Automatic Dependent SURVEILLANCE Broadcast

ADS-B uses GPS instead of ground-based radar to determine aircraft position, and is now required for operations in the airspace defined by FAR 91.225. ADS-B provides enhanced navigational accuracy using precise tracking via global positioning satellite (GPS) signals. Reducing risk and improving safety, the technology increases navigational coverage, especially in remote areas beyond radar range. Additionally, ADS-B enables more direct flight plans, thereby saving time, costs, and reducing emissions.  

The short answer is everyone who wants to fly above 10,000 feet. The more technical answer is that the FAA has mandated that by January 1st, 2020, all U.S. aircraft operating in airspace that requires a Mode C transponder must be equipped with ADS-B Out capabilities. While Europe has adopted similar specifications, they’ve extended the deadline to June 7, 2020. Airspace that requires a Mode C transponder (in the United States) is as follows:

• Operations within Class A, Class B, and Class C airspace.
• Operations within 30 nautical miles of the primary airport within Class B airspace from the surface to 10,000 feet msl.
• Operations above the ceiling and within the lateral boundaries of Class B and C airspace.
• Operations above 10,000 feet msl in the contiguous 48 states, excluding the airspace at and below 2,500 feet agl.
• The AIM states in Section 4-1-19(a)(3) that for airborne operations in Class G airspace, the transponder should be operating unless otherwise requested by ATC.

         There are two paths to compliance, 978UAT or 1090ES, which are simply different ADS-B datalink options. A Universal Access Transceiver, or UAT, operates on 978 MHz (978UAT). This frequency receives free weather information, although not all UATs support the optional ADS-B In.

The 1090ES datalink uses a Mode S Extended Squitter transponder (1090 MHz; “ES” refers to ADS-B information appended to the Mode S data through an extended squitter). 1090ES is required above 18,000 feet and by the growing number of countries outside of the United States with ADS-B mandates. However, 1090ES does not receive weather data.