Afraid so, since you've worked your way into a corner. Could you give an example of 'non-navigable airspace' ? Does it include uncontrolled airspace, is it off an airway...,? Since it doesn't seem to exist in any text or regulation I've ever read, I'd be interested in where it can be found and how it's defined so I know if I'm ever in it.

C'mon, this is a toy airplane site. Only us nerds read this stuff.Just admit you're making it up.