Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human-Machine Interface; Communication Breakdown
ATC Issue All Types; Conflict NMAC
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Human Factors; Procedure
During arrival into the terminal area we were level at 5;000 feet. I saw on the TCAS traffic approaching us opposite direction 500 to 400 feet below I was looking to acquire it visually then it became yellow on the TCAS then it turned into an RA which directed me to maintain vertical speed. I disconnected the auto pilot climbed about 100 feet then saw the traffic pass just to my left and below then the TCAS said clear of conflict and I returned down to 5;000 feet and reengaged auto pilot. The First Officer was Pilot Monitoring and he immediately notified ATC of our response to an RA and our slight altitude deviation and also our return to our assigned altitude when clear of the conflict this was inside Class Bravo airspace there was no traffic advisory given by ATC.
An Air Carrier pilot reported ATC failed to advise them of traffic 400 to 500 feet below them and they responded to an RA for the traffic.