A US Airways flight leaving from LaGuardia crashed into the Hudson River Thursday afternoon after birds flew into one or both of the plane's engines. All 155 people on board were rescued.
What happens when a bird flies into a plane engine? Nothing, usually—most "bird strikes" don't damage an aircraft at all. (Airplane manufacturers use bird-strike simulators to make sure engines can withstand ingestion of an animal.) But even if a bird strike does disable a plane engine, that doesn't mean a crash is inevitable. Commercial planes are designed to fly with only one engine, and pilots are trained to fly them that way. If an engine fails, the pilot has to adjust the rudder on the plane's tail in a way that creates an opposing force in order to drive the nose toward the functioning engine. At the same time, the plane's ailerons—little flaps on each wing that control the plane's "roll"—adjust to compensate for the imbalance. In the past, pilots have had to make these adjustments manually, but newer aircraft do it automatically. (Watch a bird strike here.)
How often do bird strikes cause accidents? Rarely, but it happens. Between 1955 and 2007, there were 51 collisions with birds that resulted in commercial accidents, according to the Aviation Safety Network. Military losses are apparently larger: The International Bird Strike Committee estimates (PDF) that 283 military aircraft were lost due to bird strikes between 1959 and 1999. So-called "double birds"—moments when a pair of birds hits and disables both engines—are extremely rare. (Bird strikes cause an estimated $1.2 billion per year in damage, delays, and cancellations.)
Is there any way to reduce the number of bird strikes that occur? Yes. Airport personnel often use "gas cannons"—tubes filled with gas that make noise when hooked up to spark plugs—to keep birds and other animals like deer away. They also try to make the local environment unfriendly to wildlife by clearing trees and killing other nearby vegetation with herbicides. (That can be tricky, since airports are often zoned in areas with lots of wildlife.) Airports may also adjust their flight paths depending on migratory patterns.
How does a water landing work? The FAA has a list of recommendations when it comes to "water ditching," which is the formal term for a controlled emergency descent onto water. When approaching the water, the pilot should get a sense of how the swells are forming and try to land either parallel to the swells, on the top or back side of a swell. The landing gear should not be lowered, since the drag would create a more forceful landing than otherwise. If possible, the pilot should stall the aircraft just before landing to make it as smooth as possible. Another recommendation is to steer the plane into the wind in order to slow it down. (See a list of commercial water ditchings here.)
Is it better to crash on land or water? If given the choice, pilots should ditch on land. The reason is that at 200 miles an hour, the surface tension of the water will make it just as hard as asphalt—but survivors will be more difficult to rescue. Pilots are trained to look for the large, open areas with the fewest obstructions.
What are the odds of surviving a plane crash? Pretty good. Two-thirds of people involved in major crashes survive, according to the Flight Safety Foundation. The odds of being in a crash in the first place are, of course, extremely slim—an accident with fatalities occurs only once in every 16 million commercial airline flights.
Who rescues a downed aircraft? Anyone who can. The U.S. Coast Guard, the Civil Air Patrol, the Department of Defense, and state, county, and local law-enforcement agencies have a standing agreement to provide aircraft, vessels, and ground rescue teams for aircraft emergencies. The Coast Guard and Air Force usually coordinate the rescues from one of a dozen Rescue Coordination Centers around the country.
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Explainer thanks Alison Duquette of the Federal Aviation Administration and Bill Voss of the Flight Safety Foundation.