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