Narrative:

The captain was the pilot flying (PF) and I [the first officer (first officer) 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.

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Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.