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ADS-B UAT: Double Standards in Air Navigation

About the ADS-B UAT data link development in the USA.
AUGUST, 30 / 2019 / 7 MINUTES
Фото вышки в Örnsköldsvik
General aviation (GA) and the lower airspace use play a significant role in the US economy. According to the US FAA research GA generates about 7.6 million jobs and $ 39 billion in economic benefits.
The GA pilots - 90% of civil aircraft registered in the United States - fly in the lower airspace, which is an important component of the general airspace. Visual flights rules (VFR) are used in the lower airspace. Constant control is not mandatory for GA, and flight safety has its own characteristics.
Historically, the US has used two ADS-B data links. The 1090ES standard is widespread in the world, and much has been written about it, but the situation with UAT is different. Some Russian radio equipment manufacturers regularly refer to the US experience of two ADS-B standards use, suggesting that the Russian Federation take this path. Sky Review investigated this issue, and we are ready to tell our readers about what UAT is and about the history of this standard. And also about how American airspace users are using two ADS-B standards now, and why this experience is not acceptable for Russia.
The tasks of increasing the safety level of GA flights formed the prerequisites for the creation of the UAT back in the 90s of the XX century, and the project, which is unofficially considered the starting point for the implementation of this standard, was deployed in Alaska where air traffic is crucial.
UAT (Universal Access Transceiver)
In the 90s. XX century in the United States published a plan for the transition from ground-based radar surveillance by SSR to a joint satellite and ground-based surveillance system, which outlined the strategy for updating air navigation in the country.

The UAT data line has evolved in several stages. In 1995, the first prototypes were created, and one of the most significant development moments from which UAT began to be distributed in the USA was the Capstone program. Its main objective was to increase aviation safety in Alaska, as the state had the largest percentage of aviation incidents in the United States at that time.
«In the 90s, air accidents occurred here literally every other day, and approximately every nine days, someone died.»
— says John Halinen - FAA Capstone program manager.
At the same time, GA for the region is vital because of the inaccessibility of settlements. Flights here are associated with additional risk due to changeable weather and mountainous terrain.
«" In Naknek, we have two villages located just five miles from each other, but for most of the year you cannot drive from one village to another, because there is a river between them and no bridge. There is only one school, so in high school children from the South Naknek fly there by plane. In other regions, we have children who fly airplanes to play sports. Sometimes pizza delivery is sent by plane, and, of course, the most important things that support life here are food, fuel, many of which are also delivered by air.»
— continues John Halinen.
The work within the Capstone framework was carried out in several stages and included both: airborne equipment and the appropriate ground infrastructure creation. As part of the first stage, the equipment was installed on 200 local-based aircraft, and a network of ground stations was deployed at 10 existing airfields. Ground-based transceivers and auxiliary equipment in the mountains were used to relay ADS-B signals. Thanks to ground stations, pilots also received information from secondary radars that could be seen on unequipped ADS-B aircraft airborne displays.
Позиция АЗН-В в пустыне
Universal Access Transceiver (UAT):
History, Description, Operational Experience and Implementation Status /
«I believe that below 10,000 feet in all of Alaska there is no radar coverage. We noticed that we give people the opportunity to fly not only through VFR (VFR), but also switch to IFR (IFR) when it is really more efficient and safe,»
—  says John Halinen.
For more than six years, the Capstone program has worked to improve flight safety in Alaska, primarily through the ADS-B deployment, and has shown good results - a sharp decrease in the frequency of accidents by 40% compared to non- ADS-B-equipped aircraft. As a result, the successful experience of Alaska and the developed GA in the states (according to AOPA, these are California, Texas, Florida, District of Columbia, Ohio, Arizona, etc.) contributed to the scaling of solutions. As part of the US Air Navigation Development Program NextGEN, ADS-B UAT technology is becoming one of the most important links. UAT is the first of the ADS-B standards to be certified in the USA, and the network of ADS-B stations covers almost the entire territory of the country.
UAT Features
ADS-B UAT operates at a frequency of 978 MHz and is available for US manned aircraft, which fly below 18,000 feet above sea level. What is UAT's focus on general aviation? The key difference between UAT and 1090ES is the ability to receive additional data. The FAA uses this feature to transmit meteorological information (FIS-B) and air traffic information (TIS-B).
The weather changes have a high significance for GA flights. That's why FIS-B was designed for use by general aviation pilots specifically. FIS-B was created with a completely free service, which was supposed to draw more attention to the technology. The service includes extended meteorological information, as well as temporary flight restrictions (TFRs), combines information from various sources: NEXRAD, METAR, TAF, wind data, etc. Information can be displayed on portable devices starting with an iPad running a Garmin Pilot and ending with a certified display on the aircraft panel, a list of UAT weather services is provided below, and it is worth noting that FIS-B is a solely advisory service.
Позиция АЗН-В в пустыне
What is the difference between ADS-B UAT and ADS-B ES?
Another important service is TIS-B, and it is already available not only at UAT, but also at 1090ES, provided that the aircraft are equipped with ADS-B In receivers.
Позиция АЗН-В в пустыне
FAA ADS-B ADS-B In Pilot Applications
Thanks to TIS-B, manned aircraft that are not equipped with ADS-B become visible. Ground secondary radars determine the coordinates of the manned aircraft, if the aircraft is within the range of the radar capable of providing data for the TIS-B and has a transponder. Further, the received information is relayed to all aircraft within the service radius by means of ADS-B. The airborne ADS-B In receiver will receive this information, after which it will be displayed to the pilot. TIS-B is non-regulatory, like FIS-B is.

To summarize, in short, the UAT will provide extended and free meteorological data and use it below 18,000 feet. UAT has a similar structure and the identical data transfer rate - 1 Mbit per second with another standard (1090ES).
Dual system
In 2002, the US FAA announced the creation of a dual line with 1090 MHz (1090ES) using. 1090ES makes it possible to fly at all altitudes, as well as outside the United States, since almost all ADS-B systems in the world operate at a frequency of 1090 MHz.
Part of the GA pilots decide to install 1090ES equipment, since they fly to nearby countries: Canada, Mexico, Cuba, the Caribbean. In addition, manufacturers of commercial airliners contribute to the 1090ES globalization by installing equipment directly at the factory. In 2012, EASA (European Aviation Safety Agency) confirmed the 1090ES use to ensure universal compatibility. There is an image below that shows the 1090ES and UAT use in different classes of US airspace. It is worth noting that the 1090ES is approved for use at all altitudes, while the UAT is only up to 18,000 feet.
Позиция АЗН-В в пустыне
Are You Ready for ADS-B? / Newsletters
In the USA, the ability to relay ADS-R data (1090 / UAT) also plays an important role. ADS-R allows an aircraft with ADS-B In to see neighboring aircraft with ADS-B Out regardless of the type of standard (1090ES or UAT). Manned aircraft operating on the same ADS-B frequency exchange information directly and do not require the use of ADS-R.
Today US manufacturers often make combined transponders. Such avionics can be quite compact due to the relatively close frequencies of the two standards: 978 MHz (UAT) and 1090 MHz (1090ES). There are a number of solutions from different companies on the market. For example, Garmin equipment allows you to send ADS-B Out UAT, and receive UAT and 1090ES signals. This complies with FAA requirements, which include aircraft equipping with ADS-B Out transponders by 2020, and also makes it possible to receive ADS-B 1090ES data.
Additional expenses
An interesting fact is that Australia - another country with actively used GA - refused to use a dual system due to the high cost of its implementation and redundancy. Instead, emphasis was placed on using the ADS-B 1090ES Out / In capabilities to ensure that manned aircraft can see each other directly.
Позиция АЗН-В в пустыне
Australian Goverment
Civil Aviation Safety AuthorityChapter 4 Surveillance and ADS-B
Russia is in a similar situation, since ADS-B is deploying "from scratch", and the additional costs of creating a double ADS-B infrastructure are impractical. In particular, since the ADS-B 1090ES is able to satisfy the current and growing needs of domestic aviation.
Dual ADS-B data link use is still a distinctive feature of the United States, owing to the peculiarities of the GA use and the specifics of the time period when ADS-B was introduced in the country. Note that since the UAT deployment, no country in the world began to use the two standards approach. At the same time, the USA itself additionally implemented 1090ES at all altitudes, and GA pilots install 1090ES equipment.
Manufacturers are also busy with the additional ADS-B equipment creation. Additionally, the Australian government created a number of working groups to analyze the appropriateness of the US experience replication in Australia and concluded that the two ADS-B standards are an excessive solution. ADS-B Out / In 1090ES can fully provide all the needs, and the state and industry are not ready to pay for the dual infrastructure deployment.
In conclusion
In accordance with the FAA requirements, ADS-B In remains optional in the United States, although it has a number of advantages, for example, the ability to receive ADS-B Out data directly from neighboring aircraft. With ADS-B In 1090ES it is possible to see aircraft with UAT within 15 nautical miles (providing the ADS-R rebroadcast); receive aircraft data from secondary radars (when using TIS-B); see aircraft with ADS-B Out 1090ES, which data will be received directly at potentially much greater distances. FIS-B data, we talked about above, and NOTAM are also added while using UAT. US AOPA notes that this information will be expanded and supplemented later by reports on lightning, turbulence, icing, etc.
ADS-B UAT / 1090ES In along with 4G / 5G are also tested for use on UAVs. DJI announced the installation of ADS-B In with support for UAT and 1090ES on several models of drones since 2020. One of the important advantages of ADS-B use is that commercial aviation and GA have already use ADS-B Out UAT / 1090ES transmitters and have broadcasted their data in the broadcast range. Hence, the ADS-B In receivers equipped drones immediately get the opportunity to see the surrounding manned aircraft in real time. Technology also is a component of the detect and avoid system for drones - DAA .
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