Detecting Turbulence That No One Can See Sudden Free Fall on United Flight to Hawaii Focuses Attention on FAA Program to Predict Clear-Air Bumps

By Peter N. Spotts, writer of The Christian Science Monitor | The Christian Science Monitor, December 31, 1997 | Go to article overview

Detecting Turbulence That No One Can See Sudden Free Fall on United Flight to Hawaii Focuses Attention on FAA Program to Predict Clear-Air Bumps


Peter N. Spotts, writer of The Christian Science Monitor, The Christian Science Monitor


As United Airlines jet liners roll out of hangars after routine maintenance checks, they are carrying something new: instructions in their flight computers that turn the airliners' sophisticated navigation systems into flying turbulence detectors.

The software, which United began installing a few months ago, is part of a federal effort aimed at helping commercial pilots and their passengers avoid potentially fatal encounters with rough air.

Sponsored largely by the Federal Aviation Administration (FAA) Aviation Weather research program, the effort could accelerate following a jumbo jet's encounter with turbulence over the Pacific Ocean Sunday. Two hours after leaving Narita, Japan, on a flight to Honolulu, United Airlines Flight 826 plunged 1,000 feet when it flew into what appeared to be clear-air turbulence. One passenger was killed, and 102 other people were injured. "This is a silent problem of the industry," says Larry Cornman, an atmospheric scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., and one of the researchers involved in the federal effort. Airliner encounters with turbulence seldom generate much publicity, he explains, yet they represent one of the industry's most costly safety concerns. The problem is persistent and leads to lawsuits, workers' compensation claims, and sometimes-lengthy absences as crew members recover from injuries. What is turbulence? Turbulence often is linked to severe weather, such as thunderstorms, which can generate violent updrafts and downdrafts, or to passing weather fronts. But the toughest turbulence to detect, measure, and forecast involves clear air. At high altitudes, clear-air turbulence is a byproduct of the jet stream, a river of air moving as fast as 170 m.p.h. As the air flow speeds by the slower air around it, friction at the boundaries can generate waves of air that act much like ocean waves - they build until they become unstable and break, generating turbulence. Closer to the ground, the wind's encounter with mountains can set up turbulence as it tries to flow around and through them. When the wind flows over the top, it can deliver a series of "punches" to the layers of air above it, setting up undulations of air known as gravity waves. These can spread out from their points of origin like ripples in a pond. And like the waves the jet stream spawns, gravity waves can grow as they travel, until they, too, break. …

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