I don't know of such a FAR. I think its just the general private
property thing at the state level (once the plane touches the ground,
its subject to local laws). However, the FARs do define an airport as
"the place of intended landing".

-Robert, CFI


Mark Hansen wrote:
I don't have my book here at the moment, so I can't quote the
specific FARs, but I think they say you must have permission
before landing. Because all land is owned by someone (generally)
you cannot land anywhere without permission.