Narrative:

I was working corp jet X, a departure off cgx wbound. I climbed the corp jet X to 12000 ft. He was level at 12000 ft about ord 180/20 on a 280 degree heading. Air carrier Y was an ord arrival at 11000 ft coming from the southwest. A known VFR aircraft Z (another aircraft that approach was talking to) was at 10500 ft in the same vicinity. Ord arrival controller pointed out VFR traffic to air carrier Y. I shipped corp jet X to ZAU frequency 127.07. Air carrier Y started to climb because of TCASII alert off VFR aircraft. Air carrier Y was climbing up into corp jet X. I tried to coordinate with arrival controller as he was also trying to resolve confliction. It appeared that VFR aircraft was west of air carrier Y and no factor before air carrier Y responded to his TCASII alert. Supplemental information from acn 265103: we were level at 11000 ft. Ord approach control had us on a heading, vectoring for runway 27L at ord. Approach called VFR traffic at 10500 ft at our 11 O'clock position. I told ATC no contact. TCASII showed traffic 500 ft below us. The traffic was within 1 mi when TCASII told us to monitor vertical speed. TCASII then showed traffic 400 ft below us and climbing. TCASII told us to climb. We started climbing and called approach and told them we were climbing out of 11000 ft because of a TCASII alert. TCASII then told us to monitor vertical speed. TCASII then told us to reduce climb. We reduced. At 11500 ft we had visual contact with a corporate jet. He was about 1000 ft above us. Approach then told us of the corporate jet conflict. TCASII called clear of conflict. We started descending back to 11000 ft and leveled. If the VFR traffic at 10500 ft didn't climb the situation would never have happened.

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Original NASA ASRS Text

Title: AN ACR MLG RESPONDING TO A TCASII ALERT ON VFR TFC, CLBED TO WITHIN 1 MI AND 500 FT OF AN IFR CORP ACFT.

Narrative: I WAS WORKING CORP JET X, A DEP OFF CGX WBOUND. I CLBED THE CORP JET X TO 12000 FT. HE WAS LEVEL AT 12000 FT ABOUT ORD 180/20 ON A 280 DEG HDG. ACR Y WAS AN ORD ARR AT 11000 FT COMING FROM THE SW. A KNOWN VFR ACFT Z (ANOTHER ACFT THAT APCH WAS TALKING TO) WAS AT 10500 FT IN THE SAME VICINITY. ORD ARR CTLR POINTED OUT VFR TFC TO ACR Y. I SHIPPED CORP JET X TO ZAU FREQ 127.07. ACR Y STARTED TO CLB BECAUSE OF TCASII ALERT OFF VFR ACFT. ACR Y WAS CLBING UP INTO CORP JET X. I TRIED TO COORDINATE WITH ARR CTLR AS HE WAS ALSO TRYING TO RESOLVE CONFLICTION. IT APPEARED THAT VFR ACFT WAS W OF ACR Y AND NO FACTOR BEFORE ACR Y RESPONDED TO HIS TCASII ALERT. SUPPLEMENTAL INFO FROM ACN 265103: WE WERE LEVEL AT 11000 FT. ORD APCH CTL HAD US ON A HDG, VECTORING FOR RWY 27L AT ORD. APCH CALLED VFR TFC AT 10500 FT AT OUR 11 O'CLOCK POS. I TOLD ATC NO CONTACT. TCASII SHOWED TFC 500 FT BELOW US. THE TFC WAS WITHIN 1 MI WHEN TCASII TOLD US TO MONITOR VERT SPD. TCASII THEN SHOWED TFC 400 FT BELOW US AND CLBING. TCASII TOLD US TO CLB. WE STARTED CLBING AND CALLED APCH AND TOLD THEM WE WERE CLBING OUT OF 11000 FT BECAUSE OF A TCASII ALERT. TCASII THEN TOLD US TO MONITOR VERT SPD. TCASII THEN TOLD US TO REDUCE CLB. WE REDUCED. AT 11500 FT WE HAD VISUAL CONTACT WITH A CORPORATE JET. HE WAS ABOUT 1000 FT ABOVE US. APCH THEN TOLD US OF THE CORPORATE JET CONFLICT. TCASII CALLED CLR OF CONFLICT. WE STARTED DSNDING BACK TO 11000 FT AND LEVELED. IF THE VFR TFC AT 10500 FT DIDN'T CLB THE SIT WOULD NEVER HAVE HAPPENED.

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.