Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (mon) 6; Air Traffic Control Time Certified In Pos 1 (yrs) 2
Workload; 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
Airspace Structure; Procedure
I was working arrival sectors combined. It was a busy and complex session with numerous BFI arrivals; lots of VFR targets; practice approaches in and through my airspace. Aircraft X checked in and was descended and positioned on the downwind for the ILS into BFI. The whole session I had been observing VFR aircraft in the vicinity of the BFI approach course. As such; I was proactively scanning to avoid potential conflicts; as such had already occurred about an hour before. As I turned Aircraft X to the base leg; I saw a VFR target (Aircraft Y) just northwest of the FAF tracking the localizer outbound and issued the traffic to Aircraft X. Aircraft X was looking; but very clear about not having the traffic in sight. I elected to vector Aircraft X across the localizer until the VFR was no factor prior to issuing the approach clearance for the ILS. Aircraft X landed without incident.Closest proximity between Aircraft X and the VFR was 1.59 miles laterally and 500 feet vertically. My decision to take Aircraft X across their approach course was mainly based on the fact that VFR targets positioned like this do not typically remain 500 feet below the crossing altitude at the FAF. As such; the only way I could ensure there was no conflict was to delay the turn to final for Aircraft X. If the VFR were receiving traffic advisories from ATC; we would at least be able to restrict their altitude; or have them inform us of their intention to remain at or below an altitude that does not conflict with our arrivals to BFI.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.
S46 TRACON Controller reported an aircraft on approach near the ILS Runway 14R FAF TOGAE at BFI was in conflict with an unidentified VFR aircraft and had to be vectored off the approach for separation.