Cessna 152
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 150; Flight Crew Total 7600; Flight Crew Type 500
Communication Breakdown; Other / Unknown
Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action
Human Factors
I was conducting a training flight with a student. We were established on right downwind for Runway 20. We had already completed three touch-and-go landings and were continuing for a fourth. My student (in the left seat) suddenly observed an aircraft flying in front of us; from left to right. The aircraft then made a left turn to enter downwind in front of us. I made a call on CTAF stating that we were on downwind; now number two for landing. There was no response from the aircraft ahead of us until I called him on CTAF directly. He verbally acknowledged my transmission; apologized; and then stated that he would 'make a 180' on downwind so that we could proceed as we had planned. The pilot also stated on CTAF that he had been making radio calls prior to entering the traffic pattern. My student and I never heard any radio transmissions from this aircraft. When he completed his turn; he was headed directly toward us. I took control of our aircraft and made a left descending turn to avoid the other aircraft. When we turned; the pilot of the other aircraft also made a left turn; which was toward the runway. This aircraft then proceeded along the downwind leg; in the opposite direction to current traffic. There was another Cessna 172 established on right downwind behind us. The disruptive aircraft announced on CTAF a few seconds later that he was 'now number three' for landing. My student and I continued and made a full stop landing. The disruptive aircraft also made a full-stop landing behind the Cessna 172 which was between us in the traffic pattern.
C152 instructor pilot reports a conflict in the traffic pattern Aircraft Y enters on the downwind without announcing on the CTAF.  When Aircraft Y is finally contacted the pilot elects to make a 180 degree turn to reenter and a NMAC occurs.