A bird strike—sometimes called birdstrike, avian ingestion (only if in an engine), bird hit, or BASH (for Bird Aircraft Strike Hazard)—is a collision between an airborne animal (usually a bird or bat) and a human-made vehicle, especially aircraft. The term is also used for bird deaths resulting from collisions with human-made structures such as power lines, towers and wind turbines (see Bird-skyscraper collisions and Towerkill). A bug strike is an impairment of an aircraft or aviator by an airborne insect.
Bird strikes are a significant threat to flight safety, and have caused a number of accidents with human casualties. The number of major accidents involving civil aircraft is quite low and it has been estimated that there is only about 1 accident resulting in human death in one billion (109) flying hours. The majority of bird strikes (65%) cause little damage to the aircraft; however the collision is usually fatal to the bird(s) involved.
Most accidents occur when the bird hits the windscreen or flies into the engines. These cause annual damages that have been estimated at $400 million within the United States of America alone and up to $1.2 billion to commercial aircraft worldwide.
- 1 Event description
- 2 Species
- 3 Countermeasures
- 4 Incidents
- 5 Bug strike
- 6 See also
- 7 References
- 8 External links
Bird strikes happen most often during takeoff or landing, or during low altitude flight. However, bird strikes have also been reported at high altitudes, some as high as 6,000 m (20,000 ft) to 9,000 m (30,000 ft) above the ground. Bar-headed geese have been seen flying as high as 10,175 m (33,383 ft) above sea level. An aircraft over the Ivory Coast collided with a Rüppell's Vulture at the astonishing altitude of 11,300 m (37,100 ft), the current record avian height. 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 m (3,000 ft) and 61% occur at less than 30 m (100 ft).
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 and the plane is at a low altitude where birds are more commonly found.
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. The energy of a 5 kg (11 lb) bird moving at a relative velocity of 275 km/h (171 mph) approximately equals the energy of a 100 kg (220 lb) weight dropped from a height of 15 metres (49 ft). However, according to the FAA only 15% of strikes (ICAO 11%) actually result in damage to the aircraft.
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 thus crash, as in the case of US Airways Flight 1549.
Remains of the bird, termed snarge, are sent to identification centers where forensic techniques may be used to identify the species involved. These samples need to be taken carefully by trained personnel to ensure proper analysis and reduce the risks of zoonoses.
Sacramento International Airport has had more bird strikes (1,300 collisions between birds and jets between 1990 and 2007, causing an estimated $1.6 million in damage) than any other California airport. Sacramento International Airport has the most bird strikes of any airport in the west and sixth among airports in the US, according to the FAA, as it is located along the Pacific Flyway, a major bird migration path.
The animals most frequently involved in bird strikes are large birds with big populations, particularly geese and gulls in the United States. In parts of the US, Canada Geese and migratory Snow Geese populations have risen significantly while feral Canada Geese and Greylag Geese have increased in parts of Europe increasing the risk of these large birds to aircraft. In other parts of the world, large birds of prey such as Gyps vultures and Milvus kites are often involved. 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. Bird strikes above 500 feet (150 m) altitude are about 7 times more common at night than during the day during the bird migration season.
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.
An animal hazard reported from London Stansted Airport in England is rabbits: they get run over by ground vehicles and planes, and they pass large amounts of droppings, which attract mice, which attract owls, which become another birdstrike hazard.
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.
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, not the aircraft, must pass the test. Multiple strikes (from hitting a bird flock) on twin engine jet aircraft are very serious events because they can disable multiple aircraft systems, requiring emergency action to land the aircraft, as in the January 15, 2009, forced ditching of US Airways Flight 1549.
Modern jet aircraft structures must be able to withstand one 1.8 kg (4 lb) collision; the empennage (tail) must withstand one 3.6 kg (8 lb) bird collision. Cockpit windows on jet aircraft must be able to withstand one 1.8 kg (4 lb) bird collision without yielding or spalling.
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).
Many jet engine manufacturers include white spirals in the centre of their engines. While on the ground this serves as an indicator to crew that the engine is running, in the air it appears as a white circle which discourages birds from flying into the engine.
Though there are many methods available to wildlife managers at airports, no single method will work in all instances and with all species. Wildlife management in the airport environment can be grouped into two broad categories: non-lethal and lethal. Integration of multiple non-lethal methods with lethal methods results in the most effective airfield wildlife management strategy.
Non-lethal management can be further broken down into habitat manipulation, exclusion, visual, auditory, tactile, or chemical repellents, and relocation.
One of the primary reasons that wildlife is seen on airports is an abundance of food. Food resources on airports can be either removed or made less desirable. One of the most abundant food resources found on airports is turfgrass. This grass is planted to reduce runoff, control erosion, absorb jet wash, allow passage of emergency vehicles, and to be aesthetically pleasing (DeVault et al. 2013) However, turfgrass is a preferred food source for species of birds that pose serious risk to aircraft, chiefly the Canada goose (Branta canadensis). Turfgrass planted at airports should be a species that geese do not prefer (e.g. St. Augustinegrass) and should be managed in such a way that reduces its attractiveness to other wildlife such as small rodents and raptors (Commander, Naval Installations Command 2010, DeVault et al. 2013). It has been recommended that turfgrass be maintained at a height of 7-14 inches through regular mowing and fertilization (U.S. Air Force 2004).
Wetlands are another major attractant of wildlife in the airport environment. They are of particular concern because they attract waterfowl which have a high potential to damage aircraft (Federal Aviation Administration 2013). With large areas of impervious surfaces, airports must employ methods to collect runoff and reduce its flow velocity. These best management practices often involve temporarily ponding runoff. Short of redesigning existing runoff control systems to include non-accessible water such as subsurface flow wetlands (DeVault et al. 2013), frequent drawdowns and covering of exposed water with floating covers and wire grids should be employed (International Civil Aviation Organization 1991). The implementation of covers and wire grids must not hinder emergency services.
Though excluding birds from the entire airport environment is virtually impossible, it is possible to exclude deer and other mammals that constitute a small percentage of wildlife strikes. Three meter high fences made of chain link or woven wire, with barbed wire outriggers, are the most effective. When used as a perimeter fence, these fences also serve to keep unauthorized persons off of the airport (Seamans 2001). Realistically every fence must have gates. Gates that are left open allow deer and other mammals onto the airport. 4.6 meter long cattle guards have been shown to be effective at deterring deer up to 98% of the time (Belant et al. 1998).
Hangars with open superstructures often attract birds to nest and roost in. Hangar doors are often left open to increase ventilation especially in the evenings. Birds in hangars are in close proximity to the airfield and their droppings are both a health and damage concern. Netting is often deployed across the superstructure of a hangar denying access to the rafters where the birds roost and nest while still allowing the hangar doors to remain open for ventilation and aircraft movements. Strip curtains and door netting may also be used but are subject to improper use (e.g. tying the strips to the side of the door) by the personnel in the hangar concern (U.S. Air Force 2004, Commander, Naval Installations Command 2010).
There have been a variety of visual repellent and harassment techniques used in airport wildlife management. They include using birds of prey and dogs, effigies, and lasers. Birds of prey have been used with great effectiveness at landfills were there were large populations of feeding gulls (Cook et al. 2008). Dogs have also been used with success as visual deterrents and means of harassment for birds at airfields (DeVault et al. 2013). However airport wildlife managers must consider the risk of knowingly releasing animals in the airport environment. Both birds of prey and dogs must be monitored by a handler when deployed and must be cared for, when not deployed. Airport wildlife managers must consider the economics of these methods (Seamans 2001).
Effigies of both predators and conspecifics have been used with success to disperse gulls and vultures. The effigies of conspecifics are often placed in unnatural positions where they can freely move with the wind. Effigies have been found to be the most effective in situations where the nuisance birds have other options (e.g. other forage, loafing, and roosting areas) available. Time to habituation varies. (Seamans et al. 2007, DeVault et al. 2013).
Lasers have been used with success to disperse several species of birds. However, lasers are species specific as certain species will only react to certain wavelengths. Lasers become more effective as ambient light levels decrease, thereby limiting effectiveness during daylight hours. Some species show a very short time to habituation (Airport Cooperative Research Program, 2011). The risks of lasers to aircrews must be evaluated when determining whether or not to deploy lasers on airfields (Federal Aviation Administration 2012).
Auditory repellents are commonly used in both agricultural and aviation contexts. Devices such as propane exploders (cannons), pyrotechnics, and bioacoustics are frequently deployed on airports. Propane exploders are capable of creating noises of approximately 130 decibels (Wildlife Control Supplies). They can be programmed to fire at designated intervals, can be remote controlled, or motion activated. Due to their stationary and often predictable nature, wildlife quickly become habituated to propane cannons. Lethal control may be used to extend the effectiveness of propane exploders (Washburn et al. 2006).
Pyrotechnics utilizing either an exploding shell or a screamer can effectively scare birds away from runways. They are commonly launched from a 12 gauge shotgun or a flare pistol, and as such, can be aimed allowing control personnel to “steer” the species that is being harassed. Birds show varying degrees of habituation to pyrotechnics. Studies have shown that lethal reinforcement of pyrotechnic harassment has extended its usefulness (Baxter and Allen 2008). Screamer type cartridges are still intact at the end of their flight (as opposed to exploding shells that destroy themselves) constituting a foreign object damage hazard and must be picked up. The use of pyrotechnics is considered “take” by the U.S. Fish and Wildlife Service (USFWS) and USFWS must be consulted if federally threatened or endangered species could be affected. Pyrotechnics are a potential fire hazard and must be deployed judiciously in dry conditions (Commander, Naval Installations Command, 2010, Airport Cooperative Research Program 2011).
Bioacoustics, or the playing of conspecific distress or predator calls to frighten animals, is widely used. This method relies on the animal’s evolutionary danger response (Airport Cooperative Research Program 2011).However, bioacoustics are species specific and birds may quickly become habituated to them and they should not be used as a primary means of control (U.S. Air Force 2004, Commander, Naval Installations Command 2010).
Sharpened spikes to deter perching and loafing are commonly used. Generally, large birds require different applications than small birds do (DeVault et al. 2013).
There are only two chemical bird repellents registered for use in the United States. They are methyl anthranilate and anthraquinone. Methyl anthranilate is a primary repellent that produces an immediate unpleasant sensation that is reflexive and does not have to be learned. As such it is most effective for transient populations of birds (DeVault et al. 2013). Methyl anthranilate has been used with great success at rapidly dispersing birds from flightlines at Homestead Air Reserve Station (Engeman et al. 2002). Anthraquinone is a secondary repellent that has a laxative effect that is not instantaneous. Because of this it is most effective on resident populations of wildlife that will have time to learn an aversive response (Izhaki 2002, DeVault et al. 2013).
Relocation of raptors from airports is often considered preferable to lethal control methods by both biologists and the public. There are complex legal issues surrounding the capture and relocation of species protected by the Migratory Bird Treaty Act of 1918 and the Bald and Golden Eagle Protection Act of 1940. Prior to capture, proper permits must be obtained and the high mortality rates as well as the risk of disease transmission associated with relocation must be weighed. Between 2008 and 2010, U.S. Department of Agriculture Wildlife Services personnel relocated 606 red-tailed hawks from airports in the United States after the failure of multiple harassment attempts. The return rate of these hawks was 6%, however the relocation mortality rate for these hawks was never determined(DeVault et al. 2013).
Lethal wildlife control on airports falls into two categories: reinforcement other non-lethal methods and population control.
The premise of effigies, pyrotechnics, and propane exploders is that there a perceived immediate danger to the species to be dispersed. Initially, the sight of an unnaturally positioned effigy or the sound of pyrotechnics or exploders is enough to elicit a danger response from wildlife. As wildlife become habituated to non-lethal methods the culling of small numbers of wildlife in the presence of conspecifics can restore the danger response (Baxter and Allan 2008, Cook et al. 2008, Commander, Naval Installations Command 2010, DeVault et al. 2013).
Under certain circumstances lethal wildlife control is needed to control the population of a species. This control can be localized or regional. Localized population control is often used to control species that are residents of the airfield such as deer that have bypassed the perimeter fence. In this instance sharpshooting would be highly effective, such as is seen at Chicago O’Hare International Airport (DeVault et al. 2013).
Regional population control has been used on species that cannot be excluded from the airport environment. A nesting colony of laughing gulls at Jamaica Bay Wildlife Refuge contributed to 98-315 bird strikes per year, from 1979-1992, at adjacent John F. Kennedy International Airport (JFK). Though JFK had an active bird management program that precluded birds from feeding and loafing on the airport, it did not stop them from overflying the airport to other feeding sites. U.S. Department of Agriculture Wildlife Services personnel began shooting all gulls that flew over the airport, hypothesizing that eventually the gulls would alter their flight patterns. They shot 28,352 gulls in two years (approximately half of the population at Jamaica Bay and 5-6% of the nationwide population per year). Strikes with laughing gulls decreased by 89% by 1992. However this was more a function of the population reduction than the gulls altering their flight pattern (Dolbeer et al. 1993, Dolbeer et al. 2003, DeVault et al. 2013).
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 and should avoid migratory routes, 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 (910 m) as rapidly as possible as most birdstrikes occur below 3,000 feet (910 m). 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 () of the bird, defined by the equation where is the mass and is the relative velocity (the difference of the velocities of the bird and the plane if they are flying in the same direction and the sum if they are flying towards each other). 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 body density of the bird is also a parameter that influences the amount of damage caused.
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. 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.
The Federal Aviation Administration (FAA) estimates the problem costs US aviation 400 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; according to the Wright Brothers' 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.
In 1911 French pilot Eugene Gilbert encountered an angry mother eagle over the Pyrenees Mountains en route from Paris to Madrid during the great aviation race held that year between those two cities. Gilbert, flying an open-cockpit Bleriot XI, was able to ward off the large bird by firing pistol shots at it but not killing it.
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 control cables. 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 aircraft crashed into Boston harbor shortly after take-off, with 62 fatalities out of 72 passengers. Subsequently, minimum bird ingestion standards for jet engines were developed by the FAA.
NASA astronaut Theodore Freeman was killed when a goose shattered the plexiglass cockpit canopy of his Northrop T-38 Talon, resulting in shards being ingested by the engines, leading to a fatal crash.
In 1995, a Dassault Falcon 20 crashed at a Paris airport during an emergency landing attempt after sucking lapwings into an engine, which caused an engine failure and a fire in the airplane's fuselage; all 10 people on board were killed.
On September 22, 1995, a U.S. Air Force Boeing E-3 Sentry AWACS aircraft (Callsign Yukla 27, serial number 77-0354), crashed shortly after take off from Elmendorf AFB. The aircraft lost power in both port side engines after these engines ingested several Canada Geese during takeoff. It crashed about two miles (3 km) from the runway, killing all 24 crew members on board.
On November 28, 2004, the nose landing gear of KLM Flight 1673, a Boeing 737-400, struck a bird during takeoff at Amsterdam Airport Schiphol. The incident was reported to air traffic control, the landing gear was raised normally and the flight continued normally to its destination. Upon touching down at Barcelona International Airport, the aircraft started deviating to the left of the runway centreline. The crew applied right rudder, braking and the nose wheel steering tiller but could not keep the aircraft on the runway. After it veered off the paved surface of the runway at about 100 knots, the jet went through an area of soft sand. The nose landing gear leg collapsed and the left main landing gear leg detached from its fittings shortly before the aircraft came to a stop perched over the edge of a drainage canal. All 140 passengers and six crew evacuated safely, but the aircraft itself had to be written off. The cause was discovered to be a broken cable in the nose wheel steering system caused by the bird collision. Contributing to the snapped cable was the improper application of grease during routine maintenance which led to severe wear of the cable.
In April 2007, a Thomsonfly Boeing 757 from Manchester Airport to Lanzarote Airport 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 two plane spotters on opposite sides of the airport, as well as the emergency calls picked up by a plane spotter's radio.
The Space Shuttle Discovery also hit a bird (a vulture) during the launch of STS-114 on July 26, 2005, although the collision occurred soon after lift-off and at low speed, with no obvious damage to the shuttle.
On November 10, 2008, Ryanair Flight 4102 from Frankfurt to Rome made an emergency landing at Ciampino Airport after multiple bird strikes caused both engines to fail. After touchdown, the left main landing gear collapsed, and the aircraft briefly veered off the runway. Passengers and crew were evacuated through the starboard emergency exits.
On January 4, 2009, a Sikorsky S-76 helicopter hit a Red-tailed Hawk in Louisiana. The hawk hit the helicopter just above the windscreen. The impact forced the activation of the engine fire suppression control handles, retarding the throttles and causing the engines to lose power. Eight of the nine persons on board died in the subsequent crash; the survivor, a passenger, was seriously injured.
On January 15, 2009, US Airways Flight 1549 from LaGuardia Airport to Charlotte/Douglas International Airport ditched into the Hudson River after experiencing a loss of both turbines. It is suspected that the engine failure was caused by running into a flock of geese at an altitude of about 975 m (3,200 feet), shortly after takeoff. All 150 passengers and 5 crew members were safely evacuated after a successful water landing. On May 28, 2010, the NTSB published its final report into the accident.
Flying insect strikes, like bird strikes, have been encountered by pilots since aircraft were invented. Future United States Air Force general Henry H. Arnold nearly lost control of his Wright Model B in 1911 after a bug flew into his eye while he was not wearing goggles, distracting him.
In 1986 a Boeing B-52 Stratofortress on a low-level training mission entered a swarm of locusts. The insects' impacts on the aircraft's windscreens rendered the crew unable to see, forcing them to abort the mission and fly using the aircraft's instruments alone. The aircraft eventually landed safely. In 2010 the Australian Civil Aviation Safety Authority (CASA) issued a warning to pilots about the potential dangers of flying through a locust swarm. CASA warned that the insects could cause loss of engine power and loss of visibility; and blocking of an aircraft's pitot tubes, causing inaccurate airspeed readings.
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- US Airways Plane Crashes Into Hudson River
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|Wikimedia Commons has media related to Bird strike.|
- A photo gallery of the bird strike conseguence between aircraft and birds
- International Bird Strike Committee
- Bird Strike Committee Canada
- BSC USA
- Aviation Hazard Advisory System
- Australian Aviation Wildlife Hazard Group
- The FlySafe Bird Avoidance Model (FlySafe-BAM)
- List of significant bird strikes