Any Unknown or Unlisted Aircraft Manufacturer
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Conflict NMAC; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Aircraft
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Human Factors
Made visual contact with a GA aircraft on final approach to SEA runway 16R ahead of us. Continuing down the glideslope; we came to within 300 feet of the aircraft and a TCAS RA was issued; we climbed clear of the conflict and were then able to return to our glide path and make a stabilized approach and landing.Given the location of the aircraft relative to the approach path it is likely the GA aircraft had violated Seattle's Class B airspace; which is obviously not something we can control. However the TCAS system worked as designed and conflict was avoided without any abrupt maneuvering. Beyond additional focus on airspace awareness within the GA community; I do not have any additional recommendations.
Air carrier flight crew reported TCAS Alert on approach.