EMB140 EXPERIENCED TCAS RA ON DSCNT FOR VISUAL APCH TO TVC AT APPROX 3200 FT; CITING LATE FREQ CHANGE TO TWR FROM M98.

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APCHING TVC; AND AFTER BEING CLRED FOR A VISUAL APCH; WE QUERIED MSP APCH IF WE SHOULD SWITCH TO TWR; WE WERE TOLD; 'NO; YOU HAVE TFC 12 O'CLOCK POS; XX MI; 2700 FT ORBITING.' (I BELIEVE WE WERE DSNDING THROUGH ABOUT 6000 FT.) THE TA'S GIVEN BY ATC WERE GIVEN ONLY TO OUR ACFT POS AND ALT; NOT DIRECTION OF FLT. WE TURNED AWAY FROM THE RPTED POS OF THE TFC WHILE MONITORING OUR TCAS. WE BEGAN TURNING TOWARDS THE RWY TO THE W OF RPTED TFC; BELIEVING THIS WOULD ALLOW US TO DIVERGE FROM THE CONFLICT ACFT; THUS ALLOWING US TO CONTINUE DSCNT TO THE RWY AND INTO CTLED CLASS D AIRSPACE. EVEN AS WE HAD ALTERED OUR HDG BY AS MUCH AS 25 DEGS; WE WERE STILL ADVISED TFC 12 O'CLOCK POS; SEVERAL TIMES; THEN OFF TO YOUR R (WE RESPONDED THAT THE TFC WAS NOT IN SIGHT TO EACH ADVISORY). WE INITIATED A CLB AS WE CAME TO ABOUT 500 FT ABOVE SAID ACFT. AT THE SAME MOMENT WE INITIATED THE CLB; WE RECEIVED A TCAS RA TO 'CLB;' WHICH WE WERE ALREADY RESPONDING TO; AND I VERIFIED THE MINIMUM CLB RATE WAS BEING ATTAINED. I SAW THE MARGIN OF SEPARATION AS LOW AS 300 FT. AS WE CLRED THE CONFLICT I ADVISED MSP APCH OF THE RA AND WE WERE CLBING. WE LEVELED AT 4000 FT. THE REMAINING PORTION OF THE FLT WAS UNEVENTFUL. I ASKED IF THAT ACFT WAS TALKING TO TWR. WE WERE THEN INFORMED YES. WHEN I PHONED TWR ON THE GND; THEY SAID THE ACFT WAS VFR AND FLYING A PRACTICE APCH TO RWY 28. THE TWR INFORMED US THAT THEY INSTRUCTED APCH TO HAND US OFF TO TWR BECAUSE OF THAT TFC. APCH CTL DID NOT EVER HAND US OFF; EVEN AFTER WE ASKED TO SWITCH OVER TO TWR.