Alright, but can be improved.
Well, for your first game, it's certainly nice and sound. I couldn't find any bugs, the artwork was good and it was pretty complete. Of course, it can certainly be improved. Here are a couple of tips I thought of.
Never, and I say NEVER, have the framerate of Flash set to 12fps, 24 is the minimum for games like this.
Try adding some background music or some sound effects, perhaps a crash when you, er, crash.
Finally, try adding an animation for when you press/release the Space Bar, it doesn't look very pretty the way the plane jerks in one direction or the other.
Still, it's a nice game, kept me interested for a bit. Keep it up!