Girl on a Plane by Miriam Moss.

Jordan, 1970.
After a summer spent with her family, fifteen-year-old Anna is traveling back to her English boarding school alone. But her plane never makes it home.
Anna’s flight is hijacked by Palestinian guerrillas. They land the plane in the Jordanian desert, switch off the engines and issue their demands. If these are not met within three days, they will blow up the plane, killing all the hostages.
The heat on board becomes unbearable; food and water supplies dwindle. Anna begins to face the possibility she may never see her family again.
Time is running out . . .