Definition
A surveillance system in which an aircraft automatically transmits position, altitude, and other flight data over a data link to a specific, named recipient — typically an air traffic control facility — under a one-to-one contract between that aircraft and that recipient. Unlike ADS-B, which broadcasts to anyone in range, ADS-A reports are addressed only to the agreed receiving party and are usually used in oceanic and remote airspace where radar coverage is unavailable.
Plain English
The aircraft sends its position and flight data automatically, but only to one specific air traffic control facility it has set up a link with — not to everyone nearby.
Context Anchor
Seen in discussions comparing ADS-A with ADS-B and other aircraft surveillance systems in instrument flying and air traffic control material.
Derivation
The key word is Addressed. In communications, an addressed message is sent to one named recipient — like a letter with a specific name on the envelope — rather than being shouted to a room. That contrasts directly with ADS-B, where the B stands for Broadcast and the data goes out to everyone in range.
Why Pilots Care
Supports more selective and potentially bandwidth-efficient data exchange with air traffic control in instrument flight environments.
Analogy
It is like sending a text message to one person instead of making an announcement over a loudspeaker. The information may be similar, but the way it is delivered is different.
Intuition Check
“Addressed” does not mean the aircraft is being given a street address. Here it means the data message is aimed at a specific receiver. “Dependent” does not mean unreliable. Here it means the system depends on the aircraft’s own equipment for its position information.
Example Sentence 1
Flying across the North Atlantic, the crew's position reports were sent automatically to oceanic control via ADS-A.
Example Sentence 2
ADS-A differs from broadcast systems by directing surveillance information only to the intended recipients.