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 

VerDate Sep<11>2014 

09:06 Jun 28, 2024

Jkt 262046

PO 00000

Frm 00253

Fmt 8010

Sfmt 8010

Y:\SGML\262046.XXX

262046

jspears on DSK121TN23PROD with CFR