Narrative:

During climbout; passing through about FL250; we received a fuel master caution with associated fuel imbalance pictured on the main fuel tank gauge display. As I recall; when we first noticed the imbalance after receiving the caution; we had about 7;300 pounds in the left main and 6;100 pounds in the right with the right going down quickly. We started with the fuel imbalance alert checklist in the QRH. As we worked through the possible causes listed in the checklist; we enlisted the help of a captain that was jumpseating and riding in the back to help us look for visible signs of a fuel leak. As he was looking for that out the passenger windows; we tried the crossfeed valve and it appeared to work correctly; meanwhile; the right tank was going down at a rate of double or a little faster than double of the left tank. The jumpseating captain then joined us on the flight deck as we decided an extra opinion and help would be beneficial. It was determined that it would be necessary to continue to the engine fuel leak checklist. By this time we had climbed to and leveled off at FL350. As we looked ahead at the checklist and saw that it mandated an engine shutdown; we declared an emergency with center and coordinated our return to the departure airport. We were now heading west back when I ran the engine fuel leak checklist. That checklist then refers to the engine failure/shutdown checklist. I read through every item and every note in all the checklists and conferred with both these captains to ensure that we weren't missing something or misdiagnosing the problem before we shut down that #2 engine. All three of us agreed that the fuel was going down on the right side at a rapid rate and it warranted continuing with the shutdown checklist. At this time; as I recall; we had about 6;900 in the left tank and about 5;400 in the right. The checklist was run and the right engine was shutdown. We made a long slow controlled descent back into the runway with no further incident. We were greeted by the fire trucks; informed tower that we needed no further assistance; and proceeded to the gate where we were met by several maintenance personnel; a chief pilot and several other people. After our long descent with the right motor shut down; upon arrival at the gate; the fuel gauges were nearly equal again. We had time on our next deadhead flight to review what we'd done. The question comes to mind that what if it was an issue with the fuel crossfeed valve that we somehow overlooked? We feel that we checked it adequately during the event enough to rule it out; but the possibility exists. We feel that if anything we erred to the side of safety in making an air return. We did have questions about why the engine shutdown was mandated through the series of checklists; but can only assume it is to reduce the chance of fire from not knowing where the fuel leak could be. I felt good about our CRM; teamwork; and the added benefit of having an additional captain helping back up our decisions.

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Original NASA ASRS Text

Title: A B737-700 FUEL MASTER CAUTION alerted when the right tank fuel quantity decreased more quickly than the left tank and after completing the Fuel Leak Checklist the crew shutdown the right engine; declared an emergency and returned to the departure airport. A faulty crossfeed valve was suspected.

Narrative: During climbout; passing through about FL250; we received a Fuel Master Caution with associated fuel imbalance pictured on the main fuel tank gauge display. As I recall; when we first noticed the imbalance after receiving the caution; we had about 7;300 LBS in the left main and 6;100 LBS in the right with the right going down quickly. We started with the Fuel Imbalance Alert Checklist in the QRH. As we worked through the possible causes listed in the checklist; we enlisted the help of a Captain that was jumpseating and riding in the back to help us look for visible signs of a fuel leak. As he was looking for that out the passenger windows; we tried the crossfeed valve and it appeared to work correctly; meanwhile; the right tank was going down at a rate of double or a little faster than double of the left tank. The jumpseating Captain then joined us on the flight deck as we decided an extra opinion and help would be beneficial. It was determined that it would be necessary to continue to the Engine Fuel Leak Checklist. By this time we had climbed to and leveled off at FL350. As we looked ahead at the checklist and saw that it mandated an engine shutdown; we declared an emergency with Center and coordinated our return to the departure airport. We were now heading west back when I ran the Engine Fuel Leak Checklist. That checklist then refers to the Engine Failure/Shutdown Checklist. I read through every item and every note in all the checklists and conferred with both these Captains to ensure that we weren't missing something or misdiagnosing the problem before we shut down that #2 Engine. All three of us agreed that the fuel was going down on the right side at a rapid rate and it warranted continuing with the Shutdown Checklist. At this time; as I recall; we had about 6;900 in the left tank and about 5;400 in the right. The checklist was run and the right engine was shutdown. We made a long slow controlled descent back into the runway with no further incident. We were greeted by the fire trucks; informed Tower that we needed no further assistance; and proceeded to the gate where we were met by several Maintenance personnel; a Chief Pilot and several other people. After our long descent with the right motor shut down; upon arrival at the gate; the fuel gauges were nearly equal again. We had time on our next deadhead flight to review what we'd done. The question comes to mind that what if it was an issue with the fuel crossfeed valve that we somehow overlooked? We feel that we checked it adequately during the event enough to rule it out; but the possibility exists. We feel that if anything we erred to the side of safety in making an air return. We did have questions about why the engine shutdown was mandated through the series of checklists; but can only assume it is to reduce the chance of fire from not knowing where the fuel leak could be. I felt good about our CRM; teamwork; and the added benefit of having an additional Captain helping back up our decisions.

Data retrieved from NASA's ASRS site 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.