Hold L1 + L2 + R1 + R2 at the loading screen after receiving your mission orders. (The word "Cheat" in the upper corner of the mission screen confirms correct entry.)

(Note: The helicopter can still crash into mountains.)

Hold L1 + L2 + R2 + X at the loading screen after receiving your mission orders. (The word "Cheat" in the upper corner of the mission screen confirms correct entry.)