Taming the winds for safer flight
They look like bird-shaped weather vanes sitting atop stilts - and, in fact, have been mistaken by duck hunters for game. But the humble sensors distributed around the marshy perimeter of the New Orleans airport are part of the latest efforts to pierce one of civilian aviation's worst weather problems: wind shear.
New detectors turned on a few weeks ago, together with several already in place, are intended to help local officials better detect these sudden shifts of wind, which can toss a jumbo jet like a box kite. A more advanced warning system - this one using Doppler radar - is being tested at Denver's airport.
Both are part of a broadening effort by aviation authorities and the airlines industry to cope with these infrequent but deadly phenomena, amid growing evidence of their destructive potential.
Wind shear is a sudden change in the direction or speed of an airflow. One particularly headstrong type of wind shear, a ''microburst,'' is caused by a downward burst of cool air from the bottoms of clouds. This often occurs during thunderstorms. As the air columns approach the ground they spread out, generating strong surface winds that can wreak havoc with planes landing or taking off.
Such forces have been known to cause damage to houses and other property. This month, for instance, a violent wind burst was blamed for capsizing a riverboat on the Tennessee River in which 11 people were killed. But the main concern surrounds the danger with aircraft.
At least 16 accidents resulting in deaths or injuries have been attributed to wind shear in the past 20 years. Among these have been some of the nation's worst air disasters, including one at Kennedy International Airport in 1975 (112 killed) and another at New Orleans in 1982 (154 killed). Efforts to detect these violent downdrafts and train pilots to deal with them have been under way since at least the mid-1970s. But now, with advances in technology, there are renewed efforts on several levels:
* In the short term, the predominant warning system will be a series of ground-based sensors already in place at some airports. Since 1978, the Federal Aviation Administration (FAA) has installed 59 of these systems. Fifty-one more are to be put in by the end of 1985. The ''low-level wind-shear alert system'' (LLWAS), in brief, includes a series of sensors distributed around an airfield and linked to a computer. These compare wind patterns from the outside of the airfield to those in the middle. Major deviations signal a wind shear. What the FAA recently installed at New Orleans is an expanded and upgraded version of LLWAS. Instead of six sensors, the airport now has 11. A more sophisticated computer is also being used. How well it works will affect the types of systems still to be installed at other airports.
* In the midterm, probably by the late 1980s, airports should get help from a multimillion-dollar forecasting system planned by the National Weather Service. At the heart of the Nexrad (next-generation weather radar) system will be Doppler radar. It can pick up readings from the movement of insects, dust particles, and water vapor in the atmosphere. It helps gauge not only the size and intensity of storms but also wind speed, direction, and precipitation.
Backed by the FAA and the Defense Department, the Weather Service envisions a grid of at least 160 ground stations set up across the country. They would be for general forecasting. But among those tapping into the more detailed weather reports - including information about wind shear - would be airports.
* Further off, airports are expected to be fitted with their own Doppler systems in the 1990s. The benefit over ground-based sensors: LLWAS senses shears as they occur near ground level. Doppler probes the atmosphere, and, with its higher resolution, can help pinpoint microbursts at birth. Scientists hope eventually to achieve a 5- to 15-minute advance warning.
It is this type of system that is now undergoing a 45-day test at Denver's Stapleton International Airport. Results won't be conclusive for some time. In the first week of operation, the Doppler system spotted about a dozen microbursts within five miles of the airport. Several flights were held or rerouted, says Dr. John McCarthy, director of this and one other wind-shear project at the National Center for Atmospheric Research in Boulder, Colo.
Ideally, scientists envision detection systems that will combine all these methods, and also use data from sensors on board aircraft themselves (several are being tested). But that's only wishful thinking for now. Widespread use of Doppler at airports is probably a decade away. Even then it will be costly: probably $1 million to $2 million just for the hardware. There is manpower to consider, too. At least two meteorologists are involved in interpreting data from the radar and other sources in the Denver project. But eventually much of the process should be automated.
Despite these technological thrusts, though, the main defense for now against the wind-shear problem lies with pilots themselves. Some airlines are expanding programs aimed at teaching pilots how to recognize and handle wind shear. United , for instance, will kick off a program next month that includes more advanced instruction on simulators, as well as new booklets and videotapes on the subject. Yet some believe too many pilots are unprepared. ''I'd say 99 percent of the pilots in this country do not truly appreciate the magnitude of the threat,'' says Dr. McCarthy.
