On Oct. 15, 2008, four people died in Aurora, Ill., after the medevac helicopter they were in crashed at night. The accident still is under investigation by the National Transportation Safety Board, but the accident reportedly occurred when the helicopter’s rotor blades clipped a radio tower guy wire, causing the blades to break off. The particularly tragic nature of the collision — one of the victims was a 13-month-old patient — has rekindled the always smoldering debate about towers and the hazards they present to aircraft and birds.
Unfortunately, “there is only so much you can do to mark a tower,” said George Osgood, president of P&R Technologies in Portland, Ore. “The FAA’s guidelines for tower marking are sufficient to do the job if they are followed. The use of approved lighting and tower painting are enough to keep aircraft safe, especially if they are using up-to-date maps and monitoring their flight paths conscientiously.”
Even with these provisos, however, towers keep getting hit by aircraft. Meanwhile, migrating birds often collide with guy wires during cloudy or foggy nights due to visibility problems, or when they are disoriented by red tower lights.
“Long wavelengths of light in the red and orange part of the spectrum have been shown to produce disorientation, or a change in the direction of orientation, in the five species of migratory birds that have been tested,” explained biologist Dr. Robert Beason in a speech cited by the U.S. Fish and Wildlife Service.
“If this resulting disorientation causes the birds to circle, to be unable to establish its directional cues, it would increase the probability of striking either the tower or the guy wires,” he added.
So what can be done to reduce incidents of flying objects striking towers? Here are a few solutions — some reality, others theory just waiting to be put into action.
Adequate tower lighting is at the heart of aircraft-collision prevention. If aircraft pilots can see towers clearly at night, chances are that they will steer clear of them. Conversely, if a pilot is not paying proper attention to his location, or if his instrumentation is not adequate to the task, no amount of lights will prevent his aircraft from hitting guy wires.
To ensure adequate tower lighting, the FAA requires tower operators to install dual Number 810 aviation obstruction lights on towers under 150 feet in height. The reason is simple: “If one light in a pair burns out, the second serves as a backup until someone can be sent up the tower,” Osgood said. Of course, it is possible for the second light to burn out shortly afterward; this usually occurs during the coldest, windiest part of the year — or so it always seems to those who have to climb the towers and replace the lights.
What can be done to minimize the likelihood of inconvenient lighting failures? One answer is to replace incandescent bulbs with longer-lasting light-emitting diodes (LEDs). Although LEDs are expensive — a dual 810 LED beacon costs $445 versus $160 for its incandescent equivalent — such light sources will last 11 years or more, Osgood said. “At that point, they start to degrade by losing 5% of their light output per year, rather than just burning out. But if they remain hermetically sealed against moisture and the elements, they will still keep running for years,” he said. The lower amount of electricity consumer by LEDs compared with incandescent bulbs means that they will “pay for themselves within the first year,” he added.
Meanwhile, a more futuristic solution has been proposed and patented by Dr. Hossein Eslambolchi, retired chief technology officer for AT&T. The design incorporates a lens system that is attached to the tower and coupled to a fiber optic cable, which is used to magnify and radiate light to the lens. The light is generated by a ground-based electrical system.
In an interview with Urgent Communications, Eslambolchi said that using such an approach “changes all the traditional tasks and responsibilities” of tower lighting.
“All maintenance is accomplished on the ground, such as bulb replacement and maintenance on the flasher,” he said. “Once the fiber has been installed and tested, no one should ever have to climb the tower to do any routine maintenance. Lightning strikes are all but eliminated since the lens and fiber optic cables are made of non-conductive glass.”
The term “bird brained” sums up the problem tower operators have when it comes to deterring bird strikes, particularly on guy wires. Unlike humans, birds can’t grasp the physics of guyed tower design or deduce its consequences. Consequently, they are prone to fly into unmarked guy wires during hazy conditions, or when the wires are not obvious due to trees and other distracting elements.
Because birds don’t tend to fly into lights like moths do, the logical solution would be to string lighting along guy wires to keep them away. However, the sheer cost of doing so, and of powering and maintaining such lighting, is not economically feasible.
An affordable alternative is offered by Sarasota, Fla.-based Bird Busters, which offers the FireFly Bird Diverter system developed by P & R Technologies of Portland Ore.
The FireFly uses a series of 3.5- by 7-inch acrylic plastic panels attached at specified intervals on guy wires. Each panel is covered with fluorescent reflective sheeting that absorbs UV radiation to emit “glow-in-the-dark” light for up to 12 hours at a stretch. According to the company, the Firefly produces an initial light emission of 6 lumens per cubic meter that reduces to 1 lumen one to two hours after sunset. Because each panel is moved by wind and wire vibration, birds see what appears to be a string of animated glowing obstacles in their flight path and turn away from them.
“Since birds typically fly 40 to 50 feet above the ground, we recommend that clients install FireFly panels starting at this height, with a space of 30 feet or less between each panel,” said Jack Wagner, owner of Bird Busters. FireFly panels also are useful for marking utility lines and other obstructions prone to aircraft impact, such as wires strung across rivers and canyons.
Beyond these options, there are other things tower operators can do to reduce aircraft/bird collisions.
First, the effectiveness of tower lighting and painting systems can be enhanced by public-awareness campaigns, such as contacting local pilots and airlines to ensure that they know where towers are located. Second, the best way to minimize bird strikes is to locate towers away from popular migratory paths. Given how difficult it is to win zoning approval for any kind of tower construction, adding this requirement may seem like one more headache. However, if a proposed tower can be shown to protect migrating birds due to its location, approval may be easier to obtain.