First, you would have to have a gravity system. The y coordinate of the plane would be decreased by the gravity variable. Then you would have the plane's force pushing up which would be adding to the y coordinate to raise the plane. Change the values to move up and down.
You would also have it that if it is below the ground, it would push on top of it.
if objecty < get ground height(matrixnumber,objectx,objecty)
objecty = get ground height(matrixnumber,objectx,objecty)
endif
The answer to the great question of life, the universe and everything is 42.