Extended Squitter (or 1090 ES) is the Mode S transport protocol for ADS-B operation. 1090 MHz extended squitter is an ADS-B link for air carrier, commercial, and private aircraft. With 1090ES, the Mode S transponder supports an extended squitter (ES) message. Currently, this message provides position, velocity, and heading information.

The ES versions of the Garmin GTX33, GTX-330, and GTX-330D transponders comply with FAA TSO C-166A which dictates the minimum performance standards (MPS) for 1090 MHz ADS-B equipment. Existing Garmin GTX Mode S transponders without ES can be upgraded through Garmin to include the Extended Squitter feature. On average the Extended Squitter option costs an additional $1000-$1500 USD.

It is very important to note that in order for the ES data to be broadcasted, the transponder must be interfaced to a compatible GPS that meets TSO C145a/C146a. These TSOs explains the performance standards for WAAS GPS receivers. As of 2009, the CNX80, GNS480, GNS400W/500W series and G1000 are the only Garmin GPS receivers that meet this criteria.