Date: 202106
Local time of day: 1801-2400
Location: SEA.Airport, WA
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B SEA
ATC / advisory: TRACON S46
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Anomaly: Conflict Airborne Conflict; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Procedure; Environment - Non Weather Related
Primary problem: Environment - Non Weather Related

Narrative: ATC slowed us to 210; 190; then 170 KIAS; and then vectored us at 4;000 feet on a base leg for the visual approach to [Runway] 34L. As we rolled out on our base leg vector heading; a B737 was 3 miles ahead; at our 11 o' clock and about 1;000 feet above. ATC had us follow that traffic; cleared visual approach 34L. In the flight deck; we discussed the options to increase our separation; and reduce wake turbulence; behind the preceding aircraft. We decided to make the turn as square as possible without blowing through the localizer (visual approaches were also being conducted on the parallel Runway 34R); and stay one dot high on the glide path. We made a square turn to intercept the localizer; but the aircraft was still only about three miles ahead. As we began our descent below 4;000 feet; we encountered wake turbulence. Significant control inputs were required to correct for the resulting 'Dutch Roll' motion (wing lateral roll/rocking motion coupled with tail wag directional motion). The turbulence lasted for approximately 15-20 seconds; as we raised our glide path to about one dot above; which allowed us to exit the wake turbulence by about 3;000 feet. We maintained a higher glide path for the rest of the approach; keeping us clear of the turbulence for the rest of the visual approach to landing. Although the aircraft remained under positive control throughout the turbulence encounter; and within stable visual approach parameters for the entire approach; the motion was very uncomfortable and noticeable to everyone on board. Checking with our flight attendants after the event; no one in the cabin was injured; but a lot of passengers were understandably giving the flight attendants weird looks. Both flight attendants had recognized the motion as wake turbulence as it was occurring.A busy airport can present challenges with aircraft separation and wake turbulence avoidance; especially on visual approaches. ATC requested a specific speed for sequencing; presumably to fit us in behind the B737 and in front of other arrivals. Under other circumstances where the preceding aircraft is at the same altitude or lower; three miles of spacing behind a B737 may not have resulted in wake turbulence. It is a larger aircraft but not a heavy. However; in this case; the higher altitude of the preceding aircraft guaranteed that we would start out below its glide path; at least until we could cross its glide path to become established on a higher glide path. Therefore; the spacing really was not adequate for wake turbulence avoidance; since additional time should have been allowed for the vortices to dissipate prior to our crossing of the preceding aircraft's glide path (and those vortices). We suspect ATC was not accounting for the higher altitude of the preceding aircraft when they stacked us in so close behind the preceding aircraft. In the future; we will be more assertive and ask ATC for a lower speed; or for delay vectors; prior to the visual approach; even if that means ATC has to work harder to fit us in somewhere else in the sequence.




Synopsis: E175 Captain reported encountering wake turbulence on approach to SEA in trail of a B737.