ADS-B

The future of air traffic control


The first attempts to provide a semblance of ATC were based on simple “rules of the road” established by the European sponsored International Convention for Air Navigation in 1919 and were implemented at London’s Croydon Airport in 1921. In the United States, Archie League, who controlled aircraft using colored flags at what is today Lambert-St. Louis International Airport, is often considered the first air traffic controller. Initial air traffic regulations were established in the United States by the passage of the Air Commerce Act of 1926.

Around 1930, radio-equipped control towers were established by some local authorities, and instrument flying had recently begun. Within a few years several airlines jointly established the first airway traffic control centers to safeguard their aircraft against midair collisions. In 1936 this preliminary effort was transferred to the federal government, and the first-generation air traffic control system was born. Several U.S. airlines using the Chicago, Cleveland, and Newark airports agreed in the mid-1930s to coordinate the handling of airline traffic between those cities. Shortly after, the first airway traffic control center opened at Newark, NJ. Centers at Chicago and Cleveland followed.

The primary method of controlling the immediate airport environment is visual observation from the control tower. Tower controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 2 to 5 nautical miles, depending on the airport procedures. Radar displays are also available to controllers at some airports. They may use a radar system including both primary surveillance and secondary surveillance for airborne traffic approaching and departing. These displays include the position of various aircraft and data tags that include aircraft identification, speed, heading, altitude, and position data.

Project Capstone was an FAA undertaking in southeastern Alaska starting in the late 1990s. This initiative equipped general aviation aircraft and commercial carriers with equipment capable of sending aircraft GPS position, speed, and heading along with normal transponder information. Ground stations were added to distribute this information to air traffic controllers along with the capability to share pertinent data with other aircraft up to a 150-mile range. The results reflected a drop in accidents of about 40 percent in the target area.

Automatic Dependent Surveillance Broadcast (ADS-B) is a relatively new technology that allows flight crew members and air traffic controllers to view traffic with a significantly higher degree of precision than current systems.

Three data links are currently being explored for relaying the ADS-B position reports and allow air-to-air information transfer along with air-to-ground: 1,090 MHz Mode S extended squitter (ES); universal access transceiver (UAT); and VHF Data Link (VDL) Mode 4.

In 2002 the FAA announced a dual link decision using 1,090 MHz ES and UAT as mediums for the ADS-B system in the United States.

1090ES
With 1090ES, the existing Mode S transponder (TSO C-112 or a stand-alone 1,090 MHz transmitter) supports a message type known as the extended squitter (ES). Mode S, or mode select, despite also being called a mode, is actually a radically improved system intended to replace ground-based air traffic radar facilities.

It is a periodic message that provides position, velocity, heading, time, and, in the future, intent. To enable an aircraft to send an extended squitter message, the transponder is modified (TSO C-166A) and aircraft position and other status information is routed to the transponder. ATC ground stations and traffic collision avoidance system (TCAS)-equipped aircraft already have the necessary 1,090 MHz (Mode S) receivers to receive these signals, and would only require enhancements to accept and process the additional extended squitter information. The Eurocontrol (European organization for the safety of air navigation) CASCADE program uses 1090ES exclusively.

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