270 

14 CFR Ch. I (1–1–14 Edition) 

§ 23.904 

established and included in the Air-
plane Flight Manual, approved manual 
material, or applicable operating plac-
ards. Means must be provided for— 

(i) Restarting any engine of a multi-

engine airplane in flight, and 

(ii) Stopping any engine in flight, 

after engine failure, if continued en-
gine rotation would cause a hazard to 
the airplane. 

(2) In addition, for commuter cat-

egory airplanes, the following apply: 

(i) 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. 

(ii) If hydraulic propeller feathering 

systems are used for this purpose, the 
feathering lines must be at least fire 
resistant under the operating condi-
tions that may be expected to exist 
during feathering. 

(e) 

Starting and stopping (turbine en-

gine). 

Turbine engine installations 

must comply with the following: 

(1) The design of the installation 

must be such that risk of fire or me-
chanical damage to the engine or the 
airplane, as a result of starting the en-
gine in any conditions in which start-
ing is to be permitted, is reduced to a 
minimum. Any techniques and associ-
ated limitations must be established 
and included in the Airplane Flight 
Manual, approved manual material, or 
applicable operating placards. 

(2) There must be means for stopping 

combustion within any engine and for 
stopping the rotation of any engine if 
continued rotation would cause a haz-
ard to the airplane. Each component of 
the engine stopping system located in 
any fire zone must be fire resistant. If 
hydraulic propeller feathering systems 
are used for stopping the engine, the 
hydraulic feathering lines or hoses 
must be fire resistant. 

(3) It must be possible to restart an 

engine in flight. Any techniques and 
associated limitations must be estab-
lished and included in the Airplane 
Flight Manual, approved manual mate-
rial, or applicable operating placards. 

(4) It must be demonstrated in flight 

that when restarting engines following 
a false start, all fuel or vapor is dis-
charged in such a way that it does not 
constitute a fire hazard. 

(f) 

Restart envelope. An altitude and 

airspeed envelope must be established 
for the airplane for in-flight engine re-
starting and each installed engine 
must have a restart capability within 
that envelope. 

(g) 

Restart capability. For turbine en-

gine powered airplanes, if the min-
imum windmilling speed of the en-
gines, following the in-flight shutdown 
of all engines, is insufficient to provide 
the necessary electrical power for en-
gine ignition, a power source inde-
pendent of the engine-driven electrical 
power generating system must be pro-
vided to permit in-flight engine igni-
tion for restarting. 

[Amdt. 23–14, 38 FR 31822, Nov. 19, 1973] 

E

DITORIAL

N

OTE

: For F

EDERAL

R

EGISTER

ci-

tations affecting § 23.903, see the List of CFR 
Sections Affected, which appears in the 
Finding Aids section of the printed volume 
and at 

www.fdsys.gov. 

§ 23.904

Automatic power reserve sys-

tem. 

If installed, an automatic power re-

serve (APR) system that automatically 
advances the power or thrust on the op-
erating engine(s), when any engine 
fails during takeoff, must comply with 
appendix H of this part. 

[Doc. No. 26344, 58 FR 18970, Apr. 9, 1993] 

§ 23.905

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) Each featherable propeller must 

have a means to unfeather it in flight. 

(d) The propeller blade pitch control 

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

(e) All areas of the airplane forward 

of the pusher propeller that are likely 
to accumulate and shed ice into the 
propeller disc during any operating 
condition must be suitably protected 
to prevent ice formation, or it must be 
shown that any ice shed into the pro-
peller disc will not create a hazardous 
condition. 

(f) Each pusher propeller must be 

marked so that the disc is conspicuous 

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