Date: 202007
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Dawn
Aircraft: Small Transport; Low Wing; 2 Turboprop Eng
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Landing
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Reporter organization: Air Taxi
Reporter function: Pilot Flying; Captain
Reporter qualification: Air Traffic Control Fully Certified; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Observer
When detected: Taxi
Result: General None Reported / Taken
Contributing factors: Procedure; Human Factors
Primary problem: Procedure

Narrative: I was on an IFR flight to ZZZ to pick up passengers for a Part 135 flight. I received vectors to ZZZ and Approach Control asked what approach I would like at ZZZ. I requested a visual to Runway XL at ZZZ. I reported the airport in sight and canceled IFR. I do not recall whether or not we were cleared for the visual approach to XL or not. Change to advisory frequency was approved. (ZZZ Tower does not open for another 20 minutes). I switched to the CTAF frequency and announced left base to Runway XL. There were no other aircraft in the pattern. Shortly after my radio transmission I heard a very muffled and unreadable transmission only being able to make out [Number sequence] 'XYZA.' A few minutes later I announced turning final to Runway XL. A moment later the same unreadable transmission was received again only able to make out [number sequence] 'XYZA'. I thought this was someone on the wrong advisory frequency of XYZ.A. We landed uneventful on Runway XL and taxied to the FBO. After I shutdown and was exiting the aircraft; an Airport Authority truck pulled up.Person X wearing a COVID-19 face mask began yelling at me. Person X stated that 'Runway XL is closed and I told you twice' 'Runway XL is closed use Runway YY or ZZ'I apologized and told Person X that there was no NOTAM for XL being closed and approach said nothing about it; nor did the AWOS.Person X again repeated herself saying 'I told you twice that XL was closed. I said we heard two transmissions and that I only heard XYZA both times. After the incident I reexamined the NOTAMs for ZZZ and there were none mentioning Runway XL. ATC did not mention it. The AWOS did not mention it. The AF/D does state that when the Tower is closed; Runway XL is Available with PPR.Contributing factors to this incident: Person X with Airport Authority trying to give instructions on a hand held radio while wearing a very heavy COVID-19 Mask making transmission unreadable. Had this transmission been received; a slight turn to final to Runway YY would have been made. Better review of the AF/D or getting the PPR.


Second narrative: Me and my Captain were on an IFR flight plan ZZZ to pick up passengers for a Part 135 flight. We received vectors for ZZZ and Approach Control asked what approach I would like at ZZZ. I requested a visual to Runway XL at ZZZ and we received vectors for final. I reported the airport in sight and canceled IFR. I do not recall if we were cleared for the visual to Runway XL or not. We switched to advisory frequency after being approved by ATC. ZZZ Tower was closed at this moment and will not open for another 20 minutes or so. My Captain switched to CTAF frequency and announced a left base for Runway XL. There were no other aircraft inbound to ZZZ at this time. I was focused on flying but could hear someone speaking on the frequency; but it was not clear what they were saying. My Captain says he believed he understood someone say [number sequence] 'XYZA'. We announced our positions 'Turning final Runway XL'; 'Short final Runway XL' 'Clear runway XL'; and so on. We then taxied to the FBO. After shutting down the plane; an Airport Authority truck pulled up. Person X wearing a COVID-19 face mask began yelling at us. Person X said that Runway XL was closed.We apologized for landing on Runway XL; but there was no NOTAM about it; approach said nothing about it; and AWOS didn't mention it either. We told Person X we couldn't understand the transmissions over the radio as they were not coming in clearly; and my Captain told Person X he could just barely understand the words [Number sequence] XYZA.After the incident we re-examined the NOTAMs for ZZZ and there were none mentioning Runway XL. The AWOS did not mention it. The AFD does not state that when the tower is closed; Runway XL is available with PPR.Contributing factors to this incident:Person X working for Airport Authority trying to give instructions over the radio on a hand held radio while wearing heavy face mask had unreadable transmissions. If we received a clear transmission of Runway XL being closed a slight turn to Runway YY would have been made with no problems.


Synopsis: Air taxi flight crew reported landing at an airport and being advised that the runway was closed.