In the air Aircraft is supported by a upward force acting in the 90° to the direction of the movement of the flight path called “Lift” (which is produced by the resultant of low pressure area above the wing and high pressure area below the wing).
This upward force balances the “Weight” (which is the pull of the gravity acting from the Centre of the Gravity of the Aircraft towards the Earth, due to the Aircraft mass) in the air.
As the Aircraft moves in the air “Drag”, which is produced due to the resistance caused by the flow of the air when the Aircraft passes through the air, this Drag is balanced by a force produced by the engine known as “Thrust” which acts in the straight ahead direction and pulls the Aircraft ahead.
Under the influence of these four forces the Aircraft is in the state of the Equilibrium and it continues to fly.
The Aircraft continues to fly due to the “Inertia”