Federal Aviation Administration, DOT

Section 25.929

and the unbalance created by such failure or release.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-54, 45 FR 60173, Sept.
11, 1980; Amdt. 25-57, 49 FR 6848, Feb. 23, 1984;
Amdt. 25-72, 55 FR 29784, July 20, 1990; Amdt.
25-126, 73 FR 63345, Oct. 24, 2008]

spaschal on DSK3GDR082PROD with CFR

Section 25.907 Propeller
tigue.

vibration

and

fa-

This section does not apply to fixedpitch wood propellers of conventional
design.
(a) The applicant must determine the
magnitude of the propeller vibration
stresses or loads, including any stress
peaks
and
resonant
conditions,
throughout the operational envelope of
the airplane by either:
(1) Measurement of stresses or loads
through direct testing or analysis
based on direct testing of the propeller
on the airplane and engine installation
for which approval is sought; or
(2) Comparison of the propeller to
similar propellers installed on similar
airplane installations for which these
measurements have been made.
(b) The applicant must demonstrate
by tests, analysis based on tests, or
previous experience on similar designs
that the propeller does not experience
harmful effects of flutter throughout
the operational envelope of the airplane.
(c) The applicant must perform an
evaluation of the propeller to show
that failure due to fatigue will be
avoided throughout the operational life
of the propeller using the fatigue and
structural data obtained in accordance
with part 35 of this chapter and the vibration data obtained from compliance
with paragraph (a) of this section. For
the purpose of this paragraph, the propeller includes the hub, blades, blade
retention component and any other
propeller component whose failure due
to fatigue could be catastrophic to the
airplane. This evaluation must include:
(1) The intended loading spectra including all reasonably foreseeable propeller vibration and cyclic load patterns, identified emergency conditions,
allowable overspeeds and overtorques,
and the effects of temperatures and humidity expected in service.

(2) The effects of airplane and propeller operating and airworthiness limitations.
[Amdt. 25-126, 73 FR 63345, Oct. 24, 2008]

Section 25.925

Propeller clearance.

Unless smaller clearances are substantiated, propeller clearances with
the airplane at maximum weight, with
the most adverse center of gravity, and
with the propeller in the most adverse
pitch position, may not be less than
the following:
(a) Ground clearance. There must be a
clearance of at least seven inches (for
each airplane with nose wheel landing
gear) or nine inches (for each airplane
with tail wheel landing gear) between
each propeller and the ground with the
landing gear statically deflected and in
the level takeoff, or taxiing attitude,
whichever is most critical. In addition,
there must be positive clearance between the propeller and the ground
when in the level takeoff attitude with
the critical tire(s) completely deflated
and the corresponding landing gear
strut bottomed.
(b) Water clearance. There must be a
clearance of at least 18 inches between
each propeller and the water, unless
compliance with Section 25.239(a) can be
shown with a lesser clearance.
(c) 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 cuffs and stationary parts of the airplane; and
(3) Positive clearance between other
rotating parts of the propeller or spinner and stationary parts of the airplane.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-72, 55 FR 29784, July 20,
1990]

Section 25.929 Propeller deicing.
(a) If certification for flight in icing
is sought there must be a means to prevent or remove hazardous ice accumulations that could form in the icing
conditions defined in Appendix C of

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