Date: 202101
Local time of day: 1801-2400
Location: S46.TRACON, WA
Flight conditions: VMC
Aircraft: Medium Transport
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B SEA
ATC / advisory: TRACON S46
Second aircraft: Small Aircraft
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Time Pressure; Situational Awareness; Distraction
Second reporter function: Approach
Anomaly: ATC Issue All Types; Conflict Airborne Conflict
Detector: Automation Air Traffic Control; Automation Aircraft RA; Person Air Traffic Control
Result: Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Company Policy; Airspace Structure
Primary problem: Airspace Structure

Narrative: [Aircraft X] was being vectored for an ILS approach into BFI RWY (Runway) 14R by the Arrival West (1W); Arrival East (1E); Boeing Arrival (1D); and Paine (1P) sectors combined. As [Aircraft X] was being vectored traffic was issued for two VFR aircraft on 1200 codes transitioning both north and south through the localizer for Runway 14R. Due to this traffic I left [Aircraft X] at 3;000 ft. and obtained a point-out with SEA Final (1F). Despite this altitude; [Aircraft X] responded to a TCAS RA and; in an effort to protect the sea final approach course; I turned [Aircraft X] right to a heading 220. As [Aircraft X] turned southbound I observed a C172; [Aircraft Y]; being vectored for the ILS Runway 20 approach into PWT. I turned [Aircraft X] further right to a northwest heading; and measured the distance between [Aircraft X] and [Aircraft Y]. I observed approximately 3.3 miles between the two and since I had already issued the turn; I judged that sufficient separation and attempted to continue working to not fall further behind. [Aircraft X] turned slower than anticipated and caused a separation error between themselves and [Aircraft Y]. The root of this issue is the continual constant conflict between IFR jets into BFI and VFR aircraft transitioning through the localizer in both north and south flow. It is a well-known; persistent issue that has been thoroughly reported for several years. Several solutions have been proposed; but none have been adapted.The only fix for this issue is a restructuring of the Seattle Class B airspace to protect the finals in both directions at BFI. I have personally submitted redesigns for this issue that both protect BFI; and in doing so protect SEA; and allow VFR operations in and out of BFI; and are not unduly hindering to the general aviation community. If safety is truly the priority of the FAA and the Seattle region; changes will be initiated immediately. I understand the process for airspace changes take time; however; the changes will never take place if the process is not started. When the inevitable aircraft incident finally occurs; I hope that no one dies and I am not on position.


Second narrative: [Aircraft Y] was on vector; at 2;500 ft.; to ILS Runway 20 approach at PWT. [Aircraft X]; controlled by W Sector; was on final to Runway 14R at BFI and experienced a TCAS RA with an uncontrolled VFR aircraft. The W Controller was already at a high level of complexity and volume as sectors were combined. The BFI Runway 14R final is in close proximity to PWT 20 mile final and is also underneath the Runway 16 finals at SEA. With limited options [Aircraft X] was turned to the southwest towards [Aircraft Y] with only 500 ft. between them. There are many factors that lead to this situation. These include airport proximities; sector overload; traffic complexity. There is also the issue of lack of controlled and protected airspace in and out of BFI. This is an issue controllers have been bringing to local management for years. The workforce is metaphorically beating our heads against a wall as we are asking for help and are given zero assistance in return. The final to BFI is underneath the SEA finals so we are forced to descend large; fast turbojet aircraft out of Class Bravo airspace into a very high VFR traffic area. This leads numerous TCAS situations. Many suggestions have been brought up through established reporting procedures so I will not waste my time typing them out again. The feeling of a lack of support for change is disheartening. There needs to be change made into airspace and procedures for aircraft landing at BFI; and this should be done for both arrival directions at BFI.


Synopsis: Two S46 Approach controllers reported an aircraft on an ILS Approach to BFI had to be vectored away from two conflicting VFR aircraft not in communication with ATC which resulted with the BFI aircraft losing separation with a fourth aircraft on an ILS approach to another airport. Both reporters emphasized these situations are a recurring issue due to the insufficient Class B protected airspace in the SEA/S46 airspace.