Areas in which a visible or invisible hazard, or hazards, exists should be lighted in accordance with the following specifications.

(1) The obstruction lighting prescribed hereinafter is in addition to such lighting as may be necessary on any natural or manmade obstruction located within the hazard area.

(2) Specification "I-1."

(a) An area in which a visible or invisible hazard, or hazards, to aircraft exists.

(b) There should be mounted on top of a tower or other suitable structure, located near the center of the area, at least one rotating beacon producing aviation red flashes. The frequency of its flashes should be such as hereinbefore specified for rotating beacons.

(3) Specification "I-2."

(a) A large area in which a visible or invisible hazard, or hazards, to aircraft exists.

(b) There should be installed at two or more places around the perimeter of the area a rotating beacon, mounted on top of a tower or other suitable structure, producing aviation red flashes. The beacons should be located in a manner to insure unobstructed visibility of at least one of the beacons from aircraft at any normal angle of approach. The frequency of its flashes should be such as hereinbefore specified for rotating beacons.