ACR X TCASII RA NON ADHERENCE TO ATC CLRNC UNAUTH DSCNT FROM ASSIGNED ALT DUE TO GHOST TARGET. EVASIVE ACTION DSND.

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I WAS WORKING W ARR AT O'HARE APCH. ACR X WAS INBOUND AT 11000 FT MSL LEVEL; ACR X ADVISED HE WAS DSNDING FOR AN RA. I OBSERVED ACR X LEAVING 10700 FT MSL. I ASKED HIM HOW LOW WAS HE GOING TO NEED. (THERE WAS SATELLITE TFC SHUTTLING E TO W BELOW HIM AT 5000 FT MSL AND W TO E AT 4000 FT MSL.) I TOLD ACR X TO MAINTAIN 7000 FT MSL IF HE COULD CONCUR. ACR X ADVISED 7000 FT MSL WOULD BE FINE. THIS WAS ANOTHER CASE OF AN INTERRUPTION OF THE FREQ DURING A HVY RUSH. IT ALSO DISTRACTED MY ATTN TEMPORARILY AWAY FROM THE OTHER 6 ACFT ON MY FREQ. THERE WAS NOT ANY TFC NEAR ACR X. THE CLOSEST TFC WAS 5 MI BEHIND HIM (MUCH SLOWER TFC) AT 8000 FT MSL. I FEEL THAT UNTIL THE BUGS HAVE BEEN WORKED OUT; THIS SYS SHOULD NOT BE USED TO SEPARATE ACFT. SUPPLEMENTAL INFO FROM ACN 237688: THE TCASII WAS DISRUPTIVE TO THE CTLR'S PLANS BECAUSE THIS TYPE OF INTERRUPTION TOOK PLACE IN THE MOST CRITICAL PART OF AN ARR RUSH (THE BEGINNING). THERE WAS NOT ANY TFC WITHIN 10 MI OF ACR X AT THE SAME ALT. THE TFC THAT WAS 10 MI AHEAD AND 10 MI BEHIND WERE FLYING THE SAME DIRECTION AND AT THE SAME SPD.