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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243 

Federal Aviation Administration, DOT 

§ 25.365 

accounting for propeller control sys-
tem malfunction, including quick 
feathering, acting simultaneously with 
1g level flight loads. In the absence of 
a rational analysis, a factor of 1.6 must 
be used. 

(2) The limit engine torque to be con-

sidered under paragraph (a)(1) of this 
section must be obtained by— 

(i) For turbopropeller installations, 

multiplying mean engine torque for the 
specified power/thrust and speed by a 
factor of 1.25; 

(ii) For other turbine engines, the 

limit engine torque must be equal to 
the maximum accelerating torque for 
the case considered. 

(3) The engine mounts, pylons, and 

adjacent supporting airframe structure 
must be designed to withstand 1g level 
flight loads acting simultaneously with 
the limit engine torque loads imposed 
by each of the following conditions to 
be considered separately: 

(i) Sudden maximum engine decelera-

tion due to malfunction or abnormal 
condition; and 

(ii) The maximum acceleration of en-

gine. 

(b) For auxiliary power unit installa-

tions, the power unit mounts and adja-
cent supporting airframe structure 
must be designed to withstand 1g level 
flight loads acting simultaneously with 
the limit torque loads imposed by each 
of the following conditions to be con-
sidered separately: 

(1) Sudden maximum auxiliary power 

unit deceleration due to malfunction, 
abnormal condition, or structural fail-
ure; and 

(2) The maximum acceleration of the 

auxiliary power unit. 

[Amdt. 25–141, 79 FR 73468, Dec. 11, 2014] 

§ 25.362

Engine failure loads. 

(a) For engine mounts, pylons, and 

adjacent supporting airframe struc-
ture, an ultimate loading condition 
must be considered that combines 1g 
flight loads with the most critical 
transient dynamic loads and vibra-
tions, as determined by dynamic anal-
ysis, resulting from failure of a blade, 
shaft, bearing or bearing support, or 
bird strike event. Any permanent de-
formation from these ultimate load 
conditions must not prevent continued 
safe flight and landing. 

(b) The ultimate loads developed 

from the conditions specified in para-
graph (a) of this section are to be— 

(1) Multiplied by a factor of 1.0 when 

applied to engine mounts and pylons; 
and 

(2) Multiplied by a factor of 1.25 when 

applied to adjacent supporting air-
frame structure. 

[Amdt. 25–141, 79 FR 73468, Dec. 11, 2014] 

§ 25.363

Side load on engine and auxil-

iary power unit mounts. 

(a) Each engine and auxiliary power 

unit mount and its supporting struc-
ture must be designed for a limit load 
factor in lateral direction, for the side 
load on the engine and auxiliary power 
unit mount, at least equal to the max-
imum load factor obtained in the yaw-
ing conditions but not less than— 

(1) 1.33; or 
(2) One-third of the limit load factor 

for flight condition A as prescribed in 
§ 25.333(b). 

(b) The side load prescribed in para-

graph (a) of this section may be as-
sumed to be independent of other flight 
conditions. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5672, Apr. 8, 
1970; Amdt. 25–91, 62 FR 40704, July 29, 1997] 

§ 25.365

Pressurized compartment 

loads. 

For airplanes with one or more pres-

surized compartments the following 
apply: 

(a) The airplane structure must be 

strong enough to withstand the flight 
loads combined with pressure differen-
tial loads from zero up to the max-
imum relief valve setting. 

(b) The external pressure distribution 

in flight, and stress concentrations and 
fatigue effects must be accounted for. 

(c) If landings may be made with the 

compartment pressurized, landing 
loads must be combined with pressure 
differential loads from zero up to the 
maximum allowed during landing. 

(d) The airplane structure must be 

designed to be able to withstand the 
pressure differential loads cor-
responding to the maximum relief 
valve setting multiplied by a factor of 
1.33 for airplanes to be approved for op-
eration to 45,000 feet or by a factor of 

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