Heading Into Thick Air

By By Jeffrey Kluger

The first thing you notice when your plane suddenly begins to drop is that you're becoming weightless. For those who like roller coasters, the sensation may not be too bad. Quickly, however, zero-G can become negative-G, meaning anything not fastened or seat-belted down will slam into the ceiling. Food trays get tossed, cutlery gets flung, carry-ons fly up as tray tables bang down. After a few seconds the plane stabilizes, and anything--or anyone--stuck to the ceiling crashes to the floor. Another case of midair turbulence is quickly over.

Last week United Airlines Flight 826 from Tokyo experienced this special brand of aviation hell, leading to 83 injuries and one death. Though life-threatening turbulence happens far less often than the mild rumbles most flyers experience, it is still all too common. On average, 17 U.S.-based planes get slapped around enough to cause injuries each year; between 1980 and 1995, 129 people were seriously hurt, two fatally.

Things might have been different in last week's disaster if the pilots had had some warning of what was coming. About half the time, turbulence is a side effect of storms. When pilots see roiling clouds ahead, they can take evasive action or at least warn passengers to belt up.

But what struck Flight 826 was so-called clear-air turbulence, which occurs when there is scarcely a puff of cloud in a pilot's path. CAT can be caused by a lot of things, including a change in direction of the jet stream, a clash of opposing air masses or a swirl of wind rising off a mountain. Not only is the phenomenon invisible, both to the eye and to radar, but it can also be highly localized, lurking in a patch of sky as small as 1,000 ft. across. When CAT hits, says retired United Airlines captain Andy D. Yates Jr., it is "like an anvil in the sky."

Currently, the best defense pilots have against such sky skids is an alert by other pilots up ahead who have just traversed a pool of unsteady air. But NASA and private industry may soon have a better way: they are designing a sort of infrared radar that would let planes scan the sky for agitated particles in the air characteristic of CAT. NASA plans to test the device next spring but does not know when it will be operational. In the meantime, the FAA is improving the pilot reporting system by equipping planes with software that measures even mild turbulence and flashes data to the ground, where computers collate the information and beam it back up to all planes in the area.

Of course, the most advanced turbulence-warning system on earth will not do a bit of good unless passengers heed those warnings by using the low-tech but highly effective anti-turbulence device known as the seat belt. Since 1980, only two serious turbulence-related injuries were suffered by properly strapped-in passengers. And although United says the FASTEN SEAT BELT sign was on last week, many passengers were, as passengers often do, simply ignoring it.

--By Jeffrey Kluger. With reporting by Jerry Hannifin/Cape Canaveral

With reporting by Jerry Hannifin/Cape Canaveral