Two RAF planes were flying unidentified when they came within 200 feet of a Belfast-bound passenger flight last October, a British aviation report this week revealed.
A mid-air collision was only avoided by luck, the official air-miss report by Airprox found.
Airprox, which works under the auspices Britain's Civil Aviation Authority and the Ministry of Defence, said the planes came within 200 to 300 feet of each other while flying over Scotland last October.
One of the RAF pilots quoted in the report said the near-collision was "deeply disturbing".
The incident, over Burrow Head, near the Solway Firth, on October 27th last year, involved two RAF Hawk jets and a Flybe Airways DCH-8 plane carrying 46 passengers and crew from Newcastle to Belfast City Airport.
The Hawks were on a training mission when a student pilot in one of the Hawks made a visual identification of the Belfast-bound plane. Shortly afterward, air traffic control in Prestwick noted the presence of another craft in close proximity to the Belfast-bound plane.
The Flybe crew were radioed but by that time the aircraft's paths had crossed. The reading on the radar video recording showed the contact points for the planes had merged.
The report says a mid-air crash was avoided because the fighter planes flew under the DCH-8. "In the board's view any separation [between the planes] that existed was purely fortuitous," the report said.
The report said a transponder - which sends and detects radar signals - on the leading Hawk either failed, had been inadvertently switched off, or was left on standby.
The Flybe aircraft was fitted with receiving equipment, but no warning was received . The report noted the non-sighting of the Hawks by the DCH 8 pilots "and, effectively, a non-sighting by the Hawk leader".
Airprox, which does blame or identify the operators of planes involved in an investigation, noted the aircraft were "equally entitled" to be using the airspace at the time.
The near-collision was the only one last year found to be a "Category A" risk - the highest classification.