The Calculators of Calm

Just how far out of their way will airlines go to give you a smooth ride?

The DC-8 lost its left outboard engine and 19 feet of wing and fell 500 feet in 10 seconds, but landed safely. (NCAR)
Air & Space Magazine | Subscribe

(Continued from page 1)

Turbulence can result in so many kinds of financial losses that exact numbers are hard to come by, but the Commercial Aviation Safety Team, a government-industry partnership, has been trying to ascertain and understand costs associated with turbulence as part of an overall mission to study air travel safety. According to Sherry Borener, an analyst at the U.S. Department of Transportation’s Volpe Center, CAST found that, among other things, an unscheduled inspection coupled with one day of out-of-service costs totals about $24,000 per incident. A diversion to another airport because of turbulence costs anywhere between $25,000 and $150,000, depending on the airline and the number of passengers affected. Estimates of losses due to delays and cancellations run as high as $866 million a year.

Flight attendants, who spend most of their time on their feet, are most vulnerable to injuries. Northwest Airlines has even produced a training video based on a recent incident in which one of its flights approached an area of reported severe turbulence: Following a request from the cockpit, passengers and crew were returning to their seats to buckle up when a flight attendant noticed that a door in the galley had an open latch. Behind the door was a rack that could have spilled onto another crew member if the turbulence was rough enough. Just as the attendant stood to lock the latch, a violent downdraft slammed the aircraft; the attendant was knocked to the ceiling, and injured her head and arm.

Candace Kolander, the Association of Flight Attendants’ coordinator for air safety, health, and security, says that in 1996, the most recent year for which she has data, in one airline, flight attendants reported 310 turbulence-related injuries, resulting in more than 3,500 lost work days. These are only reported injuries. The CAST study estimates that for every reported injury, more than 15 go unreported; reported injuries alone cost the industry approximately $26 million a year.

And then there are the costs incurred when a passenger sues because of an injury. Darryl Jenkins, a visiting professor at Embry-Riddle Aeronautical University in Prescott, Arizona, who has researched flight-related insurance and litigation issues, says that while airlines will contest some claims, court costs and the chance of bad publicity often force them to settle. In the mid- to late 1990s, he says, “it cost about $30,000 to settle the average claim.” CAST’s summary of findings states that litigation costs have “dramatically increased,” with one recent settlement reaching $10 million.

According to Borener, CAST has estimated that from 1988 to 2001, turbulence cost the industry $31 billion. That number doesn’t include costs nearly impossible to calculate: After a bad encounter with turbulence, people who are generally fearful of flying may get on airplanes even less; other passengers, angry that they got no food service while the aircraft was bouncing and lurching, may refuse to fly the airline again. Occasionally, however, the consequences of a rough flight can be known precisely: In 1999, American Airlines shelled out $2 million to a group of 13 passengers who convinced the court that their flight crew’s failure to take steps such as lighting the “Fasten seat belt” sign in advance of storm-related turbulence caused “psychological distress,” because the passengers thought they were going to die.

Turbulence comes in two forms: convective and clear air. The first involves updrafts and downdrafts created by hot rising air and cool, moist falling air—both of which you find in and around thunderstorms. Fortunately, moisture reflects on weather radar, making convective turbulence visible and somewhat predictable. Storms can also cause clear air turbulence, but CAT, as meteorologists call it, usually manifests itself in the jet stream—the west-to-east winds that gust just below the tropopause (the separation between the troposphere—the lower portion of the atmosphere where “weather” happens—and the stratosphere, at roughly 30,000 to 35,000 feet over the continental U.S.). One of the big causes of CAT is the phenomenon known as mountain waves: surface winds that hit mountains and then swirl upward, sometimes for miles, in powerful gusts.

Garry Hinds, manager of United’s meteorology department, likens the jet stream to a stream of water. “If the stream is straight and moving quickly, you can get in it and there’s really no problem,” he says. “But put rocks in that stream, causing white water, and that’s what mountain wave is—the atmosphere running into the rocks and getting pummeled and spun—and you get wind shear, which is simply a change in wind speed and direction. That generates breaking waves of air, just like breaking waves of water. The difference between the waves in the atmosphere and the waves in the ocean is you can’t see waves in atmosphere.” Well, for the most part.

“ ‘Clear air’ is kind of a misnomer,” says scientist Larry Cornman of the National Center for Atmospheric Research in Boulder, Colorado. “People use that because pilots fly around and get hit by something they don’t see. You can have a mountain wave, which has water vapor that condenses, and so you can actually see the lower part of the wave structure.”

Avoiding those waves is one primary job of the dispatcher, who begins working on finding a route even before passengers arrive at the airport. When U.S. Airway’s Andelmo starts a shift at the airline’s operations center in Pittsburgh, the dispatcher who is about to go off duty briefs him on air traffic control issues, the weather in general, and turbulence in particular. Before planning routes, Andelmo reviews weather information provided over the Internet by the National Weather Service, Weather Services International, and the National Oceanic and Atmospheric Administration (forecasts, turbulence alerts, and pilot reports—“pireps”—can be seen at

These sources show thunderstorms and provide the dispatcher with a map of all recent pilot reports of moderate or worse clear-air turbulence. Trouble is, CAT is so mercurial that pireps may be obsolete after only 20 minutes. “Turbulence is like a secondary atmospheric effect,” says United meteorologist John Goldman. “You can forecast wind shear, you can forecast atmospheric stability, but it’s a combination of those things that causes turbulence, and within an area where there is turbulence, it’s not going to be observed at all locations. It’s very random.”

Comment on this Story

comments powered by Disqus