I am a plane freak and still don't like this portrait. It looks like the plane is sniffing your armpit and everything is WAY too far away for my taste. Sorry ...
I'm sorry to say that I found many flaws in this picture. First of all, I think horizons are generally meant to be horizontal. Second, I don't like the composition, with the very narrow crop on the right, and the plane sniffing the gir's armpit. Furthermore, the picture makes me think of a funny-mood-holiday snapshots. Funny moods are okay, holiday snapshots are okay as well, but leave them in your family album.
Most important however, the backlight makes the girl face hard to see, which I think is essential in a portrait
Last-minute though it may be (it certainly feels impromptu), I think this really works. The backlighting is lovely, and the positioning of the subject and her shadow is perfect. The only blemish: a distracting line of sunspots. Use post-processing to clean those up, and I think you have a real winner here. 7 from me.
I'm assuming you used your timer, otherwise this great photo belongs to someone else. I gave out ten '10's this time and you deservedly got one of them (in my opinion which usually doesn't mean a lot). It's definitely NOT a 'studio' shot but it beats a lot of those images with POW- emotion, real emotion. Keep going!