Aircraft hijacking (also known as skyjacking and aircraft piracy) is the take-over of an aircraft, by a person or group, usually armed. In most cases the pilot is forced to fly according to the orders of the hijackers.
Alternatively one of the hijackers flies the plane himself. The latter was the case in the September 11, 2001 attacks on the World Trade Center; hijackers took flying lessons as preparation, or were selected by Al-Qaeda based partly on flying skills.
In one case the official pilot hijacked the plane: in October, 1998, on an Air China flight from Beijing to Kunming in Yunnan, he flew to Taiwan after threatening to crash the plane killing the passengers if the other members of the crew prevented him from flying to Taiwan.
Unlike the hijacking of land vehicles or ships, skyjacking is usually not perpetrated in order to rob the cargo. Rather, most aircraft hijackings are committed to use the passengers as hostages in an effort to obtain transportation to a given location, to hold them for ransom, or, as in the case of the American planes that were hijacked to Cuba during the 1960s and 70s, the release of comrades being held in prison. Another common motive is publicity for some cause or grievance. Since the use of hijacked planes as suicide missiles in September 11, 2001 attacks, hijacking is a different kind of security threat — though similar usages had apparently been attempted by Samuel Byck in 1974 and on Air France Flight 8969 in 1994.
Hijackings for hostages have usually followed a pattern of negotiations between the hijackers and the authorities, followed by some form of settlement -- not always the meeting of the hijackers' original demands -- or the storming of the aircraft by armed police or special forces to rescue the hostages. Prior to September, 2001, the policy of most airlines was for the pilot to comply with hijackers' demands in the hope of a peaceful outcome. Since then, policies have reversed course, in favor of arming and armoring the cockpit.
Options for preventing hijacking include screening to keep weapons off the airplane, putting air marshals on the flight, and fortifying the cockpit to keep hijackers out.
