Narrative:

A few minutes prior to this event; a fast moving VFR target appeared and started climbing rapidly northbound towards aircraft on the FYTTE4 arrival into ord. Traffic was called to an IFR aircraft to which aircraft called 'traffic in sight'. The second time traffic was called the VFR aircraft appeared to parallel the IFR aircraft's course. I stopped the IFR arrival twice higher. The incident in question involves the same VFR aircraft. I later found it to be aircraft Y after I called approach to have the tower tell the pilot to call ZAU ARTCC after landing.aircraft X was descending via the FYTTE4 arrival into ord. This VFR target appeared off of aircraft X's right side and traffic was called. The VFR target was at his 2 o'clock and 4 miles rapidly climbing out of 12000 feet unverified; type unknown at the time. The second time the traffic was called aircraft X responded to an RA and leveled off at 16600 feet. The VFR aircraft appeared to have climbed 4;000 feet in 29 seconds.the VFR aircraft a high performance turbojet; fighter style aircraft. In the six years I have been in this area; this aircraft routinely rapidly climbs and maneuvers very close to other aircraft especially towards aircraft descending into chicago. Other co-workers who have been in my area many more years than I have also have observed this. I'm certain the pilot will say he is practicing see and avoid. 'See and avoid' and a collision between known aircraft operating in the system has a middle ground; in this case called negligence. This is a high performance aircraft operating in a dangerous/reckless manner in very; very close proximity to other high performance turbofan aircraft. The pilot cannot plead ignorance about the nature of operations north of the airport he has been based at for many years. It is my opinion the flight standards should be contacted pertaining to this manner. Outside of taking away a pilot's license to operate their aircraft; you cannot force a pilot to operate in a safe manner.

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Original NASA ASRS Text

Title: ZAU Center Controller observed a personal high performance turbojet maneuvering in the vicinity of aircraft on arrival into ORD resulting in an RA.

Narrative: A few minutes prior to this event; a fast moving VFR target appeared and started climbing rapidly northbound towards aircraft on the FYTTE4 arrival into ORD. Traffic was called to an IFR aircraft to which aircraft called 'traffic in sight'. The second time traffic was called the VFR aircraft appeared to parallel the IFR aircraft's course. I stopped the IFR arrival twice higher. The incident in question involves the same VFR aircraft. I later found it to be Aircraft Y after I called Approach to have the Tower tell the pilot to call ZAU ARTCC after landing.Aircraft X was descending via the FYTTE4 arrival into ORD. This VFR target appeared off of Aircraft X's right side and traffic was called. The VFR target was at his 2 o'clock and 4 miles rapidly climbing out of 12000 feet unverified; type unknown at the time. The second time the traffic was called Aircraft X responded to an RA and leveled off at 16600 feet. The VFR aircraft appeared to have climbed 4;000 feet in 29 seconds.The VFR aircraft a high performance turbojet; fighter style aircraft. In the six years I have been in this area; this aircraft routinely rapidly climbs and maneuvers very close to other aircraft especially towards aircraft descending into Chicago. Other co-workers who have been in my area many more years than I have also have observed this. I'm certain the pilot will say he is practicing see and avoid. 'See and avoid' and a collision between known aircraft operating in the system has a middle ground; in this case called negligence. This is a high performance aircraft operating in a dangerous/reckless manner in very; very close proximity to other high performance turbofan aircraft. The pilot cannot plead ignorance about the nature of operations north of the airport he has been based at for many years. It is my opinion the Flight Standards should be contacted pertaining to this manner. Outside of taking away a pilot's license to operate their aircraft; you cannot force a pilot to operate in a safe manner.

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.