Cockpit Confidential by Patrick Smith Page A

their occupants. With respect to the latter, these are typically people who fell or were thrown about because they weren’t belted in. About sixty people, two-thirds of them flight attendants, are injured by turbulence annually in the United States. That works out to about twenty passengers. Twenty out of the 800 million or so who fly each year in this country.
    Anecdotal evidence suggests that turbulence is becoming more prevalent as a byproduct of climate change. Turbulence is a symptom of the weather from which it spawns, and it stands to reason that as global warming intensifies certain patterns, experiences like the one I had over Maine will become more common.
    Because turbulence is so unpredictable, I am known to provide annoying, noncommittal answers when asked how best to avoid it.
    â€œIs it better to fly at night than during the day?” Sometimes.
    â€œShould I avoid routes that traverse the Rockies or the Alps?” Hard to say.
    â€œAre small planes more susceptible than larger ones?” It depends.
    â€œThey’re calling for gusty winds tomorrow. Will it be rough?” Probably, but who knows.
    â€œWhere should I sit, in the front of the plane or in the back?”
    Ah, now that one I can work with.
    While it doesn’t make a whole lot of difference, the smoothest place to sit is over the wings, nearest to the plane’s centers of lift and gravity. The roughest spot is usually the far aft—the rearmost rows closest to the tail.
    As many travelers already know, flight crews in the United States tend to be a lot more twitchy with the seat belt sign than those in other countries. We keep the sign on longer after takeoff, even when the air is smooth, and will switch it on again at the slightest jolt or burble. In some respects, this is another example of American overprotectiveness, but there are legitimate liability concerns. The last thing a captain wants is the FAA breathing down his neck for not having the sign on when somebody breaks an ankle and sues. Unfortunately, there’s a cry-wolf aspect to this; people get so accustomed to the sign dinging on and off, seemingly without reason, that they ignore it altogether.
Just after takeoff we were tossed around very roughly. The captain told us we’d been hit by “wake turbulence.” What is this, and how dangerous is it?
    If you can picture the cleaved roil of water that trails behind a boat or ship, you’ve got the right idea. With aircraft, this effect is exacerbated by a pair of vortices that spin from the wingtips. At the wings’ outermost extremities, the higher-pressure air beneath is drawn toward the lower pressure air on top, resulting in a tight, circular flow that trails behind the aircraft like a pronged pair of sideways tornadoes. The vortices are most pronounced when a plane is slow and the wings are working hardest to produce lift. Thus, prime time for encountering them is during approach or departure. As they rotate—at speeds that can top 300 feet per second—they begin to diverge and sink. If you live near an airport, stake out a spot close to a runway and listen carefully as the planes pass overhead; you can often hear the vortices’ whip-like percussions as they drift toward the ground.
    As a rule, bigger planes brew up bigger, most virulent wakes, and smaller planes are more vulnerable should they run into one. The worst offender is the Boeing 757. A mid-sized jet, the 757 isn’t nearly the size of a 747 or 777, but thanks to a nasty aerodynamic quirk it produces an outsized wake that, according to one study, is the most powerful of any airplane.
    To avoid wake upsets, air traffic controllers are required to put extra spacing between large and small planes. For pilots, one technique is to slightly alter the approach or climb gradient, remaining above any vortices as they sink. Another trick is to use the wind. Gusts and choppy air will break up vortices or otherwise move them