ACR Y DSCNT THROUGH OCCUPIED ALT TCASII TA RA HAD LTSS FROM SMT X. EVASIVE ACTION TAKEN CLB. SYS ERROR.

Narrative

SMT X WAS VECTORED OVER ATL IN AN IFR CORRIDOR NBOUND INTO FTY AT 5000 FT. THE SECTOR WAS BECOMING VERY BUSY AT THE TIME WITH VARIOUS DEPS AND ARRS. THE ARRS INTO FTY WERE OF VARIOUS TYPE PERFORMANCE. THROUGH THE ASSISTANCE OF A HDOF CTLR COORD WAS IMPLEMENTED TO TURN AND DSND THE SMT X EARLY TOWARDS THE ILS 8 FINAL. AFTER ARRIVING OVER THE TOP OF A LEDGE OF AIRSPACE (3000 FT TO SURFACE) USED FOR FTY'S LOC; THE CTLR TURNED SMT X ON A DOWNWIND HDG TOWARDS FINAL. IN THE MEANTIME; AN ACR Y INBOUND TO ATL WAS VECTORED OVER THE TOP AND DSNDED EARLY FOR AN ILS APCH FOR RWY 8L. THE SPLITTING OFF OF FINAL SECTORS FOR ATL AND THE BUSY TFC OF SATELLITE CONTRIBUTED TO A HURRIED VECTOR FROM THE CTLR. SUPPLEMENTAL INFO FROM ACN 210803: I WAS WORKING A HDOF POS. MY RADAR CTLR HAD TFC SBOUND CLBING TO 6000. THE OTHER ACFT WAS NBOUND AT 5000. I COORDINATED A HDG AND DSCNT THROUGH ANOTHER CTLR AIRSPACE WHICH WAS APPROVED. SUPPLEMENTAL INFO FROM ACN 210889: I WAS FLYING ACR Y ON DOWNWIND (270 DEG HDG) FOR RWY 8L IN ATL AT 7000 FT MSL AND INSTRUCTED TO DSND TO 4000 FT THEN FURTHER INSTRUCTED TO DSND TO 2800 FT. SPDBRAKES WERE EXTENDED TO INCREASE DSCNT RATE. DSNDING THROUGH 4500 FT; I WAS INSTRUCTED TO TURN L TO 180 DEGS (BASE LEG). AT APPROX 3600-3800 FT MSL AND TURNING THROUGH 230 DEGS; A TCASII TA FOLLOWED BY THE APPEARANCE OF AN ACFT SYMBOL (10 MI RANGE) BELOW US AND CLBING. THIS WAS FOLLOWED BY A RA MONITOR DSCNT FOLLOWED BY ANOTHER RA CLB/CLB. PWR WAS ADDED; CLB ATTITUDE WAS ESTABLISHED AND SPDBRAKES WERE STOWED. AUTOPLT WAS DISCONNECTED WHEN CLB/CLB ADVISORY WAS RECEIVED. WE CLBED TO APPROX 3800 FT; THEN ATC TOLD US TO MAINTAIN 3600 FT. AFTER LNDG; I SPOKE WITH THE APCH CTL SUPVR AND HE SAID WE MISSED SMT X BY ABOUT 100 FT VERT. TCASII WORKED WELL AND GAVE US OUR FIRST INDICATION OF THE OTHER ACFT.