background image

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 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00233

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR

background image

224 

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— 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00234

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR