CTLR VECTORED DESCENDING CPR-SMT ACROSS THE PATH OF AND INTO CONFLICT WITH AN ACR-LGT ALSO DESCENDING.

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LGT X WAS INBND TO STL FROM THE SE ON THE MODUC 4 STAR DSNDING TO 100. SMT Y RPTED ON FREQ IN THE VICINITY OF FAM DSNDING TO FL240. SMT Y WAS CLRD TO 70 AND TOLD TO EXPECT 25 S OF CPS AT 40. AT THIS SAME TIME THERE WERE 3 OTHER ACFT DSNDING TO 40 LNDG AT STL SATELLITE ARPTS. THESE 3 WERE LOW PERFORMANCE ACFT. SPDS LESS THAN 180 KTS. SMT Y WAS PLACED ON A HDG OF 030 DEGS TO PARALLEL TFC AND CLRD TO CROSS 25 S OF CPS AT 40 (IF POSSIBLE) PLT ACKNOWLEDGED HE WOULD TRY. SMT Y WAS OBVIOUSLY NOT GOING TO MAKE THE RESTRICTION SO WAS PLACED ON A HDG OF 070 DEGS TO AVOID STL AIRSPACE. THIS HDG WOULD TAKE SMT Y ACROSS THE MODUC 4 STAR IN FRONT OF LGT X. LGT X WAS PLACED ON A HDG OF 270 DEGS AS SEP WAS DECREASING. SMT Y WAS TURNED LEFT TO A HDG OF 040 DEGS. SMT Y WAS CLRD TO MAINTAIN 150 (MODE C 156); LGT X MODE C (152). SMT Y ACKNOWLEDGED CLRNC THEN ADVISED HE WAS AT '14 AND 1/2. DO YOU WANT US TO GO BACK?' (I THOUGHT THE REPLY WAS 148; DO YOU WANT US TO GO BACK.) I ADVISED AFFIRMATIVE. SMT Y WAS ASKED TO SAY ALT AND THE REPLY WAS 146 CLBING BACK TO 150. AFTER LAT SEP WAS RE-ESTABLISHED SMT Y WAS CLRD TO 40 AND ISSUED HDGS BACK TO CPS. VERT SEP SHOULD HAVE BEEN ESTABLISHED EARLIER. THE ZKC/STL LOA REQUIRES US AT TIMES TO HAVE TURBO JET ACFT LNDG AT SATELLITE ARPTS AT 4000' AS MUCH AS 35 NM FROM THE ARPT. THIS CAN BE VERY DIFFICULT TO ACCOMPLISH; ESPECIALLY WHEN THE LOW ALT CTLR INITIALLY TALKS TO THE ACFT DSNDING TO FL240 ONLY 5 MINS FROM THE XING POINT. I WOULD LIKE TO SEE MORE UPDATES PER MIN ON DATA BLOCKS. SMT Y MODE C SHOWED 156--ACTUAL ALT 145.