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Winter/Spring 1997

Deicing forecasts unclog LaGuardia and O'Hare Airports

by Anatta
UCAR Communications

This winter, two of the nation's busiest and snowiest airports, LaGuardia in New York City and O'Hare in Chicago, are testing a new data-gathering and display system to aid airlines in making deicing decisions. The system, which predicts snow conditions up to 30 minutes ahead of time, was developed at NCAR under the leadership of Roy Rasmussen (Research Applications Program) and funded by the Federal Aviation Administration (FAA).

Deicing a United Airlines plane at Denver's Stapleton International Airport, now closed. (Photo courtesy of United Airlines.)

Icing on aircraft waiting for takeoff can be a serious safety hazard. Only 0.8 millimeters of ice on top of the wing increases drag and reduces airplane lift by 25%. Deicing, however, is an expensive proposition: with deicing fluids costing $2-4 per gallon, airlines can spend tens of thousands of dollars in a single day, with additional costs for flight cancellations and delays. A 30-minute forecast allows airlines to save by deicing more efficiently and keeping flights on schedule.

Delta and USAir are using the new system at LaGuardia through March. American and United, which tested a prototype system at O'Hare last year, are participating there through April. The FAA will evaluate the system through user surveys and cost/benefit analyses.

The system, named the Weather Support to Deicing Decision Making (WSDDM), builds on Rasmussen's finding that icing corresponds to the amount of water in snow rather than to visibility during snowfall. Visibility is often used by the National Weather serivce to estimate whether snowfall is light, moderate, or heavy, and it has been adapted by the aviation industry as a factor in deicing and takeoff decisions. In studying a number of takeoff crashes due to icing, Rasmussen noticed that visibility varied widely at the time of the accidents. He determined that large, dry snowflakes were less of a threat to aviation than small, wet, and heavy flakes, even though the larger snowflakes reduced visibility to a greater degree.

WSDDM uses surface weather stations, snow-weighing gauges, and Doppler radars to measure snow water content and accumulation, air temperature and humidity, and wind speed and direction. These data are processed immediately and displayed in the participating airlines' control towers and operations centers, as well as the Marine Air Terminal at LaGuardia and the New York Traffic Control office in Westbury, Long Island. The displays show a graph of snow water content from the snow-weighing gauges, combined with images of snow bands moving toward or away from the airport, garnered from the National Weather Service's NEXRAD radar network.

Nowcasts (0-30 minutes) are expected to aid airport officials, including ground personnel deicing the planes, airpline station control managers coordinating flights, airport managers in charge of plowing the runways, and air traffic controllers deciding how long to hold planes at gates. "Pilots have already become more aware that visibility can be misleading when it comes to aircraft icing," says Rasmussen. "Now we can give them quantitative measurements indicating the real potential of snow to form ice on aircraft."

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Edited by Carol Rasmussen, carolr@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Tue Apr 4 13:38:24 MDT 2000