When you get to the airfield, look for a nice, open area. There should be a hill of rubble near that area.

Go on top of it and crouch, there should be a plane in front of you, at the bottom of the hill.

Special Infected will always spawn to the left of the plane and the Tank will come from the right.

When you hear the Tank music, run to the plane under the hill and crouch under the plane.

The Tank cannot get you and will most likely smack the other side of the plane (in which case you can shoot its legs from under the plane).

After the Tank dies, run back up to the top of the hill, rinse, and repeat.