B777 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 300; Flight Crew Total 15700; Flight Crew Type 3000
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Returned To Departure Airport
Aircraft
At our first abeam [fuel] checkpoint approximately 1:00 hour into the flight; we noted the fuel score was off by minus 2;500 pounds. We checked progress page 2 on the FMC and monitored the Totalizer vs. calculated figures. The Totalizer was decreasing at an abnormally high rate compared to normal. The disparity eventually reached a fuel score of minus 7;000 pounds. We accomplished the checklists; conferred with Dispatch and Maintenance Control and determined the best course of action was to return to ZZZ. We determined we did not have a fuel leak from the main tanks and could safely continue to ZZZ but that an overweight landing would be the safest choice of action. Dumping fuel with an unreliable fuel quantity system seemed a bad option. ATC; ZZZ Fire; Dispatch; Maintenance Control and Cabin Crew were all advised and responded professionally. The landing was uneventful.
I was the Pilot Monitoring. Approaching ZZZZZ intersection; I recorded the fuel and noted a 2;700 pound discrepancy. We looked at progress page 2 fuel values and noted the Totalizer fuel decreasing at a rapid rate. We looked at the fuel synoptic and it indicated that the center tanks were using fuel at an unusually high rate. It became obvious that a fuel imbalance was imminent; so we reviewed the appropriate checklists and contacted Dispatch and Maintenance Control. We did get a fuel disagree EICAS which led us to the Fuel Leak Checklist. Initially we had a 2;700 pound discrepancy that went up to 7;000 pounds. Upon discussion with Dispatch and Maintenance Control; we returned to ZZZ and [requested priority]. After performing the Fuel Leak Checklist; we switched to the L and R main tanks and the center tank seemed to stabilize. We went back to the center tank and it was still stable and seemed to be operating normally. Since we had what seemed to be a fuel leak; we decided to land overweight and not dump fuel as we weren't sure of our fuel status and if we had a leak or not. We landed at 620;000 [pounds]; used the longest runway; flaps 30 and auto brakes 4. We had the emergency vehicles meet us and they reported that they didn't see any fuel leakage or spillage. We returned to the gate still indicating a 7;000 pound imbalance between Totalizer and calculated fuel values. When we shut down engines; the fuel values both went to the Totalizer value (the lower of the two). We debriefed with mechanics and shared all the information we had and exchanged phone numbers in case of any further questions or findings.
B777 flight crew reported discovering a rapidly decreasing fuel quantity indication at the first enroute checkpoint.