When Hughes shows his stunt pilots on the set of Hell's Angels that he can make a tight turn, he goes up himself to show them but crashes. The crash footage is actually taken from Ace Eli and Rodger of the Skies (1973).
When Noah Dietrich visits Hughes in the hospital lounge, Hughes is watching rough footage of his film Hell's Angels. This is actually black & white footage taken from The Blue Max (1966).
What is supposed to be the Hughes XF-11 aircraft is actually a WWII P-38 fighter (however, this is understandable since the real XF-11 would have been unavailable for the movie).