B777-200
Dispatch Dispatcher
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Landed As Precaution
Aircraft; Company Policy; Procedure
The flight crew noticed a discrepancy between the fuel totalizer and the calculated fuel of approximately 7;000 lbs when they contacted dispatch. The dispatcher; the crew and tech tried to ascertain whether or not they had a fuel leak or were over burning in the left engine (due to a fuel imbalance between the left and right wing tanks) or had a malfunctioning totalizer. Once tech was able to get a snapshot of the fuel tanks; it was determined that the totalizer was working correctly and the discrepancy was now over 10;000 lbs between the totalizer and the calculated fuel. The flight diverted and made an emergency landing. According to all the position reports I had received that included the fuel; the fuel was the same as the flight plan fuel. This is due to the fact that all the position reports are based on the calculated fuel. The calculated fuel is based on what the FMC calculates the fuel flow [is] through the engines. The only way a fuel leak will be detected is when the crew cross checks the totalizer fuel against the calculated fuel. One of the reasons that the FAA requires position reports with time; altitude and fuel is so we (dispatchers) are aware of possible over burns or fuel leaks. This procedure on the B777 of only reporting the calculated fuel on automated position reports seems like an unsafe procedure; as the dispatcher is not getting an accurate reading of the fuel actually in the tanks of an aircraft.I believe there is a way that the totalizer fuel could be put into the free text part of the position report as an extra safety step. I do not know if there is a way to program the B777 to report the totalizer fuel instead of the calculated fuel in the automated position reports.
Dispatcher reported the flight crew discovered a fuel leak on their B777 that would have gone unnoticed by the Dispatcher because enroute fuel reports transmitted to Dispatch are calculated rather than actual fuel on board numbers.