226 

14 CFR Ch. I (1–1–19 Edition) 

§ 25.177 

(v) The airplane trimmed for level 

flight with the power required in para-
graph (b)(1)(iv) of this section. 

(2) With the landing gear retracted at 

low 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

SR

1

, nor 

speeds greater than the minimum 
speed of the applicable speed range pre-
scribed in paragraph (b)(1), nor speeds 
that require a stick force of more than 
50 pounds), with— 

(i) Wing flaps, center of gravity posi-

tion, and weight as specified in para-
graph (b)(1) of this section; 

(ii) Power required for level flight at 

a speed equal to (

V

MO

+ 1.3 

V

SR

1

)/2; and 

(iii) The airplane trimmed for level 

flight with the power required in para-
graph (b)(2)(ii) of this section. 

(3) With the landing gear extended, 

the stick force curve must have a sta-
ble slope at all speeds within a range 
which is the greater of 15 percent of the 
trim speed plus the resulting free re-
turn 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

SR

1

, nor speeds 

greater than 

V

LE,

nor speeds that re-

quire a stick force of more than 50 
pounds), with— 

(i) Wing flap, center of gravity posi-

tion, and weight as specified in para-
graph (b)(1) of this section; 

(ii) 75 percent of maximum contin-

uous power for reciprocating engines 
or, for turbine engines, the maximum 
cruising power selected by the appli-
cant as an operating limitation, except 
that the power need not exceed that re-
quired for level flight at 

V

LE

; and 

(iii) The aircraft trimmed for level 

flight with the power required in para-
graph (b)(3)(ii) of this section. 

(c) 

Approach. 

The stick force curve 

must have a stable slope at speeds be-
tween 

V

SW

and 1.7 

V

SR

1

, with— 

(1) Wing flaps in the approach posi-

tion; 

(2) Landing gear retracted; 
(3) Maximum landing weight; and 

(4) The airplane trimmed at 1.3 

V

SR

1

 

with enough power to maintain level 
flight at this speed. 

(d) 

Landing. 

The stick force curve 

must have a stable slope, and the stick 
force may not exceed 80 pounds, at 
speeds between 

V

SW

and 1.7 

V

SR

0

with— 

(1) Wing flaps in the landing position; 
(2) Landing gear extended; 
(3) Maximum landing weight; 
(4) The airplane trimmed at 1.3 V

SR0

 

with— 

(i) Power or thrust off, and 
(ii) Power or thrust for level flight. 
(5) The airplane trimmed at 1.3 

V

SR

0

 

with power or thrust off. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–7, 30 FR 13117, Oct. 15, 
1965; Amdt. 25–108, 67 FR 70827, Nov. 26, 2002; 
Amdt. 25–115, 69 FR 40527, July 2, 2004] 

§ 25.177

Static lateral-directional sta-

bility. 

(a) The static directional stability 

(as shown by the tendency to recover 
from a skid with the rudder free) must 
be positive for any landing gear and 
flap position and symmetric power con-
dition, at speeds from 1.13 V

SR1

, up to 

V

FE

, V

LE

, or V

FC

/M

FC

(as appropriate for 

the airplane configuration). 

(b) The static lateral stability (as 

shown by the tendency to raise the low 
wing in a sideslip with the aileron con-
trols free) for any landing gear and flap 
position and symmetric power condi-
tion, may not be negative at any air-
speed (except that speeds higher than 
V

FE

need not be considered for flaps ex-

tended configurations nor speeds high-
er than V

LE

for landing gear extended 

configurations) in the following air-
speed ranges: 

(1) From 1.13 V

SR1

to V

MO

/M

MO

. 

(2) From V

MO

/M

MO

to V

FC

/M

FC

, unless 

the divergence is— 

(i) Gradual; 
(ii) Easily recognizable by the pilot; 

and 

(iii) Easily controllable by the pilot. 
(c) The following requirement must 

be met for the configurations and speed 
specified in paragraph (a) of this sec-
tion. In straight, steady sideslips over 
the range of sideslip angles appropriate 
to the operation of the airplane, the ai-
leron and rudder control movements 
and forces must be substantially pro-
portional to the angle of sideslip in a 

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