The actual airplane used in the final scene was a French Morane-Saulnier MS.230 standing in for a Fokker E.V. The story line was taken from the July 3, 1918 death of Haupmann Wilhelm "Willli" Reinhardt. I guess the story was too good to pass up so Hunter put it in the book. From Wikipedia article on Wilhelm Reinhardt:
In popular culture[edit]
The death of Reinhard flying a prototype is closely paralleled in the book and film
The Blue Max.