Narrative:

The aircraft was fueled to 22.0 for our flight and our estimated fuel at takeoff would have been 21.4 which would be 9100 in each main and 2.9 in the center tank. The first officer was the PF and I was the PNF. Fuel flow was normal during the climb check through 10;000 feet. While we were still climbing to our initial cruising altitude of 33;000 feet; the PF announced 'center tanks are empty; center pumps off'. I visually and verbally concurred that the center tanks were at zero and the center pumps were off. At top of our climb; our fuel total was 17.1 and was notated on the release. This was estimated to be 22 minutes into the flight. I made a PA to turn off the seatbelt sign. I then ate a snack. I typically do a fuel check every 15 minutes; in addition to when we reach the next checkpoint on our route. At approximately 34 minutes into the flight; I looked at the fuel gauge and was in disbelief at what I saw. I pointed it out to the PF and we both had to take a minute to accept the readings on the fuel gauge. We had fuel in the center tank and fuel had burned down in the mains which exceeds the limitations of the aircraft. I looked up at the center pump switches and saw that they were off. I initially feared I had left the switches off prior to takeoff and questioned myself out loud but the PF confirmed that we had indeed burned the center tanks to zero and he had turned the switches off. The left main tank had about 5;000 pounds of fuel; the right main had about 7;500; and the center had 3;500. I did not write the numbers down but I am certain that we had 5;000 in the left main; 3;500 in the center; and a 2;500 pound imbalance from the right main which was another limitation that was exceeded. This fuel imbalance and fuel transfer had occurred in approximately 10 minutes of flight time. The first thought was to deviate to the nearest airport but we decided we needed to troubleshoot the issue first before the imbalance became unmanageable. We were approaching gjt and would divert there if we were unable to resolve the issue. The QRH did not have a procedure that directly addressed this issue. Aileron trim was not used and there was only a slight bank to the left on the flight controls. I cannot recall the exact sequence of what we did to resolve the issue. It was a combination of turning on the center pumps and turning off the left mains to stop fuel from entering the center tank. We determined right away that our fuel in the mains and center tank was usable. The next issue of concern was to correct the fuel imbalance and get it within limits. I have some past experience with fuel issues and know that an imbalance can negatively affect aircraft controllability; especially at slow airspeeds during landing. When the imbalance was within 1500 pounds; our next concern was cg so we burned the fuel out of the center tank until it reached zero. Then we proceeded to correct the imbalance between the two main tanks to zero. We had to leave the center pumps on; even though the tank was indicating zero fuel; to ensure fuel did not migrate through the check valves into the center tank. During this process; we called maintenance control (we still had fuel in the center tank and a 1500 lb imbalance when we called). Communication with maintenance and dispatch was difficult. My best guess is we were right about the halfway point in our flight; so we had been troubleshooting for about 20 minutes from when we first saw the issue. We continually lost communication with maintenance control. By the time we were able to finally conclude that we were ok to continue; we were about 280 miles from our destination. Our tanks were finally balanced at 5;000 pounds in each main and zero in the center tank. After that; all fuel pumps were left in the on position. While descending; with all the fuel pumps still on; fuel began to migrate into the center tank again. We landed with at least 150 pounds in the center tank; and the left main was about 300 pounds less than the right main tank even though we had balanced both mains and the center tank was at zero. Our total at the gate was 8;400 pounds of fuel. We landed and contract maintenance met the aircraft. The mechanic performed a procedure to clear debris from the check valves in the center tank. When he tested the results; the test failed; fuel was still pumping into the center tank. He had to perform the flushing procedure 3 times to clear the debris and get a successful test and clear us for flight. I confirmed with maintenance control prior to flight that an inspection was not required for exceeding the 1500 pound fuel imbalance limitation. Would like a procedure in the QRH for this type of issue. We are trained to monitor the instruments at all times but fuel checks are taught to be done at checkpoints on the flight plan rather than at time intervals. It was my military training of checking the fuel more frequently that caught an error that may have gotten us into a difficult situation.

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Original NASA ASRS Text

Title: MD80 Captain experiences fuel migration from the left wing tank to the center tank after the center tank pump switches have been turned off. The left wing tank pumps are turned off and the center tank pumps are turned on for the remainder of the flight; resulting in balanced wings and negligible fuel in the center tank at landing.

Narrative: The aircraft was fueled to 22.0 for our flight and our estimated fuel at takeoff would have been 21.4 which would be 9100 in each main and 2.9 in the center tank. The First Officer was the PF and I was the PNF. Fuel flow was normal during the climb check through 10;000 feet. While we were still climbing to our initial cruising altitude of 33;000 feet; the PF announced 'Center tanks are empty; center pumps OFF'. I visually and verbally concurred that the center tanks were at zero and the center pumps were off. At top of our climb; our fuel total was 17.1 and was notated on the release. This was estimated to be 22 minutes into the flight. I made a PA to turn off the seatbelt sign. I then ate a snack. I typically do a fuel check every 15 minutes; in addition to when we reach the next checkpoint on our route. At approximately 34 minutes into the flight; I looked at the fuel gauge and was in disbelief at what I saw. I pointed it out to the PF and we both had to take a minute to accept the readings on the fuel gauge. We had fuel in the center tank and fuel had burned down in the mains which exceeds the limitations of the aircraft. I looked up at the center pump switches and saw that they were off. I initially feared I had left the switches off prior to takeoff and questioned myself out loud but the PF confirmed that we had indeed burned the center tanks to zero and he had turned the switches off. The left main tank had about 5;000 pounds of fuel; the right main had about 7;500; and the center had 3;500. I did not write the numbers down but I am certain that we had 5;000 in the left main; 3;500 in the center; and a 2;500 pound imbalance from the right main which was another limitation that was exceeded. This fuel imbalance and fuel transfer had occurred in approximately 10 minutes of flight time. The first thought was to deviate to the nearest airport but we decided we needed to troubleshoot the issue first before the imbalance became unmanageable. We were approaching GJT and would divert there if we were unable to resolve the issue. The QRH did not have a procedure that directly addressed this issue. Aileron trim was not used and there was only a slight bank to the left on the flight controls. I cannot recall the exact sequence of what we did to resolve the issue. It was a combination of turning on the center pumps and turning off the left mains to stop fuel from entering the center tank. We determined right away that our fuel in the mains and center tank was usable. The next issue of concern was to correct the fuel imbalance and get it within limits. I have some past experience with fuel issues and know that an imbalance can negatively affect aircraft controllability; especially at slow airspeeds during landing. When the imbalance was within 1500 pounds; our next concern was CG so we burned the fuel out of the center tank until it reached zero. Then we proceeded to correct the imbalance between the two main tanks to zero. We had to leave the center pumps on; even though the tank was indicating zero fuel; to ensure fuel did not migrate through the check valves into the center tank. During this process; we called Maintenance Control (we still had fuel in the center tank and a 1500 lb imbalance when we called). Communication with Maintenance and Dispatch was difficult. My best guess is we were right about the halfway point in our flight; so we had been troubleshooting for about 20 minutes from when we first saw the issue. We continually lost communication with Maintenance Control. By the time we were able to finally conclude that we were OK to continue; we were about 280 miles from our destination. Our tanks were finally balanced at 5;000 pounds in each main and zero in the center tank. After that; all fuel pumps were left in the on position. While descending; with all the fuel pumps still on; fuel began to migrate into the center tank again. We landed with at least 150 pounds in the center tank; and the left main was about 300 pounds less than the right main tank even though we had balanced both mains and the center tank was at zero. Our total at the gate was 8;400 pounds of fuel. We landed and contract maintenance met the aircraft. The mechanic performed a procedure to clear debris from the check valves in the center tank. When he tested the results; the test failed; fuel was still pumping into the center tank. He had to perform the flushing procedure 3 times to clear the debris and get a successful test and clear us for flight. I confirmed with Maintenance Control prior to flight that an inspection was not required for exceeding the 1500 pound fuel imbalance limitation. Would like a procedure in the QRH for this type of issue. We are trained to monitor the instruments at all times but fuel checks are taught to be done at checkpoints on the flight plan rather than at time intervals. It was my military training of checking the fuel more frequently that caught an error that may have gotten us into a difficult situation.

Data retrieved from NASA's ASRS site as of April 2012 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.