AL 2008-01
11 July 2008
Transport Canada Civil Aviation (TCCA) is aware of three occurrences where the torque meter gear, part number (P/N) 6893673, developed a fracture and failed, resulting in an unscheduled engine shut down.
Rolls-Royce utilizes the same torque meter gear, P/N 6893673, (see photo) in both the 250-C30 and 250-C47 series turboshaft engine gearboxes. Over the years, design improvements have been made to improve the reliability of the subject gear.
Commercial Engine Bulletin (CEB) 72-6049, was issued to advise customers that the pinion and torque meter gears had been redesigned to eliminate premature wear. The CEB recommends new gears be installed whenever the affected parts are directly available for removal and have been deemed unserviceable for any reason. CEB 72-6061 notified customers that that the power gears (pinion gear, torque meter gear, and power takeoff gear) had been redesigned to improve reliability. Compliance is presently a customer option.
Rolls-Royce no longer manufactures P/N 6893673 torque meter gears. This torque meter gear is however still approved for use as long as it is serviceable and is installed in accordance with CEB 72-6061.
The Rolls-Royce 250-C30 and 250-C47 series turboshaft engine gearbox is maintained on-condition therefore there is no requirement for the gearbox to be opened at any specific time-in-service. Rolls-Royce does require a general inspection and visual check for wear on the drive splines and gear teeth to be performed any time the gearbox is opened.
If the gearbox technical records indicate more than 3500 hours have elapsed, since the gears were new or last magnetically inspected, all gears are to have a magnetic particle inspection (MPI) carried out.
Considering the “on-condition” status of the gearbox, there is potential for the gearbox to continue in service beyond 3500 hours without being removed or opened for inspection.
Although, this situation may not be significant for the newly redesigned torque meter gear introduced by CEB 72-6061, the MPI interval for the discontinued P/N 6893673 gear may be significant.
TCCA recommends maintenance technicians and operators determine if the Rolls-Royce 250-C30 and 250-C47 series turboshaft engine gearbox in their helicopter contains the P/N 6893673 torque meter gear. Also review of the gearbox technical records is recommended to establish the time since new, or in-service hours, and to determine if the 3500 hours MPI has been exceeded. Illumination of the engine chip light warning, when the MPI has been exceeded, is an indication of a pending torque meter gear failure.
TCCA strongly urges operators schedule the recommended MPI in the near future and consider replacing P/N 6893673 torque meter gears, in accordance with CEB 72-6061 at the first/next opportunity.
Similar defects or further occurrences of this nature, or malfunctions, defects and failures occurring on any aeronautical product should be reported to Transport Canada, Continuing Airworthiness, in accordance with CAR 591, mandatory Service Difficulty Reporting requirements.
For further information, contact Marcel Gauthier, Continuing Airworthiness, Ottawa. Telephone 613-952-4364 or facsimile 613-996-9178 or e-mail gauthmr@tc.gc.ca.
For Director, National Aircraft Certification
Derek Ferguson
Acting Chief, Continuing Airworthiness
Note: For the electronic version of this document, please consult the following Web address:
https://tc.canada.ca/en/aviation/aircraft-airworthiness/aircraft-certification