On 16 May 2011, while in the cruise, on a scheduled passenger flight from Changi Airport, Singapore, to Melbourne, Australia. The crew of the Qantas Airways, Airbus A380-842 (A380) aircraft, registered VH-OQI (OQI), noticed a significant discrepancy between the aircraft's fuel state and the fuel predictions. The crew monitored the fuel over the flight and determined that 3.8 Tonne of excess fuel had been used over a 6 hour period.
The excess fuel usage could not be explained. Due to the potential for delays at Melbourne, the crew opted to divert to Adelaide Airport, where an uneventful landing was made.
Subsequent examination of the aircraft found no evidence of fuel leaks. Engine ground runs confirmed normal fuel flow to all engines. The flight data recorder was analysed by the Australian Transport Safety Bureau, which confirmed fuel flow during the flight was in accordance with the commanded thrust.
Subsequent investigation by the manufacturer and operator identified that for a period of about 4 hours during the flight, the speed brake lever (SBL) was set away from its stowed position of -5° to the +3.6°position. As a result, the aircraft spoilers were deflected into the airstream increasing drag and consequently fuel burn. The crew were not alerted to this as warnings are only displayed to the crew at or above the +5° SBL position.
As a result of the incident, Airbus plans to reduce the alerting position of the speed brake lever angle from +5° to +2.4°.
Airbus have also updated the standard operating procedures (SOP) to highlight that spoiler extension may occur without a crew alert.