FLC OF A SUPER MD80 STOPPED DSCNT DURING A VISUAL APCH DUE TO A TCASII TA AND THEN WAS INSTRUCTED BY APCH CTL TO CLB BACK TO THEIR ORIGINAL APCH ALT. THE CREW OBSERVED ANOTHER ACFT CROSS UNDERNEATH THEM AT 700 FT GOING TO ANOTHER RWY.

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LOCATION: DFW 350 DEG RADIAL/8 DME. WX CLR; VFR RETURN TO DFW ON JEN5 ARR FROM TUS. WE WERE ASSIGNED RWY 17C COMING FROM THE W. ON VECTORS TO A SHORT BASE LEG; WE WERE ASSIGNED BY ATC TO MAINTAIN 4000 FT UNTIL INTERCEPTING THE LOC. CLRED VISUAL APCH TO RWY 17C. AS WE WERE TURNING TO FINAL; INTERCEPTING THE LOC; WE STARTED A RATE OF DSCNT AS WE WERE SHOWING ALMOST 2 DOTS ABOVE GS ON THE ILS. PASSING 3800 FT; WE GOT A TA ON THE TCASII AND APCH IMMEDIATELY CAME UP AND CALLED FOR US TO CLB IMMEDIATELY BACK TO 4000 FT. AS WE INITIATED A MANUAL CLB BACK TO 4000 FT WE SAW TFC UNDERNEATH US ON A ANGLING BASE; FINAL TO RWY 18R. WE BOTTOMED OUT AT ABOUT 3600 FT; REINTERCEPTED THE LOC AND DID THE SLAM-DUNK TO GET BACK ON FINAL TO BE IN THE GROOVE AT 1000 FT. I BELIEVE ATC SHOULD NOT HAVE CLRED US FOR THE VISUAL APCH AFTER THE 4000 FT TO INTERCEPT INSTRUCTIONS; OR THEY COULD HAVE TOLD US THEY HAD XING TFC UNDERNEATH US THAT WE HAD TO CLR BEFORE DSNDING. CLRED FOR THE VISUAL FROM A 2 DOT HIGH ON THE GS PRECIPITATES A DSCNT TO GET DOWN ON THE GLIDE PATH BEFORE 1000 FT. COULD HAVE BEEN A NEAR MISS WITHOUT TCASII OR APCH INTERVENTION.