Narrative:

At cruise FL330 vicinity elsto (near stl), we received a fuel imbal EICAS message. Captain noticed that the fuel was below planned by 3000-4000 pounds. We had just checked the fuel a few mins prior and the fuel was on plan. We suspected fuel leak and altered the relief pilot (on break) to visually examine the engines and wing areas. No visual indicators of a fuel leak were detected. The fuel indication in the left main tank was decreasing rapidly from 63000 pounds (right tank quantity) to 47000 pounds. We elected to divert to stl initially while we ascertained the problem. ATC asked us if we wanted to declare an emergency. The captain said yes. We went through the fuel imbal checklist and turned on the xfeeds and turned off the left tank fuel pumps. We also went through the suspected fuel leak checklist. This checklist directs us to shut down an engine and we weren't ready for that yet. We were less than 100 NM from stl. While heading for stl, the fuel quantity was 47000 pounds left tank, 63000 pounds right tank, and 12000 pounds center tank. During our descent to FL180, we noticed that the left tank fuel level was no longer decreasing. The aircraft was dispatched with a fuel sensor status message problem. The left fuel quantity then increased to 51000 pounds and then disappeared completely. At that time we elected to enter holding and coordination with dispatch. After further examining the problem we were confident that the problem was a fuel quantity sensor. We elected to divert to ord where maintenance and passenger support were more readily available. During our divert to ord, the fuel indicators returned to a normal balanced condition. We terminated the emergency, dumped fuel (about 53000 pounds) to maximum landing weight. We terminated fuel dumping before 10000 ft MSL and made an uneventful landing on the longest available runway.

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Original NASA ASRS Text

Title: DIVERSION TO AN ALTERNATE BY A B777 FLT WHEN THE CREW DECIDES TO DIVERT TO AN ARPT WITH AN ADEQUATE MAINT FACILITY AFTER EXPERIENCING FUEL GAUGE PROBS, LNDG AT ORD, IL.

Narrative: AT CRUISE FL330 VICINITY ELSTO (NEAR STL), WE RECEIVED A FUEL IMBAL EICAS MESSAGE. CAPT NOTICED THAT THE FUEL WAS BELOW PLANNED BY 3000-4000 LBS. WE HAD JUST CHKED THE FUEL A FEW MINS PRIOR AND THE FUEL WAS ON PLAN. WE SUSPECTED FUEL LEAK AND ALTERED THE RELIEF PLT (ON BREAK) TO VISUALLY EXAMINE THE ENGS AND WING AREAS. NO VISUAL INDICATORS OF A FUEL LEAK WERE DETECTED. THE FUEL INDICATION IN THE L MAIN TANK WAS DECREASING RAPIDLY FROM 63000 LBS (R TANK QUANTITY) TO 47000 LBS. WE ELECTED TO DIVERT TO STL INITIALLY WHILE WE ASCERTAINED THE PROB. ATC ASKED US IF WE WANTED TO DECLARE AN EMER. THE CAPT SAID YES. WE WENT THROUGH THE FUEL IMBAL CHKLIST AND TURNED ON THE XFEEDS AND TURNED OFF THE L TANK FUEL PUMPS. WE ALSO WENT THROUGH THE SUSPECTED FUEL LEAK CHKLIST. THIS CHKLIST DIRECTS US TO SHUT DOWN AN ENG AND WE WEREN'T READY FOR THAT YET. WE WERE LESS THAN 100 NM FROM STL. WHILE HEADING FOR STL, THE FUEL QUANTITY WAS 47000 LBS L TANK, 63000 LBS R TANK, AND 12000 LBS CTR TANK. DURING OUR DSCNT TO FL180, WE NOTICED THAT THE L TANK FUEL LEVEL WAS NO LONGER DECREASING. THE ACFT WAS DISPATCHED WITH A FUEL SENSOR STATUS MESSAGE PROB. THE L FUEL QUANTITY THEN INCREASED TO 51000 LBS AND THEN DISAPPEARED COMPLETELY. AT THAT TIME WE ELECTED TO ENTER HOLDING AND COORD WITH DISPATCH. AFTER FURTHER EXAMINING THE PROB WE WERE CONFIDENT THAT THE PROB WAS A FUEL QUANTITY SENSOR. WE ELECTED TO DIVERT TO ORD WHERE MAINT AND PAX SUPPORT WERE MORE READILY AVAILABLE. DURING OUR DIVERT TO ORD, THE FUEL INDICATORS RETURNED TO A NORMAL BALANCED CONDITION. WE TERMINATED THE EMER, DUMPED FUEL (ABOUT 53000 LBS) TO MAX LNDG WT. WE TERMINATED FUEL DUMPING BEFORE 10000 FT MSL AND MADE AN UNEVENTFUL LNDG ON THE LONGEST AVAILABLE RWY.

Data retrieved from NASA's ASRS site as of July 2007 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.