FACTUAL INFORMATION
At about 1921 CST, on 13 July 2004, the left engine of a
Fairchild Industries Inc. SA227 DC aircraft, registered VH-KEX,
failed during the climb phase after takeoff. The aircraft was being
operated on a scheduled passenger service from Ceduna to Adelaide,
South Australia with 2 crew and 17 passengers.
The crew continued the climb and levelled off at 2,500 ft. The
crew broadcast a PAN1 and returned
the aircraft to Ceduna aerodrome where the engine was replaced and
the aircraft returned to service.
A subsequent examination of the engine, a Garrett TPE331-12UHR,
by the operator, in the presence of Australian Transport Safety
Bureau (ATSB) investigators, found that the turbine rotating
airseal had failed transversely through the cooling holes around
the centre of the cylindrical section. That resulted in the
liberation of the seal flange and substantial damage to the
downstream turbine module (refer Figures 1 and 2).
Since 1995, the engine manufacturer had received four reported
failures of the rotating airseal for the TPE331-12 engine. These
failures were attributed to progressive thermal cracking. As a
result, the manufacturer introduced several service bulletins
related to modifications to improve core engine airflow and the
introduction of a Fluorescent Penetrant Inspection (FPI) to the
rotating airseal. The requirements of these service bulletins had
been complied with on this engine during manufacture and FPI was
performed at scheduled intervals as required by the
manufacturer.
A review of the engine's maintenance history revealed that the
aircraft operator's maintenance schedule was in compliance with the
manufacturer's requirement and utilised Engine Condition Trend
Monitoring (ECTM), a maintenance procedure to monitor the health of
an engine. ECTM data did not reveal any degradation of engine
performance. At the time of the failure, the rotating airseal had
completed 12,326 cycles since new (CSN). The airseal had a
manufacturer's recommended life of 20,000 CSN.
The last recorded inspection of the rotating airseal was a FPI
at 6,997 hours since new (TSN) and 9,060 CSN by the operator.
At 8,234 TSN and 10,607 CSN, the engine had been subjected to a
sudden stoppage as a result of a kangaroo strike. Following that
event, an uncommanded stoppage inspection was carried out by the
operator. That inspection did not require an examination of the
rotating airseal. A further 815 hours (1,129 cycles) later, the
engine's propeller governor failed. The operator performed a
precautionary overheat inspection of the engine with no defects
found.
At the time of the release of this report, the manufacturer had
not advised the ATSB of any actions taken as a result of this
incident.
The failure of the rotating airseal was consistent with
progressive thermal cracking.