Aviation communications frequency crunch hits densely populated areas

Officials from the Federal Aviation Administration (FAA) in Washington and the Mitre Corp. in McLean, Va., recently completed an analysis of "choke points" in the U.S. National Air Space (NAS).

Jul 1st, 2001

By J.R. Wilson

Officials from the Federal Aviation Administration (FAA) in Washington and the Mitre Corp. in McLean, Va., recently completed an analysis of "choke points" in the U.S. National Air Space (NAS) — essentially traffic jams in the air caused by a lack of sufficient ATC frequencies for air/ground communications. The biggest problems generally occur at altitudes higher than 18,000 and in high-density air traffic regions, such as the Northeast. But other areas also can be affected.

The Cleveland en-route air traffic center, which handles high-altitude traffic over the Great Lakes and Ohio Valley, needed a frequency for a new sector. Because no new frequency was available, they had to take a frequency for a new automated weather observation station (AWOS). As a result, the weather station, although installed, has been left to gather dust until officials can somehow find a frequency for it.

The choke point analysis looked at why delays were becoming so prevalent within a triangle that extends from Chicago to Boston to Atlanta.

"One of the culprits turned out to be some en-route sectors, many in the Cleveland Center, that filled up with airplanes and exceeded the capacity of the controller running that sector to deal with that number of airplanes," says Jim Chadwick, director of communications, navigation and surveillance systems at Mitre's Center for Advanced Aviation Systems Development. "Each sector has a peak instantaneous airplane count. With the current traffic in some sectors, those were being exceeded, causing delays."

Each sector controller requires a separate frequency, so relieving peak instantaneous airplane count overload by subdividing the sectors means finding more frequencies to assign.

"A number of those choke points have evolved over time to about 19 new requirements — in a center where we've already had difficulty finding one new frequency," Chadwick says, adding the FAA then tasked Mitre to determine if — and how — those needed frequencies can be found. "We believe we can do the 19, but it will require shuffling frequencies some distance away to accommodate that.

"If you have a requirement for a new frequency at Dayton, Ohio, you need to put a new transmitter there.," Chadwick explains. "To do that, you have to move a frequency assignment in Lexington, Kentucky. To move that assignment, you have to move a frequency assignment in Memphis — and to do that affects the frequency assignment in Texarkana and so forth, creating a daisy chain effect. Eventually, we project — certainly within the next 10 years — even by shuffling things around all over the country, you won't be able to find a hole. And that's when the capacity of the system will be reached."

If someone wants to build a major airport in Fargo, N.D., for example, there is no problem because there are plenty of available frequencies in that remote location, Chadwick points out. But finding new frequencies in New Jersey is a different matter. And, unfortunately for the system, far more people are and will be flying to Newark, N.J., Boston, Philadelphia, New York, and Washington than to Fargo.

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