Welcome to EAA Chapter 1373!

The X chapter

Tired of ADS-B? Then skip this post!

Every pilot has heard of ADS-B, the system that enables aircraft to broadcast their position and receive the position of other aircraft within the area. (For more info look at our FAQ and Glossary.)

On January 1, 2020, all aircraft must be equipped with ADS-B Out to fly in airspace where a transponder is required today. By the way, don’t count on the FAA extending this deadline because that’s not going to happen.

But there’s a lot of airspace where you can legally fly without ADS-B Out. Just stay away from Class B and C, and below 10,000 feet MSL (or below 2,500 AGL if over 10,000 MSL). Many aircraft owners will choose not to equip ADS-B Out and will simply stay out of the airspace that requires it.

Why am I not seeing traffic with my portable ADS-B receiver?



To entice aircraft owners to equip, the FAA provides free weather (FIS-B) and traffic (TIS-B) information through ADS-B. You can receive this information using a portable ADS-B In receiver even if you don’t have ADS-B Out. However, there’s a catch (that I didn’t understand until recently).

Unlike weather, which is broadcast continuously, ADS-B traffic is only transmitted in response to specific prompts.


Flight Information Service or FIS-B, which includes weather, TFRs, and special use airspace info, is continually broadcast on the UAT frequency (978MHz). Traffic Information Services (TIS-B) is only broadcast when triggered by an aircraft equipped with ADS-B Out.

Thus, if you are flying with only ADS-B In (or you’ve a portable receiver in your car or at home) you won’t see all traffic unless there is an ADS-B Out-equipped aircraft within range that will “wake up” nearby ground stations and trigger them to begin broadcasting TIS-B. Even then, the traffic info being broadcast will be relevant to that other aircraft and might not be relevant to you.

One final note for those of you who have ADS-B Out in the panel but use a portable receiver for ADS-B In: Make sure your ADS-B Out transponder is configured to indicate you are capable of receiving ADS-B In. Otherwise your transponder will not wake up ground stations even though you have ADS-B Out.

Where are ADS-B ground stations located?


On a side note, for unknown reasons the FAA has decided not to publish the location of ADS-B ground stations. However, you can get this info from your ADS-B In receiver and some people have begun to map them out. The graphic below shows the location of ground stations in this area (shown as a yellow push-pin). These towers look similar to a cellular network tower, and in fact the ADS-B is sometimes added to an existing cell tower. So, unlike a VOR, they're difficult to pick out by sight.

ADS-B_Towers

Ed.: Added the screen shot below that shows local towers.

ForeFlight screenshot - 16Oct19

I hope you found this info useful. ADS-B is not going away so no doubt this will not be the last you hear about it. Be sure to post in the Forums if you have comments or questions.

—Alan Collins, EAA 1373 Webmaster

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