47 CFR 95.317: Registration of antenna structures that may constitute a menace to air navigation.

(a) Each antenna structure used for a Personal Radio Service station is subject to the antenna structure rules set forth in part 17 of this chapter. In particular, the owner of an antenna structure that is more than 60.96 m (200 ft) in height above ground level (see § 17.7 of this chapter for specific criteria) may be required to notify the FAA and register the antenna structure with the FCC.

(b) Further, stations located on or near a military or public-use airport with an antenna structure that is more than 6.10 meters (20 feet) high may have to obey additional restrictions. The highest point of the antenna must not exceed one meter above the airport elevation for every hundred meters of distance from the nearest point of the nearest airport runway. Differences in ground elevation between the antenna and the airport runway may complicate this formula. For stations near an airport, see http://appsint.fcc.gov/UlsApp/AsrSearch/towairSearch.jsp to figure the maximum allowable height of the antenna. Consult part 17 of the FCC's Rules for more information (47 CFR part 17).