I do not know all the aspects and interpretations of the law. I do know of cases in New York City where the air rights of one property are sold to an adjacent property. If the plot having the air rights is owned by a different party then the land owner of the adjacent property, then the first land owner needs to sell his air rights to the second land owner.
You state "he can't." I state I think that it is a crazy system. I guess you don't live in New York City.