What are ADS–B Transponders?

Global air traffic will soon be watched from above, under a constellation of 66 Low–Earth Orbit satellites. Ground–based surveillance radar is limited to line of sight; it is a challenge in mountainous regions and non–existent over oceans. The global umbrella network of Automatic Dependent Surveillance–Broadcast (ADS–B) satellites will safely allow aircraft to fly closer to one another (15 nautical miles over the ocean, down from 40) and permit shorter routes and optimal altitudes, thus saving fuel and time and lowering carbon emissions. Mandatory compliance begins in U.S. airspace on New Year’s Day, and Canada follows in 2021. Many countries and airlines are already using ADS–B: Air Canada adopted it last March.

December 2, 2019
An illustration of a ADS-B Transponder in space

ADS–B Ins and Outs

  1. All airliners must be retrofitted with a transponder to support ADS–B. Small aircraft also need this equipment if they want to fly in certain airspace.

  2. There are two types of ADS–B transponders: ADS–B Out (which transmits the aircraft’s navigation data) and ADS–B In, whereby a pilot can see the location, speed, direction and altitude of other aircraft.

  3. Before ADS–B, 70 percent of the globe was beyond the reach of surveillance, including the North and South Poles, oceans, mountainous regions and even deserts and jungles.

Portrait of Air Canada's Captain Doug Morris
Photo: Reynard Li

Doug Morris is an author, meteorologist, instructor and Air Canada captain on the Boeing 787.