A Wildcat helicopter came within 30 metres of a motorised paraglider and had to make a sharp turn to avoid a crash, a report has revealed.
The pilot said he was flying at 2000ft when he spotted another aircraft in his 11 o'clock, less than 100 metres away.
He had to make a downwards turn to avoid a collision and only just missed the glider, by around 30 metres.
The paramotor appeared to continue without concern after the incident and could not be traced despite investigations.
The Wildcat pilot assessed the risk of collision as 'very high'.
The incident happened on October 27, 2017, over Shaftesbury in Dorset, but the details have only just been released in a report by the UK Airprox board.
If two aircraft are set to be travelling head-on or nearly head-on, then both pilots are required to turn right.
Under the Air Navigation Order 2016, a paramotor is defined as a 'glider', which means if the aircraft paths would bring them to a collision then the Wildcat pilot is required to give way.
Testimony from the Wildcat pilot, radar photographs/video recordings and a report from the operating authorities were passed onto the Airprox board, which investigation incidents involved aircraft in UK airspace.
The board noted that this incident was a 'timely reminder to all aviators that paramotors can be encountered almost anywhere outside controlled airspace and are not bound by the more restrictive launch site requirements of paragliders and hang gliders'.
Board members were disappointed that they could not find the paramotor pilot and therefore, said it was 'difficult' to say if the pilot had seen the Wildcat or not.
Members were told that paramotor pilots often wear noise-reducing helmets/ear defenders, therefore they may have not heard the Wildcat.
A pilot's vision, meanwhile, can sometimes be obscured by their canopy.
The paramotor was fortunate to not encounter any serious problems from the Wildcat's downwash (downward airstream from the helicopter's rotating blade), according to members of the board.
The board initially wondered if it had been a late sighting by the Wildcat pilot but that was later dismissed due to the fact that paramotors can be difficult to see depending on their angle and weather conditions.
The incident was described as a conflict in Class G airspace that had been resolved by the Wildcat pilot.
It was noted that the pilot did take action to avoid a collision, albeit later than he would have liked.
It was risk assessed as Category B - safety much reduced.