A spectator has been killled at a gliding competition at Husbands Bosworth airfield in Leicestershire.
A joint investigation into the crash has been launched.
A plane collided with the man who was taken to hospital by air ambulance but pronounced dead on arrival at the Queen's Medical Centre in Nottingham.
A 25-year-old man was arrested and questioned by officers following the accident on Tuesday afternoon but he has since been released.
A post mortem examination was due to be carried out on Wednesday.
Police have not yet formally identified the dead man.
The accident is being investigated by Leicestershire Police and the Air Accident Investigation Branch.
The victim had been watching the 4th FAI Junior World Gliding Championships.