6.4.6 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.
6.5 Chimneys, Flare Stacks, and Similar Solid Structures.
The recommended number of top-level light units depends on the diameter of the structure at the highest point of a structure. The lights should be installed at the highest point, however, top level chimney lights may be installed as low as 20 feet (6.10 m) below the top to minimize deposit build-up due to emissions (see Figure A-10). The number of lights per level below is the minimum recommended.
1. Structures 20 feet (6.10 m) or less in diameter. Three light units per level
2. Structures exceeding 20 feet (6.10 m) but not more than 100 feet (31 m) in diameter. Four light units per level.
6.6 Prominent Buildings and Similar Extensive Obstructions.
With the exception of wind turbines, 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 installed on the same horizontal plane at the highest portion, or edge, of the prominent obstructions. Light units should be placed to ensure that the light is visible to a pilot approaching from any direction. Lights should be displayed to indicate the extent of the obstruction as follows:
1. Structures 150 feet (45.72 m) or less in any horizontal direction. If the structure/extensive obstruction is 150 feet (45.72 m) or less horizontally, at least one light should be displayed on the highest point at each end of the obstruction’s major axis. If this is impractical because of the overall shape, display a double obstruction light in the center of the highest point.
2. Structures exceeding 150 feet (45.72 m) in at least one horizontal direction. If the structure/extensive obstruction exceeds 150 feet (45.72 m) horizontally, at least one light should be displayed for each 150 feet (45.72 m), or fraction thereof, of the overall length of the major axis. At least one of these lights should be displayed on the highest point at each end of the obstruction. Additional lights should be displayed at approximately equal intervals not to exceed 150 feet (45.72 m) on the highest points along the edge between the end lights. If an obstruction is located near a landing area and two or more edges are the same height, the edge nearest the landing area should be lighted.
3. Structures exceeding 150 feet (45.72 m) AGL. Lights should be installed on the highest point at each end. At intermediate levels, lights should be displayed for each 150 feet
(45.72 m), or fraction thereof. The vertical position of these lights should be equidistant between the top lights and the ground level as the shape and type of obstruction will permit. One such light should be displayed at each outside corner on each level with the remaining lights evenly spaced between the corner lights.
6.7 Group of Obstructions.
With the exception of wind turbines, when individual structures within a group of obstructions differ in height and are spaced no more than 150 feet (45.72 m) apart, the prominent structures within the group should be lighted in accordance with the standards for individual obstructions based on its corresponding height. Shorter structures within the group of obstructions do not need to be lighted. When structures are shorter than the prominent structure and located on the outside of the group of obstructions, those structures should be lighted in accordance with the standards for individual obstructions based on its corresponding height. In addition to lighting the shorter structures on the outside of the group, at least one flashing light should be installed either at the top of the tallest, most prominent center structure, or on a dedicated tower that is located near the center of the group and is the same height as the most prominent structure. Light units should be placed on the structures to ensure that the lights are visible to a pilot approaching from any direction. If one or more of the structures within the group are a solid mass (nonskeletal), additional lighting may be necessary to make sure that the light is not being blocked by the more prominent structure(s). For the purpose of marking and lighting these structures, a group of obstructions is considered to be three or more structures.
6.8 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 may be necessary and should not derogate the lighting system’s intended purpose.
CHAPTER 7. HIGH-INTENSITY FLASHING WHITE OBSTRUCTION LIGHT
SYSTEMS
7.1 Purpose.
High-intensity (L-856) flashing white obstruction lights provide the highest degree of conspicuity both day and night. Recommendations on lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
Use extreme caution when using high-intensity flashing white lights. Using a 24-hour, highintensity flashing white light system in urban/populated areas is not normally recommended due to their tendency to merge with background lighting in these areas at night. This makes it extremely difficult for some types of aviation operations (i.e., medevac) and police helicopters to see these structures. Additionally, this type of system in urban and rural areas often results in complaints.
7.2 Standards.
High-intensity flashing white obstruction lights should be used during daytime with automatically selected, reduced intensities for twilight and nighttime operations. When highintensity white obstruction lights are operated 24 hours a day, other methods of marking and lighting may be omitted. This system should not be recommended on structures 700 feet (213.36
m) AGL or less unless an FAA aeronautical study shows otherwise. The number of light levels needed is shown in, Figures A-13 and A-14.
7.3 Control Device.
Light intensity is controlled by a device (photocell) that changes the light’s 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 subparagraphs 7.3.1 and 7.3.2 above should be reversed when changing from the night-to-day mode
7.4 Units per Level.
One or more light units are needed to obtain the desired horizontal coverage. The number of light units recommended per level (except for the supporting structures of catenary wires and
buildings) depends upon the average outside diameter of the specific structure and the horizontal beam width of the light fixture. Light units should be installed to ensure an unobstructed view of the system by a pilot approaching from any direction. The number of lights recommended below is the minimum.
1. Structures 20 feet (6.10 m) or less in diameter. Three light units per level.
2. Structures exceeding 20 feet (6.10 m) but not more than 100 feet (30.48 m) in diameter. Four light units per level.
3. Structures exceeding 100 feet (30.48 m) in diameter. Six light units per level.
4. Structures exceeding 200 feet (60.96 m) in diameter. Eight light units per level.
7.5 Installation Guidance.
On most obstruction high-intensity light fixtures, the effective peak intensity of the light beam can be adjusted from zero-to-eight degrees above the horizon. Standard installation should place the top light at zero degrees to the horizontal and all other light units installed in accordance with Table 7-1.
Table 7-1. Light Unit Elevation Above the Horizontal
Height of Light Unit Above Terrain
Degrees of Elevation Above
Exceeding 500 feet AGL
Above 400 feet to 500 feet AGL
Above 300 feet to 400 feet AGL
300 feet AGL or less
1. Vertical Aiming. When terrain, nearby residential areas, or other situations dictate, the light beam may be further elevated above the horizontal. The main beam of light at the lowest level should not strike the ground closer than 3 SM (4.83 kilometers (k)) from the structure.
If additional adjustments are necessary, the lights may be individually adjusted upward, in one-degree increments, starting at the bottom. Excessive elevation may reduce its conspicuity by raising the beam above a collision course flight path.
2. Relocation or Omission of Light Units. Light units should not be installed in such a manner that the light pattern/output is disrupted by the structure.
a. Lowest Level. The lowest level of light units may be installed at a higher elevation than normal on a structure if the surrounding terrain, trees, or adjacent building(s) would obscure the lights. In certain instances, as determined by the FAA, the lowest level of lights may be eliminated.
b. Two Adjacent Structures. When two structures are within 500 feet (152.40 m) of each other and the light units are installed at the same levels, the sides of the structures facing each other do not need be lighted (see Figures A-11 and A-12). However, all lights on both structures must flash simultaneously, except for adjacent catenary support structures.
Vertical placement of the lights should be adjusted to either or both structures’ intermediate levels to place the lights on the same horizontal plane. If one structure is higher than the other, a complete level of lights should be installed on the higher structure that extends above the top of the lower structure. If the structures are of such heights that the levels of lights cannot be placed in identical horizontal planes, then the light units should be placed so that the center of the horizontal beam patterns do not face toward the adjacent structure. For example, structures situated north and south of each other should have the light units on both structures installed on a northwest/southeast and northeast/southwest orientation.
c. Three or More Adjacent Structures. The treatment of a cluster of structures as an individual or a complex of structures will be determined by the FAA, taking into consideration the location, heights, and spacing of other structures.
7.6 Radio and Television Towers and Similar Skeletal Structures.
1. Mounting Lights.
The number of levels recommended depends on the height of the structure, excluding antennas and similar appurtenances. At least three lights should be installed on each level and mounted to ensure that the effective intensity of the full horizontal beam coverage is not impaired by the structural members.
2. Top Level.
One level of lights should be installed at the highest point of the structure. If the highest point is a rod or antenna incapable of supporting a lighting system, then the top level of lights should be installed at the highest portion of the main skeletal structure. If guy wires come
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