Codes and Standards

Back to Contents

Chapter 11. Marking and Lighting of Catenary and Catenary Support Structures - High Intensity Flashing White Lights

110. PURPOSE.

Lighting catenary support structures with a high intensity (L-857) flashing white lighting system provides the highest degree of conspicuity both day and night. In addition, the umque sequential/simultaneous flashing light system alerts pilots of the associated catenary wires.

111. STANDARDS.

When this system is operated 24 hours a day, marking of the support strucUa'e is not necessary.

a, Levels. A system of three levels of sequentially flashing light units should be installed on each supporting structure or adjacent terraha. Install one level at the top of the structure, one at the height of the lowest point in the catenary, and one level approximately midway between the other two light levels. The middle level should normally be at least 50 feet (15m) from the other two levels. The middle light unit may be deleted when the distance between the top and the bottom light levels is less than 100 feet (30m). I/the installation presents a potential danger to maintenance personnel, or when necessary for lighming protection, the top level of lights may be mounted as low as 20 feet (6m) below the highest point of the structure.

b. Top Levels, One or more lights should be installed at the top of the structure to provide 360-de~ coverage.

c. Flash Sequence. The flash sequence should be middle, top level, and bottom level with all lights on the same level flashing simultaneously. The time delay between flashes of levels is designed to present a unique system display.

d, Flash Rate. Each series of flashes is repeated 60 times every minute.

e. Synchronization. Although desirable, the corresponding light levels on associated supporting towers of a catenary crossing need not flash simultaneously.

f. Horizontal Coverage. The light units at the middle level and bottom level should be installed so as to provide a minimum of 180--degree coverage centered perpendicular to the flyway. Where a catenary crossing is situated near a bend in a river, canyon, etc., or is not perpendicular to the flyway, the horizontal beam should be directed to provide the most effective light coverage to warn pilots approaching from either direction of the catenary wires.

g. Variation. The vertical and horizontal arrangements of the ligh~ may be subject to the structural limits of the towers and/or adjacent terrain. A tolerance of 20 percent from uniform spacing of the bottom and middle light is allowed. If the base of the supporting structure(s) is higher than the lowest point in the catenary, such as a canyon crossing, one or more lights should be installed on the adjacent terrain at the level of the lowest point in the span. These lights should be installed on the structure or terrain at the height of the lowest point in the catenary.

h. Structures Exceeding 500 Feet (II5m) AGL When high intensity white lights are operated 24 hours a day, others methods of marking and lighting may be omitted. This system should not be recommended on structures 500 feet (153m) AGL or less unless and FAA aeronautical study shows otherwise.

112. CONTROL DEVICE.

The light intensity is controlled by a device that changes the intensity when the ambient light changes. The system should automatically change intensity steps when the northern sky illumination in the Northern Hemisphere on a vertical surface is as follows:

a. Day-to-Twilight. This should not occur before the illumination drops to 60 footcandles (645.8 lux), but should occur before it drops below 35 footcandles (376.7 lux). The illuminance sensing device should, if practical, face the northern sky in the Northern Hemisphere.

b. Twilight--to-Night. This should not occur before the illumination drops below 5 footcandles (53.8 lux), but should occur before it drops below 2 footcandles (21.5 lux).

c. Night-to-Day. The intensity changes listed in (a.) and Co. ) above should be reversed when changing from the night to day mode.

113. AREA SURROUNDING CATENARY SUPPORT STRUCTURES.

The area in the immediate vicinity of the supporting structure's base should be clear of all items and/or objects of natural growth that could interfere with the line-of-sight between a pilot and the structure's lights.

114. THREE OR MORE CATENARY SUPPORT STRUCTURES.

Where a catenary wire crossing requires three or more supporting structures, the inner structures should be equipped with enough light units per level to provide a full coverage.

115. CATENARY LIGHTING.

Lighted markers are avm'lable for increased night conspicuity of high-voltage (69KV or higher) transmission line catenary wires. Lighted markers provide conspicuity both day and night; installation, size, color, and pattern should follow the guidelines of paragraphs 34 and 36. These markers should be used for increased night conspicuity of high-voltage (69KV or higher) 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. The marker should be used on the highest energized line. If the lighted markers are installed on a line other than the highest catenary, then 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 can be no 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 (91cra). Smaller 20-inch (5 lcm) markers are permitted on less extensive power lines or on power lines below 50 feet (1Sm) 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. Markers should be spaced equally along the wire at intervals of approximately 200 feet (6lin) or fraction thereof. Intervals between markers should be less in critical areas near hmway ends (i.e., 30 to 50 feet). If lighted markers are installed on a line other than the highest catenary, then markers specified in paragraph 34 should be used in addition to the light markers. The maximum distance between the line energizing the lighted marker and the highest catenary above the lighted marker can be no more than 20 feet. 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.

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.

Back to Contents