Narrative:

Aircraft X on vectors for the ILS runway 13R approach at bfi level at 2;200 feet. As I turned aircraft X to the intercept heading and cleared him for the approach I scanned ahead for VFR traffic in vicinity of the final approach course. I found what I usually find; which was a VFR target on the approach course climbing to the northwest at 1;600 feet. I immediately advised aircraft X of the traffic and alerted him that the aircraft may continue to climb. When I observed the mode-C of the VFR tick from 1;600 feet to 1;700 feet I immediately cancelled the approach clearance for aircraft X and have him a right turn to avoid and maintain 2;200 feet. Aircraft X subsequently reported the traffic in sight as they passed and I gave him a new approach clearance from the other side of the localizer. Aircraft X continued to bfi without further incident.this is another report of a continued problem within our airspace. [A review] indicated that the closest proximity between the two aircraft was .43NM lateral and 400 feet vertical (assuming the mode-C of the VFR was accurate).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 solution(s) 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.

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Original NASA ASRS Text

Title: S46 Approach Controller reported a conflict between an air carrier on an ILS approach to BFI and unidentified VFR traffic crossing the final approach course. Controller immediately turned the air carrier to the right in order to resolve the conflict. Reporter stated this is a common occurrence with VFR aircraft transiting a very busy and narrow corridor without communication with ATC.

Narrative: Aircraft X on vectors for the ILS RWY 13R approach at BFI level at 2;200 feet. As I turned Aircraft X to the intercept heading and cleared him for the approach I scanned ahead for VFR traffic in vicinity of the final approach course. I found what I usually find; which was a VFR target on the approach course climbing to the northwest at 1;600 feet. I immediately advised Aircraft X of the traffic and alerted him that the aircraft may continue to climb. When I observed the Mode-C of the VFR tick from 1;600 feet to 1;700 feet I immediately cancelled the approach clearance for Aircraft X and have him a right turn to avoid and maintain 2;200 feet. Aircraft X subsequently reported the traffic in sight as they passed and I gave him a new approach clearance from the other side of the localizer. Aircraft X continued to BFI without further incident.This is another report of a continued problem within our airspace. [A review] indicated that the closest proximity between the two aircraft was .43NM lateral and 400 feet vertical (assuming the Mode-C of the VFR was accurate).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 solution(s) 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.

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.