Federal Aviation Administration, DOT

Section 25.175

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]

[Amdt. 25-7, 30 FR 13117, Oct. 15, 1965]

STABILITY

Section 25.175 Demonstration of static longitudinal stability.

Section 25.171 General.
The airplane must be longitudinally,
directionally, and laterally stable in
accordance with the provisions of
SectionSection 25.173 through 25.177. In addition,
suitable stability and control feel
(static stability) is required in any condition normally encountered in service,
if flight tests show it is necessary for
safe operation.

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 continuous power for reciprocating engines or
the maximum power or thrust selected
by the applicant as an operating limitation 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 VSR1.
(b) Cruise. Static longitudinal stability must be shown in the cruise condition 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 percent of the trim speed plus the resulting 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 VSR1, nor
speeds greater than VFC/MFC, nor speeds
that require a stick force of more than
50 pounds), with - 
(i) The wing flaps retracted;
(ii) The center of gravity in the most
adverse position (see Section 25.27);
(iii) The most critical weight between the maximum takeoff and maximum landing weights;
(iv) 75 percent of maximum continuous power for reciprocating engines or
for turbine engines, the maximum
cruising power selected by the applicant as an operating limitation (see
Section 25.1521), except that the power need
not exceed that required at VMO/MMO;
and

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-7, 30 FR 13117, Oct. 15,
1965]

spaschal on DSK3GDR082PROD with CFR

speeds above or below the desired trim
speeds if exceptional attention on the
part of the pilot is not required to return to and maintain the desired trim
speed and altitude.

Section 25.173 Static longitudinal stability.
Under the conditions specified in
Section 25.175, the characteristics of the elevator control forces (including friction)
must be as follows:
(a) A pull must be required to obtain
and maintain speeds below the specified trim speed, and a push must be required 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 VFC/MFC, whichever is
appropriate, or lower than the minimum speed for steady unstalled flight.
(b) The airspeed must return to within 10 percent of the original trim speed
for the climb, approach, and landing
conditions specified in Section 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
Section 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 section, it is permissible for the airplane,
without control forces, to stabilize on

225

VerDate Sep<11>2014

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00235

Fmt 8010

Sfmt 8010

Y:\SGML\247046.XXX

247046