Enter one of the following codes at the main menu. Enabling a code will prevent the game from being saved and will also disable the unlocking of achievements.

In-game cheat menu
Press Y, LT, D-pad Left, RT, D-pad Right, LB at the main menu.

All planes
Press LT, Right Analog-stick Left, RT, Right Analog-stick Right, LB, Y at the main menu.

All missions
Press Right Analog-stick Up, Right Analog-stick Down, LB, RB, Right Analog-stick Left, Right Analog-stick Right at the main menu.