A B757 ADMITTED THAT HE LANDED WITH A FUEL IMBAL.

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WE LANDED WITH A LATERAL FUEL IMBAL OF APPROX 4000 LBS BTWN THE WING TANKS. THE L WING HAD APPROX 8000 LBS AND THE R TANK HAD APPROX 4000 LBS. THE MAX LATERAL IMBAL FOR ALL OPS IS 1950 LBS. ALTHOUGH I ENSURED THE TOTAL FUEL AMOUNT WAS ADEQUATE THROUGHOUT THE FLT; AS WELL AS THE PROJECTED TOTAL FUEL FOR LNDG; I DID NOT NOTICE THE IMBAL BTWN THE OUTER TANKS. THIS WAS CAUSED BY NOT NOTICING THE FUEL XFEED WAS OPEN; RESULTING IN FUEL BEING USED FROM THE TANK WITH HIGHER FUEL PRESSURE. THE B757'S FUEL XFEED IS NORMALLY ONLY OPENED TO CORRECT FUEL IMBALS; SO IT IS LEFT IN THE CLOSED POS FOR TKOF. THERE'S NO EICAS MESSAGE TO ALERT THE CREW TO THE STATUS OF THE FUEL XFEED. THERE'S ONLY AN OBSCURE LIGHT IN THE SWITCH; TO INDICATE ITS POS. I'M NEW TO THE B767/757; AND AM USED TO THE A300'S FUEL PANEL DESIGN WHICH ALLOWS THE CREW TO EASILY RECOGNIZE THE XFEED'S POS. WE WERE ALERTED TO THE FUEL IMBAL BY THE ANNUNCIATION OF THE FUEL CONFIGN WARNING ON EICAS; BUT I DISREGARDED IT; THINKING IT WAS A RESULT OF CTR TANK FUEL BEING PRESENT WITH THE CTR TANK PUMPS BEING OFF. AS A RESULT OF AN ACR ACCIDENT; WE ARE REQUIRED TO BURN DOWN TO 1000 LBS IN THE CTR TANK. IF WE FORGET; AND BURN TOO MUCH FUEL (RESULTING IN LESS THAN 1000 LBS IN THE CTR TANK); WE'RE REQUIRED TO ANNOTATE THAT IN THE LOGBOOK. AS A RESULT; MOST PLTS ARE INCLINED TO TURN THE PUMPS OFF PRIOR TO 1000 LBS REMAINING IN THE CTR TANK. THE FUEL CONFIGN EICAS WARNING ILLUMINATES WHEN THERE IS 1200 LBS OR MORE OF FUEL REMAINING IN THE CTR TANK WITH THE FUEL PUMPS OFF. IT'S ALSO NOT UNCOMMON FOR THE FUEL CONFIGN EICAS WARNING TO ILLUMINATE DUE TO TURB; OR PITCH CHANGES; IF THE FUEL REMAINING IN THE CTR TANK IS JUST BELOW 1200 LBS REMAINING. THEREFORE; IT'S BECOME A 'QUASI-NORMAL' INDICATION. TO PREVENT THIS FROM OCCURRING IN THE FUTURE; I PLAN ON ENSURING THE FUEL XFEED IS CLOSED DURING THE 'BEFORE STARTING ENGS CHKLIST' AND TO RESPECT THE FUEL CONFIGN EICAS WARNING.