329 

Federal Aviation Administration, DOT 

§ 25.1105 

T

ABLE

1—I

CING

C

ONDITIONS FOR

G

ROUND

T

ESTS

—Continued 

Condition 

Total air temperature 

Water concentration 

(minimum) 

Mean effective par-

ticle diameter 

Demonstration 

3. Large drop condi-

tion.

15 to 30 

°

F (

¥

9 to 

¥

1 

°

C).

Liquid—0.3 g/m

3

........

100 microns (min-

imum).

By test, analysis or com-

bination of the two. 

(c) 

Supercharged reciprocating engines. 

For each engine having a supercharger 
to pressurize the air before it enters 
the carburetor, the heat rise in the air 
caused by that supercharging at any 
altitude may be utilized in determining 
compliance with paragraph (a) of this 
section if the heat rise utilized is that 
which will be available, automatically, 
for the applicable altitude and oper-
ating condition because of super-
charging. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–38, 41 FR 55467, Dec. 20, 
1976; Amdt. 25–40, 42 FR 15043, Mar. 17, 1977; 
Amdt. 25–57, 49 FR 6849, Feb. 23, 1984; Amdt. 
25–72, 55 FR 29785, July 20, 1990; Amdt. 25–140, 
79 FR 65526, Nov. 4, 2014] 

§ 25.1101

Carburetor air preheater de-

sign. 

Each carburetor air preheater must 

be designed and constructed to— 

(a) Ensure ventilation of the pre-

heater when the engine is operated in 
cold air; 

(b) Allow inspection of the exhaust 

manifold parts that it surrounds; and 

(c) Allow inspection of critical parts 

of the preheater itself. 

§ 25.1103

Induction system ducts and 

air duct systems. 

(a) Each induction system duct up-

stream of the first stage of the engine 
supercharger and of the auxiliary 
power unit compressor must have a 
drain to prevent the hazardous accu-
mulation of fuel and moisture in the 
ground attitude. No drain may dis-
charge where it might cause a fire haz-
ard. 

(b) Each induction system duct must 

be— 

(1) Strong enough to prevent induc-

tion system failures resulting from 
normal backfire conditions; and 

(2) Fire-resistant if it is in any fire 

zone for which a fire-extinguishing sys-
tem is required, except that ducts for 
auxiliary power units must be fireproof 

within the auxiliary power unit fire 
zone. 

(c) Each duct connected to compo-

nents between which relative motion 
could exist must have means for flexi-
bility. 

(d) For turbine engine and auxiliary 

power unit bleed air duct systems, no 
hazard may result if a duct failure oc-
curs at any point between the air duct 
source and the airplane unit served by 
the air. 

(e) Each auxiliary power unit induc-

tion system duct must be fireproof for 
a sufficient distance upstream of the 
auxiliary power unit compartment to 
prevent hot gas reverse flow from burn-
ing through auxiliary power unit ducts 
and entering any other compartment 
or area of the airplane in which a haz-
ard would be created resulting from the 
entry of hot gases. The materials used 
to form the remainder of the induction 
system duct and plenum chamber of 
the auxiliary power unit must be capa-
ble of resisting the maximum heat con-
ditions likely to occur. 

(f) Each auxiliary power unit induc-

tion system duct must be constructed 
of materials that will not absorb or 
trap hazardous quantities of flammable 
fluids that could be ignited in the 
event of a surge or reverse flow condi-
tion. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–46, 43 FR 50597, Oct. 30, 
1978] 

§ 25.1105

Induction system screens. 

If induction system screens are 

used— 

(a) Each screen must be upstream of 

the carburetor; 

(b) No screen may be in any part of 

the induction system that is the only 
passage through which air can reach 
the engine, unless it can be deiced by 
heated air; 

(c) No screen may be deiced by alco-

hol alone; and 

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