MLG CAPT ALLOWED THE FUEL CROSS SHIP BAL TO EXCEED ACFT LIMITATIONS IN ZLC CLASS A AIRSPACE.

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I WAS MANUALLY XFEEDING FUEL AT CRUISE ALT WHEN I BECAME DISTR; FORGETTING ABOUT THIS XFEED OP UNTIL A SIGNIFICANT IMBAL DEVELOPED -- APPROX 1800 LBS OUT OF BAL; 800 LBS OVER LIMIT. WE CORRECTED THE PROB PRIOR TO TOP OF DSCNT AND REMAINDER OF FLT WAS NORMAL. AUTOFLT WAS CORRECTING FOR THE IMBAL. HOWEVER; I DID NOT NOTICE THE SLOW CHANGE IN BANK ANGLE TOWARD THE LIGHT SIDE. I HAD BEGUN THE XFEED WHILE THE FO WAS OUT OF THE COCKPIT (IN THE LAVATORY) AND I'M NOT SURE I TOLD HIM I WAS XFEEDING. THE FLT ATTENDANT FOLLOWED THE FO INTO THE COCKPIT. WITH PUTTING AWAY THE MASK; TALKING WITH HER AND SUBSEQUENTLY PUTTING AWAY DEP PLATES AND LOOKING OVER APCH PLATES; I COMPLETELY FORGOT ABOUT THE XFEED -- PROBABLY +/-30 MINS. CONTRIBUTING TO MY INATTN; I HAD FAILED TO USE A 'REMINDER.' USUALLY I ATTACH MY IDENT BADGE TO THE YOKE. I THINK FATIGUE PLAYED A ROLE IN DEVIATING FROM MY NORMAL HABIT PATTERN. IN ADDITION; I WAS WEARING 'READING' GLASSES -- SOMETHING I HADN'T DONE MUCH BEFORE. WHILE I REVIEWED THE APCH; THE GLASSES ARE GOOD FOR READING; BUT BLURRED THE INST PANEL. ALL OF THESE FACTORS PLAYED THEIR SMALL ROLES IN THIS EVENT. BUT I THINK FATIGUE WAS THE BIGGEST. IT HAD BEEN A LONG DAY ALREADY AND I WAS NOT VERY ALERT. THINGS I PLAN TO DO DIFFERENTLY: 1) ALWAYS INFORM FO OF XFEED. 2) WHEN AN OBVIOUS DISTR PRESENTS ITSELF; TERMINATE XFEED AND RETURN TO IT WHEN THE DISTR -- WHATEVER IT IS -- IS GONE. 3) ALWAYS USE A REMINDER -- PERHAPS A MORE VISIBLE ONE AS WELL -- FOR DIMLY LIT COCKPITS AT NIGHT. 4) BE ALERT FOR FATIGUE. OBVIOUSLY; I HADN'T SCANNED THE INST PANEL IN CLOSE TO 30 MINS! 5) GET SOME OF THOSE SMALLER; 1/2 SIZE 'READERS' THAT D NOT OBSTRUCT VISION ABOVE MID LEVEL.