Sacha Dench, who was attempting a first world tour from mainland Britain to raise awareness about climate change, was seriously injured after a paramotor crash in the West Highlands of Scotland.
Dan Burton, a member of his support staff, was killed in the incident.
Ms Dench had been dubbed the “human swan” as she attempted a climate challenge around Britain 3,000 miles ahead of the Cop26 conference set to start on October 31.
In a statement, the directors of Conservation Without Borders, which was founded by Ms Dench, said the accident occurred near Loch Na Gainmhich in the far north of Scotland.
The statement read: “We are sorry to have to confirm that Dan Burton, the support paramotor, died as a result of the accident.
“Sacha Dench is seriously injured and is treated in hospital. His injuries are serious but not life threatening
“Both very experienced paramotors, our hearts go out to the family of Dan Burton to whom we offer our deepest condolences.
“The incident has been followed up by police and medics and investigations are underway to establish the details of the accident.”
The statement added that the families of those involved had been informed and the Round Britain Climate Challenge would now be suspended.