Date: 202107
Local time of day: 1201-1800
Location: S46.TRACON, WA
Flight conditions: VMC
Weather elements / visibility: 20
Light: Daylight
Aircraft: Falcon 2000
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B SEA
ATC / advisory: TRACON S46
Second aircraft: B737-900
Reporter organization: Corporate
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Regained Aircraft Control
Contributing factors: Environment - Non Weather Related; Procedure
Primary problem: Ambiguous

Narrative: While descending via the CHINS4 arrival into BFI (Seattle/King County Boeing Field); on the segment between 'HUMPP' and 'AUBRN'; passing approximately 14;500 ft. MSL at 250 kts. IAS; I encountered wake turbulence. Temporary loss of control was experienced as the aircraft rolled right; back left; and strongly back right again - with the final bank angle in the roll estimated to be beyond 30 but not more than 50 degrees wing down to the right before I could fully react. During the course of the roll and recovery; automation (including autopilot and auto throttle) was disengaged; and at no time did the EGPWS 'BANK ANGLE' warning sound. I stopped the roll and regained controlled flight with full and smooth application of left aileron; while adding power and climbing out of the perceived vortex. Once clear; automation was restored; the event briefed amongst the crew; and I instructed the PNF (Pilot not Flying) to radio Seattle Approach indicating we had 'encountered wake turbulence' and that 'we were attempting to re-establish on the arrival'. The Approach Controller acknowledged the transmission and advised we were following a Boeing 737-900 series sequenced for SEA (Seattle). From there; a normal descent and approach was conducted to the destination airport. No aircraft faults/failures/malfunctions/warnings; nor exceedances were experienced at any time before; during; or after the event. I was aware of the altitude and spacing regarding the traffic ahead on the arrival; with use of TCAS indications and relative altitude; as well situational awareness provided by our aircraft's INAV display. Spacing and distance appeared more than adequate considering the flight conditions; as the preceding aircraft was consistently indicating around 2;500 ft. below our level and well ahead on the arrival. At no time were we given advisories from ATC in regards to traffic ahead; nor caution on wake turbulence.This event was truly unexpected; however; I must credit flight training providers with modeling extremely accurate wake turbulence simulation scenarios that helped me to quickly identify; and recover properly from this real life upset. Experiencing this is a reminder that wake turbulence can be encountered during a descent profile - especially on an RNAV arrival with 'at-or-above/below' vertical crossing restrictions that could result in brief level offs at slower airspeeds which could lead to preceding aircraft generating stronger than expected vortices.




Synopsis: Falcon 2000 Captain reported momentary loss of control after encountering wake turbulence on approach to BFI airport.