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.

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.

Universal access transceiver
The UAT system is specifically designed for ADS-B operation. UAT has a lower cost and greater uplink capacity than 1,090ES. Although 978 MHz resides in the assigned portion of the aeronautical spectrum, in the United States 978 is used for transmission of airborne ADS-B reports and for broadcast of ground-based aeronautical information. UAT users have access to ground-based aeronautical data including traffic information services and flight information services including weather and NOTAMS.

VDL Mode 4
The VDL Mode 4 system could utilize one or more of the existing aeronautical VHF frequencies as the radio frequency physical layer for ADS-B transmissions. It is best used for short message transmissions between a large number of users

VDL Mode 4 uses a protocol (STDMA, invented by Hakan Lans in 1988) that allows it to be self-organizing, meaning no master ground station is required. In November 2001 this protocol was published by International Civil Aviation Organization (ICAO) as a global standard.

In the flight deck, a generic display would be used to provide the crew with surveillance information about other aircraft and would include existing devices such as TCAS.

ADS-B is a reality and worldwide implementation has already begun. The FAA plan was started in 2006 and deployment to key sites such as Juneau, AK; the Gulf of Mexico; Philadelphia; and Louisville, KY, are forecast to be operational by 2010. The nationwide system is scheduled to be in place around 2013 with required aircraft compliance expected in 2020. European compliance is currently expected around 2012.

Not only can ADS-B equipped aircraft contribute position information, but so can ground support vehicles with a GPS and a UAT.

While recently being included in a golf outing and riding in the golf cart equipped with a GPS, I noticed a high-lighted blip traveling along the cart path. It took a minute but I figured out this represented a “Beverage Cart.” I then noticed a “Push to Call” function on the GPS. When the cart person got to us and took care of the important business, I asked to look at the GPS in the refreshment cart and there it was, an ADS-B system — just not using aviation radio frequencies.

I wholeheartedly approve the concept.

Jim Sparks has been in aviation for 30 years and is a licensed A&P.

EUROCONTROL’s new system
On March 23, 2009, Eurocontrol’s Maastricht Control Center unveiled its new air traffic control system. Air traffic control over Belgium, the Netherlands, Luxembourg, and northwest Germany will now be exclusively provided via the new flight data processing system. The old system from the early 1970s will be permanently shut down.

This flight data processing system is the first of its kind in Europe to be developed in accordance with European standards on interoperability between systems. It is based on the philosophy behind the Single European Sky, an initiative launched in 2004 by the European Commission. In order to respond to the needs and future challenges of the air transport industry, the Maastricht Center and its partners are currently working on the creation of a functional airspace block, “FAB Europe Central” (FABEC), which aims to implement multinational management of the airspace of six countries (Germany, Belgium, France, Luxembourg, the Netherlands, and Switzerland). For more information visit