If you need help progressing in the game then try entering the following codes to enable the corresponding feature, the codes must be entered quickly for them to work.

Unlock ALL Campaign Missions and Planes:
At the 'Main' menu hold L2 + R2 and press Square, L1, R1, Triangle(2), R1, L1, Square.

Invincibility:
Pause gameplay and hold L2. Then press Square, Triangle(2), Square, hold R2 and press Triangle, Square(2), Triangle. To disable the code enter it in again.

Increase Weapon Damage:
Pause gameplay and hold L2. Then press L1(2), R1, hold R2 and press R1(2), L1. To disable the code enter it in again.

Unlock Vampire MK1:
When you have unlocked the Vampire go to the 'Main' menu and hold L2 + R2 and press L1(2), Triangle(2), Square, L1. If you have entered the code in correctly the MK1 version of the plane will become available.