On Sept. 15, 2011, the FAA published an Emergency Airworthiness Directive (EAD) for certain Pratt & Whitney PT6A engines. The emergency AD, numbered 2011-20-51, was prompted by failures of certain first stage reduction sun gears manufactured by Timken Alcor Aerospace Technologies, Inc. (TAATI) under a part manufacturer approval (PMA). The engines affected are PT6A-15AG, -27, -28, -34, -34AG, -34B and -36. About 80 of these gears are suspected to have the anomaly and about half have already been taken out of service. If not corrected, this condition could result in failure of the shaft portion of the sun gear which will result in engine shutdown.
The emergency AD is effective upon receipt. This AD applies to the listed engines which have had maintenance done to the power section module involving first stage reduction sun gear replacement since Feb. 3, 2010 having the TAATI sun gear, part number (P/N) E3024765, serial numbers (S/Ns) PC5-091 through PC5-176 installed. For affected engines, remove the replacement first stage reduction sun gear and the interacting planet gear within 15 operating hours or 15 days after receipt of this AD.