By now you have heard that ADS-B is required, or will soon be required, to operate in specified airspace in the US. But, what exactly is ADS-B and why is it required?
ADS-B is an acronym for Automatic Dependent Surveillance-Broadcast. ADS-B is surveillance technology. It is augmenting or replacing passive surveillance systems that are in use today.
Why is ADS-B required? Today, there are two types of surveillance systems to detect, identify and track targets. They are both passive surveillance systems. The primary system is radar. Radar systems have limited range and the ability to discriminate between multiple targets. The secondary system is the Mode A/C beacon system. Mode A/C transponders can distinguish between multiple targets but require transmit-reply interrogations from the radar sites. These radar signals can attenuate in heavy precipitation and have slow refresh rates. This requires air traffic controllers to increase the spacing between aircraft. Greater separation means less aircraft in the airspace at a given time. A decrease is the number of aircraft effects inbound aircraft wanting access to the same airspace. Inbound aircraft are delayed thereby reducing overall system capacity and throughput. This ripple effect decreases operator efficiency. In addition to inefficient flight operations, ground-based radar sites are expensive to maintain. ADS-B is required to reduce costs and inefficiencies caused by ground-based systems and to increase system throughput and capacity.
Here’s what ADS-B means:
Automatic: From the time an aircraft’s avionics system is powered-on, until the time it is powered-off, the surveillance system is “automatically” transmitting its precise position and identification information. The only pilot action required is to power-up the avionics and ensure the correct Flight ID is entered into the ADS-B equipment.
Dependent: The quality of the information that is transmitted to Air Navigation Service Providers (ANSPs), pilots, service vehicle operators, and other users is “dependent” on the aircraft’s avionic system.
Surveillance: The aircraft’s avionics system derives its precise position information from the Global Navigation Satellite System (GNSS), its heading and velocity information from the aircraft’s Air Data Computer, its Flight ID, unique registration code, navigation accuracy, other aircraft capabilities from information that is preset into the ADS-B system at installation. This is the “surveillance” information that is needed for identification and the safe separation of aircraft.
Broadcast: The aircraft’s precise GNSS position is “broadcast” once every second. The other bits of surveillance information are “broadcast” every quarter-second. ADS-B systems provide more aircraft and flight information than was ever possible with passive surveillance systems. Active surveillance is as different from passive surveillance as a black and white television display is from a high-definition LED display.
ADS-B is high-definition surveillance for the 21st Century. It is modernizing the way air navigation service providers detect, identify, and track traffic. ADS-B is transforming the global airspace and is a cornerstone of NextGen air traffic modernization. It will ensure safe and efficient operations into the 21st century.
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