Wow- looking forward to this documentary film and of course it would be great to have the score album out . Previously Horner did the superb THE HORSEMEN COMETH documentary about the famous P-51 mustang which also had a very limited blu ray and cd combo release (which I now come to own due to a generous friend on this board)
There was digitally and it was available on iTunes for a long time. I now can't find it. If you can, its well worth every penny you spend on it. The Horsemen music is a highlight of Horner's career. It contains shades of In Country, The Spiderwick Chronicles, and The Rocketeer and encompasses everything so powerful about Horner's music. This is his romantic and sweeping side at its best.
Here's a YouTube video of a performance the Horseman did to the music. The music begins at 1:37. Obviously the music is obscured by the noise of the planes at times, but it gives you a good idea of what's going on:
Here, too, is the interview Horner did for the Horsemen at the time the piece was debuted. The interview is scored at first with a sub piece he wrote called "The Fourth Horsemen" that contains a serene rendition of the theme that recurs in the main flight demonstration music. Also features tons of session footage and, later, samples of the flight music.