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
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 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
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.