Aircraft hijacking is an illegal activity where people seize control of an airplane. It is usually considered an act of terrorism and carries stiff penalties under law. Also sometimes known as skyjacking, it poses a serious threat to the safety of people on board the aircraft, as well as people on the ground. The goal of aircraft hijacking is usually threat and intimidation, rather than theft of the airliner.
People can use several techniques to gain control of a plane. One involves incapacitating the crew and taking control of the aircraft. This requires the ability to pilot the plane, as well as overriding controls such as the autopilot. Other hijackers intimidate the crew with threats, forcing the pilot and cabin crew to obey them, or use bribery. Theoretically, it's also possible for a pilot to hijack her own plane, but this is extremely rare. The aircraft hijacking may be announced via the plane's radio, especially if the goal is to frighten people on the ground.
Hijackers often intend to use the passengers on the plane as hostages, threatening to kill them unless demands are met. The hijackers may demand money, safe passage to a country where they cannot be pursued, or other concessions in exchange for the safety of the passengers. In some cases, people have hijacked a plane with the primary goal of forcing the pilot to land in a different end destination in the hope of avoiding law enforcement or causing chaos. Other pilots have taken over planes with the intent to use the aircraft as weapons, as seen in the United States in 2001 when multiple hijackings and subsequent crashes of commercial airliners resulted in the deaths of thousands of people when the aircraft were flown into large office buildings in New York and Washington, DC, as well as into the ground in Pennsylvania
Airlines use a number of measures to reduce the threat of aircraft hijacking. Passengers are carefully evaluated at security checkpoints, and devices that could act as weapons are confiscated by security personnel. Some people are placed on no fly lists with the goal of keeping people known to be a security risk from boarding planes in the first place, although this can create the problem of accidentally flagging innocent people who happen to share a name with a suspected terrorist.
Safety measures in the sky are also used. Law enforcement officers like air marshals can be stationed randomly on planes to intervene if an aircraft hijacking occurs. The flight deck on commercial airliners is typically locked while the plane is in flight so potential hijackers cannot access the cockpit and threaten the flight crew. While it is possible to threaten passengers and cabin crew, the hijackers will not be able to take over the plane itself.