Date: 201701
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Inflight Event / Encounter Fuel Issue
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Weather
Primary problem: Weather

Narrative: Normal operations until 5 hours into flight.We operated in 'econ' which showed greater fuel and still an on time arrival; and very near flight planned M.84. We operated and climb near as the flight plan indicated; and we held steady at 200 to 400 LBS ahead on fuel; and 200 to 500 LBS under burn; again until 5 hours into flight.At crew change we first went to 600 LBS behind from 200 LBS ahead and to 600 LBS over burn from 300 LBS under burn. We received ATC clearance to cruise M.83 for the crossing as this was close to 'econ' and indicated about 1;200 LBS better fuel at landing. Tailwind had drop about 20 KTS from flight plan.Fuel flows where averaging under the flight plan. The burn and fuel was noted to relief crew. Upon return from rest increased over burn was noted to me at 140W as 2;100 LBS and behind 2;000 LBS gross. Inflight highest over noted as 2;600 LBS if memory serves. We noted a 6;000 LBS over burn after landing; but I failed to check number carefully as we subtracted planned flight burn from the total burn (not the flight burn); the over burn was 1;386 LBS when subtracting the flight planned fuel burn from the actual flight burn; there was 2;900 LBS taxi out burn; and 2;000 LBS taxi in burn. We took off 5;000 LBS under flight plan weight; so I do find it strange that we burned extra fuel; we were able to save another 1;000 LBS as ATC cleared us direct to fix on the approach deleting the arrival and we did a constant descent saving that 1;000 LBS; which if added to the 1;386 LBS = 2;300 LBS very close to the highest over burn calculated in cruise near the end of the flight. There are good notes on the master flight plan to be utilized in the investigation. I have noticed that the burn and fuel does well and then starts slowly over burn about half way into flight; winds aloft and ground speed difference and temperature. Difference don't seem to explain this change half way into flight. We did request a reweigh of the cargo. Normal operation approach; landing; taxi in; shutdown and post flight.The crew and I wonder about cargo over weight; as there has been some cases of this in past; and perhaps fuel bias problems. Our error in calculating the over burn once on the ground was not helpful as well to the most accurate information; but I've corrected that calculation in the report and other will look at this as well. Continue to look into the cargo weight and fuel bias; thanks for your time and effort. I attached some pics of the master flight plan; not best quality; but may help in short term.




Synopsis: Boeing 777 Captain reported a discrepancy in the FMC fuel remaining estimate. Initially it showed they would be landing with extra fuel; then 5 hours into the flight it showed they would be landing with less fuel than planned. It may have been due to an un-forecasted wind shift.