airplane

Send it to an airfield.

But it is already in an air field. Any time i try to move it, it became a truck!

If you send planes to a destination outside their flight range or to a province center whithin flight range but whithout usable airfield, they automatically turn into trucks and drive.

If planes (or rockets) stand on an airfield wich becomes damaged to less than level 1, then the airfield is out of service and the planes become trucks also.

Should it be that planes are shown as trucks on an intact airfield, move them back and forth briefly (or reload the game).

PS

Planes and rockets cannot occupy or hold provinces. So if a province where are only planes or missiles but no defending ground units is attacked, the province is immediately conquered without fight and the planes or rockets also become trucks as well.

In my first game over a year ago, I moved airplanes from a zoomed out position and once in a while they would turn into trucks. I learned to zoom in when moving airplanes to ensure that they were truly moving into an airfield ...

You have your airfield sabotaged