B767 CREW TAKES EVASIVE ACTION FROM AN RJ IN ZBW CLASS E AIRSPACE AFTER ASSUMING VISUAL SEPARATION CLB DSCNT FROM EACH OTHER.

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AFTER DEPARTING BOS; WE WERE ON ZBW FREQ AT 14000 FT. TFC WAS CALLED AT 15000 FT AT 10 O'CLOCK POS. THE TFC AT 15000 FT RPTED US IN SIGHT AND WAS CLRED TO REMAIN IN VISUAL CONTACT. WE THEN ACQUIRED AND RPTED THE TFC IN SIGHT AND SUBSEQUENTLY CLRED TO FL230 AND TO REMAIN VISUAL. I INITIATED THE CLB ON AUTOPLT VERT SPD AT ABOUT 1500 FPM. THE FO AND I WATCHED THE TFC AND BOTH COMMENTED ON HOW CLOSE IT LOOKED. AFTER A FEW SECONDS; I DISCONNECTED THE AUTOPLT IN ANTICIPATION OF LOWERING THE NOSE. ABOUT THEN; THE TCASII ISSUED AN RA AND I LOWERED THE NOSE MORE. THE OTHER ACFT WENT OVER US L TO R AND A CLR OF CONFLICT WAS HEARD. SOON; THE CTLR ASKED IF WE HAD DIFFICULTY KEEPING THE TFC IN VISUAL CONTACT. THE FO RPTED NO. WE SAW THE TFC COMING AND I STARTED TO REACT BEFORE THE TCASII; BUT IT STILL WAS TOO CLOSE FOR COMFORT. IN OVER 30 YRS OF FLYING LARGE ACFT; THIS IS A FIRST. I DON'T THINK IT IS SAFE TO ALLOW VISUAL SEPARATION FOR JET ACFT. IT IS TOO HARD TO JUDGE THE SEPARATION AND CLOSURE RATES. I WILL NOT ACCEPT ONE AGAIN AND THERE IS AN ASSUMPTION ON BOTH AIRPLANES THAT YOU THINK YOU KNOW WHAT THE OTHER WILL DO; BUT YOU DON'T. BOTH THE COPLT AND I AGREE WE WILL JUST TAKE THE RADAR SEPARATION NEXT TIME WITH NO ASSUMPTIONS. SUPPLEMENTAL INFO FROM ACN 565898: HE CLRED US TO CLB TO FL230. I TOLD CTR WE HAD TFC AND WERE CLBING TO FL230. CTR TOLD US TO MAINTAIN VISUAL SEPARATION AS WELL. THE CAPT STARTED THE CLB IN VERT SPD. AT THIS TIME; THE RJ WAS ABOUT 5 MI AND HDG NW. WE WERE HDG W. AS WE STARTED TO CLB; I LOOKED AT THE RJ AND IT APPEARED TO BE TURNING TOWARD US. I WAS GETTING READY TO SAY SOMETHING TO THE CAPT WHEN WE GOT A TCASII TA. THE CAPT DISENGAGED THE AUTOPLT AND I LOOKED AT THE RJ AGAIN AND HE WAS STILL TURNING INTO US. THE CAPT WAS LOWERING THE NOSE AS THE RJ FLEW BEHIND US. I GUESSED THE DISTANCE TO BE AROUND 800 FT. AS THE RJ WAS PASSING BEHIND; WE GOT A MOMENTARY 'DSND' RA. A FEW MOMENTS LATER; CTR CALLED AND ASKED IF WE HAD ANY TROUBLE MAINTAINING A VISUAL WITH THE RJ AND I SAID NO. I FEEL IT WAS HARD TO JUDGE CLOSURE IN OUR CLB AND NEXT TIME I WOULD NOT CALL VISUAL ON THE TFC. I THINK THE RJ WAS TURNING TO PASS BEHIND US; BUT DID NOT REALIZE HE WAS CLOSING THE DISTANCE BTWN US. THE SIT DEVELOPED QUICKLY; SO NEXT TIME I WILL STAY AT A LOWER ALT TILL THE CONFLICTING TFC HAS PASSED.