Turbulence is a common part of air travel but in rare cases, it can be dangerous — and even fatal.
The death of a passenger on a flight from London to Singapore Tuesday has raised concerns about how hazardous it can be.
A stealthy form of turbulence known as clear-air turbulence caused the Singapore Airlines flight to plunge 6,000 feet — leaving a 73-year-old British grandfather dead and more than 30 passengers injured.
Turbulence is a weather phenomenon that occurs when a plane enters a region of disturbed air filled with eddies and swirls that tend to cause annoying bumps on a flight, according to the US National Weather Service (NWS).
It is typically caused by mountains, storms or jet streams in the atmosphere, and turbulence is broken down into four stages: light, moderate, severe and extreme.
Most passengers only experience light or moderate turbulence, which causes cabins to shake and unsecured objects to bounce around.
During severe turbulence, a plane can suffer abrupt changes in altitude that may cause pilots to momentarily lose control of the aircraft and send unsecured occupants flying out of their seats.
In extreme turbulence, the entire plane is throttled about violently in the air swirls and becomes impossible to control — with the force even capable of causing structural damage to the aircraft.
The Singapore Airlines flight was hit by a severe form of clear-air turbulence — which is cloudless and can’t be seen, Paul Williams, a professor of atmospheric science at the University of Reading in the UK, explained in a statement.
“It can be difficult to avoid because it doesn’t show up on the weather radar in the flight deck,” Williams said, adding that a “detailed analysis of the meteorological circumstances and the particular type of turbulence that caused today’s fatality will take some time.”
This type of turbulence is typically found at 40,000-60,000 feet, aviation academic and commercial pilot Guy Gratton told the BBC.
Turbulence is the leading cause of injuries to passengers and flight crew on commercial airlines, according to the Federal Aviation Administration.
A total of 34 passengers and 129 crew members were seriously injured due to turbulence from 2009 to 2022, according to the National Transportation Safety Board.
However, because airlines are not required to report minor injuries, the total number of people hurt due to turbulence is likely higher.
Still, with 3 million passengers flying in and out of US airports every day alone, injuries as a result of turbulence is rare.
Williams noted that the last casualty caused by clear-air turbulence was on Dec. 28, 1997, on a United Airlines flight from Tokyo to Honolulu.
Violent turbulence can cause planes to rise and fall between 2,000 to 6,000 feet at a time in jolts of sudden drops, according to the NWS, with the Singapore Airlines flight experiencing the effect in just five minutes.
Such a plunge shoots any unsecured object or passenger into the air, which is just what travelers saw on Tuesday’s flight.
“Suddenly the aircraft starts 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 seatbelt was launched immediately into the ceiling,” said Dzafran Azmir, a 28-year-old student on board the flight.
“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.”
A 2023 study by the University of Reading found that reports of severe turbulence have shot up over the past four decades, with climate change being the leading cause.
“We now have strong evidence that turbulence is increasing because of climate change,” said Williams, who co-authored the study. “We recently discovered that severe clear-air turbulence in the North Atlantic has increased by 55% since 1979.
“Our latest future projections indicate a doubling or trebling of severe turbulence in the jet streams in the coming decades, if the climate continues to change as we expect,” Williams warned.