327 

Federal Aviation Administration, DOT 

§ 25.1093 

(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 
could be damaged by foreign objects 
entering the air inlet, it must be shown 
by tests or, if appropriate, by analysis 
that the induction system design can 
withstand the foreign object ingestion 
test conditions of §§ 33.76, 33.77 and 
33.78(a)(1) of this chapter without fail-
ure of parts or components that could 
create a hazard. 

[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. 
25–100, 65 FR 55854, Sept. 14, 2000] 

§ 25.1093

Induction system icing pro-

tection. 

(a) 

Reciprocating engines. 

Each recip-

rocating engine air induction system 
must have means to prevent and elimi-
nate icing. Unless this is done by other 
means, it must be shown that, in air 
free of visible moisture at a tempera-
ture of 30 F., each airplane with alti-
tude engines using— 

(1) Conventional venturi carburetors 

have a preheater that can provide a 
heat rise of 120 F. with the engine at 60 
percent of maximum continuous power; 
or 

(2) Carburetors tending to reduce the 

probability of ice formation has a pre-
heater that can provide a heat rise of 
100 

°

F. with the engine at 60 percent of 

maximum continuous power. 

(b) 

Turbine engines. 

Except as pro-

vided in paragraph (b)(3) of this sec-
tion, each engine, with all icing protec-
tion systems operating, must: 

(1) Operate throughout its flight 

power range, including the minimum 

descent idling speeds, in the icing con-
ditions defined in Appendices C and O 
of this part, and Appendix D of part 33 
of this chapter, and in falling and blow-
ing snow within the limitations estab-
lished for the airplane for such oper-
ation, without the accumulation of ice 
on the engine, inlet system compo-
nents, or airframe components that 
would do any of the following: 

(i) Adversely affect installed engine 

operation or cause a sustained loss of 
power or thrust; or an unacceptable in-
crease in gas path operating tempera-
ture; or an airframe/engine incompati-
bility; or 

(ii) Result in unacceptable temporary 

power loss or engine damage; or 

(iii) Cause a stall, surge, or flameout 

or loss of engine controllability (for ex-
ample, rollback). 

(2) Operate at ground idle speed for a 

minimum of 30 minutes on the ground 
in the following icing conditions shown 
in Table 1 of this section, unless re-
placed by similar test conditions that 
are more critical. These conditions 
must be demonstrated with the avail-
able air bleed for icing protection at its 
critical condition, without adverse ef-
fect, followed by an acceleration to 
takeoff power or thrust in accordance 
with the procedures defined in the air-
plane flight manual. During the idle 
operation, the engine may be run up 
periodically to a moderate power or 
thrust setting in a manner acceptable 
to the Administrator. Analysis may be 
used to show ambient temperatures 
below the tested temperature are less 
critical. The applicant must document 
the engine run-up procedure (including 
the maximum time interval between 
run-ups from idle, run-up power set-
ting, and duration at power), the asso-
ciated minimum ambient temperature, 
and the maximum time interval. These 
conditions must be used in the analysis 
that establishes the airplane operating 
limitations in accordance with § 25.1521. 

(3) For the purposes of this section, 

the icing conditions defined in appen-
dix O of this part, including the condi-
tions specified in Condition 3 of Table 1 
of this section, are not applicable to 
airplanes with a maximum takeoff 
weight equal to or greater than 60,000 
pounds. 

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