MD80 FLC FOLLOWS TCASII RA ON APCH TO RWY 17L AT DFW.

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DURING ARR AT DFW FROM THE NE ON THE WILBR ARR; WE WERE CLRED FOR A VISUAL APCH TO RWY 17L. AS WE DSNDED FROM 5000 FT TO 3000 FT DURING A L TURN TO FINAL; TFC WAS RPTED BY REGIONAL APCH CTL OFF OUR R SIDE ON APCH TO RWY 17C. WE OBSERVED THAT TFC AND CONTINUED OUR L TURN TO INTERCEPT RWY 17L FINAL. AS WE CONTINUED OUR TURN TO FINAL; THE TFC FELL BEHIND OUR FIELD OF VIEW. APCH HANDED US OFF TO DFW TWR. AS WE INTERCEPTED FINAL; AFTER CHANGING TO TWR FREQ BUT BEFORE CONTACTING TWR; THE PREVIOUSLY RPTED TFC CAUSED OUR TCASII TO GIVE US A CORRECTIVE RA REQUIRING US TO CHANGE FROM OUR DSCNT TO A CLB. THE TFC HAD MOVED FROM OFF OUR R SIDE TO BEHIND AND BELOW US AND WAS NO LONGER VISIBLE. AS WE WERE OCCUPIED COMPLYING WITH THE RA; DFW TWR CONTACTED US AND ADVISED US TO CLB DUE TO A CONFLICT WITH THE ACFT BELOW AND BEHIND US. WE CLBED TO 3500 FT AND THE TCASII RA ABATED. I BELIEVE OUR CLOSEST APCH TO THE OTHER ACFT TO HAVE BEEN; ACCORDING TO TCASII DISPLAYED INFO; 400 FT ALT SEPARATION AND LESS THAN 1/2 MI LATERAL SEPARATION WITH THE ACFT IMMEDIATELY BEHIND AND BELOW US. AT THAT TIME THAT TFC CHKED IN WITH DFW TWR AND WAS CLRED TO LAND ON RWY 17L. WE EXECUTED A MISSED APCH BY FOLLOWING TWR INSTRUCTIONS.