A bird strike (sometimes called birdstrike, bird ingestion (for an engine), bird hit, or bird aircraft strike hazard (BASH)) is a collision between an airborne animal (usually a bird or bat) and a moving vehicle (usually an aircraft). The term is also used for bird deaths resulting from collisions with structures, such as power lines, towers and wind turbines (see bird–skyscraper collisions and towerkill).
A significant threat to flight safety, bird strikes have caused a number of accidents with human casualties. There are over 13,000 bird strikes annually in the US alone. However, the number of major accidents involving civil aircraft is quite low and it has been estimated that there is only about one 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.
The Canada goose has been ranked as the third most hazardous wildlife species to airborne and ground vehicles (behind deer and vultures), with approximately 240 goose–aircraft collisions in the United States each year. 80% of all bird strikes go unreported.
Most accidents occur when a bird (or birds) collides with the windscreen or is sucked into the engine of jet aircraft. These cause annual damages that have been estimated at $400 million within the United States alone and up to $1.2 billion to commercial aircraft worldwide. In addition to property damage, collisions between man-made structures and conveyances and birds is a contributing factor, among many others, to the worldwide decline of many avian species.
The International Civil Aviation Organization (ICAO) received 65,139 bird strike reports for 2011–14, and the Federal Aviation Administration counted 177,269 wildlife strike reports on civil aircraft between 1990 and 2015, growing 38% in seven years from 2009 to 2015. Birds accounted for 97%.
Event description
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 above the ground. Bar-headed geese have been seen flying as high as above sea level. An aircraft over the Ivory Coast collided with a Rüppell's vulture at the altitude of , the current record avian height. The majority of bird collisions occur near or at 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 and 61% occur at less than .
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 point of impact. The energy of the impact increases with the square of the speed difference. High-speed impacts, as with jet aircraft, can cause considerable damage and even catastrophic failure to the vehicle. The energy of a bird moving at a relative velocity of approximately equals the energy of a weight dropped from a height of . 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, with corresponding damage. Depending on the damage, aircraft at low altitudes or during take-off and landing often cannot recover in time. US Airways Flight 1549 is a classic example of this. The engines on the Airbus A320 used on that flight were torn apart by multiple bird strikes at low altitude. There was no time to make a safe landing at an airport, forcing a water landing in the Hudson River.
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).
