Recommendation R20020121

Recommendation issued to: Federal Aviation Administration (FAA)

Recommendation details
Output No: R20020121
Date issued: 12 June 2002
Safety action status:
Background: Why this Recommendation was developed

Output text

Safety Recommendation

The Australian Transport Safety Bureau recommends that the United States Federal Aviation Administration examine the circumstances of electrical discharge damage to the number-1 bearing of the Pratt and Whitney (Canada) PT6A engine models equipped with TRW Lucas starter-generators and develop an appropriate safety assurance strategy.

Initial response
Date issued: 25 February 2003
Response from: Federal Aviation Administration (FAA)
Action status: Monitor
Response text:

The Office of Accident Investigation convened a Safety Recommendation Review Board to review the enclosed response to FAA Safety Recommendation 02.207. As a result, the Review Board classified this recommendation as "Closed-Acceptable Action."

FAA Recommendation 02.207:

Safety Recommendation 02.207 recommended that the FAA examine the circumstances of electrical discharge damage to the number one bearing of the Pratt & Whitney Canada (PWC) PT6A engine models equipped with TRW Lucas (now Goodrich) starter-generator models 23078 and 23085 and develop an appropriate safety assurance strategy.

Chicago ACO Response:

As discussed in the Australian Transport Safety Bureau Air Safety Occurrence Report (200003399) which resulted in FAA Safety Recommendation 02.207, the issue has to do with failure of the number one bearing in certain PWC PT6A-60 series engines (causing engine failure) apparently due to electrical discharge damage (EDD). Evidence suggests that an electrical current from the starter-generator gear shaft passes through the accessory gear train and the compressor splined coupling. It appears that the electric current initiates spalling damage to the engine number one bearing.

At the time of the Australian Report there had been seventeen engine failures on the worldwide PT6A fleet attributed to EDD, according to the engine manufacturer. Five of these involved an Australian operator of Shorts 360 aircraft. Other failures occurred on Beech 1900 and Beech King Air aircraft. These are all twin-engine aircraft. In addition, there has been a recent failure of a PT6A-67B engine apparently due to EDD in a single-engine Pilatus PC-12/45 aircraft which resulted in an accident.

The Chicago Aircraft Certification Office (ACO) has discussed this matter with Goodrich (TRW Aeronautical Systems, Lucas Aerospace), Transport Canada, and with ANE-142 which has cognizance of the PWC PT6A engines. We were unable to ascertain the root cause of the problem. These starter-generators (and other similar design Goodrich starter-generators) used in other aircraft installations have not experienced the EDD bearing problem. Accordingly, the FAA has decided to publish a Special Airworthiness Information Bulletin (SAIB) with general information directed to owners and operators of aircraft with the specified PWC PT6A-60 series engines. It alerts them to the condition and recommends that the existing instructions regarding starter-generator maintenance, proper grounding of the starter-general, and periodic checking of engine oil for possible early detection of bearing deterioration be followed. A copy of this SAIB is attached. It is possible that investigation of the Pilatus PC-12/45 accident mentioned above will lead to more specific and detailed guidance.

ATSB Note: A copy of the SAIB (Special Airworthiness Information Bulletin) is available from the ATSB on request.

On 9 October 2007, the ATSB issued R20070022 in relation to subsequent occurrences of EDD in PWC PT6A engines. The ATSB reclassifies this recommendation as Closed - Partially Accepted

Further correspondence
Date issued: 30 April 2008
Response from: Federal Aviation Administration (FAA)
Response status: Closed - Partially Accepted
Response text:
Last update 03 April 2012