It would float away into space and implode.
Gravity and wind resistance.
If you were on a plane and had no weight to you you would float in the plane like there was no gravity, even though there is but if the plane was angled precisely you can float in the plane as if gravity was turned off. But this only lasts a few minutes as you come closer to land.
Gravity on the plane itself, the weight of any occupants (force of gravity on occupants), and any force applied by weather influences such as wind.
Gravity is the driving force behind:- wind (convection currents can only happen in a gravity field) ice (Ice moves and erodes under the pull of the force of gravity) Landslides (here the motive power is the pull of gravity)
All over it. Gravity attracts every molecule in the Universe to every other molecule. When you leave your seat and walk to the rest room while in a plane, it is gravity that holds you down to the floor. As a simplifying approximation, engineers often treat gravity as applying a force on the center of mass of an object.
The moment you fall out of a plane you will be affected by only two forces: gravity and wind resistance. Gravity will pull you towards the ground at 9.8m/s^2 and wind resistance will try to slow you down. Eventually you will reach a top speed called terminal velocity which can range from about 117-125mph.
Gravity on a plane is less then on a hill because you are away from the earth, However gravity in a plane over a hill is more then gravity on a plane over a valley at the same altitude above sea level.
If a plane is in level flight, gravity (weight) is equal to lift.
Wind, rain, fire, gravity , glacier retraction, waves. Moving water, ice, wind and gravity are the agents of erosion.
If you were going to treat all of the forces acting on a plane at a specific point that point would be the CG (Center of Gravity), which is usually measured in inches aft of the datum (a non-physical point used by engineers to define the center of gravity).
Gravity is the driving force behind all agents of erosion. If there is no gravity, rain will not fall and running water will not happen. Similarly, wind, glacial activity and waves are driven by gravity.
The wind pushes the plane helping it stay in the air.