A huge number of portable ADS-B receivers has hit the market in the last couple of years, giving pilots instant access to traffic and weather information on their iPad or Android tablets. Weather is broadcast continuously so there isn’t much mystery there. But traffic data is somewhat limited. This can make ADS-B confusing as pilots try to make sense of exactly how and where it works.
Here’s a breakdown of how ADS-B operates from our friends at Sporty’s Pilot Shop that will hopefully clear things up for those of us who are having a hard time keeping straight the nuances of the technology.
There are three basic scenarios that will cover the vast majority of cases. The first and most likely case is the situation where you’re flying with a portable ADS-B receiver but don’t have an ADS-B Out transponder installed in your panel. In this case, you’ll receive target information for any airplane that is transmitting ADS-B Out via air-to-air, but you won’t pick up Mode C target information. (Most airplanes do not have ADS-B Out, but this will change after 2020 when the FAA’s mandate goes into effect.)
The second scenario comes into play if you are flying with a portable ADS-B receiver and no ADS-B Out transponder but you are close to another aircraft that is ADS-B Out-equipped and within range of an ADS-B ground station. In this case, the ADS-B Out airplane can relay traffic information to your ADS-B receiver in a 30-mile bubble. In this case, you will see in-range Mode C and ADS-B targets.
If you have an ADS-B Out transponder in your airplane, you’ll be continuously transmitting to the ground stations and creating your own bubble of traffic information. In this best-case scenario, you’ll see all radar traffic within a 30-mile diameter and 3,500 feet of your altitude.
For a graphical breakdown of we’ve just explained, check out Sporty’s ADS-B 101 tutorial.
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