EXCERPTED FROM:

U.S. Department of Transportation

Advisory Circular AC 70/7460-1J

AVAILABLE AT:

Markers are used to highlight structures when it is impractical to make them conspicuous

by painting. Markers may also be used in addition to aviation orange and white paint when

additional conspicuity is necessary for aviation safety. They should be displayed in

conspicuous positions on or adjacent to the structures so as to retain the general definition

of the structure. They should be recognizable in clear air from a distance of at least 4,000

feet (1219m) and in all directions from which aircraft are likely to approach. Markers should

be distinctively shaped, i.e. spherical, cylindrical, so they are not mistaken for items that are

used to convey other information. They should be replaced when faded or otherwise

deteriorated.

     a. Spherical Markers. Spherical markers are used to identify overhead wires. Markers

may be of another shape, i.e., cylindrical, provided the projected area of such markers will

not be less than that presented by a spherical marker.

     1. Size and Color.

            (a) The diameter of the markers used on extensive catenary wires across canyons,

lakes, rivers, etc., should be not less than 36 inches (91cm). Smaller 20-inch (51cm)

spheres are permitted on less extensive power lines or on power lines below 50 feet (15m)

above the ground and within 1,500 feet (458m) of an airport runway end. Each marker

should be a solid color such as aviation orange, white, or yellow. (See paragraph 131 for

color standards.)

      2. Installations.

            (a) Spacing. Markers should be spaced equally along the wire at intervals of

approximately 200 feet (61m) or fraction thereof. Intervals between markers should be less

in critical areas near runway ends (i.e., 30 to 50 feet). They should be displayed on the

highest wire or by another means at the same height as the highest wire. Where there is

more than one wire at the highest point, the markers may be installed alternately along

each wire if the distance between adjacent markers meets the spacing standard. This

method allows the weight and wind loading factors to be distributed.

           (b) Pattern. An alternating color scheme provides the most conspicuity against all

backgrounds. Mark overhead wires by alternating solid colored markers of aviation orange,

white, and yellow. Normally, an orange sphere is placed at each end of a line and the

spacing is adjusted (not to exceed 200 feet) to accommodate the rest of the markers. When

less than four markers are used, they should all be aviation orange.

Lighted markers should be used for increased night conspicuity of high-voltage (69KV or

higher) transmission line catenary wires. These markers should be used on transmission

line catenary wires near airports, heliports, across rivers, canyons, lakes, etc. The lighted

markers should be manufacturer certified as recognizable from a minimum distance of

4,000 feet (1219m) under nighttime, minimum VFR conditions or having a minimum

intensity of at least 32.5 candela. The lighting unit should emit a steady burning red light.

They should be used on the highest energized line. If the markers are installed on a line

other than the highest catenary, then spherical markers specified in paragraph 34 should

be used in addition to the lighted markers. (The maximum distance between the line

energizing the lighted markers and the highest catenary above the lighted marker should

be more than 20 feet.) Markers should be distinctively shaped, i.e., spherical, cylindrical, so

they are not mistaken for items that are used to convey other information. They should be

visible in all directions from which aircraft are likely to approach.

             a. Size and Color. The diameter of the markers used on extensive catenary wires across

canyons, lakes, rivers, etc., should be not less than 36 inches (91cm). Smaller 20-inch

(51cm) markers are permitted on less extensive power lines or on power lines below 50

feet (15m) above the ground and within 1,500 feet (458m) of an airport runway end. Each

marker should be a solid color such as aviation orange, white, or yellow. (See paragraph

131 for color standards.)

            b. Installations.

                   1. Spacing. Lighted markers should be spaced equally along the wire at intervals of

approximately 200 feet (61m) or fraction thereof. Intervals between markers should be less

in critical areas near runway ends (i.e., 30 to 50 feet). If lighted markers are installed on a

line other than the highest catenary, then spherical markers specified in paragraph 34

should be used in addition to the lighted markers. The maximum distance between the line

energizing the lighted markers and the highest catenary above the lighted markers should

be no more than 20 feet. The lighted markers may be installed alternately along each wire

if the distance between adjacent markers meets the spacing standard. This method allows

the weight and wind loading factors to be distributed.

                  2. Pattern. An alternating color scheme provides the most conspicuity against all

backgrounds. Mark overhead wires by alternating solid colored markers of aviation orange,

white, and yellow. Normally, an orange marker is placed at each end of a line and the

spacing is adjusted (not to exceed 200 feet) to accommodate the rest of the markers. When

less than four markers are used, they should all be aviation orange.

46. PLACEMENT FACTORS.

The height of the structure AGL determines the number of light levels. The light levels may

be adjusted slightly, but not to exceed 10 feet, when necessary to accommodate guy wires

and personnel who replace or repair light fixtures. Except for catenary support structures,

the following factors should be considered when determining the placement of obstruction

lights on a structure.

      a. Red Obstruction Lighting Systems. The overall height of the structure including all

appurtenances such as rods, antennas, obstruction lights, etc., determines the number of

light levels. (See APPENDIX 1., FIG 11.)

      b. Medium Intensity Flashing White Obstruction Lighting Systems. The overall height of

the structure including all appurtenances such as rods, antennas, obstruction lights, etc.,

determines the number of light levels. (See APPENDIX 1., FIG 12.)

       c. High Intensity Flashing White Obstruction Lighting Systems. The overall height of the

main structure excluding all appurtenances such as rods, antennas, obstruction lights, etc.,

determines the number of light levels. (See APPENDIX 1., FIG 13.)

       d. Dual Obstruction Lighting Systems. The overall height of the structure including all

appurtenances such as rods, antennas, obstruction lights, etc., is used to determine the

number of light levels for a medium intensity white obstruction light/red obstruction dual

lighting system. The overall height of the structure excluding all appurtenances is used to

determine the number of light levels for a high intensity white obstruction light/red

obstruction dual lighting system. (See APPENDIX 1., FIG 7.)

         e. Adjacent Structures. The elevation of the tops of adjacent buildings in congested

areas may be used as the equivalent of ground level to determine the proper number of

light levels required.

         f. Shielded Lights. If any light is shielded by an adjacent object, horizontal placement of

the lights should be adjusted or additional lights should be mounted on that object to retain

or contribute to the definition of the obstruction.

47. MONITORING OBSTRUCTION LIGHTS.

Although some obstruction lighting systems have redundant features, they should be

closely monitored by visual or automatic means. It is extremely important to visually inspect

obstruction lighting in each operating intensity at least once every 24 hours on systems

without automatic monitoring. In the event a structure is not readily accessible for visual

observation, a properly maintained automatic monitor should be used. This monitor should

be designed to register the malfunction of any light on the obstruction regardless of its

position or color. The monitor (aural or visual) should be located in an area generally

occupied by responsible personnel. In some cases, this may require a remote monitor in an

attended location. All obstruction lights should be visually inspected on a regular basis.

An ATPWEB98