Ace Pilot: Famed stunt Pilot Frank Tallman did all of the tricky flying scenes (most notably Minderbinder's low level attack on his own airfield) and included an amusing account of his role in making the film in his 1973 memoir Flying The Old Planes
Just Plane Wrong: Averted at great expense: Tallmantz Aviation put together a full squadron of 16 B-25 bombers including their own two camera planes for the film. (The B-25 was a popular camera plane because it was big, fast, stable, rugged and had several gunner's positions that made excellent camera stations.) A seventeenth non-flyable derelict was restored to barely-flyable condition, ferried to the set and expended during filming. Despite the great expense involved the aircraft sequences, which took three months and some 1500 flying hours to film, only make up approximately 12 minutes of the finished movie.
Mildly Military: According to Tallman the production crew all wore military uniforms during filming so they could go about their business in the background without worrying about spoiling any shots. Most aircrew were veterans who mostly wore their old military ranks but some couldn't resist giving themselves significant promotions, much to Tallman's amusement.
Throw It In: Since most of the location filming took place on a small airfield in rural Mexico the entire production was set up like a military encampment including uniforms so they could film in any direction at any time without worrying too much about who or what showed up in the background. The men conducting maintenance and flight operations in the background really are conducting flight operations in the background. Why bother hiring a bunch extras to portray men servicing aircraft when you can just film the mechanics actually doing it?