To make it a reality: communication, navigation, and surveillance
By Jim Sparks
This free flight version is not to be confused with what you get from the airlines after paying for so many flight segments. In this case free flight is a concept, one that had its seed planted in 1998.
As it stands today the nation’s air traffic follows a well-defined route structure from point to point. Like the nation’s highway system these routes provide limited direct access from city to city. In other words to get from one metropolis to another several highways may have to be utilized. The fact is the air routing structure across the continental United States uses about 5 percent of the total airspace. Wouldn’t it be great to fly from Dallas to New York and not have to turn left at Atlanta? Just imagine the savings in both time and aircraft operating cost.
But on the other hand there are drawbacks. What would happen to air traffic control? With aircraft approaching or leaving any sector in any direction, how are safety margins to be maintained? Sixty years ago when the first radar systems were created for the sole purpose of tracking aircraft to ensure adequate in-flight separation, it was the job of the air traffic controller to project in his mind any potentially lethal situation. With the number of aircraft operating today and expectations for the worldwide fleet doubling by 2010, an already overburdened system would be incapable of controlling the flow. In fact the current system has been related to the telephone company of old where a switchboard operator had to manually plug and unplug each connection.
What do we need?
Communication, navigation, and surveillance (CNS) are the areas that need to be addressed to make free flight a reality along with the concept of air traffic management (ATM) rather than air traffic control (ATC).
Digital electronics is the one primary factor that will provide the means of achieving the goal. Current levels of automation make it realistic for a potential conflict between converging aircraft to be anticipated as much as 20 minutes prior and appropriate actions conveyed to the flight crews to prevent the encounter. Satellite navigation enables the pilot to have pinpoint accuracy in determining aircraft position and with programs like Reduced Vertical Separation Minimums (RVSM) and Required Navigation Performance (RNP), capabilities of the aircraft are enhanced where it can safely operate in a high traffic area in close proximity to other machines.
How far are we from realizing benefits from this concept? In January 2003 the United Parcel Service (UPS) became the first major U.S. air carrier to get U.S. Federal Aviation Administration certification for the installation of Automatic Dependent Surveillance -Broadcast (ADS-B) systems. Although this will not allow unrestricted free flight, UPS is predicting a 20 percent increase in efficiency within a three-year time span as a result.
Aircraft including ADS-B systems have the ability to transmit their specific position along with airspeed, altitude, and attitude information on a digital data link up to 150 miles to either a ground-based receiver linked to the air traffic control network or even to other ADS-B equipped aircraft. Unlike ATC Primary and Secondary Surveillance Radar systems, low altitude and even operation on the ground can be tracked which can aid in assisting the ever prevalent ground congestion at many airports. This will also provide an additional safety margin for aircraft operating in a nonradar environment. Most importantly pilots and air traffic controllers can see the same real-time situations emerging together.
The technology is not in fact limited to aircraft. The possibility exists where airport ground vehicles could be equipped with the system, which could all but eliminate runway incursions or other communications-related ground mishaps. The same data link used here can also transmit weather data, flight information, and flight advisories.
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