A plane was forced to do an emergency landing after an evacuation slide inflated inside the cabin as it flew almost 40,000ft over Kansas on Sunday.
No one on the flight, from Chicago to Orange County in California, was hurt in the unexplained incident.
Taylor Martinez, a professional American football player and app entrepreneur, was one of the 96 passengers on board.
Tweeting a picture of the slide bursting into the cabin, he called it the “scariest flight of all time”.
Michael Schroeder, who was on his way home to California, told the Wichita Eagle flight attendants said they had never seen anything like it.
“I heard a kind of loud pop and hissing noise and I turned around to the back and that slide that would normally go outside the plane so you can slide down in an emergency had for some odd reason deployed inside the plane while we were flying," he said.
“Fortunately nobody was back there.”
The pilot immediately used the intercom to tell passengers he would land as soon as possible.
There were initial reports that a passenger tried to open a door during the flight but a spokesman for the US Federal Aviation Administration said they were false and it would be “impossible” at that altitude.
The flight left Chicago shortly after 8.30pm local time and landed in Wichita at 10.30pm, where passengers were taken to overnight accommodation and investigators boarded the plane.
A spokesman for United Airlines said maintenance crew would inspect the Boeing 737-700 to determine why the slide inflated.
He added: “The flight diverted to Wichita, Kansas, after the emergency evacuation slide accidentally deployed. No one was injured and the flight landed safely.
“We are flying in another aircraft to resume the flight and get our customers to their final destination as quickly as possible.”