SMT Y NON ADHERENCE TO ATC INSTRUCTION. HAD LTSS FROM SMA X. SYS ERROR.

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SMA X ; A PA 28; WAS ON ILS 30L APCH AT CPS; TO BE FOLLOWED ON THE APCH 5 MINS LATER BY SMT Y AN AC69. THE WIND WAS 120 AT 11. I ADVISED BOTH ACFT THAT THE CLOUD BASES WERE RPTED AT 600 FT (RIGHT AT CIRCILING MINIMA) AND THAT IF THEY BROKE OUT HIGHER; A R DOWNWIND CIRCLE TO RWY 12R WAS APPROVED. X RPTED CIRCLING; AS Y WAS MAKING INITIAL CALL. I INSTRUCTED Y TO RPT ACORE (THE OM); AND ADVISED X TO KEEP PATTERN IN CLOSE. Y RPTED BRAKING OUT BELOW CIRCLING MINIMUMS; AND WOULD LAND STRAIGHT IN RWY 30L. (Y HADN'T RPTED ACORE). I LOOKED OUT AND THE Y WAS SHORT FINAL FOR RWY 30L - X WAS SHORT FINAL RWY 12R. I INSTRUCTED Y TO GAR; AND CALLED STL APCH TO COORDINATE MISSED APCH INSTRUCTIONS. WHILE I WAS ON THE LANDLINE WITH STL APCH; Y ADVISED ME THAT Y COULD LAND RWY 12R. I BELIEVE THAT A LOSS OF STANDARD IFR SEPARATION EXISTED; AND THAT A NEAR RWY INCURSION OCCURED (WITH BOTH ACFT LNDG OPPOSITE DIRECTION). IN MY OPINION; Y'S FAILURE TO RPT THE OM; AND THE LACK OF BRITE OR TARDIS RADAR MONITORING EQUIP CONTRIBUTED TO THE SIT.