LOSS OF TFC SEPARATION.

Narrative

M FLT NOV/XX/94 IAD-DEN; ACFT T; A DC10-10 IN CRUISE FL280; APPROX 65 MI SW OF STL VOR ON J110 WBOUND. AT XA18Z WE GOT A 'TFC; TFC' TA ON TCASII. THE TARGET WAS 12 O'CLOCK ON TCASII; OPPOSITE DIRECTION; SHOWING 28900 FT DSNDING. THE SO LOCATED THE TFC VISUALLY AT 12 O'CLOCK. TCASII SHOWED THE DISTANCE AT 15-18 MI. THE TA WAS FOLLOWED SHORTLY BY A 'DSND; DSND NOW' RA. I STARTED DSCNT FOLLOWING GUIDANCE ON THE VSI; AND HAD THE FO ADVISE ATC THAT WE ARE DSNDING IN RESPONSE TO AN RA. THE CTLR'S RESPONSE WAS APPROX 'DON'T DSND; TURN R TO HDG 360 DEGS.' RIGHT AFTER THAT HE INSTRUCTED US TO TIGHTEN UP THE TURN. BY THIS TIME THE RA CHANGED TO 'MONITOR VERT SPD' AND OUR ALT WAS ABOUT 27600 FT. THE FO OBSERVED THE CONFLICTING TFC'S ALT ON TCASII AT 28400 FT STILL DSNDING; THEN APPEARED TO START CLBING. I OBSERVED THE TFC PASSING JUST TO OUR L VISUALLY WHILE ON TCASII THE FO OBSERVED THE TARGET AND ALT READOUT PASS OVER AND JUST TO THE L OF THE CTR MARK ON THE TCASII SCREEN; 20 MI SCALE. ATC CLRED US TO FL270 FOR A WHILE; THEN BACK TO FL280; DIRECT TO BUM VOR AND ON COURSE. I ADVISED ATC AT THAT TIME THAT WE WERE FILING AN NMAC RPT. TCASII MAY HAVE SAVED 2 MORE.