Mystery pilot 'risked collision' during formation training
UK Airprox BoardThe pilot of a light aircraft risked a mid-air collision by attempting to join a formation training flight, an airprox report has found.
The "deliberate action" was reported by the pilots of two Tiger Moth biplanes over Cambridgeshire in December.
Investigators said the aircraft made an "extremely unwise manoeuvre" which may have "impeded their flight".
They have yet to identify the light aircraft involved - or its pilot - five months on.
The airprox report detailed how the biplane pilots, flying vintage DH82 De Havilland Tiger Moths, had taken off from Cambridge for formation training on Saturday, 16 December.
At 11:44 GMT, another aircraft, thought to be a Vans RV6 or RV9, "came from behind and joined for several minutes," it said.
The mystery aircraft was about 100ft to the left and rear, one pilot told investigators, before it "dived and broke away, going unsighted".
The pilot described what he saw as a "deliberate action" and assessed the risk of collision as "high".
At the time, the aircraft were flying at about 1500ft (457m), the report said.
However, the airprox board concluded "reluctantly that they had insufficient information to assess the risk".
"Perhaps the light aircraft pilot was flying towards the DH82 formation to look at the vintage aircraft out of curiosity rather than trying to join the formation," the board added.