Cheat mode:
Enter "SHPONGLE" as a name to unlock all aircraft and levels. Note: The effects of the code will be disabled if the game is saved.

Anti-aircraft guns:
Flying close to the ground causes the anti-aircraft guns to overshoot your plane. They cannot fire below a certain point due to the risk of hitting their own men.

Aircraft:
On all levels that contain multiple aircraft bogies, the best solution is to wipe out all aircraft by flying low to the ground, then pulling up on the stick to get a missile lock to destroy them. Take one bogie out at a time, then fly back close to the ground and start the process all over again.