Broadcast Writer

By Vicki W. Kipp
Site Management & Technology magazine, Sep 1, 2002

Tower lighting is necessary for one reason: aircraft safety. If not for the fact that flyways and towers occupy some of the same altitudes, towers could be less conspicuous. Without airplanes, helicopters and hot air balloons, towers could be painted to match the skyline, and be made to blend in discreetly. But as long as towers and aircraft co-exist, towers that present a hazard to air navigation need to be marked accordingly.

Joint regulation

Towers fall under the authority of both the Federal Aviation Administration (FAA), which regulates tall structures that could be perilous to aeronautical navigation, and the Federal Communications Commission (FCC), which oversees broadcast towers.

Generally, towers that are 200 feet or taller require paint and/or obstruction lighting (Figure 1). Lighting and marking requirements will be listed on a station license. Details about lighting guidelines can be found in Part 17 of the FCC Rules and Regulations ‘Construction Lighting and Marking of Antenna Structures.’

New towers

When a new tower is built, one of the greatest challenges is to get the tower licensed. Both the FCC and the FAA must review the FAA form 7460-1 Notice of Proposed Construction for the new tower to determine if the tower would present a hazard. The FCC requires the FAA to review the safety of any tower more than 200 feet above ground level (AGL) or any tower within a certain proximity to public use airports.

For towers that apply for FAA approval, a study will be done to analyze how the tower will affect aeronautical navigation. If the proposed tower were declared to be a physical hazard by the FAA, the FCC would deny the construction permit application.

Topics studied by the FAA include approaches to nearby airports, including all instrument approach, departure, and missed approach paths, closeness to airways and nearness to Visual Flight Rules (VFR) flyways. A VFR flyway is any landmark — such as a road, river, or railroad — that a pilot may use to assist with direction finding during marginal flying conditions.

An FAA review of any tower that is less than 200 feet tall and not near any aeronautical facilities is optional.

However, it would be prudent to notify the FAA as a way to ensure that you haven’t missed a risk that could come back to haunt you later.

One tricky issue is that when the rule says “not near any aeronautical facilities,” it means existing facilities as well as facilities that have been planned and have filed notification with the FAA. If you don’t file with the FAA for a review, you may not be aware of pending sites that could conflict with your tower.

Temporary lights

If your existing tower is undergoing construction, and the tower lighting is affected, it is your responsibility to implement temporary lighting. Install a temporary light, of similar type and intensity to the regular light, at the top of the tower.

You also might need to install interim lights at periodic levels of the tower.

Lights on for safety

Flashing beacons — A large pulsing light that warns pilots of a tower’s presence is called a beacon (Figure 2). Beacons can be either red or white, but red is more widely tolerated by neighbors.

Beacons are characterized by their flash rate. Forty flashes per minute (FPM) is a common rate. Flashing beacons are required at the top and periodic intermediate levels of tall towers.

Towers that contain only beacon lighting must be painted.

Sidelights — Sidelights, otherwise known as red obstruction lights (Figure 3, 4), are constant burning red lights that help pilots identify an obstruction to their flight path.

According to FAA/FCC guidelines, all red obstruction lighting must be turned on from sunset to sunrise. Continuously lit sidelights are required on the outside corners of the structure of a skeletal tower, per the FAA/FCC rules.

For example, three lights per level are required for a triangular structure, while four lights per level are required for a square structure. The diameter of a tower structure also affects the number of lights required per level for that tower.

Medium- and high-intensity stobe lighting — Unpainted towers are often required to display medium or high intensity strobe lighting (Figure 5). Unless otherwise specified, all medium and high intensity white strobe lights are to be lit at all times. Strobe lights flash brightly for visibility during the day and flash less brightly at night.

In fact, the FAA requires that white strobe lights have considerably less light intensity at night than during the day. While high-intensity strobe lighting can have a peak intensity of 270,000 candelas during the day, it is limited to 20,000 candelas at twilight, and 2,000 candelas at night.

High-intensity strobe lights are required on towers within VFR airspace. For structures shorter than 500 feet AGL, high intensity white strobe lights are not recommended. For structures taller than 500 feet, the tower owner may be allowed to choose between painting the tower or installing high intensity strobe lights. In the long term, it is more economical to install strobe lights. The FAA must approve high-intensity strobe lights before they are installed.

Resistance to night strobe lighting

It is not unusual for the neighbors of a tower equipped with high intensity white strobe lights to complain to their elected officials about excessive brightness at night.

As a result of widespread public outcry about white strobe lighting, the FAA and FCC have cut back on strobe lighting requirements for shorter towers, and suggested a dual-lighting plan. Building codes began requiring that towers had either red lights and paint, or a dual lighting systems with red lights at night.

Dual lighting

A dual lighting system uses a blend of beacons, side lights, and strobe lights. Dual lighting can solve conflicts when tower neighbors object to nighttime white strobe lights. A dual lighting system for an unpainted tower may encompass strobe lights for day visibility and flashing red beacons and obstruction lights at night. Using a dual lighting system allows the tower owners to avoid the expense of maintaining orange and white tower paint.

Monitoring lighting

Operation of lights is controlled by a photocell (Figure 6) mounted on the tower which senses the level of sunlight visible and powers the lights on or off. The FCC Rules Section 17.47 requires that any radio or television station where tower lighting is mandated must either observe tower lights, visually or by automated monitoring system, at least once every 24 hours to ensure that all lights are operating properly.

If you don’t wish to do daily inspections, the other option is to install an automated alarm system that will detect any lighting failure and send an alarm to you. At least once every three months, you must inspect all of your tower’s automatic and mechanical devices, indicators, and alarm systems for proper operation.

If you follow the requirements of FCC Rules 17.47, it is unlikely that the FCC would find that your station would have tower lights out without you knowing it first.

However, hypothetically, a tower light could be burned out for almost a full day before being noted since the tower light check is only required once every 24 hours.

Furthermore, if the FCC notes or receives a complaint about inoperable tower lights that have not been reported to the FAA, a considerable fine could be levied.

Lighting failure

If a flashing beacon or strobe light should fail for more than 30 minutes, you must notify the nearest FAA Flight Service Station (FSS) at once. It is essential to notify the FSS about a lighting failure in order to prevent aircraft collision and to limit your liability if an aircraft should hit the tower.

The telephone number for your local FSS should be posted at the transmitter control point. When you call the FSS to report an light outage, you will need to report the seven digit tower registration number, the number of lights involved, the height of the tower above mean sea level and ground level, the reason for the failure (if known), and the probable date for the completion of repairs. When you make the report, you will have to supply the FSS with your name, title, address, and telephone number. It is recommended that you make a note of the time and date that the lighting outage was called in, and the name of the FSS official that you spoke with.

The FSS will issue a Notice to Airman (NOTAM). This NOTAM will be included in the preflight briefing when a pilot calls in to file a flight plan. The NOTAM data also is included in the announcements on the Automatic Terminal Information Service (ATIS), an airport-to-plane transmission which pilots monitor before taxiing for departure and prior to landing.

NOTAM information will be disseminated by the FAA for 15 days unless they are notified that the lights have been restored to normal operation. If the FAA hasn’t heard from you by the end of the 15-day NOTAM period, the NOTAM will be automatically cancelled under the presumption that the repairs are complete. If the FAA didn’t cancel NOTAMs after 15 days, some NOTAMs would go on infinitely. If the light has not been restored to normal operation within 15 days, you must notify the FAA. The FAA will reissue the NOTAM and inform the FCC that you have a lighting problem. If at all possible, you want to avoid having a notification such as this in your file. While you do need to call the FAA if a beacon or strobe light fails, you do not need to notify them if a side light fails.

However, the side light should be repaired or replaced promptly. Many flashing beacons contain two bulbs in each fixture. You are required to notify the FAA even if just one of the bulbs fails.

Drawback of lighting

Lights, high intensity strobe lights in particular, are often favored over painting a tower because lights are perceived as being less expensive to maintain. However, tower lights are not without their hassles. Light bulbs burn out. Electrical line to the bulbs can be shorted out by rain. Lighting hardware can become corroded. Lights can be cracked by chunks of falling ice. Lights can lose their power source during a power outage.

Additional hazards to lights include disgruntled hunters that shoot at lighting, and troublemakers who climb towers to steal obstruction lights.

Tower painting

You can easily spot a painted tower at a great distance due to its vibrant coat of international orange and aviation white. Daytime visibility of the tower is the purpose of these loud stripes. These colors are specified for towers because they provide maximum visibility of the structure by contrast in colors. Towers up to 700 feet are marked with seven equal width stripes with the top and bottom being orange. Taller towers require between nine and 13 stripes depending on the height.

Time to paint

Federal standard FED-STD-595 lists the standards for chromaticity and luminance for a freshly painted tower. Weather, scaling, oxidation, and chipping cause painted towers to fade.

Whenever a painted tower begins to fade beyond the limits of the FAA orange color tolerance chart, it must be repainted. The FAA or tower paint vendors can supply you with a color tolerance chart. Since the effect of weathering will be the greatest at the top of the tower, it is best to make your color comparison there. Check and maintain the brightness of your tower paint routinely because the FAA can cite your station and levy considerable fines if your tower paint is out of tolerance.

Repainting your tower is an expensive and labor-intensive proposition. The paint used on towers has qualities that make it robust enough to stand up to outdoor use. These characteristics factor into the cost of the paint. Regardless of how good the paint is, it will peel off or fade every few years.

The paint must be replaced by hand. Although it might seem quicker and easier to spray paint the tower, that is not a realistic plan. The spray paint can spatter for hundreds of yards with the slightest wind.

Although international orange might look striking on a tower, it will not be well received if it lands on a house or vehicle. When you are painting a few hundred feet up on a tower, there is bound to be a breeze. Since wind at the higher altitudes doesn’t get worn down by ground-level friction, wind speed increase proportionately with height above ground level.

Tower paint is applied by technicians wearing “paint-mitts.” Paint mitts are large textured gloves dipped in paint which are spread over every structural element of the tower. A physically powerful adult can paint 100 feet of an average tower in a full day. When hiring a tower painter, be cautious of swindlers who quote bargain rates and paint with amazing speed. These cons paint only the underside of the tower since it is the only portion visible from the ground.

Conclusion

When the FAA or FCC requires a tower to be marked or lit, the tower must be illuminated solely or by a combination of red beacons, white strobes, red obstruction lights, and orange and white paint stripes. The FAA and FCC have strict rules for the operation and maintenance of tower lights and markings.

Kipp is a broadcast engineer.

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