Narrative:

After reaching cruise altitude 'fuel confign' light came on indicating 2000# heavier in right fuel tank. Since this is sometimes a gauge error I decided to see if the fuel would balance on its own. As time went on, right tank stayed same and left tank went down at rate of feeding both engines but the xfeed valve indicated closed. I called system airborne maintenance (sam) and asked for help in understanding how this could happen. Sam had no answer as to how it could be. He asked if we really had an imbalance, as the difference between tanks grew to 10000#, the airplane was not wing heavy. With 0 trim the turn to right (high tank) was very slight. Flight test called and said if had a 7000 pounds imbalance the aileron control yoke would be displaced 45 degrees. Aileron was about 2 degrees left, not far from normal with 0 rudder trim. At this time it was not certain if we had an imbalance or fuel gauge error. Maintenance wanted aircraft on ground in slc, so with all the uncertainty of what really was happening, imbalance or fuel gauge, we landed at slc. Upon parking the airplane had 11400# difference, but the aircraft flew normally during approach. Landed 12000 pounds over maximum landing weight. It was safer to land than stay airborne to burn-out fuel. This aircraft has no fuel dump system. With all the correlating and coordinating at slc with slc line maintenance, passenger service, sfo maintenance, F/a's, passenger and dispatch, it was a very busy time. We rechked valve operation, line maintenance cleared aircraft (evidently minor inspection for landing over maximum gross), dispatch concurred and we flew aircraft to jfk with no further incident. Aircraft is now having a new fuel x-feed valve installed.

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Original NASA ASRS Text

Title: IMBALANCE OF FUEL--APPEARED TO BE WORSENING. FLT LANDED, DETERMINED CROSSFEED STUCK. CROSSFEED VALVE FREED, FLT CONTINUED TO DESTINATION.

Narrative: AFTER REACHING CRUISE ALT 'FUEL CONFIGN' LIGHT CAME ON INDICATING 2000# HEAVIER IN RIGHT FUEL TANK. SINCE THIS IS SOMETIMES A GAUGE ERROR I DECIDED TO SEE IF THE FUEL WOULD BALANCE ON ITS OWN. AS TIME WENT ON, RIGHT TANK STAYED SAME AND LEFT TANK WENT DOWN AT RATE OF FEEDING BOTH ENGS BUT THE XFEED VALVE INDICATED CLOSED. I CALLED SYS AIRBORNE MAINT (SAM) AND ASKED FOR HELP IN UNDERSTANDING HOW THIS COULD HAPPEN. SAM HAD NO ANSWER AS TO HOW IT COULD BE. HE ASKED IF WE REALLY HAD AN IMBALANCE, AS THE DIFFERENCE BTWN TANKS GREW TO 10000#, THE AIRPLANE WAS NOT WING HEAVY. WITH 0 TRIM THE TURN TO RIGHT (HIGH TANK) WAS VERY SLIGHT. FLT TEST CALLED AND SAID IF HAD A 7000 LBS IMBALANCE THE AILERON CONTROL YOKE WOULD BE DISPLACED 45 DEGS. AILERON WAS ABOUT 2 DEGS LEFT, NOT FAR FROM NORMAL WITH 0 RUDDER TRIM. AT THIS TIME IT WAS NOT CERTAIN IF WE HAD AN IMBALANCE OR FUEL GAUGE ERROR. MAINT WANTED ACFT ON GND IN SLC, SO WITH ALL THE UNCERTAINTY OF WHAT REALLY WAS HAPPENING, IMBALANCE OR FUEL GAUGE, WE LANDED AT SLC. UPON PARKING THE AIRPLANE HAD 11400# DIFFERENCE, BUT THE ACFT FLEW NORMALLY DURING APCH. LANDED 12000 LBS OVER MAX LNDG WT. IT WAS SAFER TO LAND THAN STAY AIRBORNE TO BURN-OUT FUEL. THIS ACFT HAS NO FUEL DUMP SYS. WITH ALL THE CORRELATING AND COORDINATING AT SLC WITH SLC LINE MAINT, PAX SVC, SFO MAINT, F/A'S, PAX AND DISPATCH, IT WAS A VERY BUSY TIME. WE RECHKED VALVE OPERATION, LINE MAINT CLRED ACFT (EVIDENTLY MINOR INSPECTION FOR LNDG OVER MAX GROSS), DISPATCH CONCURRED AND WE FLEW ACFT TO JFK WITH NO FURTHER INCIDENT. ACFT IS NOW HAVING A NEW FUEL X-FEED VALVE INSTALLED.

Data retrieved from NASA's ASRS site as of August 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.