Incident Overview
An internal inspection of the engines following a flight revealed erosion damage to the high-pressure turbine (HPT) blades of both engines. The flight crew had reported a power loss and a banging sound from the left engine, along with variations in engine parameters recorded by the flight data recorder (FDR). The right engine experienced a reduction in power that did not affect the crew's decision to return to Perth.
Left Engine Findings
The erosion to the left engine's HPT was identified as a likely contributor to the power loss and abnormal sounds. Skippers Aviation had an engine condition trend monitoring program in place. A change in the trend for the left engine triggered an alert, prompting a borescope inspection and a power assurance run, which confirmed erosion. An enhanced maintenance program was initiated to monitor the damage, in accordance with the engine manufacturer's requirements.
Right Engine Evaluation
The crew also noted a reduction in right engine power. However, the subsequent inspection found less severe erosion compared to the left engine. The right engine responded normally to power lever inputs for the remainder of the flight. The Australian Transport Safety Bureau (ATSB) concluded that the decrease in right engine power was unlikely due to a mechanical issue. Possible causes included a transient engine problem, a technical failure in the throttle mechanism, crew action, or distraction. The FDR did not record throttle position data, so the exact reason could not be determined.
Maintenance and Monitoring
Technical documentation available to Skippers Aviation aided in detecting and monitoring the erosion, but the engine maintenance manual did not specify a tip clearance limit. The ATSB noted that the occurrence happened while the engines were under close monitoring, and the enhanced maintenance program met manufacturer requirements.