A bird strike (sometimes called birdstrike, bird ingestion (for an engine), bird hit, or bird aircraft strike hazard (BASH)) is a collision between a flying animal (usually a bird, occasionally bat) and a moving vehicle (typically an aircraft, occasionally high-speed train or automobile). The term is also used for bird deaths resulting from collisions with high-rise buildings, towers (see bird–skyscraper collisions and towerkill) and tall structures such as overhead power lines and wind turbines.
A significant threat to aviation safety, bird strikes have caused a number of accidents with human casualties. Nevertheless, the number of major accidents involving civil aircraft is quite low, and the majority of bird strikes cause little damage to the aircraft despite usually being fatal to the bird(s) involved. Efforts have been made to mitigate both the risk and severity of bird strike incidents.
Factors affecting probability Bird strikes are more likely to occur at low altitudes. Strikes have been reported to occur most during the takeoff, climb, approach, and landing phases of flight. Many aircraft fly above the altitudes than birds typically fly, reducing risk of strike at higher altitudes. However, bird strikes have still been reported at high altitudes, some as high as above the ground. For instance, an aircraft over the Ivory Coast collided with a Rüppell's vulture at the altitude of , the current record avian height.Thomas Alerstam, David A. Christie, Astrid Ulfstrand. Bird Migration (1990). Page 276.
Higher bird activity during certain seasons leads to more bird strikes. During winter, fewer bird strikes are recorded, whereas young birds fledging from nests in the summer and bird migration in spring and autumn leads to higher bird strike rates. The largest numbers of strikes happen during the spring and fall migrations. Bird strikes above altitude are about 7 times more common at night than during the day during the bird migration season.
Location affects bird strike probability since different bird species with distinct builds and behaviors reside in different locations. At airports, the presence of food, water and shelter increase bird strike probability. In general, a higher local density of birds near an airport will result in an increased strike rate.
The characteristics of an aircraft also affect the probability of a bird strike occurring. Turbofan engines, which the majority of commercial aircraft use, are more likely to ingest birds during a bird strike due to their large size and suction effect. An aircraft that is quieter is also more difficult for birds detect quickly enough to divert their flight path and successfully avoid collision.
Factors affecting severity
The majority of bird strikes do not cause actual damage to the aircraft. According to the FAA, only 15% of strikes (ICAO 11%) actually result in damage to the aircraft. For the strikes that do cause aircraft damage, the severity of the damage depends on the aircraft's velocity, the part of the aircraft that is struck, and the number and size of the bird(s) involved in the strike.
The aircraft's velocity and the total mass of the bird(s) involved in the strike contribute to the kinetic energy of the collision, which affects the severity of the strike. A higher aircraft velocity and larger total mass of the bird(s) involved in the strike leads to a higher collision kinetic energy, which increases the likelihood that the bird strike will result in aircraft damage. Because of this, it is more likely for bird strikes to cause damage at higher altitudes where the aircraft's velocity is higher and where larger birds fly.
The majority of bird strikes hit the front of the aircraft. The severity of the bird strike is typically much higher when the strike hits the engine(s), as this can lead to ingestion of the bird(s) into the engine and subsequent loss of engine power. Additionally, aircraft with two engines instead of three or four engines, which include the majority of the world's aircraft, are more susceptible to severe danger from ingestion since there is less redundancy. Reporting and statistics The International Civil Aviation Organization (ICAO) Bird Strike Information System (IBIS) collects data on wildlife strikes globally, with 214,734 reports from 156 states being included in the 2022 to 2024 analysis. However, globally, about 50% of all bird strikes still go unreported. Reporting for bird strikes is mandatory in some countries, such as in Australia and within the European Union, and is primarily voluntary in other countries, such as in the United States. Though it is a conservative estimate to account for incomplete reporting, bird strikes are estimated to cost at least $1 billion in damage annually to commercial aircraft worldwide.
United States airport statistics Aggregated records from the FAA National Wildlife Strike Database for civil aircraft in the United States show that some airports account for a disproportionate share of strikes that result in aircraft damage. In an open multi-decade aggregate of those reports, Sacramento International Airport () ranked first among US airports by count of damaging wildlife strikes ( reported damaging strikes in the published freeze), with Salt Lake City International Airport () among the next highest (). Rankings depend on reporting practices and traffic volume; the FAA has long noted that wildlife-strike reporting in the United States is largely voluntary for civil operators. The species struck most often are not the ones most likely to cause damage: in the same aggregate, perching songbirds account for about 41% of identified strikes but damage aircraft in about 1.5% of reports, whereas deer account for under 1% of strikes yet damage aircraft in about 82% of reported cases. These are rates per reported strike rather than per flight hour, so each is conditional on a report having been filed.
Species Following a strike, 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 infection (zoonoses).
Most bird strikes involve 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 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 mainly from waterfowl (30%), gulls (22%), raptors (20%), and pigeons and doves (7%). The Smithsonian Institution's Feather Identification Laboratory has identified turkey vultures as the most damaging birds, followed by Canada geese and white pelicans, all of which are very large birds. In terms of frequency, the laboratory most commonly finds mourning doves and horned larks involved in the strike.
Vultures and geese have been ranked the second and third most hazardous kinds of wildlife to aircraft in the United States, after deer (which encroach runways and collide with aircraft taking off and landing), with approximately 240 goose–aircraft collisions in the United States each year. Vehicular collisions were one of the primary contributors to the near–extinction of the California Condor and remains a threat to the species following its reintroduction into the wild.
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 in turn attract owls, which then become another birdstrike hazard.Television program "Stansted: the Inside Story", 6 to 7 pm, Sunday 6 March 2011, Fiver (TV channel)
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.
Vehicle design Most large commercial jet engines include design features that ensure they can shut down after ingesting a bird weighing up to . The engine does not have to survive the ingestion, just be safely shut down. This is a standalone requirement, meaning the engine alone, not the aircraft, must pass the test. Multiple strikes (such as from hitting a flock of birds) on twin-engine jet aircraft are very serious events because they can disable multiple aircraft systems. Emergency action may be required to land the aircraft, as in the January 15, 2009 forced ditching of US Airways Flight 1549.
As required by the European Aviation Safety Agency (EASA)'s CS 25.631 or the Federal Aviation Administration (FAA)'s 14 CFR § 25.571(e)(1) post Amdt 25-96, modern jet aircraft structures are designed for continued safe flight and landing after withstanding one bird impact anywhere on the aircraft (including the flight deck windshields). Per the FAA's 14 CFR § 25.631, they must also withstand one bird impact anywhere on the empennage. Flight deck windows on jet aircraft must be able to withstand one bird collision without yielding or spalling. For the empennage, this is usually accomplished by designing redundant structures and protected locations for control system elements or protective devices such as splitter plates or energy-absorbing material. Often, one aircraft manufacturer will use similar protective design features for all of its aircraft models, to minimize testing and certification costs. Transport Canada also pays particular attention to these requirements during aircraft certification, considering there are many documented cases in North America of bird strikes with large Canada geese which weigh approximately on average, and can sometimes weigh as much as .
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. Current certification efforts are mainly conducted with limited testing, supported by more detailed analysis using computer simulation,V. Bheemreddy et al., "Study of Bird Strikes Using Smooth Particle Hydrodynamics and Stochastic Parametric Evaluation," Journal of Aircraft, Vol. 49, pp. 1513–1520, 2012. although final testing usually involves some physical experiments (see birdstrike simulator).
Based on US National Transportation Safety Board recommendations following US Airways Flight 1549 in 2009, EASA proposed in 2017 that engines should also be capable of sustaining a bird strike in descent. During descent, turbofans turn more slowly than during takeoff and climb. This proposal was echoed a year later by the FAA; new regulations could apply for the Boeing NMA engines.
Wildlife management
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 Non-lethal management can be further broken down into habitat manipulation, exclusion, visual, auditory, tactile, or chemical repellents, and relocation.
Habitat manipulation