A short primer on turbulence

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.

(joel castillo)

“Planes don’t come crashing out of the sky,” said Patrick Smith, a pilot with 20 years of experience. (One exception: If you’re Denzel Washington playing a tortured soul who lands a plane upside down in the new film “Flight.” )

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 number one concern of fearful fliers,” said Smith, who hosts the Web site Ask the Pilot. “If I get 10 letters from nervous fliers, nine of them are questions about rough air.”

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. Armed with this knowledge, we can sprout wings of confidence that will carry us gently through the rough spots.

What is it?

Class, pull out your e-notebooks for Turbulence 101.

By simple definition, turbulence is a disturbance in the regular flow of air. (Experts often use water as an analogy, such as an eddy on a river or a fish in the waves.) 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. (For visual proof, check out the YouTube video of Boeing testing the wing strength of the 787.)

“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 aluminium 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, when rumbling storms dominate the weather forecasts. Low-level turbulence is associated with strong winds, terrain and buildings, while wake vortex turbulence results from a lift as strong as a tornado. Finally, if you’ve ever flown over the Rockies and landed at Denver’s international airport, you’ve probably witnessed your cup of coffee shimmy and shake. The culprit: mountain wave turbulence.