Skyhawk 172/Cutlass 172
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 2; Flight Crew Total 243; Flight Crew Type 243
Communication Breakdown; Other / Unknown
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Landing Without Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
General None Reported / Taken
Human Factors; Procedure
Personal VFR flight in a rented C172S aircraft; departed at approximately XA:30; no flight plan filed. Flight service called via phone prior to departure. No adverse weather; TFRs or unexpected NOTAMs (other than gusty winds) were reported.  Departure runway aligned well with current gusty winds. Flight route direct and estimated time enroute 35 minutes. Originally lined up for a RWY 22 landing but after discussion via CTAF with other aircraft executing practice landings on the field the agreement was reached that winds favored 31. Landed runway 31; full stop and parked for on-field dinner for approximately 1 hour.  Departure at approximately XC:20 under VFR without flight plan. Tuned in ATIS frequency 128.3 approximately 15 miles Northwest of ZZZ on COM2. Was expecting to hear tower recorded ATIS message but heard standard automated recorded AWOS message reporting standard weather and runway and construction NOTAM. Message reporting winds 260@7; visibility 10; skies clear; Temp 26; Dewpoint 8; alt 2994. Statement that CTAF is 120.5 when tower is closed. Tower normally closes at XE00; but assumption was made that tower closed early due to very light traffic in the area.  Monitored CTAF/Tower frequency 120.5 from 15 miles Northwest of ZZZ to approximately 6.5 miles Northwest of ZZZ. Made call on CTAF reporting 6 miles North; no response on CTAF. Proceeded South to enter left downwind. Announced entering left downwind on CTAF 120.5; no response on CTAF. At this time PIC noticed flashing lights on airport boundary from emergency responder vehicles. Situation was near airport boundary; and a non-factor for the runway. (Approximately 70-80 yards from runway) Announced left base and final on CTAF; no response. Sun very low on horizon on final at approximately 3 o'clock position but general visibility to start of runway environment not significantly impacted. Landed without issue and turned to taxi off at taxiway C. (right turn) Upon turning noticed a black SUV parked next to runway about 500 feet beyond taxiway C. (not on runway) Also noticed SUV with flashing lights crossing grass area from airport boundary. Taxied to ramp and parked with SUV with flashing lights following.After parking person identified themselves as the airport administrator and claimed that I had landed at a closed airport and was not cleared to land. He also informed that there was an aircraft accident on the field approximately 1 hour prior. I explained that I was on CTAF/tower frequency; reporting position and intention from 6 miles North to landing. He claimed that he has been communicating via handheld radio; but stated that CTAF was 121.5; then stated that it was 121.7; neither of which is correct. He also claimed that tower was flashing light gun signals. No light gun signals seen; perhaps due to sun angle. Unknown why light gun signals were being used instead of communication on CTAF; or if there really were light gun signals sent. He also stated that there was a vehicle on runway at the time of landing; which was not seen. (nor was a vehicle seen on the runway in approach photos taken by passenger in aircraft).
C172 pilot reports departing on a flight to a nearby airport. Upon return; when the ATIS is tuned AWOS is heard; indicating that the Tower may be closed. The CTAF/Tower frequency is used for position reports with no response from anyone. During landing; vehicles with flashing lights are noted; but none are on the runway. After parking the reporter is informed by an airport administrator that he has landed at a closed airport.