B747-400 FO DISCOVERS ERROR IN FUEL ON BOARD VERSUS THAT SPECIFIED ON WEIGHT MANIFEST.

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FLT PLAN WAS INCORRECTLY FILED WITH A 98700 LB ERROR BY DISPATCHER. THIS RESULTED IN A WRONG FINAL WT MANIFEST BEING SENT TO THE CREW BASED ON A TOG OF 581556 LBS INSTEAD OF 679900 LBS. I WAS LUCKY TO PICK UP ON THE ERROR BECAUSE THE TOG WTS WERE SIGNIFICANTLY DIFFERENT AND THE TRIM REQUIRED ON THE FINAL WT MANIFEST WAS SIGNIFICANTLY DIFFERENT FROM THE TRIM REQUIRED IN THE FMC. THE FINAL WTS TRIM WAS 4.4 AND THE FMC SAID 5.5; A DIFFERENCE OF 1.1. AFTER DISCUSSING WITH THE CAPT; I NOTIFIED DISPATCH AND LOAD PLANNING OF THE INCORRECT FLT PLAN AND FINAL WTS. LOAD PLANNING SENT A MESSAGE THAT 'THE STATION HAD REVISED THE FINAL LOAD PLAN.' WE RECEIVED A NEW FLT PLAN AND NEW FINAL WTS BEFORE DEP. IN HINDSIGHT THE NEW 'FINAL WTS' WERE PROBABLY STILL WRONG. THE NEW 'FINAL WT MESSAGE' HAD A TRIM OF 5.0 AND THE FMC SAID THE TRIM SHOULD BE 5.5; A DIFFERENCE OF .5. I SET THE 5.5 BASED ON THE FMC AND WE TOOK OFF. IT APPEARS THERE IS NO SAFETY CHK BTWN THE FLT PLAN; FUEL BOARDED; AND THE FINAL WTS. WHERE DOES THE FUEL FIGURE COME FROM THAT IS USED ON THE FINAL WTS? THERE IS OBVIOUSLY A BREAKDOWN IN THE FINAL WTS VALIDATION PROCESS THAT CAN RESULT IN THE CREW TAKING OFF WITH A 100000 LB TOG ERROR. THERE IS NO FLEET SOP OR GUIDANCE GIVEN IN THE FLT MANUAL TO HELP CATCH THIS ERROR. IF THERE IS; THEN IT IS NOT BEING EFFECTIVELY TAUGHT IN TRAINING AND NOT BEING USED DURING LINE OPS. I ROUTINELY WATCH MOST B747-400 FO'S ON THE LINE SET THE TRIM BASED ON WHAT THE FINAL WT PAPERWORK SAYS; AND NEVER XCHK THE FMC. IT IS OBVIOUS BECAUSE THE NUMBERS ARE ROUTINELY .1 OFF. USUALLY THE MISTAKE WOULD BE CAUGHT BY THE BEFORE TKOF CHKLIST; BUT I ALSO MANY TIMES OBSERVE CAPTS USE THE TRIM SETTING PRINTED ON THE FINAL WTS PAPERWORK WHEN THEY CHK THE TRIM AND RESPOND TO THE CHKLIST. FLT PARTICULARS: DISPATCHER COMMENTS ON FLT PLAN SAID: 'ACFT WAS PREFUELED TO 268.5 FOR AN INTL FLT; ASKED TO DEFUEL DOWN TO 184.0.' HOWEVER; FLT PLAN CLRED FUEL WAS 88.5 INSTEAD OF 184.0. I BELIEVE THE B747 FMC SOFTWARE USES A SIMPLE LOOK UP TABLE; WHICH GIVES A PRESET TRIM VALUE BASED ON THE MACH ENTERED BY THE PILOT. IT DOES NOT DO A GROSS ERROR CHK BASED ON THE NOSE GEAR POS; ACTUAL MACH; AND ACTUAL GROSS WT.