B777-222 FLT CREW MONITORS FUEL SYSTEM SUSPECTING POSSIBLE LEAK.

Narrative

AFTER APPROX 30 MINS OF LEVEL CRUISE; A FUEL IMBAL EICAS MESSAGE WITH PROCEDURAL SYMBOL APPEARED. LOOKING INTO THE SITUATION THE FOLLOWING WAS NOTED: 1) L TANK 59.3; CTR 9.0; R 62.5. 2) SPREAD OF APPROX 700 LBS BTWN TOTALIZER AND FMC CALCULATED FUEL. 3) FUEL SCORE INITIALLY DOWN BY APPROX 1200 LBS. 4) NO APPARENT AILERON IMBAL WAS NOTED. WE BROUGHT UP THE IRREGULAR PROC; KEPT MONITORING THE FUEL LOAD AND CONTACTED DISPATCH TO ESTABLISH A PHONE PATCH WITH MAINT. AFTER CHKING THE APPROPRIATE MAINT PAGES; NO FUEL GAUGE ERROR WAS INDICATED. WE ALSO SENT THE OFF DUTY PLT TO CHK FOR FUEL LEAKS FROM THE WINGS; ENGS OR OTHER STRUCTURES. THE FO NOTED SOME ATOMIZED FUEL APPEARING EVERY 10 SECONDS FROM THE L FUEL DUMP NOZZLE. MAINT WAS NO HELP IN TRYING TO IDENT A FUEL LEAK/UNCOMMANDED XFER TO THE FUEL DUMP SYS. WE CONTINUED TO MONITOR THE FUEL TANK QUANTITIES; NOTING THE APPARENT LOSS OF APPROX 100 LBS EVERY 10 MINS FROM THE L TANK. FUEL FEED WAS CTR TANK TO ENGS. THE APPARENT LOSS CEASED AT 59000 LBS REMAINING IN THE L TANK. WE MONITORED THE FUEL AFTER CTR TANK FUEL WAS DEPLETED TO 1800 LBS; WITH NO OTHER LOSS NOTED. THE PROC FOR XFEED WAS FOLLOWED; AND FUEL CLOSELY MONITORED FOR THE REMAINDER OF THE FLT WITH NO OTHER LOSS INDICATIONS NOTED. THE FUEL SCORE IMPROVED TO A PLUS SCORE WITHIN A FEW HRS. DIVERSION POTENTIAL WAS DISCUSSED WITH DISPATCH SHOULD THE NEED ARISE. AN UNEVENTFUL APCH AND LNDG IN SFO ENSUED. A DETAILED MAINT WRITE-UP WAS ACCOMPLISHED WITH MAINT ADVISED.