Luftrausers

There are five weapons, five bodies and five engines, resulting in 125 combinations to start with. There is a special sixth weapon, body and engine that must be used together, making it a total 126 combinations. After you have unlocked all the components, keep the weapon and body the same while changing the engine. After cycling through all the engines, change the body and change the engines. After cycling through the bodies with a particular weapon, change the weapon, then recycle through the bodies and engines in the same manner. You do not need to play an entire game with the plane. Fly momentarily, then commit suicide.

To kill yourself, hold [Fire] at the pause menu. Mission statuses, unless otherwise specified, will persist and completed missions are not revoked for suicide.