Federal Aviation Administration, DOT § 25.1103
(1) There must be means to prevent that would adversely affect engine op- hazardous quantities of fuel leakage or eration or cause a serious loss of power overflow from drains, vents, or other or thrust— components of flammable fluid systems (i) Under the icing conditions speci- from entering the engine or auxiliary fied in appendix C, and power unit intake system; and (ii) In falling and blowing snow with- (2) The airplane must be designed to in the limitations established for the prevent water or slush on the runway, airplane for such operation. taxiway, or other airport operating (2) Each turbine engine must idle for surfaces from being directed into the 30 minutes on the ground, with the air engine or auxiliary power unit air inlet bleed available for engine icing protec- ducts in hazardous quantities, and the tion at its critical condition, without air inlet ducts must be located or pro- adverse effect, in an atmosphere that is tected so as to minimize the ingestion at a temperature between 15° and 30 °F of foreign matter during takeoff, land- (between ¥9° and ¥1 °C) and has a liq- ing, and taxiing. uid water content not less than 0.3 (e) If the engine induction system grams per cubic meter in the form of contains parts or components that drops having a mean effective diameter could be damaged by foreign objects not less than 20 microns, followed by entering the air inlet, it must be shown momentary operation at takeoff power by tests or, if appropriate, by analysis or thrust. During the 30 minutes of idle that the induction system design can operation, the engine may be run up withstand the foreign object ingestion periodically to a moderate power or test conditions of §§ 33.76, 33.77 and thrust setting in a manner acceptable 33.78(a)(1) of this chapter without fail- to the Administrator. ure of parts or components that could (c) Supercharged reciprocating engines. create a hazard. For each engine having a supercharger to pressurize the air before it enters [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–38, 41 FR 55467, Dec. 20, the carburetor, the heat rise in the air 1976; Amdt. 25–40, 42 FR 15043, Mar. 17, 1977; caused by that supercharging at any Amdt. 25–57, 49 FR 6849, Feb. 23, 1984; Amdt. altitude may be utilized in determining 25–100, 65 FR 55854, Sept. 14, 2000] compliance with paragraph (a) of this section if the heat rise utilized is that § 25.1093 Induction system icing pro- which will be available, automatically, tection. for the applicable altitude and oper- (a) Reciprocating engines. Each recip- ating condition because of super- rocating engine air induction system charging. must have means to prevent and elimi- [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as nate icing. Unless this is done by other amended by Amdt. 25–38, 41 FR 55467, Dec. 20, means, it must be shown that, in air 1976; Amdt. 25–40, 42 FR 15043, Mar. 17, 1977; free of visible moisture at a tempera- Amdt. 25–57, 49 FR 6849, Feb. 23, 1984; Amdt. ture of 30 F., each airplane with alti- 25–72, 55 FR 29785, July 20, 1990] tude engines using— (1) Conventional venturi carburetors § 25.1101 Carburetor air preheater de- have a preheater that can provide a sign. heat rise of 120 F. with the engine at 60 Each carburetor air preheater must percent of maximum continuous power; be designed and constructed to— or (a) Ensure ventilation of the pre- (2) Carburetors tending to reduce the heater when the engine is operated in probability of ice formation has a pre- cold air; heater that can provide a heat rise of (b) Allow inspection of the exhaust 100° F. with the engine at 60 percent of manifold parts that it surrounds; and maximum continuous power. (c) Allow inspection of critical parts (b) Turbine engines. (1) Each turbine of the preheater itself. engine must operate throughout the flight power range of the engine (in- § 25.1103 Induction system ducts and cluding idling), without the accumula- air duct systems. tion of ice on the engine, inlet system (a) Each induction system duct up- components, or airframe components stream of the first stage of the engine
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supercharger and of the auxiliary (b) No screen may be in any part of power unit compressor must have a the induction system that is the only drain to prevent the hazardous accu- passage through which air can reach mulation of fuel and moisture in the the engine, unless it can be deiced by ground attitude. No drain may dis- heated air; charge where it might cause a fire haz- (c) No screen may be deiced by alco- ard. hol alone; and (b) Each induction system duct must (d) It must be impossible for fuel to be— strike any screen. (1) Strong enough to prevent induc- tion system failures resulting from § 25.1107 Inter-coolers and after-cool- normal backfire conditions; and ers. (2) Fire-resistant if it is in any fire Each inter-cooler and after-cooler zone for which a fire-extinguishing sys- must be able to withstand any vibra- tem is required, except that ducts for tion, inertia, and air pressure load to auxiliary power units must be fireproof which it would be subjected in oper- within the auxiliary power unit fire ation. zone. (c) Each duct connected to compo- EXHAUST SYSTEM nents between which relative motion could exist must have means for flexi- § 25.1121 General. bility. For powerplant and auxiliary power (d) For turbine engine and auxiliary unit installations the following apply: power unit bleed air duct systems, no (a) Each exhaust system must ensure hazard may result if a duct failure oc- safe disposal of exhaust gases without curs at any point between the air duct fire hazard or carbon monoxide con- source and the airplane unit served by tamination in any personnel compart- the air. ment. For test purposes, any accept- (e) Each auxiliary power unit induc- able carbon monoxide detection meth- tion system duct must be fireproof for od may be used to show the absence of a sufficient distance upstream of the carbon monoxide. auxiliary power unit compartment to (b) Each exhaust system part with a prevent hot gas reverse flow from burn- surface hot enough to ignite flammable ing through auxiliary power unit ducts fluids or vapors must be located or and entering any other compartment shielded so that leakage from any sys- or area of the airplane in which a haz- tem carrying flammable fluids or va- ard would be created resulting from the pors will not result in a fire caused by entry of hot gases. The materials used impingement of the fluids or vapors on to form the remainder of the induction any part of the exhaust system includ- system duct and plenum chamber of ing shields for the exhaust system. the auxiliary power unit must be capa- (c) Each component that hot exhaust ble of resisting the maximum heat con- gases could strike, or that could be ditions likely to occur. subjected to high temperatures from (f) Each auxiliary power unit induc- exhaust system parts, must be fire- tion system duct must be constructed proof. All exhaust system components of materials that will not absorb or must be separated by fireproof shields trap hazardous quantities of flammable from adjacent parts of the airplane fluids that could be ignited in the that are outside the engine and auxil- event of a surge or reverse flow condi- iary power unit compartments. tion. (d) No exhaust gases may discharge [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as so as to cause a fire hazard with re- amended by Amdt. 25–46, 43 FR 50597, Oct. 30, spect to any flammable fluid vent or 1978] drain. (e) No exhaust gases may discharge § 25.1105 Induction system screens. where they will cause a glare seriously If induction system screens are affecting pilot vision at night. used— (f) Each exhaust system component (a) Each screen must be upstream of must be ventilated to prevent points of the carburetor; excessively high temperature.
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