Narrative:

We departed las vegas with an aircraft that had an mco (maintenance carry over) item relating to the left maintenance tank fuel quantity indication. It was not a problem that rendered the left system inoperative or even required that drip stick readings be made on that tank. During the preflight, we noted that the left and right fuel tanks had been fueled properly and that they were reading equally, according to the gauges. Shortly after leveloff, the fuel confign light came on and we noticed that there was a difference between the left and right gauges. Our initial thought was that this was erroneous and was a result of the previous mco (maintenance carry over) item. I then clicked off the autoplt and noticed that the left wing was heavier than the right wing. The first officer and I then decided to xfeed from the left to right side, assuming that the tanks really were out of balance. The first officer reached up and opened the xfeed valve and turned off the right pumps. We began to correct the imbalance, but there was still some difference upon landing. We wrote up this new problem and had maintenance at lax look at the situation. They could not find a reason for the fuel imbalance. My concern is that the original MEL item did not require that the tanks be checked with drip stick readings. I think any time you have a fuel problem of any kind that drip stick readings should be made as a precautionary backup. Had drip stick readings been taken at las, it might have detected the problem earlier.

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Original NASA ASRS Text

Title: B757 CREW WAS DISPATCHED WITH AN INOP FUEL QUANTITY GAUGE.

Narrative: WE DEPARTED LAS VEGAS WITH AN ACFT THAT HAD AN MCO (MAINT CARRY OVER) ITEM RELATING TO THE L MAINT TANK FUEL QUANTITY INDICATION. IT WAS NOT A PROB THAT RENDERED THE L SYS INOP OR EVEN REQUIRED THAT DRIP STICK READINGS BE MADE ON THAT TANK. DURING THE PREFLT, WE NOTED THAT THE L AND R FUEL TANKS HAD BEEN FUELED PROPERLY AND THAT THEY WERE READING EQUALLY, ACCORDING TO THE GAUGES. SHORTLY AFTER LEVELOFF, THE FUEL CONFIGN LIGHT CAME ON AND WE NOTICED THAT THERE WAS A DIFFERENCE BTWN THE L AND R GAUGES. OUR INITIAL THOUGHT WAS THAT THIS WAS ERRONEOUS AND WAS A RESULT OF THE PREVIOUS MCO (MAINT CARRY OVER) ITEM. I THEN CLICKED OFF THE AUTOPLT AND NOTICED THAT THE L WING WAS HEAVIER THAN THE R WING. THE FO AND I THEN DECIDED TO XFEED FROM THE L TO R SIDE, ASSUMING THAT THE TANKS REALLY WERE OUT OF BAL. THE FO REACHED UP AND OPENED THE XFEED VALVE AND TURNED OFF THE R PUMPS. WE BEGAN TO CORRECT THE IMBALANCE, BUT THERE WAS STILL SOME DIFFERENCE UPON LNDG. WE WROTE UP THIS NEW PROB AND HAD MAINT AT LAX LOOK AT THE SIT. THEY COULD NOT FIND A REASON FOR THE FUEL IMBALANCE. MY CONCERN IS THAT THE ORIGINAL MEL ITEM DID NOT REQUIRE THAT THE TANKS BE CHKED WITH DRIP STICK READINGS. I THINK ANY TIME YOU HAVE A FUEL PROB OF ANY KIND THAT DRIP STICK READINGS SHOULD BE MADE AS A PRECAUTIONARY BACKUP. HAD DRIP STICK READINGS BEEN TAKEN AT LAS, IT MIGHT HAVE DETECTED THE PROB EARLIER.

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.