Narrative:

An E190 was descending to 9;000 ft from 10;000 ft. A VFR overflight BE36 reported level at 8;500 ft; altitude varied by 100-200 ft at times. Both aircraft were issued traffic as targets were likely to merge. At approximately 2 miles lateral separation the BE36 reported the E190 in sight. The E190 was immediately informed that traffic had them in sight; and response was 'we are responding to an RA'. The aircraft did not say they were climbing; but I believe they stopped the descent and climbed 100 ft-200 ft. At the time the BE36; even though he had reported being level at 8;500 ft; altitude indicated 8;600 ft. I don't believe they were at the time; but aircraft may have been inside bravo airspace. The BE36 was not instructed to maintain visual separation from the E190. The supervisor was not immediately available; but was notified about 2-3 minutes after the incident. I reported to the supervisor that the E190 had responded to an RA; but that I didn't think there was an evasive maneuver; just decreased rate of descent. After thinking about the situation more; I believe the E190 may have climbed 100-200 ft. I should have stopped the E190 at a higher altitude since the BE36 was indicating 100 ft-200 ft difference; anticipating that there could possibly be a TCAS event. I think more frequent training and actually hearing from pilots how TCAS works could help controllers be more aware of such a situation. Also more training; on how if a pilot reports a specific altitude and has the right altimeter setting and altitude differs by 100 ft how does this have an effect on TCAS.

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Original NASA ASRS Text

Title: L30 Controller described a TCAS RA event between a descending air carrier and a VFR aircraft in level flight. The VFR aircraft observed the air carrier but was not instructed to maintain visual separation.

Narrative: An E190 was descending to 9;000 FT from 10;000 FT. A VFR overflight BE36 reported level at 8;500 FT; altitude varied by 100-200 FT at times. Both aircraft were issued traffic as targets were likely to merge. At approximately 2 miles lateral separation the BE36 reported the E190 in sight. The E190 was immediately informed that traffic had them in sight; and response was 'We are responding to an RA'. The aircraft did not say they were climbing; but I believe they stopped the descent and climbed 100 FT-200 FT. At the time the BE36; even though he had reported being level at 8;500 FT; altitude indicated 8;600 FT. I don't believe they were at the time; but aircraft may have been inside Bravo airspace. The BE36 was not instructed to maintain visual separation from the E190. The supervisor was not immediately available; but was notified about 2-3 minutes after the incident. I reported to the supervisor that the E190 had responded to an RA; but that I didn't think there was an evasive maneuver; just decreased rate of descent. After thinking about the situation more; I believe the E190 may have climbed 100-200 FT. I should have stopped the E190 at a higher altitude since the BE36 was indicating 100 FT-200 FT difference; anticipating that there could possibly be a TCAS event. I think more frequent training and actually hearing from pilots how TCAS works could help controllers be more aware of such a situation. Also more training; on how if a pilot reports a specific altitude and has the right altimeter setting and altitude differs by 100 FT how does this have an effect on TCAS.

Data retrieved from NASA's ASRS site as of July 2013 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.