Safety Recommendation
The Australian Transport Safety Bureau recommends that Transport
Canada, as the state of design for PT6A engines, review the
continued airworthiness of PT6A series engines, with regard to its
susceptibility to failure of the number-1 bearing, as a result of
EDD sustained from a starter-generator malfunction.
Transport Canada responded to this proposed safety
recommendation (draft recommendation I) in the ATSB draft report by
stating:
TC continually monitors the continuing airworthiness of the PT6A
engine. According to the latest P&WC data (1Q/2007), the 12
months in-flight shut down (IFSD) rate for the PT6A series engines
is 0.004 per 1000 hours (0.011 for the PT6A-114/-114A series
engines), which is well within the acceptable certification
requirement of 10E-5. The IFSD rate due to EDD would be
expected to be much lower than the above IFSD rate. TC
suggests that the TSB or ATSB request P&WC provide the
in-flight shut down rate due to electrical discharge damage (EDD)
problems.
ATSB comment:
The ATSB does not accept Transport Canada's suggestion that
either the Transportation Safety Board of Canada or the ATSB should
seek further EDD related IFSD rates from the engine manufacturer.
As the responsible airworthiness authority, the ATSB believes that
TC should actively seek any data required to review the continued
airworthiness of the PT6A series engines in relation to potential
failures as a result of EDD. That review should consider not
only the IFSD rate, but also the potential serious consequences of
sudden engine failure in single-engine, passenger-carrying
operations. As such, the ATSB now formally issues the safety
recommendation as R20070020.
Transport Canada has reviewed the continued airworthiness of
PT6A series engines, with regard to its susceptibility to failure
of the number-1 bearing, as a result of EDD sustained from a
starter-generator malfunction. Transport Canada Civil Aviation
(TCCA) has determined the failure/reliability rate to be well
within the recognised industry reliability target of 10E-5. 10E-5
is only an industry target for reliability (one failure for every
100,000 hours, which roughly translates to one failure every 20
years, if an engine is utilized 5000 hours per year, or every 40
years if the engine is operated 2500 hours per year).
TCCA notes, as a result of P&WC actions related to operator
awareness and inspection criteria, the previous low occurrence rate
of incidents related to EDD has been further reduced to a level
where, in 2007, there has only been one EDD event and no
EDD-related In-Flight Shutdowns (IFSD) reported to P&WC for
450,000 hours of reported operation for PT6A-114 series
engines.
Present In-Service data does not indicate any unsafe condition
presented as a result of the ATSB investigation into EDD on the
smaller PT6A engines. TCCA continues to review, with P&WC, all
aspects of the continued airworthiness of PT6A series engines.
