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How it Works: Traffic Information Service-BroadcastHow it Works: Traffic Information Service-Broadcast

TIS-B or not TIS-B?

Wouldn’t it be great if a display on your instrument panel—or an iPad in your lap—could show you other aircraft flying in the vicinity of your airplane?
How it Works

The aircraft on the right has ADS-B. However, it cannot directly “see” the aircraft on the left, equipped only with a transponder. TIS-B shares its position, as determined by ATC radar, with ADS-B-equipped aircraft.

Illustration by Steve Karp

Well, that technology exists today, and Traffic Information Service—Broadcast (TIS-B) is a big part of it. But to understand TIS-B, it really helps to discuss the broader enabling technology, Automatic Dependent Surveillance-Broadcast (ADS-B).

ADS-B uses GPS satellites instead of ground-based radar to determine aircraft position. The FAA has mandated ADS-B Out equipage for operations after January 1, 2020, in any airspace where a transponder is required today. ADS-B In, which is optional, provides the ability to “see” other ADS-B-equipped airplanes.

However, aircraft equipped only with traditional Mode A/C transponders are invisible to ADS-B equipment. That’s where TIS-B comes in.

TIS-B takes the position and altitude of an air traffic control radar target, converts that information into a format that’s compatible with ADS-B, and then broadcasts the information to aircraft equipped with either of the two U.S. ADS-B datalinks, the 1090-MHz extended squitter (1090ES) and the 978-MHz universal access transceiver (978UAT) frequencies.

For a pilot to benefit from TIS-B, his or her aircraft must be equipped with ADS-B In, and operating in airspace with radar coverage.

Mike Collins

Mike Collins

Technical Editor
Mike Collins has worked for AOPA’s media network since 1994. He holds a private pilot certificate with an instrument rating.

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