How ADS-B Works
At the core of the ADS-B system is the continuous and automatic transmission of aircraft positional data, enabled by satellite navigation and radio broadcasting. An ADS-B Out-equipped aircraft calculates its own position using a high-integrity Global Navigation Satellite System (GNSS) receiver. This position, along with other flight parameters such as velocity, identification, and barometric altitude, is encoded into a data message and transmitted via a radio frequency.
There are two primary data link formats used in ADS-B: the 1090 MHz Extended Squitter (1090ES) and the 978 MHz Universal Access Transceiver (UAT). Aircraft flying above 18,000 feet or operating internationally typically use 1090ES, which extends the capabilities of the Mode S transponder by adding additional broadcast messages (squitters). In contrast, general aviation aircraft operating below 18,000 feet in the U.S. may use UAT, which has the additional benefit of supporting uplinks of traffic and weather data from ground stations (TIS-B and FIS-B).
ADS-B messages are broadcast approximately once per second, allowing for real-time tracking of aircraft with far greater resolution than traditional radar. These messages contain a wealth of information, including the aircraft’s 24-bit ICAO address, latitude and longitude, velocity vector, vertical rate, and flight identification. This broadcast is non-directional and can be received by any compatible system within range—typically up to 250 nautical miles in optimal conditions.
On the receiving end, ground-based ADS-B receivers collect these messages and forward them to ATC facilities, where they are integrated into traffic management systems. In aircraft equipped with ADS-B In, the broadcast data from other aircraft is decoded and displayed on cockpit multifunction displays, enhancing pilot situational awareness.
The system is dependent on time-synchronized data, which is why GNSS not only provides positioning but also acts as the system’s time reference. This synchronization ensures consistency between messages received across the surveillance network and supports accurate aircraft tracking.
Compared to radar, which can have latency of 5 to 12 seconds and may struggle with low-level coverage, ADS-B provides faster updates and better resolution. This enables more precise separation standards, particularly in remote and oceanic airspace where ground radar is unavailable.
Visual Aids
- Diagram of ADS-B message flow (aircraft to aircraft and aircraft to ground)
- Animation showing periodic broadcasts and reception range
- Example of decoded 1090ES message content, bit field by bit field