What is air turbulence and how worried should I be about it?

Turbulence has always been a risk factor in aviation, but the ferocity of “sudden extreme turbulence” experienced on a Singapore Airlines flight from London to Singapore this week was out of the ordinary.

In a separate incident on Sunday, six passengers and six crew members were injured following turbulence on a flight from Doha, Qatar, to Ireland.

The death of a passenger in the Singapore Airlines incident, multiple serious injuries to others and the extent of internal damage to the Boeing aircraft caused widespread shock. Inevitably, this prompted questions on whether climate disruption – ie, a warming world – is making turbulence worse?

What happened?

The plane encountered turbulence over the Irrawaddy Basin in Myanmar. Data on Flight Radar 24, a website that compiles public information about flights, said it dropped from 37,000 feet to 31,000 in a few minutes but some media reports had erroneously reported the pilots’ initial descent toward Bangkok as the turbulence event. “While the aircraft may have continued to experience turbulence during that descent, it was a standard descent to a new flight level controlled by altitude selection in the aircraft’s autopilot,” it noted.

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It’s unclear what caused the episode. Satellite data showed a strong storm beginning to form and bubble into higher elevations, suggesting the atmosphere in the region was becoming unstable. The plane was also moving toward other storms developing nearby.

How rare are casualties?

On international scheduled flights, fatalities directly caused by turbulence are rare. Pilots are usually able to give advance warning of most types of turbulence and ensure all on board are strapped in – the most important advice in minimising risk.

On smaller private planes or business jets, serious injuries or deaths have been more frequent, with the US National Transport Safety Board recording more than 100 injuries and dozens of deaths in just over a decade on domestic flights, though fatalities mostly occurred when turbulence caused planes to crash. On bigger planes, turbulence presents risks of head or other injuries to people who could be thrown around the cabin if not strapped in, or they could be struck by flying debris.

What is turbulence?

This phenomenon is caused by the meeting of air at different temperatures, pressure or velocity, where different wind patterns collide – not unlike boats suddenly encountering choppy waters.

While some weather and geographical conditions – such as thunderstorms, mountain ranges and appearance of certain clouds – can signal turbulence ahead, there is also “clear-air turbulence” at high altitudes, which can take pilots by surprise, occurring without warning.

Forecasts showing incoming weather fronts or air flow over mountains could demonstrate a higher probability of clear-air turbulence. “But you can’t see it,” Stuart Fox, director of flight and technical operations at global airline body the International Air Transport Association (IATA), told the Guardian. “Airflow strength and direction can change rapidly, and the forecasts can only indicate the likelihood.” Such wind shears can knock aircraft off course and cause them to lose altitude quickly or lurch violently.

Pilots can be guided by reports from aircraft ahead that they could be flying into the same turbulence. Certain parts of the world are known to present higher risk. The Singapore Airlines incident took place within the intertropical convergence zone, where thunderstorms are notorious. Thunderstorms are prominently displayed on navigation displays – but it may not be possible to circumvent a storm cluster, as such clusters can stretch beyond 50 nautical miles.

Is climate disruption making turbulence worse?

There is evidence that turbulence is worsening with climate change, as CO² emissions affect air currents. Weather patterns are more disturbed with a warmer atmosphere. Scientists at Reading University have concluded that higher temperatures were increasing levels of turbulence encountered on transatlantic flights. Incidents of severe turbulence increased by 55 per cent between 1979 and 2020, owing to changes in wind velocity at high altitudes.

Researcher Prof Paul Williams said this showed predicted choppier skies had already arrived and the aviation industry needed to invest in better systems to forecast and detect turbulence.

Clear air turbulence, which occurs most frequently at high altitudes and in winter, could triple by the end of the century, he suggested, while other types of turbulence were increasing at all flight altitudes.

While allowance has always to be made for the ferociousness of natural weather, his research suggests we could encounter bumpier flights in coming years, with all the risks that brings for passengers and crews.

– Story updated on May 24th to include Flight Radar 24 explanation on the aircraft’s “standard descent” to a new flight level.