Learn how to create an aeroplane shooting game in a complete tutorial made of 5 parts: Player Movement, Shooting Bullets, Adding Enemies, Collisions, Scoring and HUD.
You can use Actionscript, Flash Professional or Flash Builder to write the game.
Instead, write a few scenes, or get some of your gameplay to work.
Then set a realistic deadline for yourself, and don't change it.
Perhaps you are interested in creating a cute story in which the main character can end up with one of several love interests.