Everything seemed calm as Toby Pearl sat in his economy class seat in row 43 on a flight from London to Singapore. In an instant, all hell broke loose: personal items, food, and even people were thrown through the cabin, crashing into overhead compartments and causing oxygen masks to deploy from the ceiling.

The huge Boeing 777 plane operated by Singapore Airlines had collided with a focus of turbulence, so violent that it left one dead and dozens seriously injured. Pearl was one of the passengers who provided first aid to those affected immediately after the impact. Still, they could do nothing for the life of a 73-year-old British man who apparently died of a suspected heart attack.

“The seat belt light came on and almost immediately after the turbulence occurred, myself, followed by a large number of people, were thrown into the air hitting the roof,” Pearl said after the plane made a emergency landing in Bangkok. “I felt like we had crashed, I thought the plane was going down. “You could hear glass breaking in the back of the cabin.”

At an altitude of 11,200 meters and with about two hours to go before the plane landed in Singapore, the twin-aisle plane was suddenly and forcefully shaken by what Pearl described as a “big bang” that caught everyone off guard, followed by a smaller and “more manageable” impact. The plane consequently quickly initiated an emergency diversion to Bangkok, according to data from flight tracking service Flightradar24.

According to emergency crews, seven people were seriously injured and hospitalized. Others, including Pearl, underwent medical checks and received complimentary hamburgers before being cleared to continue their journey.

Although high-altitude turbulence is not rare, fatalities are. This phenomenon can be caused by rising pockets of warm air, or cumulonimbus clouds that are usually accompanied by gusts and storms. At higher altitudes, aircraft can suddenly encounter clear air turbulence caused by differences in the speed of air masses.

Between 2014 and 2018, around 240 cases of severe turbulence were reported to European aircraft manufacturer Airbus SE. According to a briefing document on the phenomenon, passengers and crew were injured on 30% of long-haul flights where such incidents were reported and on 12% of short-haul flights.