Automatic Dependent Surveillance-Broadcast is the cornerstone technology behind modern aircraft tracking. Here is everything you need to know about how it works and why it matters.
ADS-B stands for Automatic Dependent Surveillance-Broadcast. Let us break down each word:
Unlike traditional radar-based surveillance where a ground station actively interrogates aircraft, ADS-B is a cooperative system where aircraft voluntarily broadcast their own position derived from GPS satellite navigation. This means better accuracy, lower infrastructure costs, and coverage in areas where radar cannot reach, such as over oceans and in remote terrain.
The ADS-B system has a straightforward operating principle:
The key advantage over radar is precision: ADS-B positions are typically accurate to within 30 meters (GPS-derived), compared to radar accuracy of 200-500 meters. Updates also occur much more frequently (every second vs. every 4-12 seconds for radar).
ADS-B Out is the transmitting component. Aircraft equipped with ADS-B Out broadcast their position, identity, and other data for others to receive. This is the component mandated by the FAA and is what community receiver networks and platforms like AeroScope use to track aircraft. All aircraft operating in controlled US airspace above 10,000 feet (and in other defined areas) must have ADS-B Out installed as of January 1, 2020.
ADS-B In is the receiving component. Aircraft equipped with ADS-B In can receive broadcasts from other aircraft and from ground stations (TIS-B and FIS-B). This enables cockpit displays showing nearby traffic (similar to TCAS but with more detail) and weather information. ADS-B In is not mandated by the FAA but provides significant situational awareness benefits to pilots, especially in general aviation.
Two radio frequencies are used for ADS-B in the United States:
The international standard used worldwide. Aircraft operating above 18,000 feet (Class A airspace) in the US must use 1090ES. It is compatible with existing Mode S transponders and is the frequency used by all international commercial aviation. This is the primary frequency that community ADS-B networks and AeroScope monitor. Range from ground receivers is typically 200-300 nautical miles.
A US-only frequency option for aircraft operating below 18,000 feet. UAT was designed to be a lower-cost alternative for general aviation. It also carries TIS-B (traffic) and FIS-B (weather and NOTAM) data. UAT is not used outside the United States, so aircraft that operate internationally must have 1090ES. Some community ADS-B receivers monitor both frequencies.
Each ADS-B broadcast contains the following key data fields that platforms like AeroScope use for tracking and analysis:
| FIELD | DESCRIPTION | EXAMPLE |
|---|---|---|
| ICAO Address | Unique 24-bit aircraft identifier assigned by ICAO | A1B2C3 |
| Callsign | Flight identification (airline + flight number or registration) | UAL123 |
| Latitude | GPS-derived latitude in decimal degrees | 40.6413 |
| Longitude | GPS-derived longitude in decimal degrees | -73.7781 |
| Altitude | Barometric or geometric altitude in feet | 35,000 ft |
| Ground Speed | Speed over the ground in knots | 450 kts |
| Track / Heading | Direction of travel in degrees from true north | 270° |
| Vertical Rate | Rate of climb or descent in feet per minute | -1,200 fpm |
| Squawk | 4-digit transponder code assigned by ATC | 1200 |
| Category | Aircraft size/type category (light, large, heavy, rotorcraft) | A3 (Large) |
On January 1, 2020, the FAA's ADS-B Out mandate (14 CFR 91.225) went into effect. This rule requires ADS-B Out equipment for aircraft operating in:
This mandate has dramatically increased ADS-B coverage in US airspace, making services like AeroScope possible with a high degree of completeness. Similar mandates exist or are being implemented in Europe (through the Single European Sky ATM Research program), Australia, and other regions.
ADS-B development began in the 1990s as part of the FAA's Next Generation Air Transportation System (NextGen). Early trials were conducted in Alaska, where radar coverage was limited and ADS-B provided a transformative improvement in surveillance capability over remote terrain.
The technology has evolved significantly since those early days. Space-based ADS-B, using satellite constellations like Aireon (hosted on Iridium NEXT satellites), now provides global coverage including over oceans where no ground-based receivers exist. This has enabled real-time tracking of flights over the Atlantic, Pacific, and polar routes for the first time.
Looking ahead, ADS-B is expected to play a central role in the integration of drones and urban air mobility vehicles into the national airspace system through Remote ID requirements, which are essentially ADS-B-like broadcasts for unmanned aircraft.