Turbulence 101 or "Turbulence for Dummies"
Useful information for fearful flyers
Jet wake or wash turbulence
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. (One exception: If you're Denzel Washington playing a tortured soul who turns a plane upside down to stop its dive 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 travellers 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 website 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.
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.
"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. If stuck in an ugly patch, they will attempt to steer the plane toward calmer air, climbing to a higher altitude or changing course.
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.
"In general, we have a reasonably good idea of where the rough air is," said Smith. "But it can be more of an art than a science."
PINNING DOWN TURBULENCES
To help take the guesswork out of the pin-the-tail-on-the-turbulence game, physicists and other industry specialists are working on innovations that detect unsettled air.
For instance, Boeing installed the Vertical Gust Suppression System in the new 787 Dreamliner. VGSS 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. Passengers will probably sleep right through the tweak.
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. (Quick debriefing: Stars appear to twinkle when upset air bends and bobbles the light as it travels through the atmosphere; same deal with radio waves. Apologies for crushing the fantasy of stargazers who thought that little aliens living on stars were flicking their bedroom lights on and off.) At this early stage, no planes are equipped with the GPS unit.
Cornman, who was instrumental in the GPS program, is also tackling the turbulence issue at the federally funded center. Under the sponsorship of the Federal Aviation Administration (FAA), he and collegues developed the In Situ Turbulence Reporting Program, detection software that allows participating airlines (Delta, United and Southwest so far) to share reports on rough air.
Also in his bag of new tricks: radar software that can track "stuff embedded in the air," a useful tool for recognizing convective turbulence, and "lidar," lasers that detect small particles in visibly clear air and measure their motion. Delta uses the new radar capability, and the Hong Kong airport has installed the uber-lasers. Researchers are also throwing some brain cells at improving weather forecasting, which could inform pilots of upcoming chop.
"Turbulence is pretty dynamic," he said. "Pinning it down is pretty hard."
BELIEVE THE NUMBERS
If you're a nervous passenger, you've most likely heard this one before: Flying is safer than driving.
Don't argue with the prophet, because it's true.
"Commercial air traffic, in terms of turbulence, is pretty darn safe," said Cornman. As evidence, he cited the last crash caused by turbulence - in 1966 near Mount Fuji in Japan.
In 2010, the National Highway Traffic Safety Administration reported 9,442,000 car accidents, including more than 22,000 fatalities and almost 2 million injuries. The same year, the National Transportation Safety Board (NTSB) documented one major accident and 14 injuries on commercial planes, and no fatalities.
But don't be so quick to unbuckle your seatbelt and freely roam the cabin. Turbulence is the No. 1 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. Over the same period, the NTSB investigated 10 turbulence-related accidents.
"If people followed the rules," said Smith, "the statistics would be even lower."
Protecting yourself is as easy as insert, click, adjust. Even when the pilot turns off the sign, keep your seatbelt on. If the plane suddenly jolts, you don't want to bump heads with the ceiling.
You can also reduce the intensity of turbulence with a little planning. Larger jets provide more stability than smaller planes. For example, in the same wily patch of air, a passenger in a 747 might feel a mild bounce, while a traveler in a six-seat Cessna might complain of moderate bumps. Also, choose a seat in the middle rows, over the wings, instead of in the front or back of the cabin.
"Imagine a soda straw. Hold it in the middle and see how it flops," explained Tillotson of the phenomenon. "Air pushes on the wing. The nose and tail bounce."
Most important, remember that the rockiness will pass. With this as your mantra, sit back and enjoy the short ride on the atmosphere's waves.
"Instead of the seatbelt sign," said Cornman, "the pilot should turn on the 'wheee!' sign."
I'll throw up my hands to that.