Recommendation

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