Pratt & Whitney Canada all PT6A series engines - Service Difficulty Advisory

AV 2006-06
5 July 2006

Hot section borescope inspections

The engine hot section components (combustion liner, large and small exit ducts, fuel nozzles, compressor turbine (CT) nozzle vanes and CT blades) are continuously subjected to very hot temperatures, kinetic energy and significant air pressures.  Periodic visual (borescope) inspection of these components has been shown as an effective means of early detection of hot section distress, providing for improved reliability and cost effective refurbishment.

A recent CT blade fracture event would likely have been prevented had the operator followed the recommended borescope inspection specified in the applicable maintenance manual. Early detection of fractures and other CT blade distress can prevent inflight shutdowns and other expensive collateral damage, should a blade aerofoil be liberated.

Expensive downstream damage to the power turbine (PT) guide vanes and PT disc will almost certainly occur in such an event. Regular borescope inspections are an essential element in detecting the onset of distress and preventing secondary damage in the hot section and exhaust area.

Transport Canada Civil Aviation (TCCA) recommends that operators comply with the recommended borescope inspections prescribed in the relevant PT6A maintenance manual. Additionally, TCCA request your attention to P&WC Service Information Letter (SIL) PT6A-116 that is applicable to all PT6A engines.

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

For further information, please contact a Transport Canada Centre (TCC), or contact Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, Ontario, telephone 613 952-4358, facsimile 613 996-9178 or e-mail

For Director, Aircraft Certification

Robin Lau
Acting Chief, Continuing Airworthiness

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