D10 CTLR ALLEGES NMAC WHEN SEQUENCING 3 ACR JETS ONTO FINAL APCH AT DFW.

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I WAS WORKING THE FEEDER E POS DURING A BUSY ARR PUSH. I ASSIGNED ACR X A HDG TO GET HIM UP IN THE ARR SEQUENCE; WHICH HE READ BACK. HE FAILED TO MAKE THE TURN; RESULTING IN AN NMAC WITH AN E145. ACR X HAD SEVERAL MI TO MAKE THE TURN. IF HE WOULD HAVE; THE NMAC WOULD NOT HAVE OCCURRED. SUPPLEMENTAL INFO FROM ACN 461905: WE (ACFT Y) WERE GIVEN A VECTOR TO INTERCEPT ILS LOC RWY 35C AND SLOW TO 180 KIAS. FO (PF) BEGAN TO SLOW ACFT FROM 245 KIAS. FLT X AHEAD OF US WAS TOLD TO MAINTAIN 210 KIAS OR GREATER; AS HE WAS #1 FOR THE RWY. WE WERE THEN TOLD TO SLOW TO 170 KIAS. AS WE INTERCEPTED ILS LOC RWY 35C; FLT X AHEAD OVERSHOT THE LOC AS IT ATTEMPTED TO JOIN IT. WE RPTED THIS TFC IN SIGHT. THE CTLR; CONCERNED OVER SEPARATION; QUERIED THE FLT X THAT IT WAS AT 210 KIAS. FLT X STATED IT WAS AT 210 KIAS. FROM OUR PERSPECTIVE; IT APPEARED TO BE SLOWER THAN THAT. ATC THEN ASKED IF WE WERE AT 170 KIAS YET. THE CAPT STATED THAT WE WERE NOT AT 170 KIAS; BUT WERE SLOWING THROUGH 180 KIAS. AT THIS TIME; FLT X WAS ABOUT 2 MI AHEAD AND APPEARED TO BE INCREASING ITS SPD. ATC THEN ASKED IF WE WERE IN OUR L TURN TO 270 DEGS YET. CAPT STATED WE HAD NOT RECEIVED THAT VECTOR. ATC THEN ISSUED AN IMMEDIATE TURN TO 270 DEGS; WHICH WE COMPLIED WITH. FROM THIS POINT WE RECEIVED NUMEROUS VECTORS BUT NEVER A CLB INSTRUCTION. THIS SUBSEQUENTLY PLACED US IN FRONT OF ANOTHER FLT Z; WHICH WE HAD IN SIGHT. WE RECEIVED A TCASII RA TO DSND; AT THE SAME TIME ATC ISSUED A CLB TO 6000 FT. THE OTHER FLT Z ALSO HAD US IN SIGHT; AND DID NOT CHANGE ALT AS IT WAS INTERCEPTING ITS ASSIGNED ILS LOC AND WAS TURNING AWAY FROM US. FO LOWERED THE NOSE INTO THE GREEN UNTIL OUR RA ENDED; THEN BEGAN AN IMMEDIATE CLB TO 6000 FT. WE MAINTAINED 170 KIAS THROUGH THIS ENTIRE TIME; VECTORS TO ILS RWY 35C LOC AFTER THIS WERE UNEVENTFUL. IN OUR JUDGEMENT; THE CTLR WAS DOING A VERY GOOD JOB. I THINK HE MISJUDGED OUR ABILITY TO SLOW THE EMB145 FROM 245 KIAS TO 180 KIAS THEN 170 KIAS. THE FLT X AHEAD OF US MAY HAVE BEEN SLOWER THAN 210 KIAS OR GREATER ATC HAD ASSIGNED. WE THINK IT WOULD BE HELPFUL IF ACFT WERE GIVEN ASSIGNED AIRSPDS BY APCH AS WE MAKE OUR INITIAL CONTACT. FROM OUR PICTURE; THE CTLR OVERREACTED BY VECTORING US OFF THE APCH. THIS MADE SEPARATION THAT MUCH MORE DIFFICULT AND SUBSEQUENTLY PLACED US IN JEOPARDY WITH ANOTHER ACFT.