4. Dual Lighting. This system consists of red lights for nighttime and high- or medium-intensity flashing white obstruction lights for daytime and twilight. When a dual lighting system incorporates medium-intensity flashing white lights on structures 700 feet (213.36 m) AGL or less or high-intensity flashing white lights on structures greater than 700 feet (213.36 m) AGL, other methods of marking the structure may be omitted.
5. Lighted Spherical Markers. Lighted markers are available for increased night conspicuity of high-voltage (69 kV or greater) transmission line catenary wires and should be manufacturercertified 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
6. Aircraft Detection Lighting System. Lights are controlled by sensor based systems designed to detect aircraft approaching a single obstacle or group of obstacles and automatically activate the appropriate obstruction lights until the aircraft has departed the area and the lights are no longer needed. This technology reduces the impact of nighttime lighting on nearby communities and migratory birds, as well as, extends the life expectancy of obstruction lights.
7. Obstruction Lights During Construction. As the height of the structure exceeds each level at which permanent obstruction lights would be recommended, two or more lights of the type specified in the determination should be installed at that level. Temporary high- or mediumintensity flashing white lights, if recommended in the determination, should be operated 24 hours a day until all permanent lights are in operation. In either case, two or more lights should be installed on the uppermost part of the structure any time it exceeds the height of the temporary construction equipment. They may be turned off for periods when they could interfere with construction personnel. If practical, permanent obstruction lights should be installed and operated at each level as construction progresses. The lights should be positioned to ensure that a pilot has an unobstructed view of at least one light at each level when approaching from any direction.
8. Obstruction Lights in Urban Areas. When a structure is located in an urban area where there are numerous other white lights (e.g., streetlights), red obstruction lights with painting or a medium-intensity dual system is recommended. White lighting is not normally recommended on structures less than 200 feet (60.96 m) or within 3 NM of an airport.
4.4 Inspection, Repair, and Maintenance.
To ensure the proper candela output for fixtures with incandescent lamps, the voltage provided to the lamp filament should not vary more than plus or minus three percent of the lamp’s rated voltage. The input voltage should be measured at the closest disconnecting means to the lamp fixture with the lamp operating during the hours of normal operation (for strobes, the input voltage of the power supplies should be within 10 percent of rated voltage).
Lamps should be replaced after being in operation for approximately 75 percent of their rated life or immediately upon failure.
Flashtubes in a light unit should be replaced immediately upon failure, when the peak effective intensity falls below specification limits, when the fixture begins skipping flashes, or at the manufacturer’s recommended intervals.
Due to the effects of harsh environments, light fixture lenses should be visually inspected every 24 months or when the light fixture fails for ultraviolet (UV) damage, cracks, crazing, dirt buildup, etc., to ensure the certified light output has not deteriorated (see Chapter 2, paragraph
2.4 for reporting requirements in case of failure). Lenses that have cracks, UV damage, crazing, or excessive dirt buildup should be cleaned or replaced.
4.5 Nonstandard Lights.
Moored balloons, chimneys, church steeples, and similar obstructions may be floodlighted by fixed search light projectors installed at three or more equidistant points around the base of each obstruction. The searchlight projectors should provide an average illumination of at least 15 footcandles (161.46 lux) over the top one-third of the obstruction.
4.6 Placement Factors.
The height above ground level (AGL) of the structure determines the number of light levels. The light levels may be adjusted slightly, but not to exceed 10 feet (3.05 m) when necessary to accommodate guy wires and personnel who replace or repair light fixtures. Except for catenary wire support structures, the following factors should be considered when determining the placement of obstruction lights on a structure:
1. Red Obstruction Lighting Systems. The structure’s overall height, including all appurtenances, such as rods, antennas, and obstruction lights, determines the number of light levels.
2. Medium-Intensity Flashing White Obstruction Lighting Systems. The structure’s overall height, including all appurtenances such as rods, antennas, and obstruction lights, determines the number of light levels.
3. High-Intensity Flashing White Obstruction Lighting Systems. The main structure’s overall height, excluding all appurtenances, such as rods, antennas, and obstruction lights, determines the number of light levels.
4. Dual Obstruction Lighting Systems. The structure’s overall height, including all appurtenances, such as rods, antennas, and obstruction lights, is used to determine the number of light levels for a medium-intensity white obstruction light/red obstruction dual lighting system. The structure’s overall height, excluding all appurtenances, is used to
determine the number of light levels for a high-intensity white obstruction light/red obstruction dual lighting system.
5. Aircraft Lighting Detection System. The system should be designed with sufficient sensors and mounted with a clear view to provide complete detection coverage for aircraft that enter a three-dimensional volume of airspace, or coverage area, around an obstruction(s). The system 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 defined volume and remain on for a specified time expected for the aircraft to depart the coverage area.
6. Lighted Spherical Markers. 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 should be installed on the highest energized line. 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.
7. 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 correct number of light levels required.
8. Shielded Lights. If an adjacent structure or object blocks the visibility of an obstruction light, the light’s horizontal placement should be adjusted or additional lights should be mounted on that object to retain or contribute to the definition of the obstruction.
9. Nesting of Lights. Care should be taken to ensure that obstruction lights do not become blocked or “nested” as new antennas, hardware, or appurtenances are added to the top of a structure. If new equipment is added that blocks the obstruction light’s visibility, the light fixtures must be relocated and/or raised so that it is not blocked by the new equipment. For example, when new larger cellular antenna panels are fitted to older towers, the obstruction light will need to be raised so that it is not blocked by the larger antenna panels. The widest structure, appurtenance, lightning rod, or antenna that can be placed in front of an obstruction light (excluding the L-810 light) without significantly blocking the obstruction light’s visibility should be no wider than 7/8 of an inch. Due to their smaller size, L-810 lights should not be blocked by any structure.
4.7 Monitoring Obstruction Lights.
Obstruction lighting systems should be closely monitored by visual or automatic means. It is extremely important to visually inspect obstruction lighting in all operating intensities 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. When using remote monitoring devices, the system’s communication and operational status should be confirmed at least once every 24 hours. The monitor (aural or visual) should be located in an area generally occupied by the responsible personnel. In some cases, this may require a remote monitor in an attended location. For each structure, a log should be maintained in which the lighting system’s daily operations status is recorded. Light fixture lenses should be replaced if serious cracks, hazing, dirt buildup, etc., has occurred.
4.8 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.
4.9 Light Shields.
In general, light shields are not permitted because of the adverse effects they have on the obstruction light fixture’s photometrics. In addition, these shields can promote undesired snow accumulation, bird nesting, and wind loading.
4.10 Distractions.
When obstruction lights are in proximity to a navigable waterway, they may distract vessel operators. To avoid interference with marine navigation, coordinate with the Office of Navigation Systems, United States (U.S.) Coast Guard before installing the lighting system. The contact information for the U.S. Coast Guard is:
Commandant (CG-NAV-1) U.S. Coast Guard 2703 Martin Luther King Jr. Avenue, Southeast STOP 7418 Washington, DC 20593-0001 Telephone: 202-372-1546
CHAPTER 5. RED OBSTRUCTION LIGHT SYSTEM
5.1 Purpose.
Red steady burning (L-810) and flashing (L-810 F or L-864) Obstruction Light Systems are used to increase conspicuity during nighttime, however additional marking and/or lighting during daytime and twilight is required. Recommendations on lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
5.2 Standards.
The red obstruction light system is composed of flashing omnidirectional lights (L-864) and/or steady-burning or flashing (L-810/L-810 (F)) lights. When one or more levels are comprised of flashing lights, the lights should flash simultaneously. To determine the number of light levels needed, refer to Figure A-6.
1. Single Obstruction Light. A single red obstruction light may be used when more than one obstruction light is required either vertically or horizontally, or when maintenance is needed, and can be installed within a reasonable time.
a. Top level. A single steady-burning light may be used to identify low structures, such as airport instrument landing system buildings, as well as long horizontal structures, such as perimeter fences and building roof outlines.
b. Intermediate level. Single flashing or steady-burning lights (as appropriate for size and type of structure) may be used on skeletal and solid structures when more than one level of lights is installed and there are two or more single lights per level.
2. Double Obstruction Light. A double steady-burning light should be installed when used as a top light, at each end of a row of single obstruction lights, and in areas or locations where the failure of a single unit could cause an obstruction to be totally unlighted.
a. Top level. Structures 150 feet (45.72 m) AGL or less should have one or more double steady-burning lights installed at the highest point and operating simultaneously.
b. Intermediate level. Double flashing or steady-burning lights (as appropriate for size and type of structure) should be installed at intermediate levels when a malfunction of a single light could create an unsafe condition and in remote areas where immediate maintenance cannot be performed. Both units may operate simultaneously, or a transfer relay may be used to switch to a spare unit should the active system fail.
c. 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.
5.3 Control Device.
Red obstruction lights should be operated by an acceptable control device (e.g., photocell, timer, etc.) adjusted so the lights will be turned on when the northern sky illuminance reaching a vertical surface falls below a level of 60 foot-candles (645.83 lux) but before reaching a level of 35 foot-candles (376.73 lux). The sensing device should, if practical, face the northern sky in the Northern Hemisphere (see AC 150/5345-43, Specification for Obstruction Lighting Equipment).
The control device should turn the lights off when the northern sky illuminance rises to a level of not more than 60 foot-candles (645.83 lux). The lights may also remain on continuously.
5.4 Alternate Method of Displaying Obstruction Lights.
In certain cases, instead of installing lights on the obstruction, the FAA may recommend the placement of a light(s) on an adjacent pole of equal height.
5.5 Poles, Towers, and Similar Skeletal Structures.
The following standards apply to radio and television towers, supporting structures for overhead transmission lines, and similar structures.
1. Top-Mounted Obstruction Lights.
a. Structures 150 feet (45.72 m) AGL or less. Two or more steady-burning red (L- 810) lights should be installed in a manner to ensure an unobstructed view of one or more lights by a pilot.
b. Structures exceeding 150 feet (45.72 m) AGL. At least one red flashing (L- 864) light should be installed in a manner to ensure an unobstructed view of one or more lights by a pilot.
c. Appurtenances 40 feet (12.19 m) or less. If a rod, antenna, or other appurtenance 40 feet
(12.19 m) or less in height is incapable of supporting a red flashing light, then it may be placed at the base of the appurtenance. If the mounting location does not allow an unobstructed view of the light by a pilot approaching in any direction, then additional lights should be added.
d. Appurtenances exceeding 40 feet (12.19 m). If a rod, antenna, or other appurtenance exceeding 40 feet (12.19 m) in height is incapable of supporting a red flashing light, a
supporting mast with one or more lights should be installed adjacent to the appurtenance.
Adjacent installations should not exceed the appurtenance’s height and be within 40 feet
(12.19 m) of the tip to allow the pilot an unobstructed view of at least one light. If the rod, antenna, or other appurtenance is 7/8 inch wide or more, at least two lights must be installed on the supporting mast to provide the necessary unobstructed view.
2. Mounting Intermediate Levels. The number of light levels is determined by the height of the structure, including all appurtenances, as shown in , Figure A-6. The number of lights on each level is determined by the shape and height of the structure. These lights should be mounted to ensure an unobstructed view of at least one light by a pilot approaching in any direction.
a. Steady-burning lights (L-810).
i. Structures 150 feet (45.72 m) AGL or less. Two or more steady-burning lights should be installed diagonally or on diametrically opposite positions.
ii. Structures exceeding 150 feet (45.72 m) AGL. These structures do not require steadyburning lights.
b. Flashing lights (L-810 F). For structures exceeding 150 feet (45.72 m) but not more than 350 feet (106.68 m), two or more flashing lights should be mounted outside at diagonally opposite positions at intermediate levels. These lights should be configured to flash simultaneously with the L-864 flashing light on the top of the structure at a rate of 30 flashes per minute (fpm) (± 3 fpm).
c. Flashing lights (L-864).
i. Structures 350 feet (106.68 m) AGL or less. These structures do not require flashing (L-864) lights at intermediate levels.
ii. Structures exceeding 350 feet (106.68 m) AGL. At intermediate levels, two (L-864) lights should be mounted outside at diagonally opposite positions.
5.6 Chimneys, Flare Stacks, and Similar Solid Structures (except Hyperbolic Cooling Towers).
5.6.1 Number of Light Units.
The number of units recommended depends on the diameter of the structure at the top. The number of lights recommended below is the minimum (see Figure A- 10).
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.
5.6.2 Top-Mounted Obstruction Lights.
1. Structures 150 feet (45.72 m) AGL or less. L-810 lights should be installed horizontally at regular intervals at or near the top.
2. Structures exceeding 150 feet (45.72 m) AGL. At least three L-864 lights should be installed.
3. Chimneys, Cooling Towers, and Flare Stacks. Lights may be displayed as low as 20 feet
(6.10 m) below the top (, Figure A-7) to avoid the obscuring effect of deposits and heat generally emitted by this type of structure. It is important that these lights are readily accessible for cleaning and lamp replacement. It is understood that with flare stacks, as well as any other structures associated with the petrol-chemical industry, normal lighting requirements may not be necessary. This could be due to the location of the flare stack/structure within a large, well-lighted, petrol-chemical plant, or the fact that the flare, or working lights surrounding the flare stack/structure, is as conspicuous as obstruction lights.
5.6.3 Mounting Intermediate Levels.
The number of light levels is determined by the height of the structure including all appurtenances. Structures between 150 feet and 350 feet (45.72 m and 106.68 m) AGL should have a second level of steady-burning red light units installed approximately at the midpoint of the structure and in a vertical line with the top level of lights. Structures exceeding 350 feet
(106.68 m) AGL should have a second level of flashing light units. For cooling towers 600 feet
(182.88 m) AGL or less, intermediate light levels are not necessary.
1. Steady-burning (L-810) lights. The recommended number of light levels is shown in Figure A-6. At least three lights should be installed on each level.
2. Flashing (L-864) lights. The recommended number of light levels is shown in Figure A-6.
a. Structures 350 feet (106.68 m) AGL or less. These structures do not need intermediate levels of flashing lights.
b. Structures exceeding 350 feet (106.68 m) AGL. At least three flashing (L-864) lights should be installed on each level in a manner allowing an unobstructed view of at least one light.
5.7 Prominent Buildings, Bridges, 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 installed on the same horizontal plane at the highest portion, or edge, of the prominent obstructions. Light units should be placed to
ensure the light is visible to a pilot approaching from any direction. If the structure is a bridge (see Figure A-8) and is over navigable water, the sponsor must obtain prior approval of the lighting installation from the Commander of the District Office of the U.S. Coast Guard to avoid interference with marine navigation. Steady-burning 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/bridge/extensive obstruction is 150 feet (45.72 m) or less horizontally, at least one steady-burning light (L-810) 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/bridge/extensive obstruction exceeds 150 feet (45.72 m) horizontally, at least one steady-burning 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. Steady-burning red obstruction lights should be installed on the highest point at each end. At intermediate levels, steady-burning red 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. A steady-burning red light should be displayed at each outside corner on each level with the remaining lights evenly spaced between the corner lights.
4. Exceptions. Flashing red lights (L-864) may be used instead of steady-burning lights if early or special warning is necessary. These lights should be displayed on the highest points of an extensive obstruction at intervals not exceeding 3,000 feet (914.40 m). At least three lights should be displayed on one side of the extensive obstruction to indicate a line of lights.
5. 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.
5.8 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 are 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.
CHAPTER 6. MEDIUM-INTENSITY FLASHING WHITE OBSTRUCTION LIGHT
SYSTEMS
6.1 Purpose.
Medium-intensity flashing white (L-865) obstruction lights may provide conspicuity both day and night. Recommendations on lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
Using a 24-hour, medium-intensity, flashing white light system in urban/populated areas is not normally recommended due to their tendency to blend with the background lighting in these areas at night. This makes it extremely difficult for some types of aviation operations, i.e., medical-evacuation (medevac) and police helicopters to see these structures. Using this type of system in urban and rural areas often results in complaints. In addition, this system is not recommended on structures within 3 NM of an airport.
6.2 Standards.
The medium-intensity flashing white light system is normally composed of flashing omnidirectional lights. Medium-intensity flashing white obstruction lights may be used during daytime and twilight with automatically selected, reduced intensity for nighttime operation.
When this system is used on structures 700 feet (213.36 m) AGL or less, other methods of marking and lighting the structure may be omitted. Aviation orange and white paint is always required for daytime marking on structures exceeding 700 feet (213.36 m) AGL. This system is not normally recommended on structures 200 feet (60.96 m) AGL or less. The number of light levels needed is shown in Figure A-9.
6.3 Control Device.
The 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 illumine sense 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 6.3 1 above should be reversed when changing from the night-to-day mode.
6.4 Radio and Television Towers and Similar Skeletal Structures.
6.4.1 Mounting Lights.
The number of levels recommended depends on the height of the structure, including antennas and similar appurtenances.
1. Top levels. One or more lights should be installed at the highest point to provide 360-degree coverage, ensuring an unobstructed view by a pilot approaching from any direction.
2. Appurtenances 40 feet (12.19 m) or less . If a rod, antenna, or other appurtenance 40 feet
(12.19 m) or less in height is incapable of supporting the medium -intensity flashing white light, then it may be placed at the base of the appurtenance. I f the mounting location does not allow an unobstructed view of the medium -intensity flashing white light by a pilot approaching from any direction, then additional lights should be added.
3. Appurtenances exceeding 40 feet (12.19 m). If a rod, antenna, or other appurtenance exceeds 40 feet (12.19 m) above the tip of the main structure, a medium -intensity flashing white light should be placed within 40 feet (12.19 m) from the top of the appurtenance. If the appurtenance (such as a whip antenna) is incapable of supporting the light, one or more lights should be mounted on a pole adjacent to the appurtenance. Adjacent installations should not exceed the height of the appurtenance and be within 40 feet (12.19 m) of the tip to allow the pilot an unobstructed view of at least one light. If the 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.
6.4.2 Mounting Intermediate Levels.
At intermediate levels, two or more lights (L-865) should be mounted outside at diagonally or diametrically opposite positions of intermediate levels. The lowest light level should not be less than 200 feet (60.96 m) AGL.
6.4.3 Lowest Levels.
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.
6.4.4 Structures 700 feet (213.36 m) AGL or less.
When medium-intensity flashing white lights are used during nighttime and twilight only, marking is required for daytime. When operated 24 hours a day, other methods of marking and lighting are not required.
6.4.5 Structures exceeding 700 feet (213.36 m) AGL.
Medium intensity lights should be used during nighttime, twilight, and may be used 24 hours a day. Additionally, marking is always required for daytime. The number of light levels needed is the same as high intensity lights as shown in Figures A-13 and A-14.