AN MLG ACR CREW HAD A FAILURE IN THE CTR FUEL TANK TRANSFER SYS THAT WAS NOT NOTICED FOR AN HR AND A HALF.

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3 1/2 HR FLT FROM W COAST (LAX TO ORD). AT 10000 FT CLB CHK I ANNOUNCED AS PNF 'CHKLIST COMPLETE THROUGH 10000 FT; CTR PUMPS WORKABLE.' MEANING WE HAD FUEL IN OUR CTR FUEL TANK (MLG) AND PUMPS WERE FEEDING THE FUEL FROM CTR TANK TO ENGS. HOWEVER; APPROX 1 1/2 HRS LATER; I NOTICED THAT THE FUEL WAS NOT FEEDING FROM THIS TANK EVEN THOUGH A LARGE QUANTITY OF FUEL REMAINED. ONE OF THE 2 PUMPS IN THIS TANK HAD FAILED AND THE FUEL FEEDING THE ENGS WAS FROM THE WING TANKS. WE COMPLETED OUR ABNORMAL CHKLIST FOR THIS SITUATION AND THE FLT WAS COMPLETED TO OUR ORIGINAL DEST WITHOUT INCIDENT. I AM VERY AWARE OF THIS POTENTIAL FUEL PROBLEM. I KEEP A FUEL LOG AND PERIODICALLY CHK THE FUEL READINGS. ALSO; I AM WELL AWARE OF THE MLG PROBLEMS WITH LACK OF WARNING FOR FUEL PUMP FAILURE. DESPITE WRITING THE FUEL TANK READINGS DOWN; WE ALMOST FAILED TO NOTICE THIS SITUATION. EVEN THOUGH I WROTE DOWN THE FIGURES; I DIDN'T LET THE NUMBERS SINK IN; MOSTLY DUE TO FATIGUE. THIS MLG FUEL PUMP PROBLEM IS VERY INSIDIOUS AND REQUIRES MORE THAN WRITING NUMBERS DOWN; BUT FOCUS AND VIGILANCE IN MONITORING THE FUEL BURN WHEN FUEL IS IN THE CTR TANK.