"taken as literally not navigable" as in a mountain is not navigable. "When taken in the legal context it means it is illegal to navigate through." OK, it’s illegal to navigate through a mountain. Thank you for clarifying that. I don't think that's a law I will be challenging anytime soon.
Maybe drive a nail through your head to provide a place for knowlege to soak through. I think it is clear that Iam saying you may be able to fly through "air space that is classified as navigable" (does that suit you?), but cannot legally do so.