AVIATION investigators arrived in Bangkok today to learn how and why severe turbulence sent a Singapore Airlines plane into a sudden dive that tossed passengers and crew around the cabin, leaving a British man dead and dozens of others injured.

Twenty people remained in intensive care in hospital after Flight SQ321, which was flying from London’s Heathrow airport to Singapore, hit the turbulence on Tuesday over the Andaman Sea.

The Boeing 777, which carried 211 passengers and 18 crew members, descended 6,000 feet in about three minutes, the carrier said.

The captain diverted the plane to Bangkok’s Suvarnabhumi Airport, where medical teams evaluated those aboard and sent over 80 to hospital.

Singapore Airlines sent a special flight to Bangkok on Tuesday night to pick up those well enough to travel.

The airline said that 131 passengers and 12 crew members arrived shortly after 5am at Singapore’s Changi Airport.

Six crew members and 79 passengers stayed in Bangkok, where the majority remained in hospital, said Singapore Airlines chief executive Goh Choon Phong.

Samitivej Srinakarin Hospital, where most of the injured were taken, said 20 people were being treated in intensive care while 27 others have been discharged. The ICU patients include six Britons, six Malaysians, three Australians, two Singaporeans and one person each from Hong Kong, New Zealand and the Philippines, it said.

The hospital said that nine people underwent surgery on Tuesday and five more operations were expected to be completed on Wednesday. It said it had provided 104 people with medical care.

“I’ve only a cut in my eye and a chipped tooth, it could be way worse,” said Josh Silverstone, 24, who was discharged from the hospital on Wednesday. “Everything was fine until I arrived back in the airport and I couldn’t stop vomiting. I couldn’t walk, it was pretty bad.”

“I woke up on the floor, I didn’t realise what happened, I must’ve hit my head somewhere,” the Londoner said.

“There were people laying out on the floor, they were paralysed.”

Mr Silverstone added that he was so scared that he bought in-flight internet access to message his mother. “I wasn’t trying to scare her, but I said: ‘I love you’.”

British passenger Andrew Davies told Sky News that the seatbelt sign had come on just before the turbulence, but crew members didn’t have time to take their seats.

“Every single cabin crew person I saw was injured in some way or another, maybe with a gash on their head,” Mr Davies said.

“One had a bad back, who was in obvious pain.”

Officers from Singapore’s Transport Safety Investigation Bureau arrived in Bangkok late on Tuesday, Singapore Transport Minister Chee Hong Tat said today.

He said that the US National Transportation Safety Board is also sending an accredited representative and four technical advisers to support the investigation because the incident involved a Boeing plane.

Thai officials had withheld the name of the dead man, but British media identified him as Geoffrey Kitchen, 73, who was going on a six-week holiday with his wife. She was among the passengers taken to hospital in Bangkok.

Mr Kitchen was described as formerly working in the insurance industry, and in retirement was continuing his decades-long involvement with amateur theatre.

A Thai airport official said Mr Kitchen might have had a heart attack, though that hadn’t been confirmed.