Lasers' aim is fewer air traffic delays

Finding planes' wake could let them follow one another more closely


DENVER -- As planes mosey 800 feet overhead, on their way to touch down at Denver International Airport, there is a ghostly roar - caused by turbulence left in the engines' wakes, mostly in the form of two horizontal tornadoes, one near each wingtip.

On bad-weather days, it is the fear of those tornadoes, called wake vortexes, that determines how close the next airplane can follow. That, in turn, determines how many airplanes can land on a runway in an hour.

But in a windblown wheat field two miles north of the runway end, something new is listening to that roar. These are giant laser "ears" that can pinpoint the airplanes' wake and watch it sink, blow sideways in the crosswind or decay like skywriting.

Finding the location of the invisible tornado could be crucial to reducing air traffic delays. On good days, planes can follow one another at a distance of three miles or a little less, while taking care to stay upwind of the plane ahead, to avoid the wake turbulence.

But when pilots cannot see each other and predict the vortex location, controllers are supposed to direct them to stay three to six miles apart, depending on plane type. Planes are most vulnerable to the vortexes as they are landing because that is when they are flying most slowly, and slow planes have poor control if a vortex starts to roll them over.

Planes also generate the strongest vortex when they are slow because they tend to be flying with the nose pitched up, said William Cotton, president of the company performing the test here, Flight Safety Technologies of Mystic, Conn. Cotton was formerly the chief technical pilot with United Airlines.

Vortexes are not an issue at airports with low traffic counts but are especially serious at busy airports with a mix of traffic..

A number of planes have crashed because of wake turbulence over the years. In 1972, a DC-9 crashed at Greater Southwest Airport in Fort Worth because of wake turbulence left by a larger DC-10 that had been two miles in front.

Flight Safety, after seven years of testing, hopes to have a system in place by next year that could tell controllers when the wake vortex is not a factor, increasing the capacity of some runways by 20 percent. Federal Aviation Administration rules require controllers to consider parallel runways that are fewer than 2,500 feet apart as a single runway because a vortex could drift from one to the other. If the system cuts bad-weather delays as predicted, some experts say, it could save tens of millions of dollars a year at a busy airport.

Not everyone is convinced that the concept is practical, or that even if it is, that the approach by Flight Safety is the right one. The federal investment, about $15 million since the late 1990s was not the choice of the Federal Aviation Administration or NASA; it was ordered by Congress. And there are competing ways to locate the vortexes.

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