Since planes fly because of air pressure variance between the top and bottom of the wings, would an increase in gravity really make them fall? The weight of air would increase by the same relative amount as the weight of the plane.”Most plausible-ish answer so far: If gravity suddenly increased, yes, planes would fall out of the sky. When a plane is maintaining a constant altitude, the force of gravity and the force of lift are equal. If gravity were suddenly increased, there would no longer be an equilibrium, and the plane would drop. When a plane is flying it needs its Lift force to be greater than its weight.