Sundowner 23
Flight Crew Private
Flight Crew Last 90 Days 8; Flight Crew Total 134
Time Pressure; Situational Awareness; Confusion; Communication Breakdown
Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Took Evasive Action; Flight Crew Became Reoriented
Human Factors; Procedure
At the end of a personal flight to two nearby airports for landing we returned to the airport where the plane is based.  We made standard position reports to the CTAF from approximately 5nm to the south west of the airport when we received an early frequency change approval from the Class D tower at ZZZ.  We made an additional position report at 2 miles to the southwest of the field.The position report included direction; and distance to the airport; and information that we were on a 45 degree entry to the right downwind for runway 10.  Winds favored runway 10; and other pilots on CTAF stated they were using 10.When we made our call at 3 miles out from the south west; a new pilot announced position on CTAF of 3 miles out; to the west.  Myself and my passenger (CFI ASEL; but riding as passenger not instructor) began looking for the potentially conflicting traffic to the left side of our plane based on the position report.We made a third position report at 1/2-1 nm from the field that we were turning right downwind for runway 10.  At this time we saw an additional plane in the pattern on downwind; we had heard no radio communications from this plane.  The plane was approximately 50 feet higher altitude than our plane; and approximately 200 feet away.  I took evasive action turning 45 degrees to the left and dropping an additional 100 feet of altitude.  I decided to turn to the left as the plane was to our right side; and I opted to turn away from them rather than towards them.  I quickly re-acquired sight of this plane after evasive action and found them 500 feet behind me; and 500 feet further from the runway from me; and 100-150 feet above me both on downwind.  We announced our intentions to depart the pattern straight north; and lost sight of the other plane as we continued north; it was either too far behind us; or turned.  I flew straight and level to the north of the field as I allowed the adrenaline to settle from the near collision; and then returned to the airport to land without incident.  During this time; myself and my passenger heard very faint calls on the radio that may or may not have been from the other plane involved.  We confirmed that we could hear other planes in the pattern; and had verified our transmit capabilities with the ZZZ tower just minutes prior.After landing; we saw the conflicting traffic had already landed; and was taxiing back for a departure.  We tried calling the plane on CTAF; and got no response.  We decided to inform the workers at the FBO of a possible radio issue on the plane; so they could inform the pilot on his return; or address the issue if it was a rental provided by the FBO.  My passenger (CFI ASEL) went to the FBO to relay this info as I tied down the plane.  In the FBO; he found another CFI who said he had been in that plane for the near collision; and that the radio volume was turned to 'zero' and that was the issue.  It seemed that they could neither transmit nor receive communications on their radio at the time.
I later found the CFI who was in the other participating aircraft; who stated that they had their radio volume turned down to the point that other aircraft radio calls were inaudible. I stated that their radio transmissions were quite broken and quiet as well.I believe the probable causes contributing to the incident could have been the inability for the other aircraft to hear our radio transmissions entering the pattern so as to consequently respond. In our cockpit; I could have taken up the responsibility of checking for traffic out of the right side of the aircraft instead of looking over the PIC's shoulders and let him handle the traffic scanning on his side of the aircraft. We may have been able to see the collision hazard a bit sooner with a better traffic scan technique.
A pilot; and his rated passenger; reported a near miss with another aircraft in a CTAF landing pattern after an instructor in the other aircraft later acknowledged his aircraft radio volume was near OFF.