So I was told that since these categories (especially air) are kind of vague, I should build whatever came to mind when thinking about the category. The first thing that came to mind when thinking about air was air-craft. So I built this green and white helicopter. Did I tell you it's also functional? The blades can be tilted slightly as you can see on the picture bellow (just like real choppers do to maneuver). Also, the blades are connected by an axle to the motor and a handle at the bottom of the chopper. A person can rotate the handle counterclockwise and "charge" up the motor, then let go and the motor will turn the blades clockwise as illustrated in the video bellow.
Quite fitting for the category! The only 2 problems I have is that the back is flat until the tail (or whatever it's called, I don't know helicopter parts) comes out. The tail is also a bit short, for these two reasons Connor gets my vote.
So we're dealing with two aircraft here, but what helps your build is the function. It's always nice to see a function, no matter how simple. However, Connor also included an atmosphere which is what gave him the edge, and it's why he receives my vote.