Plain English Meaning
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.
Full 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.
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.