Date: 201812
Local time of day: 0001-0600
Location: SEA.Airport, WA
Flight conditions: IMC
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B SEA
ATC / advisory: TRACON S46; Tower SEA
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Communication Breakdown; Confusion
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Airspace Structure; Human Factors; Procedure; Weather
Primary problem: Human Factors

Narrative: The Captain was flying an autopilot coupled ILS approach to RWY 16R. The visibility was 2 miles in rain with about a 1;000 foot ceiling. While the surface winds were approximately 160 at 30 kts; there was a 45 knot direct cross wind that was causing speed fluctuations about 5 to 15 knots until about 800 AGL. Turbulence was moderate until about 800 feet AGL. We intercepted the ILS about 18 miles out and shortly after we were told to contact the Tower at FINKA (FAF). The First Officer was working the radios and he switched to the Tower outside of FINKA. The Seattle Tower soon asked us if we were on frequency and we were cleared to land. The landing was uneventful. Once we cleared RWY 16L we were told by Seattle Ground to contact the Seattle TRACON Duty Manager by telephone. It would appear we were the cause of a near miss because the FO switched the radio frequency from Final Approach to the Tower too soon (SEA Approach Control's opinion). We were never instructed to switch to the SEA Tower exactly at FINKA by ATC. We were told to contact the Seattle Tower at FINKA (there was nothing about monitoring SEA Final). Anyway; there was an aircraft that went Missed Approach at Boeing Field due to wind shear and we were told to do a Go Around (we never heard the call because the FO had switched the frequency to the Tower prior to FINKA). According to SEA TRACON; our failure to monitor the SEA Approach Control Frequency caused way too many problems. It would appear from the conversation; he did not think we were capable of flying into Seattle on a daily basis. [Name removed] told us that we should have known to monitor the SEA Final Approach Control Frequency until FINKA. I have asked several Captains who fly for [Airline] and are based in SEA about this and they knew nothing. There is nothing on the 10-7; 10-9; Approach Chart; etc. The First Officer performed just like he would at LAX; SFO; DEN; DFW; etc. What SEA Approach Control wanted us to do seems to be some form of 'Tribal Knowledge'. I think the cause and contributing factors have been covered above. It should be stated; there appeared to be some wind shear issues at Boeing Field. We were never alerted by ATC that I can remember to monitor the SEA Final Approach Control Frequency until FINKA. We were just told when handed off to the SEA Tower to contact them at FINKA. As the Flying Pilot/Captain; I think this whole Near Mid Air incident 'stinks'. Is ATC trying to cover themselves because a situation became a 'Perfect Storm'? I have flown into Seattle since 2002 on a regular basis and since 2008 on an almost weekly basis in all types of weather. This is the first time I have heard anything about monitoring the final approach frequency until FINKA until after the fact. I would recommend a meeting with the SEA ATC Facility Manager and get the official procedures from him. I would issue an ALERT Message. And there probably need to be some notes on the 10-7; 10-9; Approach Plate; Flight Release; etc. regarding what SEA Approach Control wants pilots to comply with when flying the ILS to 16R; 16L; or 16C. From my perspective; I think we flew the flight very professionally. I was shocked and surprised when we were told to contact the SEA Approach Control Duty Manager on arrival at the gate. I think my First Officer would share my opinions too.




Synopsis: Air carrier Captain reported an airborne conflict on approach into Seattle with an missed approach aircraft from BFI that was not identified due to an early frequency change to the tower.