Federal Aviation Administration, DOT § 25.925

Home , Blade pitch, Propeller (aeronautics)

speed of the engines, following the § 25.907 Propeller vibration and fa- inflight shutdown of all engines, is in- tigue. sufficient to provide the necessary This section does not apply to fixed- electrical power for engine ignition, a pitch wood propellers of conventional power source independent of the en- design. gine-driven electrical power generating (a) The applicant must determine the system must be provided to permit in- magnitude of the propeller vibration flight engine ignition for restarting. stresses or loads, including any stress (f) Auxiliary Power Unit. Each auxil- peaks and resonant conditions, iary power unit must be approved or throughout the operational envelope of meet the requirements of the category the airplane by either: for its intended use. (1) Measurement of stresses or loads [Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as through direct testing or analysis amended by Amdt. 25–23, 35 FR 5676, Apr. 8, based on direct testing of the propeller 1970; Amdt. 25–40, 42 FR 15042, Mar. 17, 1977; on the airplane and engine installation Amdt. 25–57, 49 FR 6848, Feb. 23, 1984; Amdt. for which approval is sought; or 25–72, 55 FR 29784, July 20, 1990; Amdt. 25–73, (2) Comparison of the propeller to 55 FR 32861, Aug. 10, 1990; Amdt. 25–94, 63 FR similar propellers installed on similar 8848, Feb. 23, 1998; Amdt. 25–95, 63 FR 14798, airplane installations for which these Mar. 26, 1998; Amdt. 25–100, 65 FR 55854, Sept. 14, 2000] measurements have been made. (b) The applicant must demonstrate § 25.904 Automatic takeoff thrust con- by tests, analysis based on tests, or trol system (ATTCS). previous experience on similar designs that the propeller does not experience Each applicant seeking approval for harmful effects of flutter throughout installation of an engine power control the operational envelope of the air- system that automatically resets the plane. power or thrust on the operating en- (c) The applicant must perform an gine(s) when any engine fails during evaluation of the propeller to show the takeoff must comply with the re- that failure due to fatigue will be quirements of appendix I of this part. avoided throughout the operational life [Amdt. 25–62, 52 FR 43156, Nov. 9, 1987] of the propeller using the fatigue and structural data obtained in accordance § 25.905 Propellers. with part 35 of this chapter and the vi- (a) Each propeller must have a type bration data obtained from compliance certificate. with paragraph (a) of this section. For (b) Engine power and propeller shaft the purpose of this paragraph, the pro- rotational speed may not exceed the peller includes the hub, blades, blade limits for which the propeller is certifi- retention component and any other cated. propeller component whose failure due (c) The propeller blade pitch control to fatigue could be catastrophic to the system must meet the requirements of airplane. This evaluation must include: §§ 35.21, 35.23, 35.42 and 35.43 of this (1) The intended loading spectra in- chapter. cluding all reasonably foreseeable propeller vibration and cyclic load pat- (d) Design precautions must be taken terns, identified emergency conditions, to minimize the hazards to the airplane allowable overspeeds and overtorques, in the event a propeller blade fails or is and the effects of temperatures and hu- released by a hub failure. The hazards midity expected in service. which must be considered include dam- (2) The effects of airplane and pro- age to structure and vital systems due peller operating and airworthiness lim- to impact of a failed or released blade itations. and the unbalance created by such failure or release. [Amdt. 25–126, 73 FR 63345, Oct. 24, 2008]

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as § 25.925 Propeller clearance. amended by Amdt. 25–54, 45 FR 60173, Sept. 11, 1980; Amdt. 25–57, 49 FR 6848, Feb. 23, 1984; Unless smaller clearances are sub- Amdt. 25–72, 55 FR 29784, July 20, 1990; Amdt. stantiated, propeller clearances with 25–126, 73 FR 63345, Oct. 24, 2008] the airplane at maximum weight, with

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the most adverse center of gravity, and that during any reversal in flight the with the propeller in the most adverse engine will produce no more than flight pitch position, may not be less than idle thrust. In addition, it must be the following: shown by analysis or test, or both, (a) Ground clearance. There must be a that— clearance of at least seven inches (for (i) Each operable reverser can be re- each airplane with nose wheel landing stored to the forward thrust position; gear) or nine inches (for each airplane and with tail wheel landing gear) between (ii) The airplane is capable of contin- each propeller and the ground with the ued safe flight and landing under any landing gear statically deflected and in possible position of the thrust reverser. the level takeoff, or taxiing attitude, (2) Each system intended for inflight whichever is most critical. In addition, use must be designed so that no unsafe there must be positive clearance be- condition will result during normal op- tween the propeller and the ground eration of the system, or from any fail- when in the level takeoff attitude with ure (or reasonably likely combination the critical tire(s) completely deflated of failures) of the reversing system, and the corresponding landing gear under any anticipated condition of op- strut bottomed. eration of the airplane including (b) Water clearance. There must be a ground operation. Failure of structural clearance of at least 18 inches between elements need not be considered if the each propeller and the water, unless probability of this kind of failure is ex- compliance with § 25.239(a) can be tremely remote. shown with a lesser clearance. (3) Each system must have means to (c) Structural clearance. There must prevent the engine from producing be— more than idle thrust when the revers- (1) At least one inch radial clearance ing system malfunctions, except that it between the blade tips and the airplane may produce any greater forward structure, plus any additional radial thrust that is shown to allow direc- clearance necessary to prevent harmful tional control to be maintained, with vibration; aerodynamic means alone, under the (2) At least one-half inch longitudinal most critical reversing condition ex- clearance between the propeller blades pected in operation. or cuffs and stationary parts of the airplane; and (b) For propeller reversing systems— (3) Positive clearance between other (1) Each system intended for ground rotating parts of the propeller or spin- operation only must be designed so ner and stationary parts of the air- that no single failure (or reasonably plane. likely combination of failures) or mal- function of the system will result in Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as unwanted reverse thrust under any ex- amended by Amdt. 25–72, 55 FR 29784, July 20, pected operating condition. Failure of 1990] structural elements need not be consid- § 25.929 Propeller deicing. ered if this kind of failure is extremely remote. (a) For airplanes intended for use (2) Compliance with this section may where icing may be expected, there be shown by failure analysis or testing, must be a means to prevent or remove or both, for propeller systems that hazardous ice accumulation on propel- allow propeller blades to move from lers or on accessories where ice accu- the flight low-pitch position to a posi- mulation would jeopardize engine per- tion that is substantially less than formance. that at the normal flight low-pitch po- (b) If combustible fluid is used for sition. The analysis may include or be propeller deicing, §§ 25.1181 through supported by the analysis made to 25.1185 and 25.1189 apply. show compliance with the require- § 25.933 Reversing systems. ments of § 35.21 of this chapter for the propeller and associated installation (a) For turbojet reversing systems— components. (1) Each system intended for ground operation only must be designed so [Amdt. 25–72, 55 FR 29784, July 20, 1990]

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