NMAC BTWN AN MD88 TURNING FINAL FROM A VISUAL BASE LEG AND A DORNIER; DO228 ON APCH TO THE SAME PARALLEL RWY. RPTR ABORTED APCH AND BEGAN TO CLB IN RESPONSE TO A TCASII RA.

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WE WERE ON A FLT FROM ATL TO TYS AT NIGHT RUNNING ON SCHEDULE. WE WERE BEING VECTORED FOR A VOR RWY 23L APCH. WX WAS NOT A FACTOR; VISIBILITY WAS 7 MI. I SUGGESTED TO THE CTLR THAT IF HE WOULD VECTOR US CLOSER TO THE ARPT I WOULD ACCEPT A VISUAL APCH. HE DID THIS AND A SHORT TIME LATER; ASKED IF WE HAD THE FIELD IN SIGHT. WE DID AND A SHORT TIME LATER HE CLRED US VISUAL TO RWY 23R (NO MENTION OF TFC). HE ASKED US TO CALL OUR BASE TURN. DUE TO WORKLOAD OF CONFIGURING THE ACFT AND RADIO TALK WE WERE LATE MAKING THE CALL. AT THIS POINT WE WERE BOTH AWARE THAT HE WAS WORKING ANOTHER ACFT ON ANOTHER FREQ BUT WE WERE NOT AWARE THAT THIS ACFT WOULD POSE ANY CONFLICT SINCE WE DID NOT HAVE HIM IN SIGHT (AN ACR Y COMMUTER). AS WE BEGAN OUR TURN TO FINAL THE CTLR POINTED OUT THE TFC AT 1 O'CLOCK POS. MY COPLT ACKNOWLEDGED THE TFC AND SAID 'CONFIRM YOU WANT US ON THE L NOW.' HE SAID THIS FOR 2 REASONS. ONE; TO GET THE CTLR STRAIGHTENED OUT ON WHICH RWY WE WERE CLRED TO; AND TWO; TO LET ME KNOW THAT WE NOW NEEDED TO BE LINING UP FOR THE L. THERE WAS NO IMMEDIATE RESPONSE FROM THE TWR. TO ADD TO THE CONFUSION; I HAD MISSED THE CALL ABOUT THE TFC. ALL I HEARD WAS 'CONFIRM YOU WANT US ON THE L.' ALL I KNEW AT THIS POINT WAS THAT THERE WAS A CONFLICT OVER WHICH RWY WE WERE TO LAND ON; NOT EVEN REALIZING THAT THERE WAS ANOTHER ACFT ON FINAL THAT WAS A POTENTIAL CONFLICT. WHEN THE TCASII TFC WENT OFF FOLLOWED 3 SECONDS LATER BY THE RA 'CLB' I SIMPLY EXECUTED THE RA AND ABORTED THE APCH. FOLLOWING THE RA I LEVELED MY WINGS AND COMMENCED AN IMMEDIATE CLB. THE RESULT WAS THAT OUR ACFT CROSSED THE FLT PATH OF THE COMMUTER ACFT. MY COPLT WAS ABLE TO KEEP THE ACFT IN SIGHT UNTIL WE WERE CLR OF CONFLICT. AT NO TIME DID WE BELIEVE THAT WE WOULD COLLIDE WITH THE OTHER ACFT.