What happened
During a flight operated by Skippers Aviation, the crew of a DHC-8-315, registration VH-XKJ, experienced a loss of power and an audible banging sound from the left engine. This prompted the crew to declare a PAN-PAN call and initiate a return to Perth. During the flight, the crew also noted a reduction in power from the right engine, though this occurred after the decision to return had already been made.
The investigation
An investigation into the event focused on the condition of the engines following the flight. Post-flight internal inspections revealed that the high-pressure turbine blades in both engines had suffered erosion damage. While such degradation is expected due to high temperatures and low clearances, the erosion in the left engine was significant enough to disrupt airflow and reduce efficiency. This degradation was identified as the likely cause of the power loss and the noise reported by the crew.
Engine condition trend monitoring by the operator had previously triggered an alert for the left engine, leading to a borescope inspection. While the operator had implemented an enhanced maintenance program to monitor the damage in line with manufacturer requirements, the engine maintenance manual lacked a specific limit for tip clearance. Regarding the right engine, although erosion was also present, it was less severe than that of the left engine. The investigation found that the right engine's power reduction was unlikely to be caused by a mechanical engine issue, though the exact cause of the torque reduction could not be confirmed because the flight data recorder did not capture throttle position data.
Findings
- Excessive erosion to the high-pressure turbine blades of the left engine was the primary factor in the power loss.
- The operator's maintenance and monitoring of the engine erosion were consistent with the manufacturer's technical documentation and requirements.
- The reduction in power on the right engine was not attributed to mechanical failure, with potential causes including transient issues or throttle mechanism failure.