To earn this achievement, you must complete Area 5 on Hell difficulty. Hell difficulty unlocks once you've completed the game on Expert. Basically, Hell difficulty is the same as Expert mode, except that you're required to use the F-1, the worst plane in the game (typically, a max of 4 short-range missiles, ~8 bombs, or combinations along those lines).
Well, you don't have to do it that way.
When you complete Expert difficulty, make sure you carry over your unlocked planes to Hell mode, particularly the F-22A. Once you do, make a copy of your save file just in case, and then rename your file.
Guess what? You can now use any plane.
Guess what else? You have unlimited ammo (as in Beginner difficulty).
Yes, it's cheap. But, after playing through this game twice and then getting repeatedly raped on Hell difficulty, you'll thank me.
Credit to Cromanaz33 @ x360a:
http://www.xbox360achievements.org/forum/showthread.php?t=15...