Date: 202006
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Landing
Aircraft component: Communication Systems
Component problem: Improperly Operated
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Landing Without Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Human Factors; Environment - Non Weather Related
Primary problem: Human Factors

Narrative: Due to a radio/intercom switch issue; coupled with expectation bias with which I made the assumption that the ZZZ Tower was closed; I ended up landing at ZZZ without radio contact with the Tower.The flight was VFR from ZZZ1 to ZZZ routing over ZZZ2. Flying over ZZZ2; I listened on the ATIS frequency and heard no letter identifier with the weather information because the Tower closed early (XA00L from NOTAM versus XF00L from airport directory). I made my area report on the Tower frequency as I flew over; using it as a CTAF. There was another aircraft that was working in the pattern; making reports on the CTAF; as well. I recall thinking that the COVID-19 crisis had even reached State X; where the Tower was closed early.Approaching ZZZ; I monitored on COMM2 what I thought was an ATIS frequency (only to realize later that it was an ASOS frequency) and of course; got no letter identifier with the weather information. This started me down the path to assuming that perhaps ZZZ Tower had closed early; like ZZZ2. With all the irregularities occurring around the world due to the COVID-19 crisis; it seemed reasonable.I then switched to COMM1 and made a radio call to Tower on Tower frequency; receiving no answer. Because there was no letter identifier on what I had thought was an ATIS frequency and no apparent answer after repeated queries to Tower; I assumed the Tower was closed and made my normal position reports; entering the pattern as if it was an uncontrolled field; using the CTAF frequency. What I did not realize is that I was neither receiving or transmitting on COMM1. The switches on the intercom panel were sticking and I failed to verify the transmit light; relying merely on the tactile touch of the button.There was no other traffic at ZZZ and I landed uneventfully. The airport appeared deserted; which only seemed to confirm my impression that the tower must have closed early due to the COVID-19 crisis. I parked the aircraft and it was not until two days later when departing did I realize that I had not been transmitting over COMM1 due to a switch problem and that the Tower had not been closed; but had still been in operation the night I landed.What contributed to this incident was my bias to assume the Tower had closed early like the Tower at ZZZ2. The fact that I did not hear the expected letter identifier that I am accustomed to at a Tower airport when I listened to ASOS--thinking it was ATIS--kept me going down this path of assumption. And then when I could not raise Tower; that seemed to only verify my assumptions. These assumptions prevented me from checking the radio switches when I did not receive a reply from the Tower and I instead continued to transmit as if at an uncontrolled field; not realizing that I was neither transmitting nor receiving.If I had not been operating under my false assumption; for example; if I was at my home field where I knew the tower was open and I was not getting a reply to my queries; I would have checked the intercom switches more carefully; tried a different frequency; or otherwise worked a potential radio issue. Instead; I attributed what was actually a radio issue to; 'Oh; Tower must be closed due to COVID.'As far as the switch issue; a qualified A&P mechanic has addressed it and the same issue should not happen again. This was a wake-up call for me. As a professional pilot; I fly around the world. In this new COVID-19 world; it was easy to chalk up irregularities to the 'new normal.' As aviators; we cannot ever allow ourselves to stray from our normal procedures and protocols. This incident painfully reminded me of the need to constantly check my assumptions.




Synopsis: Pilot reported landing without clearance due to a sticky radio switch and lack of incoming radio transmission; and thinking the Tower was closed due to COVID-19.