Narrative:

I was working west arrival at O'hare approach. Air carrier X was inbound at 11000 ft MSL level, air carrier X advised he was descending for an RA. I observed air carrier X leaving 10700 ft MSL. I asked him how low was he going to need. (There was satellite traffic shuttling east to west below him at 5000 ft MSL and west to east at 4000 ft MSL.) I told air carrier X to maintain 7000 ft MSL if he could concur. Air carrier X advised 7000 ft MSL would be fine. This was another case of an interruption of the frequency during a heavy rush. It also distracted my attention temporarily away from the other 6 aircraft on my frequency. There was not any traffic near air carrier X. The closest traffic was 5 mi behind him (much slower traffic) at 8000 ft MSL. I feel that until the bugs have been worked out, this system should not be used to separate aircraft. Supplemental information from acn 237688: the TCASII was disruptive to the controller's plans because this type of interruption took place in the most critical part of an arrival rush (the beginning). There was not any traffic within 10 mi of air carrier X at the same altitude. The traffic that was 10 mi ahead and 10 mi behind were flying the same direction and at the same speed.

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Original NASA ASRS Text

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

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.