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310 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.901 

as not to endanger the airplane, per-
sonnel, or operation of the installed 
electrical/electronic systems. 

[Amdt. 25–123, 72 FR 63405, Nov. 8, 2007] 

Subpart E—Powerplant 

G

ENERAL

 

§ 25.901

Installation. 

(a) For the purpose of this part, the 

airplane powerplant installation in-
cludes each component that— 

(1) Is necessary for propulsion; 
(2) Affects the control of the major 

propulsive units; or 

(3) Affects the safety of the major 

propulsive units between normal in-
spections or overhauls. 

(b) For each powerplant— 
(1) The installation must comply 

with— 

(i) The installation instructions pro-

vided under §§ 33.5 and 35.3 of this chap-
ter; and 

(ii) The applicable provisions of this 

subpart; 

(2) The components of the installa-

tion must be constructed, arranged, 
and installed so as to ensure their con-
tinued safe operation between normal 
inspections or overhauls; 

(3) The installation must be acces-

sible for necessary inspections and 
maintenance; and 

(4) The major components of the in-

stallation must be electrically bonded 
to the other parts of the airplane. 

(c) For each powerplant and auxiliary 

power unit installation, it must be es-
tablished that no single failure or mal-
function or probable combination of 
failures will jeopardize the safe oper-
ation of the airplane except that the 
failure of structural elements need not 
be considered if the probability of such 
failure is extremely remote. 

(d) Each auxiliary power unit instal-

lation must meet the applicable provi-
sions of this subpart. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5676, Apr. 8, 
1970; Amdt. 25–40, 42 FR 15042, Mar. 17, 1977; 
Amdt. 25–46, 43 FR 50597, Oct. 30, 1978; Amdt. 
25–126, 73 FR 63345, Oct. 24, 2008] 

§ 25.903

Engines. 

(a) 

Engine type certificate. (1) Each en-

gine must have a type certificate and 

must meet the applicable requirements 
of part 34 of this chapter. 

(2) Each turbine engine must comply 

with one of the following: 

(i) Sections 33.76, 33.77 and 33.78 of 

this chapter in effect on December 13, 
2000, or as subsequently amended; or 

(ii) Sections 33.77 and 33.78 of this 

chapter in effect on April 30, 1998, or as 
subsequently amended before Decem-
ber 13, 2000; or 

(iii) Comply with § 33.77 of this chap-

ter in effect on October 31, 1974, or as 
subsequently amended prior to April 
30, 1998, unless that engine’s foreign ob-
ject ingestion service history has re-
sulted in an unsafe condition; or 

(iv) Be shown to have a foreign object 

ingestion service history in similar in-
stallation locations which has not re-
sulted in any unsafe condition. 

N

OTE

: § 33.77 of this chapter in effect on Oc-

tober 31, 1974, was published in 14 CFR parts 
1 to 59, Revised as of January 1, 1975. See 39 
FR 35467, October 1, 1974. 

(3) Each turbine engine must comply 

with one of the following paragraphs: 

(i) Section 33.68 of this chapter in ef-

fect on January 5, 2015, or as subse-
quently amended; or 

(ii) Section 33.68 of this chapter in ef-

fect on March 26, 1984, or as subse-
quently amended before January 5, 
2015, unless that engine’s ice accumula-
tion service history has resulted in an 
unsafe condition; or 

(iii) Section 33.68 of this chapter in 

effect on October 31, 1974, or as subse-
quently amended prior to February 23, 
1984, unless that engine’s ice accumula-
tion service history has resulted in an 
unsafe condition; or 

(iv) Be shown to have an ice accumu-

lation service history in similar instal-
lation locations which has not resulted 
in any unsafe conditions. 

(b) 

Engine isolation. The powerplants 

must be arranged and isolated from 
each other to allow operation, in at 
least one configuration, so that the 
failure or malfunction of any engine, or 
of any system that can affect the en-
gine, will not— 

(1) Prevent the continued safe oper-

ation of the remaining engines; or 

(2) Require immediate action by any 

crewmember for continued safe oper-
ation. 

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311 

Federal Aviation Administration, DOT 

§ 25.907 

(c) 

Control of engine rotation. There 

must be means for stopping the rota-
tion of any engine individually in 
flight, except that, for turbine engine 
installations, the means for stopping 
the rotation of any engine need be pro-
vided only where continued rotation 
could jeopardize the safety of the air-
plane. Each component of the stopping 
system on the engine side of the fire-
wall that might be exposed to fire must 
be at least fire-resistant. If hydraulic 
propeller feathering systems are used 
for this purpose, the feathering lines 
must be at least fire resistant under 
the operating conditions that may be 
expected to exist during feathering. 

(d) 

Turbine engine installations. For 

turbine engine installations— 

(1) Design precautions must be taken 

to minimize the hazards to the airplane 
in the event of an engine rotor failure 
or of a fire originating within the en-
gine which burns through the engine 
case. 

(2) The powerplant systems associ-

ated with engine control devices, sys-
tems, and instrumentation, must be de-
signed to give reasonable assurance 
that those engine operating limitations 
that adversely affect turbine rotor 
structural integrity will not be exceed-
ed in service. 

(e) 

Restart capability. (1) Means to re-

start any engine in flight must be pro-
vided. 

(2) An altitude and airspeed envelope 

must be established for in-flight engine 
restarting, and each engine must have 
a restart capability within that enve-
lope. 

(3) For turbine engine powered air-

planes, if the minimum windmilling 
speed of the engines, following the 
inflight shutdown of all engines, is in-
sufficient to provide the necessary 
electrical power for engine ignition, a 
power source independent of the en-
gine-driven electrical power generating 
system must be provided to permit in- 
flight engine ignition for restarting. 

(f) 

Auxiliary Power Unit. Each auxil-

iary power unit must be approved or 

meet the requirements of the category 
for its intended use. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5676, Apr. 8, 
1970; Amdt. 25–40, 42 FR 15042, Mar. 17, 1977; 
Amdt. 25–57, 49 FR 6848, Feb. 23, 1984; Amdt. 
25–72, 55 FR 29784, July 20, 1990; Amdt. 25–73, 
55 FR 32861, Aug. 10, 1990; Amdt. 25–94, 63 FR 
8848, Feb. 23, 1998; Amdt. 25–95, 63 FR 14798, 
Mar. 26, 1998; Amdt. 25–100, 65 FR 55854, Sept. 
14, 2000; Amdt. 25–140, 79 FR 65525, Nov. 4, 
2014; Amdt. No. 25–148, 87 FR 75710, Dec. 9, 
2022; 88 FR 2813, Jan. 18, 2023] 

§ 25.904

Automatic takeoff thrust con-

trol system (ATTCS). 

Each applicant seeking approval for 

installation of an engine power control 
system that automatically resets the 
power or thrust on the operating en-
gine(s) when any engine fails during 
the takeoff must comply with the re-
quirements of appendix I of this part. 

[Amdt. 25–62, 52 FR 43156, Nov. 9, 1987] 

§ 25.905

Propellers. 

(a) Each propeller must have a type 

certificate. 

(b) Engine power and propeller shaft 

rotational speed may not exceed the 
limits for which the propeller is certifi-
cated. 

(c) The propeller blade pitch control 

system must meet the requirements of 
§§ 35.21, 35.23, 35.42 and 35.43 of this 
chapter. 

(d) Design precautions must be taken 

to minimize the hazards to the airplane 
in the event a propeller blade fails or is 
released by a hub failure. The hazards 
which must be considered include dam-
age to structure and vital systems due 
to impact of a failed or released blade 
and the unbalance created by such fail-
ure or release. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–54, 45 FR 60173, Sept. 
11, 1980; Amdt. 25–57, 49 FR 6848, Feb. 23, 1984; 
Amdt. 25–72, 55 FR 29784, July 20, 1990; Amdt. 
25–126, 73 FR 63345, Oct. 24, 2008] 

§ 25.907

Propeller vibration and fa-

tigue. 

This section does not apply to fixed- 

pitch wood propellers of conventional 
design. 

(a) The applicant must determine the 

magnitude of the propeller vibration 
stresses or loads, including any stress 

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