Congestion

Congestion

Digital data link is the key to the successful future of the Air Traffic Control System

By Jim Sparks

March 2001

While driving home from the airport after a particularly long day I observed that at 10:00 at night, the travel time to my home was about half of what it took me to get to work that morning. I followed exactly the same route; however, at this late hour, there were very few other cars on the road. It was also evident that the computer-controlled traffic lights were in my favor.
Like many in the aircraft maintenance field, I have to travel frequently by commercial airlines. Just like highways on the ground, skyways tend to reach a point of saturation. When this occurs, air traffic control has to meter the flow in a fashion similar to computerized or synchronized traffic lights on the way to work.

Stretching the radio frequency spectrum
With aircraft manufacturers producing new aircraft at a rapid pace and new maintenance techniques keeping older aircraft flying longer, certain actions are needed to avoid gridlock. Additional aircraft promote development of new airports and expansion of those that already exist. Of course, airport growth puts additional demands on the radio frequency spectrum. It has been anticipated by the Federal Aviation Administration that in the US alone, the number of airport operations will increase almost 15 percent and airlines are already gearing up for a 100 percent increase in the number of passengers within the next 15 years.
Congestion is also present when it comes to Very High Frequency (VHF) radio communications. Flight crews may now converse with several air traffic controllers, Approach Control, Ground Control, and in numerous situations, Flight Operations departments. Each of these communications will generally require use of a different radio frequency. In certain geographic areas where many major airports are located within a short distance of each other, situations arise that can overload the radio waves.

FM Immunity
FM Immunity is another current issue. It has been determined that commercial FM broadcast stations may have the ability to interfere with the FM Navigation Receivers in the aircraft. This could possibly desensitize the deflection of course indicators and may cause actual aircraft displacement from a desired course. As of January 2001, most ICAO countries have restricted operation in their airspace by non-FM Immune aircraft. The modification to ensure compliance is accomplished by the radio manufacturer or an authorized shop facility. Unfortunately, receivers not certified as FM Immune do not provide flight crews with a warning of erroneous signals.
Compliance with this rule is recognized by a note on a flight plan that will identify the aircraft eligibility. It is this note that will enable the regional Air Traffic Control to determine placement of the aircraft in a suitable place within the network.

New methods for improvement
Current Air Traffic Control is not, as some believe, an organization subsidized by the railroads for the purpose of discouraging travel by air. New methods are being reviewed and imposed to enhance Air Traffic Management (ATM). These include improvements in Communications, Navigation and Surveillance (CNS). Some prime examples of improvements in navigation include Reduced Vertical Separation Minimums (RVSM), which will enable aircraft to fly at 1,000 feet versus 2,000-feet vertical distance to another aircraft. To qualify for this capability, operators must show compliance of tight tolerances with altitude indicating equipment as well as demonstrate the aircraft’s ability to fly at a specific altitude without significant deviation. In addition, there is the Reduced Navigation Performance (RNP) specification, which enables aircraft to operate with reduced horizontal distances and is predicated on the aircraft being equipped with redundant position sensing equipment. Compliance with RNP and RVSM are part of the foundation for the future Free Flight Concept, which involves the automation of many tasks now carried out by air traffic controllers. Also, some of the authority that controllers now possess would be shifted to pilots.