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Fact Sheet – Automatic Dependent Surveillance-Broadcast (ADS-B)

For Immediate Release

May 2, 2006
Contact: Rebecca Trexler
Phone: (202) 267-3883

What is ADS-B?

Simply put, ADS-B is the future of air traffic control. Instead of using radar data to keep aircraft at safe distances from one another, in the future, signals from Global Positioning Satellites will provide air traffic controllers and pilots with much more accurate information that will help keep aircraft safely separated in the sky and on runways.

Eventually, with ADS-B, some of the responsibility for keeping safe distances between aircraft will shift from air traffic controllers on the ground to pilots who will have displays in the cockpits pinpointing all the air traffic around them, along with local weather displays.

How does ADS-B work?

ADS-B works by having aircraft transponders receive GPS signals and use them to determine the aircraft’s precise location in the sky.

The system converts that position into a unique digital code and combines it with other data from the aircraft’s flight monitoring system — such as the type of aircraft, its speed, its flight number, and whether it is turning, climbing, or descending.

The code containing all of this data is automatically broadcast from the aircraft’s transponder once a second using the 1090 Mode S Extended Squitter for commercial planes and the 978 MHz Universal Access Transceiver for general aviation aircraft.

Aircraft equipped to receive the data and ADS-B ground stations up to 200 miles away receive these broadcasts. ADS-B ground stations add radar-based targets for non-ADS-B-equipped aircraft to the mix and send the information back up to all equipped aircraft — this function is called Traffic Information Service-Broadcast (TIS-B). ADS-B ground stations also send aircraft information from the national weather service and flight information, such as temporary flight restrictions — this is called Flight Information Service-Broadcast (FIS-B).

Pilots see this information in their cockpit traffic display screens. Air traffic controllers will see the information on displays they are already using, so little additional training would be needed. ADS-B signals are transmitted once per second, providing a more accurate tracking system for pilots and controllers.

What are the benefits of ADS-B? 

When properly equipped with ADS-B, both pilots and controllers will, for the first time, see the same real-time displays of air traffic. Pilots will have much better situational awareness because they will know where their own aircraft are with greater accuracy, and their displays will show them all the aircraft in the air around them. Pilots will be able to maintain safe separation from other aircraft with fewer instructions from ground-based controllers. At night and in poor visual conditions, pilots will also be able to see where they are in relation to the ground using on-board avionics and terrain maps.

In addition to improved safety in the sky, ADS-B will help reduce the risk of runway incursions. Both pilots and controllers will see the precise location on runway maps of each aircraft and even equipped ground vehicles, along with data that shows where they are moving. These displays are clear and accurate, even at night or during heavy rainfall.

ADS-B will also increase capacity, because the more accurate tracking means aircraft will be able to fly safely and more predictably with less distance between them. And, because ADS-B accuracy also means better predictability, air traffic controllers will be better able to manage the air traffic arriving and departing from congested airports, resulting in even more gains in capacity.

With its combined increases in safety, efficiency and capacity, and reductions in cost, ADS-B is critical to the agency’s Next-Generation Air Transportation System plan for meeting the nation’s predicted tripling of demand in coming years.

Why adopt ADS-B?

Although radar technology has advanced, it is essentially a product of 1940s World War II technology. Radar occasionally has problems discriminating airplanes from migratory birds and rain “clutter.” Secondary surveillance systems can determine what objects are because they interrogate transponders; however, both primary and secondary radars are very large structures that are expensive to deploy, need lots of maintenance, and require the agency to lease real estate to situate them.

ADS-B, on the other hand, receives data directly from the transmitters, rather than passively scanning for input like radars, so does not have a problem with clutter. ADS-B ground stations are inexpensive compared to radar, and are the size of mini refrigerators that essentially can go anywhere, so they minimize the required real estate. In addition, ADS-B updates once a second and locates aircraft with much more precision.

ADS-B also provides greater coverage, since ADS-B ground stations are so much easier to place than radar. Remote areas where there is no radar can now have precise surveillance coverage.

What has been done to date?

The FAA established the Capstone and Safe Flight 21 programs as joint government/industry initiatives to demonstrate the capabilities of advanced surveillance systems and air traffic procedures using ADS-B in a real-world environment.

To get preliminary assessments of the costs, benefits, operational safety and security, and architectural requirements for ADS-B, the FAA conducted a series of operational evaluations in Alaska and the Ohio Valley. RTCA (a scientific advisory group that assists the FAA on technical issues) developed the initial avionics standards for the new system, and the FAA conducted three joint government/industry meetings in 2001 to gather user and industry feedback.

Using the results of these evaluations, the FAA conducted a broad assessment of ADS-B technical link performance from 1999 through 2001 that resulted in the FAA’s ADS-B “link decision” in June 2002. In summary, the link decision selected two ADS-B frequencies for use in the national airspace system — the 1090 Extended Squitter (1090 ES) and Universal Access Transceiver (UAT). The 1090 ES will be used by commercial aircraft, while UAT was selected for general aviation and vehicles. Revisions and development of additional avionics standards by RTCA followed in 2003 and 2004.

On September 9, 2005, the FAA officially committed to moving toward establishing ADS-B as the basis for air traffic control in the future. Moving to ADS-B will allow the agency to eventually begin decommissioning some of the current infrastructure of ground radars in favor of a system that uses much more precise satellite data and provides greater benefit to everyone who uses the national airspace system.

What are the next steps?

The FAA reserved $80 million for fiscal year 2007 to begin the initial implementation of ADS-B in the national airspace system. This includes continuing to support the ADS-B infrastructure already installed along the East Coast and integrating ADS-B surveillance into the FAA’s current air traffic control systems.

With ADS-B, the FAA plans to let vendors install and maintain the equipment, and to lease services from them, just as the agency today buys telcom services from telecommunications companies. This will both reduce costs and give the agency greater flexibility. Once the ADS-B infrastructure is in place, vendors will likely use the system’s capabilities to offer even more services to pilots and airlines.

The agency is also looking at the possibility of rulemaking that would mandate the avionics necessary for implementing ADS-B across the national airspace system.

The full evolution of ADS-B would take up to twenty years, taken in manageable segments of equipage and ground-station installation, with some legacy radars maintained throughout to provide a back-up system. However, benefits in improved safety and capacity, and better efficiency for airlines, would accrue with each step of the implementation.

The agency plans a meeting of its Joint Resources Council in June of this year to determine more exactly the near-term steps in beginning the transition to ADS-B.


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