You'll start in a big building, and you can exit by going all the way to your left, and out this ramp. Just out the door, is this building, where you go inside.

The building has two guards, who are easily disposed of. You can then simply collect the plane key from the table.

Exit the building, and watch to kill a nearby guard. Follow along the building where you started, all the way to it's end and around the corner to find the tank.

Climb onto the tank, press "B" to take control of it. Once inside, switch to tank shells. Heading down the runway, destroy this gun emplacement on the left, at the end of this building.

Turn to the right, and bomb the missile battery on top of this structure, to the right of the plane. (don't hit the plane!). Continue down the runway to the left side, near the end to take out the two guns there, the first one is on the left.

Turn around to take out the one on the right side, and after it blows up, drive back to the plane, exit the tank with "B", and enter the plane with "B". Be sure not to run over the plane with the tank, or it will be destroyed.