Ads-B Supply and Demand
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The Federal Aviation Administration (FAA) is transitioning from a system of ground-based navigation aids to one based upon a satellite-based Global Positioning System (GPS). Radar and other ground-based navaids limit the amount of airspace available and can increase travel distance, since aircraft must follow one navigational fix to another. Under GPS, several sequenced satellites orbiting the earth each transit an omnidirectional signal that reaches a receiver on the aircraft, which with precise timing information calculates a radius of distance from each satellite. The intersection of at least three spherical surfaces allows for the automated calculation of the aircraft’s position. This process provides highly accurate information for en route navigation. GPS is already being used for navigation in oceanic and en route airspace.
In order to enhance the accuracy and reliability of GPS so that it can be used as a primary means of navigation and nonprecision approaches, the FAA has been augmenting the system with a nationwide network of reference stations that will receive and refine signals from the GPS satellites. Known as the Wide Area Augmentation System (WAAS), these enhancements will allow so-called “differential” GPS to be used as a primary means of navigation for en route travel and nonprecision approaches in the United States, as well as near-precision approaches. WAAS will also allow a pilot to determine a horizontal and vertical position within 6 to 7 meters, compared with the 100-meter accuracy available today from the basic GPS service. The FAA is also testing other applications of GPS, such as Automatic Dependent Surveillance-Broadcast (ADS-B) as part of its transition from central control to “Free Flight” concepts. The aim of Free Flight is to give pilots greater flexibility to determine optimal routes and speeds, thereby improving the overall efficiency and capacity of the airspace system. Though promising, such capacity-enhancing systems require more than FAA certification and investment; they require the installation of appropriate equipment in airports and aircraft, the training of pilots, the availability of safe and certifiable avionics, and other private-sector commitments and investments. ADS-B coupled with cockpit display of traffic information (CDTI), can help the pilot maintain desired separation more precisely.
ADS-B and Increased AARs
ADS-B provides tools that assist the controller in better assigning runways and sequencing aircraft; and radar systems that permit, for example, simultaneous instrument approaches on closely spaced parallel runways. Currently in order to conduct simultaneous independent ILS approaches, parallel runways need to be spaced by at least 4,300 feet. (Federal Aviation Administration, 2006, chap.5) Unfortunately many airports, especially those located in the Northeastern United States, were built many years ago and have little land to expand to meet this distance. A typical arrival rush, in IFR conditions, to a major airport whose parallel runways are not spaced by 4,300 feet, daily has the demand to exceed a typical airport acceptance rate (AAR) of 32-36 aircraft per hour. With the addition and approval of ADS-B, coupled with WAAS and LAAS, the confidence level of the exact position of the aircraft on both finals could be greatly enhanced over what radar systems provide today. The result could be to allow simultaneous operations to be much closer spaced parallel runways thus improving the AAR dramatically. The result would be an increase in capacity with little fixed capital investment into such high cost items as new runways and taxiways and new land based navigational aids such as instrument landing systems. Refer to the graph below.
The FAA believes it could increase capacity by 10 percent or more in several important airports with significant delay problems, such as Newark, La Guardia, and Philadelphia (FAA 2001). A cornerstone of the FAAs Next Generation Air Transportation System (NGATS), ADS-B is unofficially estimated to cost close to $2 billion, including 15 years of operational and maintenance support.
Ever since the invention of radar in the 1930’s, air traffic controllers and flight operations personnel, and the military have had the privilege to be the only entities that could see the entire air traffic “picture” on their displays. The user, for example a pilot, has not had the advantage of having the information that a controller does. Any veteran pilot or controller is familiar with the phrase, “what’s our sequence?” The installation