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 take-off, 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 take-off 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 take-off 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 take-off 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 take-off.