325 

Federal Aviation Administration, DOT 

§ 25.1043 

§ 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-
ation. 

(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 
itself. 

(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, 
1976] 

C

OOLING

 

§ 25.1041

General. 

The powerplant and auxiliary power 

unit cooling provisions must be able to 
maintain the temperatures of power-
plant components, engine fluids, and 

auxiliary power unit components and 
fluids within the temperature limits 
established for these components and 
fluids, under ground, water, and flight 
operating conditions, and after normal 
engine or auxiliary power unit shut-
down, or both. 

[Amdt. 25–38, 41 FR 55467, Dec. 20, 1976] 

§ 25.1043

Cooling tests. 

(a) 

General. 

Compliance with § 25.1041 

must be shown by tests, under critical 
ground, water, and flight operating 
conditions. For these tests, the fol-
lowing apply: 

(1) If the tests are conducted under 

conditions deviating from the max-
imum ambient atmospheric tempera-
ture, the recorded powerplant tempera-
tures must be corrected under para-
graphs (c) and (d) of this section. 

(2) No corrected temperatures deter-

mined under paragraph (a)(1) of this 
section may exceed established limits. 

(3) For reciprocating engines, the fuel 

used during the cooling tests must be 
the minimum grade approved for the 
engines, and the mixture settings must 
be those normally used in the flight 
stages for which the cooling tests are 
conducted. The test procedures must be 
as prescribed in § 25.1045. 

(b) 

Maximum ambient atmospheric tem-

perature. 

A maximum ambient atmos-

pheric temperature corresponding to 
sea level conditions of at least 100 de-
grees F must be established. The as-
sumed temperature lapse rate is 3.6 de-
grees F per thousand feet of altitude 
above sea level until a temperature of 

¥

69.7 degrees F is reached, above which 

altitude the temperature is considered 
constant at 

¥

69.7 degrees F. However, 

for winterization installations, the ap-
plicant may select a maximum ambi-
ent atmospheric temperature cor-
responding to sea level conditions of 
less than 100 degrees F. 

(c) 

Correction factor (except cylinder 

barrels). 

Unless a more rational correc-

tion applies, temperatures of engine 
fluids and powerplant components (ex-
cept cylinder barrels) for which tem-
perature limits are established, must 
be corrected by adding to them the dif-
ference between the maximum ambient 
atmospheric temperature and the tem-
perature of the ambient air at the time 
of the first occurrence of the maximum 

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