Safety Recommendation
The Australian Transport Safety Bureau recommends that Pratt
& Whitney Canada, in conjunction with Transport Canada,
incorporate measures to electrically isolate the starter-generator
gear-shaft input coupling spline and the engine number-1 main shaft
bearing of all Pratt & Whitney Canada PT6A series engines.
Pratt and Whitney responded to this proposed safety
recommendation (draft recommendation A) in the ATSB draft report by
stating:
P&WC is pursuing the incorporation of a non-conductive
insert in the design of our new models of PT6A engines. As
this feature requires an extensive re-design of the gear, the oil
seal, and the accessory housing, it is not practicable to be
incorporated into the existing fleet of engines.In our earlier review of this issue, it was determined that the
more practical solution was to incorporate a non-conductive element
into the shaft of the starter-generator unit. While the
Starter-Generator manufacturer proposed several designs, P&WC
is not aware that any have been developed to the production
stage.
ATSB comment:
The ATSB does not accept that P&WC's response to the draft
recommendation is adequate and believes that P&WC should take a
pro-active role and work in conjunction with Transport Canada to
develop an effective method to electrically isolate
starter-generators in the existing fleet of PT6A series engines in
order to eliminate the possibility of engine failure due to EDD. As
such the ATSB now formally issues safety recommendation
R20070015.
