Flight Crew Air Transport Pilot (ATP)
Other / Unknown
Conflict Airborne Conflict
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Procedure; Human Factors
On approach to 16R at SEA; clear; VMC; just prior to 1;000 feet AGL; we received a TCAS TA; then a momentary RA. This was caused by a single engine prop departing BFI. They made right downwind departure; which I think is not normal. This caused them to be closer to the arrival path into SEA. I saw the traffic at our 7-8 o'clock position before the RA. Traffic was well behind us and proceeding behind our path. We got the RA for about 5 seconds to monitor vertical speed. The First Officer; pilot flying; followed the RA. After; we were able to continue the approach on Glide Slope with no issues. Reported the event to SEA Tower on approach. Right downwind departure from BFI should not be allowed when aircraft are landing 16's to SEA. Even if they remain low; the rate of climb will trigger an RA possible with traffic on approach to 16; as [it] did to us.
EMB-170 Captain reported an RA with traffic on a nonstandard departure from BFI.