What happened
On August 24, 1997, an Air France Airbus A320-211, registration F-GHQH, was operating a scheduled flight from Paris to Lorient. Approximately twelve minutes after takeoff, the crew received an "ADVISORY FUEL" message on the ECAM screen, indicating a fuel imbalance between the wings.
To address the imbalance, the crew followed the Quick Reference Handbook (QRH) and opened the intercommunication valve to transfer fuel from the right tank to the left. While the initial transfer appeared successful, the imbalance recurred shortly after. The crew attempted a second transfer but eventually ceased the operation due to a rapid decrease in fuel quantity in the right tank, suggesting a leak.
During the approach to Lorient, the crew maintained a higher glide slope in anticipation of a potential engine failure. Approximately eight minutes before touchdown, the left engine shut down because the fuel pumps could no longer draw fuel from the depleted left tank. The aircraft completed a successful single-engine landing at 20:20 UTC. Upon arrival at the parking stand, the crew noted the left tank was empty, while approximately 800 kg of fuel remained in the right tank.
The investigation
The investigation focused on identifying the source of the fuel loss, which totaled approximately 5.2 tonnes of the 8.4 tonnes initially on board. While no external leak was visible during the flight, maintenance teams inspected the aircraft the following day. By activating the fuel pumps during a fuel transfer to the left wing, investigators were able to locate the leak at the left engine's fuel filter module. The inspection revealed that four of the six bolts securing the filter cover had been sheared off.