It's one of my favorite films.
I first saw it on TV for the noon-time matinee when I was a little kid.
Being an aviation buff from a ripe young age, it instantly appealed to me.
Recently it became available on iTunes (I've never been able to find a copy of the DVD).
A couple of things I noticed.
The wings on a Fokker Dr.1 are cantilevered. The outer struts are basically decorative and were added to salve the fears of the Luftstreitkräfte. Kessler's losing of those struts and one aileron should not have been fatal.
The movie concludes in 1931 and notes that Pepper dies in 1931. I don't think that the character really died. I think his "death" was faked and he started over under an assumed name. Pepper had been shown having a willingness to lie and assume other identities. Why not take advantage of flying over the hill in a "damaged too badly to land" airplane and sink it in a lake or something. They show about ten crashes where people survived in the film, one more is believable.