Narrative:

Working boeing sector stand-alone due to flight check aircraft maneuvering in the airspace. VFR; high volume and complexity. Aircraft X; landing bfi on the localizer for runway 13R at bfi. As I cleared aircraft X for the visual approach; I called traffic on a VFR tag; aircraft Y; at 2100 ft heading northeast towards the final approach course for 13R. Aircraft X subsequently reported traffic in sight; but still encountered a TCAS-RA with respect to the VFR. The supervisor was immediately made aware of the TCAS-RA and aircraft X continued on the visual approach without further incident.this is another report of a continued problem within our airspace. The VFR traffic crossed approximately 1 NM northwest of isoge from the southwest to the northeast; directly through the final approach course 100 ft below; and then climbing through; our required crossing altitude at isoge on the ILS. A review of the falcon replay indicated that before the VFR and aircraft Y crossed paths; the separation was .71NM laterally and 600 ft vertically. Fortunately; aircraft Y only climbed 100 ft in response to the TCAS-RA; because had the aircraft elected to execute a complete go-around it would have been much worse. The seattle final was busy; there were aircraft on the downwind in the vicinity of aircraft X; and a flight check aircraft doing arcs across the seattle finals at 1900 ft in the class bravo airspace.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 TRACON Controller reported a VFR aircraft caused an airborne conflict north of the BFI area. This is a recurring issue.

Narrative: Working Boeing sector stand-alone due to Flight Check aircraft maneuvering in the airspace. VFR; high volume and complexity. Aircraft X; landing BFI on the localizer for runway 13R at BFI. As I cleared Aircraft X for the visual approach; I called traffic on a VFR tag; Aircraft Y; at 2100 ft heading NE towards the final approach course for 13R. Aircraft X subsequently reported traffic in sight; but still encountered a TCAS-RA with respect to the VFR. The supervisor was immediately made aware of the TCAS-RA and Aircraft X continued on the visual approach without further incident.This is another report of a continued problem within our airspace. The VFR traffic crossed approximately 1 NM NW of ISOGE from the SW to the NE; directly through the final approach course 100 ft below; and then climbing through; our required crossing altitude at ISOGE on the ILS. A review of the FALCON replay indicated that before the VFR and Aircraft Y crossed paths; the separation was .71NM laterally and 600 ft vertically. Fortunately; Aircraft Y only climbed 100 ft in response to the TCAS-RA; because had the aircraft elected to execute a complete go-around it would have been much worse. The Seattle final was busy; there were aircraft on the downwind in the vicinity of Aircraft X; and a Flight Check aircraft doing arcs across the Seattle finals at 1900 ft in the Class Bravo airspace.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.