Aeroplane body is so desighned, when it is flying in the air, air is freely flowing on top surface but getting stagnated at bottom surface. Due to this pressure difference is developed between top and bottom surfaces. At bottom surface due to stagnation of air flow, pressure is more than that of top surface.
Hence net upward force which is called lift acting on the air plane which is much more compared to its weight. Forward force which is called thrust is given by jet engine. Drag force is due to air resistance experienced by the moving aeroplane. Thrust is more than drag. Hence due to the net upward force and net forward force the aeroplane is flying in the forward direction without falling due to gravity