'Runway Contamination' Presents Challenges to Pilots

BRUSSELS, Belgium (AP) -- In a number of recent aviation accidents, the presence of water, slush, snow, rubber deposits or other materials on runways has been a contributing factor in the crash.

Runway contamination, as it is known in aviation circles, has become a source of growing concern as airports become clogged with an ever-increasing number of takeoffs and landings -- and may have played a role in Tuesday's crash of an Airbus 320 at Sao Paulo's Congonhas airport that killed 189 people.

"When it comes to plane excursions, it's usually (due to) contaminated runways, like it sounds this one was with the water," said Jim Burin, director of the technical program for the Flight Safety Foundation. "The length itself is not a problem, but the runway's condition is critical."

Contamination is defined as the presence of any material which impedes braking performance by lessening friction between the airplane's tires and the runway surface.

It differs from foreign object damage caused by bird strikes, hail or bits of metal left behind by planes. In both cases, airport ground crews are tasked with regularly cleaning up the runways.

"Our position is that airport operators should do as much as possible to mitigate the effects of such contaminants," said Gideon Ewers, spokesman for the International Federation of Air Line Pilots' Associations.

"Runways should be designed to promote rapid drainage and increase friction characteristics,'' he said.

Regulations in the United States, Canada, and most European nations allow for only 1/2 inch (12 millimeters) of contaminants on runways. These include standing water, slush, ice or snow or rubber deposits from multiple landings which become highly slippery in wet weather.

In the case of snow, regulations permit 2.2 inches (60 millimeters) if it's dry or hard-packed with sand.

Runway contamination has been an element in a number of recent accidents.

In 2005, an Air France Airbus 340 shot off a wet runway at Toronto airport after touchdown, and caught fire. All 309 people on board survived.

That same year, a Southwest Airlines skidded off a runway at Chicago's Midway International Airport and careered through an airport fence and onto a busy street, killing the passenger in a passing car.

After that, the U.S. National Transportation Safety Board instructed airlines to change the way they calculate stopping distances on slick runways to allow for more landing room.

The problem is seen as potentially deadly in situations when pilots decide to abort takeoffs _ usually as the result of the loss of an engine -- when decreased braking action could push the airliner past the end of the runway.

As a result, NASA, the National Aeronautics and Space Administration, has conducted a series of tests aimed at improving friction between airplane tires and runway surfaces in order to enhance braking performance.

The tests found that cutting transverse grooves into the landing surface "gives the sort of performance that approaches that of a dry runway."

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