A Saab 340B aircraft, registered VH-EKN, was being operated on a
scheduled flight from Orange to Sydney, NSW. The crew reported
that, shortly after takeoff, as they were setting climb power, they
heard a `bang' similar to the sound of a compressor stall. The left
engine gauges indicated zero torque and excessive inter-turbine
temperature (ITT). The left over temperature and ignition lights
illuminated, followed by a master warning annunciation. The crew
carried out the engine failure procedure and, having shut down the
left engine, returned to Orange and landed.
Eight days later, the crew of another Saab 340B, registered
VH-OLM, operated by the same company, reported that shortly after
takeoff from Orange, the right engine displayed characteristics
consistent with a compressor stall (ATSB Occurrence 200300078). On
that occasion, after the crew carried out the appropriate checklist
procedures, normal engine operation and indications were restored
and the flight continued to Sydney without further incident.
The affected engines from both aircraft were removed for
examination at the manufacturer's overhaul facility. The engine
manufacturer, after reviewing the recorded engine data, identified
that a number of similar conditions, that may have affected the
engines, had existed during both flights. Both events had occurred
on the first flight of the day. On both occasions a significant
temperature inversion existed at approximately 1,000 ft above
ground level, and the compressor stalls occurred when the crews
were adjusting the power setting from takeoff power to climb power.
The engine manufacturer's assessment concluded that a combination
of environmental conditions and engine operating procedures had led
to both events and made several recommendations to the
operator.
Those recommendations included changes to both the maintenance
program and to the operation of the engines. They called for
compressor washes to be conducted every 200 hours, or more
frequently as determined by the operating environment. In the weeks
prior to the occurrences there had been significant airborne
particles in smoke from bushfires. That may have contributed to
contamination of the compressor blades and consequently the
engine's susceptibility to compressor stalling. The engine
manufacturer also recommended that the operator consider amending
the takeoff configuration to include selecting the Environmental
Control System (ECS) to ON for the first flight of the day. Use of
the ECS opens the bleed air valves and reduces the likelihood of
compressor stalls. Its use on the first flight of the day would
counteract the conditions of temperature inversions that were
usually more pronounced in the early morning.
Additionally, the engine manufacturer issued an alert service
bulletin, SB CT7-TP S/B 72-A0328, Revision 1, dated 8 April 2003,
which required checking that the correct rigging schedule of the
engine variable inlet guide vanes (VIGV) had been implemented.
Rigging of the VIGV to the specified schedule was used to reduce
engine susceptibility to compressor stalls in the range of
environmental conditions encountered during routine operations. The
operator reported that, although the requirements of the service
bulletin had been incorporated into its engine maintenance program,
the rigging schedule check had not been completed on the occurrence
engines. The service bulletin was subsequently incorporated into
the USA Federal Aviation Administration Emergency Airworthiness
Directive 2003-08-52, dated 15 April 2003 and subsequently mandated
in Australia by the Civil Aviation Safety Authority as
Airworthiness Directive AD/CT7/9 on 16 April 2003.
The operator reported that its maintenance program and standard
operating procedures had been changed in accordance with the engine
manufacturer's recommendations and that all engines in its fleet
had been inspected in accordance with the requirements of the
engine manufacturers service bulletin. Subsequently, there have
been no further reports of compressor stalls in the climb after
takeoff.