applies to catenary support structures, radio and television towers, and similar skeletal structures.
To be effective, paint should be applied to all inner and outer surfaces of the framework.
3.4 Paint Patterns.
Various types of paint patterns are used to mark structures. The pattern is determined by the size and shape of the structure. The following patterns are recommended:
3.4.1 Solid Pattern.
Obstacles should be painted aviation orange if the structure’s horizontal and vertical dimensions do not exceed 10.5 feet (3.20 m).
3.4.2 Checkerboard Pattern.
Alternating rectangles of aviation orange and white are normally displayed on the following structures:
1. Water, gas, and grain storage tanks (see Figures A-3, A-4, and A-5).
2. Buildings, as required.
3. Large structures exceeding 10.5 feet (3.20 m) across, having a horizontal dimension that is equal to or greater than the vertical dimension.
3.4.3 Size of Patterns.
The sides of the checkerboard pattern should measure not less than five feet (1.52 m) or more than 20 feet (6.10 m) and should be as nearly square as possible. However, if it is impractical because of the size or shape of a structure, the sides of the patterns may be less than five feet
(1.52 m). The pattern should be arranged so that each outer corner of the structure will be painted aviation orange.
3.4.4 Alternate Bands.
Alternate bands of aviation orange and white are normally displayed on the following structures:
1. Communication towers and catenary support structures.
2. Poles.
3. Smokestacks.
4. Skeletal framework of storage tanks and similar structures.
5. Structures that appear narrow from a side view that are 10.5 feet (3.20 m) or less across, and the horizontal dimension is less than the vertical dimension
6. Coaxial cable, conduits, and other cables attached to the face of a tower. 3.4.5.
3.4.5 Color Band Characteristics.
Bands for structures of any height (see Figure A-6) should be:
1. Equal in width, provided each band is not less than 1 1/2 feet (0.46 m) or more than 100 feet
(30.48 m) wide.
2. Perpendicular to the vertical axis with the bands at the top and bottom painted orange.
3. An odd number of bands on the structure.
4. Equal and in proportion to the structure’s AGL height.
5. Approximately one-seventh the height, if the structure is equal to or less than 700 feet
(213.36 m) AGL. For each additional 200 feet (60.96 m) or fraction thereof, add one additional orange and one additional white band. Table 4-1 shows the required band widths based on the height of the structure.
Table 3-1. Structure Height to Bandwidth Ratio
If a structure is: Then Band Width:
Greater Than
Equal to or Less Than Band Width
10.5 feet (3.20 m)
700 feet (213.36 m)
1/7 of
700 feet (213.36 m)
900 feet (274.32 m)
1/9 of
900 feet (274.32 m)
1,100 feet (335.28 m)
1/11 of
1,100 feet (335.28 m)
1,300 feet (396.24 m)
1/13 of
3.4.6 Structures With a Cover or Roof.
If the structure has a cover or roof, the highest orange band should be continued to cover the entire top of the structure (see Figures A-3 and A-4).
3.4.7 Skeletal Structures Atop Buildings.
If a flagpole, skeletal structure, or similar object is erected on top of a building, the combined height of the object and building will determine whether marking is recommended. However, only the height of the object filed with the FAA determines the width of the color bands.
3.4.8 Partial Marking.
If marking is recommended for only a portion of a structure because the lower portion of the structure is shielded by other objects or terrain, the width of the bands on the exposed portion should still be determined by the overall height of the structure. Paragraph 3.4.5 provides details on calculating the width of the paint bands. A minimum of three bands should be displayed on the exposed portion of the structure. If the exposed portion of the structure is not large enough to have at least three bands, the width of the bands may be reduced equally so that three equally sized bands can be fit. This will ensure that the marking pattern provides sufficient contrast for a pilot to locate the structure.
3.4.9 Teardrop Pattern.
Spherical water storage tanks with a single, circular standpipe support may be marked in a teardrop-striped pattern. The tank should show alternate stripes of aviation orange and white.
The stripes should extend from the top center of the tank to its supporting standpipe. The width of the stripes should be equal, and the width of each stripe at the greatest girth of the tank should not be less than five feet (1.52 m) nor more than 15 feet (4.57 m) (see Figure A-5).
3.4.10 Community Names.
If it is desirable to paint the name of the community on the side of a tank or other structure, the stripe pattern may be broken to serve this purpose. This open area should have a maximum height of three feet (0.91 m) (see Figure A-5).
3.4.11 Exceptions.
Structural designs not conducive to standard markings may be marked as follows:
1. If it is not practical to paint the roof of a structure in a checkerboard pattern, it may be painted solid orange.
2. If a spherical structure is not suitable for an exact checkerboard pattern, the shape of the rectangles may be modified to fit the shape of the surface.
3. Storage tanks not suitable for a checkerboard pattern may have alternating bands of aviation orange and white or a limited checkerboard pattern applied to the upper one- third of the structure.
4. The skeletal framework of certain water, gas, and grain storage tanks may be excluded from the checkerboard pattern.
3.5 Unlighted Markers.
Unlighted markers are used to identify structures and to make them more conspicuous when it is impractical to paint them. Unlighted markers may also be used with aviation orange and white paint when additional conspicuity is necessary for aviation safety. Unlighted markers 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, daytime visibility from a distance of at least 4,000 feet (1,219.20 m) and in all directions from which aircraft are likely to approach. Unlighted markers should be distinctively shaped, i.e., spherical or cylindrical, so that they are not mistaken for items that are used to convey other information. They should be replaced when faded or otherwise deteriorated.
3.5.1 Spherical Markers.
Spherical markers are primarily used to identify overhead wires and catenary transmission lines that are less than 69 kilovolts (kV). Markers may be of another shape, i.e., cylindrical, provided the projected area of such markers is not less than that presented by a spherical marker.
1. Size and Color.
The diameter of the markers used on extensive catenary wires (catenary wires that cross canyons, lakes, rivers, etc.) should not be less than 36 inches (91.44 centimeter (cm)).
Smaller 20-inch (50.80-cm) spheres are permitted on less extensive catenary wires or on power lines below 50 feet (15.24 m) AGL and within 1,500 feet (457.20 m) of an airport runway end. Each marker should be a solid color, specifically aviation orange, white, or yellow.
2. Installation.
a. Spacing. Unlighted markers should be spaced equally along the wire at approximately 200-foot (60.96 m) intervals, or fraction thereof. There should be less space between markers in critical areas near runway ends (i.e., 30 feet to 50 feet (9.14 m to 15.24 m)).
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 of 200 feet or less. This method distributes the weight and wind- loading factors (see Figures A-21 and A-22).
b. Pattern. An alternating color scheme provides the most conspicuity against all backgrounds. Unlighted markers should be installed 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 (60.96 m)) to accommodate the rest of the markers. When less than four markers are used, they should all be aviation orange.
c. Wire Sag. Wire Sag, or droop, will occur due to temperature, wire weight, wind, etc.
Twenty-five feet (7.62 m) is the maximum allowable distance between the highest wire installed with marker balls and the highest wire without marker balls, and must 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. 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.
3.5.2 Flag Markers.
Flags are used to mark certain structures or objects when it is technically impractical to use spherical markers or paint. Flag markers must be mounted at the highest point of the structure to ensure visibility. Some common examples of structures that may utilize this type of markers include, temporary construction equipment and vehicles, oil and drilling rigs, cranes, and derricks.
1. Minimum Size. Each side of the flag marker should be at least two feet (0.61 m) in length.
2. Color Patterns. Flags should be colored as follows:
a. Solid. Aviation orange.
b. Orange and White. Arrange two triangular sections, one aviation orange, and the other white to form a rectangle.
c. Checkerboard. Flags three feet (0.91 m) or larger should be a checkerboard pattern of aviation orange and white squares, each one foot (0.30 m) plus or minus 10 percent.
3. Shape. Flags should be rectangular in shape and have stiffeners to keep them from drooping in calm wind.
4. Display. Flag markers should be displayed around, on top, or along the highest edge of the obstruction. When flags are used to mark extensive or closely grouped obstructions, they should be displayed approximately 50 feet (15.24 m) apart. The flag stakes should be strong enough to support the flags and be higher than the surrounding ground, structures, and/or objects of natural growth.
3.6 Unusual Complexities.
The FAA may also recommend appropriate marking in an area in which grouped obstructions present a common obstruction to air navigation.
3.7 Omission or Alternatives to Marking.
The alternatives listed below require FAA review and concurrence prior to making changes. See subsequent chapters for specific guidance. High-Intensity Flashing White Lighting Systems are more effective than aviation orange and white paint and therefore can be recommended instead of paint marking. This is particularly true under certain ambient light conditions involving the position of the sun relative to the direction of flight. High-intensity lighting systems should not be used on structures 700 feet (213.36 m) AGL or less, however, when operated during daytime, twilight, or 24 hours a day, other methods of marking and lighting may be omitted.
3.7.1 Medium-Intensity Flashing White Lighting Systems are operated during daytime and twilight on structures 700 feet (213.36 m) AGL or less, but generally not on structures less than 200 feet
(60.96 m) AGL. When used, other methods of marking may be omitted.
Note: Sponsors must ensure that alternatives to marking are coordinated with the FCC for structures under its jurisdiction prior to making the change.
CHAPTER 4. LIGHTING GUIDELINE
4.1 Purpose.
This chapter describes the various obstruction lighting systems used to identify structures that have been determined to require added conspicuity. The lighting standards in this AC are the minimum necessary for aviation safety. Recommendations for lighting structures can vary, depending on terrain features, weather patterns, geographic location, and number of structures.
4.2 Standards.
The standards outlined in this AC are based on using light units that meet specified intensities, beam patterns, color, and flash rates as stated in AC 150/5345-43, Specification for Obstruction Lighting Equipment. The AC may be obtained from:
www.faa.gov/airports/resources/advisory_circulars/index.cfm/go/document.current/doc umentnumber/150_5345-43.
4.3 Lighting Systems.
Obstruction lighting may be displayed on structures as follows (refer to subsequent chapters for details):
1. Aviation Red Obstruction Lights. Use flashing lights and/or steady-burning lights during nighttime. Tower structures are typically marked with flashing red lights. Buildings and smaller obstructions located near airports should be marked with steady-burning red lights.
2. Medium-Intensity Flashing White Obstruction Lights. Medium-intensity flashing white obstruction lights may be used during daytime and twilight with automatic reduced intensity selected 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.
3. High-Intensity Flashing White Obstruction Lights. High-intensity flashing white obstruction lights may be used during daytime, with automatically selected reduced intensities for twilight and nighttime operations. When this system is used, other methods of marking and lighting the structure may be omitted. This system should not be used on structures 700 feet
(213.36 m) AGL or less, unless an FAA aeronautical study shows otherwise.
Note: All flashing lights on a structure should flash simultaneously except for catenary support structures, which have a distinct flashing sequence between the levels of lights (see paragraph 12.4).
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.