Apr 19, 2010

bird strikes

Five people died in Oklahoma in March 2008 when their Cessna hit a white pelican during takeoff. Last November, a western grebe shattered the windshield of a small plane and crashed just over the pilot's head into the back wall of the cockpit. According to an FAA report published in September, planes have struck 30 species of duck since 1990.

About 7,000 bird strikes are reported each year, up from around 2,500 in the early 90s. The bird always dies, but damage to the plane ranges from trivial to expensive to tragic. A gadwall sucked into a descending jet's engine in 2008 left a $900,000 repair bill, though the plane landed safely.

Reporting of wildlife strikes is voluntary. Sometimes feathers and remains are sent to museums for identification, but many reports just say "unknown bird." The vast majority of the 168 reported strikes at the airport near me are "unknown bird or bat."

Birds are more likely to be hit on approach than takeoff, and one reason may be that birds are harder to see against a background of land than against sky. Many bird strikes occur on or near the ground as startled birds flush into harm's way. You know Capt. Sullenberger for his heroic water landing in New York City last year, but he also flew the plane into a flock of geese. Pilots get warnings about statistical risks, but not about actual flocks.

Bird strikes are heaviest from July through October, when birds are migrating southward, and drop off significantly in winter. There are more juvenile birds during those months as well. Bird strikes caused $308 million in damage in the U.S. over the past two decades. Terrestrial animals, primarily white-tailed deer, get hit too, often as the plane lands. This caused $38 million damage over two decades. Bats did $3 million worth of damage.

The good news from the study is that populations of many large, native birds are on the rise. Planes are more likely to strike geese, turkeys, eagles, vultures, cranes, cormorants and pelicans because those birds are all increasing in number.

Gulls are hit most often, followed by doves and pigeons, then hawks. Most damage from bird strikes happens when heavier birds are hit, and birds smaller than a dove rarely cause problems. Birds that prefer flat, open habitats -- killdeer, horned larks, kestrels -- show up on the victims list far out of proportion to their abundance, and you can also deduce from those lists that many airports are adjacent to wetlands and shoreline.

Not much is known about small-bird strikes. Impacts with warblers and other small migrants would not leave much evidence of the calamity nor much opportunity for pilots to identify their victims. Many migratory birds fly at night, when pilots have no chance of avoiding or seeing birds.

Fortunately, the aviation industry teamed up with biologists to develop the Avian Hazard Advisory System, which incorporates not just historical data about wildlife strikes, but also basic biological data and weather radar. Birds migrate when weather systems give them a tailwind, and they cross the Gulf of Mexico in large flocks that show up on radar, so this tie-in to weather data adds fine resolution to the risk assessments. With the frequency of air travel and the populations of birds both on the rise, good risk analysis is critical.

Airport managers are also learning ways to better exclude wildlife from danger zones, and one sad conclusion from studying strikes is that airports are poor neighbors for wildlife refuges and nature parks.

No comments: