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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