VISUAL SEPARATION -- THIS ACR CAPT IS TOLD THAT A DSNDING ACR HAD HIS ACFT IN SIGHT AND THAT HE WAS NOW CLRED TO CLB USING VISUAL SEPARATION TECHNIQUES. THE OTHER ACR APPARENTLY COULD NOT MAINTAIN SEPARATION AS THIS RPTR WAS FORCED TO FOLLOW 'RA' DIRECTIONS FOR SAFETY.

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WHILE CLBING OUT FROM DTW; ZOB CLRED US TO 15000 FT. AT ABOUT THE SAME TIME I HEARD CTR ADVISE A EMB120 COMMUTER ACFT OF OUR POS AND ALT. COMMUTER ACFT RPTED THAT THEY HAD VISUAL CONTACT WITH US. CTR THEN ISSUED THE COMMUTER A VISUAL DSCNT CLRNC TO 14000 FT. THE CTLR THEN INFORMED ME THE COMMUTER HAD ME VISUALLY AND WOULD STAY CLR AND I WAS RECLRED TO FL230. THE COMMUTER APPEARED ON MY TCASII AFTER SEVERAL MOMENTS AND BOTH MY FO AND I SPOTTED HIM VISUALLY. AT ABOUT 15100 FT IT BECAME APPARENT TO MYSELF AND MY FO THAT WE WERE ON A COURSE THAT WOULD INTERCEPT THE DSNDING COMMUTER. WITHIN MOMENTS TCASII ADVISED US TO DSND; WHICH WE DID AND INFORMED ATC OF THE TCASII RA. DSNDED TO 14400 FT WHICH REMOVED THE CONFLICT. WE THEN BEGAN OUR CLB AGAIN. I BELIEVE THE COMMUTER MAY NOT HAVE HAD US IN SIGHT. ALSO; MY EXPERIENCE HAS BEEN THAT HIGH RATES OF DSCNTS ON THE PART OF 1 ACFT WITH HIGH RATES OF ASCENT ON THE PART OF THE OTHER ACFT WILL GENERATE A TCASII RA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT SAID THAT HE DID NOT INITIALLY SEE THE EMB120 BRASILIA; HOWEVER THE FO SAW THE ACFT AND HE SAID THAT IT WAS ON A COLLISION COURSE JUST AS THE TCASII 'RA' ACTIVATED. HE PUSHED OVER HIS DC9-30 AND MISSED THE EMB120 BY ABOUT 1400 FT VERTLY AND 1 MI HORIZLY. THE RPTR SAID THAT HE HAS BEEN SAVED BY TCASII BEFORE.