CAPT OF WDB ACR ACFT MADE GAR TO ASSURE SEPARATION WITH A DEPARTING ACFT ON A 'CROSS RWY' DUE TO THE TWR RELEASING THE OTHER ACFT FOR TKOF WHEN THE RPTING ACFT WAS ON SHORT FINAL.

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THIS INCIDENT OCCURRED WHILE CONDUCTING AN ILS DME 27 APCH UNDER VMC CONDITIONS AT BOS ARPT. WE HAD BEEN CLRED FOR THE APCH TO MAINTAIN 180 KTS TO THE FINAL FIX; RIPIT; BUT DUE TO HVY FREQ CONGESTION; WERE NOT HANDED OFF TO TWR BY APCH CTL AT RIPIT. WE CONFIGURED FOR LNDG AT RIPIT AND SWITCHED TO TWR ABOUT 5 MI FROM THE RWY ON OUR OWN. THE TWR ADVISED US TO SLOW TO MINIMUM APCH SPD TO ALLOW A TKOF ON RWY 22L. TWR CLRED THE ACFT INTO POS TO BE READY FOR IMMEDIATE TKOF. WE INFORMED TWR THAT WE WERE AT MINIMUM SPD ALREADY. TWR GAVE OTHER ACFT TKOF CLRNC. TWR THEN ISSUED IMMEDIATE TKOF CLRNC TO ACFT ON RWY 22L AND ADVISED US TO BE PREPARED FOR A GAR. SHE SEEMED TO NOT BE FULLY IN CTL OF HER DUTIES AND HESITANT ABOUT INSTRUCTIONS TO BOTH OUR FLT AND OTHER ACFT. THE FO AND SO BEGAN LOOKING IN VAIN FOR THE ACFT ON TKOF ROLL AS I FLEW THE ACFT. SINCE RWY 27 CROSSES RWY 22L I FELT THAT A CONFLICT WOULD EXIST SHOULD THE ACFT ON RWY 22L ABORT DURING OUR LNDG ROLL. WE EXECUTED A GAR AT ABOUT 300 FT AGL AT WHICH TIME I OBSERVED THAT THE OTHER ACFT HAD BECOME AIRBORNE. SINCE STANDARD DEP PROCS REQUIRE ACFT DEPARTING RWYS 22L/R TO TURN L TO A HDG OF 140 DEGS IMMEDIATELY AFTER TKOF AND THE IMC MISSED APCH FOR RWY 27 REQUIRES A L TURN TO INTERCEPT THE 154 DEG RADIAL OF BOS VOR; I ELECTED TO PASS BEHIND AND TO THE R OF THE DEPARTING ACFT TO AVOID AN INFLT CONFLICT WITH BOTH ACFT IN L TURNS HEADED IN THE SAME DIRECTION. TWR GAVE US A NW HDG AND AN ALT FOR RESEQUENCING BACK TO RWY 27. IN MY OPINION; TKOF CLRNC TO OTHER ACFT SHOULD NOT BE ISSUED WHEN OTHER ACFT ARE ON SHORT FINAL TO XING RWYS. THE WORKLOAD OF MY CREW WAS SUCH THAT WE COULD NOT SAFELY COMPLETE COCKPIT CHKLISTS AND LOOK FOR DEPARTING TFC ON XING RWYS AT THE SAME TIME. OUR ONLY SOLUTION WAS TO EXECUTE A GAR RATHER THAN PLACE OUR ACFT ON A COLLISION COURSE WITH DEPARTING TFC.