each airplane with four or more
engines must also maintain trim in
rectilinear flight with the most unfa-
vorable center of gravity and at the
climb speed, configuration, and power
required by § 25.123(a) for the purpose of
establishing the en route flight paths
with two engines inoperative.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5671, Apr. 8,
1970; Amdt. 25–38, 41 FR 55466, Dec. 20, 1976;
Amdt. 25–108, 67 FR 70827, Nov. 26, 2002;
Amdt. 25–115, 69 FR 40527, July 2, 2004]
S
TABILITY
§ 25.171
General.
The airplane must be longitudinally,
directionally, and laterally stable in
accordance with the provisions of
§§ 25.173 through 25.177. In addition,
suitable stability and control feel
(static stability) is required in any con-
dition normally encountered in service,
if flight tests show it is necessary for
safe operation.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–7, 30 FR 13117, Oct. 15,
1965]
§ 25.173
Static longitudinal stability.
Under the conditions specified in
§ 25.175, the characteristics of the eleva-
tor control forces (including friction)
must be as follows:
(a) A pull must be required to obtain
and maintain speeds below the speci-
fied trim speed, and a push must be re-
quired to obtain and maintain speeds
above the specified trim speed. This
must be shown at any speed that can be
obtained except speeds higher than the
landing gear or wing flap operating
limit speeds or
V
FC
/M
FC,
whichever is
appropriate, or lower than the min-
imum speed for steady unstalled flight.
(b) The airspeed must return to with-
in 10 percent of the original trim speed
for the climb, approach, and landing
conditions specified in § 25.175 (a), (c),
and (d), and must return to within 7.5
percent of the original trim speed for
the cruising condition specified in
§ 25.175(b), when the control force is
slowly released from any speed within
the range specified in paragraph (a) of
this section.
(c) The average gradient of the stable
slope of the stick force versus speed
curve may not be less than 1 pound for
each 6 knots.
(d) Within the free return speed range
specified in paragraph (b) of this sec-
tion, it is permissible for the airplane,
without control forces, to stabilize on
speeds above or below the desired trim
speeds if exceptional attention on the
part of the pilot is not required to re-
turn to and maintain the desired trim
speed and altitude.
[Amdt. 25–7, 30 FR 13117, Oct. 15, 1965]
§ 25.175
Demonstration of static longi-
tudinal stability.
Static longitudinal stability must be
shown as follows:
(a)
Climb. The stick force curve must
have a stable slope at speeds between
85 and 115 percent of the speed at which
the airplane—
(1) Is trimmed, with—
(i) Wing flaps retracted;
(ii) Landing gear retracted;
(iii) Maximum takeoff weight; and
(iv) 75 percent of maximum contin-
uous power for reciprocating engines or
the maximum power or thrust selected
by the applicant as an operating limi-
tation for use during climb for turbine
engines; and
(2) Is trimmed at the speed for best
rate-of-climb except that the speed
need not be less than 1.3
V
SR1
.
(b)
Cruise. Static longitudinal sta-
bility must be shown in the cruise con-
dition as follows:
(1) With the landing gear retracted at
high speed, the stick force curve must
have a stable slope at all speeds within
a range which is the greater of 15 per-
cent of the trim speed plus the result-
ing free return speed range, or 50 knots
plus the resulting free return speed
range, above and below the trim speed
(except that the speed range need not
include speeds less than 1.3
V
SR1
, nor
speeds greater than
V
FC
/M
FC,
nor speeds
that require a stick force of more than
50 pounds), with—
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