Things That Go Bump in the Flight, Part 2

For too many passengers, the word "turbulence" when spoken over a public address system in flight conjures up scary images of things being tossed all over the cabin and a cockpit full of sweating pilots fighting for control.

And why wouldn't it? Between our constant warnings to keep your seat belts fastened in flight and Hollywood's obsession with the myth that airliners just stop flying and drop like a rock when they hit any bumps in the air (accompanied by hundreds of screaming extras), the word and the very concept of "turbulence" have taken on a dark and sinister nature.

But Reality No. 1 is this: Almost all the in-flight turbulence airliners fly through is absolutely not threatening or dangerous, and we pilots work very hard, and with almost perfect success, to avoid the type that is.

Designed to Handle Rough Rides

A boat pushing through choppy waters provides a fairly good analogy. The ride can be pretty rough, even to the point of throwing you around, but as long as the boat is sturdy and designed to be at home in such conditions, there's no danger to the boat -- only danger to people if they're knocked to the deck.

While there is absolutely no such thing as an "air pocket" (sorry, Hollywood), air does have bumps. More clearly stated, our atmosphere is seldom a still, quiet ocean of stable air molecules just sitting side by side with no vertical or horizontal currents. If it was, we wouldn't be having this discussion, because there would be no turbulence.

Instead, our atmosphere is filled with updrafts and downdrafts and jetstreams and different currents of air at different temperatures swirling and blowing and rising and falling, and sometimes coming together like the roiled waters of two streams converging. When our wings fly through those changing currents and disruptions, they act like spring-loaded, shock-absorbed wheels on a bumpy road and the smooth ride of the attached fuselage we're in becomes shaky -- sometimes so much so that it can knock us off our feet if we're trying to walk down an airborne aisle.

Reality No. 2: Airliners are designed to easily take far more turbulence than we can handle personally. In other words, it may scare us silly but it can't hurt the airplane.

Modern jetliners are very strong, well-engineered machines designed to flex and twist and absorb even the type of airborne shaking we call "severe turbulence" (which we avoid like the plague). To a jetliner, bouncing along in moderate turbulence that can scare you to death and throw things around an unsecured cabin is just another day at the office -- what it's designed to do.

Severe turbulence is something we very seldom encounter and are prohibited from flying into. This class of extreme wind currents is encountered mainly in thunderstorms and other major weather disruptions, which airline pilots are required to avoid by at least 25 miles. Since virtually every airliner has color weather radar, pilots can clearly see, day or night, the type of storms that can produce severe turbulence hundreds of miles before we get close to them.

Clear air turbulence, or "CAT," just refers to light or moderate turbulence encountered in clear air versus turbulence in clouds.

Why You Should Buckle Up

So what should you think about when we use the "T" word on the PA?

Mainly, whether your seat belt is buckled and whether you've got a cup of coffee balanced on the edge of your laptop keyboard (not a good idea). In other words, turbulence is a comfort issue, not a safety issue.

Flying for long periods with a lot of bouncing around is tiring, and all airline pilots struggle to smooth out the ride as fast as possible by asking other airline crews nearby over the radio which altitudes are smoothest and then requesting a climb or descent to those flight levels. Sometimes, however, every single altitude feels like a rutted road. What you can be sure of is that airline pilots work very hard to keep the cabin feeling as steady as your living room.

Oh, as to definitions, there is "chop" and there is "turbulence." Chop is the light, short-period vibrations or jiggles that are annoying but not really disruptive to most things you will be doing at your seat. Light chop is barely noticeable, while moderate chop is an irritant. (There is no severe chop.)

Turbulence is a more profound shaking motion, up and down or sideways or both. Light turbulence can knock over a cup of coffee, and moderate turbulence can knock over anyone trying to walk or stand. And yes, sometimes a sudden, unexpected encounter with moderate turbulence can even spill your Coke, roil your stomach and elicit gasps throughout the cabin without being a bit dangerous to your strapped-in self or the aircraft.

But wait a minute. If that's all there is to it, then why the keep-the-belts-fastened thing?

Because the truth is that every few years, somewhere in the world among the tens of millions of commercial flights, a flight crew will accidentally fly through the top of a fast-rising or building storm (often at night or in solid clouds) and encounter a few seconds of severe turbulence. When that happens, if your seat belt is off, so are all bets that you're not going to be propelled up into the ceiling and then dropped back on an armrest and left badly injured.

There's perhaps a one in 100 million chance per airline flight that such might happen, but when it's so easy to stay buckled up, why not guarantee a committed relationship with your seat cushion?

John J. Nance, ABC News' aviation analyst, is a veteran 13,000-flight-hour airline captain, a former U.S. Air Force pilot and a lieutenant colonel in the Air Force Reserves. He is also a New York Times best-selling author of 17 books, a licensed attorney, a professional speaker, and a founding board member of the National Patient Safety Foundation. A native Texan, he now lives in Tacoma, Wash.