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Service Difficulty Advisory

AV 2006-05
4 July 2006

Pratt and Whitney Canada PT6A-38, -40, -41, -41AG, -42, -42A, and -62, Series Engines Replacement of First Stage Sun Gear and Planet Gears at Overhaul

Introduction

This document is to advise registered owners, operators, and certificated repair facilities of all aircraft equipped with Pratt and Whitney Canada (P&WC) PT6A-38, -40, -41, -41AG, -42, -42A and -62 series engine models, of several incidents involving damage to the first stage reduction sun gear and planet gears.

These incidents indicate that all operators and/or overhaul shops may not always be following the P&WC overhaul manual criteria or that the engine overhaul was completed prior to the relevant overhaul manual revision.

This revision changed the criteria for the specified models, and states that the first stage sun gear and planet gears must be replaced at scheduled overhaul regardless of the condition of these parts.  P&WC revised their overhaul manuals in December 1999 to include these requirements.

These engines are installed on, but not limited to, Piper Cheyenne III, Raytheon Beech A200-C12A, -A200 UC12B, -A200CT (US12F), -A200CT (RUC12D), -B200C (UC12M), King Air 200C, RC-12DGR, Super King Air 200 and the Pilatus Turbo trainer PC-9.

Background

In September 1999, PT6A operators and P&WC’s global network of factory-owned and independent designated overhaul facilities were notified of this overhaul manual revision by P&WC Service Information Letter, SIL No. PT6A-078, and revised overhaul manuals were provided at that time. 

Risk analysis and safety management programs indicate that compliance with the current maintenance manual requirements of inspecting the chip detector every 100 hours and the oil filter every 200 hours will provide for early indications of wear and corrective action, resulting in reduced safety risks.

Recent events have highlighted the fact that some operators and/or overhaul shops, especially those not overseen by the P&WC system, may not have followed these requirements. This has resulted in reduced reliability of the first stage reduction gear train and in some cases caused inflight shutdowns.

Recommendations

Transport Canada strongly recommends that you replace the first stage reduction sun gear and planet gears during scheduled overhaul, and follow the prescribed maintenance practices outlined in the specific engine Maintenance Manuals.

Any further defects or occurrences should be reported to Transport Canada, Continuing Airworthiness, Ottawa via the Service Difficulty Reporting Program

For further information contact a Transport Canada Centre, or call Mr. Robin Lau, Continuing Airworthiness, Ottawa, telephone 613 952-4461, facsimile 613 996-9178 or e-mail laur@tc.gc.ca.

For Director, Aircraft Certification

Robin Lau
Acting Chief, Continuing Airworthiness

Note: For the electronic version of this document, please consult the following Web address: www.tc.gc.ca/eng/civilaviation/certification/menu.htm