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.

FMI: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/994D43AAE16A4BF68625790C005F46A7?OpenDocument