Fri, Sep 16, 2011
Issues Found With Certain First Stage Reduction Sun Gears
The FAA has sent a notice of an emergency AD (2011-20-51) to
owners and operators of Pratt & Whitney Canada PT6A-15AG, -27,
-28, -34, -34AG, -34B, and -36 series turboprop engines.
The move was prompted by failures of certain first stage
reduction sun gears, manufactured by Timken Alcor Aerospace
Technologies, Inc. These gears are manufactured under a part
manufacturer approval (PMA) as replacement parts for installation
in propeller reduction gearbox assemblies of Pratt & Whitney
Canada PT6A-15AG, -27, -28, -34, -34AG, -34B, and -36 series
turboprop engines. About 80 of these sun gears are suspect for
having a manufacturing anomaly. About half of the suspect sun gears
have already been taken out of service. This condition, if not
corrected, could result in failure of the shaft portion of the sun
gear, which will result in an engine in-flight shut down, possible
uncontained engine failure, aircraft damage, and serious
injuries.
The AD was issued after the FAA evaluated of all the relevant
information, and determined the unsafe condition described
previously is likely to exist or develop in other products of the
same type design. The FAA has found that the risk to the flying
public justifies issuing this AD on an emergency basis.
The AD requires the removal of affected PMA replacement Timken
Alcor Aerospace Technologies, Inc. first stage reduction sun gear
and the interacting planet gears, from the propeller reduction
gearbox assembly, within 15 operating hours or 15 days after
receipt of this AD, whichever occurs first.
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