This is without a doubt the hardest challenge in the game. The trick is memorizing the pattern and methodically taking out each plane in sequence. If you try to just randomly shoot them down, it’s never going to happen.
The flight patterns of the 10 planes shown in the clip are always exactly the same—with one exception. Sometimes plane 4 collides with another in a fiery ball of fail right at the outset. Just restart from checkpoint if that happens. Second, after your first attempt, the right half of the screen will be obscured by smoke and clouds. Rest assured, the planes are still in there, still flying the same pattern. If you can’t see them, shoot where you know they should be. As the bombers move from right to left, they will eventually disappear behind the other airship. If you don’t shoot them all down before that happens, you’re pretty much screwed; restart from checkpoint. Good luck and god speed my friends.