According to GB news the plane fell 6000 feet. 
A 73-year-old British man has died and more than 30 other people have been injured on a Singapore Airlines flight from London which was hit by severe turbulence.
The Singapore-bound Boeing 777-300ER was diverted to Bangkok, making an emergency landing at 15:45 local time (08:45 GMT).
Passengers said the aircraft suddenly dropped - and people and objects were thrown around the cabin.
The flight was carrying 211 passengers and 18 crew, Singapore Airlines said. It offered its deepest condolences to the family of the deceased, who has yet to be named.
LIVE: Follow all the latest news and updates
“I was covered in coffee,” Andrew from London told BBC 5 Live. “During the few seconds of the plane dropping, there was an awful screaming and what sounded like a thud."
Andrew said once the turbulence had settled, he had been able to help a woman "screaming in agony" who had a "gash on her head".
Andrew says passengers are being kept in a special part of the airport in Bangkok. "I will get on another flight, these are very rare occurrences," he said.
Another passenger told Reuters news agency the aircraft suddenly started "tilting up and there was shaking".
"So I started bracing for what was happening, and very suddenly there was a very dramatic drop so everyone seated and not wearing a seatbelt was launched immediately into the ceiling," 28-year-old student Dzafran Azmir said.
"Some people hit their heads on the baggage cabins overhead and dented it, they hit the places where lights and masks are and broke straight through it."
The airline said 31 people who were on board the plane had been taken to hospital.
"The remaining passengers and crew are being examined and given treatment where necessary at Suvarnabhumi International Airport in Bangkok."
The statement added that the airline was working with Thai authorities to provide medical assistance to passengers, and was sending a team to Bangkok to provide any additional help needed.
Thai authorities have despatched ambulances and emergency teams to Suvarnabhumi Airport.
Singapore's Transport Minister Chee Hong Tat said the government would provide assistance to the passengers and their families.
"I am deeply saddened to learn about the incident on board Singapore Airlines flight SQ321 from London Heathrow to Singapore," he posted in a statement on Facebook.
It is still not clear how events unfolded. Turbulence is most commonly caused by aircraft flying through cloud, but there is also "clear air" turbulence which is not visible on a jet's weather radar.
“Injuries from severe turbulence are relatively rare in the context of millions of flights operated.
"However, severe turbulence can be dramatic and lead to severe injuries or sadly in this case a fatality," aviation expert John Strickland told the BBC.
Flight crews are also trained in how to respond to turbulence, he added.
"It is not for nothing that airlines recommend keeping seat belts loosely fastened throughout a flight, be it long or short," he added.
Research has shown that climate change will make severe turbulence more likely in the future.
https://www.bbc.co.uk/news/articles/c8889d7x8j4o
A 73-year-old British man has died and more than 30 other people have been injured on a Singapore Airlines flight from London which was hit by severe turbulence.
The Singapore-bound Boeing 777-300ER was diverted to Bangkok, making an emergency landing at 15:45 local time (08:45 GMT).
Passengers said the aircraft suddenly dropped - and people and objects were thrown around the cabin.
The flight was carrying 211 passengers and 18 crew, Singapore Airlines said. It offered its deepest condolences to the family of the deceased, who has yet to be named.
LIVE: Follow all the latest news and updates
“I was covered in coffee,” Andrew from London told BBC 5 Live. “During the few seconds of the plane dropping, there was an awful screaming and what sounded like a thud."
Andrew said once the turbulence had settled, he had been able to help a woman "screaming in agony" who had a "gash on her head".
Andrew says passengers are being kept in a special part of the airport in Bangkok. "I will get on another flight, these are very rare occurrences," he said.
Another passenger told Reuters news agency the aircraft suddenly started "tilting up and there was shaking".
"So I started bracing for what was happening, and very suddenly there was a very dramatic drop so everyone seated and not wearing a seatbelt was launched immediately into the ceiling," 28-year-old student Dzafran Azmir said.
"Some people hit their heads on the baggage cabins overhead and dented it, they hit the places where lights and masks are and broke straight through it."
The airline said 31 people who were on board the plane had been taken to hospital.
"The remaining passengers and crew are being examined and given treatment where necessary at Suvarnabhumi International Airport in Bangkok."
The statement added that the airline was working with Thai authorities to provide medical assistance to passengers, and was sending a team to Bangkok to provide any additional help needed.
Thai authorities have despatched ambulances and emergency teams to Suvarnabhumi Airport.
Singapore's Transport Minister Chee Hong Tat said the government would provide assistance to the passengers and their families.
"I am deeply saddened to learn about the incident on board Singapore Airlines flight SQ321 from London Heathrow to Singapore," he posted in a statement on Facebook.
It is still not clear how events unfolded. Turbulence is most commonly caused by aircraft flying through cloud, but there is also "clear air" turbulence which is not visible on a jet's weather radar.
“Injuries from severe turbulence are relatively rare in the context of millions of flights operated.
"However, severe turbulence can be dramatic and lead to severe injuries or sadly in this case a fatality," aviation expert John Strickland told the BBC.
Flight crews are also trained in how to respond to turbulence, he added.
"It is not for nothing that airlines recommend keeping seat belts loosely fastened throughout a flight, be it long or short," he added.
Research has shown that climate change will make severe turbulence more likely in the future.
https://www.bbc.co.uk/news/articles/c8889d7x8j4o
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