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Recommendation issued to: Pratt and Whitney - Canada (United Aircraft Of Canada)

Recommendation details
Output No: R20000109
Date issued: 01 March 2001
Safety action status:
Background: Why this Recommendation was developed

Output text

The Australian Transport Safety Bureau recommends that Pratt and Whitney Canada investigate the re-instigation of regular borescope inspections of PW118A reduction gear-box input shafts with below recommended thickness carburised case depth (pre SB 21323), regardless of the Service Bulletin state of the engine.

Initial response
Date issued: 19 March 2002
Response from: Pratt and Whitney - Canada (United Aircraft Of Canada)
Action status: Closed - Not Accepted
Response text:

Response R20000109

Pratt and Whitney Canada (PWC) indicated that the response from Transport Canada (TC) to R20000110 incorporated information supplied from PWC on all of the matters raised. Therefore the TC response is included for this recommendation:

Transport Canada (TC) has assessed the need for regular borescope inspections of PW 118A reduction gear-box with below recommended thickness of carburised case depth (pre SB 21323), regardless of the Service Bulletin state of the engine.

The shaft failure, as investigated by Pratt & Whitney Canada, was deemed to have been caused by the gradual spalling of the shaft gear teeth over an extended period of time. Since this spalling has, in the past, been linked to input shaft failures, the periodic requirement to check gearbox chip detectors and their associated circuitry continues to be in place in the engine maintenance schedule. Pratt & Whitney Canada confirmed that there is no non-destructive test that may be applied to determine the depth of the input shaft carburised case, thus precluding the introduction of a reliable cost effective check to determine which shafts would be candidates for additional inspections.

The Service Difficulty Report (SDR) database revealed no other reported incidents associated with PW118A gearbox input shaft failures. This leads Transport Canada to conclude that the shaft failure incident detailed in the ATSB report to be an isolated case. Consequently Transport Canada does not deem it necessary to reinstate previously applied borescope inspections. The industry will be best served by relying on the existing chip detector inspections to verify the extent of gradual wear leading to eventual failure. The existing manufacturer's recommendations also provide the necessary precautions, which indicate a need for in-depth investigation in the event that chip detectors show evidence of gradual degradation.

 
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Last update 05 April 2012