LESS THAN STANDARD SEPARATION WHEN AN ACR-MLG IS DESCENDED TO THE ALT ALREADY OCCUPIED BY CPR-SMT.

Narrative

I WAS WORKING ARR W AND S AT IND. WE WERE VERY BUSY LNDG ACFT ON RWY 13 AND DEPARTING ACFT ON RWY 22R. AT X50 AM; I RECEIVED A RADAR HDOF ON MLG X INBND FROM THE NE; WELL OUTSIDE MY AIRSPACE. THE SUPVR ASKED ME TO WORK THIS AND 2 OTHER ACFT INBND FROM THE NE DUE TO THE HIGH WORKLOAD THE OTHER ARR CTLR WAS ALREADY EXPERIENCING. AT X54 AM I TOLD MLG X TO REDUCE SPD TO 200 KTS AND THEN DSND AND MAINTAIN 10000' MSL. DUE TO TFC ON MY SIDE OF THE LOC; I DID NOT NOTICE SMT Y AT 10000' ALSO INBND FROM THE NE. MLG X OVERTOOK SMT Y AND SEP DECREASED TO 1 MI AT THE SAME ALT. TURNS WERE THEN ISSUED TO INCREASE SEP. THE COMPUTER C/A DID NOT ACTIVATE UNTIL THE ACFT WERE ALREADY TURNING TO DIVERGING HDGS. I BELIEVE MODERATE TO HEAVY TFC AND HAVING TO WORK ACFT WELL OUTSIDE MY AIRSPACE CONTRIBUTED TO THE ERROR. I RECOMMEND THAT WORKLOAD BE MORE EVENLY DISTRIBUTED TO ARR CTLRS VIA A FEEDER CTLR; AND INCREASED FLOW CTL AND HOLDING PATTERNS SHOULD BE USED DURING IFR WX CONDITIONS TO RELIEVE CONGESTION ON THE DOWNWINDS SO THAT ARR CTLRS CAN CONCENTRATE MORE ON THE FINAL APCH. PLEASE NOTE THE FINAL EXTENDED TO 25-30 MI FROM THE ARPT AND BOTH ARR CTLRS WERE HAVING TO ISSUE S-TURNS ON THE DOWNWIND UNTIL OPENINGS OCCURRED ON THE FINAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: THE CAUSE OF THE SYS ERROR WAS DETERMINED TO BE THAT RPTR DSNDED HIS ACFT IN ANOTHER CTLR'S SECTOR W/O FIRST GETTING PERMISSION. THE SUPVR THAT ASKED RPTR TO WORK THIS MLG IN THE OTHER APCH CTLR'S AIRSPACE EXPECTED RPTR TO VECTOR THE MLG OVER THE ARPT; INTO HIS AIRSPACE BEFORE HE DSNDED FOR APCH. THIS; HOWEVER; WAS NOT SAID TO THE RPTR NOR WERE ANY SPECIAL INSTRUCTIONS GIVEN WITH THE HDOF. RPTR STATED THAT THERE WAS A FAC-WIDE MISUNDERSTANDING ABOUT THE LETTER OF AGREEMENT BTWN IND APCH CTL AND ZID. SINCE THIS SYS ERROR; THE ENTIRE FAC HAS BEEN BRIEFED ON THIS AIRSPACE MATTER AND A SPECIAL COMMITTEE HAS BEEN FORMED TO REVIEW AIRSPACE MATTERS AND RECOMMEND IMPROVEMENTS. RPTR HAS BEEN SELECTED FOR THIS COMMITTEE.