327 

Federal Aviation Administration, DOT 

§ 25.1091 

§ 25.1045

Cooling test procedures. 

(a) Compliance with § 25.1041 must be 

shown for the takeoff, climb, en route, 
and landing stages of flight that cor-
respond to the applicable performance 
requirements. The cooling tests must 
be conducted with the airplane in the 
configuration, and operating under the 
conditions, that are critical relative to 
cooling during each stage of flight. For 
the cooling tests, a temperature is 
‘‘stabilized’’ when its rate of change is 
less than two degrees F. per minute. 

(b) Temperatures must be stabilized 

under the conditions from which entry 
is made into each stage of flight being 
investigated, unless the entry condi-
tion normally is not one during which 
component and the engine fluid tem-
peratures would stabilize (in which 
case, operation through the full entry 
condition must be conducted before 
entry into the stage of flight being in-
vestigated in order to allow tempera-
tures to reach their natural levels at 
the time of entry). The takeoff cooling 
test must be preceded by a period dur-
ing which the powerplant component 
and engine fluid temperatures are sta-
bilized with the engines at ground idle. 

(c) Cooling tests for each stage of 

flight must be continued until— 

(1) The component and engine fluid 

temperatures stabilize; 

(2) The stage of flight is completed; 

or 

(3) An operating limitation is 

reached. 

(d) For reciprocating engine powered 

airplanes, it may be assumed, for cool-
ing test purposes, that the takeoff 
stage of flight is complete when the 
airplane reaches an altitude of 1,500 
feet above the takeoff surface or 
reaches a point in the takeoff where 
the transition from the takeoff to the 
en route configuration is completed 
and a speed is reached at which compli-
ance with § 25.121(c) is shown, which-
ever point is at a higher altitude. The 
airplane must be in the following con-
figuration: 

(1) Landing gear retracted. 
(2) Wing flaps in the most favorable 

position. 

(3) Cowl flaps (or other means of con-

trolling the engine cooling supply) in 
the position that provides adequate 
cooling in the hot-day condition. 

(4) Critical engine inoperative and its 

propeller stopped. 

(5) Remaining engines at the max-

imum continuous power available for 
the altitude. 

(e) For hull seaplanes and amphib-

ians, cooling must be shown during 
taxiing downwind for 10 minutes, at 
five knots above step speed. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–57, 49 FR 6848, Feb. 23, 
1984] 

I

NDUCTION

S

YSTEM

 

§ 25.1091

Air induction. 

(a) The air induction system for each 

engine and auxiliary power unit must 
supply— 

(1) The air required by that engine 

and auxiliary power unit under each 
operating condition for which certifi-
cation is requested; and 

(2) The air for proper fuel metering 

and mixture distribution with the in-
duction system valves in any position. 

(b) Each reciprocating engine must 

have an alternate air source that pre-
vents the entry of rain, ice, or any 
other foreign matter. 

(c) Air intakes may not open within 

the cowling, unless— 

(1) That part of the cowling is iso-

lated from the engine accessory section 
by means of a fireproof diaphragm; or 

(2) For reciprocating engines, there 

are means to prevent the emergence of 
backfire flames. 

(d) For turbine engine powered air-

planes and airplanes incorporating aux-
iliary power units— 

(1) There must be means to prevent 

hazardous quantities of fuel leakage or 
overflow from drains, vents, or other 
components of flammable fluid systems 
from entering the engine or auxiliary 
power unit intake system; and 

(2) The airplane must be designed to 

prevent water or slush on the runway, 
taxiway, or other airport operating 
surfaces from being directed into the 
engine or auxiliary power unit air inlet 
ducts in hazardous quantities, and the 
air inlet ducts must be located or pro-
tected so as to minimize the ingestion 
of foreign matter during takeoff, land-
ing, and taxiing. 

(e) If the engine induction system 

contains parts or components that 

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