Definition
A type of automatic broadcast transmitted by a Mode S transponder that contains an extended set of data beyond the basic identity and altitude reply. The Extended Squitter (often called 1090ES) carries information such as aircraft position, velocity, identification, and intent, broadcast on 1090 MHz once per second without being interrogated. It is the data-link format used by ADS-B Out in much of the world.
Plain English
A longer message that a Mode S transponder broadcasts on its own, containing the aircraft's position, speed, and ID. It is sent regularly without anyone asking for it, and it is the signal that lets ADS-B work.
Context Anchor
Seen in transponder, ADS-B Out, surveillance, and aircraft equipment discussions.
Derivation
Squitter comes from the radio engineering term for a brief, unsolicited transmission that a transponder sends on its own rather than in reply to an interrogation. Extended means the message is longer than the basic squitter, with room for the additional position and velocity data needed for ADS-B.
Why Pilots Care
Aircraft equipped with this meet ADS-B Out mandates and provide real-time traffic data that improves safety and situational awareness in controlled airspace.
Analogy
It is like a name tag that also announces your location every few moments. Instead of waiting for someone to ask, the aircraft keeps broadcasting the information automatically.
Intuition Check
Extended does not mean longer range here; it means the message contains more data than a basic Mode S broadcast. Squitter does not mean a reply to radar; it means the transponder sends the message automatically.
Example Sentence 1
The aircraft's Mode S Extended Squitter broadcasts its GPS position once per second, satisfying the ADS-B Out requirement.
Example Sentence 2
During preflight the pilot confirmed the transponder was set to transmit Mode S Extended Squitter for regulatory compliance.