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| (Photo courtesy United Airlines.) |
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| (Photo courtesy United Airlines.) |
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Ice buildup on aircraft waiting to depart can be a serious safety hazard. As little as 0.8 millimeter of ice on the upper wing surface increases drag and reduces airplane lift by 25%. With deicing fluids ranging from $2 to $4 a gallon, battling ice buildup can cost airlines tens of thousands of dollars on a single snowy day, in addition to the expense of flight cancellations and delays. The new system's half-hour forecasts could mean big savings for airlines through more effective deicing practices and fewer cancellations.
The FAA will evaluate the Weather Support to Deicing Decision Making (WSDDM) at both airports through user surveys and cost/benefit analyses. If successful, it will become a standard feature for those airlines willing to pay for its operation at airports regularly besieged by winter weather.
At La Guardia, Delta and USAir are participating from early January through March. American and United, who helped test a prototype of the system last year at O'Hare with encouraging results, are participating there again this winter, from mid-January through April.
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| Chuck Wade and Roy Rasmussen |
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During the demonstration, surface weather stations, snow-weighing gauges, and Doppler radars are measuring snowfall accumulation, temperature, humidity, wind speed and direction, and the water content of snow. The data are being processed instantly and displayed graphically on video monitors at both the Delta control tower and the Marine Air Terminal at La Guardia, the New York Traffic Control (TRACON) office in Westbury, USAir's operations center in Pittsburgh, and the Delta operations center in Atlanta. At O'Hare, monitors are being installed at United's station control, tower, and flight operations center.
The monitors show bands of snow detected by the National Weather Service (NWS) WSR-88D radar network as they move toward or away from the airport. Data from special snow-weighing gauges strategically placed in and near the airports are displayed as a simple graph showing the water content of snow at various locations--a key factor in deicing decisions. The resulting short-term nowcasts (0-30 minutes) based on these and other meteorological data are expected to aid airport officials, including ground personnel deicing the planes, airline 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.
The new technology is a direct result of scientific research. Roy found that the potential of snow to form ice on an airplane's wings and fuselage corresponds to the amount of water in the snow rather than to reduced visibility during snowfall. Visibility is often used by the National Weather Service 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 (see list below), Roy found that visibility at the time of the accidents varied widely. He determined that large, dry snowflakes were less of a threat than small, heavy flakes holding more water, though the former reduce visibility to a greater degree. The snow-weighing gauges used in this winter's test at O'Hare and LaGuardia will measure the actual liquid content of the snow.
"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."
NCAR has placed two snow-weighing gauges at La Guardia, two at John F. Kennedy Airport, and one at Newark Airport nearby in New Jersey. In the Chicago area, gauges will be placed at O'Hare, at Midway Airport, in the city of Wilmette, and at the College of Du Page (southwest of O'Hare). •Anatta
See last March's Staff Notes Monthly for a report on RAP's snow-weighing research at the Marshall site.
| Month/Year | Aircraft Type | Location | Icing Conditions |
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| 12/68 | DC-9 | Sioux City, Iowa* | Light, freezing drizzle; fog |
| 11/78 | DC-9 | Newark, N.J.* | Snow, fog |
| 2/79 | Nord 262 | Clarksburg, Wyo. | Frozen snow |
| 2/80 | Bristol 253 | Boston, Mass.* | Light snow, fog |
| 1/82 | B0737 | Washington, D.C.* | Snow |
| 2/85 | DC-9 | Philadelphia, Pa.* | Light, freezing drizzle, ice pellets |
| 12/85 | DC-8 | Gander, Newfoundland | Light, freezing drizzle |
| 11/87 | DC-9 | Denver, Colo.* | Snow |
| 3/89 | F-28 | Dryden, Ontario | Snow |
| 3/92 | F-28 | New York, N.Y.* | Snow |
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| Frank McDonough and Marcia Politovich |
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| Ben Bernstein |
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Last year, at the request of the FAA, Ben created an algorithm, or mathematical problem-solving procedure, to automate freezing-drizzle advisories for areas smaller than those covered in general icing advisories. Due in large part to cooperative research by the AWC and NCAR, the areas of the advisories have become more specific over the past few years.
The research flights provide a good test of the new algorithm, which Ben calls the "stovepipe" because it uses data from observations on the ground to characterize what's happening in a stovepipe-shaped column of air at higher elevations. The experiment is also testing a new algorithm, developed by Jotharim Vivekanandan, that detects supercooled water droplets in cloud tops by examining infrared and visible-light readings from the NOAA Geostationary Operational Environmental Satellite-8 satellite.
NASA Lewis scientists will use flight data to improve icing simulation tools such as their icing research tunnel and their computer code for ice accretion. Working with AWC forecasters, the NCAR team will use the experiment's results to streamline pilot weather advisories issued at Kansas City.
Another step will be instructional materials for operational forecasters and pilots. Training modules, which include interactive CD-ROMs and Internet access, are being developed by the Cooperative Program for Operational Meteorology, Education and Training. They should reach forecasters and pilots by mid-1998. •Zhenya Gallon
"They said they were getting large-droplet icing near Cleveland and were interested in doing a second flight that afternoon. They asked us where they should go, and we said, 'Toledo,'" recalls Ben. He and Frank had a good mental picture of what was going on from looking at data before they left Colorado and at hotels along the way. In addition, there was the freezing drizzle hitting their windshield.
Meanwhile, they figured out how to make the defroster work without overtaxing the engine, and started heading eastward on the two-hour drive to Cleveland. They wanted to be there when the Twin Otter took off on its afternoon run. The freezing drizzle turned to snow as they headed east, but Ben and Frank made it to Cleveland that afternoon.
The Twin Otter, however, was stuck on the ground. Every plane files a flight plan before takeoff that includes alternate airports for landing in bad weather. There were no alternate airports with acceptable conditions near Toledo in the hours before the Comair commuter plane flew through the same area on its way to Detroit Metropolitan Airport. "As much as they wanted to go, they couldn't," says Ben. If they had, "they would have sampled that case very close to the location and time of the crash." Documenting such an accident with high-quality, in-flight data would have been "rare, perhaps unprecedented," he adds.
As luck would have it, NOAA's GOES-8 satellite was down that day. Despite missed opportunities, the NCAR team has data from GOES-9 and from the morning flight that may prove useful to crash investigators at the National Transportation Safety Board. The investigation will take time, and in-flight icing may not be implicated. Nevertheless, as Marcia Politovich put it, for the in-flight icing experiment team, 9 January was "an interesting day." •Zhenya Gallon