Telecom towers, tall buildings, pylons and others, are all classed as hazards to the navigation of aircraft. As such there are laws and regulations regarding the heights of such structures. The height and proximity to airports or helipads have a bearing on the obstruction light standards. The Federal Aviation Administration (FAA) published the requirements for telecom tower obstruction lighting.
The FCC 14 CFR Vol2 part 77 details all the requirements for obstruction lighting systems. In this article, we will exam section 77.17 which pertains to the standards based on tower heights and location in relation to airfields.
Objects, or structures, whether fixed or mobile are deemed to pose a hazard to air navigation if they fall into the following categories
- The height of the object is greater than 200 feet (60 meters) Above Ground Level (AGL).
- The height of the object is greater than 200 feet AGL, or above the established airport elevation, whichever is higher and is within 3 nautical miles of airstrips (excluding heliports) with the longest runway of 3,200 feet.
The FAA will be responsible for the analysis and review of any structure, or proposed structure and determining its hazard to air navigation. In addition, these structures may cause interference with ATC, radar and direction finders. The effects on VFR and IFR arrival and departure traffic and minimum flight altitudes should also be considered.
Voluntary marking of towers lower than 200 feet
Although there is no requirement, the FAA encourages towers lower than 200 feet, especially in rural areas, to be marked, painted or lit accordingly in order to make them more conspicuous to air navigation. They can be painted with alternating bands of orange and white. Guy lines on towers should also be covered in high visibility sleeves or equipped with cable balls.
Telecom Tower Obstruction Lighting
There are different requirements for aviation obstruction lighting determined by the height and proximity to airports.
Red Aviation Lights – Steady burning or flashing red strobe lights should be equipped for night time use on all structures that are 200 feet AGL or higher. In addition smaller buildings or towers closer to airports may also be marked with steady burning red lights.
Medium Intensity White Strobe Lights – These lights should be used for daytime / twilight with reduced intensity for nighttime. When installed on towers 700 feet or less AGL there is no requirement for other marking methods to be used. Aviation white/orange banding is always required for daytime structures over 700 feet. This system is generally not recommended for any structures lower than 200 feet.
High-Intensity White Strobe Lights – These lights are utilized in a similar fashion to medium intensity lights. However, they should not be used on any structures lower than 700 feet unless the FAA deems them as necessary.
Dual Lighting System – This combines red lighting for nighttime usage and high or medium intensity white lighting for daytime and twilight hours. Medium intensity white strobes are used on structures lower than 700 feet, and high-intensity white strobes for those over 700 feet.
It should also be noted that all lights be synchronous in their flashing.
Monitoring, Inspection and Maintenance of Tower Obstruction Lights
Quarterly and Annual light inspections should be conducted (QLI / ALI) Quarterly inspections can be waived which can be a significant cost saving.
Lights should be monitored for proper candela output. Fixed light voltages should not vary more than +/- 3%. For strobes the voltage should not be more than +/- 10% of rated voltage. All lights should be replaced once they reach 75% of their rated life. On strobes when peak intensity falls specification limits.
Regardless of any remote monitoring systems that may be used, a visual inspection must be performed at a minimum of every 24 months. Typically lights are damaged by UV light causing crazing, cracked lenses and dirt build-up.
FAA Obstruction Light Placement
The height of the structure affects the placement of obstruction warning lights. The light positions may be adjusted +/- 10 feet (3 meters) where necessary in order to accommodate wires, guys and so on.
The number of lights and lighting levels is determined by the structure height, as illustrated in the below diagrams.
Top Mounted Obstruction Lights
Structures 150 Feet (46 m) AGL or less require two or more steady-burning red (L810) lights. These should be installed in a manner to ensure an unobstructed view of one or more lights by a pilot.
Structures Exceeding 150 Feet (46 m) AGL must be equipped with 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
Intermediary Level Obstruction Lights
The number of light levels is determined by the height of the structure, including all appurtenances, as shown in Figure below. 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.