Published: January 21, 2009
Almost anything that pumps air, even a vacuum cleaner, has a filter to keep contaminants out. Why not jet engines?
Because chicken wire stretched over the engine cowling could easily make a bird hit into a much more serious problem, experts say, and would certainly make ordinary operation more difficult.
After the crash of US Airways Flight 1549 on Jan. 15, investigators said that one of the areas they would examine is how jet engines handle incoming birds and other extraneous objects. The pilot, who brought the plane down safely in the Hudson River, allowing all 155 passengers and crew members to evacuate, has said that both engines failed because they were struck by birds shortly after the plane took off from La Guardia Airport.
While the National Transportation Safety Board will take months to determine whether bird strikes indeed caused the engine failures, investigators said on Wednesday that they had found a feather and evidence of “soft body impact damage” on the right engine. The left engine broke from the airplane after it hit the water, but police divers found it on Wednesday on the river bottom.
John Goglia, a former member of the National Transportation Safety Board and a former aircraft mechanic, said chicken wire would barely make a difference in a bird hit, and a heavier screen might break and be sucked into the engine as well; there it would be more of a problem than bird bodies, which are easier for the engine blades to chop up and pass through.
He likened a bird to a bullet. The problem last week was that the airplane was moving fast and hitting an object that was almost stationary, relatively speaking. “The problem is the ability to withstand an eight-pound object moving at 250 miles per hour,” he said.
Depending on the size of the plane, engines are expected to withstand a hit from a bird of four to eight pounds, but some birds, like the kind that may have hit Flight 1549, can be larger. “These are geese that came from Canada, liked America, stayed and got fat,” Mr. Goglia said. “They can still fly, but they don’t go very far. They’ve been seen up quite high, too.”
Over the years, the Federal Aviation Administration has required that new engine be able to handle larger and larger birds, but the strategy has always been to allow them to move through an engine, not to keep them out. And a lot can be drawn into an engine, because engines suck air as if they were in the neck of a funnel, so the area from which they can pull in birds is far larger than their openings.
The airlines are wary of screens. “Anything strong enough to take that kind of impact would weigh so much that you couldn’t operate it,” said Basil Barimo, vice president for operations and safety at the Air Transport Association, the trade organization of the big airlines.
And screens would be a problem in normal operation, he and other experts said. Magdy S. Attia, an associate professor in the aerospace engineering department at Embry-Riddle Aeronautical University, in Daytona Beach, Fla., said a screen or grate in front of the engine would produce turbulence in the air behind it, and what the engine needs is a smooth flow of air. If the flow is disrupted, the compressor at the front of the engine may stall, causing the engine to lose lift.
Professor Attia said he had actually put a screen across the opening of a jet engine, but it was not on a plane; it was on a drag racer. The reason was debris at ground level. “Jet engines are designed for runways,” he said. “Runways are nice and clean and well maintained; on raceways, nobody worries about that stuff.”
While engines are built to withstand bird strikes, new air traffic control technology may be making it more difficult to avoid them. The F.A.A. wants to move away from radar, which sometimes sees flocks of birds, and instead have airplanes radio in their positions, as determined by GPS. Birds, of course, carry no radios.
The federal government already operates weather radars that see birds and do something that F.A.A. radars generally do not: estimate altitude. But these are not well integrated into the air traffic system.
Mr. Goglia, the former safety board member, said his view of aviation safety was heavily influenced by an event in October 1960, when he was 16 and lived near Logan Airport in Boston. An Eastern Airlines turboprop, a now nearly extinct model called the Electra, crashed on takeoff after it flew through a flock of starlings; 62 of the 72 on board were killed. Mr. Goglia, then a scuba diver, was called out to help recover bodies from Winthrop Bay.
Mr. Goglia is circulating a call for a “bird summit.”
In the past radar equipment was developed to detect wind shear, he said. “Why can’t radar be designed to spot something as big as a flock of birds?” he asked. “If aircraft manufacturers can design a missile shield, why not a Canada goose shield?”