ACR L1011 FLC DSNDING ON VECTORS FOR SEQUENCED APCH OBSERVED A TCASII TA RA. FLC OBSERVED CLBING B737 INITIATING EVASIVE TURN AND DSCNT. B737 FLC BROUGHT EVASIVE ACTIONS TO APCH CTLR'S ATTN; WHO TRIED TO APPLY VISUAL SEPARATION. ACTIONS INSUFFICIENT AND NOT TIMELY TO MAINTAIN STANDARD SEPARATION CRITERIA.

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ON ARR TO BOSTON; REQUESTED RWY 22 INSTEAD OF RWY 27. WAS GIVEN VECTORS (020 DEG HDG) AND DSCNT TO 6000 FT. ACFT AT 11000 FT TOLD TO SLOW; AMEND ALT TO 7000 FT. STARTED DSCNT. RECEIVED TCASII TA FOLLOWED BY RA. FO FLYING; SAW OTHER ACFT CLBING. OTHER ACFT (B737) MADE TURN AWAY FROM US. I TALKED TO TRACON SUPVR IN BOSTON. HE WAS AWARE OF INCIDENT AND INVESTIGATING. I FEEL THAT MY REQUEST TO THE RWY 22 CHANGED THEIR ARR PLAN TO RWY 27 AND THEY DID NOT ADJUST DEPARTING TFC PROPERLY. SUPPLEMENTAL INFO FROM ACN 409195: SAW OTHER ACFT; LOOKED AT TCASII; SHOWED 10000 FT CLBING. OTHER ACFT QUERIED ATC; SAID THEY SAW US AND WOULD MAINTAIN VISUAL. I STOPPED OUR DSCNT AND MAINTAINED VISUAL. OTHER ACFT MADE L TURN AND STOPPED THEIR CLB. SUPPLEMENTAL INFO FROM ACN 409559: PASSING APPROX 10000 FT WHEN THE FO VERBALIZED THAT TFC ON TCASII WAS APPEARING TO CLOSE ON US. WE THEN HEARD THE APCHING TFC QUERY ABOUT TFC (US) AT THEIR 12 O'CLOCK POS. ATC ASKED IF THEY HAD US VISUALLY AND THEY RESPONDED YES. ATC THEN TOLD THEM TO MAINTAIN VISUAL SEPARATION. WE HAD VISUAL ON THE TFC AND THEY WERE TURNING AWAY FROM US; SO WE DID NOT CHANGE COURSE. WE WERE ON VECTORS. MY BEST GUESS IS THE OTHER ACFT WAS OFF COURSE OR ATC FAILED TO RECOGNIZE THE TFC CONFLICT IN A TIMELY FASHION. SUPPLEMENTAL INFO FROM ACN 409031: WE SPOTTED AN L1011 AT 11 O'CLOCK; L TO R; AT 11000 FT DSNDING. AN IMMEDIATE EVASIVE MANEUVER TO AVOID COLLISION WAS TAKEN: 45 DEG L BANK; DSNDING TURN TO 9500 FT. ATC NOTIFIED/ CONFLICT RESOLVED. SUPPLEMENTAL INFO FROM ACN 408889: I WAS ON A COMBINED POS AND DID NOT NOTICE THE CONFLICT UNTIL B737 PLT MADE A COMMENT ABOUT IT.