Nineteen people were killed during the botched attempt led by Zaid Hasan Abd al-Latif Safarini, who has admitted his responsibility for the raid. The verdict was announced on Tuesday by the US Justice Department.
The incident unfolded on 5 September 1986, when Safarini and three accomplices took control of the plane at a stop in Karachi on its way from Bombay to New York.
The pilot and flight engineer managed to escape through a cockpit window, thus making takeoff impossible.
The hijackers demanded the release of Palestinian prisoners held in Cyprus, but opened fire after Pakistani authorities refused to accede to their demands.
Those killed included two Americans. Seventy-two other people were injured. A former member of the Abu Nidal group, Safarini had already served 15 years in a Pakistani jail, was released and recaptured by Americans in September 2001.