Narrative:

Aircraft was westbound descending from 23;000 feet to 10;000 feet as per the letter of agreement with approach. The approach controller had accepted the handoff of aircraft. I was going to ship communications to approach. The aircraft was leaving around 15;000 feet when aircraft said he was responding to an RA. There was a VFR limited data block in the area that is believed to be a VFR test aircraft; which are often working in the area; but traffic was never issued to the aircraft because it was never a factor until the VFR made a rapid turn combined with a rapid descent. After stating he was responding to an RA aircraft asked what I wanted him to do. My reply was to have his aircraft do whatever the RA had instructed him to do. I assumed the VFR aircraft was in contact with the approach control facility; so I thought the best course of action was to transfer communications of aircraft to approach.the test aircraft often cancel their IFR clearances after they are done with their high altitude checks; and work VFR before returning to land. Often times they do this and request to go VFR without flight following. These aircraft are making extreme maneuvers in high performance aircraft at high speeds combined with rapid climbs and descents in an area just east of the airport. My recommendation would be to either have these aircraft be required to be in contact with ATC or at least have them in a designated area away from the regular arrival and departure aircraft in and around the airport.

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Original NASA ASRS Text

Title: ZKC Center Controller reported a descending aircraft reported an NMAC with an unidentified VFR target performing abrupt maneuvers.

Narrative: Aircraft was westbound descending from 23;000 feet to 10;000 feet as per the Letter of Agreement with Approach. The Approach Controller had accepted the handoff of Aircraft. I was going to ship communications to approach. The aircraft was leaving around 15;000 feet when Aircraft said he was responding to an RA. There was a VFR limited data block in the area that is believed to be a VFR test aircraft; which are often working in the area; but traffic was never issued to the Aircraft because it was never a factor until the VFR made a rapid turn combined with a rapid descent. After stating he was responding to an RA Aircraft asked what I wanted him to do. My reply was to have his aircraft do whatever the RA had instructed him to do. I assumed the VFR aircraft was in contact with the approach control facility; so I thought the best course of action was to transfer communications of Aircraft to approach.The test aircraft often cancel their IFR clearances after they are done with their high altitude checks; and work VFR before returning to land. Often times they do this and request to go VFR without flight following. These aircraft are making extreme maneuvers in high performance aircraft at high speeds combined with rapid climbs and descents in an area just east of the airport. My recommendation would be to either have these aircraft be required to be in contact with ATC or at least have them in a designated area away from the regular arrival and departure aircraft in and around the airport.

Data retrieved from NASA's ASRS site 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.