December 17, 2015 — The Federal Aviation Administration has issued new obstruction marking and lighting rules for towers, which reduce the need for high-intensity lights in some cases and clarify the applications of flashing L-810s. The rules, known as Advisory Circular 70/7460-1L, replaced AC70/7460-1K.
Previously, high-intensity lights had to be deployed above 500 feet on a tower, or the structure had to be painted. With the release of this circular, medium-intensity white and medium-intensity dual obstruction lights are now authorized on towers up to and including 700 feet above ground level (AGL). Cort Walker, Drake Lighting director business development, told AGL Link that the rule change mostly affects broadcasters, which operate tall towers.
“Because of the expense of a high-intensity lighting systems, many broadcasters have traditionally opted to paint their towers,” Walker said. “Sales to broadcasters of medium-intensity lighting systems should increase, because they are considerably less expensive.”
When medium-intensity flashing white lighting systems are operated during daytime and twilight on structures 700 feet AGL or less, other methods of marking may be omitted, the circular said.
For structures exceeding 151 feet but not more than 350 feet, the circular prescribes that two or more flashing L-810 lights should be mounted outside at diagonally opposite positions of intermediate levels. These lights should flash simultaneously with the L-864 flashing light on the top of the structure at a rate of 30 flashes per minute.
“Studies have shown that steady burning lights attract birds, so they are requiring flashing marker lights,” Walker said.
Triple-beacon systems will no longer be required to have marker lights, which will save money for tower owners, he added. However, the flashing L-810 lighting recommendation has a delayed effective date until September 15, 2016.
The circular states that if an object larger than 7/8-inch in diameter, such as a lightning rod, blocks a beacon, the beacon must either be moved above the object or a second beacon must be added. Drake Lighting anticipates increased need for two-beacon systems in 2016.
Additionally, the circular warns that obstruction lights should 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 fixture must be relocated so that it is not blocked by the new equipment.
For a copy of the circular, go to