Transport Safety Investigation Bureau (TSIB) of Singapore released the final report on Singapore Boeing 777-200ER, turn back due to fuel discrepancy.
On 16 April 2014, while flying from Singapore to Johannesburg, the flight crew of a Boeing B777-200ER was prompted with a “FUEL DISAGREE” aircraft system message one hour into the flight. The flight crew noticed that, the fuel quantity onboard as calculated by the Flight Management Computer (FMC) based on the quantity of the fuel that had burnt off during the flight was less than the fuel quantity as measured by the aircraft’s fuel quantity indicating system (FQIS), and the difference between these two quantities was increasing.
After consulting the airline’s maintenance centre, the flight crew decided to return to Singapore. The aircraft landed in Singapore without incident.
After landing, and subsequent calculation showed that the aircraft had departed with some 127 tonnes of fuel, instead of 86 tonnes as displayed to the flight crew by the FQIS.
The flight crew initially instructed the RDO, to fuel the aircraft to a total fuel quantity of 82 tonnes. The flight crew later gave an instruction for a final total fuel quantity of 86 tonnes
The CT had earlier noted from the cockpit fuel quantity indicator before the refuelling operation that there was about 5.5 tonnes of fuel in the aircraft remaining from the previous flight. The uplift of 121.5 tonnes of fuel would make a total of about 127 tonnes. This would mean 41 tonnes above the target figure of 86 tonnes.
In order to check the quantity of fuel on the aircraft, the team’s lead technician performed a ‘magnastick’ check, a manual reading using floating gauges.
The cause of the overfuel situation was that the B777-200ER aircraft was erroneously recognised as a B777-200 version by the FQIS owing to a fault in the PSM. This had resulted in the eight sensors within the mid-section of the centre fuel tank of the B777-200ER not being computed by the aircraft’s FQIS and caused an under-reading of the fuel quantity.
The CT and LT underwent training on refuelling operation which included theory on magnastick check. However, there were no practical session on magnastick check during their training on refuelling operation. In addition, magnastick check was not a commonly performed task in the course of their work.