What happened
During the cruise phase of flight, approximately 84 minutes after departure, the left engine of the aircraft experienced an uncommanded shutdown. The flight crew did not receive any prior warnings or notice of changing engine parameters, a fact later confirmed by flight data. While the aircraft was positioned near Norfolk Island at the time of the failure, the crew elected to proceed to Sydney Airport. This decision was based on the fact that Sydney was on their direct flight path and offered more favorable weather forecasts, a long runway for a straight-in approach, and superior emergency response capabilities compared to the changeable conditions at Norfolk Island.
The investigation
Investigators examined the mechanical state of the engine and the flight data recorded during the event. The investigation determined that the shutdown was caused by the separation of the radial driveshaft. This failure created a mechanical discontinuity between the engine core and the accessory gearbox. Consequently, the pressure from the main fuel pump, which is driven by the accessory gearbox, was lost, causing the engine to fail. The damage to the driveshaft also made it impossible for the crew to restart the engine while in flight.
Additionally, investigators noted that the cockpit voice recorder (CVR) audio from the incident had been inadvertently overwritten during maintenance following the event. While this meant direct audio evidence of crew coordination and decision-making was unavailable, the flight data and air traffic control recordings were sufficient to verify the crew's accounts of the incident.