Narrative:

[We were] waiting on taxiway to depart with 21;000 pounds of fuel in the center tank with both center tank pump switches 'on'; both engines running. Simultaneously both center fuel pump switches displayed 'low press' warning lights. Pulled off taxiway to trouble shoot and call maintenance. It was determined we should return to the gate. After about two hours of trouble shooting mechanic said maintenance control determined cause was a new system installed on aircraft as a result of the twa 747 center tank explosion. He told me he and the other station mechanics assisting him were unaware of any such system on our fleet and I told him that the flight crews are also unaware of any such system. We were both incredulous. He told me this system shuts down the center pumps at some point with low fuel in the center tank even if the crew should forget. Incredible-- a system on my aircraft I have no knowledge of; can't control; and may leave me with thousands of pounds of unusable fuel in the center tank. The problem could not be fixed and the aircraft went to the hanger. I find it hard to believe that no information about this system has been given to flight crews. In a dire emergency with low fuel our procedure is to use fuel in all tanks no matter the amount. With this system I cannot depend on remaining center tank fuel. Crossing the atlantic or using watrs for island flying I can imagine several scenarios where this could be a very dangerous problem.

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Original NASA ASRS Text

Title: A B757's center tank fuel pumps displayed 'LOW PRESS' as the aircraft held short for takeoff with 21;000 LBS in the center tank. A system modification designed to prevent a tank explosion with low center tank fuel quantity malfunctioned.

Narrative: [We were] waiting on taxiway to depart with 21;000 LBS of fuel in the center tank with both center tank pump switches 'on'; both engines running. Simultaneously both center fuel pump switches displayed 'low press' warning lights. Pulled off taxiway to trouble shoot and call Maintenance. It was determined we should return to the gate. After about two hours of trouble shooting Mechanic said Maintenance Control determined cause was a new system installed on aircraft as a result of the TWA 747 center tank explosion. He told me he and the other station mechanics assisting him were unaware of any such system on our fleet and I told him that the flight crews are also unaware of any such system. We were both incredulous. He told me this system shuts down the center pumps at some point with low fuel in the center tank even if the crew should forget. INCREDIBLE-- A system on my aircraft I have no knowledge of; can't control; and may leave me with thousands of pounds of unusable fuel in the center tank. The problem could not be fixed and the aircraft went to the hanger. I find it hard to believe that no information about this system has been given to flight crews. In a dire emergency with low fuel our procedure is to use fuel in all tanks no matter the amount. With this system I cannot depend on remaining center tank fuel. Crossing the Atlantic or using WATRS for island flying I can imagine several scenarios where this could be a very dangerous problem.

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.