An investigation has revealed that a jet fighter and a civilian aircraft came within a couple of hundred feet of each other over Caithness.
The risk of collision was given the second highest rating – where safety was not assured.
The “worrying” incident in which the Royal Air Force Typhoon fighter – from RAF Lossiemouth – flew without a working secondary surveillance radar (SSR) and did not see the Jetstream aircraft, has led to changes by the RAF.
Typhoon departures without a serviceable SSR are not now permitted other than for exceptional operational requirements.
Both planes were apportioned a degree of blame for the incident by the UK Airprox Board, which investigates near misses.
The incident happened about 27 nautical miles south-east of Wick, at 8.25am on June 14.
The BAE Jetstream 41 pilot saw the Typhoon, ‘ballooning’ in the window in the 9 o’clock position and closing fast.
The report said: “The pilot deemed a collision was close, disconnected the auto-pilot, and pushed the nose down to increase separation.
“Both captain and first officer were somewhat unsettled by this event. It was agreed by both pilots they were within 250 feet – plus or minus 50 feet [of the other aircraft].”
The risk of collision was assessed as ‘high’.
The Typhoon pilot, who was on a training sortie, was unaware of the near miss until informed after the flight. He was part of a group of three planes and was tasked to go ahead to check the weather.
In its assessment, the board said: “We quickly and unanimously agreed that, because they were both in the see-and-avoid environment of Class G airspace, the cause of the Airprox had been a late-sighting by the JS41 pilot and a non-sighting by the Typhoon pilot.
“The board then turned its attention to the risk and noted that, although the two aircraft passed close to each other horizontally, it seemed from the JS41 pilot’s report that, after his manoeuvre, they had probably been separated by about 300ft vertically.
“Although this was clearly a worrying incident, the board did not consider that it represented a situation where separation had been reduced to the minimum risk Category A.
“The JS41 pilot had seen the Typhoon, albeit at a late stage, and had taken action, subject to the capability of his aircraft, to increase vertical separation.
“Consequently, it was assessed that, although safety margins had been much reduced below the norm, the incident was risk category B.”