Narrative:

Air carrier X reported on frequency 40 mi northwest of ord and no other observed traffic near his altitude. However, there were numerous VFR targets at the time. The controller was tending to other duties at east arrival handoff when air carrier X said he had an RA and was climbing. When the controller looked air carrier X was at 10600 ft and a VFR aircraft was passing off to his left at 9500 ft descending. Air carrier X did not have him in sight.

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Original NASA ASRS Text

Title: ACR X TCASII RA CLB FROM VFR Y DSCNT THROUGH OCCUPIED ALT. EVASIVE ACTION TAKEN. SEE AND AVOID CONCEPT.

Narrative: ACR X RPTED ON FREQ 40 MI NW OF ORD AND NO OTHER OBSERVED TFC NEAR HIS ALT. HOWEVER, THERE WERE NUMEROUS VFR TARGETS AT THE TIME. THE CTLR WAS TENDING TO OTHER DUTIES AT E ARR HDOF WHEN ACR X SAID HE HAD AN RA AND WAS CLBING. WHEN THE CTLR LOOKED ACR X WAS AT 10600 FT AND A VFR ACFT WAS PASSING OFF TO HIS L AT 9500 FT DSNDING. ACR X DID NOT HAVE HIM IN SIGHT.

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.