A320
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 13
Workload; Time Pressure; Communication Breakdown; Distraction; Situational Awareness
ATC Issue All Types; Conflict NMAC
Air Traffic Control Issued Advisory / Alert
Human Factors
I was training on LCL. There was a line of thunderstorms to east with moderate to extreme precipitation. Runways XXR/XXC/XXL in use. Aircraft X was on an ILS Runway XXR approaching ZZZZZ the final approach fix when he checked on the frequency. I issued traffic to Aircraft X at his two o'clock and 2nm; same altitude moving south toward him type unknown suggest you descend. I then called ZZZ sector and asked him if he was talking to the unidentified aircraft in the Class C and he said negative. I went back to Aircraft X and updated him on the traffic at his one o'clock and 1nm southbound type unknown and Aircraft X reported him in sight. Aircraft X went underneath the unidentified aircraft by about 400 ft. and landed without incident. I asked Aircraft X on arrival what type aircraft it was and he stated some sort of Cessna. Traffic [should be] issued sooner to Aircraft X via the approach sector.
TRACON Controller reported an NMAC occurred between a large transport on final approach and small aircraft which was not in communication with ATC.