What causes turbulence on flights and which routes around the world are most affected?

A Qatar Airways flight has encountered turbulence above Turkey, injuring 12 passengers and crew. The flight from Doha to Dublin landed safely after the episode, which caused people to “hit the roof” of the plane.

The news comes just five days after the death of a British passenger and injuries to 104 others after a Singapore Airlines flight hit sudden turbulence above Myanmar, causing it to dramatically lose altitude.

We know turbulence is a common part of flying – but are some routes more prone? And where is it the worst?

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What is turbulence?

Turbulence is felt when a plane flies through relatively disturbed air, which is responsible for “abrupt sideways and vertical jolts”, according to Australia’s Civil Aviation Safety Authority. Turbulence is the leading cause of in-flight injuries to crew and passengers.

The agency defines eight types of turbulence, including thunderstorm, thermal, frontal and “mountain wave”, which fall into six categories of severity.

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Where is turbulence most common?

Generally, turbulence is expected over high mountains, oceans, the equator and when entering jet streams, according to Dr Guido Carim Jr, head of Griffith Aviation at Griffith University. But, clear air turbulence – normally caused by a very sudden change in the wind direction – can occur anywhere and at any time. 

“Magnificently complex factors interact to create turbulence,” the former pilot says adding that bushfires can cause it. “Radar technology to detect turbulence is improving but, despite all the instruments onboard, we cannot accurately predict where and when turbulence will be.”

He has flown international routes over the Andes where it is mandatory to turn on the seatbelt sign when approaching the mountains. 

The Bay of Bengal during monsoon season is notoriously turbulent, as is flying over the Alps – “but, sometimes you don’t even notice”, he said.

High humidity and temperatures tend to make turbulence stronger, so flying from London to New York City in the summer months is likely to be bumpier than flying the same route in December, he says.

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What are the world’s most turbulent flight routes?

The Swedish turbulence forecasting site Turbli uses data from the US National Oceanic and Atmospheric Administration and the UK Met Office.

Its most turbulent routes in 2023 were: Santiago, Chile to Santa Cruz, Bolivia; Almaty, Kazakhstan to Bishkek, Kyrgyzstan; Lanzhou to Chengdu, China; Centrair to Sendai, Japan; and Milan, Italy to Geneva, Switzerland. Milan to Zurich, Switzerland was in 10th place. 

The most turbulent countries to fly above in April, according to the site, were French Polynesia, Fiji, Pakistan, Namibia and Uruguay. The South Pacific ranked as the most turbulent ocean to fly over.

None registered above a light turbulence eddy dissipation rate (edr) of 20. Extreme turbulence occurs above 80edr. 

Australian Transport Safety Bureau figures show that globally in 2023, there were 3,047 commercial aircraft incidents. Of those, 236 were caused by weather.

So far in 202, there have been 790 commercial aircraft incidents, of which 52 were caused by weather. 

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Source: The Guardian