AN air ambulance was seconds away from colliding in mid-air with a plane performing aerobatic spinning manoeuvres that had safety equipment switched off, it has emerged.

The Yorkshire Air Ambulance (YAA) helicopter had been cruising at 1,519ft near Kirkbymoorside, North Yorkshire, towards its base at RAF Topcliffe, near Thirsk, at 3.30pm on July 12 last year, when the pilots saw a light aerobatics aircraft "suddenly appear" 200ft directly above them.

An official report said the YAA crew saw the two-seat Extra Flugzeugbau EA-300 plane, which was being used for a lesson on flat-spinning - where planes tumble like a leaf out of the sky - too late to take action and graded the "very close" encounter as being among the most serious incidents it examines.

The pilot of the aerobatics plane, who had been conducting the lesson above Wombleton Airfield with the aircraft's transponder - a device that emits an identifying signal - switched off, had not seen the oncoming helicopter at all.

The incident near the former Second World War RAF Bomber command base came less than a week after YAA crews were put on alert as millions of people lined the streets of Yorkshire for the Tour de France.

A report by the UK Airprox Board, which examines incidents in which the distance between aircraft as well as their relative positions and speed may compromise safety, states the aerobatics plane then descended below the YAA helicopter on a track towards the moors.

The YAA pilots, who assessed the risk of collision as high, watched as the two-seat EA-300 aircraft seconds later began a rapid climb over the national park.

The Extra EA-300 pilot said checks were carried out before and after each spin and that visual cues were required for the exercise, so both he and his pupil were looking out of the cockpit at all times.

The report concluded while both pilots had equal responsibility to avoid a collision, the YAA had right of way if the Extra EA-300 plane was overtaking, adding that the aerobatics plane had been in a blind spot for the helicopter.

It states: "This served as a salutary reminder as to the value of always flying with Mode C [altitude encoder and altimeter]... the board were bewildered as to why the Extra crew would have decided not to do so."

A YAA spokeswoman said: "The Yorkshire Air Ambulance always flies to the highest safety standards - the area around RAF Topcliffe is very busy with air traffic."