Date: 202004
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Small Aircraft
Operator: FBO
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Landing
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Reporter organization: FBO
Reporter function: Pilot Flying; Instructor
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Commercial
Human factors: Distraction
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Landing Without Clearance
Detector: Person Observer
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Procedure; Human Factors; Chart Or Publication; Environment - Non Weather Related
Primary problem: Human Factors

Narrative: Myself and another CFI landed at a non-towered airport that was NOTAMed 'CLSD TO TRANSIENT' aircraft.During the COVID-19 slowdown; our flight school had ceased all student training and was only flying occasional proficiency flights with either a solo instructor or dual instructors. This was a dual instructor flight and the first such dual flight for either of us in over a month (it was solo ops only before this). We had just finished a simulator proficiency flight and headed to the airport. Our profile was local: depart ZZZ1; simulated XC to ZZZ2; diversion to ZZZ then simulated XC to ZZZ3; diversion to ZZZ4 and return to ZZZ1. Landings were planned at ZZZ; ZZZ4 and ZZZ1. We split up the pre-flight and introduced the new sanitizing procedures our school had implemented the day before. Our weather checks were brief; as it was clearly a 'nice' day. METAR; TAF and local radar showed no concerns apart from some turbulent and gusty conditions. No SIGMETs or worrisome AIRMETs. Weight and balance was good and we were pretty familiar with the airports we were going to. I took the first leg to ZZZ. As I began the startup checklist; I remembered I forgot to check the NOTAMs. I asked my co-pilot (another instructor) if he had gotten a chance to check the NOTAMs and if not; could he check while I started up. He responded in the affirmative that he checked. I clarified; confirming that he checked for both airports we intend to land at. Again; he responded in the affirmative; stating we were good to go. With this; we continued on. Upon arriving at ZZZ; we observed and communicated with a local aircraft departing the airport towards the south; presumably doing flight training over the lake. This pilot made no attempt to inform us the airport was closed and his presence left little doubt that the airport was open. We continued inbound; making all the appropriate CTAF calls. When closer; we observed no signage was placed near or on the runway (such as an 'X'). We began doing pattern work and prior to taking off to begin our third lap; a voice on CTAF informed us the airport was closed to transient aircraft (presumably someone in the FBO). Surprised; I apologized and advised we would depart the area after taking off. Upon returning to ZZZ1; I checked and sure enough; there was a NOTAM set to expire within 24 hours stating the airport was closed to transient aircraft. I asked my co-pilot/fellow instructor who had earlier confirmed there were no NOTAMs and he said he must have missed it.-ZZZ was one of only a handful of airports approved for this week's proficiency flight by our flight school. Had it not been listed (or no list provided); it is unlikely we would have gone there. -My fellow instructor confirming there were no NOTAMs.-The current COVID-19 slowdown and new sanitizing procedures had changed our procedures just enough to potentially affect our normal flow of operations.-Observing and communicating with an aircraft departing ZZZ immediately prior to our arrival certainly seemed to end any doubt (if there was any) about the airport's open/close status.-No markings on or near the runway to indicate airport closure.Ultimately there is no excuse. I regret not checking the NOTAMs myself; but I am also disappointed that another experienced instructor missed this vital NOTAM. However; we are all human and sometimes we might miss the handful of coded identifiers that mark an airport closed. Thankfully; the airport was only closed to transient aircraft and there were never a safety risk.




Synopsis: Pilot reported doing pattern work; practice landings and takeoffs at an airport that had been NOTAMed closed.