I wonder if they actually sought permission for such a title - or even if it was necessary to do so?
I believe copyright doesn't apply to titles (unless a title's been trademarked), and there are quite a few examples of two completely different books coincidentally sharing the same title. And it's only half the title in this case.
Bit of a cheek anyway. Sounds like a case of "we'll trick the audience into thinking that it is based on a popular children's comic and then deny that that was our intention".
Well maybe. Assuming that the flight number is the same in the original German film, maybe the screenwriter was deliberately adding a little Tintin reference as an homage, or simply subconsciously borrowing that flight number because it sounded just right, without knowing where he heard it. You could say very much the same thing about Hergé calling his comic strip hero Tintin, which may have been a deliberate or subconscious borrowing from Benjamin Rabier's 19th century Tintin-Lutin cartoon.
I take your point that whoever then re-titled the film in French does seem to have been using the fact that the flight number is 714 to make the film's new title very Tintin-sounding. But maybe they too meant it as an homage, rather than a devious attempt to get people watching the film under false pretences!
It's an interesting Tintin reference you've dug up in any case.