Recommendation

CASA responded to this proposed safety recommendation in the
ATSB draft report by stating:

The proposed mandatory maintenance instruction is aimed at
capturing an EDD event before an engine IFSD occurs
due to bearing failure.  If the EDD events are captured
through starter-generator shaft inspection and follow-on
maintenance actions are carried out before engine failure, fitment
of accessory gearbox (AGB) chip detector indication system in the
cockpit may prove to be of marginal benefit, if any.  The time
between chip detector indication and the actual failure is known to
be a few minutes.

CASA maintenance instructions are an interim measure until
engine or starter manufacturers assume the responsibility and
address the core problem from a design point of view.  CASA
does not believe that the fitment of [an] AGB chip detector
indication system in the cockpit will bring the safety benefits
anticipated by ATSB [R20070024].  CASA will, however, continue
monitoring the effectiveness of mandatory maintenance
instructions.

ATSB comment:

The ATSB does not accept CASA's suggestion that accessory
gearbox chip detector systems are of marginal benefit. As indicated
in this investigation, the accessory gear-box chip detector warning
system fitted to the incident aircraft was instrumental in
providing a prior warning of impending engine failure, allowing the
pilot time to select a safe place to land. As such, the ATSB now
formally issues the safety recommendation as R20070024

CASA's position on this issue remains unchanged, and CASA adopts
its response to Recommendation O as its response to formal
Recommendation R20070024.