title-14-part-25-sec25-365

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.

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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244

14 CFR Ch. I (1–1–24 Edition)

§ 25.367

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

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

must be com-

puted by the following formula:

= PA

where,

= Maximum opening in square feet, need

not exceed 20 square feet.

P = (A

/6240) + .024

= 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)(1) Except as provided in para-

graph (g)(2) of this section, bulkheads,
floors, and partitions in pressurized
compartments for occupants must be
designed to withstand the conditions
specified in paragraph (e) of this sec-
tion. In addition, reasonable design
precautions must be taken to minimize
the probability of parts becoming de-
tached and injuring occupants while in
their seats.

(2) Partitions adjacent to the opening

specified in paragraph (e)(2) of this sec-
tion need not be designed to withstand
that condition provided—

(i) Failure of the partition would not

interfere with continued safe flight and
landing; and

(ii) Designing the partition to with-

stand the condition specified in para-
graph (e)(2) of this section would be im-
practical.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–54, 45 FR 60172, Sept.
11, 1980; Amdt. 25–71, 55 FR 13477, Apr. 10,
1990; Amdt. 25–72, 55 FR 29776, July 20, 1990;
Amdt. 25–87, 61 FR 28695, June 5, 1996; Amdt.
No. 25–149, 88 FR 38382, June 13, 2023]

§ 25.367

Unsymmetrical loads due to

engine failure.

(a) The airplane must be designed for

the unsymmetrical loads resulting
from the failure of the critical engine.
Turbopropeller airplanes must be de-
signed for the following conditions in
combination with a single malfunction
of the propeller drag limiting system,
considering the probable pilot correc-
tive action on the flight controls:

(1) At speeds between

and

the

loads resulting from power failure be-
cause of fuel flow interruption are con-
sidered to be limit loads.

(2) At speeds between

and

the

loads resulting from the disconnection
of the engine compressor from the tur-
bine or from loss of the turbine blades
are considered to be ultimate loads.

(3) The time history of the thrust

decay and drag build-up occurring as a
result of the prescribed engine failures
must be substantiated by test or other
data applicable to the particular en-
gine-propeller combination.

(4) The timing and magnitude of the

probable pilot corrective action must