A B777 CAPT DIVERTED FOR FUEL AFTER THE ACFT BURNED SOME RESERVE FUEL DURING AND EBND ATLANTIC CROSSING FLT.

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SOON AFTER DEP WE NOTED AN INCREASING DISCREPANCY BETWEEN PLANNED AND ACTUAL FUEL AT EACH SUCCESSIVE CHK POINT ALONG THE RTE OF FLT. WE ALSO NOTED THE FMS PROJECTED ARR FUEL AT ZZZZ WAS ABOUT 8000 LBS LESS THAN THE FLT PLAN AND FLT PROGRESS PROJECTIONS. THIS INCREASED TO MORE THAN 9000 LBS AS THE FLT PROGRESSED. THE ACFT APPEARED TO BE BURNING FUEL AT A NORMAL FUEL FLOW RATE. HOWEVER; THE FUEL FLOW DATA USED BY FLT PLANNING APPEARED TO HAVE BEEN MUCH LESS THAN ACTUAL. AS WE CONTINUED ONTO THE TRACK; IT BECAME APPARENT THAT WE WOULD MOST LIKELY ARRIVE AT ZZZZ WITHOUT SUFFICIENT ALTERNATE AND RESERVE FUEL FOR OUR ALTERNATE. ADDITIONALLY; AFTER WE WERE ALREADY ON THE TRACK; DISPATCH NOTIFIED US THAT WE HAD INSUFFICIENT ETP FUEL AND DID NOT HAVE ANY ACCEPTABLE ETPS WITH THE FUEL ONBOARD. WE ELECTED TO LAND AT ZZZZ1 FOR ADDITIONAL FUEL. HOWEVER; PER THE DISPATCHER'S ADVICE; WE CONTINUED ON THE TRACK WITHOUT AN ETP OR ALTERNATES THAT PROVIDED REQUIRED LOSS-OF-ENGINE DIVERSION OPTIONS. DISPATCH SENT US THE FOLLOWING TWO TEXT MESSAGES DURING OUR FLT THAT HIGHLIGHT THE PROBS. 1) AT XA34: 'I DID SOME CHKING. 3 OF THE LAST 4 DAYS ON THIS FLT HAVE OVER-BURNED BY MORE THAN 8000 LBS. THE 4TH OVER-BURNED BY 2100 LBS. WE ARE GETTING INTO THIS WITH OPS ENGINEERING. ALL OF THOSE FLT WERE ON OR CLOSE TO FLT PLAN TIME. REGARDING OUR FUEL PROB; RIGHT NOW IF CAPT CONCURS I RECOMMEND WE CONTINUE AND MONITOR THE FUEL. IF/WHEN WE GET TO A POINT WHERE WE DO NOT HAVE RESERVES AND FUEL TO ALTERNATE WE CAN LOOK AT A SHORTER ALTERNATE OR SWITCHING PLAN TO A RE-RELEASE TO LOWER ENRTE RESERVES. OF COURSE WE CAN ALWAYS LOOK AT STOPPING IF NECESSARY. IF I HAD TO PICK THE PLACE NOW IT WOULD PROBABLY BE ZZZZ1 BASED ON WX BUT THAT MAY CHANGE.' 2) AT XB45: 'JUST ONE OTHER FYI. BASED ON THE OVER-BURN YOU DO NOT HAVE ETP FUEL. IT IS LEGAL TO CONTINUE. ZZZ2 IS NO GOOD AS ALTERNATE DUE TO FORECAST 70 KT WINDS. ZZZZ3 IS NOT A LEGAL ALTERNATE DUE TO A TEMPORARY CONDITION OF 0800 METERS IN FOG. IF IT WERE LEGAL IT WOULD HAVE AN ETP POINT OF 3 HRS 58 MINS AND A FUBO OF 46105 WHICH IS ABOUT 1600 LBS CHEAPER THAN ZZZZ1.'