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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