Automatic Dependent Surveillance – Broadcast (ADS-B) is the backbone of the next generation ATC system, and is the most rapidly-evolving portion of the avionics industry.
All ADS-B users transmit their location via ADS-B "Out", increasing safety by reducing traffic conflicts.
The most basic capability is called ADS-B "Out". This allows ADS-B-equipped aircraft transmit their position and velocity vector every second. As a result, ATC has a much better understanding of their position and movement relative to other air traffic, particularly in areas with marginal radar coverage (due to distance, terrain, etc.) When people talk about the 2020 ADS-B mandate, they are typically discussing ADS-B "Out". The ADS-B system works best when all the aircraft in a given airspace broadcast their position.
There are two types of ADS-B "Out" Transmitters:
- 978 MHz Universal Access Transceiver (978 UAT) Transmitters are allowed up to 18,000 feet altitude. These tend to be the less expensive solutions.
- 1090 MHz Extended Squitter (1090ES) Transmitters are permitted at any altitude and required above 18,000 feet. They are also required for operation in Class A airspace. These avionics tend to be both more capable and more expensive.