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Federal Aviation Administration, DOT 

§ 25.905 

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-

(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 

(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-

(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-

(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, 

§ 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


(a) Each propeller must have a type 


(b) Engine power and propeller shaft 

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

(c) The propeller blade pitch control 

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

(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 

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