visible to pilots approaching the hazard. High-voltage (69 kilovolts (kV) or greater) transmission
lines are typically mounted on large catenary support structures and should be fitted with lighted
markers to provide sufficient conspicuity in both day and nighttime conditions. Transmission
lines that are less than 69 kV are typically mounted on smaller catenary support structures and
should be fitted with unlighted markers that provide daytime conspicuity.
11.3.1
Lighted Catenary Markers.
Lighted markers provide increased nighttime conspicuity of high-voltage (69 kV or greater)
transmission line catenary wires. However, since lighted markers require a minimum line load to
operate, it should be noted that the lights may not be operational under certain transmission
system conditions, such as power outages or line maintenance. Whenever possible, these lighted
markers should be used on transmission line catenary wires near airports, heliports, across rivers,
canyons, lakes, areas of known risk to aviation, etc.
The lighted markers should be manufacturer-certified as, visible and recognizable from a
minimum distance of 4,000 feet (1,219.20 m) under nighttime conditions and under minimum
VFR conditions, and have a minimum intensity of at least 32.5 candelas. Markers should be
distinctively shaped, i.e., spherical or cylindrical, so that they are not mistaken for items used to
convey other information. The lighting unit should emit a steady-burning red light and be
mounted on the highest energized line, visible to a pilot approaching from any direction. If the
lighted markers are installed on a line other than the highest catenary wire, then unlighted
markers should be used in addition to the lighted markers (see Figure A-24).
1.
Size and Color.
The diameter of the markers (lighted and unlighted) used on extensive catenary wires that cross
canyons, lakes, rivers, etc., should not be less than 36 inches (91.44 cm). The 20-inch (50.80
centimeters (cm)) markers, or smaller 12-inch (30.48 cm) markers, are permitted on less
extensive catenary wires or on power lines below 50 feet (15.24 m) above the ground and within
1,500 feet (457.20 m) of an airport runway end. Each lighted marker should be a solid color;
specifically aviation orange, white, or yellow. Transmission lines that are configured in a
“double-bundled” arrangement would typically require the larger 36-inch (91.44 cm) markers,
however the next smaller size marker may be used to prevent the marker from rubbing against
the parallel transmission line.
Note: For the purposes of this advisory circular, the term “extensive” is used to describe
catenary wire crossings that extend across an open area that an aircraft could be
reasonably expected to fly at or below the altitude that the catenary wires are suspended.
“Less extensive” is used to describe catenary wire crossings that extend across an open
area that an aircraft could reasonably be expected to fly at or above the same altitude.
2.
Installation.
a.
Spacing. Lighted markers should be spaced equally along the wire at intervals of