The US Federal Aviation Authority is investigating a mid-air "plane swap" stunt that ended with an aircraft crashing into an Arizona desert.
Pilots Luke Aikins and Andy Farrington were expected to reach 4,265 metres before sending their planes into nosedives. At the same time, each man would jump out of one aircraft and land in the other.
Instead, as the pilots were in mid-air during Sunday's live-stream event, one of the Cessna-182 planes went into a spiral and crashed.
The pilot reached the ground safely thanks to a parachute, The New York Times reported, citing the FAA. The other pilot regained control of his plane and also landed safely.
The FAA said it will investigate the botched attempt. The event was a year in the making, said its sponsor, the energy-drink Red Bull.
Red Bull had billed the stunt as a "first-of-its-kind jump". The event was live-streamed on the Hulu subscription service. No spectators were present at the site.
The event was not available for streaming on Hulu on Tuesday.
The FAA had rejected a request to exempt federal regulations that cover the safe operation of an aircraft. The request was sought because the planes would have been unmanned during the swap.
The agency said the exemption "would not be in the public interest" and that it "cannot find that the proposed operation would not adversely affect safety", said FAA official Robert C Carty in a letter obtained by NBC News.
Aikins and Farrington have completed more than 5,000 jumps together, Red Bull said.