together at the top, it may be necessary to install this level of lights as low as 10 feet (3.05 m) below the top. If the appurtenance (rod, antenna, etc.) exceeds 40 feet (12.19 m) above the main structure, a high-intensity, flashing white light (L-856) should be mounted on the highest point (see Figure A-7). If the appurtenance (such as a whip antenna) is incapable of supporting a medium-intensity light, one or more lights should be installed on a pole adjacent to the appurtenance. The pole should not exceed the height of the appurtenance and no lower than 40 feet (12.19 m) from the top, allowing a pilot an unobstructed view of at least one light in any direction. If the pole, rod, antenna, or other appurtenance is 7/8 of an inch wide or more, at least two lights must be installed on the supporting mast to provide the necessary unobstructed view.
3. Ice Shields.
Where icing is likely to occur, metal grates or similar protective ice shields should be installed directly over each light unit to prevent falling ice or accumulation from damaging the light units. The light should be mounted in a manner to ensure an unobstructed view of at least one light by a pilot approaching from any direction.
7.7 Antenna or Similar Appurtenance Light.
When a structure lighted by a high-intensity, flashing white light system is topped with an antenna or similar appurtenance exceeding 40 feet (12.19 m) in height, a high- intensity flashing white light (L-856) should be placed within 40 feet (12.19 m) from the tip of the appurtenance.
This light should operate 24 hours a day and flash simultaneously with the rest of the lighting system. The location of the appurtenance light is shown in, Figure A-14. Structures with an appurtenance 40 feet (12.19 m) or less in height should be lit in accordance with Figure A-13.
7.8 Chimneys, Flare Stacks, and Similar Solid Structures.
The number of light levels depends on the height of the structure, excluding appurtenances.
Three or more lights should be installed on each level to ensure an unobstructed view by the pilot. Normally, the top level lights are on the highest point of a structure, however, top level chimney lights may be installed as low as 20 feet (6.10 m) below the top to minimize deposit buildup due to emissions.
7.9 Prominent Buildings and Similar Extensive Obstructions.
When objects within a group of obstructions are approximately the same overall height above the surface and are located a maximum of 150 feet (45.72 m) apart, the group of obstructions may be considered an extensive obstruction. Light units should be placed to ensure that the light is visible to a pilot approaching from any direction. These lights may require shielding, such as louvers, to ensure minimum adverse impact on local communities.
Light units should be installed on the same horizontal plane at the highest portion or edge of the prominent obstructions and displayed to indicate the extent of the obstruction as follows:
1. Obstructions 200 feet (60.96 m) or less in either horizontal dimension. Three or more light units should be installed at the highest portion of the structure to ensure that at least one light is visible to a pilot approaching from any direction. Light units may be mounted on a single pedestal at or near the center of the obstruction. If the light units are placed more than 10 feet
(3.05 m) from the center point of the structure, use a minimum of four light units.
2. Obstruction exceeds 200 feet (60.96 m) in one horizontal dimension, but is 200 feet (60.96
m) or less in the other. Two light units should be placed on each of the shorter sides. These light units may be installed either adjacent to each other at the midpoint of the obstruction’s edge or at (near) each corner, with the light unit aimed to provide 180 degrees of coverage at each edge. One or more light units should be installed along the overall length of the major axis at approximate equal intervals, not to exceed a distance of 100 feet (30.48 m) from the corners or from each other.
3. Obstruction exceeds 200 feet (60.96 m) in both horizontal dimensions. The light units should be equally spaced along the overall perimeter of the obstruction at intervals of 100 feet
(30.48 m), or fraction thereof.
7.10 Hyperbolic Cooling Towers.
High intensity light units should be installed to ensure an unobstructed view of at least two lights by a pilot approaching from any direction.
1. Number of light units. The number of units recommended depends on the diameter of the structure at the top, as shown in Figure A-15. The minimum number of light units recommended is indicated below.
a. Structures exceeding 100 feet (30.48 m) but not more than 200 feet (60.96 m) diameter.
Six light units per level.
b. Structures exceeding 200 feet (60.96 m) in diameter. Eight light units per level.
7.11 Special Cases.
When lighting systems are installed on structures located near highways, waterways, airport approach areas, etc., caution should be exercised to ensure that the lights do not distract or otherwise cause a hazard to motorists, vessel operators, or pilots on an approach to an airport. In these cases, shielding or adjusting the aim of the vertical or horizontal light may be necessary.
This adjustment should not derogate the lighting system’s intended purpose. Such adjustments may require an additional review, as described in paragraph 7.5.
CHAPTER 8. DUAL LIGHTING WITH RED/MEDIUM-INTENSITY FLASHING
WHITE LIGHT SYSTEMS
8.1 Purpose.
This dual lighting system includes red lights (L-864) for nighttime and medium-intensity and flashing white lights (L-865) for daytime and twilight use. This lighting system may be used in lieu of operating a medium-intensity flashing white lighting system at night. There may be some populated areas where nighttime use of medium- intensity light systems may cause significant environmental concerns. Using the dual lighting system should reduce/mitigate those concerns and complaints. Recommendations for lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
8.2 Installation.
The light units should be installed as specified in Chapters 4, 5, and 6. The number of light levels needed is dependent on the height of the obstruction, as shown in Figure, A-16.
8.3 Operation.
Light systems should be operated as specified in Chapter 4, 5, and 6. These systems should not be operated simultaneously; however, there should be no more than a 2-second delay when changing from one system to the other. Outage of the uppermost red light must cause the white obstruction light system to activate and operate in its specified “night” step intensity.
8.4 Control Device.
The light system is controlled by a device (photocell) that changes the intensity of the lights when the ambient light changes. The illuminance sensing device should, if practical, face the northern sky in the Northern Hemisphere and the system should automatically change intensity steps when the illuminance reaching a north-facing vertical surface is as follows:
1. Twilight-to-Night. This should not occur before the illumination drops below 5 foot-candles
(53.82 lux) but should occur before it drops below 2 foot-candles (21.53 lux).
2. Night-to-Day. The intensity changes listed in subparagraph 8.4.1 above should be reversed when changing from the night-to-day mode.
8.5 Antenna or Similar Appurtenance Light.
1. When a structure equipped with a dual lighting system is topped with an antenna or similar appurtenance exceeding 40 feet (12.19 m) in height, a medium -intensity flashing white (L-
865) and a flashing red light (L-864) should be placed within 40 feet (12.19 m) from the tip of the appurtenance. The white light should operate during daytime and twilight and the red
light during nighttime. These lights should flash simultaneously with the rest of the lighting system.
2. When a structure equipped with a dual lighting system is topped with an antenna or similar appurtenance less than 40 feet (12.19 m) in height and exceeds 7/8 of an inch, a minimum of two medium-intensity flashing white (L-865), flashing red lights (L-864) should be placed immediately below, within 40 feet (12.19 m) from the tip of the appurtenance (see Figure A-
17). The white light should operate during daytime and twilight and the red light between the hours of sunset and sunrise. These lights should flash simultaneously with the rest of the lighting system.
8.6 Omission of Marking.
When medium-intensity white obstruction lights are operated on structures 700 feet (213.36 m) AGL or less during daytime and twilight, other methods of marking may be omitted.
CHAPTER 9. DUAL LIGHTING WITH RED/HIGH-INTENSITY FLASHING
WHITE LIGHT SYSTEMS
9.1 Purpose.
This dual lighting system includes red lights (L-864) for nighttime and high-intensity flashing white lights (L-856) for daytime and twilight use. This lighting system may be used in lieu of operating a flashing high intensity white lighting system at night. There may be some populated areas where nighttime use of high-intensity lights may cause significant environmental concerns and complaints. Using the dual lighting system should reduce/mitigate those concerns.
Recommendations on lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
9.2 Installation.
The light units should be installed as specified in Chapters 4, 5, and 7. The number of light levels needed is dependent on the height of the structure as shown in Figures A-18 and A-19.
9.3 Operation.
Lighting systems should be operated as specified in Chapters 4, 5, and 7. These systems should not be operated simultaneously; however, there should be no more than a 2-second delay when changing from one system to the other. Outage of the uppermost red light must cause the white obstruction lighting system to activate and operate in its specified “night” step intensity.
9.4 Control Device.
The light intensity is controlled by a device (photocell) that changes the light intensity when the ambient light changes. The illuminance-sensing device should, if practical, face the northern sky in the Northern Hemisphere and the system should automatically change intensity steps when the illuminance reaching a north-facing vertical surface is as follows:
1. Day-to-Twilight. This should not occur before the illumination drops to 60 foot-candles
(645.83 lux) but should occur before it drops below 35 foot-candles (376.74 lux).
2. Twilight-to-Night. This should not occur before the illumination drops below 5 foot-candles
(53.82 lux) but should occur before it drops below 2 foot-candles (21.53 lux).
3. Night-to-Day. The intensity changes listed in subparagraph 9.4.1 and 9.4.2 above should be reversed when changing from the night to day mode.
9.5 Antenna or Similar Appurtenance Light.
When a structure using this dual lighting system is topped with an antenna or similar
appurtenance exceeding 40 feet (12.19 m) in height, a high-intensity flashing white light (L-856) and a red flashing light (L-864) should be placed within 40 feet (12.19 m) from the tip of the appurtenance (see Figure A-18). The white light should operate during daytime and twilight and the red light during nighttime. Structures with an appurtenance 40 feet (12.19 m) or less in height should be lit in accordance with see Figure A-19.
9.6 Omission of Marking.
When high-intensity white obstruction lights are operated during daytime and twilight, other methods of marking may be omitted.
CHAPTER 10. AIRCRAFT DETECTION LIGHTING SYSTEMS
10.1 Purpose.
Aircraft Detection Lighting Systems (ADLS) are sensor-based systems designed to detect aircraft as they approach an obstruction or group of obstructions; these automatically activate the appropriate obstruction lights until they are no longer needed by the aircraft. This technology reduces the impact of nighttime lighting on nearby communities and migratory birds and extends the life expectancy of the obstruction lights.
10.2 General Standards.
10.2.1. The system should be designed with sufficient sensors to provide complete detection coverage for aircraft that enter a three-dimensional volume of airspace, or coverage area, around the obstruction(s) (Figure A-20), as follows:
1. Horizontal detection coverage should provide for obstruction lighting to be activated and illuminated prior to aircraft penetrating the perimeter of the volume, which is a minimum of 3 NM (5.56 km) away from the obstruction or the perimeter of a group of obstructions. In some situations, such as when the 3 NM perimeter is not achievable, lighting uncontrolled by the ADLS may be required.
2. Vertical detection coverage should provide for obstruction lighting to be activated and illuminated prior to aircraft penetrating the volume, which extends from 200 feet above the ground up to 1,000 feet (304.80 m) above the highest part of the obstruction or group of obstructions, for all areas within the 3 NM (5.56 km) perimeter defined in subparagraph
10.2.1.1 above.
3. In some circumstances, it may not be possible to meet the volume area defined above because the terrain may mask the detection signal from acquiring an aircraft target within the 3 NM (5.56 km) perimeter. In these cases, the sponsor should identify these areas in their application to the FAA for further evaluation.
4. In some situations, lighting not controlled by the ADLS may be required when the 3 NM
(5.56 km) perimeter is not achievable to ensure pilots have sufficient warning before approaching the obstructions.
10.2.2. The ADLS should activate the obstruction lighting system in sufficient time to allow the lights to illuminate and synchronize to flash simultaneously prior to an aircraft penetrating the volume defined above. The lights should remain on for a specific time period, as follows:
1. For ADLSs capable of continuously monitoring aircraft while they are within the 3 NM/1,000 foot (5.56 km/304.80 m) volume, the obstruction lights should stay on until the aircraft exits the volume. In the event detection of the aircraft is lost while being
continuously monitored within the 3 NM/1,000 foot (5.56 km/304.80 m) volume, the ADLS should initiate a 30-minute timer to keep the obstruction lights on until the timer expires.
This should provide the untracked aircraft sufficient time to exit the area and give the ADLS time to reset.
2. For ADLSs without the capability of monitoring aircraft targets in the 3 NM/1,000 foot (5.56 km/304.80 m) volume, the obstruction lights should stay on for a preset amount of time, calculated as follows:
a. For single obstacles: seven minutes.
b. For groups of obstacles: (the widest dimension of the group in nautical miles + 6) x 90 seconds, equals the number of seconds the light(s) should remain on.
10.2.3. Approval of an ADLS will be on a case-by-case basis and may be modified, adjusted, or denied based on proximity of the obstruction or group of obstructions to airports, low-altitude flight routes, military training areas, or other areas of frequent flight activity. It may be appropriate to keep certain obstructions closest to these known activity areas illuminated during the nighttime hours, while the remainder of the group’s obstruction lighting is controlled by the ADLS.
10.2.4. Project sponsors requesting the use of ADLS should indicate the location of the proposed sensors, range of each sensor, and a visual indication showing how each sensor’s detection arc provides the full horizontal and vertical coverage, as required under paragraph 10.2.1 on their application maps or diagrams. In the event that detection coverage is not 100 percent due to terrain masking, project sponsors should provide multiple maps or diagrams that indicate coverage at the affected altitudes. A sample diagram is shown in Figure A-20.
10.2.5. Types of ADLS component or system failure events.
1. In the event of an ADLS component or system failure, the ADLS should automatically turn on all the obstruction lighting and operate in accordance with this AC as if it was not controlled by an ADLS. The obstruction lighting must remain in this state until the ADLS and its components are fully restored.
2. In the event that an ADLS component failure occurs and an individual obstruction light cannot be controlled by the ADLS, but the rest of the ADLS is functional, that particular obstruction light should automatically turn on and operate in accordance with this AC as if it was not controlled by an ADLS, and the remaining obstruction lights can continue to be controlled by the ADLS. The obstruction lighting will remain in this state until the ADLS and its components are restored.
3. Complete light failure should be addressed in accordance with Chapter 2, paragraph 2.4.
10.2.6. The ADLS’s communication and operational status must be checked at least once every 24 hours to ensure both systems are operational.
10.2.7. The ADLS should be able to detect an aircraft with a cross-sectional area of one square meter or more within the volume, as required in subparagraphs 10.2.1.1. and 10.2.1.2.
10.2.8. Each ADLS installation should maintain a log of activity data for a period of no less than the previous 15 days. This data should include, but not be limited to, the date, time, duration of all system activations/deactivations, track of aircraft activity, maintenance issues, system errors, communication and operational issues, lighting outages/issues, etc.
10.2.9. Operational frequencies.
1. Unlicensed devices (including FCC Part 15) cannot be used for this type of system.
2. Any frequency used for the operation of ADLS must be individually licensed through the FCC.
CHAPTER 11. MARKING AND LIGHTING OF CATENARY AND CATENARY
SUPPORT STRUCTURES
11.1 Purpose.
This chapter provides guidelines for marking and lighting catenary and catenary support structures. For the purpose of marking and lighting, catenary is defined as suspended wires (or lines) kept at a defined mechanical tension by supporting structures. These wires may be either energized or non-energized and are used for transmission, distribution, or other purposes, as defined. The recommended marking and lighting of both the structures and wires provides day and night conspicuity and assists pilots in identifying and avoiding catenary wires and associated support structures. Catenary lines that are suspended across open areas such as rivers, canyons, and lakes create a unique hazard to pilots. The term “violation area” is used to describe these open areas within the catenary span that an aircraft would most likely encounter the wires.
11.2 Lighted Spherical Markers.
11.2.1. Lighted markers are available for increased night conspicuity of high-voltage (69 kV or greater) 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 (1,219.20 m) under nighttime conditions, minimum Visual Flight Rules (VFR) conditions, or having a minimum intensity of at least 32.5 candelas. The lighting unit should emit a steady-burning, red light.
11.2.2. Lighted markers should be installed on the highest energized line. If the lighted markers are installed on a line other than the highest catenary, then markers specified in paragraph 11.3.2, 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 no more than 25 feet (7.62 m) and must not violate the sag requirements of the transmission line design (see Figure A-25).
Lighted markers should be distinctively shaped, (i.e., spherical or 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. 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 (see Figure A-21).
When a catenary wire crossing requires three or more supporting structures, the inner structures should be equipped with enough light units per level to provide full coverage from which aircraft are likely to approach.
11.3 Catenary Marking Standards.
Catenary wires should be marked with lighted or unlighted marker balls to make the wires more
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
approximately 200 feet (60.96 m), or a fraction thereof. Intervals between markers should be less in critical areas near runway ends, i.e., 30 feet to 50 feet (9.14 m to 15.24 m). If the lighted markers are installed on a line other than the highest catenary wire, then unlighted markers specified in paragraph 11.3.2, should be used in addition to the lighted markers. The lighted markers may be installed alternately along each wire if the distance between adjacent markers meets the 200-foot (60.96m) 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. Lighted and unlighted markers should be installed by alternating solidcolored 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 (60.96 m)) to accommodate the rest of the markers. When less than four markers are used, they should all be aviation orange (see Figure A-24).
c. Wire Sag. Wire sag or droop will occur due to temperature, wire weight, wind, etc. The maximum sag distance between the line energizing the lighted markers and the highest catenary wire above the lighted markers should be no more than 25 feet (7.62 m), and it should not violate the sag requirements of the transmission line design.
d. Adjacent Lines. Catenary crossings with multiple transmission lines require appropriate markers when the adjacent catenary structure’s outside lines are greater than 200 feet
(60.96 m) away from the center of the primary structure (see Figure A-23). If the outside lines of the adjacent catenary structure are within 200 feet (60.96 m) or less from the center of the primary structure, markers are not required on the adjacent lines (see Figure A-22). If the catenary crossing is within close proximity to an airport, specifically within 1,500 feet (458 m) of an airport runway end, then all catenary lines should be marked, regardless of their proximity to each other.
11.3.2 Unlighted Catenary Markers.
Unlighted markers provide increased daytime conspicuity of non-high-voltage (less than 69 kV) transmission line catenary wires. These unlighted markers should be used on transmission line catenary wires near airports, heliports, across rivers, canyons, lakes, areas of known risk to aviation, etc. where lighted markers are not possible.
The unlighted markers should be manufacturer-certified as recognizable from a minimum distance of 4,000 feet (1,219.20 m) under daytime, VFR conditions. Markers should be distinctively shaped, i.e., spherical or cylindrical, so that they are not mistaken for items used to convey other information. Unlighted markers should be mounted on the highest catenary line, visible to a pilot approaching from any direction.