August 1, 2005
By Alton K. Marsh
Recent articles in AOPA Pilot triggered these questions from readers: What do you do when you see a bird just ahead? Should you descend, climb, continue straight ahead, or turn? Most pilots believe that the bird will dive. Well, not always.
Some of the best insight into bird behavior comes from wildlife biologists at the U.S. Department of Agriculture Wildlife Services laboratory near Sandusky, Ohio. Research biologist Richard A. Dolbeer and his colleagues recently combed 56,000 civil-aviation bird strike records from 1990 to 2003, and found 633 in which pilots noted what the bird did or didn't do.
There were 266 reports out of the 633 involving birds encountered in the air. Of those, the greatest number — 73 — dived or descended to avoid the airplane, as you might expect. But 46 birds climbed. Sixty-two had no reaction at all — perhaps they just shrugged their wings as if to say, "Oh well." Five unfortunate birds attempted to out-fly the aircraft. Four, including those on the ground, got angry, attacked, and lost. Of those, a killdeer intentionally flew at a landing aircraft at Morgantown, West Virginia. A Canada goose attacked an Ohio State University training aircraft at Columbus, Ohio, as it taxied by a nest. It first bit at the wing tips and then swooped toward the prop — its last swoop before becoming a wheel chock. The pilot got out, removed it, and taxied on.
Continuing with the findings, 27 of the 266 birds attempted to avoid the aircraft using an "unknown maneuver," and another 19 flew away but circled back toward the aircraft. So what's the lesson? Scientists are coming up with the answers.
Dolbeer also found that the more dangerous altitudes for bird strikes are at two levels, between 600 and 800 feet and between 1,000 and 2,000 feet — in other words, traffic pattern altitudes. Here are some lessons you can take with you into the cockpit:
Dolbeer and fellow scientists Carol Washburn and Sandra E. Wright found that at altitudes higher than 500 feet, birds would typically dive to avoid an aircraft. Thus, above 500 feet, pilots should expect to fly over birds. Below 500 feet, birds exhibit a variety of behaviors including climbing.
Also, birds try to avoid light beams at night.
Anecdotal evidence and limited experimental data suggest pulsating landing lights might reduce bird strikes. Research is continuing into this at Sandusky by research wildlife biologist Bradley Blackwell.
In the jet world, it appears that as jet engines become quieter, bird strikes increase. One air carrier detected slightly reduced bird strike rates after painting the jet engine spinners white. Anything that increases contrast seems to help birds to avoid airplanes. Birds see colors in the ultraviolet range beyond what humans can see, and that information may be useful in future research on markings for aircraft that could reduce bird strikes.
The biggest airports often have a resident wildlife biologist on staff who works full time to keep birds away. Grid squares of wires above water bodies such as detention basins prevent geese from making their required long glide to a landing, and geese are afraid to try to dive between the squares. Rapid drainage systems assure that even after a heavy rain there is no standing water to attract birds. Trained dogs race to herd the birds away at some airports, while at others airport officials pull out the paint guns, blasting away to give larger birds a bad day. Robot machines simulate gunshots and play calls of predator birds over loudspeakers. But what can smaller airports do?
Airports with limited budgets are contracting with wildlife biologists to seek advice. Pilots can help the biologists by making bird strike reports. Report forms are available on AOPA Online ( www.aopa.org/members/files/topics/wildlife.html). Military researchers are attempting to forecast bird activity in military airspace and post the information on the Web.
There are few exact answers for the pilots hoping to avoid a blast of bird guts, feathers, and blood through the windscreen. There are general rules, however, that reduce the risk.
Airports near water usually have bird problems, as Thomas Griffing found out on July 9, 2004, while making a morning charter flight to islands in Lake Erie. He was flying a Britten-Norman Islander when a 2.5-pound herring gull came through the windshield above Put-in-Bay on South Bass Island, injuring him. He was in cruise at 500 feet on his way to Middle Bass Island. He saw the gull for a split second as it came up from below, braced himself, and heard what sounded like a gunshot. The bird came through the three-eighths-inch-thick windscreen, hitting him in the forehead and sending his sunglasses and headset sailing. "It wasn't windy," Griffing said, "because the fuselage pressurized [preventing air flow through the cabin]." The bird cut him below his eyes. His main concern was that he was losing so much blood that he might pass out. Griffing landed safely and was transported from Middle Bass Island by a medical helicopter: The cuts required 32 stitches.
A year ago Paul Fullerton, manager of the Mackinac County Airport at St. Ignace, Michigan, took off at night in a Piper Cherokee Six to pick up charter passengers and was climbing through 50 feet at about 100 knots when he struck two Canada geese. The landing lights were still on — a fact that should have made the aircraft more visible to the birds that had been sitting on the runway. It didn't. One hit the lower cowling, damaging it and springing the top engine cowling loose, causing it to separate from the aircraft. The other hit the left wing, smashing through it like a hammer and caving in the fuel tank, resulting in a massive fuel leak. He continued the climb, made a 180-degree turn (the aircraft was flying well), and returned to the runway.
Pilots may associate bird activity with nesting activities: That's not the problem. The worst months for bird strikes are August through October, not spring, because young birds have grown up enough to learn to fly, but lack air smarts. They're neither wise to airplanes nor skilled in avoiding them, but they don't hit aircraft on purpose. "No species of bird is suicidal," Dolbeer said.
About twice as many bird strikes occur during the day (63 percent) compared to night (27 percent), with the remainder (10 percent) occurring during dawn and dusk. The majority of strikes occur in the approach phase of flight, but most have little effect on the flight. Engine shutdowns are always a concern with jets, of course. During the 14-year period from 1990 through 2003, 26,493 flights experiencing a strike continued with no problems. Only 2,235 resulted in precautionary landings and 1,072 strikes caused an aborted takeoff. There were 251 engine shutdowns, and most were multiengine jet aircraft.
The Aeronautical Information Manual lists the location of flyways and suggestions for reducing strikes. These include a general response of climbing over birds (above 500 feet) and also avoiding areas of known bird concentrations, especially when flying at low altitudes during bird migration. Migrating birds generally climb to 5,000 or 6,000 feet, ascending higher as they burn fat. They like it up there because there is less drag where the air is thinner. The late astronaut Gordon Cooper said in an interview years before his death that he once hit a duck while flying his twin-engine airplane at 20,000 feet. Emperor geese have been seen at 35,000 feet above Mount Everest. Awareness of migratory patterns is useful for pilots, but Canada geese have come to the United States to stay year-round. Thus, there is a greater danger than just during migratory periods. In 1990 there were 1 million resident Canada geese in the United States, but today there are 3.6 million.
During research for this article, some of you were asked on AOPA Online for locations of serious bird problems, and several good suggestions were made. But a few couldn't resist a good pun. One reader suggested tongue in cheek that all birds be equipped with transponders, but withdrew that idea when he realized that birds are already squawking. Ready for another one? The scientists in Sandusky who come in direct contact with wild birds say they have to be careful not to contract that dreaded avian disease, chirpies, because it is untweetable. (It is so dreaded because it is a "canarial" disease, you see.) They do take their work seriously, though, realizing the millions of dollars of damage that birds can do to airplanes, and they hope one day to forecast the bird threat day to day, as the military now does for some of its special-use airspace. For now, don't trust anything with feathers.
E-mail the author at firstname.lastname@example.org.
Links to additional information about bird strikes may be found on AOPA Online ( www.aopa.org/pilot/links.shtml).
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