ADS-B 101 What It Is, and What It Means to You

by the FAA Surveillance and Broadcast Services Office

As the demand for our nation’s airspace grows, NextGen improvements are helping to guide and track aircraft more precisely and on routes that are more direct. The shift to smarter technologies is making air travel safer, more convenient, and more environmentally friendly.

Automatic Dependent Surveillance-Broadcast (ADS-B) is a foundational NextGen technology that uses information from the GPS satellite system to track aircraft in real time and improve situational awareness. Pilots will be able to fly safely with less assistance from air traffic control (ATC). ATC will be able to manage the flow of traffic far better than current infrastructure allows. “ADS-B increases safety and efficiency to help meet the increasing air traffic predicted in coming years,” says Bobby Nichols, FAA Surveillance Services Group Manager.

ADS-B has the following characteristics:

  • It’s Automatic — Transmits location and other information, every second (vs. transponder every 5 to 12 seconds), with no pilot action.
  • It’s Dependent — It is dependent on aircraft being equipped with a rule compliant position source and signal transmitter.
  • Surveillance through GPS information — The signal includes aircraft position and velocity vector derived from the position source, which is typically a GPS receiver. Position accuracy is independent of the distance from the ground station.
  • Broadcast of the aircraft’s position — ADS-B equipment automatically transmits data to controllers and to any aircraft equipped to receive ADS-B. ADS-B targets display in real time.

How Does ADS-B Work?

ADS-B works by having aircraft avionics regularly broadcast position, velocity, and identification information from an aircraft to ATC and other aircraft that can receive ADS-B data. Accurate position data, along with the velocity of the aircraft, is derived from satellite navigation signals received by the aircraft’s position source. ADS-B avionics integrate this information with data obtained from other aircraft sources (i.e., flight management system, altimeter, and traffic collision avoidance system (TCAS) units) to generate a comprehensive data set for the aircraft. This data is transmitted by ADS-B avionics on one of the approved ADS-B datalinks (more details in the ADS-B Mandate section) at a rate of once per second or better. It provides frequent updates for tracking aircraft movements and determining state changes of the aircraft. This transmission is referred to as ADS-B Out. Aircraft within “line of sight” equipped to receive the data and ADS-B ground stations up to approximately 250 miles away receive these broadcasts. The ADS-B ground system then processes this data and displays it to ATC for use in providing separation services to aircraft.

The ADS-B system combines other surveillance data (i.e., radar, wide area multilateration, etc.) for non-ADS-B-equipped aircraft, and subsequently transmits this information from ground stations to ADS-B-equipped aircraft as Traffic Information Service-Broadcast (TIS-B), a temporary service to encourage early ADS-B equipage and ease the transition to a NextGen surveillance environment. After the ADS-B mandate takes effect on January 1, 2020 and ADS-B equipage is near-universal, aircraft will be able to receive ADS-B surveillance data directly from other aircraft without reliance on the FAA’s ground infrastructure, bringing the situational awareness benefits of ADS-B to airspace where surveillance wasn’t previously available.

Properly equipped aircraft also receive the ADS-B Out signals from other equipped aircraft. This use of data in the aircraft on cockpit displays is referred to as ADS-B In. Ground stations also send out, on the universal access transceiver (UAT) link only, graphical weather information and flight information, such as temporary flight restrictions — this is called Flight Information Service-Broadcast (FIS-B).

ADS-B Mandate

The equipment used to broadcast GPS-derived location information, “ADS-B Out,” is mandated by January 1, 2020, for aircraft flying in certain airspace — generally the same busy airspace where transponders are required today (see Title 14 Code of Federal Regulations (14 CFR section 91.225)).

This graphic generally depicts the airspace where ADS-B Out will be required by the rule. Visit www.faa.gov/nextgen/equipadsb/airspace/ for more information.

Except for airspace along the coast of the Gulf of Mexico, if a pilot flies exclusively in airspace where a transponder is not required, then there is no mandate to equip. Also exempt are aircraft not originally certificated with an electrical system, or not subsequently certified with such a system installed, including balloons and gliders.

ADS-B is broadcast on two datalinks — 1090 MHz and 978 MHz (UAT). Your decision on which type of ADS-B Equipment you will need is based on where you fly. Aircraft operating above FL180 (18,000 feet) or internationally, must be equipped with a Mode S-transponder-based ADS-B transmitter. Aircraft operating below 18,000 feet and within ADS-B rule airspace, must be equipped with either Mode S transponder-based (1090 MHz) ADS-B equipment or Universal Access Transceiver (UAT) equipment. UAT equipment provides the ability to receive traffic and weather data provided by the FAA ADS-B network.

To meet the minimum requirements for ADS-B Out, an aircraft must be equipped with three things:

  1. A qualified GNSS receiver (see FAA Advisory Circular 20-165B, Appendix 2)
  2. An extended squitter Mode-S transponder or a UAT meeting the performance requirements of TSO-C166b or TSO-C154c
  3. Appropriate antennas

Note that portable equipment does not meet the ADS-B Out rule requirements.

Owners can install an ADS-B Out system to meet the minimum requirements of the rule, or they can also integrate with ADS-B In avionics and displays to reap the full benefits of ADS-B. Since the advantages of ADS-B In are so extensive, the FAA believes many in the general aviation community will choose to invest without an ADS-B In mandate.

Benefits for General Aviation

With ADS-B operational across the country, general aviation pilots in equipped aircraft will have access to services that provide a new level of safety and efficiency.

General aviation and air taxi aircraft equipped with ADS-B Out will enjoy more efficient spacing and optimal routing in non-radar environments, including the busy airspace in the Gulf of Mexico, mountainous regions of Colorado, and the lower altitudes of Alaska.

The precise surveillance provided by ADS-B also improves life-saving search-and-rescue operations. Air traffic controllers tracking aircraft with ADS-B Out have much better information about last reported positions and velocity, helping to take the “search” out of search and rescue.

“Owners who choose to add avionics and displays for ADS-B In will receive truly transformative services” says David Gray, FAA Surveillance and Broadcast Services program manager. “With ADS-B In, general aviation pilots — for the first time — will see much of what air traffic controllers see on their ATC display. Cockpit displays will show the location of aircraft in the skies around them, creating an environment of shared situational awareness.”

With an ADS-B In system that receives the UAT link, graphical weather displays help pilots make more efficient route decisions and avoid the dangers of hazardous weather. These systems also receive notices of important flight information, such as temporary flight restrictions or closed runways.

“ADS-B pilot advisory services are provided at no subscription cost to the user,” adds Gray.

Regulation Reminder – All ADS-B equipped aircraft are required to operate their ADS-B Out transmitter at all times including while on the surface of the airport — 14 CFR section 91.225(f).

When to Equip With ADS-B

Throughout the country, general aviation aircraft owners are equipping with ADS-B. In December 2016, the FAA detected over 22,000 general aviation and air taxi aircraft that are equipped with rule-compliant ADS-B Out. The data also shows that about 20,000 aircraft are equipped with ADS-B In avionics.

“The FAA is encouraging owners to equip as soon as possible to capture the benefits of ADS-B and to ensure they will be able to continue flying in designated airspace when the rule goes into effect in January 2020” says Nichols. “Because the rule has been published since 2010, there are no plans to extend the deadline beyond that date.”

If you are unsure where to begin your path to ADS-B equipage, check out the FAA’s Equip ADS-B website: www.faa.gov/nextgen/equipadsb. This valuable online tool contains a searchable database of ADS-B avionics solutions provided by the manufacturers of all commercial and GA aircraft, frequently asked questions, and other information to help you make an informed decision.

Some may wonder whether costs will come down in the next few years. “That is difficult to predict, but it is not expected given that units are now available for as little as $2,000,” says FAA Air Traffic Systems Technical Advisor Doug Arbuckle. “If too many aircraft owners wait to equip, suppliers and installers will not be able to keep up with demand and prices could possibly increase as the rule deadline draws near.”

There are no obstacles now for owners to equip with ADS-B. All of the necessary standards for certification and operational approvals have been in place since 2011. Additional guidance, such as operations specifications and guidance for field approval, has also been published.

The transformation made possible by ADS-B will improve safety, increase efficiency, and reduce the cost and complexity of the air traffic control system. The sooner aircraft owners equip, the sooner they will enjoy the many benefits of ADS-B surveillance.

Learn More

The FAA Surveillance and Broadcast Services (SBS) Office is responsible for implementing Automatic Dependent Surveillance-Broadcast (ADS-B) technology into the National Airspace System (NAS).

This article was originally published in the March/April 2017 issue of FAA Safety Briefing magazine.
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