Incident Overview
On 16 April 2014, a Boeing 777-200ER registered as 9V-SVC, operated by Singapore Airlines, was en route from Singapore to Johannesburg when the flight crew received a "FUEL DISAGREE" warning approximately one hour after departure. The aircraft returned to Singapore and landed without incident. There were no injuries to persons or damage to the aircraft, and the flight crew did not encounter any handling difficulties.
Refuelling and Pre-Departure
The aircraft was scheduled to depart at 0130 hours Singapore time. Refuelling began at 0013 hours under the supervision of a Certifying Technician (CT) and a Lead Technician (LT) from an aircraft maintenance service provider. The flight crew initially requested 82 tonnes of fuel, later amended to 86 tonnes total. The refuelling dispenser operator (RDO) delivered fuel, and the LT stopped the operation when the Integrated Refuel Panel (IRP) indicated 86 tonnes. However, the RDO's receipt showed 121.5 tonnes uplifted. The CT noted that the aircraft had about 5.5 tonnes remaining from the previous flight, so 121.5 tonnes uplift would total about 127 tonnes—41 tonnes above the target.
The CT informed the flight crew of the discrepancy, and a manual fuel quantity check using magnasticks (fuel measuring sticks) was performed. The CT delegated the check to the LT, who only measured the centre fuel tank because the CT assumed the main wing tanks were full. Based on the LT's readings and that assumption, the CT calculated a total fuel of 86.001 tonnes. The flight crew accepted this figure, which matched the IRP and cockpit indication, and the aircraft departed at 0200 hours.
In-Flight Events and Return
About one hour into the flight, the Engine Indicating and Crew Alerting System (EICAS) displayed a "FUEL DISAGREE" message. The flight crew observed that the FMC-calculated fuel quantity (based on fuel burned) was less than the FQIS-measured quantity, and the difference was increasing. After consulting the airline's maintenance centre, the crew decided to return to Singapore. The aircraft landed safely.
Post-Flight Investigation
After landing, a manual measurement using magnasticks confirmed the aircraft had departed with approximately 127 tonnes of fuel. The investigation revealed that the IRP had been configured for a Boeing 777-200 (with a smaller centre tank) rather than the 777-200ER, causing the FQIS to incorrectly indicate 86 tonnes. The magnastick check was inadequate as the main wing tanks were not measured, and the CT did not personally perform the check as required by the fuelling manual.
Probable Cause
The incident occurred because the flight crew and ground personnel were not aware of the actual fuel load due to a combination of factors: the IRP was set to the configuration of a Boeing 777-200, leading the FQIS to indicate 86 tonnes when the actual load was about 127 tonnes; the magnastick check was inadequate because ground personnel assumed the main wing tanks were full and did not check them; and the certifying technician delegated the magnastick check to the lead technician instead of performing it himself, contrary to the fuelling manual.