MD80 CREW IN IMC TAKES EVASIVE ACTION AFTER RECEIVING TCASII RA ON APCH TO DFW.

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THE CAPT WAS THE PF INBOUND TO DFW. WE WERE TALKING TO APCH CTL AND HAD BEEN CLRED FOR THE ILS RWY 35C APCH. I HAD THE AUTOPLT COUPLED AND AS WE REACHED TUFFO; I STARTED A 1000 FPM DSCNT FROM 4000 FT TO 3000 FT. ABOUT 1/2 WAY DOWN WE RECEIVED A TCASII WARNING 'TFC; TFC.' THE FO AND I IMMEDIATELY LOOKED AT THE TCASII SCREEN WHICH WAS AT THE 5 MI SCALE; AND OBSERVED AN AMBER CIRCLE 400 FT BELOW; SLIGHTLY BEHIND AND TO THE R; WELL WITHIN 1 MI LATERALLY. THE TFC WAS IN LEVEL FLT. I IMMEDIATELY CUT MY DSCNT RATE. AT 200 FT VERT SEPARATION AND THE SAME LATERAL SEPARATION; I DISCONNECTED THE AUTOPLT AND STARTED TO CLB. THE LOWEST DSCNT POINT WAS 100 FT FROM THE TARGET. WE CONTINUED TO CLB TO 4500 FT AND LEVELED OFF. WE ONLY RECEIVED THE ONE TCASII WARNING BUT FROM WHAT WE HAD ON THE SCREEN; I THOUGHT IT WAS IMPERATIVE THAT WE GOT VERT SEPARATION AS QUICKLY AS POSSIBLE. DURING THIS ENTIRE TIME APCH CTL WAS TALKING TO OTHER ACFT AND THE PNF WAS UNABLE TO BREAK IN UNTIL JUST BEFORE ISSUE. WHEN CONTACT WAS MADE APCH CTL TOLD US TO GO TO TWR FREQ. THE FO ASKED IF APCH HAD SEEN OUR TFC CONFLICT. HE SAID THERE WAS A SAAB BEHIND US ON THE ILS TO RWY 35R. I GOT THE IMPRESSION FROM THE INFLECTION IN HIS VOICE THAT HE HAD MISSED THE ENTIRE INCIDENT. TFC WAS NOW CLR; ABOUT 3 MI PLUS; BEHIND AND TO THE R. I RETAINED THE GS AND COMPLETED THE APCH AND LNDG TO RWY 35C.