Dash 8 Series Undifferentiated or Other Model
Air Traffic Control Fully Certified
Human-Machine Interface; Situational Awareness; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented
Airport; Human Factors; Airspace Structure; ATC Equipment / Nav Facility / Buildings
Aircraft X responded to a TCAS RA that he thought was erroneous and returned to airport on a visual approach. There was no traffic observed on the radar [at] the time of the event; nor was there any observed traffic within 10 minutes before and after the event. Aircraft X did refer to himself as [an incorrect flight number] a few times while communicating. It took me a minute to realize it was him calling; because I initially thought Aircraft X was trying to pick up IFR. I did verify that the aircraft was VMC with terrain and the airport in sight before issuing the visual approach because he had descended below the [minimum IFR altitude]. I also informed him the minimum IFR altitude was 5000 feet.
ATC Center Controller reported an aircraft descended below the Minimum IFR Altitude and reported a TCAS/RA while there appeared to be no traffic in the area.