DN Staff

January 17, 2009

6 Min Read
US Airways Water Landing for The Birds?

A US Airways jetliner en route from New York's LaGuardia Airport to Charlotte, NC made a dramatic unscheduled landing yesterday afternoon - in the Hudson River off Midtown Manhattan. All 150 passengers and five crew members aboard Fight 1549 survived this rare ditching of a large commercial jet.

Early speculation about the cause of the accident has focused on the possibility that the jetliner, an Airbus A320, lost power in both of its engines after flying through a flock of geese and sucking some of these big waterfowl into the engines, a problem known as "bird ingestion." With the National Transportation Safety Board (NTSB) investigation just getting off the ground today, it will be some time before we know whether bird ingestion actually caused this accident.

Yet it's no secret in aviation circles that flocking birds pose a serious and growing threat to aviation safety. "The problem has been under the public's radar scope for many years, even though bird strikes have always had the potential to bring down a large aircraft," says John Ostrom, chair of the Bird Strike Committee, an industry organization dedicated to reducing the risks posed by flocking birds and other types of wildlife.

According to the Federal Aviation Administration's National Wildlife Strike Database, there have been 79,972 bird strikes on civil aircraft from 1990 to 2007 as well as more than 1,700 collisions with bats and mammals on the ground. Factor in the military, and the bird strike problem gets even bigger. For example, the U.S. Air Force reported more than 5,000 reported bird in 2007 alone.

All these wildlife strikes have taken a human tool, resulting in 11 deaths and 197 injuries from the civilian strikes reported by the FAA. Figures from the Bird Strike Committee paint an even bleaker picture. The committee puts the number of deaths from bird strikes at 219 people globally since 1988. (The committee maintains a list of serious bird strike incidents dating back to an Orville Brothers flight in 1905. See the list here.)

The strikes also took a tool on the planes themselves, destroying forty-three civilian aircraft over that 18-year-period and resulting in reported economic losses totaling $291.1 million. And actual losses are thought to be much higher. If all wildlife strikes were reported, annual losses for civil aviation would come to more than $620 per year in the U.S. alone, according to an June 2008 FAA report on wildlife strikes.

And the bird strike threat is a growing.The FAA wildlife report notes that the annual number of reported wildlife strikes more than quadrupled from 1,759 in 1990 to a record 7,666 in 2007. More than 97.5 percent of these collisions involve birds rather than animals on the ground. The report cites increases in air traffic and increases in wildlife population as two factors behind the increase. Air traffic increased from 18 million aircraft movements in 1980 to 28 million in 2007. And non-migratory canada geese alone, to take one example of a big bird, experienced a mean growth rate of 7.3 percent yearly from 1980 to 2006.

What's more, airlines fly have started to fly more two-engine jets over the years. Not only does the shift to two-engine planes remove a measure of redundancy found on older three- and four-engine planes, but the FAA report also cites some evidence that relatively quiet modern planes engines are harder for birds to detect and avoid.

"As a result of these factors, experts within the Federal Aviation Administration, U.S. Department of Agriculture, and U.S. Air Force expect the risk, frequency, and potential severity of wildlife-aircraft collisions to grow over the next decade," the FAA report concludes.

So what's to be done? Solutions to the bird strike problem can be found on the ground and on the wing. Some of the ground-based solutions come down to sound wildlife management programs on and near airport grounds.

But technology comes into play too. Ostrom reports a rising interest in using radar systems to look for the presence of flocking birds near airports. "What's really important from an avoidance standpoint is how much meat is up in the air, and that's what radar can tell us," he says, drawing an analogy with radar systems used to monitor the weather.

Other solutions, though, will have involve the planes themselves, particularly the engines.

As the FAA report notes, wildlife strikes have damaged a variety of plane structures over the years. Yet the greatest number of strikes, 32 percent, involved the engines.

Engine makers already design for the possibility of bird strikes and perform physical ingestion tests prescribed by the FAA as part of their engine certification standards. Those tests involve firing one or more birds carcasses of various sizes into the engine's first rotating stage at 200 knots. All the while, the engine runs at specified loading conditions. To pass, the engine can't have a sustained thrust reduction to less than 50 percent of the maximum rated takeoff power. It also has to keep running and meet thrust requirements during a run-on period after the ingestion.

The procedures and bird weights change with the type and size of engine. But GE Aviation supplied some information about the small-, medium- and large-bird tests it conducts, using its GE 90 engine as an example.

The large-bird test for that engine required an eight-lb bird for the first time, so the company used a Canada goose carcass. Prior to the GE-90, a four-lb mallard duck was the large bird of choice. The medium-bird test called for four to six Herring gulls weighing 2.5 lbs apiece, while the small-bird test involved California gulls each weighing 1.5 lbs. Some engine programs have also required a test that shoots 15 four-ounce starling carcasses into the engine.

To fire birds into the engine, GE has developed 50-ft-long pneumatic guns as part of its test rig. The guns typically shoot the birds into the stationary test engine at speeds between 250 and 350 ft per second, though some military tests have gone up to 750 ft per second.

GE Aviation declined to comment on the specific design strategies it used to pass the tests. "It's some of the most proprietary stuff we do," says Rick Kennedy, a company spokesman.

One question that may surface after Flight 1549 accident is whether the FAA regulations themselves, which govern the design practice, are adequate. In 2007, the FAA amended its rules governing upping the bird ingestion requirement to account for the growing threat posed by flocking birds weighing more than 2.5 lbs. During the comment period for that rule change, the NTSB raised concern that the amended rules didn't go far enough, arguing that the FAA's new maximum bird weight of 8 lbs and de-rated thrust conditions didn't represent the worst-case scenario that planes could encounter in the real world-where a Canada goose, for example, can weigh ten-plus pounds. The FAA didn't concur with NTSB's recommendations.

With what looks like a catastrophic bird strike in the news again, even one that wasn't as disastrous as it might have been, the FAA's bird ingestion standards will likely draw some renewed interest.

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