Narrative:

Once on radar vectors at 10000 ft MSL and 250 KIAS after beuty intersection the first officer discovered that the main tanks were out of balance: left 8850 pounds; center 200 pounds; right 5250 pounds. I directed the first officer to get out the QRH while I set up the fuel panel: opened xfeed valve; kept left main tank pumps; kept center tank pumps off; turned right pumps off. QRH was not much of a help. While trying to understand what the problem is and how to solve it; the autoplt kicked off and the airplane wanted to roll slowly to the left confirming to me that we had a fuel imbalance. However; I did not notice prior to that a large yoke deflection. While having just started hand-flying and re-trimming the aircraft I let the airplane climb to 10400 ft MSL before correcting back to 10000 ft MSL. ATC immediately called us and I told the controller that we had a fuel imbalance and that we have to correct this before we can start our approach into lga. I brought the imbalance within limits before starting the final approach; but due to runway change and breaking off the first final approach due to spacing; and an overshoot caused by a 44 KTS crosswind at 1500 ft MSL to runway 31 we ended up landing with main tanks completely in balance. While I am fully aware that I should have caught the imbalance much earlier (I usually and routinely look at the complete fuel panel) I still; while writing this; cannot understand how the 'failed' tank is able to feed both engines even during high fuel flow demands and additionally bleed fuel back into the center tank. We never had an annunciator light illuminate.

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Original NASA ASRS Text

Title: MD80 FLT CREW HAS A FUEL IMBALANCE WHILE ENRTE.

Narrative: ONCE ON RADAR VECTORS AT 10000 FT MSL AND 250 KIAS AFTER BEUTY INTXN THE FO DISCOVERED THAT THE MAIN TANKS WERE OUT OF BAL: L 8850 LBS; CTR 200 LBS; R 5250 LBS. I DIRECTED THE FO TO GET OUT THE QRH WHILE I SET UP THE FUEL PANEL: OPENED XFEED VALVE; KEPT L MAIN TANK PUMPS; KEPT CTR TANK PUMPS OFF; TURNED R PUMPS OFF. QRH WAS NOT MUCH OF A HELP. WHILE TRYING TO UNDERSTAND WHAT THE PROB IS AND HOW TO SOLVE IT; THE AUTOPLT KICKED OFF AND THE AIRPLANE WANTED TO ROLL SLOWLY TO THE L CONFIRMING TO ME THAT WE HAD A FUEL IMBALANCE. HOWEVER; I DID NOT NOTICE PRIOR TO THAT A LARGE YOKE DEFLECTION. WHILE HAVING JUST STARTED HAND-FLYING AND RE-TRIMMING THE ACFT I LET THE AIRPLANE CLB TO 10400 FT MSL BEFORE CORRECTING BACK TO 10000 FT MSL. ATC IMMEDIATELY CALLED US AND I TOLD THE CTLR THAT WE HAD A FUEL IMBALANCE AND THAT WE HAVE TO CORRECT THIS BEFORE WE CAN START OUR APCH INTO LGA. I BROUGHT THE IMBALANCE WITHIN LIMITS BEFORE STARTING THE FINAL APCH; BUT DUE TO RWY CHANGE AND BREAKING OFF THE FIRST FINAL APCH DUE TO SPACING; AND AN OVERSHOOT CAUSED BY A 44 KTS XWIND AT 1500 FT MSL TO RWY 31 WE ENDED UP LNDG WITH MAIN TANKS COMPLETELY IN BAL. WHILE I AM FULLY AWARE THAT I SHOULD HAVE CAUGHT THE IMBALANCE MUCH EARLIER (I USUALLY AND ROUTINELY LOOK AT THE COMPLETE FUEL PANEL) I STILL; WHILE WRITING THIS; CANNOT UNDERSTAND HOW THE 'FAILED' TANK IS ABLE TO FEED BOTH ENGS EVEN DURING HIGH FUEL FLOW DEMANDS AND ADDITIONALLY BLEED FUEL BACK INTO THE CTR TANK. WE NEVER HAD AN ANNUNCIATOR LIGHT ILLUMINATE.

Data retrieved from NASA's ASRS site as of January 2009 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.