French investigators have determined that a skydiver was accidentally ejected from a climbing Cessna 208 after he partially opened the exit in order to cool the cabin.

Fourteen skydivers and a single pilot had been on board the aircraft, operated by the Vannes Bretagne sports parachuting school located about 100km northwest of Nantes.

Three experienced individuals and two students were set to jump from 1,200m (3,940ft) with another eight, plus the instructor, jumping from 4,000m.

One of the experienced skydivers was sat adjacent to the rear exit, which had a shutter curtain drawn down.

He partially opened the shutter by about 10cm to ventilate the cabin – as previously agreed with the pilot – at a height of around 450m. Sat facing the rear of the aircraft, he used his foot as a wedge to keep the shutter open.

French investigation authority BEA says this was normal practice during summer months, although the door is supposed to be kept shut below 500m to ensure adequate recovery height should anyone fall.

As the instructor started checking students’ equipment, BEA says the skydiver wedging the door shifted his position slightly, dislodging his parachute extractor handle from its housing.

Air flowing past the open shutter snatched the handle, causing his main parachute canopy to deploy into the external airstream beneath the left-hand horizontal stabiliser, and forcibly pulling him through the shutter.

The skydiver fractured his leg as he struck the exit frame, but – once outside the aircraft – remained sufficiently aware to realise both his main and emergency canopies had deployed.

“He kept the two canopies separate to avoid entanglement until he reached the ground where he was able to land,” says BEA, although it adds that he suffered fractures of five lumbar vertebrae on impact.

The skydiver held a federal instructor qualification and had completed 3,600 jumps. He was quickly located by emergency services following the incident on 1 August last year.

BEA says that, during the occurrence, the pilot felt strong vibrations on the control column and, concerned that there might be an elevator fault, commenced a descent. The vibrations stopped but he opted to land as a precaution. The aircraft sustained minor damage to the exit door frame and shutter slats.