241 

Federal Aviation Administration, DOT 

§ 25.351 

taking into account, as separate condi-
tions, the effects of— 

(1) Propeller slipstream cor-

responding to maximum continuous 
power at the design flap speeds 

V

F,

and 

with takeoff power at not less than 1.4 
times the stalling speed for the par-
ticular flap position and associated 
maximum weight; and 

(2) A head-on gust of 25 feet per sec-

ond velocity (EAS). 

(c) If flaps or other high lift devices 

are to be used in en route conditions, 
and with flaps in the appropriate posi-
tion at speeds up to the flap design 
speed chosen for these conditions, the 
airplane is assumed to be subjected to 
symmetrical maneuvers and gusts 
within the range determined by— 

(1) Maneuvering to a positive limit 

load factor as prescribed in § 25.337(b); 
and 

(2) The vertical gust and turbulence 

conditions prescribed in § 25.341(a) and 
(b). 

(d) The airplane must be designed for 

a maneuvering load factor of 1.5 g at 
the maximum take-off weight with the 
wing-flaps and similar high lift devices 
in the landing configurations. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–46, 43 FR 50595, Oct. 30, 
1978; Amdt. 25–72, 55 FR 37607, Sept. 17, 1990; 
Amdt. 25–86, 61 FR 5221, Feb. 9, 1996; Amdt. 
25–91, 62 FR 40704, July 29, 1997; Amdt. 25–141, 
79 FR 73468, Dec. 11, 2014] 

§ 25.349

Rolling conditions. 

The airplane must be designed for 

loads resulting from the rolling condi-
tions specified in paragraphs (a) and (b) 
of this section. Unbalanced aero-
dynamic moments about the center of 
gravity must be reacted in a rational 
or conservative manner, considering 
the principal masses furnishing the re-
acting inertia forces. 

(a) 

Maneuvering. The following condi-

tions, speeds, and aileron deflections 
(except as the deflections may be lim-
ited by pilot effort) must be considered 
in combination with an airplane load 
factor of zero and of two-thirds of the 
positive maneuvering factor used in de-
sign. In determining the required aile-
ron deflections, the torsional flexi-
bility of the wing must be considered 
in accordance with § 25.301(b): 

(1) Conditions corresponding to 

steady rolling velocities must be inves-
tigated. In addition, conditions cor-
responding to maximum angular accel-
eration must be investigated for air-
planes with engines or other weight 
concentrations outboard of the fuse-
lage. For the angular acceleration con-
ditions, zero rolling velocity may be 
assumed in the absence of a rational 
time history investigation of the ma-
neuver. 

(2) At 

V

A,

a sudden deflection of the 

aileron to the stop is assumed. 

(3) At 

V

C,

the aileron deflection must 

be that required to produce a rate of 
roll not less than that obtained in 
paragraph (a)(2) of this section. 

(4) At 

V

D,

the aileron deflection must 

be that required to produce a rate of 
roll not less than one-third of that in 
paragraph (a)(2) of this section. 

(b) 

Unsymmetrical gusts. The airplane 

is assumed to be subjected to unsym-
metrical vertical gusts in level flight. 
The resulting limit loads must be de-
termined from either the wing max-
imum airload derived directly from 
§ 25.341(a), or the wing maximum air-
load derived indirectly from the 
vertical load factor calculated from 
§ 25.341(a). It must be assumed that 100 
percent of the wing air load acts on one 
side of the airplane and 80 percent of 
the wing air load acts on the other 
side. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5672, Apr. 8, 
1970; Amdt. 25–86, 61 FR 5222, Feb. 9, 1996; 
Amdt. 25–94, 63 FR 8848, Feb. 23, 1998] 

§ 25.351

Yaw maneuver conditions. 

The airplane must be designed for 

loads resulting from the yaw maneuver 
conditions specified in paragraphs (a) 
through (d) of this section at speeds 
from V

MC

to V

D

. Unbalanced aero-

dynamic moments about the center of 
gravity must be reacted in a rational 
or conservative manner considering the 
airplane inertia forces. In computing 
the tail loads the yawing velocity may 
be assumed to be zero. 

(a) With the airplane in unacceler-

ated flight at zero yaw, it is assumed 
that the cockpit rudder control is sud-
denly displaced to achieve the result-
ing rudder deflection, as limited by: 

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242 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.353 

(1) The control system on control 

surface stops; or 

(2) A limit pilot force of 300 pounds 

from V

MC

to V

A

and 200 pounds from V

C

/ 

M

C

to V

D

/M

D

, with a linear variation 

between V

A

and V

C

/M

C

. 

(b) With the cockpit rudder control 

deflected so as always to maintain the 
maximum rudder deflection available 
within the limitations specified in 
paragraph (a) of this section, it is as-
sumed that the airplane yaws to the 
overswing sideslip angle. 

(c) With the airplane yawed to the 

static equilibrium sideslip angle, it is 
assumed that the cockpit rudder con-
trol is held so as to achieve the max-
imum rudder deflection available with-
in the limitations specified in para-
graph (a) of this section. 

(d) With the airplane yawed to the 

static equilibrium sideslip angle of 
paragraph (c) of this section, it is as-
sumed that the cockpit rudder control 
is suddenly returned to neutral. 

[Amdt. 25–91, 62 FR 40704, July 29, 1997] 

§ 25.353

Rudder control reversal condi-

tions. 

Airplanes with a powered rudder con-

trol surface or surfaces must be de-
signed for loads, considered to be ulti-
mate, resulting from the yaw maneu-
ver conditions specified in paragraphs 
(a) through (e) of this section at speeds 
from V

MC

to V

C

/M

C

. Any permanent de-

formation resulting from these ulti-
mate load conditions must not prevent 
continued safe flight and landing. The 
applicant must evaluate these condi-
tions with the landing gear retracted 
and speed brakes (and spoilers when 
used as speed brakes) retracted. The 
applicant must evaluate the effects of 
flaps, flaperons, or any other aero-
dynamic devices when used as flaps, 
and slats-extended configurations, if 
they are used in en route conditions. 
Unbalanced aerodynamic moments 
about the center of gravity must be re-
acted in a rational or conservative 
manner considering the airplane iner-
tia forces. In computing the loads on 
the airplane, the yawing velocity may 
be assumed to be zero. The applicant 
must assume a pilot force of 200 pounds 
when evaluating each of the following 
conditions: 

(a) With the airplane in unacceler-

ated flight at zero yaw, the flightdeck 
rudder control is suddenly and fully 
displaced to achieve the resulting rud-
der deflection, as limited by the con-
trol system or the control surface 
stops. 

(b) With the airplane yawed to the 

overswing sideslip angle, the flightdeck 
rudder control is suddenly and fully 
displaced in the opposite direction, as 
limited by the control system or con-
trol surface stops. 

(c) With the airplane yawed to the 

opposite overswing sideslip angle, the 
flightdeck rudder control is suddenly 
and fully displaced in the opposite di-
rection, as limited by the control sys-
tem or control surface stops. 

(d) With the airplane yawed to the 

subsequent overswing sideslip angle, 
the flightdeck rudder control is sud-
denly and fully displaced in the oppo-
site direction, as limited by the control 
system or control surface stops. 

(e) With the airplane yawed to the 

opposite overswing sideslip angle, the 
flightdeck rudder control is suddenly 
returned to neutral. 

[Amdt. No. 25–147, 87 FR 71210, Nov. 22, 2022] 

S

UPPLEMENTARY

C

ONDITIONS

 

§ 25.361

Engine and auxiliary power 

unit torque. 

(a) For engine installations— 
(1) Each engine mount, pylon, and ad-

jacent supporting airframe structures 
must be designed for the effects of— 

(i) A limit engine torque cor-

responding to takeoff power/thrust and, 
if applicable, corresponding propeller 
speed, acting simultaneously with 75% 
of the limit loads from flight condition 
A of § 25.333(b); 

(ii) A limit engine torque cor-

responding to the maximum contin-
uous power/thrust and, if applicable, 
corresponding propeller speed, acting 
simultaneously with the limit loads 
from flight condition A of § 25.333(b); 
and 

(iii) For turbopropeller installations 

only, in addition to the conditions 
specified in paragraphs (a)(1)(i) and (ii) 
of this section, a limit engine torque 
corresponding to takeoff power and 
propeller speed, multiplied by a factor 

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