Synopsis
On 18 July 2022, at 2110 UTC, a Qantas Airways Boeing 737-838, registered VH-VZO, operated as flight QF933, departed Brisbane Airport, Queensland, on a scheduled passenger flight to Perth Airport, Western Australia. There were 174 people on board, including two flight crew members. The aircraft had the operator-required minimum fuel onboard, and the planned fuel was independently verified as sufficient.
Sequence of Events
During the cruise, the aircraft descended from flight level 340 to flight level 280 but was not flown at the speed schedule displayed on the flight plan. A Mach number faster than planned was flown, resulting in approximately 700–800 kg of extra fuel used in the first part of the flight. The flight crew detected this extra fuel burn and, after consultation with another aircraft's crew, climbed early. While this resulted in a stronger headwind, the fuel burn reduced to approximately the planned rate later. At the decision point, the crew assessed they had enough fuel to continue to Perth, though less than planned.
During the approach to Perth, air traffic control (ATC) advised the crew that longer than expected traffic delays were anticipated, with a delay of approximately 16 minutes, exceeding the promulgated advisory of 10 minutes. Review of Airservices Australia data showed ATC had applied required priority. However, the timing of this advice meant the aircraft did not have enough holding fuel to meet the reserve requirement. The aircraft was relatively close to Perth, limiting opportunities to reduce fuel consumption further.
The flight crew declared a fuel MAYDAY to receive priority landing and preserve the required fuel reserve. The aircraft landed with its final reserve fuel intact.
Findings
The ATSB found that the deviation from the planned speed schedule resulted in extra fuel burn of 600–700 kg. Despite this, sufficient fuel remained at the decision point. The aircraft's inability to hold for the extra delay due to insufficient holding fuel led to the MAYDAY declaration. The flight crew's decision to declare a MAYDAY ensured priority approach and maintained fuel reserves.
Safety Message
Sophisticated flight planning and monitoring systems allow accurate fuel usage determination. This incident illustrates that deviations from the plan can reduce airborne options. Flight crew should alert ATC if required fuel reserve may not be met, and declare a fuel MAYDAY if necessary to receive priority.