ADS-B: Twice as nice

This is the 12th in a series of articles looking at the impact of the Next Generation Air Transportation System (NextGen) on GA pilots.

Are two systems better than one? For Automatic Dependent Surveillance-Broadcast, the cornerstone of the Next Generation Air Transportation System (NextGen), the answer is yes and no.

Any time there are “fixes” put into a program, things very seldomly go smooth. But again that’s me using the experience I have had in newer technologies not only with aviation but with consumer electronics. When fixes are put in place, an avalanche of rules, procedures, and committees are added to the mix, taking up more space, more time and, of course, more money.

The dual system ADS-B we discussed last time is a perfect example of this. To recap: We have the big boys generally using 1090ES (Extended Squitter) ADS-B systems, while the general aviation guys use the more robust UAT (Universal Access Transceiver ) ADS-B system. On top of that is another system, called ADS-R for repeater, which sends out information every second so that those with UAT can see those with 1090 and vice versa. You also need to remember that UATs in the US max out at 18,000 feet. Got it?

You also need to know what is mandated by the FAA. By the year 2020, all aircraft flying in certain areas are required to have ADS-B Out. If you are going to be flying in Class A, B, or C airspace, you’ve got to have ADS-B Out. Additionally, any aircraft in E airspace above 10,000 feet and within a Mode C veil also must have ADS-B Out.

While it’s not mandated, ADS-B In is really a no brainer at this point. In fact most decent GPS receivers today, whether they be portables or panel-mounted devices, have the capability for ADS-B In, which means you can receive and take information in, such as weather, traffic avoidance, and all the rest of the goodies that come with TIS-B (Traffic Information Service-Broadcast) and FIS-B (Flight Information Service-Broadcast).

Between the two, the mandated ADS-B Out is the big monster because it has to send out information that is dead nuts (which means manufactured to very tight tolerances). You know, like CERTIFIED! Any time you add that swear word to the mix the price only goes up.

Let’s take a look at a typical GA installation for both systems that we may see in your airplane. We will use the illustration presented here.

Obviously there is a little bit more going on here than your normal everyday GA airplane. First notice that we still have the basics, which are transponders and altimeters. However we also will need a 980UAT ADS-B Out system, a GPS with WAAS, two additional antennas and, to make it all nice and pretty, some kind of display device.

We use two antennas to guarantee reception from both top (up) and bottom (down) of the aircraft. This allows for a much broader coverage in the traffic avoidance department. With TIS-B, all other traffic is linked directly to the cockpit by way of the ADS-B ground infrastructure. That information is combined with additional data from the Secondary Surveillance Radar system so that when using TIS-B, you will see all airplanes in the area, whether they are ADS-B equipped or not.

However, there is on gotcha here. To increase the efficiency of the system to prepare for the number of aircraft expected to be flying in the next 50 years, TIS-B is not on all the time. Yep, I said that right. The system is smart enough to only come on when needed. For a ground station to even start to transmit TIS-B data to an aircraft, two factors must come into play: The aircraft that has ADS-B Out must be transmitting both In and Out; plus there has to be other traffic somewhere in the vicinity of that aircraft. This means that if a non-ADS-B-equipped airplane is in an area and there is no ADS-B aircraft present, the system does not transmit that data. Hmmm, interesting.

If you look at the illustration a little closer and you will notice that the display is showing weather for this particular set up. This weather is by way of ADS-B In and it is free, no subscriptions needed.

It’s also important to know that FIS-B weather and other data is only broadcast where ground stations are located. It is transmitted all the time with no need to be “triggered” by another ADS-B aircraft and it only is received by UATs.

Next month we will dig deeper into these features and dig out of it more details that generally do not surface in most reports on NextGen.

See you then.

Jeffrey Boccaccio is a private pilot and chief engineer at MatchBox Aeronautical Systems. You can reach him at or

Speak Your Mind