Ashland Municipal Airport - 433 Dead Indian Memorial Road, Ashland, OR 97520 - Office: (541) 488 1964

ADS-B How Does it Work?

Automatic dependent surveillance-broadcast (ADS-B) is a surveillance technology for tracking aircraft as part of the Next Generation Air Transportation System (NextGen). The United States required the majority of aircraft operating within its airspace to be equipped with some form of ADS-B Out by December 31, 2019.

ADS-B, which consists of two different services, “ADS-B Out” and “ADS-B In”, will be replacing radar as the primary surveillance method for controlling aircraft worldwide. In the United States, ADS-B is an integral component of the NextGen national airspace strategy for upgrading or enhancing aviation infrastructure and operations. The ADS-B system can also provide traffic and government generated graphical weather information through TIS-B and FIS-B applications. ADS-B enhances safety by making an aircraft visible, real-time, to ATC and to other appropriately equipped ADS-B aircraft with position and velocity data transmitted every second. ADS-B data can be recorded and downloaded for post-flight analysis. ADS-B also provides the data infrastructure for inexpensive flight tracking, planning, and dispatch.

ADS-B Out periodically broadcasts information about each aircraft, such as identification, current position, altitude, and velocity, through an onboard transmitter. ADS-B Out provides air traffic controllers with real-time position information that is, in most cases, more accurate than the information available with current radar-based systems. With more accurate information, ATC will be able to position and separate aircraft with improved precision and timing.

ADS-B In is the reception by aircraft of FIS-B and TIS-B data and other ADS-B data such as direct communication from nearby aircraft. The system relies on two avionics components—a high-integrity GPS navigation source and a datalink (ADS-B unit). There are several types of certified ADS-B data links, but the most common ones operate at 1090 MHz, essentially a modified Mode S transponder, or at 978 MHz. The FAA would like to see aircraft that operate below 18 000’ use the 978 MHz link since this will help alleviate further congestion of the 1090 MHz frequency. To obtain ADS-B capability at 1090 MHz, one can install a new transponder or modify an existing one if the manufacturer offers an ADS-B upgrade. You will also need to add a certified GPS.

Two solutions are being used as the physical layer for relaying the ADS-B position reports:

  • Universal Access Transceiver (UAT)
  • 1,090 MHz Mode S Extended Squitter (ES)

Universal Access Transceiver (UAT)

A Universal Access Transceiver (UAT) refers to a data link intended to serve the majority of the general aviation community. The data link is approved in the Federal Aviation Administration’s “final rule” for use in all airspace except class A (above 18 000 ft. MSL). UAT is intended to support not only ADS-B, but also Flight Information Service – Broadcast (FIS-B), Traffic Information Service – Broadcast (TIS-B), and, if required in the future, supplementary ranging and positioning capabilities Due to the set of standards required for this rule, it is seen as the most effective application for general aviation users.

UAT will allow aircraft equipped with “out” broadcast capabilities to be seen by any other aircraft using ADS-B In technology as well as by FAA ground stations. Aircraft equipped with ADS-B In technology will be able to see detailed altitude and vector information from other ADS-B Out equipped aircraft as well as FIS-B and TIS-B broadcasts. The FIS-B broadcast will allow receiving aircraft to view weather and flight service information including AIRMETs, SIGMETs, METARs, SPECI, National NEXRAD, Regional NEXRAD, D-NOTAMs, FDC-NOTAMs, PIREPs, Special Use Airspace Status, Terminal Area Forecasts, Amended terminal aerodrome forecasts (TAFs), Winds and Temperature Aloft. These broadcasts serve to provide early adopters of the technology with benefits as an incentive for more pilots to use the technology before 2020. Aircraft receiving traffic information through the TIS-B service will see other aircraft in a manner that is similar to how all aircraft will be seen after they have equipped by 2020. The availability of a non-subscription weather information service, FIS-B, provides general aviation users with a useful alternative to other monthly or annual fee-based services.

The UAT system is specifically designed for ADS-B operation. UAT is also the first link to be certified for “radar-like” ATC services in the United States.

1090 MHz Extended Squitter (1090ES)

In 2002 the FAA announced a dual link decision using 1090 MHz ES and UAT as media for the ADS-B system in the United States, with the 1,090 MHz extended squitter ADS-B link for air carrier and private or commercial operators of high-performance aircraft, and Universal Access Transceiver (UAT) ADS-B link for the typical general aviation user.

With 1090ES, the existing Mode S transponder (TSO C-112 or a standalone 1,090 MHz transmitter) supports a message type known as the extended squitter (ES) message. It is a periodic message that provides position, velocity, time, and, in the future, intent. The basic ES does not offer intent since current flight management systems do not provide such data – called trajectory change points.

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 aircraft equipped with traffic collision avoidance system (TCAS) already have the necessary 1090 MHz (Mode S) receivers to receive these signals, and only require enhancements to accept and process the additional Extended Squitter information. As per the FAA ADS-B link decision and the technical link standards 1090ES does not support FIS-B service.

ADS-B provides many benefits to both pilots and air traffic control that improve both the safety and efficiency of flight.

  • Traffic – When using an ADS-B In system a pilot is able to view traffic information surrounding aircraft. This information includes altitude, heading, speed, and distance to aircraft.
  • Weather – Aircraft equipped with UAT ADS-B In technology will be able to receive weather reports, and weather radar through flight information service-broadcast (FIS-B).
  • Terrain – ADS-B In technology, broadcasts a terrain overlay for pilots to view in the cockpit.
  • Flight information – Traffic Information Service-Broadcast (TIS-B, not to be confused with FIS-B) transmits readable flight information such as TFRs and NOTAMs to aircraft equipped with either UAT or 1090ES ADS-B systems.

Unlike some alternative in-flight weather services currently being offered commercially, there are no subscription fees to use ADS-B services or its various benefits in the US. The aircraft owner will pay for the equipment and installation, while the Federal Aviation Administration (FAA) will pay for administering and broadcasting all the services related to the technology.


Situational awareness

ADS-B makes flying significantly safer for the aviation community by providing pilots with improved situational awareness. Pilots in an ADS-B In equipped cockpit will have the ability to see, on their in-cockpit flight display, other traffic operating in the airspace as well as access to clear and detailed weather information. They will also be able to receive pertinent updates ranging from temporary flight restrictions (TFRs) to runway closings.

Improved visibility

Even aircraft only equipped with ADS-B out will be benefited by air traffic controllers ability to more accurately and reliably monitor their position. When using this system both pilots and controllers will see the same radar picture. Other fully equipped aircraft using the airspace around them will be able to more easily identify and avoid conflict with an aircraft equipped with ADS-B Out. With past systems such as the traffic alert and collision avoidance system (TCAS) aircraft could only see other aircraft equipped with the same technology. With ADS-B, information is sent to aircraft using ADS-B In, which displays all aircraft in the area, even those not equipped with ADS-B technology. ADS-B provides better surveillance in fringe areas of radar coverage. ADS-B does not have the siting limitations of radar. Its accuracy is consistent throughout the range. In both forms of ADS-B (1090ES & 978 MHz UAT), the position report is updated once per second. The 978 MHz UAT provides the information in a single, short duration transmission. The 1090ES system breaks the ADS-B position report message into 5 segments due to capacity limitations of the 1090ES technology.

ADS-B enables improved safety by providing

  • Radar-like IFR separation in non-radar airspace
  • Increased VFR flight following coverage
  • ATC final approach and runway occupancy, reducing runway incursions on the ground
  • More accurate search and rescue response although ADS-B can transmit “aircraft down” data, the FAA has stated that there is no intention to perform even a study of ADS-B’s effectiveness in an “aircraft down” situation simply based on the fact that ADS-B equipment has no requirement to be crash worthy, as compared to the current “black box” recorder. ADS-B was demonstrated to the Civil Air Patrol (CAP) in March 2003 by AOPA via flight demonstrations for possible integration of the technology in CAP activities.
  • Improved visual acquisition especially for general aviation under VFR or MVFR
  • Cockpit final approach and runway occupancy
  • Visual separation in VFR and MVFR conditions
  • VFR-like separation in all weather conditions
  • Real-time cockpit weather display
  • Real-time cockpit airspace display

Reduced environmental impact

ADS-B technology provides a more accurate report of an aircraft’s position. This allows controllers to guide aircraft into and out of crowded airspace with smaller separation standards than it was previously possible to do safely. This reduces the amount of time aircraft must spend waiting for clearances, being vectored for spacing and holding. Estimates show that this is already having a beneficial impact by reducing pollution and fuel consumption.

In the EU airspace aircraft with a weight above 5,700 kilograms (13,000 lb.) or a max cruise of over 250 knots will be required to carry ADS-B from 2017 (new planes from 2015).