What happened
On 23 August 2016, a Regional Express Saab 340 aircraft, registered VH-ZRJ, was performing a scheduled passenger flight from Ballina/Byron Gateway Airport to Sydney. The flight was carrying 22 passengers and three crewmembers. Due to a wet runway, the crew had selected the environmental control system (ECS) to the OFF position during takeoff procedures.
During the initial climb, while the landing gear was being retracted, the crew experienced loud bangs and a significant degradation in left engine performance. Instrument readings showed rapid fluctuations and high inter-turbine temperatures. The cabin crew reported seeing flames emanating from the left engine. The flight crew identified the event as a compressor stall and initiated failure management procedures, which included reducing power on the left engine and maximizing thrust on the right.
Despite attempts to manage the stall using the operator's quick reference handbook procedures, the condition persisted. The crew subsequently shut down the left engine and feathered the propeller. The aircraft returned to Ballina via an RNAV approach and landed safely. During the landing roll, the aircraft experienced a slight rightward deviation due to asymmetric drag, which the captain corrected by adjusting the right engine thrust lever.
The investigation
The investigation confirmed that a compressor stall had occurred. Engineering reviews of the flight data showed no exceedances in torque, turbine speed, or inter-turbine temperature limits. Borescope inspections of the engine revealed no physical damage to the compressor components.
Engineers focused on the hydromechanical unit (HMU), which is responsible for controlling fuel flow and the variable geometry system used to prevent stalls. Following standard fault isolation procedures, the HMU was replaced. Subsequent ground runs showed no further defects, and the aircraft was returned to service.
Findings
- The primary cause of the engine malfunction was a compressor stall in the left engine.
- The crew effectively managed the emergency through the application of robust failure management procedures and simulator-based training.
- The replacement of the hydromechanical unit (HMU) was necessary to address the underlying cause of the stall, although no physical damage was found during inspection.