(b)
Aft-mounted propellers.In addition to the clearances speci.edinparagraph(a) of this section, an airplane with an aft mounted propeller must be designed such that the propeller will not contact the runway surface when the airplane is in the maximum pitch attitude attainable during normal takeo.s and landings.

(c)
Water clearance. There must be a clearance of at least 18 inches between each pro-peller andthe water, unless compliance with Sec.23.239 canbe shown with alesser clearance.

(d)
Structural clearance. There must be–

(1)
At least one inch radial clearance between the blade tips and the airplane structure, plus any additional radial clearance necessary to prevent harmful vibration;

(2)
At least one-half inch longitudinal clearance between the propeller blades or cu.s and stationaryparts of the airplane; and

(3)
Positiveclearancebetween otherrotatingpartsof thepropellerorspinnerand stationaryparts of the airplane.

Amdt. 23-51, E.. 3/11/96
FAR 23.929 : Engine installation ice protection.
[Propellers(except woodenpropellers)and othercomponentsof complete engineins-tallationsmustbeprotected againstthe accumulationoficeasnecessary to enablesatis-factory functioning without appreciable loss of thrust when operated in the icing condi-tions for which certi.cation is requested.] Amdt. 23-51, E.. 03/11/96
FAR 23.933 : Reversing systems.
(a) For turbojet and turbofan reversing systems–
(1) [Each system intended for ground operation only must be designed so that, during any reversal in .ight, the engine will produce no more than .ight idle thrust. In addition, it must be shown by analysis or test, or both, that–
(i)
Each operable reversercanbe restored totheforward thrustposition; or

(ii) The airplane is capable of continued safe .ight and landing under any possible position of the thrust reverser.]
(2)
Eachsystemintendedforin.ight use mustbedesigned so that no unsafe condi-tion will result during normal operation of the system, or from any failure, or likely combination of failures, of the reversing system under any operating conditionincludingground operation.Failure of structural elements need not be considered if the probability of this kind of failure is extremely remote.

(3)
Each system must have a means to prevent the engine from producing more than[idlethrust]whenthereversing systemmalfunctions; exceptthatit may produce any[greaterthrust] thatis shown to allowdirectional control tobe maintained, with aerodynamic means alone, under the most critical reversing condition expected in operation.

(b)
For propeller reversing systems–

(1)
Each system must be designed so that no single failure, likely combination of failures or malfunction of the system will result in unwanted reverse thrust under any operating condition. Failure of structural elements need not be considered if the probability of this type of failure is extremely remote.

(2)
Compliance withparagraph[(b)](1) of this section mustbe shownbyfailure analysis, or testing, or both, for propeller systems that allow the propeller blades to move from the .ight low-pitch position to a position that is sub-stantially less than the normal .ight, low-pitch position. The analysis may include orbe supportedby theanalysismadetoshowcomplianceforthetype certi.cation with Sec. 35.21 for the type certi.cation of the propeller and as-sociated installation components. Credit will be given for pertinent analysis and testing completed by the engine and propeller manufacturers.

Amdt. 23-51, E.. 03/11/96
FAR23.934:[Turbojetandturbofanenginethrustreverser systemstests.]
[Thrust reverser systems ofturbojet or turbofan engines must meet the requirements of Sec. 33.97 of this chapter or it must be demonstrated by tests that engine operation and vibratory levels are not a.ected.] Amdt. 23-43, E.. 5/10/93
　
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