Those red lights at great heights make the sky safer to fly

UI Power Plant
Aviation warning beacons sit atop the UI Power Plant smokestacks. These red lights, found in numerous high places across the UI campus, warn pilots of what lies below—usually buildings, broadcast transmission masts, and anything else they need to stay away from. Photo by Tom Jorgensen.

Flying at night over the dark Iowa countryside, Bob Hartman knows home is near when he sees six blinking red lights on the horizon, hovering over the brightness of Iowa City.

The lights sit atop the two smokestacks of the University’s power plant, warning pilots like him to be careful when they get close.

“The smokestacks are a great guide when you’re flying to the hospital at night,” says Hartman, one of the Air Care air ambulance pilots. “You can key on them because you can see them from miles away, and those red lights really shine through all the other lights in Iowa City.”

They burn at night like red fireflies, their gentle blinking strangely soothing for something designed to prevent aviation catastrophes. Known in the dry professional lingo as aviation warning beacons (although, really, red fireflies is so much more poetic), the beacons warn pilots of what lies below—usually buildings, broadcast transmission masts, and anything else they need to stay away from.

The lights are required by FAA regulation of any building or structure above a certain size, says Allan Culbert, shop manager in Facilities Management.

“The simplest rule is that any structure 200 feet or greater in height Above Ground Level—or AGL—must be equipped with warning lights,” Culbert says. “The FAA may also recommend lighting on structures lower than 200 feet AGL if closer than 1,500 feet of an airport runway end.”

The lights come in many colors—amber, blue, green, yellow, and rotating beacons made up of combinations of them—that are coded for how they aid navigation, or whether the airport is military or civilian. But red is the most commonly used for warning pilots away from a hazard.

The bulbs are about eight inches long and burn at 620 watts, fairly unspectacular looking, like Christmas tree lights on steroids. Dozens of them are found at the highest points of the UI campus, alerting pilots flying into the Iowa City Airport or the University of Iowa Hospitals and Clinics’ helipad. The largest number—47—dot the roofline of the hospital building, serving as both guides and warnings for air ambulance pilots.

Replacing a bulb on a tower costs about $620: $20 for the bulb, and $600 to pay someone with the training, the guts, and the insurance policy to climb to the top of a tower or smokestack hundreds of feet in the air.

Reinow and Slater residence halls, which lie in the helipad’s approach from the south, are ringed with lights on their roofs. So is the press box and scoreboard at Kinnick Stadium, which obstructs the helipad from the west.

Two of the campus’s most prominent lights—and the ones that help guide Hartman home—are the three beacons at the top of each of the power plant smokestacks, two of the University’s tallest structures. One of the stacks also has three red lights at its midpoint, and two flashing white strobe lights that blink during the day, another FAA requirement for a structure of its size. Hartman says there was a time once when white strobes were thought to be the ideal warning beacon, their incessant bright blasts of light unmissable in the night and more attention grabbing than the traditional reds.

But soon pilots reported that while they could see the strobe flashes from what seemed like halfway around the planet, they were having serious problems with them.

“There’s no depth perception,” says Hartman, who remembered the early days of strobe lights when he flew helicopters in the Army in the 1970s. “You can’t tell how far away the light is, it’s hard to determine the shape of the landing area, and they’re distracting.”

Soon, the white strobes were relegated to daytime duty and the red lights were turned back on at night.

The University also maintains beacons at two radio transmission masts for WSUI and KSUI radio, one 300-footer on the Oakdale campus that beams both AM and FM signals to their respective transmitters, and another 285-footer that supports the WSUI-AM transmitter south of Hills (the KSUI-FM transmitter is on a mast near West Branch that is owned by Iowa Public Television).

Jim Davies, chief engineer at the radio stations, says that mast lights are different from lights on buildings in that they have to be seen from further away. To enhance the light, each beacon is placed in a Fresnel lens, a three-foot tall capsule with glass walls several inches thick that reflects and refracts the light into something brighter that’s visible from a greater distance.

The bulbs are not terribly expensive, only about $20, Davies says, and replacing one on, say, the hospital roof is as easy as changing the bulb in your kitchen. But replacing a bulb on a tower costs about $620: $20 for the bulb, and $600 to pay someone with the training, the guts, and the insurance policy to climb to the top of a tower or smokestack hundreds of feet in the air (or, in the case of the KVLY-TV tower in North Dakota, the world’s tallest, more than 2,000 feet).

“It’s a tremendous feeling when you’re up there; you just have to trust your safety equipment. It’s much more stable than a ladder,” says Davies, who climbed towers occasionally when he was younger. “You have to climb straight up, so it taxes your muscles.”

The lights have a lifespan of about two years, although Davies says that “sometimes, lightning will force that issue.”

But are so many lights needed? Drive around and it seems structures that anyone with even bad vision couldn’t miss have warning lights on them. Without so many beacons, would planes and helicopters suddenly be crashing into buildings and TV towers?

Well, maybe. Hartman says that while aviation maps often alert pilots to the presence of towers and buildings (and, increasingly, wind turbines), they are not perfect guides. They don’t indicate every hazard, eventually become outdated, and don’t show the exact location of the hazard, so a light is needed for a more precise mark.

The lights also perform an important function of reassuring passengers.

“Oh, yes, we notice the lights,” says Diane Lamb, an AirCare flight nurse who has had more than a few tight landings at accident scenes and was comforted by the lights outside the window guiding her safely.

It’s unclear how much the University pays for the electricity to light the bulbs, but Davies says at 620 watts per bulb, it’s probably not cheap. He estimates the cost of keeping each radio transmitter tower lit with two bulbs is about $200 a month.

Those costs, however, may be setting up a change in the warning beacon business. New-generation LED lights flash more insistently, and use only 10 percent of the energy of conventional bulb beacons. While that saves a considerable sum on electricity, it might bring an end to the days of the blinking red fireflies.

“I like these old red lights because they give you a nice, peaceful feeling that you don’t get with the red strobes,” Davies says. “I’ll miss that.”