Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness
Conflict Airborne Conflict
Air Traffic Control Provided Assistance; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Airspace Structure; Company Policy; Procedure; Human Factors
I responded to an RA on downwind leg into PAE.  We were level at 4;000 feet abeam PAE landing south and had to descend due to a general aviation aircraft that was proceeding towards us and not in communication with ATC. ATC made efforts to reach the aircraft; but was unable. We were given a lower altitude and a turn to the northeast. There was little else we could do to prevent or avoid this situation.
Air Carrier Captain reported taking evasive action responding to an RA for an unidentified VFR aircraft on their approach course to PAE airport.