DUE TO CVG SPACING CTL ACTIONS; CL65 INITIATES SPD REDUCTION TO FOLLOW LNDG TFC AHEAD WHILE SUBSEQUENT ACFT EXECUTES A GAR.

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APCH WAS VECTORING ACFT X TOWARD FINAL FOR RWY 18L AND ASKED IF WE HAD THE PRECEDING 'BAC JET' Y IN SIGHT. STILL ON BASE; WE DECIDED NOT TO CALL THE TFC IN SIGHT DUE TO THE HAZE. APCH THEN VECTORED US ONTO THE RWY 18L LOC AND; AS WE JOINED; THE BAC JET WAS CLRLY IN SIGHT BOTH VISUALLY AND ON TCASII SHOWING 3 MI AHEAD. WE TOLD APCH THAT THE BAC JET WAS IN SIGHT. APCH THEN CLRED US FOR THE RWY 18L VISUAL APCH AND TOLD US TO BOTH FOLLOW THE BAC JET AND MAINTAIN 170 KIAS UNTIL FRAZE; THE IFR FAF. PRIOR TO OUR REACHING FRAZE; WE WERE INDICATING 170 KIAS BUT THE SEPARATION WITH THE BAC JET BEGAN TO DECREASE RAPIDLY AS EVIDENCED BY TCASII. AS THE LATERAL DECREASED TO 2 MI; THE CAPT AND I DECIDED THAT IN ORDER TO MAINTAIN A SAFE IN TRAIL DISTANCE WE WOULD HAVE TO BEGIN SLOWING FROM 170 KIAS. SO WE CONFIGURED AND SLOWED ENOUGH TO MAINTAIN THE 2 MI SEPARATION. HOWEVER; THE ACFT Z BEHIND US; WHO WAS INITIALLY ONLY 3 MI BEHIND US; WAS MAINTAINING THE ASSIGNED SPD AND HAD CLOSED TO APPROX 1 1/2 MI BEHIND US. ATC THEN ASKED THE ACFT BEHIND US IF THEY WOULD BE ABLE TO CONTINUE. THERE WAS SOME DISCUSSION OF MAKING S-TURNS FOR SPACING. MEANWHILE WE ASKED WHAT THE BAC JET'S GND SPD WAS. ATC'S RESPONSE WAS 100 KTS; SO WE CONFIGURED TO MATCH THAT SPD OVER THE GND. THE ACFT BEHIND US ELECTED TO GO AROUND. WE MAINTAINED THE 2 MI SEPARATION AND LANDED WITHOUT INCIDENT. THE BOTTOM LINE IS THAT BY ACCEPTING THE VISUAL APCH TO FOLLOW PRECEDING TFC THAT WE HAD CALLED IN SIGHT; THE RESPONSIBILITY FOR MAINTAINING SAFE IN TRAIL AND WAKE TURB SEPARATION BECAME OUR RESPONSIBILITY. AND; AS IT TURNED OUT; THE CLRNC INSTRUCTIONS TO BOTH FOLLOW THE TFC AND MAINTAIN 170 KIAS TO FRAZE WERE INCOMPATIBLE ONCE THE BAC JET BEGAN TO SLOW. AT LEAST WE SLOWED TO MAINTAIN SAFE SEPARATION BY MATCHING THE GND SPD OF THE PRECEDING TFC. AT THAT POINT WE COULD HAVE BEEN MORE HELPFUL/CORRECT BY SPECIFICALLY NOTIFYING ATC THAT WE WERE UNABLE TO MAINTAIN 170 KIAS DUE TO DECREASING SEPARATION AND THAT WE WERE SPECIFICALLY 'REQUESTING AN AMENDED CLRNC.' BUT; THE SIT WOULD HAVE BEEN EVIDENT ON RADAR IN THE TWR CAB; AND ATC WAS INVOLVED IN PLENTY OF DISCUSSION WITH THE PARTIES INVOLVED AS THE EVENT UNFOLDED. IN THE FUTURE; I'LL KEEP MY DISTANCE AND NOTIFY ATC OF THE NEED TO SLOW/REQUEST AN AMENDED CLRNC.