How to tell if physics object is in air?

I have a 2D car, like those dirt bike games, how can i tell if its in the air? :) Thanks

When it is not overlapping the ground I think.

Object car -> is overlapping object Ground.

Right-click: Invert

Move the sprite 1 pixel down, check for overlap with ground then move the sprite back up.

every tick:

----Sprite| set isInAir to true

----Sprite| set Y: y+1

Sprite| is overlapping ground:

----Sprite| set isInAir to false

every tick:

----Sprite| set Y: y-1

Thanks guys got it working now :)