Understanding ADS-B and the FAA Mandate

As the demand for our nation’s airspace grows, the FAA is focusing on “NextGen” improvements to help guide and track aircraft more precisely, making air travel safer, more convenient, and environmentally friendly.

Automatic Dependent Surveillance-Broadcast (ADS-B) is a foundational NextGen technology that the FAA is mandating for aircraft flying in certain airspace by January 1, 2020. Here’s what you should know about ADS-B, courtesy of the FAA Surveillance and Broadcast Services Office and March/April issue of the FAA Safety Briefing magazine.

ADS-B uses information from the GPS satellite system to track aircraft in real time and improve situational awareness. In addition to increasing flight safety and efficiency, pilots will be able to fly with less assistance from air traffic control (ATC).

Some key characteristics of ADS-B

Transmissions are automatic – Transmits location and other information, every second (vs. transponder every 5 to 12 seconds), with no pilot action.

ADS-B is dependent – To work, an aircraft must be equipped with a rule compliant position source and signal transmitter.

Surveillance via GPS information – ADS-B 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.

Broadcasts an aircraft’s position – ADS-B equipment automatically transmits data to controllers and to any aircraft equipped to receive ADS-B, and ADS-B targets display in real time.

An overview of how it works

As a high-level overview, this is how ADS-B works:

1. A plane with the proper ADS-B aircraft avionics will regularly broadcast position, velocity, and identification information from an aircraft to ATC and other aircraft that can receive ADS-B data.
2. Accurate position data, along with the velocity of the aircraft, is determined from satellite navigation signals received by the aircraft’s position source.
3. ADS-B avionics integrate this information with data obtained from other aircraft sources, such as flight management system, altimeter, and traffic collision avoidance system (TCAS) units to generate a comprehensive data set for the aircraft.
4. This data is transmitted by ADS-B avionics on one of the approved ADS-B datalinks at a rate of once per second or better. It provides frequent updates for tracking aircraft movements and determining state changes of the aircraft.
5. 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.
6. The ADS-B ground system then processes this data and displays it to ATC for use in providing separation services to aircraft.
   

ADS-B Out mandated by Jan. 1, 2020

The equipment used to broadcast GPS-derived location information, called “ADS-B Out,” is being mandated by the FAA 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.)

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).

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 teir plane with ADS-B Out.

Also exempt are aircraft not originally certificated with an electrical system, or not subsequently certified with such a system installed, including balloons and gliders.

Note that 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:

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.

Regarding ADS-B adoption, 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 believes that the sooner aircraft owners equip, the sooner they will enjoy the many benefits of ADS-B surveillance.

Source: FAA Safety Briefing magazine

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