Airplane navigation can't be done without coordinate geometry. The entire region where the aeroplanes fly is digitized using sophisticated technologies. They make a model of earth using GPS, RADAR etc which is represented in a co-ordinate space in computers. The location of different air-crafts are denoted there using different co-ordinate points. Then the aeroplanes are instructed to go in a certain direction to reach the destination. They are also guided so that there is no accident with other air-crafts.