Federal Aviation Administration, DOT § 23.925

with paragraph (a) of this section. For no hazard to the airplane under all op- the purpose of this paragraph, the pro- erating conditions. peller includes the hub, blades, blade (e) Engine power, cooling character- retention component and any other istics, operating limits, and procedures propeller component whose failure due affected by the turbocharger system in- to fatigue could be catastrophic to the stallations must be evaluated. Turbo- airplane. This evaluation must include: charger operating procedures and limi- (1) The intended loading spectra in- tations must be included in the Air- cluding all reasonably foreseeable pro- plane Flight Manual in accordance peller vibration and cyclic load pat- with § 23.1581. terns, identified emergency conditions, [Amdt. 23–7, 34 FR 13092, Aug. 13, 1969, as allowable overspeeds and overtorques, amended by Amdt. 23–43, 58 FR 18970, Apr. 9, and the effects of temperatures and hu- 1993] midity expected in service. (2) The effects of airplane and pro- § 23.925 Propeller clearance. peller operating and airworthiness lim- Unless smaller clearances are sub- itations. stantiated, propeller clearances, with the airplane at the most adverse com- [Amdt. No. 23–59, 73 FR 63345, Oct. 24, 2008] bination of weight and center of grav- § 23.909 Turbocharger systems. ity, and with the propeller in the most adverse pitch position, may not be less (a) Each turbocharger must be ap- than the following: proved under the engine type certifi- (a) Ground clearance. There must be a cate or it must be shown that the tur- clearance of at least seven inches (for bocharger system, while in its normal each airplane with nose wheel landing engine installation and operating in gear) or nine inches (for each airplane the engine environment— with tail wheel landing gear) between (1) Can withstand, without defect, an each propeller and the ground with the endurance test of 150 hours that meets landing gear statically deflected and in the applicable requirements of § 33.49 of the level, normal takeoff, or taxing at- this subchapter; and titude, whichever is most critical. In (2) Will have no adverse effect upon addition, for each airplane with con- the engine. ventional landing gear struts using (b) Control system malfunctions, vi- fluid or mechanical means for absorb- brations, and abnormal speeds and ing landing shocks, there must be posi- temperatures expected in service may tive clearance between the propeller not damage the turbocharger com- and the ground in the level takeoff at- pressor or turbine. titude with the critical tire completely (c) Each turbocharger case must be deflated and the corresponding landing able to contain fragments of a com- gear strut bottomed. Positive clear- pressor or turbine that fails at the ance for airplanes using leaf spring highest speed that is obtainable with struts is shown with a deflection cor- normal speed control devices inoper- responding to 1.5g. ative. (b) Aft-mounted propellers. In addition (d) Each intercooler installation, to the clearances specified in para- where provided, must comply with the graph (a) of this section, an airplane following— with an aft mounted propeller must be (1) The mounting provisions of the designed such that the propeller will intercooler must be designed to with- not contact the runway surface when stand the loads imposed on the system; the airplane is in the maximum pitch (2) It must be shown that, under the attitude attainable during normal installed vibration environment, the takeoffs and landings. intercooler will not fail in a manner al- (c) Water clearance. There must be a lowing portions of the intercooler to be clearance of at least 18 inches between ingested by the engine; and each propeller and the water, unless (3) Airflow through the intercooler compliance with § 23.239 can be shown must not discharge directly on any air- with a lesser clearance. plane component (e.g., windshield) un- (d) Structural clearance. There must less such discharge is shown to cause be—

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