(a) Any object that would be shielded by existing structures of a permanent and substantial character or by natural terrain or topographic features of equal or greater height, and would be located in the congested area of a city, town, or settlement where it is evident beyond all reasonable doubt that the structure so shielded will not adversely affect safety in air navigation.
(b) Any antenna structure of 20 feet or less in height except one that would increase the height of another antenna structure.
(c) Any air navigation facility, airport visual approach or landing aid, aircraft arresting device, or meteorological device, of a type approved by the Administrator, or an appropriate military service on military airports, the location and height of which is fixed by its functional purpose.
(d) Any construction or alteration for which notice is required by any other FAA regulation.
[Doc. No. 1882, 30 FR 1839, Feb. 10, 1965, as amended by Amdt. 77–5, 33 FR 5257, Apr. 2, 1968; Amdt. 77–9, 36 FR 5970, Apr. 1, 1971]