BOULDER--Weather researchers from the National Center for Atmospheric Research (NCAR) and the National Oceanic and Atmospheric Administration (NOAA) are flying a research aircraft through high winds and deploying a wide array of specialized instruments to study turbulence near the Colorado Springs, Colorado, airport in February and March. Funded by the Federal Aviation Administration (FAA), the study is a consequence of the crash of a United Airlines 737 flight into Colorado Springs on March 3, 1991, and of the more than ten major aircraft accidents and incidents that have occurred near mountains during the last ten years.

All passengers and crew died in the United crash on approach to the Colorado Springs airport. After an exhaustive investigation, the National Transportation Safety Board could not identify the cause of the accident but concluded that severe turbulence was one of two events most likely to have brought the plane down. There was a strong downslope windstorm the day of the crash.

Located just east of Pike's Peak (elevation 14,110 feet), Colorado Springs lies in the path of powerful winds rushing down the eastern slope of the Rocky Mountains. These winds and related turbulence can disrupt the operation of aircraft attempting to land or take off at the Colorado Springs airport. Known as the chinook in the western United States, the warm, dry wind is similar to the European foehn, which blows down the north side of the Alps.

The FAA requested that researchers from NOAA and NCAR, both located in Boulder, Colorado, study terrain-induced turbulence at the Colorado Springs airport as part of an effort to reduce mountain flying risks. According to NCAR's Peter Neilley, the program may lead to the development of a real-time turbulence detection and warning system for pilots and air traffic controllers at the airport. The cutting-edge system would be similar to one recently developed by NCAR for Hong Kong's new Chek Lap Kok Airport, expected to open in 1998. FAA/NCAR turbulence studies under way in Juneau, Alaska, and considered for Anchorage may ultimately lead to warning systems for those airports as well.

Turbulence is a chaotic state of the atmosphere that extends over meters or kilometers. "It's like a cloud," says Neilley. "It can completely change its shape within a few minutes." To track turbulence in Colorado Springs, NCAR and NOAA researchers are deploying a wide array of surface and airborne instruments. The National Science Foundation's King Air research aircraft, based at the University of Wyoming, will take 25 wind measurements per second as it flies through the airport's approach and departure corridors. Balloons bearing atmospheric measuring devices will be launched from an NCAR weather van and by staff at Ft. Carson Army Base.

A Doppler lidar will measure radial wind speeds to distances of over 12 miles. Due to its narrow, pencil-like beam, the lidar is able to scan near mountains while avoiding ground clutter and aircraft effects. Four wind profilers and radio-acoustic sounding systems will continuously record winds, temperatures, and turbulence above the airport and at other sites. A new infrasonic observing system, previously used to detect tornadoes, will listen to low-frequency sounds that may be associated with severe winds. Automated weather stations and a dense network of anemometers will measure surface airflow. NOAA will provide daily weather briefings at its Forecast Systems Laboratory in Boulder.

In a cooperative effort, various departments of the city of Colorado Springs are providing data from their own weather stations. The airlines, including the airport's two major commercial air carriers, United and Western Pacific, are cooperating with an FAA request that pilots make enhanced reports of turbulence as they fly in and out of the airport.

"We want to find out more about the physical nature of the hazards, test the reliability of the experimental forecasts, examine whether ground-based sensors and algorithms for detection and warning are feasible, and gather data sets to use in numerical models," says NOAA's Al Bedard.

Overall, 43% of weather-related aviation incidents are due to turbulence. Pilots face some of their most challenging and dangerous situations when flying through turbulence over or near mountainous terrain. According to a U.S. General Accounting Office report issued in 1993, the accident rate in 11 western mountain states was nearly 40% higher than in the other 37 continental states. One of the key risk factors was weather.

The NCAR portion of this research is sponsored by the National Science Foundation through an interagency agreement in response to requirements and funding by the Federal Aviation Administration's Aviation Weather Research Program. NCAR is managed by the University Corporation for Atmospheric Research under sponsorship by the National Science Foundation.