Encyclopedia
A
bird strike in
aviation, is a collision between an airborne animal and a man made vehicle, especially
aircraft. It is a common threat to aircraft safety and has caused a number of fatal
accidents.
Event description
It is believed that most potential collisions are avoided because the bird is able to change its course in time and to avoid a collision. However, the faster the vehicle, the less chance has the bird to avoid the vehicle, putting aircraft especially at risk. Most bird strikes happen close to the ground, where the majority of the birds are found . Hence bird strikes happen most often during
take off or
landing, or during low altitude flight. However, bird strikes have also been reported at high altitudes. The majority of aircraft - bird collisions occur near or on
airports during takeoff, landing and associated phases. Less than 1% of strikes occur above 760 m and 50% at less than 30 m .
The point of impact is usually any forward-facing edge of the vehicle, although with
jet engine aircraft the animal is frequently sucked into the engine, causing damage to the fans or the housing, or airflow ducts. The force of the impact depends on the weight of the animal and the speed difference and direction at the impact. The weight of the vehicle can usually be ignored since it is usually much larger than the weight of the animal. The energy of the impact increases with the square of the speed difference. Hence the energy of the impact is small at low speeds, and an impact of a small bird on for example the
windshield of an
automobile has usually only minor or no damage to the car, although it will result in major injuries or death to the bird. High speeds, however, as for example with modern jet engine aircraft will produce considerable energy and may cause considerable damage or even a total catastrophic failure to the vehicle. However, according to the
FAA only 15% of strikes actually result in damage to the aircraft. A 5 kg bird at 240 km/h equals 1/2 short ton dropped from 3 meter height.
Depending on the force of the impact, the bird strike may damage or even destroy components of the vehicle, or injure people in the vehicle. Especially
flocks of birds are dangerous, and can lead to multiple strikes, and damage, within a very brief period. Depending on the damage aircraft at low altitudes or during take off and landing often cannot recover in time and crash.
In the USA, remains of the bird, usually a bloody goo called
snarge, are sent to the
Smithsonian Institution's Feather Identification Laboratory to determine the species.
Species
The animals most frequently involved in bird strikes are large birds with big populations, with
geese and
gulls causing most serious incidents. In the US reported strikes are divided between
waterfowl ,
gulls , and
raptors . The Smithsonian Institution's Feather Identification Laboratory has identified
turkey vultures as the most damaging birds, followed by
Canada geese and
white pelicans, all very large birds. In terms of frequency, the laboratory most commonly finds
Mourning Doves and
Horned Larks involved in the strike. The largest numbers of strikes happen during the spring and fall
migrations. Striking large land-bound animals, such as
deer, can also be a problem to aircraft during take off and landing, and over 650 civil aircraft collisions with deer were reported in the U.S. between 1990 and 2004.
Strangely enough, vehicle-animal collisions at high altitude also sometimes includes species that cannot fly. The Smithsonian Institution's Feather Identification Laboratory has identified
frogs,
turtles and
snakes as the animal in the
bird strike, and on one occasion even a cat at high altitude, and at another occasion a
rabbit at an altitude of 550 metres . It is suspected that
birds of prey may carry their prey in the air, but there are also
meteorological explanations, see
raining animals for details.
Or in the rabbit case, it could be that a bird of prey fed from a dead rabbit, and then flew and was hit by a plane, and the
snarge sample recovered happened to be derived from the bird's
stomach contents.
Countermeasures
There are three basic approaches to reduce the effect of bird strikes. The vehicles can be designed to be more
bird resistant, the birds can be moved out of the way of the vehicle, or the vehicle can be moved out of the way of the birds.
Vehicle design
Most large commercial jet engines include design features that ensure they can safely shut-down after "ingesting" a bird of weighing up to 1.8 kg . Multiple or large strikes require emergency action to control damage. This limit is also applied to the rest of a modern commercial aircraft—it must be able to safely land after taking a 1.8 kg strike.
At first bird strike testing by manufacturers involved firing a bird carcass from a gas cannon and
sabot system into the tested unit. The carcass was soon replaced with suitable density blocks, often gelatin, to ease testing. Currently testing is mainly conducted with computer simulation, although final testing usually involves some physical experiments. See birdstrike simulator for details.
Bird management
To reduce birdstrikes on takeoff and landing,
airports invest in bird management and control. This includes changes to
terrain around the airport to reduce its attractiveness as a habitat to birds. Things attractive to birds like
landfill sites,
water areas, and
trees are removed to reduce the bird population around airports.
Other approaches try to scare away the birds using frightening devices, for example sounds, lights,
pyrotechnics,
radio-controlled airplanes, decoy animals/corpses, lasers, etc. Another alternative is bird capture and relocation.
Falcons are also sometimes used to cut down the bird population, as for example on
John F. Kennedy International Airport. An airport in
New Zealand uses electrified mats to reduce the number of worms that attracted large numbers of sea gulls.
Flight path
Pilots use awareness of bird habits and should avoid migratory routes , wildlife reserves, estuaries and other sites where birds may congregate. The US Military Aviation Hazard Advisory System uses a Bird Avoidance Model based on data from the Smithsonian Institution, historical patterns of bird strikes and radar tracking of bird activity.
Incidents
The
Federal Aviation Administration estimates the problem cost US aviation 600 million
dollars annually and has resulted in 195 worldwide deaths since 1988. Estimating that 80% of bird strikes are unreported, there were 4,300 bird strikes listed by the
United States Air Force and 5,900 by US civil aircraft in 2003.
The first reported bird strike was by
Orville Wright in 1905, and according to their diaries
Orville … flew 4,751 meters in 4 minutes 45 seconds, four complete circles. Twice passed over fence into Beard's cornfield. Chased flock of birds for two rounds and killed one which fell on top of the upper surface and after a time fell off when swinging a sharp curve.The first recorded bird strike fatality was reported in 1912 when aero-pioneer Cal Rodgers collided with a gull which became jammed in his aircraft controls. He crashed at
Long Beach, California, was pinned under the wreckage and drowned.
The greatest loss of life directly linked to a bird strike was on October 4, 1960 when an
Eastern Air Lines Lockheed L-188 Electra flying from Boston flew through a flock of
common starlings during take off, damaging all four engines. The plane crashed shortly after take-off into
Boston harbor, with 62 fatalities. Subsequently, minimum bird ingestion standards for jet engines were developed by the FAA.
The
Space Shuttle Discovery also hit a bird during take-off on July 26 2005, although the collision occurred early during take off and at low speeds, with no obvious damage to the shuttle, although it is not clear if the bird survived.
Urban legend
An urban legend story related to bird strikes is frequently found on the Internet. Birdstrike simulators are currently used by aircraft manufacturers and/or aviation authorities to test aircraft against birdstrikes, and usually work by firing a
chicken at the aircraft. According to the stories,
British Rail borrows this device to test the strength of the windshields on their high speed trains. On impact, the chicken shatters the windshield, breaks the operators chair, and comes to rest embedded in the engine. British Rail asks the FAA for help, and receives a one-sentence reply:
Thaw the chicken.
This urban legend was tested in two separate episodes of the television show
MythBusters is an American [i] pop science [i] television program [i] ...
. On their first try , the Mythbusters obtained a salvaged cockpit from a light aircraft, and several windshields. Upon testing, both the thawed and the frozen chickens caused nearly the same amount of damage, shattering the windshields. However, they later found out that the windshields they used were not rated for bird strikes. Revisiting the myth , they built a wooden box to hold 12 layers of window glass, and through subsequent tests, found that a frozen chicken did penetrate through more panes of glass than a thawed chicken.
In popular culture
- In the film Indiana Jones and the Last Crusade, the title character's father downs an attacking aircraft by scaring a flock of birds into its flightpath with his umbrella.
- Among Japanese aviation engineers and pilots, birds sucked into a jet engine are referred as yakitori after the popular dish.
See also
- Birdstrike simulator
- Foreign object damage
External links
