BASH (Bird Aircraft Strike Hazard)
A bird strike, bird hit, or BASH (Bird Aircraft Strike Hazard) is a collision between a bird and an aircraft. It is a common threat to flight safety, and has caused a number of accidents with human casualties.
Major accidents involving civil aircraft are quite low and it has been estimated that there is only about 1 accident resulting in human death in one billion flying hours.
The majority of bird strikes cause little damage to the aircraft but result in a great number of bird fatalities. 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.
The most spectacular recent bird strike was the U.S. Air crash in New York’s Hudson River earlier this year. Fortunately, there were no fatalities.
Bird strikes happen most often during takeoff or landing of a commercial aircraft, or during low altitude flight. However, bird strikes have also been reported at high altitudes, some as high as 19,685ft to 29,528ft above the ground. Bar-headed geese have been seen flying as high as 33,383ft above sea level.
An aircraft over a country in Africa collided with a vulture at the astonishing altitude of 37,073ft. The majority of bird collisions occur near or on airports during takeoff or landing. 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 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.
The Israeli Air Force has a larger than usual bird strike risk because Israel is on a major spring and autumn long-distance bird migration route.
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 because it is located along 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 other parts of the world, large birds of prey such as Gyps vultures and Milvus kites are often involved.
The largest numbers of strikes happen during the spring and fall migrations. Bird strikes above 500 feet altitude are about 7 times more common at night than during the day during the bird migration season.
There are three approaches to reduce the effect of bird strikes. Aircraft 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.
This is an ongoing problem between man vs. nature - a serious safety and financial problem for commercial aviation and there does not appear to be an immediate solution in sight.