What is turbulence - and how can you calm down about it?

Learn how to deal with one of air travel's most notorious discomforts.

By Michelle Z. Donahue | National Geographic | 22 February 2019

Everyone has a story about hitting a rough patch of air, those hair-raising moments when suddenly more than the plane is flying. Bellies drop, drinks slop, and people caught in the aisle lurch against seats. In rare cases, it can even mean more than bumps or bruises.

In air travel, turbulence is a certainty and a major source of flight anxiety for flyers of all stripes. But understanding what causes turbulence, where it occurs, and the high-tech tools pilots use to make air travel safer and more comfortable may help settle even the most anxious flyer's nerves.

What is turbulence?

The definition of turbulence is fairly straightforward: chaotic and capricious eddies of air, disturbed from a calmer state by various forces. If you've ever watched a placid thread of rising smoke break up into ever more disorganized swirls, you've witnessed turbulence.

Rough air happens everywhere, from ground level to far above cruising altitude. But the most common turbulence experienced by flyers has three common causes: mountains, jet streams, and storms.

Just as ocean waves break on a beach, air also forms waves as it encounters mountains. While some air passes smoothly over and onward, some air masses crowd against the mountains themselves, left with nowhere to go but up. These "mountain waves" can propagate as wide, gentle oscillations into the atmosphere, but they can also break up into many tumultuous currents, which we experience as turbulence.

Disorderly air associated with jet streams - the narrow, meandering bands of swift winds located near the poles - is caused by differences in wind velocities as an aircraft moves away from regions of maximum wind speeds. The decelerating winds create shear regions that are prone to turbulence.

And though it's easy to understand turbulence created by thunderstorms, a relatively new discovery by researchers is that storms can generate bumpy conditions in faraway skies. The rapid growth of storm clouds pushes air away, generating waves in the atmosphere that can break up into turbulence hundreds to even thousands of miles away, says Robert Sharman, a turbulence researcher at the National Center for Atmospheric Research (NCAR).

Each of these scenarios can cause "clear air turbulence," or CAT, the least predictable or observable type of disturbance. CAT is often the culprit behind moderate to severe injuries, as it can occur so suddenly that flight crew don't have time to instruct passengers to buckle up. According to the Federal Aviation Administration, 524 passengers and crew were reported injured by turbulence between 2002 and 2017.

Prediction improvements

Though weather forecasts and pilot reports are helpful for avoiding bumpy zones, they are relatively blunt tools, Sharman says. Weather models can't predict turbulence at airplane-sized scales, and pilots frequently misreport turbulent locations by many dozens of miles. At NCAR, Sharman has been working since 2005 to build much more precise "nowcasting" turbulence tools.

Here's how it works: an algorithm currently installed on around 1,000 commercial airliners analyzes information from onboard sensors to characterize each plane's movement at any given moment. Using data on forward velocity, wind speed, air pressure, roll angle, and other factors, the algorithm generates a local atmospheric turbulence level, which is fed back into a national system every minute. Used in conjunction with national weather forecasts and models, the tool annotates forecasts with real-time conditions, which in turn helps to strengthen weather prediction models.

Over 12,000 Delta Airlines pilots currently use tablets loaded with the tool to check conditions along their flight paths. In addition to the domestic planes currently equipped with the algorithm, international carriers including Qantas, Air France and Lufthansa will also join in. And Boeing has begun to offer the algorithm as a purchase option for new aircraft, Sharman says.

"We better understand the atmosphere now, and our computing ability has meant we can provide better descriptions of turbulence," Sharman says. "By its very nature, turbulence is so chaotic that you need a lot of computer power to throw at it before you can see what is actually happening. This observing strategy is a breakthrough for us."

Costs of turbulence

Part of the anxiety around turbulence is the fear of the aircraft failing. It's a natural response, especially if you've had the experience of watching a wing bend to a seemingly impossible degree.

"I once had a person in front of me start screaming that we were all going to die because she saw the wingtip flexing," recalls Marilyn Smith, an aeronautics engineer at Georgia Tech. "It's good that the wing flexes; if it was so rigid that it didn't, the plane would probably be so heavy that it couldn't fly. Everything on a plane has been tested to within an inch of its life so that it won't fail."

In addition to physical tests in labs, where full-sized aircraft are subjected to stresses above and beyond what they'd encounter while airborne, Smith says that high-powered computing has made it possible to digitally model a wider range of hypothetical scenarios. Monitoring for maintenance issues has improved as well: onboard sensors keep track of components known to be vulnerable to fatigue, and flag that part for inspection or replacement.

Could airplane design be changed to eliminate the experience of turbulence altogether? Smith says likely not, at least in the near term. One area of research is looking at the possibility of instant reaction to sudden gusts by altering the airflow around the surface of the wing itself - though Smith warns that this is an extremely difficult problem to solve while keeping an airplane lightweight, low-cost and energy efficient.

Fassi Kafyeke, head of innovation at Bombardier, is looking to electrical propulsion technology as one way of altering the shape and feel of tomorrow's airplanes. Without the need to confine smaller electric engines beneath the wing, they could be located almost anywhere on a plane's body along with multiple smaller fans to propel the plane forward.

Though design changes like those would mainly address efficiency, turbulence does play a factor in aircraft performance and energy consumption: Flight path and altitude changes to avoid turbulence is estimated to cost U.S. airlines as much as $100 million a year, and burn an additional 160 million gallons of fuel per year.

Climate shifts could exacerbate those costs even more. Paul Williams, an atmospheric scientist at the University of Reading in the U.K., has estimated that by 2050 to 2080, changes to the jet stream from climate change will result in an increase of clear-air turbulence of 113 percent over North America, and as much as 181 percent over the North Atlantic. He's currently working with Airbus to translate those projections into aircraft design parameters.

"The planes that manufacturers are designing today will still be flying in the 2050s, 60s, and 70s, and they'll need to withstand the buffeting they'll get," Williams said. "It's early stages yet, but they're already looking at whether there will be the need for tweaks to their airframes to make them more robust."

How to cope

Armed and ready though you may be with knowledge of meteorology and engineering, there are a few more solid strategies to plan for and cope with turbulence once on the plane.

Fly early in the day and sit as far forward in the plane as you're able, says Heather Poole, a flight attendant for 21 years and author of the book Cruising Attitude.

"Turbulence is worse at the back of the plane," she says. "There have been times when I've seen the folks in coach holding on like it's a rodeo, and I've had to call the cockpit because they experience it differently up there."

Stay buckled up, even when the seatbelt light is off, Poole adds, since even a loosely fastened belt will keep you from hitting your head on the overhead bins. And don't try to hand babies across the aisle or give coffee back to cabin crew who are trying to secure loose objects.

She also suggests just mentioning to your flight crew if you have anxiety - they'll go out of their way to check on you if things get bumpy. Designed by a pilot to help travelers through fears of turbulence, the Sky Guru app offers weather and turbulence forecasts for the exact route you're flying. Other apps like My Radar and Soar also can also demystify what's in the sky ahead.

"That's what the fear is about, mostly, the lack of a sense of control," Poole says. "If you learn more about the weather, and what it is, and where turbulence might be, then you have a better sense of how it happens and that you'll be okay."

Michelle Z. Donohue is a freelance writer who covers nature, science and technology. Follow her on Twitter @MZDonahue. 

PUBLISHED February 22, 2019