An official probe has said two planes came within 100 feet of each other near Peterhead.
The incident occurred on May 15 and involved an Auster and a Cessna 172, both of which were flying at around 1500ft.
The Auster pilot said he made a very late sighting of the high-wing single-engine Cessna just south of Longside Airfield.
He instinctively pulled up as the plane passed less than 150ft below him.
The UK Airprox Board, which investigates near misses, deemed the risk of collision as “high”.
Its report also found the air traffic controller had not fully understood the C172 pilot’s call that he was intending to turn at Peterhead.
As a result, the opportunity had “unfortunately been missed” to inform both of the impending potential conflict at Longside.
The Auster was also fitted with an alarm system that was unable to detect the C172.
The Board said the situational awareness and action taken was ineffective because the conflict was not detected even though the information was available – although the report pointed out that the controller was not required to monitor the aircraft.
The pilot of the Cessna 172 estimated that the other aircraft was 100-200 ft above and assessed the risk of collision as “medium.”
Pilots of both planes shared an equal responsibility for collision avoidance and not to operate in such proximity to other aircraft as to create a collision hazard, the report said.
The UK Airprox Board added that “both pilots had seen the other aircraft late and had carried out avoiding action to increase separation”.