ONE of the busiest airfields in the country has introduced changes to its air traffic control policy after two RAF planes came close to a mid-air collision near a school.

RAF Linton on Ouse, between York and Thirsk - where Prince William underwent pilots' training in 2008 - said it has overhauled procedures surrounding when planes take off following the near miss in poor visibility on November 21, last year.

The UK Airprox Board rated the incident, involving a plane piloted by an RAF tutor and a Tucano, which are used to provide basic fast-jet flying training to RAF and Royal Navy student pilots, as among the most serious near misses it investigates, stating "the safety of the aircraft may have been compromised".

A report to the board said minutes after the tutor pilot was given clearance to take off from the airfield, which has been an RAF base since 1937, and climb to 1,800ft, he received an alert from air traffic controllers as he neared Queen Ethelburga's School, Thorpe Underwood.

"As he levelled he was given the instruction to turn left heading 90 degrees and, on rolling out, noticed the indication on his TAS [true airspeed indicator] of an aircraft in his left at nine o’clock.

"On looking left he saw a Tucano taking evasive action in a right-hand turn, co-altitude."

The pilot of the Tucano, which can fly at speeds of up to 315mph, said minutes after take-off he was given the instruction “avoiding action, turn right immediately, heading 290 degress, traffic one nautical mile, 300ft”.

The report states: "Concerned by the proximity of this aircraft he rolled and pulled hard to the right onto the assigned heading.

"Throughout the incident he did not see the other aircraft; he assumed it to be the tutor that had departed ahead of him."

The tutor told the inquiry he believed a strong headwind meant he had a relatively slow ground-speed that allowed the Tucano to catch up with him in the climb and the planes would have been separated by 200ft vertically and 300m laterally had evasive action not been taken.

The RAF base said it had since replaced its two-minute rule for clearances between take-offs with a number of restrictions to ensure planes are adequately separated.

The board found the incident had been caused as the Linton procedures had allowed the Tower controller to release the Tucano into conflict with the tutor, the tutor did not maintain his flight path from take-off and the air traffic control staff had not best managed the situation.