Turbulence is, without a doubt, what nervous fliers fear most. Photo / Getty Images
Turbulence is, without a doubt, what nervous fliers fear most. Photo / Getty Images
Two cases of extreme turbulence hit the headlines last week. Injuries and vomiting were reported on an Emirates flight from New Zealand to Dubai on July 10 after a bout of "sudden and severe" turbulence rocked the aircraft three hours before landing. Cabins were trashed, trolleys overturned – and an "exit" sign fell from the wall.
A couple of days previously, an Air Canada flight from Vancouver to Sydney encountered "unforecasted and sudden turbulence" that injured 37 of those on board. "The plane just dropped," said one passenger, Stephanie Beam. "There were literally bodies on the ceiling."
Turbulence is, without a doubt, what nervous fliers (around one in 10 of us) fear most when they board an aircraft. And it is the most common cause of injury to passengers. So with two severe cases in three days, is it becoming more common? Research would suggest so, and climate change could be to blame.
Dr Paul Williams of the University of Reading's National Centre for Atmospheric Science claims that global warming could destabilise air currents at altitudes used by commercial airliners.
"Climate change is not just warming the Earth's surface, it is also changing the atmospheric winds around 32,000 feet, where planes fly," he explains. "That is making the atmosphere more vulnerable to the instability that creates clear-air turbulence (CAT). Our research suggests that we'll be seeing the 'fasten seatbelts' sign turned on more often in the decades ahead."
Indeed, according to Williams' studies, CAT – erratic air currents that occur in cloudless air at certain altitudes – could double or even triple as carbon dioxide levels rise. "The special thing about [this sort of turbulence] is that it's stronger than gravity," he says. "So the vertical motions will be happening more rapidly than gravity. If you're not seatbelted, or any objects are not secured, they will become catapults."
Food and wine bottles ended up on the floor as severe turbulence hit the Emirates flight. Photo / Twitter
The aviation industry is a leading emitter of carbon dioxide – which acts as a thermal blanket for the Earth – and is now falling victim to the very climatic change it has helped create.
Transatlantic flights are likely to be significantly impacted by rising temperatures because the effect climate change is having on the jet stream.
"Our study finds that the jet stream winds along the flight route between London and New York are getting stronger because of climate change – 15 per cent stronger in winter," William says. "This increase in the jet stream winds is going to have an impact on people's flights."
Patrick Smith, a US pilot and author of the aviation book Cockpit Confidential, remarks: "If it feels like you've been seeing more and more news stories about dramatic turbulence encounters, that's because you have. This is partly the result of the media's obsession with anything related to flying, the ease with which scary-looking videos can be shared and spread online, and the fact there are more airplanes flying than ever before. But it's also true that the skies themselves are getting bumpier."
He explains: "Evidence shows that turbulence is becoming stronger and more prevalent as a byproduct of climate change. Turbulence is a symptom of the weather from which it spawns, and it stands to reason that as global warming destabilizes weather patterns and intensifies storms, [severe turbulence] will become more common."
Figures on the number of instances of severe turbulence vary hugely, and contradict one another, but certainly anecdotally, as Smith points out, they're on the up. A spokesperson from the European Air Safety Agency (EASA) states: "It is difficult to judge if an increase in the number of turbulence reports reflects an increase in the number of times they actually occur. The increase may be the result of better reporting."
Technically, pilots can avoid turbulence by adjusting the aircraft's flight route, but the problem is that often it hits without warning. British Airways captain Steve Allright tells Telegraph Travel: "You cannot see CAT, you cannot detect it on radar, and you cannot accurately forecast it."
There's some hope, however. Boeing has been in the process of designing a new "LIDAR" laser, which can be fixed to the nose of a plane, to enable pilots to detect CAT early enough to divert from its path.
Speaking on a panel last year at the Farnborough Air Show, Boeing's Mike Sinnett said: "We had a LIDAR system that was able to look about 16km in front of the airplane and give us a clear indication of the potential for clear-air turbulence. In addition, we were using LIDAR to look for vertical gusts and configure the control laws to be able to respond to those vertical gusts, to dampen their impact on the airplane [and] make the ride smoother."
In the meantime, as dramatic as turbulence might appear, Smith is here to reassure us. "Everything about turbulence seems dangerous. However, in all but the rarest circumstances, it's not," he says. "For all intents and purposes, a plane cannot be flipped upside-down, thrown into a tailspin, or otherwise flung from the sky by even the mightiest gust or air pocket. Planes are engineered to take a remarkable amount of punishment, and they have to meet stress limits for both positive and negative G-loads. The level of turbulence required to dislodge an engine or bend a wing spar is something even the most frequent flier won't experience in a lifetime of travelling."
Injury, he adds, is almost always caused when someone isn't wearing their seatbelt – so the easiest way to avoid getting hurt is to belt up whenever you're in your seat.
Air tends to flow as a horizontal snaking river called a jet stream. A jet stream can sometimes be thousands of miles long but is usually only a few miles wide and deep. Just like a fast-flowing river swirling against the riverbank, where the edge of the jet stream interacts with slower moving air, there may be some mixing of the air which causes turbulence.
Can it be avoided?
You cannot see turbulence, you cannot detect it on radar and you cannot accurately forecast it, but there are other ways of avoiding it. "In the main we rely on reports from other aircraft, which we hear either directly or which are passed on by air traffic control," said British Airways pilot, Steve Allright. "We then consider the options available to us. Our endeavours to fly at an altitude that has been reported as smooth may be prevented by several constraints such another aircraft occupying that level, or the weight of the aircraft at that time."
Is turbulence more likely on certain routes?
Any airport is at the mercy of strong winds on any given day. The same applies to jet streams on any given route, although there is generally more chance of turbulence crossing the ITCZ (Intertropical Convergence Zone) when flying south across Africa, for example.
Flight crews around the world share a common classification of turbulence: light, moderate and severe. "Severe turbulence is extremely rare," said Allright. "In a flying career of over 10,000 hours, I have experienced severe turbulence for about five minutes in total. It is extremely uncomfortable but not dangerous. The aircraft may be deviating in altitude by up to 100 feet (30m) or so, up as well as down, but nothing like the thousands of feet you hear some people talking about."
