ADS-B Out Explained
ADS-B Out transmission refers to the component of the system that broadcasts an aircraft’s information to external receivers. This includes not only ground-based ADS-B stations but also other aircraft equipped with ADS-B In. The primary goal of ADS-B Out is to provide real-time situational data to air traffic control and nearby pilots, enabling safer and more efficient operations. In short, this is the airborne piece of the system, directly broadcasting aircraft position information to other receivers in the system.
The data transmitted includes the aircraft’s GPS-derived position, altitude (both geometric and barometric), velocity, aircraft identification (call sign), and additional information such as emergency status or on-ground indication. This data is broadcast approximately once per second, providing a far more granular and current picture of air traffic than radar-based systems.
Two primary frequencies are used for ADS-B Out transmissions: 1090 MHz Extended Squitter (1090ES) and 978 MHz Universal Access Transceiver (UAT). The 1090ES format is typically used by high-altitude and international aircraft, including commercial airliners, and is based on enhancements to the existing Mode S transponder system. UAT, on the other hand, is designed for general aviation and operates only within the United States below 18,000 feet.
ADS-B compliance in the United States is governed by 14 CFR § 91.225 and § 91.227, requiring that aircraft operating in most controlled airspace be equipped with certified ADS-B Out systems. The FAA mandates strict performance requirements, including accuracy and integrity standards, typically met by avionics certified under RTCA DO-260B or DO-282B standards.