hi·jack /'hī-ˌjak/ vt: to seize possession or control of (a vehicle) from another person by force or threat of force; specif: to seize possession or control of (an aircraft) esp. by forcing the pilot to divert the aircraft to another destination
hijack n
hi·jack·er n

Merriam-Webster’s Dictionary of Law. . 1996.

verb abduct, appropriate, arrogate, assume command, bear away, capture, carry away, carry off, commandeer, convey away, dispossess, expropriate, force, help oneself to, impress, intercept, lay hold of, make off with, make prisoner, overcome, overpower, overwhelm, pirate, plunder, secure, seize, snatch, take, take away, take by assault, take by force, take captive, take prisoner associated concepts: air piracy

Burton's Legal Thesaurus. . 2006

To commandeer a vehicle such as an airplane, bus, or ship, while in transit, in order to take it to a different destination, to steal its cargo, or to take hostages.

The Essential Law Dictionary. — Sphinx Publishing, An imprint of Sourcebooks, Inc. . 2008.

v. To take over control of a vehicle or airplane by use of the threat of force.

Webster's New World Law Dictionary. . 2000.