French investigators have disclosed that an Air France Airbus A319 was forced to make a single-engine landing at Paris Charles de Gaulle after an undetected indicator fault resulted in partial fuel exhaustion.
Investigation authority BEA – which analysed the 12 March 2014 event – says pilots operating a series of Marseille-Nantes services performed a routine discrepancy check on the theoretical and actual fuel usage, and found the difference to be just 20kg.
But BEA says the aircraft had been experiencing intermittent failure of its fuel quantity indicator, and the actual difference was 880kg.
Analysis of refuelling documents and technical log entries for the aircraft (F-GRHT) revealed several calculation errors by crews – sometimes as much as 1t – which, says BEA, suggests verifications of the calculations by the first officer was “not systematically carried out”.
This could explain, it says, why the indicator failure was not previously identified and resolved.
When a subsequent crew prepared the A319 for a Marseille-Paris flight, the jet indicated 3,780kg of fuel on board, and the pilots opted to uplift 1,200kg of fuel to bring the total to about 5,000kg.
BEA found, however, that the actual fuel on board when the engines were started was about 3,800kg and that the fuel indicator was overestimating the quantity by 1,270kg.
Just 15min after take-off an automated alert warned of a low fuel level in the left wing tank. After a check, the crew believed this was a nuisance alarm linked to a known probe failure in the outer left tank.
But during the descent to 8,000ft, nearly 1h into the flight, the crew was alerted to a pressure drop in two fuel pumps on the left-hand CFM International CFM56 engine.
This deteriorated, a few minutes later, into an engine failure. The crew declared an emergency and landed with only the right-hand powerplant running.
Maintenance personnel found that the left tank was empty and only 1,100kg of fuel – equating to 150kg above final reserve – remained in the right tank.
Inspection showed that the left and right engines had respectively burned 1,272kg and 1,525kg of fuel, confirming that the fuel-quantity indication of 5,080kg after the uplift at Marseille was a substantial overestimation.