244 

14 CFR Ch. I (1–1–19 Edition) 

§ 25.363 

(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 
1.67 for airplanes to be approved for op-
eration above 45,000 feet, omitting 
other loads. 

(e) Any structure, component or part, 

inside or outside a pressurized com-
partment, the failure of which could 
interfere with continued safe flight and 
landing, must be designed to withstand 
the effects of a sudden release of pres-
sure through an opening in any com-
partment at any operating altitude re-
sulting from each of the following con-
ditions: 

(1) The penetration of the compart-

ment by a portion of an engine fol-
lowing an engine disintegration; 

(2) Any opening in any pressurized 

compartment up to the size H

o

in 

square feet; however, small compart-
ments may be combined with an adja-
cent pressurized compartment and both 
considered as a single compartment for 
openings that cannot reasonably be ex-
pected to be confined to the small com-
partment. The size H

o

must be com-

puted by the following formula: 

H

o

= PA

s

 

where, 

H

o

= Maximum opening in square feet, need 

not exceed 20 square feet. 

P = (A

s

/6240) + .024 

A

s

= Maximum cross-sectional area of the 

pressurized shell normal to the longitu-
dinal axis, in square feet; and 

(3) The maximum opening caused by 

airplane or equipment failures not 
shown to be extremely improbable. 

(f) In complying with paragraph (e) of 

this section, the fail-safe features of 
the design may be considered in deter-
mining the probability of failure or 
penetration and probable size of open-
ings, provided that possible improper 
operation of closure devices and inad-
vertent door openings are also consid-
ered. Furthermore, the resulting dif-
ferential pressure loads must be com-
bined in a rational and conservative 
manner with 1–g level flight loads and 
any loads arising from emergency de-
pressurization conditions. These loads 
may be considered as ultimate condi-
tions; however, any deformations asso-
ciated with these conditions must not 
interfere with continued safe flight and 
landing. The pressure relief provided by 
intercompartment venting may also be 
considered. 

(g) Bulkheads, floors, and partitions 

in pressurized compartments for occu-
pants must be designed to withstand 

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