What causes turbulence and why is it getting worse?

Turbulence is a frequent occurrence during air travel, with the seatbelt light coming on and people told to return to their seats.

It’s usually mild, with a bit of buffeting and passengers ignoring warnings and getting up to go to the toilet anyway.

But as we saw yesterday, it can also cause massive disruption, and in the worst cases can even be deadly.

A Singapore Airlines flight travelling from Heathrow plunged 7,000ft in six minutes after hitting severe turbulence, sending passengers hurling into ‘somersaults’ as they hit the plane’s ceiling.

Geoffrey Kitchen, 73, is believed to have suffered a fatal heart attack when the aeroplane was buffeted flying over Myanmar.

What causes turbulence?

Turbulence is defined as the chaotic movement of air which can cause the sudden movement of an aircraft in flight, the Met Office said.

There are general four types of turbulence, caused by different things.

Some are easier to anticipate, such as when caused by thunderstorms which can be forecast and are visible far away from their looming clouds.

Some can be caused by ‘waves’ of air, which form upon contact with mountains or buildings and hit aircraft ‘like ocean waves crashing onto a beach’, which again can be anticipated due to the topography around.

‘Clear-air’ turbulence is as the name suggests harder to see, as there are no telltale clouds around.

It can be caused by jet streams, with a vertical movement which may come without warning so passengers would not be back in their seats. Thermal (convective) turbulence is also invisible and caused when there is uneven heating of the earth’s surface, often on warm days.

The final type known as ‘wake turbulence’ is produced by aircrafts themselves, as a result of the aircraft producing lift, according to the US Federal Aviation Administration (FAA).

How bad can turbulence be?

Turbulence is generally classed as one of four categorisations – light, moderate, severe and extreme.

In severe turbulence planes may be subjected to large, abrupt changes in altitude, and the aircraft may be temporarily out of control.

In extreme turbulence the aircraft is ‘violently tossed about and practically impossible to control’, according to the US National Weather Service.

How predictable is turbulence?

There are ways to guess and predict where it will happen, but ultimately it can’t be avoided completely as it can be invisible and appear as if from nowhere.

Some flight routes are more notorious than others for risk of turbulence, with Milan to Zurich and Milan to Geneva the roughest routes in Europe.

Marco Chan, a senior lecturer in aviation operations at Buckinghamshire New University, said even weather radar systems can struggle to pick it up.

‘So we just have to base that on our own experience,’ he said. ‘And of course, if we see a thunderstorm in front of us, or we are in clouds, we know there’s going to be turbulence associated, so we try to avoid them.

‘We don’t know we’re encountering turbulence until we encounter them basically,’ he added.

Mr Chan, who used to be a first officer with Hong Kong Airlines and before then with Cathay Dragon, said pilots receive ‘weather charts’ before flights and use them to predict possible areas of turbulence to avoid.

Pilots will also report any bad areas so others can avoid it.

Is turbulence getting worse?

Yes, it is getting both more frequent and stronger due to climate change, as extreme weather events around the globe are in general.

A study in 2017 found that turbulence affects could more than double in some areas, particularly at high altitudes.

But while it can of course cause problems, the risks from turbulence are relatively rare.

Mr Chan said: ‘Turbulence is of course dangerous and that is why we have so many lines of defence to try to avoid them when we can. If we cannot, we react to it.’

But he added that airlines have implemented ‘quite rigorous training’ with cabin crews and are ‘very good at managing’ turbulence’.

‘That is why it is quite rare for this to be on the news, quite rare for fatalities, injuries,’ he said.