A B757-200 CREW HAD A FUEL IMBAL EXCEEDING CROSS SHIP LIMITS.

Narrative

DEPARTED LAS-PHX WITH FUEL XFEED VALVE OPEN (PROBABLY DUE TO MAINT ACTIVITY ON THE ACFT). JUST PRIOR TO DSCNT; DURING A NORMAL PANEL SCAN; A FUEL IMBALANCE OF 3100 LBS BTWN THE L AND R MAIN TANKS WAS NOTED. WE IMMEDIATELY BEGAN FUEL BALANCING; BUT DUE TO THE SHORT LEG LENGTH; WERE UNABLE TO CORRECT THE IMBAL TO LESS THAN 2700 LBS. A NORMAL APCH AND LNDG WAS CONDUCTED WITH ABSOLUTELY NO ROLL TENDENCY OR ADVERSE HANDLING. LNDG FUEL IN THE LOW TANK WAS OVER 4000 LBS. THE FUEL DIFFERENTIAL WAS; NO DOUBT; DUE TO STRONGER PUMP PRESSURES IN THE R TANK. THE FUEL CONFIGN WARNING ON THE 757; WITH THE FAA REQUIREMENT TO MAINTAIN 1000 LBS IN THE CTR TANK; BECOMES A 'FLT CREW TRAP.' THIS LIGHT COMES ON NUMEROUS TIMES ON EACH LEG; AND ALTHOUGH WE MAKE EVERY EFFORT TO CHK FOR LOW FUEL OR AN IMBAL; UNDER HIGH WORKLOADS; THIS CAN BE NEGLECTED. THIS LIGHT HAS BECOME A 'NORMAL' LIGHT AS WELL AS AN 'ABNORMAL' LIGHT; WHICH IS A VERY POOR SIT! IF WE ARE TO HAVE A REQUIREMENT OF 1000 LBS IN THE CTR TANK; THEN WE MUST ALSO BE GIVEN AN ADEQUATE WARNING SYS; NOT ONE THAT WE HAVE BECOME ACCUSTOMED TO FOR 99% AS NORMAL; WHILE 1% OF THE TIME; A SERIOUS WARNING. SUPPLEMENTAL INFO FROM ACN 574466: UPON ARRIVING AT ACFT; FOUND THAT ACFT HAD BEEN MISFUELED WITH FUEL PUT IN CTR TANK WITHOUT MAIN TANKS BEING FILLED. UNKNOWN TO US; SOMEONE EVIDENTLY TRIED TO XFER FUEL; BECAUSE IT WAS LATER DISCOVERED THAT THE XFEED VALVE WAS OPEN. ON PREFLT COCKPIT SET UP; I MISSED THE FACT THAT THE XFEED VALVE WAS OPEN. (SHOULD BE CLOSED FOR NORMAL FLT.) AT THIS POINT; THOUGH NOT FUELED IN THE NORMAL WAY; IT WAS WITHIN LIMITATIONS. FOR THE LAST SEVERAL MONTHS; 757 OP (AD?) WITH 1000 LBS OF FUEL IN THE CTR TANKS AT ALL TIMES IS REQUIRED. UPON BURNING DOWN CTR FUEL TO 1000 LBS; CTR FUEL PUMPS ARE TURNED OFF. BECAUSE THIS IS NOT A 'NORMAL' PROC (THOUGH IS REQUIRED RIGHT NOW); THIS TURNS ON A 'FUEL CONFIGN' LIGHT; WHICH CAN MEAN; AMONG OTHER THINGS; FULL IN CTR TANK WITH PUMPS OFF OR FUEL IMBAL BTWN L AND R MAIN TANKS. THUS; FOR THE PAST FEW MONTHS; WE HAVE BECOME ACCUSTOMED TO 'IGNORING' THE 'FUEL CONFIGN' LIGHT AS IT IS A 'TEMPORARY NORMAL' FOR OUR OPERATING CONDITIONS. UNFORTUNATELY; THIS TIME; IT APPLIED ALSO TO AN IMBAL BTWN MAIN TANKS. BECAUSE THE XFEED VALVE HAD INADVERTENTLY BEEN LEFT OPEN DURING FLT; THERE WAS XFEEDING OF FUEL; WHICH CREATED AN IMBAL GREATER THAN THE ACFT LIMITATION OF 1800 LBS. WE CAUGHT THE IMBAL'S SHORTLY BEFORE ARRIVING AT PHX; BUT DID NOT HAVE TIME TO CORRECT THE IMBAL CONDITION PRIOR TO SHUTDOWN. THOUGH; OVER THE PAST MONTHS; CREWS HAVE EVEN DISCUSSED HOW WE COULD BE LULLED INTO MISSING AN IMBAL LIKE THIS; BECAUSE OF GETTING USED TO THE 'FUEL CONFIGN' LIGHT AS A 'TEMPORARY NORMAL' UNTIL A MAINT FIX IS DONE; THIS HAPPENED TO US.