Airbus A380 operators are being instructed to introduce an additional fuel-quantity check after a discrepancy observed during pre-departure preparations.
The fuel quantity indicated by on-board instruments had differed from the expected figure, calculated by combining the initial fuel with the uplifted fuel.
Investigations found that an incorrect signal from a refuel isolation valve was behind the discrepancy, says the European Aviation Safety Agency.
It states that this situation might have resulted from contamination of the isolation valve position sensor, because the valve had been indicated as closed during refuelling when it was actually open.
“This wrong signal triggers the system to use the fuel density determined during a previous flight for computation,” says EASA.
“If the real fuel density of the current refuelling is different to the previous fuel density, the resulting fuel weight indication may show a discrepancy that is potentially above the allowable limits.”
EASA warns that undetected fuel-measurement errors could result in a loss of fuel supply to the aircraft’s engines.
Airbus has temporarily revised the aircraft’s flight manual to include an additional tolerance check to ensure that indicated fuel on board, following refuelling, tallies with the sum of the initial and uplifted fuel.
EASA says the measure, the subject of an airworthiness directive, could be supplemented by further actions.