ADS-B goes further. At least once per second, the aircraft broadcasts not just ID and altitude but also the other essentials of target tracking, azimuth and range—all without interrogation from the ground.
It does this via an “extended squitter,” using a signal that is longer than most Mode S signals. With the extended squitter, the aircraft can downlink flight details such as airspeed, climb or descent rate, and magnetic heading. Other aircraft and ground stations within about 150 miles receive the information in their cockpits or consoles.
An ADS-B-equipped aircraft includes a Cockpit Display of Traffic Information, showing the pilot a view of neighboring traffic similar to what the controller sees on the ground. Other information is uplinked from the ground, including positions of nearby aircraft not equipped with ADS-B, weather data, and other updates.
Installing ADS-B will usually involve modifying the Flight Management System software and making new hard-wire connections between the FMS and the transponder.
Instead of using extended-squitter transponders broadcasting at 1090 MHz, general aviation aircraft will be equipped with simpler “universal access transceivers,” which broadcast at 978 MHz.
The transceivers will also be installed on airport ground vehicles, because ADS-B functions on the ground as well as in the air.
The development of ADS-B is continuing, with implementation coming in stages over the next decade and beyond as radars gradually are decommissioned. For older aircraft, the cost of conversion to ADS-B would be prohibitive.
So in the meantime, aircraft that do convert will be equipped with a hybrid technology, capable of handling both the old system and the new.
“If they’re interrogated, they will reply to that interrogation, but they’ll also spontaneously broadcast their information,” says Vincent Capezzuto, the FAA’s ADS-B program manager.