Narrative:

On preflight walk around; fluid was noted under number two engine. Contract maintenance came and we did an engine run on number two engine. No problems noted. Near cruise level off; I opened the fuel crossfeed valve and turned on the left center tank fuel pump as we had 500 pounds fuel in the center tank. The left center tank fuel low pressure light stayed illuminated. I turned off the left center fuel boost pump and turned on the right center tank boost pump. The right center tank fuel low pressure light stayed illuminated. I stopped trying to burn the fuel in the center tank. A few minutes later; the fuel imbalance warning illuminated. The right tank was 1;000 pounds low. I had not closed the fuel crossfeed valve. I left the crossfeed valve open and turned off the right main tank fuel pumps. I watched the fuel quantity gauges to verify that the imbalance was being corrected. After a few minutes; there was no difference in the left quantity and the right quantity was continuing to decrease. I alerted the first officer to the problem and explained what had transpired. We reviewed the fuel imbalance QRH checklist. As a precaution; we also reviewed the engine fuel leak checklist; which did not seem to apply. We were not using fuel at an excessive rate. We were not able to crossfeed and the imbalance was increasing. We contacted dispatch and explained the problem. It was a mutual agreement to divert. We declared an emergency and landed without incident. Subsequent testing by maintenance resulted in no discrepancies with the airplane. Try to ignore distractions during fuel operations.

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Original NASA ASRS Text

Title: B737-700 flight crew experiences a fuel imbalance after attempting to use 500 LBS remaining in the center tank and forgetting to turn the crossfeed off when no fuel can be used. When the imbalance is noted the fuel pumps for the low wing are turned off but the imbalance appears to grow worse. The flight diverts to a suitable airport but Maintenance can find no discrepancy.

Narrative: On preflight walk around; fluid was noted under number two engine. Contract Maintenance came and we did an engine run on number two engine. No problems noted. Near cruise level off; I opened the fuel crossfeed valve and turned on the left center tank fuel pump as we had 500 LBS fuel in the center tank. The left center tank fuel low pressure light stayed illuminated. I turned off the left center fuel boost pump and turned on the right center tank boost pump. The right center tank fuel low pressure light stayed illuminated. I stopped trying to burn the fuel in the center tank. A few minutes later; the Fuel Imbalance warning illuminated. The right tank was 1;000 LBS low. I had not closed the fuel crossfeed valve. I left the crossfeed valve open and turned off the right main tank fuel pumps. I watched the fuel quantity gauges to verify that the imbalance was being corrected. After a few minutes; there was no difference in the left quantity and the right quantity was continuing to decrease. I alerted the First Officer to the problem and explained what had transpired. We reviewed the Fuel Imbalance QRH Checklist. As a precaution; we also reviewed the Engine Fuel Leak Checklist; which did not seem to apply. We were not using fuel at an excessive rate. We were not able to crossfeed and the imbalance was increasing. We contacted Dispatch and explained the problem. It was a mutual agreement to divert. We declared an emergency and landed without incident. Subsequent testing by Maintenance resulted in no discrepancies with the airplane. Try to ignore distractions during fuel operations.

Data retrieved from NASA's ASRS site as of July 2013 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.