Narrative:

A C680 was enroute level at 080 MSL. A C402 was opposite direction eastbound assigned 070b090 MSL and a C172 VFR was also eastbound level at 055 MSL. The C402 had requested a block altitude of 070-090 MSL because of a bumpy ride and so I approved it. When the C680 was approximately 20 miles east of the C402 I issued him an expedited decent clearance to 060 MSL so he would be below him. The C680 was able to comply with no issues. Because there were approximately 5-6 aircraft in the general area; all crossing; I had vertically separated all concerned aircraft. I gave the C680 traffic calls on the opposite direction the C402 and also on a B757 aircraft approximately 5 miles north east of his position that was leaving 110 for 070 along with a wake turbulence cautionary. I did not issue him traffic advisories reference the C172 VFR below him at 055 MSL. After the traffic calls were exchanged; and no conflicts were present; I told the C680 to contact the next sector. At that precise moment he informed me he had an RA and was going to climb. I immediately told him not to climb and issued an immediate 90 degree turn south 'heading 180' in order to get him away from any other aircraft. Pilot responded in that his computer was telling him to climb and so he had to. I then replied 'roger' and to report resuming the appropriate altitude. My immediate concern was that he was going to climb into the C402 traffic above him who at the time was at 076 MSL. I then leveled off other aircraft in his vicinity until I could reassure what altitude he was going to climb to. The C680 only climbed 300 ft to a final altitude of 063 MSL before advising me he was descending back down. No separation was lost with any aircraft but it did give me a quick scare. After this happened; through data extraction and conversation with the crew; the pilot stated the climb was for an aircraft 500 ft below him. The aircraft below him was the VFR C172 whom I had not issued traffic on. My only regret or contributing factor that I saw was that I did not tell the citation jet about the VFR C172 below him level at 055 MSL. Had I told him; maybe he would have not taken such evasive action. I'm sure I didn't issue traffic to him. I just didn't get to it in time. The area I was working combined provides services to eight airports three of which have control towers. A lot of crossing VFR climbing and descending with air carrier traffic all merge in that particular area. Data blocks overlap and scope gets congested. However; I know next time I have to properly issue all traffic to a given aircraft if it is a factor.

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Original NASA ASRS Text

Title: TRACON Controller described a TCAS RA event which may have resulted because of his failure to issue VFR traffic.

Narrative: A C680 was enroute level at 080 MSL. A C402 was opposite direction eastbound assigned 070B090 MSL and a C172 VFR was also eastbound level at 055 MSL. The C402 had requested a block altitude of 070-090 MSL because of a bumpy ride and so I approved it. When the C680 was approximately 20 miles east of the C402 I issued him an expedited decent clearance to 060 MSL so he would be below him. The C680 was able to comply with no issues. Because there were approximately 5-6 aircraft in the general area; all crossing; I had vertically separated all concerned aircraft. I gave the C680 traffic calls on the opposite direction the C402 and also on a B757 aircraft approximately 5 miles north east of his position that was leaving 110 for 070 along with a wake turbulence cautionary. I did not issue him traffic advisories reference the C172 VFR below him at 055 MSL. After the traffic calls were exchanged; and no conflicts were present; I told the C680 to contact the next sector. At that precise moment he informed me he had an RA and was going to climb. I immediately told him not to climb and issued an immediate 90 degree turn south 'heading 180' in order to get him away from any other aircraft. Pilot responded in that his computer was telling him to climb and so he had to. I then replied 'roger' and to report resuming the appropriate altitude. My immediate concern was that he was going to climb into the C402 traffic above him who at the time was at 076 MSL. I then leveled off other aircraft in his vicinity until I could reassure what altitude he was going to climb to. The C680 only climbed 300 FT to a final altitude of 063 MSL before advising me he was descending back down. No separation was lost with any aircraft but it did give me a quick scare. After this happened; through data extraction and conversation with the crew; the pilot stated the climb was for an aircraft 500 FT below him. The aircraft below him was the VFR C172 whom I had not issued traffic on. My only regret or contributing factor that I saw was that I did not tell the Citation Jet about the VFR C172 below him level at 055 MSL. Had I told him; maybe he would have not taken such evasive action. I'm sure I didn't issue traffic to him. I just didn't get to it in time. The area I was working combined provides services to eight airports three of which have control towers. A lot of crossing VFR climbing and descending with air carrier traffic all merge in that particular area. Data blocks overlap and scope gets congested. However; I know next time I have to properly issue all traffic to a given aircraft if it is a factor.

Data retrieved from NASA's ASRS site as of April 2012 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.