Bird strike
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A bird strike (sometimes birdstrike, bird hit, or BASH (Bird Aircraft Strike Hazard)) in aviation is a collision between an airborne animal (usually a bird) and a man-made vehicle, especially aircraft. It is a common threat to aircraft safety, and has caused a number of fatal accidents.
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[edit] Event description
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, some as high as 6000 to 9000 meters above ground level. The majority of bird collisions occur near or on airports (90%, according to the ICAO) during takeoff, landing and associated phases. According to the FAA wildlife hazard management manual for 2005, less than 8% of strikes occur above 900 meters and 61% occur at less than 30 m (100 feet).
The point of impact is usually any forward-facing edge of the vehicle such as a wing leading edge, nose cone, jet engine cowling or engine inlet.
Jet engine ingestion is extremely serious due to the rotation speed of the engine fan and engine design. As the bird strikes a fan blade, that blade can be displaced into another blade and so forth, causing a cascading failure. Jet engines are particularly vulnerable during the takeoff phase when the engine is turning at a very high speed.
The force of the impact on an aircraft depends on the weight of the animal and the speed difference and direction at the impact. The energy of the impact increases with the square of the speed difference. Hence a low-speed impact of a small bird on a car windshield causes relatively little damage. High speed impacts, as with jet aircraft, can cause considerable damage and even catastrophic failure to the vehicle. However, according to the FAA only 15% of strikes (ICAO 11%) actually result in damage to the aircraft. The impact of a 5 kg (12 pound) bird at 240 km/h (150 mph) equals that of a 1/2 ton (1000 pound) weight dropped from a height of 3 meters (10 feet).
Bird strikes can damage vehicle components, or injure passengers. Flocks of birds are especially dangerous, and can lead to multiple strikes, and damage. 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 called snarge, are sent to the Smithsonian Institution's Feather Identification Laboratory to determine the species. [1] The Israeli Air Force has a larger than usual birdstrike risk as Israel is on a major spring and autumn long-distance bird migration route.
[edit] Species
The animals most frequently involved in bird strikes are large birds with big populations, particularly geese and gulls. In the US reported strikes are divided between waterfowl (32%), gulls (28%), and raptors (17%) (Data from the BSC USA). 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. 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.
[edit] Countermeasures
There are three 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.
[edit] Vehicle design
Most large commercial jet engines include design features that ensure they can shut-down after "ingesting" a bird weighing up to 1.8 kg (4 lb). The engine does not have to survive the ingestion, just be safely shut down. This is a 'stand alone' requirement, i.e., the engine must pass the test, not the aircraft. Multiple strikes on twin engine jet aircraft are very serious events, they can disable multiple aircraft systems, requiring emergency action to land the aircraft.
Modern jet aircraft structures must be able to withstand one four pound bird collision; the empennage (tail) must withstand one 8 pound bird collision. Cockpit windows on jet aircraft must be able to withstand one 4 pound bird collision without yielding or spawlding.
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.
[edit] Bird management
To reduce birdstrikes on takeoff and landing, airports engage in bird management and control. This includes changes to habitat around the airport to reduce its attractiveness to birds.[1] Vegetation which produces seeds, grasses which are favored by geese, manmade food, a favorite of gulls, all should be removed from the airport area. Trees and tall structures which serve as roosts at night for flocking birds or perches for raptors should be removed or modified to discourage bird use.[2]
Other approaches try to scare away the birds using frightening devices, for example sounds, lights, pyrotechnics, radio-controlled airplanes, decoy animals/corpses, lasers, dogs etc.[2]Firearms are also occasionally employed.
A successful approach has been the utilization of dogs, including German shepherds, English pointers and border collies, to scare away birds and wildlife.[citation needed] Another alternative is bird capture and relocation.
Falcons are sometimes used to harass the bird population, as for example on John F. Kennedy International Airport.[1] At Manchester Airport in England the usual type of falcon used for this is a peregrine falcon/lanner falcon hybrid, as its flight range covers the airport.
An airport in New Zealand uses electrified mats to reduce the number of worms that attracted large numbers of sea gulls.[1]
[edit] Flight path
Pilots have very little training in wildlife avoidance nor is training required by any regulatory agency. However, they should not takeoff or land in the presence of wildlife, avoid migratory routes [1], wildlife reserves, estuaries and other sites where birds may congregate. When operating in the presence of bird flocks, pilots should seek to climb above 3,000 feet as rapidly as possible as most birdstrikes occur below 3,000 feet. Additionally pilots should slow their aircraft when confronted with birds. The energy that must be dissipated in the collision is approximately the relative kinetic energy (Ek) of the bird, defined by the equation Ek = (1/2)mass X velocity2. Therefore the speed of the aircraft is much more important than the size of the bird when it comes to reducing energy transfer in a collision. The same can be said for jet engines: the slower the rotation of the engine, the less energy which will be imparted onto the engine at collision.
The US Military Aviation Hazard Advisory System uses a Bird Avoidance Model[3] based on data from the Smithsonian Institution, historical patterns of bird strikes and radar tracking of bird activity.[1] This model has been extremely successful. Prior to flight USAF pilots check for bird activity on their proposed low level route or bombing range. If bird activity is forecast to be high, the route is changed to one of lower threat. In the first year this BAM model was required as a preflight tool, the USAF Air Combat Command experienced a 70% drop in birdstrikes to its mission aircraft.
TNO a Dutch R&D Institute has developed the successful ROBIN (Radar Observation of Bird Intensity) for the Royal Netherlands Airforce. ROBIN is a near real-time monitoring system for flight movements of birds. ROBIN identifies flocks of birds within the signals of large radar systems. This information is used to give Air Force pilots warning during landing and take-off. Years of observation of bird migration with ROBIN have also provided a better insight into bird migration behaviour, which has had an influence on averting collisions with birds, and therefore on flight safety. Since the implementation of the ROBIN system at the Royal Netherlands Airforce the number of collisions between birds and aircraft in the vicinity of military airbases has decreased by more than 50%.
There are no civil aviation counterparts to the above military strategies. Some experimentation with small portable radar units has taken place at some airports. However, no standard has been adopted for radar warning nor has any governmental policy regarding warnings been implemented.
[edit] Incidents
The Federal Aviation Administration estimates the problem costs US aviation 600 million dollars annually and has resulted in over 200 worldwide deaths since 1988. In the United Kingdom the Central Science Laboratory estimates that, worldwide, the cost of birdstrikes to airlines is around US$1.2 billion annually. This cost includes direct repair cost and lost revenue opportunities while the damaged aircraft is out of service. 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 Eastern Air Lines Flight 375, a 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 the take-off of STS-114 on July 26, 2005, although the collision occurred early during take off and at low speeds, with no obvious damage to the shuttle. It is not clear if the bird survived.
NASA also lost an astronaut, Theodore Freeman, to a bird strike, he was killed when a goose shattered the plexiglass cockpit of his T-38, resulting in shards being ingested by the engines leading to a fatal crash.
Aircraft continue to be lost on a routine basis to birdstrikes. In the fall of 2006 the USAF lost a twin engine T-38 trainer to a bird strike (ducks) and in the October 2007 the US Navy lost a T-45 jet trainer in a collision with a bird.
In the summer of 2007 Delta Air Lines suffered an incident in Rome, Italy, as one of its B-767 aircraft, on takeoff, ingested yellow legged gulls into both engines. Although the aircraft returned to Rome safely, both engines were damaged and had to be changed. United Air Lines suffered a twin engine bird ingestion by a B-767 on departure from Chicago's O'Hare Field in the spring of 2007. One engine caught fire and bird remains were found in the other engine.
On April 29, 2007, a Thomsonfly Boeing 757 from Manchester Airport, UK to Lanzarote Airport, Spain suffered a bird strike when at least one bird, supposedly a heron, was ingested by the starboard engine. The plane landed safely back at Manchester Airport a while later. The incident was captured by a plane spotter, as well as the emergency call picked up by a plane spotter's radio. The video was later published. [2] [3].
[edit] In popular culture
- In the film Indiana Jones and the Last Crusade, while remembering a quotation by Charlemagne, Indy'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.[citation needed]
- In the film Thirteen Days, Navy pilot William Ecker called the obvious damages on his aircraft "bird strikes" after the first low-level reconnaissance flight over Cuba in order to avoid international conflict as he was fired upon.
- Comedian Eddie Izzard made reference to bird strike in his comedy performance Glorious, saying that it was less like 'bird strike' and more like 'engine suck'.
- In the OVA "Area 88", Invulnerable Charlie, while trying to down Shin Kazama, was killed when a seagull smashed into his F-16's canopy, causing him to lose control and crash into the water.
[edit] References
- ^ a b c d e Wired Magazine: Bird Plus Plane Equals Snarge
- ^ a b http://www.int-birdstrike.org/Standards_for_Aerodrome_bird_wildlife%20control.pdf
- ^ US Bird avoidance model
[edit] See also
[edit] External links
- International Bird Strike Committee
- Bird Strike Committee Canada
- BSC USA
- Birdstrike Control Program
- http://wildlife-mitigation.tc.faa.gov/public_html/index.html
- http://wildlife.pr.erau.edu/FAADatabase.htm
- Aviation Hazard Advisory System
- List of significant bird strikes
- ROBIN: Radar Observation of Bird Intensity
