DENVER, MAY 31 -- A new radar system designed to protect airliners from a weather phenomenon that has killed more than 650 people in the last quarter century goes into regular operation at Stapleton Airport Friday.
It will be the first of a nationwide system of wind shear-detecting radar, called Terminal Doppler Weather Radar, that will be installed by the Federal Aviation Administration (FAA) within a decade at major airports across the nation, including all three major Washington-area commercial airports and Andrews Air Force Base.
Its deployment culminates years of research prodded by the crash of Eastern Flight 66 at Kennedy Airport on June 24, 1975. That was the first crash that led experts to believe something besides pilot error was knocking airliners from the sky on takeoffs and landings.
Wind shear is an abrupt and often invisible movement of air, the deadliest of which is the microburst. A microburst is a shaft of cold air that races toward the earth at high speed, often from thunderstorms, spreading in all directions as it hits the ground.
It exists briefly, but can be extremely damaging. Microbursts of up to 70 miles per hour ripped hundreds of trees from the ground and damaged homes in Northwest Washington and suburban Maryland on June 14, 1989.
When a jetliner flies into a microburst on takeoff or landing, the plane faces a sudden headwind, then a tailwind, causing it to lose airspeed and possibly fall to earth.
Meteorologists believe 35 U.S. airline crashes have been caused by microbursts since 1964, the latest being Delta Flight 191 at Dallas-Fort Worth on Aug. 2, 1985, in which 137 people died. It also appears a Sept. 3, 1989, Cubana de Aviacion crash at Havana, which killed 115 aboard the Soviet-built IL-62 and 24 on the ground, was caused by a severe microburst.
It was not until the mid-70s that experts became suspicious that an unusual weather phenomenon was involved in crashes.
The 1975 Eastern crash at Kennedy, which killed 113, was "the beginning of a certain type of awareness that led to today's system," said John McCarthy, director of the research applications program at the National Center for Atmospheric Research in Boulder, Colo. McCarthy was one of a cadre of meteorologists and engineers who were first scoffed at by government officials but who have become the center of the effort to predict airplane-killing weather in time to avoid it.
The first 47 Terminal Doppler Weather Radars will be installed between 1992 and 1995 in the eastern two-thirds of the country -- the area roughly east of Salt Lake City and Phoenix -- at airports where thunderstorms are common. An additional 55 radars will be deployed in other locations including the West Coast.
On June 18, a Doppler radar is to begin operation at Orlando, Fla., to study whether wind shear is different in an area far more humid than Denver. The experiment will be run by Lincoln Laboratory of the Massachusetts Institute of Technology, which developed the Doppler technology along with the National Center for Atmospheric Research.
A Doppler radar forms a picture of air movement by detecting the action of things in the air, such as rain, or picked up by the air, such as seed pods.
"It sees mosquitos very very well," McCarthy said.
The radar is aided by 16 ground-based wind sensors at various points around the airport.
As the microburst air shaft starts down, the Doppler radar sometimes detects clues high in the atmosphere, allowing, perhaps, a minute or two warning before the burst hits the surface. The radar immediately detects the microburst when it hits and begins growing on the ground. It can take two to three minutes from the time a microburst hits the ground until it reaches full intensity.
The Doppler radar displays on a screen air movement that is color-coded for severity. A large red circle on the screen at or near the end of a runway prompts air traffic controllers to issue an immediate wind shear advisory, giving pilots the estimated amount of airspeed they will lose. The pilot must decide whether to try to land.
The Doppler has been tested over the past two summers at Denver, and may have saved several airliners. On July 11, 1988, five airliners in a row chose not to land as the Doppler detected a growing microburst that at its peak would have produced a windspeed loss of about 90 miles per hour, probably more than any airliner could survive. The researchers, recording the experiment with video cameras, produced a dramatic 20-minute video called "The Day All Hell Broke Loose."
The system of 102 Doppler radar installations is being built under a $282.6 million contract with the Raytheon Co. The radar has tested at a 98 percent accuracy rate, officials said.
"That's an extremely high quality of protection," McCarthy said.
Joseph M. Del Balzo, executive director for systems development at the FAA, an agency often criticized for slow deployment of new technology, also pointed out that the project is ahead of schedule.
He said that although Doppler radar has been around for many years, it probably would not have been possible to develop the current system in the 1960s or 1970s, partly because computers did not have the capacity to digest all of the information quickly enough.
In addition, until recently researchers knew little about microbursts. "There's nothing new about a downdraft, "McCarthy said. "We've known about downdrafts in thunderstorms for 120 years. What was new was the small scale . . . . The event was so small that it defied observation."