Federal Aviation Administration, DOT § 23.939
thrust when operated in the icing con- flight, low-pitch position. The analysis ditions for which certification is re- may include or be supported by the quested. analysis made to show compliance with [Amdt. 23–14, 33 FR 31822, Nov. 19, 1973, as § 35.21 for the type certification of the amended by Amdt. 23–51, 61 FR 5136, Feb. 9, propeller and associated installation 1996] components. Credit will be given for pertinent analysis and testing com- § 23.933 Reversing systems. pleted by the engine and propeller (a) For turbojet and turbofan reversing manufacturers. systems. (1) Each system intended for [Doc. No. 26344, 58 FR 18971, Apr. 9, 1993, as ground operation only must be de- amended by Amdt. 23–51, 61 FR 5136, Feb. 9, signed so that, during any reversal in 1996] flight, the engine will produce no more than flight idle thrust. In addition, it § 23.934 Turbojet and turbofan engine must be shown by analysis or test, or thrust reverser systems tests. both, that— Thrust reverser systems of turbojet (i) Each operable reverser can be re- or turbofan engines must meet the re- stored to the forward thrust position; quirements of § 33.97 of this chapter or or it must be demonstrated by tests that (ii) The airplane is capable of contin- engine operation and vibratory levels ued safe flight and landing under any are not affected. possible position of the thrust reverser. (2) Each system intended for in-flight [Doc. No. 26344, 58 FR 18971, Apr. 9, 1993] use must be designed so that no unsafe § 23.937 Turbopropeller-drag limiting condition will result during normal op- systems. eration of the system, or from any fail- ure, or likely combination of failures, (a) Turbopropeller-powered airplane of the reversing system under any op- propeller-drag limiting systems must erating condition including ground op- be designed so that no single failure or eration. Failure of structural elements malfunction of any of the systems dur- need not be considered if the prob- ing normal or emergency operation re- ability of this type of failure is ex- sults in propeller drag in excess of that tremely remote. for which the airplane was designed (3) Each system must have a means under the structural requirements of to prevent the engine from producing this part. Failure of structural ele- more than idle thrust when the revers- ments of the drag limiting systems ing system malfunctions; except that it need not be considered if the prob- may produce any greater thrust that is ability of this kind of failure is ex- shown to allow directional control to tremely remote. be maintained, with aerodynamic (b) As used in this section, drag lim- means alone, under the most critical iting systems include manual or auto- reversing condition expected in oper- matic devices that, when actuated ation. after engine power loss, can move the (b) For propeller reversing systems. (1) propeller blades toward the feather po- Each system must be designed so that sition to reduce windmilling drag to a no single failure, likely combination of safe level. failures or malfunction of the system [Amdt. 23–7, 34 FR 13093, Aug. 13, 1969, as will result in unwanted reverse thrust amended by Amdt. 23–43, 58 FR 18971, Apr. 9, under any operating condition. Failure 1993] of structural elements need not be con- sidered if the probability of this type of § 23.939 Powerplant operating charac- failure is extremely remote. teristics. (2) Compliance with paragraph (b)(1) (a) Turbine engine powerplant oper- of this section must be shown by fail- ating characteristics must be inves- ure analysis, or testing, or both, for tigated in flight to determine that no propeller systems that allow the pro- adverse characteristics (such as stall, peller blades to move from the flight surge, or flameout) are present, to a low-pitch position to a position that is hazardous degree, during normal and substantially less than the normal emergency operation within the range
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of operating limitations of the airplane range with fuel initially saturated with and of the engine. water at 80° F and having 0.75cc of free (b) Turbocharged reciprocating en- water per gallon added and cooled to gine operating characteristics must be the most critical condition for icing investigated in flight to assure that no likely to be encountered in operation. adverse characteristics, as a result of (d) Each fuel system for a turbine en- an inadvertent overboost, surge, flood- gine powered airplane must meet the ing, or vapor lock, are present during applicable fuel venting requirements of normal or emergency operation of the part 34 of this chapter. engine(s) throughout the range of oper- ating limitations of both airplane and [Amdt. 23–15, 39 FR 35459, Oct. 1, 1974, as amended by Amdt. 23–40, 55 FR 32861, Aug. 10, engine. 1990; Amdt. 23–43, 58 FR 18971, Apr. 9, 1993] (c) For turbine engines, the air inlet system must not, as a result of airflow § 23.953 Fuel system independence. distortion during normal operation, cause vibration harmful to the engine. (a) Each fuel system for a multien- gine airplane must be arranged so that, [Amdt. 23–7, 34 FR 13093 Aug. 13, 1969, as in at least one system configuration, amended by Amdt. 23–14, 38 FR 31823, Nov. 19, the failure of any one component 1973; Amdt. 23–18, 42 FR 15041, Mar. 17, 1977; (other than a fuel tank) will not result Amdt. 23–42, 56 FR 354, Jan. 3, 1991] in the loss of power of more than one § 23.943 Negative acceleration. engine or require immediate action by the pilot to prevent the loss of power of No hazardous malfunction of an en- more than one engine. gine, an auxiliary power unit approved (b) If a single fuel tank (or series of for use in flight, or any component or fuel tanks interconnected to function system associated with the powerplant as a single fuel tank) is used on a or auxiliary power unit may occur multiengine airplane, the following when the airplane is operated at the must be provided: negative accelerations within the (1) Independent tank outlets for each flight envelopes prescribed in § 23.333. engine, each incorporating a shut-off This must be shown for the greatest valve at the tank. This shutoff valve value and duration of the acceleration may also serve as the fire wall shutoff expected in service. valve required if the line between the [Amdt. 23–18, 42 FR 15041, Mar. 17, 1977, as valve and the engine compartment does amended by Amdt. 23–43, 58 FR 18971, Apr. 9, not contain more than one quart of 1993] fuel (or any greater amount shown to be safe) that can escape into the engine FUEL SYSTEM compartment. § 23.951 General. (2) At least two vents arranged to minimize the probability of both vents (a) Each fuel system must be con- becoming obstructed simultaneously. structed and arranged to ensure fuel flow at a rate and pressure established (3) Filler caps designed to minimize for proper engine and auxiliary power the probability of incorrect installa- unit functioning under each likely op- tion or inflight loss. erating condition, including any ma- (4) A fuel system in which those parts neuver for which certification is re- of the system from each tank outlet to quested and during which the engine or any engine are independent of each auxiliary power unit is permitted to be part of the system supplying fuel to in operation. any other engine. (b) Each fuel system must be ar- [Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as ranged so that— amended by Amdt. 23–7, 34 FR 13093 Aug. 13, (1) No fuel pump can draw fuel from 1969; Amdt. 23–43, 58 FR 18971, Apr. 9, 1993] more than one tank at a time; or (2) There are means to prevent intro- § 23.954 Fuel system lightning protec- ducing air into the system. tion. (c) Each fuel system for a turbine en- The fuel system must be designed gine must be capable of sustained oper- and arranged to prevent the ignition of ation throughout its flow and pressure fuel vapor within the system by—
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