The flying scenes for this movie were not shot by MGM. They were outtakes from Hell's Angels filmed by Howard Hughes.
The outtakes from "Hell's Angels" cost the life of three of the WWI ace pilots as well as injury to Howard Hughes himself when he crashed flying in one of the scenes. Since only one out of every 249 feet of film shot was used in "Hell's Angels" there was more than enough left over to lease to other films like this one. It also helped offset the tremendous cost to Hughes of filming his movie.