B757-200 ON APCH TO BOS RWY33L EXPERIENCES TCAS RA WITH ACFT ON FINAL FOR RWY 32.

Narrative

I WAS THE CAPT AND PF ON A FLT FROM ZZZ TO BOS. AFTER BEING VECTORED AND CLRED FOR A VISUAL APCH TO RWY 33L; WE WERE TOLD THERE WAS ANOTHER ACFT ON APCH TO RWY 32 TO OUR L. WHILE ON APCH AT 2400 FT MSL; WITH THE AUTOPLT ENGAGED AND THE LOC AND GS CAPTURED WE RECEIVED A TFC ALERT FOLLOWED BY AN RA TO CLB. WE EXECUTED A MISSED APCH; INFORMED THE TWR AND WERE VECTORED FOR AN UNEVENTFUL APCH TO RWY 33L. BOSTON TWR SEEMED SURPRISED THAT WE WERE GOING AROUND; STATING THAT THE OTHER ACFT HAD (US) IN SIGHT. OBVIOUSLY THE RWY CTRLINES OF RWYS 33L AND 32 CONVERGE SOMEWHERE OVER HINGHAM BAY. ACFT BEING VECTORED TO THE 2 RWYS TOO FAR OUT RUN THE RISK OF COMING CLOSER THAN THE TCAS SYS ALLOWS. IT APPEARS THAT THE OTHER ACFT; WHETHER OR NOT THEY HAD US IN SIGHT; FLEW TOO CLOSE TO US AND CAUSED THE CONFLICT. IT'S SOMEWHAT DISCONCERTING THAT BOSTON TWR WOULD VECTOR ACFT TO THE 2 RWYS AND THEN FAIL TO MONITOR CLOSELY ENOUGH TO RECOGNIZE AND WARN THEM OF THE CONFLICT; AND WOULD; MOREOVER; BE SURPRISED THAT THE PROX CAUSED AN RA.