Narrative:

After approximately 30 mins of level cruise; a fuel imbal EICAS message with procedural symbol appeared. Looking into the situation the following was noted: 1) left tank 59.3; center 9.0; right 62.5. 2) spread of approximately 700 pounds between totalizer and FMC calculated fuel. 3) fuel score initially down by approximately 1200 pounds. 4) no apparent aileron imbal was noted. We brought up the irregular procedure; kept monitoring the fuel load and contacted dispatch to establish a phone patch with maintenance. After checking the appropriate maintenance pages; no fuel gauge error was indicated. We also sent the off duty pilot to check for fuel leaks from the wings; engines or other structures. The first officer noted some atomized fuel appearing every 10 seconds from the left fuel dump nozzle. Maintenance was no help in trying to identify a fuel leak/uncommanded xfer to the fuel dump system. We continued to monitor the fuel tank quantities; noting the apparent loss of approximately 100 pounds every 10 mins from the left tank. Fuel feed was center tank to engines. The apparent loss ceased at 59000 pounds remaining in the left tank. We monitored the fuel after center tank fuel was depleted to 1800 pounds; with no other loss noted. The procedure for xfeed was followed; and fuel closely monitored for the remainder of the flight with no other loss indications noted. The fuel score improved to a plus score within a few hours. Diversion potential was discussed with dispatch should the need arise. An uneventful approach and landing in sfo ensued. A detailed maintenance write-up was accomplished with maintenance advised.

Google
 

Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.