All Secrets Achievement
Unlock all hidden contents.You unlock all the hidden content by beating the game on different difficulties. Most are unlocked by beating the game on normal, however there are a few that require you to beat the game on expert.
CFA 44 Nosferatu Fighter - Beat the game on Hard difficulty. It will appear in your hangar, purchase it for $229,500.
Music Player - Beat the game once.
Scene Viewer - Beat the game once.
Unlock Expert Difficulty- Beat the game once.
Unlock Ace Difficulty - Beat the game on expert.
SP New Game - Complete campaign once on any difficulty setting.
you also need to unlock all planes and colors.