ATSAP Success Story: Asheville, N.C.
Friday, October 12, 2012

For a while at Asheville (N.C.) Regional Airport Traffic Control Tower, faint Morse code and loud static would pop-up on the approach frequency every 30 minutes. It only lasted for a couple seconds, but it could interrupt pilot-controller transmissions and was a potential risk to safety. So a controller filed an ATSAP report.

Local Tech Ops specialists had already been trying to find the radio frequency interference on the 124.650 frequency. They then called the Technical Support Center in Columbia, S.C., and Mike Nininger, a technical support specialist there, drove up to Asheville to provide additional help.

Over the course of a couple days, he was able to make some headway. Using direction finder equipment, he developed a rough idea of where the signal was coming from.

“But it was bouncing here and there, and we weren’t getting a good direction on it,” he said. The short duration of the interference further complicated the effort. Because it was only appearing for a short period of time, Nininger didn’t have long to track it each time it popped up. Meanwhile, the interference continued. 

The interference may have been found eventually. Air Traffic Manager Grey Pelkey explained that the tower’s controllers felt ATSAP brought more attention to the issue.

In this case, ATSAP also showed that controllers can report a problem without having to identify themselves as they would filling out an outage or interference sheet.  

“The ATSAP reports absolutely helped,” said Dale Boyer, the facility’s NATCA representative. 

Indeed, ATSAP reports often motivate quick and effective responses to solve safety issues, even when formal action is not taken, according to Mike Gunn, the management Event Review Committee chair for the Eastern Service Area.

In this case, no corrective action request was filed — a formal route to resolving a safety issue — but the ATSAP report did boost Tech Ops’ awareness of the issue.

Nininger eventually partnered with Bruce Williams, a Tech Ops spectrum engineer and seasoned RFI investigator from the Southern Region, to track down the interference.

During an earlier visit, Nininger managed to capture a recording of the signal, thinking he could listen carefully to the Morse code as a way to determine its source. 

Williams and Nininger thought the interference might be coming from a public service transmitter. The FCC requires such transmitters to broadcast their identity every 30 minutes, and it’s not uncommon for that identity to be in Morse code.

But the first two letters were too faint to hear, leaving Nininger and Williams without much to go on.

So they got in a van with their RFI investigation equipment. 

They drove up to Sugarloaf Mountain, which is about 27 miles from the tower. It serves as one of the receiver sites for the frequency the interference was appearing on, and it’s high up, so Williams thought they might be able to hear the transmission more clearly.

By this point, Nininger had his watch programmed to let him know when the interference was going to occur.

He’d count down — two minutes … one minute … 30 seconds — and they’d stop the van and raise the RFI measurement antenna as high as they could to capture the transmission.

On Sugarloaf, they didn’t have much luck capturing the signal.

So they got back in the van.

They drove across Hendersonville, N.C., to a town called Laurel Park, toward a hill known as Jump Off Rock. 

They stopped about a mile from the top of the hill and raised their antenna. When the clock hit 22 minutes past the hour, the signal came in louder than before.

So they got back in the van.

They drove up toward the top of the hill, near a group of water towers, and 30 minutes later, the signal was even stronger.

Williams had a hunch the signal was coming from some telecommunication towers on top of the hill.

So they got back in the van and drove past the towers.

When the signal transmitted again, their equipment pointed back toward the towers. Now they knew where it was coming from, but there were five towers and more than a dozen antennas attached to them.

The next day, at Asheville Tower, they did a bit of research.

“We reviewed the data we collected the previous day and rummaged through the Federal Communications Commission database to determine who might be responsible for an array of emitters on the hill,” Williams said.

They were able to find the principal contractor for the towers, and they called him up and arranged to meet him on tip of the hill.

They got in the van and drove back to Laurel Park. With five towers, five associated buildings and numerous emitters in each building, they had no choice but to go through each one, working by process of elimination.

Williams, Nininger and the contractor went into one building after another, each man armed with his own spectrum analyzer and ready to receive the signal every half hour.

They found nothing in the first building, nor the second, third or fourth. But in the fifth, where there were 10 or 15 transmitters, one of the spectrum analyzers picked up interference on 124.650.

The contractor began keying the different transmitters in that building to energize the signal so when it appeared it would be bright and clear on the spectrum analyzers.

Though it was getting late in a long day, they knew they were close. And sure enough, when the contractor keyed a transmitter for the Etowah-Horse Shoe Volunteer Fire Department, they had their source.

The output power for the transmitter had been dropped to 50 watts from 100 watts, which apparently caused the transmitter’s preamplifier to malfunction, leading to the interference on 124.650.

The contractor removed the preamplifier that afternoon. The interference disappeared from the air traffic control frequency, and Williams hasn’t received any reports of radio frequency interference at Asheville Tower since.