Section 25.933

14 CFR Ch. I (1-1-19 Edition)

this part and in the portions of Appendix O of this part for which the airplane is approved for flight on propellers or on accessories where ice accumulation would jeopardize engine performance.
(b) If combustible fluid is used for
propeller deicing, SectionSection 25.1181 through
25.1185 and 25.1189 apply.

spaschal on DSK3GDR082PROD with CFR

[ Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-140, 79 FR 65525, Nov. 4,
2014]

Section 25.933 Reversing systems.
(a) For turbojet reversing systems - 
(1) Each system intended for ground
operation only must be designed so
that during any reversal in flight the
engine will produce no more than flight
idle thrust. In addition, it must be
shown by analysis or test, or both,
that - 
(i) Each operable reverser can be restored to the forward thrust position;
and
(ii) The airplane is capable of continued safe flight and landing under any
possible position of the thrust reverser.
(2) Each system intended for inflight
use must be designed so that no unsafe
condition will result during normal operation of the system, or from any failure (or reasonably likely combination
of failures) of the reversing system,
under any anticipated condition of operation of the airplane including
ground 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 means to
prevent the engine from producing
more than idle thrust when the reversing system malfunctions, except that it
may produce any greater forward
thrust that is shown to allow directional control to be maintained, with
aerodynamic means alone, under the
most critical reversing condition expected in operation.
(b) For propeller reversing systems - 
(1) Each system intended for ground
operation only must be designed so
that no single failure (or reasonably
likely combination of failures) or malfunction of the system will result in
unwanted reverse thrust under any expected operating condition. Failure of
structural elements need not be consid-

ered if this kind of failure is extremely
remote.
(2) Compliance with this section may
be shown by failure analysis or testing,
or both, for propeller systems that
allow propeller blades to move from
the flight low-pitch position to a position that is substantially less than
that at the normal flight low-pitch position. The analysis may include or be
supported by the analysis made to
show compliance with the requirements of Section 35.21 of this chapter for the
propeller and associated installation
components.
[Amdt. 25-72, 55 FR 29784, July 20, 1990]

Section 25.934 Turbojet engine thrust reverser system tests.
Thrust reversers installed on turbojet engines must meet the requirements of Section 33.97 of this chapter.
[Amdt. 25-23, 35 FR 5677, Apr. 8, 1970]

Section 25.937 Turbopropeller-drag limiting
systems.
Turbopropeller power airplane propeller-drag limiting systems must be
designed so that no single failure or
malfunction of any of the systems during normal or emergency operation results in propeller drag in excess of that
for which the airplane was designed
under Section 25.367. Failure of structural elements of the drag limiting systems
need not be considered if the probability of this kind of failure is extremely remote.
Section 25.939 Turbine
engine
operating
characteristics.
(a) Turbine engine operating characteristics must be investigated in flight
to determine that no adverse characteristics (such as stall, surge, or flameout) are present, to a hazardous degree,
during normal and emergency operation within the range of operating
limitations of the airplane and of the
engine.
(b) [Reserved]
(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause
vibration harmful to the engine.
[Amdt. 25-11, 32 FR 6912, May 5, 1967, as
amended by Amdt. 25-40, 42 FR 15043, Mar. 17,
1977]

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