Originally Posted by
Sport_Pilot
Not at all, navigable airspace is defined in the FARS and is the same as defined in the 1958 FAA act. All airspace that is not navigable airspace is thus non navigable in that it is illegal for aircraft to fly through such airspace.
Sounds more like restricted airspace to me. We, as hobbyists, are restricted to less than 400' within 3 miles of an airport, currently, without permission to fly higher. Therefore any airspace above 400' is non-navigable for us, according to your interpretation. But, other aviators are permitted to navigate in that airspace so it is both navigable and non-navigable or an oxymoron.