Hijacking is the unlawful seizure of a vehicle, plane, or boat, by force or threat. Recently, hijacking has become synonymous with skyjacking, and especially refers to those who skyjack to make a political point, to seek asylum, to gain revenge or the release of prisoners, or to obtain other concessions. The safety of persons and property is jeopardized, and the operation of air services is seriously affected. Often, under ransom terms, prisoners are released. Increased security measures on the ground and in the air, although apparently successful, may well result in increased cunning, resourcefulness and determination to thwart such measures.
The first known skyjacking was in 1930, the next in 1947, but from then on it became far more common. Between 1930 and 1960 (30 years) there were 33 skyjackings; between 1961 and 1965 (5 years) there were 22. In 1971 alone there were 87. It is clear that the two decades from 1960 to 1980 have seen the emergence of a worldwide threat to air travel, with great increases from 1968 onwards. By 1970, the occurrences of violent acts such as unlawful seizure of aircraft and other forms of unlawful interference with civil aviation had reached dangerous proportions, although there has been a downward trend since then: there were 17 "successful" skyjacks in 1984, and 17 failed, compared with 373 failed hijacks in 1973.