Feedback Issue 2/2009

Engines

Failure of Compressor High Pressure Turbine Blades

SDR Submitted:
While hovering after take-off, No.1 engine lost power (pilot reported hearing a loud bang) and the aircraft landed without further incident.

Preliminary inspection revealed failure of the power turbine (PT) disk. Subsequent tear down and investigation revealed that the primary cause of failure was actually the compressor turbine (CT) blades, with secondary damage to the PT blades.

Transport Canada Comments:
Transport Canada recommends reviewing Service Difficulty Advisories AV-2007-06 (CT Blades failure), AV 2006-06 (Borescope inspection) and AV 2006-03 (ECTM).

PT Governor

SDR Submitted:
During a scheduled removal of the power turbine governor from the engine gearbox, it was noticed that the retaining clip that secures the drivegear on the power turbine shaft was not located in the groove. The washers that are retained by the clip and sit against the drivegear were found sitting in the male spline of the gearbox drive. It appears as though the end of the driveshaft was worn down to allow the circlip to become dislodged from the groove and work its way off the shaft. The damage to the shaft could have been due to the dislodged washers sitting in the drive spline. The only item found retaining the drivegear was the spring on the backside. The maintenance engineer inspected the gearbox drive but was unable to locate the circlip.

No previous history of faulty governor operation or abnormal sounds was noted. Chip plugs and gearbox drive gears were inspected but no damage was found. Overhauled unit installed and aircraft performed a satisfactory ground run.

Transport Canada Comments:
Always perform a detailed inspection of this area prior to PT governor installation.