LGT CROSSES A RWY WHILE AN MLG IS TAKING OFF FROM THAT RWY. GND CONFLICT RESULTS.

Narrative

WAS CLRED FOR TKOF ON RWY 22L BY TWR. AN LGT ALSO ON 119.1 HAD LANDED ON RWY 27 AND WAS TOLD BY TWR TO HOLD SHORT OF 22L FOR ACFT TO TKOF ON RWY 22L. THE LGT WAS TOLD TO EXIT ON TAXIWAY E. THE LGT CREW QUERIED BOS TWR ABOUT THE TURNOFF ON TAXIWAY E. WE WERE ON TKOF ROLL AT 145 KTS (V1;-144; V4-146; V2-150) AND SAW THE LGT XING RWY 22L ON TAXIWAY E IN FRONT OF US. WE CONTINUED THE TKOF. THE LGT CLRED RWY 22L. WE WERE AT 300 FT ALT WHEN WE CROSSED THE AREA WHERE THE LGT HAD CROSSED THE RWY. WHEN BOS TWR WAS IMMEDIATELY QUERIED; BOS TWR RESPONDED THE LGT HAD BEEN TOLD TO HOLD SHORT OF RWY 22L. THE REST OF THE FLT CONTINUED NORMALLY. WE SAW THE LGT APPEAR TO BE SLOWING DOWN TO HOLD SHORT OF 22L. ONLY AFTER WE WERE COMMITTED TO TKOF DID THE LGT CROSS THE ACTIVE RWY. BOS TWR SHOULD HAVE IMMEDIATELY REQUESTED 'HOLD SHORT OF 22L CONFIRMATION' WHEN THE LGT CREW APPEARED CONFUSED ABOUT THE TAXIWAY E TURNOFF INSTRUCTIONS. AT AN ARPT WITH NUMEROUS 'IN USE' XING RWYS; TWR AND CREWS SHOULD BE EXTREMELY ATTENTIVE TO ALL HOLD AND XING INSTRUCTIONS. A SIMPLE VISUAL SCAN DOWN A RWY WHEN CLRED TO CROSS A RWY SHOULD BE INCLUDED IN HABIT PATTERNS. SUPPLEMENTAL INFO FROM ACN 186922: WE TOLD TWR THAT WE WOULD IN FACT NOT MAKE THE TURNOFF. AT THIS POINT WE WERE PRETTY MUCH STOPPED. WE HEARD TWR ISSUE A CANCELLATION TO ANOTHER ACFT'S TKOF CLRNC. TWR THEN TOLD US TO TAXI STRAIGHT AHEAD ON RWY 27; TO EXPEDITE XING 22L; EXIT AT 'X' AND HOLD SHORT OF 22R. WE READ THAT ALL BACK INCLUDING EMPHASIS ON 'CLRED TO CROSS 22L'.