B777 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Landed in Emergency Condition
Human Factors; Aircraft
I was operating as Pilot Monitoring on the flight from ZZZZ to ZZZZ1. We left the ramp with 1;400 lbs more fuel than scheduled and a payload nearly 5;000 lbs below planned. We were de-iced and departed Runway XXR at XA:14Z with 199;200 lbs of fuel. (Min fuel was 196;200). The flight progressed normally except for seeing the fuel burn being higher than the flight plan called for. When we did the first position report the fuel remaining was 1;300 lbs lower than planned. We ran the checklist for suspected fuel leak; but decided the numbers always seemed to show this and they would improve later in the flight. We changed crews and let them know what we were seeing. They continued to monitor the situation and sent a few messages to the company regarding this. When we returned from our rest period; the crew let us know we were now 3;500 lbs behind scheduled fuel. We asked for shortcuts from ATC but were told to remain on flight plan route. We got holding instructions from [destination ATC] and advised them of our low fuel state. We contacted the company to arrange for ZZZZ2 as an alternate. This took several minutes at which point the 'insufficient fuel' message showed on the EICAS we ran the checklist and again told [destination ATC] of our low fuel. They said they could not accept our new alternate unless we declared mayday fuel. The Captain elected to declare mayday fuel; and we were vectored for a landing on XYR at ZZZ1. Landing fuel was 16;900 lbs. Scheduled flight time was 10:45 and we landed at 11:05 flight time. Scheduled landing fuel was 23;577 lbs. Possible higher than declared cargo weight; possible incorrect fuel calculation.
B777 First Officer reported a higher than planned fuel burn rate with cause unknown. Aircraft landed at destination airport with 'Insufficient Fuel' message displayed under priority handling by Air Traffic Control.