INSPECTION AND CHECK
61-00-39
Page 5-8
Rev. 17 Apr/20
Propeller Owner’s Manual
139
B. Propeller Ground Idle RPM Check
WARNING:
STABILIZED GROUND OPERATION
WITHIN THE PROPELLER RESTRICTED
RPM RANGE CAN GENERATE HIGH
PROPELLER STRESSES AND RESULT IN
FATIGUE DAMAGE TO THE PROPELLER.
THIS DAMAGE CAN LEAD TO A REDUCED
PROPELLER FATIGUE LIFE, PROPELLER
FAILURE, AND LOSS OF CONTROL OF THE
AIRCRAFT. THE PROPELLER RESTRICTED
RPM RANGE IS DEFINED IN THE AIRPLANE
FLIGHT MANUAL.
(1) General
(a) Propellers with four or more blades operating on
turbine engines can be sensitive to operation within
restricted RPM ranges. These restricted ranges are
usually in the lower RPM ranges, requiring that ground
idle RPM be set above a critical minimum value.
(b) This minimum propeller idle RPM operating restriction
is the result of a specific vibratory resonant condition
known as “reactionless mode”. During operation
in these conditions the flight crew cannot feel the
resulting high propeller vibration. Ground operation at
or near an RPM that can create a reactionless mode
vibratory resonance can cause very high stresses in
the propeller blades and the hub. These high stresses
are more severe when operating in a quartering tail
wind condition.
(c) If the propeller is operated within a restricted RPM
range or below a minimum idle RPM restriction for
an extended period of time, the propeller blades and
hub can become unairworthy because of fatigue.
A failed blade or hub has the potential to cause a
catastrophic blade separation.
(d) Use the “Periodic Ground Idle RPM Check” steps in
this section to determine if the propeller is operating
within the specified RPM limits.
(e) Refer to the “Corrective Action” steps in this section
for maintenance information about propellers
operating outside of the specified RPM range.
