My vote goes to "Les Chevaliers du Ciel" ("Sky Fighters" in the English version), a 2005 film by Gérard Pirès. Very good airplane scenes, filmed by the French Air Force without special effects (they put a special camera container under a Mirage 2000 for the filming), but a really crappy story.

The picture was based on a comics series, "Tanguy et Laverdure", more or less the French equivalent of "Steve Canyon". But for reasons unknown, the principal characters were changed, and their replacements were very dull, the actors below average. "Tanguy et Laverdure" without Tanguy nor Laverdure....

https://en.wikipedia.org/wiki/Sky_Fighters