Date: 201905
Local time of day: 1201-1800
Location: BFI.Airport, WA
Flight conditions: Marginal
Weather elements / visibility: Cloudy; 10
Aircraft: Cessna Citation Undifferentiated or Other Model
Operator: Corporate
Operating under: Part 91
Flight plan: VFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B SEA
ATC / advisory: TRACON S46
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Corporate
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Confusion; Situational Awareness
Anomaly: Airspace Violation All Types; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Exited Penetrated Airspace
Contributing factors: Procedure; Environment - Non Weather Related
Primary problem: Procedure

Narrative: There were multiple layers of cloud coverage in the SEA terminal area and as we descended through 8;000' MSL in the SEA Class B airspace we became VMC. We were approximately 15nm west of BFI on a 340 degree heading for a Runway 14R downwind. ATIS was advertising ILS 14R approaches. We canceled IFR and received a Class B descent clearance with no heading or altitude restrictions. Immediately after receiving the clearance I heard SEA TRACON clear another airplane for an ILS. Approach control did inform us of that airplane. I then heard Approach turn another plane on a base heading for the ILS. Although the location was not given; because TRACON did not inform us of that plane; I assumed it would not be a factor. We continued our descent and exited the base of the Class B in that area. TRACON did not offer sequencing service; instead instructing us to contact BFI ATCT. We spotted the first airplane (a B737) and turned base close in behind it and ahead of the second airplane which ended up being 2.5nm behind us according to BFI ATCT. I knew the base of the Class B airspace over Elliot Bay was 1;800' MSL so; although we had received a Class B clearance; I had continued the descent to 1;700' MSL by the time we entered Elliott Bay. We were about 2.5 nm in trail of the B737 and flew through its wake turbulence. I reacted by leveling and inadvertently climbing slightly. Although I am not sure whether we technically reached 1;800'; I am sure we were within 100' of 1;800' so Mode C most likely indicated Class B intrusion. Being that close to the B737; while on base leg I initially considered turning to parallel its track on the upwind side for wake turbulence avoidance. However; that would not allow enough maneuvering space to gain additional separation; so I decided to fly through final to gain the necessary spacing. This subjected us to the wake event; which ended up being light turbulence. It would have been advantageous if TRACON had offered sequencing service or at least offered information about conflicting traffic to facilitate our decision on the proper course of action. In retrospect; I should have insisted on being sequenced; VFR or not. However; we were left on our own; I should have descended lower than 1;700' to give additional buffer space from the 1;800' Class B base; but I didn't want to get lower since I was anticipating maneuvering/breakout instructions from BFI ATCT due to either the in-traipreceding or l airplanes. Also; I have never read any guidance from the FAA regarding the nuances of Class B clearances. Particularly as in this case; whether a Class B clearance allows reentry after exiting; whether reentering laterally or vertically. So; I am not entirely sure a violation occurred since we had previously received the Class B clearance. If there is such guidance; it needs to be more widely distributed; particularly in the geographic areas where Class B airspace exists.




Synopsis: Citation Captain reported reentering Class B airspace after encountering wake turbulence on approach to BFI.