Narrative:

During cruise, we noticed the left fuel quantity indicator was abnormally low. We were dispatched with the right fuel quantity indicator deferred and were using the FMC totalizer to figure our fuel on board. We advised dispatch of the situation and requested a patch with maintenance. The fuel in the indicator was about 3000-4000 pounds. The totalizer showed normal burnout and each engine was burning the same amount, but the left indicator was still decreasing. We tried to determine if we had a fuel leak by running the fuel low checklist. A visual inspection of the left wing showed no signs of a leak. It was difficult determining if we had a left indicator problem or a real leak since the indicator kept going down but the totalizer showed normal fuel and normal burnout. We decided to continue toward the destination while sending messages to dispatch. We disconnected the autoplt and found that the right wing was abnormally heavy requiring 5-7 units of rudder trim to level the wings. This indicated that fuel was indeed being used out of the left tank but perhaps not the right, even though the fuel flow indicator continued to show equal burn. We did an idle descent towards the destination, found that we were #1 for the arrival and requested a short approach. We used the idle power on the left engine as much as possible and briefed the 'what if's' regarding a flameout as we now showed 400 pounds in the left tank. With an inoperative right indicator, xfeeding is not allowed so we continued to run tank to engine and tried to conserve fuel on the left side. WX was clear, we briefed the approach, ran the checklists, made the notifications, and flew a normal 2 engine approach to a normal landing. We blocked in with 200 pounds indicating in the left tank and 7900 pounds on the totalizer. Maintenance later confirmed these amounts. Supplemental information from acn 622533: I had received a call from dispatch stating she was unable to get a hold of me for a conference call with aircraft X. Contributing factors in not diagnosing unwanted fuel xfer: right fuel quantity indication and totalizer was blank. I was unable to determine if any fuel had migrated to the opposite side because of inoperative'ed right indication. Also with fuel totalizer inoperative'ed, I was unable to compare FMC calculated total fuel, to see if there was an actual fuel leak or accuracy of fuel indication between the 2 readings. All information was passed on to me by dispatcher. I had not spoken to the crew at any time during the flight. I was also occupied with numerous calls and was working with an FBO mechanic on the B767 pressurization problem at ZZZ1 during the same time. I had not asked the crew to turn off the autoplt to see if the aircraft flew right wing heavy because I was not conferenced into the radio patch by dispatch. Upon landing of aircraft, the log entry from the crew stated aircraft needed 7 units of left rudder trim to balance wings. I had not received this information from crew until he landed. By knowing this information while in-flight, I would have considered an unwanted fuel xfer and requested the crew to rebalance fuel. Aircraft was then ferried to ZZZ2 by test crew. Upon landing in ZZZ2 test crew called to report all fuel quantity indication was normal and would not duplicate any faults either. To prevent another recurrence of oversight in diagnosing an unwanted fuel xfer: 1) ensure proper communication between the flight crew and myself. 2) completely focus on the situation, regardless of workload. 3) ensure the flight crew does not have a 'heavy wing' after kicking off autoplt due to unwanted fuel xfer, regardless of fuel indication problem.

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Original NASA ASRS Text

Title: A B757-200 AT FL370, CREW NOTED L WING TANK FUEL QUANTITY DECREASING. R FUEL QUANTITY DEFERRED INOP. REQUIRED 5-7 UNITS OF RUDDER TRIM TO LEVEL ACFT. R WING HVY.

Narrative: DURING CRUISE, WE NOTICED THE L FUEL QUANTITY INDICATOR WAS ABNORMALLY LOW. WE WERE DISPATCHED WITH THE R FUEL QUANTITY INDICATOR DEFERRED AND WERE USING THE FMC TOTALIZER TO FIGURE OUR FUEL ON BOARD. WE ADVISED DISPATCH OF THE SIT AND REQUESTED A PATCH WITH MAINT. THE FUEL IN THE INDICATOR WAS ABOUT 3000-4000 LBS. THE TOTALIZER SHOWED NORMAL BURNOUT AND EACH ENG WAS BURNING THE SAME AMOUNT, BUT THE L INDICATOR WAS STILL DECREASING. WE TRIED TO DETERMINE IF WE HAD A FUEL LEAK BY RUNNING THE FUEL LOW CHKLIST. A VISUAL INSPECTION OF THE L WING SHOWED NO SIGNS OF A LEAK. IT WAS DIFFICULT DETERMINING IF WE HAD A L INDICATOR PROB OR A REAL LEAK SINCE THE INDICATOR KEPT GOING DOWN BUT THE TOTALIZER SHOWED NORMAL FUEL AND NORMAL BURNOUT. WE DECIDED TO CONTINUE TOWARD THE DEST WHILE SENDING MESSAGES TO DISPATCH. WE DISCONNECTED THE AUTOPLT AND FOUND THAT THE R WING WAS ABNORMALLY HVY REQUIRING 5-7 UNITS OF RUDDER TRIM TO LEVEL THE WINGS. THIS INDICATED THAT FUEL WAS INDEED BEING USED OUT OF THE L TANK BUT PERHAPS NOT THE R, EVEN THOUGH THE FUEL FLOW INDICATOR CONTINUED TO SHOW EQUAL BURN. WE DID AN IDLE DSCNT TOWARDS THE DEST, FOUND THAT WE WERE #1 FOR THE ARR AND REQUESTED A SHORT APCH. WE USED THE IDLE PWR ON THE L ENG AS MUCH AS POSSIBLE AND BRIEFED THE 'WHAT IF'S' REGARDING A FLAMEOUT AS WE NOW SHOWED 400 LBS IN THE L TANK. WITH AN INOP R INDICATOR, XFEEDING IS NOT ALLOWED SO WE CONTINUED TO RUN TANK TO ENG AND TRIED TO CONSERVE FUEL ON THE L SIDE. WX WAS CLR, WE BRIEFED THE APCH, RAN THE CHKLISTS, MADE THE NOTIFICATIONS, AND FLEW A NORMAL 2 ENG APCH TO A NORMAL LNDG. WE BLOCKED IN WITH 200 LBS INDICATING IN THE L TANK AND 7900 LBS ON THE TOTALIZER. MAINT LATER CONFIRMED THESE AMOUNTS. SUPPLEMENTAL INFO FROM ACN 622533: I HAD RECEIVED A CALL FROM DISPATCH STATING SHE WAS UNABLE TO GET A HOLD OF ME FOR A CONFERENCE CALL WITH ACFT X. CONTRIBUTING FACTORS IN NOT DIAGNOSING UNWANTED FUEL XFER: R FUEL QUANTITY INDICATION AND TOTALIZER WAS BLANK. I WAS UNABLE TO DETERMINE IF ANY FUEL HAD MIGRATED TO THE OPPOSITE SIDE BECAUSE OF INOP'ED R INDICATION. ALSO WITH FUEL TOTALIZER INOP'ED, I WAS UNABLE TO COMPARE FMC CALCULATED TOTAL FUEL, TO SEE IF THERE WAS AN ACTUAL FUEL LEAK OR ACCURACY OF FUEL INDICATION BTWN THE 2 READINGS. ALL INFO WAS PASSED ON TO ME BY DISPATCHER. I HAD NOT SPOKEN TO THE CREW AT ANY TIME DURING THE FLT. I WAS ALSO OCCUPIED WITH NUMEROUS CALLS AND WAS WORKING WITH AN FBO MECH ON THE B767 PRESSURIZATION PROB AT ZZZ1 DURING THE SAME TIME. I HAD NOT ASKED THE CREW TO TURN OFF THE AUTOPLT TO SEE IF THE ACFT FLEW R WING HVY BECAUSE I WAS NOT CONFERENCED INTO THE RADIO PATCH BY DISPATCH. UPON LNDG OF ACFT, THE LOG ENTRY FROM THE CREW STATED ACFT NEEDED 7 UNITS OF L RUDDER TRIM TO BAL WINGS. I HAD NOT RECEIVED THIS INFO FROM CREW UNTIL HE LANDED. BY KNOWING THIS INFO WHILE INFLT, I WOULD HAVE CONSIDERED AN UNWANTED FUEL XFER AND REQUESTED THE CREW TO REBALANCE FUEL. ACFT WAS THEN FERRIED TO ZZZ2 BY TEST CREW. UPON LNDG IN ZZZ2 TEST CREW CALLED TO RPT ALL FUEL QUANTITY INDICATION WAS NORMAL AND WOULD NOT DUPLICATE ANY FAULTS EITHER. TO PREVENT ANOTHER RECURRENCE OF OVERSIGHT IN DIAGNOSING AN UNWANTED FUEL XFER: 1) ENSURE PROPER COM BTWN THE FLT CREW AND MYSELF. 2) COMPLETELY FOCUS ON THE SIT, REGARDLESS OF WORKLOAD. 3) ENSURE THE FLT CREW DOES NOT HAVE A 'HVY WING' AFTER KICKING OFF AUTOPLT DUE TO UNWANTED FUEL XFER, REGARDLESS OF FUEL INDICATION PROB.

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.