Automatic dependent surveillance – broadcast

Automatic Dependent Surveillance – Broadcast (ADS–B) is a surveillance technology in which an aircraft determines its position via satellite navigation and periodically broadcasts it, enabling it to be tracked. The information can be received by air traffic control ground stations as a replacement for secondary radar. It can also be received by other aircraft to provide situational awareness and allow self separation.

ADS–B is "automatic" in that it requires no pilot or external input. It is "dependent" in that it depends on data from the aircraft's navigation system.

ADS–B is an element of the US Next Generation Air Transportation System (NextGen), Airports Authority of India upgrade plans in line with ICAO Global Plan Initiatives and Aviation System Block Upgrade (ASBU) and the Single European Sky ATM Research (SESAR). ADS–B equipment is currently mandatory in portions of Australian airspace, the United States requires some aircraft to be equipped by 2020 and the equipment will be mandatory for some aircraft in Europe from 2017. Canada is already using ADS-B for Air Traffic Control.

Description

ADS-B, which consists of two different services, "ADS-B Out" and "ADS-B In", could replace 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 and 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, realtime, to air traffic control (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 ground station broadcast data is typically only made available in the presence of an ADS-B Out broadcasting aircraft, limiting the usefulness of purely ADS-B In devices.

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 exclusively operate below 18,000 feet (5,500 m) use the 978 MHz link since this will help alleviate further congestion of the 1090 MHz frequency. To obtain ADS-B Out capability at 1090 MHz, one can install a new transponder or modify an existing transponder if the manufacturer offers an ADS-B upgrade, plus install a certified GPS position source if one is not already present.

Benefits

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

1. Traffic – When using an ADS-B In system, a pilot is able to view traffic information about surrounding aircraft if those aircraft are equipped with ADS-B out. This information includes altitude, heading, speed, and distance to aircraft.
2. Weather – Aircraft equipped with universal access transceiver (UAT) ADS-B In technology will be able to receive weather reports, and weather radar through flight information service-broadcast (FIS-B).
3. Flight information – Traffic information service-broadcast (TIS-B, not to be confused with FIS-B) transmits readable flight information such as temporary flight restrictions (TFRs) and NOTAMs to aircraft equipped with either UAT or 1090 ES ADS-B systems.
4. Expense - ADS-B ground stations are significantly cheaper to install and operate compared to primary and secondary radar systems.

Unlike some alternative in-flight weather services currently being offered commercially, there will be 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.

Safety

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 to runway closings.

Improved visibility

Even aircraft only equipped with ADS-B Out will benefit from 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

Efficiency

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.

Traffic capacity improvement

ADS-B enables increased capacity and efficiency by supporting:

• Better ATC traffic flow management
• Merging and spacing
• Self-separation or station keeping
• Enhanced visual approaches;
• Closely spaced parallel approaches;
• Reduced spacing on final approach;
• Reduced aircraft separations;
• Enhanced operations in high altitude airspace for the incremental evolution of the "free flight" concept;
• Surface operations in lower visibility conditions;
• Near visual meteorological conditions (VMC) capacities throughout the airspace in most weather conditions;
• Improved air traffic control services in non-radar airspace;
• Trajectory-based operations providing a gently ascending and descending gradient with no step-downs or holding patterns needed. This will produce optimal trajectories with each aircraft becoming one node within a system wide information management network connecting all equipped parties in the air and on the ground. With all parties equipped with NextGen equipage, benefits will include reduced gate-to-gate travel times, increased runway utilization capacity, and increased efficiency with carbon conservation.
• Use of ADS-B and CDTI may allow decreased approach spacing at certain airports to improve capacity during reduced-visibility operations when visual approach operations would normally be terminated (e.g., ceilings less than MVA +500).

Other applications

The ADS-B data link supports a number of airborne and ground applications. Each application has its own operational concepts, algorithms, procedures, standards, and user training.

Cockpit display of traffic information

A cockpit display of traffic information (CDTI) is a generic display that provides the flight crew with surveillance information about other aircraft, including their position. Traffic information for a CDTI may be obtained from one or multiple sources, including ADS-B, TCAS, and TIS-B. Direct air-to-air transmission of ADS-B messages supports display of proximate aircraft on a CDTI.

In addition to traffic based on ADS-B reports, a CDTI function might also display current weather conditions, terrain, airspace structure, obstructions, detailed airport maps, and other information relevant to the particular phase of flight.

Airborne collision avoidance

ADS-B is seen as a valuable technology to enhance airborne collision avoidance system (ACAS) operation. Incorporation of ADS-B can provide benefits such as:

• Decreasing the number of active interrogations required by ACAS, thus increasing effective range in high-density airspace.
• Reducing unnecessary alarm rate by incorporating the ADS-B state vector, aircraft intent, and other information.
• Use of the ACAS display as a CDTI, providing positive identification of traffic.
• Extending collision avoidance below 1,000 feet above ground level, and detecting runway incursions.

Eventually, the ACAS function may be provided based solely on ADS-B, without requiring active interrogations of other aircraft transponders.

Other applications that may benefit from ADS-B include:

• Lighting control automation and operation
• Airport ground vehicle and aircraft rescue and firefighting vehicle operational needs
• Altitude height keeping performance measurements
• General aviation operations control
• Conflict management
• ATS conformance monitoring
• Aircraft spotting where personal receivers can be used to produce a virtual radar picture

Security risk

A hacker group claimed in 2012 that it could interfere with navigation with spoof ADS-B messages because they were neither encrypted nor authenticated.

The lack of any authentication within the standard makes it mandatory to validate any received data by use of the primary radar. Because the content of ADS-B messages is not encrypted, it may be read by anybody. Flightradar24 is one such website which tracks all ADS-B flights with the use ADS-B receivers distributed all over the world.

Theory of operation

ADS-B System

The ADS-B system has three main components: 1) ground infrastructure, 2) airborne component, and 3) operating procedures.

• A transmitting subsystem that includes message generation and transmission functions at the source; e.g., airplane.
• The transport protocol; e.g., VHF (VDL mode 2 or 4), 1090ES, or 978 MHz UAT.
• A receiving subsystem that includes message reception and report assembly functions at the receiving destination; e.g., other airplanes, vehicle or ground system.

The source of the state vector and other transmitted information as well as user applications are not considered to be part of the ADS-B system.

Physical layer

Two link solutions are used as the physical layer for relaying ADS-B position reports: universal access transceiver, and 1090 MHz extended squitter.

Universal access transceiver

A universal access transceiver is 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. Since 2001 it has been providing 5 NM en-route separation (the same as mosaic radar but not 3 NM of single-site sensors) in Alaska. UAT is the only ADS-B link standard that is truly bidirectional: UAT users have access to ground-based aeronautical data (FIS-B) and can receive reports from proximate traffic (TIS-B) through a multilink gateway service that provides ADS-B reports for 1090ES-equipped aircraft and non-ADS-B equipped radar traffic. UAT equipped aircraft can also observe each other directly with high accuracy and minimal latency. Viable ADS-B UAT networks are being installed as part of the United States' NextGen air traffic system.

1090 MHz extended squitter

A simple homemade antenna can receive 1090 MHz signals.

In 2002 the Federal Aviation Administration (FAA) announced a dual link decision using the 1090 MHz extended squitter (1090 ES) link for air carrier and private or commercial operators of high-performance aircraft, and universal access transceiver link for the typical general aviation user. In November 2012, the European Aviation Safety Agency confirmed that the Europe Union would also use 1090 ES for interoperability. The format of extended squitter messages has been codified by the ICAO.

With 1090 ES, the existing Mode S transponder (TSO C-112 or a standalone 1090 MHz transmitter) supports a message type known as the extended squitter 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 would 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, 1090 ES does not support FIS-B service.

Relationship to surveillance radar

Radar directly measures the range and bearing of an aircraft from a ground-based antenna. The primary surveillance radar is usually a pulse radar. It transmits a continuous high power sequence of pulses. Bearing is measured by the position of the rotating radar antenna when it receives the reflected beam that comes from the body aircraft; and range is measured by the time it takes for the radar to receive the reflected beam.

Primary surveillance radar does not require any cooperation from the aircraft. It is robust in the sense that surveillance outage failure modes are limited to those associated with the ground radar system. Secondary surveillance radar depends on active replies from the aircraft. Its failure modes include the transponder aboard the aircraft. Typical ADS-B aircraft installations use the output of the navigation unit for navigation and for cooperative surveillance, introducing a common failure mode that must be accommodated in air traffic surveillance systems.

Type	Independent?	Cooperative?
Primary surveillance radar (PSR)	Yes: surveillance data derived by radar	No: does not depend on aircraft equipment
Secondary surveillance radar (SSR)	Yes (except for pressure altitude): aircraft range and azimuth derived by radar	Yes: requires aircraft to have a working ATCRBS transponder
Automatic dependent surveillance (ADS-B)	No: surveillance data provided by aircraft	Yes: requires aircraft to have working ADS-B function
Source: DO-242A

The antenna beam becomes wider as the aircraft gets farther away, making the position information less accurate. Additionally, detecting changes in aircraft velocity requires several radar sweeps that are spaced several seconds apart. In contrast, a system using ADS-B creates and listens for periodic position and intent reports from aircraft. These reports are generated based on the aircraft's navigation system, and distributed via one or more of the ADS-B data links. The accuracy of the data is no longer susceptible to the position of the aircraft or the length of time between radar sweeps. (However, the signal strength of the signal received from the aircraft at the ground station is still dependent on the range from the aircraft to the receiver, and interference, obstacles, or weather could degrade the integrity of the received signal enough to prevent the digital data from being decoded without errors; when the aircraft is farther away, the weaker received signal will tend to be more affected by the aforementioned adverse factors and is less likely to be received without errors in their presence. While error detection codes will allow the errors to be recognized as errors, so that the system maintains full accuracy regardless of aircraft position when the signal can be received and decoded correctly, this advantage does not equate to total indifference to the range of an aircraft from the ground station.)

Today's air traffic control (ATC) systems do not rely on coverage by a single radar. Instead a multiradar picture is presented via the ATC system's display to the controller. This improves the quality of the reported position of the airplane, provides a measure of redundancy, and makes it possible to verify the output of the different radars against others. This verification can also use sensor data from other technologies, such as ADS-B and multilateration.

Relationship to ADS-A/ADS-C

There are two commonly recognized types of ADS for aircraft applications:

• ADS-Addressed (ADS-A), also known as ADS-Contract (ADS-C)
• ADS-Broadcast (ADS-B)

ADS-A is based on a negotiated one-to-one peer relationship between an aircraft providing ADS information and a ground facility requiring receipt of ADS messages. For example, ADS-A reports are employed in the Future Air Navigation System (FANS) using the Aircraft Communications Addressing and Reporting System (ACARS) as the communication protocol. During flight over areas without radar coverage (e.g., oceanic and polar), reports are periodically sent by an aircraft to the controlling air traffic region.

The transmission delay caused by protocol or satellites is significant enough that significant aircraft separations are required. The cost of using the satellite channel leads to less frequent updates. Another drawback is that no other aircraft can benefit from the transmitted information as ACARS information is not re-broadcast from ground facilities to other aircraft.

Traffic information service – broadcast (TIS–B)

Main article: Traffic information service – broadcast

Traffic information service – broadcast (TIS–B) supplements ADS-B's air-to-air services to provide complete situational awareness in the cockpit of all traffic known to the ATC system. TIS–B is an important service for an ADS-B link in airspace where not all aircraft are transmitting ADS-B information. The ground TIS–B station transmits surveillance target information on the ADS-B data link for unequipped targets or targets transmitting only on another ADS-B link.

TIS–B uplinks are derived from the best available ground surveillance sources:

• ground radars for primary and secondary targets
• multilateration systems for targets on the airport surface
• ADS-B systems for targets equipped with a different ADS-B link

Multilink gateway service

The multilink gateway service is a companion to TIS-B for achieving interoperability between different aircraft equipped with 1090ES or UAT by using ground-based relay stations. These aircraft cannot directly share air-to-air ADS-B data due to the different communication frequencies. In terminal areas, where both types of ADS-B link are in use, ADS-B/TIS-B ground stations use ground-to-air broadcasts to relay ADS-B reports received on one link to aircraft using the other link.

Although multilink "solves" the issue of heavy airliners working on one frequency vs. light aircraft, the dual frequency nature of the system has several potential issues:

• Since two aircraft on two different ADS-B frequencies must use a ground station to talk to each other, this introduces the ground station as a point of failure, although to be fair, the 1090 signal is dependent secondary radar scans in any case (and thus cannot operate without a ground station).
• The time taken to traverse the full path from one aircraft, to the ground station, then to the second aircraft adds delay to the signal. This contrasts with two autonomous ADS-B transceivers on UAT, which have a shorter and shorter delay as they converge.
• Aircraft are frequently out of the range of ground based radar due to altitude. Radar can be blocked by mountains, and typically is not useful for coverage near an airport unless that airport itself has radar. Thus, approach, departure, and especially taxi/ground based operations are compromised (a major selling point of the system).

Because of the issues with multilink, many ADS-B manufacturers are designing ADS-B systems as dual frequency capable.

Flight information services-broadcast (FIS-B)

FIS-B provides weather text, weather graphics, NOTAMs, ATIS, and similar information. FIS-B is inherently different from ADS-B in that it requires sources of data external to the aircraft or broadcasting unit, and has different performance requirements such as periodicity of broadcast.

In the United States, FIS-B services will be provided over the UAT link in areas that have a ground surveillance infrastructure.

Another potential aircraft-based broadcast capability is to transmit aircraft measurements of meteorological data.

In the United States

Although the aviation industry is subject to variations in demand as economic conditions fluctuate, the long-term trend is a steady increase in traffic and as a result delay and congestion continue to build in the United States' busiest airports and the surrounding airspace. The Federal Aviation Administration must not only address current congestion, but also be poised to handle future demand that will surely return as the nation's economy improves. The FAA has been developing the Next-Generation Air Transportation System (NextGen) for the purpose of changing the way the National Airspace System (NAS) operates. NextGen will allow the NAS to expand to meet future demand and support the economic viability of the system. In addition, NextGen will improve safety and support environmental initiatives such as reducing congestion, noise, emissions, and fuel consumption through increased energy efficiency.

ADS-B is an essential part of the planned NextGen airspace upgrade and will create better aircraft visibility at a lower overall cost than before. ADS-B equipment is built to meet one of two sets of US government standards, DO-260B and DO-282B.

By 2020, all aircraft operating in the US airspaces listed below will be required to carry equipment that produces an ADS-B Out broadcast.

The FAA has published a rule requiring ADS-B transmitters in many types of airspace (ADS-B Out) to take effect on January 1, 2020, but there is no mandate for ADS-B In, which receives data and provides it to in-cockpit displays. The FAA airspace requirements intentionally exclude some airspace that is frequently used by general aviation.

Airspace	Altitude
A	All aircraft equipped
B	All aircraft equipped
C	All aircraft equipped
E	Above 10,000 ft MSL but not below 2,500 ft AGL

ADS-B will offer increased safety, efficiency and environmental awareness for pilots and air traffic controllers at a lower overall cost than the current radar system. Companies have already begun selling and developing aircraft hardware systems to allow general aviation aircraft owners to equip at an affordable cost.

Since the FAA has passed its final ruling on ADS-B, the uncertainty that prevented companies from producing hardware has been removed. The industry is seeing products being developed for all price points, low to high, and competitively priced equipment is nearing approval. As the technology matures more features are also becoming available creating even greater benefits for general aviation users.

Summary of final rule

This final rule will add equipage requirements and performance standards for ADS-B Out avionics. ADS-B Out broadcasts information about an aircraft through an onboard transmitter to a ground receiver. Use of ADS-B Out will move air traffic control from a radar-based system to a satellite-derived aircraft location system. Operators will have two options for equipage under this rule—the 1090 megahertz extended squitter broadcast link or the universal access transceiver broadcast link. Generally, this equipment will be required for aircraft operating in Classes A, B, and C airspace, certain Class E airspace, and other specified airspace.

The FAA has concluded that this rule will require only the performance requirements necessary for ADS-B Out. While certain requirements adopted in this rule will support some ADS-B In applications, the FAA is not adopting the higher performance standards that would enable all of the initial ADS-B In applications. Pilots should be aware that in accepting the FAA's positions regarding antenna diversity and position source accuracy, compliance with this rule alone may not enable operators to take full advantage of certain ADS-B In applications. Operators may voluntarily choose equipment that meets the higher performance standards in order to enable the use of these applications.

This system will make radar based ATC obsolete, moving the nation to a satellite derived aircraft location system.

This will make ADS-B the backbone of the NextGen ATC system coming online in 2020.

Equipping aircraft

Fleet: 250,000 GA aircraft that will need ADS-B by 2020 of which 165,000 aircraft subject to ADS-B Out (Class I and Class II aircraft that generally fly below 18 000 feet). FAA forecasts an increase in the GA fleet from 224,172 aircraft in 2010 to 270,920 aircraft in 2031, growing an average of 0.9% per year.

Funding resources

Recent (April 2011) US federal legislation via House Bill for FAA re-authorization permits an "equipping fund" that includes a portion for some general aviation aircraft. The fund would provide financing at competitive rates backed by loan guarantees. A public-private partnership has been formed as the NextGen Equipage Fund, LLC which is managed by NEXA General Partnership, LLC.

US implementation timetable

The Federal Aviation Administration ADS-B implementation is broken into three segments each with a corresponding time line. Ground segment implementation and deployment is expected to begin in 2009 and be completed by 2013 throughout the National Airspace System (NAS). Airborne equipment is user-driven and is expected to be completed both voluntarily based on perceived benefits and through regulatory actions (Rulemaking) by the FAA. The cost to equip with ADS-B Out capability is relatively small and would benefit the airspace with surveillance in areas not currently served by radar. The FAA intends to provide similar service within the NAS to what radar is currently providing (5 nmi en route and 3 nmi terminal radar standards) as a first step to implementation. However, ADS-B In capability is viewed as the most likely way to improve NAS throughput and enhance capacity.

In December 2008, Acting FAA Administrator Robert A. Sturgell gave the go-ahead for ADS-B to go live in southern Florida. The south Florida installation, which consists of 11 ground stations and supporting equipment, is the first commissioned in the United States, although developmental systems have been online in Alaska, Arizona, and along the East Coast since 2004. The completed system will consist of 794 ground station transceivers. The December 2008 action is in compliance with a late-term executive order from George W. Bush which mandated accelerated approval of NextGen.

FAA segment 1 (2006–09)

ADS-B deployment and voluntary equipment, along with rule-making activities. Pockets of development will exploit equipment deployment in the areas that will provide proof of concept for integration to ATC automation systems deployed in the NAS. It is being developed at the FAA's William J. Hughes Technical Center near Egg Harbor City, New Jersey.

FAA segment 2 (2010–14)

ADS-B ground stations will be deployed throughout the NAS, with an in-service decision due in the 2012–2013 time frame. Completed deployment will occur in 2013–14. Equipment rules have been finalized and the current standards are DO-282B for UAT and DO-260B for 1090ES:

• Airport situational awareness – a combination of detailed airport maps, airport multilateration systems, ADS-B systems and enhanced aircraft displays have the potential to significantly improve Airport Surface Situational Awareness (ASSA), and Final Approach and Runway Occupancy Awareness (FAROA).
• Oceanic In-trail – ADS-B may provide enhanced situational awareness and safety for Oceanic In-trail maneuvers as additional aircraft become equipped.
• Gulf of Mexico – in the Gulf of Mexico, where ATC radar coverage is incomplete, the FAA is locating ADS-B (1090 MHz) receivers on oil rigs to relay information received from aircraft equipped with ADS-B extended squitters back to the Houston Center to expand and improve surveillance coverage.
• Terminal Airspace – ADS-B is currently in service for two terminal airspace areas, Louisville, Kentucky, and Philadelphia, Pennsylvania.

FAA segment 3 (2015–20)

ADS-B In equipment will be based on user perceived benefit, but is expected to be providing increased situational awareness and efficiency benefits within this segment. Those aircraft who choose to equip in advance of any mandate will see benefits associated with preferential routes and specific applications. Limited radar decommissioning will begin in the time frame with an ultimate goal of a 50% reduction in the secondary surveillance radar infrastructure.

On May 27, 2010, the FAA published its final rule mandating that by 2020 all aircraft owners will be required to have ADS-B Out capabilities when operating in any airspace that currently requires a transponder (airspace classes A, B, and C, and airspace class E at certain altitudes).

On June 14, 2012, FreeFlight Systems and Chevron received STC for first rule-compliant ADS-B installation in GOMEX helicopters that was awarded by the FAA.

In India

The Airports Authority of India (AAI), which manages the country’s airspace, first commissioned Comsoft in 2012 to install ADS-B ground stations at 14 airport sites nationwide. German company Comsoft finished installing seven new ADS-B ground stations under a second phase of deployment which India subsequently integrated into its ATC system, in 2014 thus completing its ground network for automatic dependent surveillance-broadcast (ADS-B) tracking of aircraft.

In line with the International Civil Aviation Organization’s aviation system block upgrade plan, AAI has said that its ADS-B network will provide redundant, satellite-based surveillance where radar coverage exists, fill gaps in surveillance where radar coverage is not possible due to high terrain or remote airspace and enable it to share ADS-B data with neighboring countries. The network covers the Indian subcontinent, plus parts of the Bay of Bengal and the Arabian Sea.

Purpose of use

• Installing ADS-B ground stations to provide surveillance redundancy where Radar coverage exists.
• Filling surveillance gaps where surveillances coverage is not possible due to high terrain and remote areas.

Implementations by country

• Australia – Australia has full continental ADS-B coverage above FL300 (30,000 feet). ADS-B equipment is mandatory for all aircraft flying at this altitude. To achieve this level of coverage Airservices Australia operates more than 70 ADSB sites. In Australia the aviation regulator, the Civil Aviation Safety Authority mandated a phased requirement for all Instrument Flight Rules (IFR) aircraft to be equipped with ADS-B by 2 February 2017. This applies to all Australian aircraft.
• Canada – Nav Canada commissioned operational use of ADS-B in 2009 and is now using it to provide coverage of its northern airspace around Hudson Bay, most of which currently has no radar coverage. The service is also being extended to cover some oceanic areas off the east coast of Canada and Greenland. The service is expected to be later extended to cover the rest of the Canadian Arctic, and to the rest of Canada.
• Iceland – As of 2010, Isavia is in the process of installing ADS-B across the North Atlantic Ocean. The system is made up by 18 ADS-B receiver stations in Iceland, Faroe Islands, and Greenland.
• China – An American company, ADS-B Technologies created one of the largest and most successful ADS-B systems in the world (an 8-station, 350+ aircraft network that spans more than 1,200 NM across Central China). This was also the first UAT installation outside the United States. As of March 2009, more than 1.2 million incident/failure free flight hours have been flown with these ADS-B systems.
• Sweden – LFV Group in Sweden has implemented a nationwide ADS-B network with 12 ground stations. Installation commenced during spring 2006, and the network was fully (technically) operational in 2007. An ADS-B–supported system is planned for operational usage in Kiruna, Sweden, during spring 2009. Based on the VDL Mode 4 standards, the network of ground stations can support services for ADS-B, TIS-B, FIS-B, GNS-B (DGNSS augmentation) and point-to-point communication, allowing aircraft equipped with VDL 4-compliant transceivers to lower fuel consumption and reduce flight times.
• United States
  • Cargo Airline Association – Cargo carriers, notably UPS. They operate at their hub airports largely at night. Much of the benefit to these carriers is envisioned through merging and spacing the arriving and departing traffic to a more manageable flow. More environmentally friendly and efficient area navigation (RNAV) descent profiles, combined with CDTI, may allow crews to eventually aid controllers with assisted visual acquisition of traffic and limited cockpit-based separation of aircraft. The benefits to the carrier are fuel and time efficiencies associated with idle descent and shorter traffic patterns than typical radar vectoring allows.
  • Embry-Riddle Aeronautical University – ERAU has equipped their training aircraft at its two main campuses in Florida and Arizona with UAT ADS-B capability as a situational safety enhancement. The University has been doing this since May 2003, making it the first use in general aviation. With the addition of the G1000 to their fleet in 2006, ERAU became the first fleet to combine a glass cockpit with ADS-B.
  • University of North Dakota – UND has received an FAA grant to test ADS-B, and has begun to outfit their Piper Warrior fleet with an ADS-B package.
• United Arab Emirates – UAE commissioned three operational redundant ADS-B ground stations in early 2009 and is now using ADS-B to provide enhanced coverage of its upper airspace in combination and integrated with conventional surveillance radars.

System design considerations

A concern for any ADS-B protocol is the capacity for carrying ADS-B messages from aircraft, as well as allowing the radio channel to continue to support any legacy services. For 1090 ES, each ADS-B message is composed of a pair of data packets. The greater the number of packets transmitted from one aircraft, the fewer aircraft that can participate in the system, due to the fixed and limited channel data bandwidth.

System capacity is defined by establishing a criterion for what the worst environment is likely to be, then making that a minimum requirement for system capacity. For 1090 ES, both TCAS and ATCRBS/MSSR are existing users of the channel. 1090 ES ADS-B must not reduce capacity of these existing systems.

The FAA national program office and other international aviation regulators are addressing concerns about ADS-B non-secure nature of ADS-B transmissions. ADS-B messages can be used to know the location of an aircraft, and there is no means to guarantee that this information is not used inappropriately. Additionally, there are some concerns about the integrity of ADS-B transmissions. ADS-B messages can be produced, with simple, low-cost measures, which spoof the locations of multiple phantom aircraft to disrupt safe air travel. There is no foolproof means to guarantee integrity, but there are means to monitor for this type of activity. This problem is however similar to the usage of ATCRBS/MSSR where false signals also are potentially dangerous (uncorrelated secondary tracks).

There are some concerns about ADS-B dependence on satellite navigation systems to generate state vector information, although the risks can be mitigated by using redundant sources of state vector information; e.g., GPS, GLONASS, Galileo or multilateration.

There are some general aviation concerns that ADS-B removes anonymity of the VFR aircraft operations. The ICAO 24-bit transponder code specifically assigned to each aircraft will allow monitoring of that aircraft when within the service volumes of the Mode-S/ADS-B system. Unlike the Mode A/C transponders, there is no code "1200"/"7000", which offers casual anonymity. Mode-S/ADS-B identifies the aircraft uniquely among all in the world, in a similar fashion as a MAC number for an Ethernet card or the International Mobile Equipment Identity (IMEI) of a GSM phone. However, the FAA is allowing UAT-equipped aircraft to utilize a random self-assigned temporary ICAO address in conjunction with the use of beacon code 1200. 1090 ES equipped aircraft using ADS-B will not have this option.

A historical overview of FAA decision on the ADS-B link architecture for use in the National Airspace System (NAS).

Technical and regulatory documents

• Minimum Aviation System Performance Standards (MASPS)
• Minimum Operational Performance Standards (MOPS)
• DO-242A – ADS-B MASPS. Describes system-wide operational use of ADS-B.

ADS-B Out Satellite reception

A significant step forward for ADS-B is the reception by space based satellites of the ADS-B signal. This is being deployed on the Iridium satellite network, a LEO (Low Earth Orbit) satellite network that was created to deliver cell phone service anywhere on the planet. By capturing ADS-B position data from aircraft flying below the satellite, the network will give the following capabilities:

• Full air traffic control will be possible over water, in areas that radar does not currently cover.
• As is currently possible in radar covered areas, a position history will be available for lost aircraft, a la Malaysia airlines flight 370.

Note that several other systems currently exist to enable voice or text communication over large bodies of water (including Iridium itself).

The service is run by the Aireon company in cooperation with Iridium and several government oversight agencies around the world (including the FAA). They have launched Iridium satellites with ADS-B capability as of this writing, and state the system will be operational by 2018.

The system only receives ADS-B on aircraft broadcasting on the 1090 MHz frequency. This limits the system generally to large airliners, despite the fact that small aircraft are frequently off radar due to mountains blocking the signal at low altitudes. The system would also be compromised by belly mounted ADS-B antennas, due to the aircraft itself blocking the signal.

The rationale for using the Iridium satellite network for this new capability was due to:

• The Iridium satellites fly very low, and thus can receive the ADS-B out signals more reliably (transponders and ADS-B were designed for ground reception).
• Iridium satellites are replaced relatively frequently due to the increased air friction at their lower altitude, and thus lower lifespan. Thus the system would be deployed on iridium faster.
• Iridium provides worldwide coverage, including the poles.

See also

• Acronyms and abbreviations in avionics
• ASDE-X
• Automatic Identification System, a conceptually similar system for marine vessels
• Automatic Packet Reporting System (APRS), a conceptually similar GPS-based tracking system in the amateur radio service
• DO-212, minimal operational performance standards for airborne automatic surveillance (ADS)
• Eurocat (air traffic control)
• FLARM
• Flightradar24, a crowd-sourcing based website allowing ADS-B based realtime flight tracking
• Free flight (air traffic control)
• Portable Collision Avoidance System

References

 This article incorporates public domain material from websites or documents of the Federal Aviation Administration.

External links

• Android Avare ADSB Receiver