Passenger Dzafran Azmir, 28, described chaos as the turbulence hit.
“Suddenly the aircraft starts tilting up and there was shaking so I started bracing for what was happening,” he said.
“And very suddenly there was a very dramatic drop so everyone seated and not wearing seatbelts was launched immediately into the ceiling.”
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“Some people hit their heads on the baggage cabins overhead and dented it,” he added.
“They hit the places where lights and masks are and broke straight through it.”
Briton Andrew Davies told Sky News “anyone who had a seatbelt on isn’t injured”.
He said the seatbelt sign came on, but there was no time for crew to take their seats.
Mr Davies said “every single cabin crew person I saw was injured in some way or another, maybe with a gash on their head… One had a bad back, who was in obvious pain.”
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0:49
Emergency services surround plane on tarmac
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Kittipong Kittikachorn, head of Bangkok Suvarnabhumi Airport, told reporters a British man, 73, had died from probable cardiac arrest.
He said about 30 people were injured, including at least one crew member, and that many passengers couldn’t walk and had to be helped from the aircraft
It’s believed the sudden turbulence hit while people were being served breakfast, the airport boss added.
Mr Kittikachorn blamed an “air pocket” for the incident.
He said the dead man’s wife was with him at hospital and that some people with minor injuries had already been discharged.
The UK Foreign Office said it was “in contact with the local authorities” over the incident.
Flight tracking data showed the plane cruising at 37,000ft (11,280m) before dropping 6,000ft (1,830m) in around three minutes.
However, a spokesperson for FlightRadar24 said this appeared to “just be a flight level change in preparation for landing”.
There were 211 passengers and 18 crew on the plane, a Boeing 777-300ER.
There are a few forms of turbulence – where there’s a sudden change in airflow and wind speed.
Turbulence can often be associated with storm clouds, which are usually well forecast and monitored, allowing planes to fly around them.
Clear-Air Turbulence (CAT) is much more dangerous as there are no visual signs, such as clouds.
This invisible vertical air movement usually occurs at and above 15,000ft and is mostly linked to the jet stream.
There are clues on where CAT may occur, but generally it can’t be detected ahead of time, which means flight crews can be caught unaware with no time to warn passengers and put seat belt signs on.
It’s been understood for some time that climate change is increasing turbulence during flights, and the trend is set to worsen according to reports.
Social media video showed ambulances surrounding the aircraft on the tarmac.
“Singapore Airlines offers its deepest condolences to the family of the deceased,” the company said in a statement.
“We deeply apologise for the traumatic experience that our passengers and crew members suffered on this flight.”
It said it was working with Thai authorities and sending a team to Bangkok to help.
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