Challenger 350
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2.75
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Separated Traffic; Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Human Factors; Company Policy; Chart Or Publication; Airspace Structure
I was working Arrival final North flow. Aircraft X was cleared for the ILS approach. I noticed VFR traffic tracking the localizer outbound and climbing through 2100 feet. As the target appeared to be climbing; I canceled the approach clearance and issued an altitude which was; at the time; 500 feet above the VFR target's indicated altitude. Aircraft X subsequently reported the VFR aircraft in sight and I attempted to clear them for a Visual Approach; however a lower cloud layer that I was unaware of at the time precluded the aircraft from accepting my clearance.  I vectored the aircraft around again for the ILS and they landed without incident.When Aircraft X reported the VFR aircraft in sight the aircraft were separated by 1.51 miles laterally and 500 feet vertically.  Aircraft X initiated an uninstructed climb to 3200 feet after reporting the VFR in sight; which I can only assume was in response to a TCAS-RA that the pilot failed to mention specifically.  Because I had previously observed the VFR target involved; I called Tower on the shout line to determine if they knew the callsign; which they did. I gave that information to the supervisor; who subsequently called Tower on the phone to ask them to have the aircraft call the facility when they returned so that we could explain the situation they had created. The supervisor later spoke with the pilot and told me that they believed they were further offset from the inbound course and that they were unaware of where to position themselves in order to remain clear of potential conflicts. The supervisor mentioned the pilot was actually glad to hear the air traffic side of the situation; as they felt it was information they lacked.Something needs to change. The VFR aircraft are transiting a very narrow; busy corridor of airspace and are doing so without any communication with ATC. It is simply unsafe. The VFR aircraft in this area at the very least need to be in communication with ATC so that we can assign; as necessary; altitude restrictions ensuring the safety of all the aircraft involved. The solutions are not hard and while they are potentially more restrictive to VFR aircraft the bottom line is that what happens day in and day out in that airspace as it exists and operates now will eventually result in a very bad accident.
A TRACON Controller reported they had to cancel an aircraft's approach clearance and subsequently the aircraft responded to an RA for an unidentified VFR aircraft flying through the final approach course.