For the purposes of paragraph (b)(10) of this section, an airport hazard is any structure or object of natural growth located on or in the vicinity of a public airport, or any use of land in the vicinity of the airport, that obstructs the airspace needed for the landing or takeoff of aircraft or is otherwise hazardous to the landing or takeoff of aircraft. For the purposes of paragraph (b)(13) of this section, land acquisition includes the acquiring of land that is already developed as a private airport and the structures, fixtures, and improvements that are a part of realty (other than hangars, other ineligible structures and parts thereof, fixtures, and improvements).
14 C.F.R. §151.39