Making Airspace for Birds and Planes
When birds and aircraft collide, it can be disastrous. Fortunately, a combination of common sense, cutting-edge technology, and a bit of bird knowledge is making the skies safer for all.
DeFusco nodded in sympathy. "Gulls are the birds most often struck by commercial airliners, but turkey vultures are the number one species for significant mishaps," he said. "We've lost more military aircraft to them than any other bird." A combination of factors is at work. They're big birds--each weighs about four pounds. There are a lot of them, and they hang out in circular soaring patterns at 2,500 feet. "They've got a locking mechanism in their wings, so they're actually conserving energy soaring up there," said DeFusco. "And they've got no airborne predators, so they haven't developed an evasive response. When an aircraft comes at a red-tailed hawk, the hawk will dive. The turkey vulture doesn't know enough to get out of the way."
Some oak trees caught DeFusco's eye. Airport officials know that trees provide birds with shelter and food, but the Tulsa mayor likes them. DeFusco suggested pruning to let the wind pass through. "Birds roost there for the thermal cover," he said. "If you take that away, they'll look for other trees away from the runway. You lose the birds, the mayor keeps his trees."
DeFusco stepped inside a hangar, where mechanics were busy stripping down the nose of an F-16. Some bird droppings on the floor caught his eye. "That's from our local red-tail," one of the mechanics told him.
Allowing red-tailed hawks to reside at airports is a relatively new and still controversial strategy. In theory, the predatory birds discourage other birds from coming into the area. The data seem to confirm it. Officials at Seattle-Tacoma International Airport, for instance, have allowed six pairs of red-tails to nest nearby since 2001. "The resident hawks are airport savvy," says Steve Osmek, Sea-Tac's wildlife program manager. "The birds that tend to get struck are juveniles and migrants--the young and the dumb." The strategy isn't without risk. If a resident hawk caused a mishap, it could be tough to explain in a sound bite why airport officials encouraged their presence.
DeFusco had a simpler solution. "The hawk's okay," he told the hangar crew, "but really, the best thing you can do is close the big hangar doors a half-hour before sunrise and a half-hour before sunset, when smaller birds are coming home to roost."
Habitat management--grass, trees, hangar doors--is the low-tech part of DeFusco's job, and it's an easy sell to airport officials. The high-tech part is tougher. It's one thing to cut the grass higher. It's another thing entirely to convince air traffic controllers to start thinking of birds like they think of weather.
The concept, DeFusco explains, goes back to the National Weather Service's nationwide rollout of Doppler weather radar in the 1990s. The NEXRAD system--TV weathercasters use it for "your Doppler radar forecast!"--is so sensitive that it picks up flying birds, which are noise in the signal for meteorologists. "Their trash was our treasure," says DeFusco. "We could remove the weather from the signal, and what remained was birds. It was a huge breakthrough."
Using data from National Audubon's Christmas Bird Count, the U.S. Geological Survey's Breeding Bird Survey, and historical birdstrike records, the Air Force team created a database of bird traffic around the country. Real-time Doppler radar provided a secondary layer of information about current bird activity in the area. At the Air Force's Avian Hazard Advisory System (AHAS), pilots combine the two systems to determine the "bird weather" along their route. "From a pilot's perspective," says DeFusco, "the AHAS system is a measure of the amount of meat in the air in front of your airplane."
Among birders, for instance, the Skagit Valley north of Seattle is a well-known wintering ground for snow geese, trumpeter swans, and bald eagles--big birds that can bring down a small plane. Pilots may know nothing about the valley's birding reputation, but a glance at the AHAS site lets them know the area's birdstrike risk level is severe during late December.
Pilots, airfield managers, and air traffic controllers don't universally embrace the AHAS system, mainly because it represents one more piece of data they've got to think about. DeFusco was sensitive to the problem. "This isn't meant to keep you from flying," he assured the F-16 pilots in Tulsa. "It's like a weather condition--if you know a storm is coming in, that won't necessarily ground you, but you might alter your route to avoid it."
The military uses the AHAS system, but civilian airport officials have been slower to adopt it. "It's a challenge Russ and I have talked about for years," says Ron Merritt, president of DeTect, a company that specializes in aviation radar systems. "How do you get bird information to flight crews? There's no bird guy in the [air traffic control] tower. One way to think about it is like wind shear," he says, referring to the weather hazard responsible for a number of fatal crashes in the 1980s. Wind shear problems were reduced in the 1990s with the development of NEXRAD. "Years ago the FAA got serious about wind shear and implemented a system in some airports where a wind shear advisory light dings in the tower when conditions are dangerous. We'd like to do something similar for birds. When there's a swallow storm out there, nobody wants to fly into it."