Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 400
Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Airspace Structure; Human Factors
I was instructing my student arriving to OUN as instructed by Tower; and I saw traffic 300 feet below on a conflicting course. I corrected to the right to deconflict and fly in front of them as Tower called a traffic alert for me. I called back 'looking; negative contact' and Tower called Aircraft Y with a traffic alert twice with no answer. By that time; I had them in sight and called no factor as they passed off my left wingtip by 1/4 to 1/2 of a mile. The other plane's instructor was doing a stage check for a private pilot; and said he had me in sight the entire time; but was a 'bystander' in letting the traffic conflict. He didn't say anything until the traffic alert on his GPS noted the conflict; his student said; 'oh; should we turn away from that;' and then they did. Additionally; the student pilot flying with the stage check instructor changed from Tower to the local CTAF; 123.3; about 2 miles from the airport and at 500 feet AGL; which helped the confusion. I tried to reach Aircraft Y on that local traffic frequency twice but got no response. The instructor in that plane said that he heard me calling but didn't say anything as he was waiting for his student to reply.
Flight Instructor on training flight reported a Near Mid Air Collision with another aircraft.