470 

14 CFR Ch. I (1–1–14 Edition) 

§ 25.904 

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] 

§ 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 
peaks and resonant conditions, 
throughout the operational envelope of 
the airplane by either: 

(1) Measurement of stresses or loads 

through direct testing or analysis 
based on direct testing of the propeller 
on the airplane and engine installation 
for which approval is sought; or 

(2) Comparison of the propeller to 

similar propellers installed on similar 
airplane installations for which these 
measurements have been made. 

(b) The applicant must demonstrate 

by tests, analysis based on tests, or 
previous experience on similar designs 
that the propeller does not experience 
harmful effects of flutter throughout 
the operational envelope of the air-
plane. 

(c) The applicant must perform an 

evaluation of the propeller to show 
that failure due to fatigue will be 
avoided throughout the operational life 
of the propeller using the fatigue and 
structural data obtained in accordance 
with part 35 of this chapter and the vi-
bration data obtained from compliance 
with paragraph (a) of this section. For 
the purpose of this paragraph, the pro-
peller includes the hub, blades, blade 
retention component and any other 
propeller component whose failure due 
to fatigue could be catastrophic to the 
airplane. This evaluation must include: 

(1) The intended loading spectra in-

cluding all reasonably foreseeable pro-
peller vibration and cyclic load pat-
terns, identified emergency conditions, 
allowable overspeeds and overtorques, 
and the effects of temperatures and hu-
midity expected in service. 

(2) The effects of airplane and pro-

peller operating and airworthiness lim-
itations. 

[Amdt. 25–126, 73 FR 63345, Oct. 24, 2008] 

§ 25.925

Propeller clearance. 

Unless smaller clearances are sub-

stantiated, propeller clearances with 
the airplane at maximum weight, with 

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