Invulnerability:
At the loading screen (where you see the graphic of the helicopter), take the
first controller and press and hold L1,L2,R1, and R2 buttons simultaneously for
the entire time that the screen is up. As soon as Mission Screen appears, you
will see in the upper left-hand corner, the word, "Cheat". This is how you know
the trick worked. You can now not be shot down.