Expand it... To something MORE!
This is superb. The game is challenging and is pleasing. Though, the AIs' guns sometimes get jammed when you're in a certain area of a level, thus causing them to be easy kill. I noticed that you sacrificed some mechanical accuracies of the planes to make the game more fun. I wouldn't have played it if it was like the real WWI planes. They would be pretty irritating to control.
After playing the game I had a wonderful idea of an Online version. Heh, I don't know if you'd go with it but it would be great to go head-to-head against real players.