Incident Description
On 18 January 2023, a Boeing 737-838 aircraft, registered VH-XZB and operated by Qantas, was en route from Auckland, New Zealand to Sydney, Australia. Approximately 1 hour and 24 minutes after departure, while in cruise, the left engine shut down without command. The flight crew declared a MAYDAY to prioritize communications and initiated an immediate descent to flight level 240. Attempts to restart the engine in-flight were unsuccessful. The aircraft subsequently performed a single-engine landing at Sydney Airport about one hour later, which was uneventful.
Investigation Findings
The Australian Transport Safety Bureau (ATSB) examined the engine and identified that the radial driveshaft, located in the inlet gearbox, had separated. This separation caused a mechanical discontinuity between the engine core and the accessory gearbox. Loss of drive to the accessory gearbox resulted in a loss of fuel pump pressure, leading to the uncommanded shutdown. Additionally, the failed driveshaft prevented an in-flight restart. Secondary damage to some components occurred as the engine shut down.
The flight crew reported no detection of any change in parameters that might have alerted them to an impending engine issue, consistent with recorded data showing no warning. Recent maintenance had indicated a normally operating engine. The ATSB also found that the cockpit voice recorder was inadvertently overwritten during maintenance activities conducted after the aircraft arrived at Sydney Airport.
Operational Decisions
At the time of the engine failure, Norfolk Island was closer but would have required a deviation from the current track and presented changeable weather and operational conditions. In contrast, Sydney Airport was on the direct route, had favorable weather forecasts, extensive emergency response capabilities, and a long runway allowing a straight-in approach. The flight crew's decision to continue to Sydney was assessed to ensure no additional risk was introduced to an already high-workload situation.
Safety Actions Taken
In response to this incident, Qantas has enhanced its procedures to prevent inadvertent overwriting of cockpit voice recorders and flight data recorders.
Safety Message from the ATSB
The importance of training, following standard procedures, and effective communication is well established. This incident highlighted the positive benefits of effective decision-making and management of an unexpected situation. Such actions include maintaining situational awareness, utilizing all information sources, considering and evaluating all options to choose the best course of action, and frequently reviewing actions as circumstances change. Additionally, operators need to implement proper procedures to protect flight-recorded information that enhances the accuracy and effectiveness of safety investigations.