MLG BEGINNING TKOF HAS NMAC WITH MLG LNDG ON INTERSECTING RWY.

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WE WERE CLRED INTO POS TO HOLD ON RWY 9 AT BOS. DURING SECOND ENG START AND SUBSEQUENT PWR TRANSFER SOME OF OUR FMS AND PERFORMANCE DATA 'DUMPED;' SO MY FO REINSERTED SOME OF THE DATA AND FINISHED BEFORE TKOF CHKLIST JUST AS WE WERE CLRED TO TKOF. TKOF ROLL BEGAN APPROX 5 SECONDS LATER THAN USUAL. WE HAD JUST BEGUN TO ROLL WHEN AN MLG A TOUCHED DOWN ON 4R ABOUT 200 FT IN FRONT OF US. THAT'S WHEN A DIFFERENT TWR CTLR CAME ON AND TOLD US TO ABORT. IF OUR FMS DATA HADN'T' DUMPED AND WE COULD HAVE STARTED OUR TKOF ROLL WHEN CLRED; WE WOULD HAVE COLLIDED WITH THE OTHER MLG MAKING HIS LNDG. A FREAK ELECTRICAL OCCURRENCE DURING PWR TRANSFER PREVENTED A COLLISION ON THE RWY BTWN 2 MLGS. THERE'S NOTHING WE COULD HAVE DONE ABOUT IT. WE COULDN'T SEE THE APCH PATH TO 4R (BEHIND AND TO OUR R). AND WE COULDN'T HEAR THE OTHER TFC BECAUSE IN THIS RWY CONFIGN IN BOS; THEY USE 2 CTLRS ON DIFFERENT FREQS. THIS IS THE SECOND RWY INCURSION NEAR MISS SIT THAT HAS HAPPENED ON MY FLTS IN AND OUT OF BOS IN THE LAST 2 MONTHS. I DON'T THINK INTERSECTING RWY OPS SHOULD CONTINUE; UNTIL ADVANCED EQUIP TO FORECAST POTENTIAL CONFLICTS IS IN USE. THIS WAS VERY NEARLY A MAJOR AIRLINE DISASTER.