It is quite common to see the objects in a projectile motion travelling a path of trajectory. These objects in this context start with the application of force applied at the point of origin which carries it forward. And because of the influence of gravity, it comes down to the ground and ends the trajectory. But aeroplanes are machines having engines that propel them constantly. And the aerodynamics of the aeroplanes keep it lifted in the air while it moves and prevents it from coming down and making any trajectory.