Virgin Atlantic is investigating claims that an air stewardess repeatedly shouted "we're going to crash" during a flight hit by turbulence.
Virgin launched their London to Las Vegas route in 2000
Passengers reportedly began to panic and cry as the shouts rang out when the London to Las Vegas flight suddenly began "juddering".
Douglas Marshall, who was on the flight, said many passengers thought they were going to die.
The airline insisted passenger safety was its top priority.
Another passenger, Paul Gibson, told BBC Radio Five Live: "People that were walking around couldn't make it back to their seats so they had to sit on the floor and hold on to whatever they could."
He also admitted that his initial thought was that the cries had emanated from a passenger.
"I could hear there was somebody sort of crying or sort of yelping as the plane shook. My first impression was that it was a passenger so I didn't really think anything of it," he added.
The incident occurred when the Boeing 747 jumbo jet, with 451 passengers on board, hit severe turbulence.
Other passengers said people were crying and being sick after the stewardess began panicking.
Businesswoman Claire Daley told the Daily Mail: "She screamed every time we dropped and at one point chanted three times 'We're going to crash'".
"When I heard that I went to pieces. I couldn't help thinking about our kids being orphaned."
Mr Marshall, a 33-year old BBC journalist from Birmingham, was also on the flight and heard screams but did not know who they came from.
However, he confirmed that the flight crew were "very scared" when the plane hit trouble.
"If the flight crew are scared then you know something is seriously wrong," he said.
"The plane was juddering, up and down. I was trying to take a step but just ended up lying on the floor."
He eventually managed to get himself into a seat which happened to be next to a stewardess.
"It was very, very scary. Most people on that plane thought they were going to die."
Half of the passengers had to use their sick bags, he added.
A Virgin spokeswoman said: "The safety and security of passengers and crew is Virgin Atlantic's top priority.
"The flight deck will always keep passengers informed of expected flying conditions and where possible will try to avoid areas of expected turbulence."