Date: 201707
Local time of day: 0001-0600
Location: S46.TRACON, WA
Flight conditions: VMC
Light: Daylight
Aircraft: Widebody; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Approach; Descent
Airspace: Class B S46
ATC / advisory: TRACON S46
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Time Pressure; Distraction; Confusion; Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Conflict NMAC
Detector: Automation Aircraft RA; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Procedure; Environment - Non Weather Related; Airspace Structure
Primary problem: Procedure

Narrative: The Captain was the Pilot Flying (PF) and I [the First Officer (FO) was the Pilot Monitoring (PM) as we were southbound on the arrival descending in towards BFI. ATC gave us radar vectors off the arrival and looped us out to the west and then back east towards the final approach course for the ILS to 13R. Descent clearances to 5;000 then; 3;000; followed by 2;200 feet were given by ATC. Multiple traffic targets were given to us by ATC the whole way in and also showing on TCAS. On a dogleg base to final approach course we were cleared to join the localizer and told by ATC to expedite decent. We were not established yet but the glideslope was visible a dot and a half above us. (We think he wanted us lower for SEA traffic above?) The PF expedited the decent per the clearance and we joined the localizer for a long final still descending towards 2;200 feet (still below the GS) we were cleared to. We had one ATC traffic report I'm guessing in the high 2;000's that briefly showed yellow and behind us on TCAS. Shortly after and just before leveling off tracking the localizer ATC called traffic again. The TCAS screen showed a white marker close that quickly turned yellow with a TRAFFIC aural. ATC at about the same time told us to go around and climb to 3;000 feet. I estimate that we were at about 2;300 feet to level off at 2;200 at that time. The PF immediately turned the auto pilot off and initiated a climb. About the same time we started climbing the TCAS target turned red with an RA [to] CLIMB. The PF followed the VSI RA indication and I managed the FCP and radios. We leveled at 3;000 feet and got vectored around for another approach. Again with multiple ATC targets and one TCAS TRAFFIC aural. The second approach was uneventful to a normal landing and taxi in.


Second narrative: I; Captain was the Pilot Flying (PF). We were arriving from the north and planning on landing Runway 13R at BFI. Weather was VFR on a busy afternoon. We were cleared to intercept the LOC for 13R. Prior to intercepting and heading south ATC assigned me a heading of 270 'for spacing.' Shortly thereafter I was assigned a left turn back toward to LOC 'to join.' Several traffic calls from ATC throughout the vectors. I was then directed to 'expedite descent to 2200ft.' We were still well north of the airport. More traffic calls from ATC and TCAS. I deployed the speed brakes. We were flaps 5; 185kts; and descending through 3000ft. At approximately 23-2400ft ATC told me to 'climb due to traffic.' I disconnected the Autopilot; turned off the Autothrottle; and climbed. Almost immediately; the TCAS RED CLIMB came on. I climbed to 3000ft; leveled off; and TCAS warning ceased. We were again vectored to the west; north; and finally south to intercept LOC and GS. Approach and landing were uneventful with ATC calling traffic until we switched to Tower Frequency. We never did get a visual on the specific aircraft that triggered the RA.


Synopsis: A flight crew descending on vectors into BFI described multiple VFR traffic encounters; including a near miss and go-around; on the very busy arrival.