automatic levelling out airplane when near the ground?

I'm having an issue mostly with understanding what to put to get and set the values I'm trying to set. (in c#) I want to get the global rotational value of a gameobject on the y axis. I then want to take this value and plug it in to the the y axis of a line that sets the x and z global rotations to 0, thus levelling out a plane automatically.

what do I use to get and set these values according to the world space?