Recommendation

Pratt and Whitney responded to this proposed safety
recommendation (draft recommendation C) in the ATSB draft report by
stating:

As noted above, P&WC does not believe that the examination
of the engine's internal spline on-wing will accurately determine
the presence or absence of EDD, however an examination of the
starter-generator spline may be warranted.

As the nature of EDD damage is progressive, P&WC would seek
to minimize operator disruption by a recommendation that the engine
should be reworked within an appropriate time frame (say 50 hours)
and that operation within this period would be subject to
repetitive filter patch inspections per the existing engine
EMM.

ATSB comment:

As stated above, the ATSB accepts P&WC's response and agrees
that the starter-generator external spline is the most practical
and effective method to determine if there has been an EDD event.
However, the ATSB does not accept that continued operation of the
engine following an EDD event is without risk. Additionally, it has
been shown through this investigation that filter patch checks are
not a reliable means to predict an engine failure following an EDD
event.  It is the ATSB's view that, where evidence of EDD is
detected, the engine's continued reliability should be considered
suspect. As such the ATSB has reworded and now formally issues
safety recommendation R20070017.