B757-200 DISPATCHED WITH R WING FUEL QUANTITY GAUGE INOP. AT TOP OF DSCNT; CREW NOTICED DISCREPANCY IN L FUEL GAUGE. CHKED RUDDER TRIM; CONFIRMED IMBAL. NO LEAK DETECTED.

Narrative

WE WERE DISPATCHED WITH A R FUEL QUANTITY INOP. WE WERE USING CALCULATED FUEL AS IN ADDITION TO THE L FUEL GAUGE TO SUBSTITUTE FOR THE R FUEL GAUGE BEING INOP. THE FLT WAS FROM ZZZ1 TO ZZZ2 AND WE WERE AT AN ALT OF FL390. APCHING ZZZ3; I NOTICED A DISCREPANCY IN THE L FUEL QUANTITY. WHEN THE CAPT DID THE FUEL CHK OVER ZZZ3; HE SAID THAT WE WERE WITHIN 100 LBS OF OUR CALCULATED FUEL WHEN COMPARED TO THE FLT PLAN. I THEN POINTED OUT TO HIM WHAT THE L FUEL GAUGE WAS READING WELL BELOW WHAT IT SHOULD BE. WE TALKED ABOUT THE FACT THAT WE WERE USING CALCULATED FUEL; BUT THE L GAUGE SHOULD STILL BE CORRECT. AS WE CONTINUED SORTING OUT THE PROB; I POINTED OUT THAT THE ACFT SEEMED TO BE R WING HVY. I DISCONNECTED THE AUTOPLT AND IT WAS DEFINITELY R WING HVY. WE HAD STARTED TO RUN THE FUEL LEAK CHKLIST AND THE FLT ATTENDANT HAD NOT SEEN ANY LEAKS FROM THE L WING AREA. SEVERAL OF THE TROUBLESHOOTING ITEMS ON THE FUEL LEAK CHKLIST WOULD NOT HELP SINCE THE R FUEL GAUGE WAS ALREADY INOP. NOW THE CAPT WAS TALKING TO DISPATCH AND THEY WERE TRYING TO CONTACT MAINT. WE HAD STARTED DOWN BY THE TIME MAINT HAD GIVEN US THEIR ANSWER; WHICH WAS THE L FUEL GAUGE WAS INCORRECT IN ADDITION TO THE R FUEL GAUGE. THIS WAS BASED MAINLY ON THE FACT THAT THE FUEL FLOWS WERE BASICALLY EVEN AND OUR CALCULATED FUEL WAS CORRECT WITH THE FLT PLAN. WE AGREED WITH THEIR DIAGNOSIS EXCEPT FOR THE FACT THAT IT TOOK 7.5 UNITS OF L RUDDER TRIM TO GET THE WINGS LEVEL. WE WERE IN THE DSCNT BY THIS TIME AND DECIDED TO CONTINUE TO ZZZ2. WE DISCUSSED WHAT THE PROC WOULD BE IF THE ENG QUIT ON THE APCH. THE LNDG WAS UNEVENTFUL EXCEPT FOR THE HVY R WING. UPON REACHING THE GATE; THE L FUEL GAUGE SHOWED 200 LBS OF FUEL. WHEN WE RPTED FOR DUTY THE NEXT MORNING; WE FOUND OUT THAT WHEN MAINT HAD PERFORMED A DIPSTICK READING OF THE L TANK THEY FOUND THERE WAS ONLY 200 LBS OF FUEL AND THE R TANK CONTAINED 8000 LBS OF FUEL. WE DEPARTED THE GATE AT ZZZ1 WITH 20200 LBS OF FUEL AND HAD APPROX A 12000 LB BURN. WE USED 1000 LBS BEFORE TKOF AND DEPARTED WITH 19200 LBS OF FUEL. THE B757 IS NOT SUPPOSED TO XFER FUEL INFLT! WE HAD ONLY ABOUT 300 LBS OF FUEL IN THE CTR TANK SO IT WAS NOT A FACTOR IN THE EVENT.