Frequent business traveler Allen Crockett learned a painful lesson about how wind turbulence can jolt even big airline jets.
He bolted for the lavatory before landing during what had been a calm American Airlines flight from Chicago to Raleigh, N.C., in 2006. But the MD-80 suddenly lurched violently, banging Crockett's left knee against the toilet bowl to partially tear a ligament and his right hand against molding to rupture a tendon.
"Two surgeries later they still hurt," says Crockett, 50, a wireless sales executive from Clayton, N.C., who flies 125,000 miles a year.
As the skies have grown safer without a fatal U.S. airline crash in nearly four years, air-safety analysts warn that wind turbulence — which can bounce a plane dozens of feet while landing or taking off and hundreds of feet while cruising — lingers as a rare but real way of getting hurt when flying. About a dozen people suffer serious injuries in the air each year because of turbulence.
"It's the last of the unanticipated threats," says Christopher Herbster, associate professor at Embry-Riddle Aeronautical University in Florida. "It's one of the last really big hazards for things you don't know are out there."
Reports from the National Transportation Safety Board reveal that since the start of 2007, at least 49 crew members and 14 passengers were seriously injured, which typically means a trip to the hospital, in flights over the U.S. Dozens more suffer minor injuries each year.
Airlines must report incidents with injuries or serious damage to the plane to the NTSB, and they occasionally report less-serious incidents. The reports describe passengers breaking ankles or fracturing ribs while dashing to the lavatory or simply leaving a seat belt unfastened. Flight attendants are hurt even more often and often worse when thrown across the cabin like dolls or crushed by beverage carts.
The cost of violent turbulence to passengers and the airlines comes in the form of personal injury, damage to planes and occasionally emergency landings. But the industry doesn't compile or put a dollar tag on them, says Airlines for America, the group representing major U.S. airlines.
Air-traffic controllers warn pilots about storms. Pilots try to dodge rough spots. But despite precautions, turbulence is a threat to any flight.
"Even Air Force One has to fly around the thunder," President Obama said in apologizing for a late arrival July 19 in Jacksonville.
And when it hits, the only real precaution passengers have against being injured is their seat belts.
Turbulence comes generally in two ways: One is often called wind shear, when wind changes speed or direction, either vertically or horizontally. The other is when air moves up and down, subject to buoyant changes, such as in a thunderstorm.
Either way results from the aircraft traveling through changes in air currents. Herbster compares these changes in air speeds to a river in which there can be mild ripples on the surface when moving slowly or whitewater flowing faster around rocks.
"As the river flows faster, the surface becomes chaotic," Herbster says. "If it flows fast enough, you get rapids."
The hazard with clear-air turbulence is that the jostling wind isn't signaled by clouds like a storm is. Pilots try to warn each other about rough patches, but the system is imprecise.