If they are the first to build an airplane that "actually worked", then why would it be inappropriate to say they invented an airplane?
It wouldn't be appropriate to say "they were responsible for 100% of the technological development and research that led to this machine" but if that's what "invented" means then nobody has ever invented anything.
It wouldn't be appropriate to say "they were responsible for 100% of the technological development and research that led to this machine" but if that's what "invented" means then nobody has ever invented anything.