An increasing number of US airports are turning to electronic sensors to get better weather and traction information about their runways. General weather forecasts and landing reports from pilots have often been the key sources of such information. But over the last five years, dozens of civil and military airports in this country have been installing a sophisticated system of runway sensors. The aim: improved advance warning of freezing conditions.
The sensors measure the temperature of the pavement (as opposed to the air), the speed and direction of the wind, and the presence of moisture for a more precise forecast as to when chemical de-icing or sanding of the runway is needed.
The benefit is not only added safety for aircraft but also valuable dollars saved by cautious airports that tend to de-ice runways too often.
An electronic runway warning system installed at Washington's National Airport just before the city's big snow in February saved the airport at least $ 5,000 in chemicals just in the first few days. The system told officials that the pavement, which had an inch of glazed ice on it at the time, was rapidly warming despite overcast skies. So an alternate runway was used while officials waited out the meltdown.
''By the time the sun went down, it was slush, and we could broom it off,'' notes National Airport operations chief John Ogden. ''We're convinced the sensor system is a workable tool.''
Mr. Ogden adds that Washington National really bought the system for its advance-warning capabilities. It can alert airport officials as to when chemicals, which can also serve as anti-icers, should be put down to keep expected freezing rain from adhering to the runway.
Nearby Dulles International Airport is about to install a similar system. Many larger airports, including St. Louis, Kansas City, Detroit, Boston, Pittsburgh, and Chicago's O'Hare, already have runway sensors in operation.
At a hearing last May on the aircraft performance effect of runway surface conditions, managers of several of those airports told National Transportation Safety Board (NTSB) officials that the system was proving a valuable monitoring device.
''It lets me get on top of a situation fast - it's a management tool,'' Leonard Griggs, director of Lambert-St. Louis International Airport, told the NTSB panel.
To date, the only US supplier of the sensor system is Surface Systems Inc., which happens to be headquartered in St. Louis. It recently upgraded the system to include wind and dew-point information.
''A runway is like a huge heat sink,'' explains Thomas Webb, marketing manager of the firm's eastern region. ''It doesn't cool off or warm up as quickly as the air. It's expensive and chancy to put chemicals down on the runway at the wrong time. It can make the situation worse.
''But a liquid moves to a solid gradually, and this system can give airport officials 15 minutes to an hour of advance warning that things are beginning to freeze.''