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Automatic dependent surveillance-broadcast (ADS-B) is a cooperative surveillance technology for tracking aircraft. The aircraft determines its own position via satellite navigation and periodically broadcasts this via a radio frequency. ADS-B is one of the technologies selected as part of the Next Generation Air Transportation System (NextGen) and the Single European Sky ATM Research (SESAR). The United States will require the majority of aircraft operating within its airspace to be equipped with some form of ADS-B by 1 January 2020. In the EU airspace planes with a weight above 5,700 kilograms (12,600 lb) or a max cruise of over 250 knots will be required to carry ADS-B from 2017 (new planes from 2015).
ADS-B, which consists of two different services, "ADS-B Out" and "ADS-B In", could 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, realtime, 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 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.
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.
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.
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:
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.
ADS-B enables increased capacity and efficiency by supporting:
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.
ADS-B is seen as a valuable technology to enhance ACAS operation. Incorporation of ADS-B can provide benefits such as:
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:
The ADS-B system has three main components: 1) ground infrastructure, 2) airborne component, and 3) operating procedures.
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.
Two link solutions are being used as the physical layer for relaying the ADS-B position reports:
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. 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.
In 2002 the Federal Aviation Administration (FAA) announced a dual link decision using the 1,090 MHz Extended Squitter (1090 ES) 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. In November 2012, the European Aviation Safety Agency confirmed that the Europe Union would also use 1090 ES for interoperability. The formatting of the Extended Squitter messages has been codified by the ICAO.
With 1090 ES, 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 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.
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.
|Primary surveillance radar (PSR)||Yes: surveillance data derived by radar||No: does not depend on aircraft equipment|
|Secondary surveillance radar (SSR)||No: surveillance data derived by aircraft||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|
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 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 (ATCO). 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.
There are two commonly recognized types of ADS for aircraft applications:
ADS-B differs from ADS-A in that 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 Communication 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.
|It has been suggested that Traffic Information Service – Broadcast be merged into this article. (Discuss) Proposed since April 2014.|
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:
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.
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.
While there is currently a drop in air travel due to a general economic downturn, 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.
The automatic dependent surveillance-broadcast system (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.
|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. These companies include Avidyne, Aviation Communication and Surveillance Systems (a joint venture of L-3 Communications and Thales), Garmin, Intelcan, Rockwell Collins, FreeFlight Systems., and Dynon Avionics.
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.
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 1,090 megahertz extended squitter (ES) broadcast link or the Universal Access Transceiver (UAT) 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 will make ADS-B the backbone of the NextGen ATC system coming online in 2020.
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.
2007 – Early estimates stated the cost to equip a general aviation aircraft ranged from $7,644 to $10,920 for ADS-B Out and from $10,444 to $29,770 for ADS-B Out and ADS-B In, depending on aircraft type.
2009 – Assuming 2009 market prices for individual system components, a UAT retrofit was estimated at $18,000 and new at $25,000. For a 1090ES retrofit $4,200 and new at $18,000.
Recent (April 2011) US federal legislation via House Bill for FAA reauthorization permits an "equipping fund" that includes a portion for some general aviation aircraft. The fund would provide financing at competitive rates back by loan guarantees. A public-private partnership has been formed as the NextGen Equipage Fund, LLC which is managed by NEXA General Partnership, LLC.
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.
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.
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:
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.
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 1090ES, each ADS-B message is composed of a pair of data packets. The greater the number of packets transmitted from one aircraft, the lesser the number of 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 1090ES, both TCAS and ATCRBS/MSSR are existing users of the channel. 1090ES 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. 1090ES equipped aircraft using ADS-B will not have this option.
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