FUEL IMBAL ON A B767 BECAUSE OF IMPROPERLY MANAGED XFEED VALVE.

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MANY CAUSAL FACTORS GO INTO THE CHAIN OF AN ACCIDENT. FORTUNATELY; IN THIS CASE; I WAS ABLE TO INTERRUPT AND BREAK A LINK IN THE CHAIN. THE SEQUENCE WE WERE FLYING HAD BEEN ALL-NIGHT FLYING. WHILE THE CREW WAS LEGALLY RESTED; THE BACK SIDE OF THE CLOCK FLYING ALWAYS ADDS ANOTHER DIMENSION TO ANY SIT. I HAVE NOTICED ON SEVERAL OCCASIONS THE FUELER; MAINT OR SOMEBODY HAS BEEN OPENING THE FUEL XFEED AND LEAVING IT THAT WAY. DURING THE COCKPIT PREFLT CHK FOR THIS PARTICULAR FLT; IT WAS NOT NOTICED THAT THE FUEL XFEED SWITCH WAS IN THE OPEN POS. WHILE; DOING MY PROCS DURING THE BEFORE STARTING ENGS CHKLIST AND DURING THE 'JUST PRIORS' I TWICE LOOKED AT THE FUEL CTL PANEL AND FAILED TO NOTICE THE XFEED WAS OPEN. WE WERE IN A B767-200 AND WERE CARRYING THE 1000 LBS OF BALLAST FUEL WE ROUTINELY CARRY. WE HAD APPROX 1700 LBS OF FUEL IN THE CTR TANK. THE CTR TANK PUMPS WERE NEVER TURNED ON SINCE THE BULK OF THAT FUEL WAS NON USABLE ANYWAY. WITH THE 1700 LBS OF FUEL IN THE CTR TANK THE FUEL CONFIGN LIGHT WAS ON AND WE HAD AN ASSOCIATED EICAS MESSAGE. WE HAD CANCELED THE EICAS MESSAGE AND 'HAVE BEEN CONDITIONED' TO NEGLECT THE AMBER FUEL CONFIGN LIGHT DUE TO THE FUEL IN THE CTR TANK AND THE CTR TANK PUMPS BEING OFF. I AM CERTAIN PRIOR TO ENG START THE FUEL WAS IN BAL BTWN THE MAIN TANKS. AFTER AN UNEVENTFUL START-UP; TAXI OUT; TKOF AND CLB; WE WERE ON OUR WAY TO OUR DEST. AT SOME POINT DURING THE CLBOUT; I SEEM TO REMEMBER THE FUEL CONFIGN MESSAGE BEING ON THE EICAS SCREEN BUT EITHER MYSELF OR THE COPLT CANCELED IT. HEY WE KNEW WHY THE FUEL CONFIGN ALERT WAS THERE; RIGHT? ABOUT 1 1/2 HR LATER AT FL390 MACH .82 I JUST KIND OF GOT A WEIRD FEELING. THE PLANE JUST SORTA FELT FUNNY. MAYBE A STRANGE NOISE; I'M NOT SURE; BUT I STARTED LOOKING AROUND. I HAD BEEN LOOKING OVER AT THE PROGRESS ON THE FUEL LOG AND WE WERE A LITTLE BEHIND BUT ALL SEEMED OK. AS I LOOKED AROUND THE COCKPIT ATTEMPTING TO FIND THE GREMLIN; I LOOKED UP AT THE FUEL PANEL AND WAS SHOCKED TO SAY THE LEAST. THE R WING TANK HAD ABOUT 15400 LBS OF FUEL AND THE L TANK HAD ABOUT 27500 LBS. WE HAD A LATERAL FUEL IMBAL OF ABOUT 12000 LBS. I IMMEDIATELY NOTICED THAT THE XFEED SWITCH WAS OPEN. I TURNED OFF THE R MAIN TANK PUMPS AND STARTED CALCULATING. I ALSO CHKED THE FLT CTL POS INDICATORS AND NOTICED THAT THERE WAS QUITE A SPLIT IN THE AILERONS. THE HVY L WING WAS DOWN AND THE LIGHT R WING WAS UP. IT TOOK US ABOUT 1 HR 8 MINS TO BAL THE FUEL AND RETURN TO A PROPER TANK TO ENG CONFIGN. MY ANALYSIS: SEVERAL POST-INCIDENT OBSERVATIONS. WHOEVER KEEPS OPENING THE XFEED NEEDS TO MAKE A NOTE TO PUT IT BACK IN A CLOSED POS. THE FLC MUST MAKE CERTAIN THAT ALL PROCS ARE FOLLOWED COMPLETELY. DO A PROPER PREFLT AND CHK ALL THE PROPER SWITCHES FOR A PARTICULAR PANEL BEFORE SAYING 'SET AND XCHKED.' OBVIOUSLY; IF EITHER OF US HAD DONE OUR JOBS CORRECTLY; WE WOULD HAVE NOTICED THE XFEED SWITCH POS WAS INCORRECT. NEXT; DURING THE ENRTE FUEL CHKS; IT IS ESSENTIAL CREWS FOLLOW THE PROC AND NOT JUST LOOK AT THE TOTAL FUEL BUT THE POTENTIAL FOR IMBAL. BUT THE POINT I WOULD LIKE TO STRESS RATHER THAN THESE OTHER SCREW-UPS IS THE FACT I HAVE BECOME CONDITIONED TO IGNORING AN AMBER 'FUEL CONFIGN' LIGHT AND ALERT EICAS MESSAGE. WE ARE INTENTIONALLY FLYING THESE PLANES AND REMOVING THE POTENTIAL TO TAKE THE 'FUEL CONFIGN' AMBER FUEL ALERT SERIOUSLY. THAT IS WHERE THERE LIES A REAL DANGER. MAYBE THERE NEEDS TO BE A SEPARATE ALERT FOR AN IMBAL AND A CTR TANK WITH FUEL AND NO PUMPS; ETC. HAD I NOT NOTICED AND THE IMBAL INCREASED; WE MIGHT HAVE HAD A SIT WHERE THE ACFT WAS NOT CTLABLE. ALSO; THIS PROVES THE POINT THAT WITH ALL THE MAIN TANK PUMPS ON AND THE XFEED OPEN; THE STRONGER PUMPS WILL WIN AND IMBAL THE ACFT.