Tuesday, November 21, 2017
News Roundup

Flight plan: a worrywart's guide to understanding turbulence

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On a recent flight to New Orleans, our 65-seat plane was gliding through the sky as smoothly as a swan on an unruffled lake. Then it hit a bump. And another. A soda on a tray sloshed in its cup. The aircraft dipped, pitched and dropped several feet. A couple calmly set down their sandwiches and locked hands. The flight attendant suspended beverage service and strapped herself into her seat. I looked out the window, at the clear blue sky and the bunny-tail clouds, and cursed the diabolical force that I could feel but not see.

When planes hit turbulence, we often start to despair and think the worst. Falling to the ground like a disabled bird, for example. But experts tell us to banish those doomsday thoughts.

"Planes don't come crashing out of the sky," said Patrick Smith, a pilot with 20 years of experience.

Brian Tillotson, a senior technical fellow at Boeing, once comforted a nervous flier with this warm biscuit of wisdom: "This plane is designed to survive a crash, and this is nothing." He recommends that timid travelers adopt his mantra as their own high-altitude om.

Despite the hard facts and the placating statements, turbulence can rattle even fliers with nerves of reinforced steel. Two main factors weaken our resolve like kryptonite: our lack of control and our limited understanding of atmospheric conditions and airplane mechanics.

"Turbulence is far and away the No. 1 concern of fearful fliers," said Smith, who hosts the website Ask the Pilot.

Instead of staying in the dark, where things go bump in the cabin, I turned to scientific and airline industry experts and asked them to demystify turbulence and describe any advances in the art of its detection and avoidance.

Turbulence 101

By simple definition, turbulence is a disturbance in the regular flow of air. The agitated air moves up or down or sideways, putting pressure on the plane's wings. The vessel responds by pitching like a rodeo bronco or bouncing like a pogo stick. A plane, however, is not easily bullied by rogue air. It's built to resist.

"On a roller coaster, everyone is screaming for joy," said Larry Cornman, a physicist at the National Center for Atmospheric Research in Boulder, Colo. "In an aluminum tube 30,000 feet in the air, it's the same principle, but you have no control."

Atmospheric chop is not monolithic but divided into subgroups with distinct characteristics:

Clear-air turbulence is caused by variations in the jet stream. It ramps up in winter, when the jet stream — zippy air currents in the Earth's atmosphere — migrates south, and often plagues flight paths over the Pacific.

Convective turbulence is created by thunderstorms and often occurs in the summer.

Low-level turbulence is associated with strong winds, terrain and buildings.

Wake vortex turbulence results from a lift as strong as a tornado.

Mountain wave turbulence is what you have felt if you've ever flown over the Rockies and landed at Denver's international airport.

"Turbulence is normal. It's part of the sky," said Smith. "It's not about the plane but where the plane is."

Turbulence follows a rating system similar to that of a spice-o-meter at an Indian restaurant — light, moderate, severe and extreme. Cornman describes the stages, from mild to serious, as water rippling in a glass, liquid flowing out of the vessel and the cup flying through the air. Most passengers experience the swirling and spilling phases, but never the most intense situations, which can cause injuries and structural damage. When a weather system threatens such peril, pilots do their utmost to avoid the roiling air.

Pilots rely on numerous systems to track turbulence, including weather forecasts, radar, communication with air traffic control and updates from other planes in the vicinity.

Dodging rough skies

Physicists and other industry specialists are constantly looking for ways to take the guesswork out of detecting unsettled air. Boeing installed the Vertical Gust Suppression System in the new 787 Dreamliner. It acts like a super-beagle: Sensors in the plane's nose detect volatile air, then relay the message to the aircraft's brain, which automatically makes adjustments to reduce the bump.

In May, the company received a patent on another invention, a GPS unit that can read the "twinkle" of the radio waves for more than 200 miles, thereby identifying erratic air flow. (Stars appear to twinkle when upset air bends and bobbles the light as it travels through the atmosphere; same deal with radio waves.) Cornman, instrumental in the GPS unit (yet to be installed on any planes), and colleagues worked with the Federal Aviation Administration to develop software that allows participating airlines (Delta, United and Southwest so far) to share reports on rough air.

Make safe safer

While flying is indeed safer than driving — in 2010, 22,000 were killed and another 2 million injured in car accidents, while no one was killed and only 14 injured in the year's single air crash — turbulence is the leading cause of in-flight injuries, with crew members often suffering the highest number of bangs, bruises and broken bones. The FAA reported that turbulence injured five passengers and 28 crew members last year.

Here are a few things to remember for a more enjoyable flight:

• Protect yourself by keeping your seat belt on.

• Larger jets provide more stability than smaller planes.

• A seat in the middle rows, over the wings, instead of in the front or back of the cabin will feel the least turbulence.

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