. . .Got to the first MG post, took one of the Panzerfausts and let it off on one of the attacking airplanes. Takes quite a lot of time and practice and savepoint loads, but it's quite funny. Also, it appears that after you kill the first one, the second just kinda leaves you alone.
The best way to do it is as they mentioned before; wait till it swoops down. I haven't had any success in shooting them while flying by, but they *are* world objects after all. I saw one of these action boxes highlighting them when I went on the tac mode and coincidentally "caught" one in the frozen action.