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Federal Aviation Administration, DOT 

§ 25.1027 

(3) The breather does not discharge 

into the engine air induction system. 

§ 25.1019

Oil strainer or filter. 

(a) Each turbine engine installation 

must incorporate an oil strainer or fil-
ter through which all of the engine oil 
flows and which meets the following re-

(1) Each oil strainer or filter that has 

a bypass must be constructed and in-
stalled so that oil will flow at the nor-
mal rate through the rest of the sys-
tem with the strainer or filter com-
pletely blocked. 

(2) The oil strainer or filter must 

have the capacity (with respect to op-
erating limitations established for the 
engine) to ensure that engine oil sys-
tem functioning is not impaired when 
the oil is contaminated to a degree 
(with respect to particle size and den-
sity) that is greater than that estab-
lished for the engine under Part 33 of 
this chapter. 

(3) The oil strainer or filter, unless it 

is installed at an oil tank outlet, must 
incorporate an indicator that will indi-
cate contamination before it reaches 
the capacity established in accordance 
with paragraph (a)(2) of this section. 

(4) The bypass of a strainer or filter 

must be constructed and installed so 
that the release of collected contami-
nants is minimized by appropriate lo-
cation of the bypass to ensure that col-
lected contaminants are not in the by-
pass flow path. 

(5) An oil strainer or filter that has 

no bypass, except one that is installed 
at an oil tank outlet, must have a 
means to connect it to the warning 
system required in § 25.1305(c)(7). 

(b) Each oil strainer or filter in a 

powerplant installation using recipro-
cating engines must be constructed and 
installed so that oil will flow at the 
normal rate through the rest of the 
system with the strainer or filter ele-
ment completely blocked. 

[Amdt. 25–36, 39 FR 35461, Oct. 1, 1974, as 
amended by Amdt. 25–57, 49 FR 6848, Feb. 23, 

§ 25.1021

Oil system drains. 

A drain (or drains) must be provided 

to allow safe drainage of the oil sys-
tem. Each drain must— 

(a) Be accessible; and 

(b) Have manual or automatic means 

for positive locking in the closed posi-

[Amdt. 25–57, 49 FR 6848, Feb. 23, 1984] 

§ 25.1023

Oil radiators. 

(a) Each oil radiator must be able to 

withstand, without failure, any vibra-
tion, inertia, and oil pressure load to 
which it would be subjected in oper-

(b) Each oil radiator air duct must be 

located so that, in case of fire, flames 
coming from normal openings of the 
engine nacelle cannot impinge directly 
upon the radiator. 

§ 25.1025

Oil valves. 

(a) Each oil shutoff must meet the re-

quirements of § 25.1189. 

(b) The closing of oil shutoff means 

may not prevent propeller feathering. 

(c) Each oil valve must have positive 

stops or suitable index provisions in 
the ‘‘on’’ and ‘‘off’’ positions and must 
be supported so that no loads resulting 
from its operation or from accelerated 
flight conditions are transmitted to 
the lines attached to the valve. 

§ 25.1027

Propeller feathering system. 

(a) If the propeller feathering system 

depends on engine oil, there must be 
means to trap an amount of oil in the 
tank if the supply becomes depleted 
due to failure of any part of the lubri-
cating system other than the tank 

(b) The amount of trapped oil must 

be enough to accomplish the feathering 
operation and must be available only 
to the feathering pump. 

(c) The ability of the system to ac-

complish feathering with the trapped 
oil must be shown. This may be done 
on the ground using an auxiliary 
source of oil for lubricating the engine 
during operation. 

(d) Provision must be made to pre-

vent sludge or other foreign matter 
from affecting the safe operation of the 
propeller feathering system. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–38, 41 FR 55467, Dec. 20, 

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