A runaway aircraft took off on its own when the pilot could not get into the cockpit on time after swinging the front propellor.
The classic biplane ran in circles on the ground at speeds of up to 60mph before taking off and flying on its own for 200m. It then crashed into trees at the edge of Goodwood airfield on Sunday.
Had it cleared the trees it is believed the plane, which was headed towards nearby Chichester, West Sussex, could have flown for around 150 miles on a full tank of fuel.
The small plane had just been refuelled before the incident and its pilots had 'swung' the propellers to restart the engine before getting inside to fly it.
But the aircraft - a 1940 model built in the style of a Tiger Moth - began moving before the pilot had a chance to board it.
Goodwood staff sprayed the plane with foam to stop it catching fire after the crash.
The Stampe was one of a number of aircraft at the airfield for the Goodwood Breakfast Club - a monthly event which displays vintage cars, motorbikes and aircraft for enthusiasts.
Malcolm Phillips, 67 of Emsworth, Hants, was at the event and took pictures of the plane coming down to the ground behind the trees.
The retired aircraft engineer said: "There were hundreds of people there watching as the plane ran amok, haring round in circles.
"We didn't know which way it was going to go and it was worrying that it could head towards the crowd, other planes or the clubhouse."
Mr Phillips said he thought there were about 400 people watching when the plane took off at 11am on Sunday.
He added: "Normally the idea is that you swing the propellers and have the handbrake on and chocks under the wheels.
"You also need to make sure the throttle is only set at low revs.
"Something clearly went wrong and it jumped over the chocks - I suspect what might have happened is that the throttle became loose."
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