TIS-B, ADS-R, and the Ghost Target - How the Ground Network Stitches Together the Traffic on Your Screen, From the Avionics Hangars at Oshkosh

That ghost target shadowing your airplane on the traffic display isn’t a broken receiver. Your ADS-B traffic picture isn’t assembled airplane-to-airplane - it’s stitched together by a network of more than 700 FAA ground stations and rebroadcast up to you. The ghost appears when that ground network briefly fails to recognize that your ADS-B signal and your radar return are the same aircraft, and echoes you back as traffic.

Why do I see a second target on top of my own airplane?

Occasionally the surveillance system fails to correlate two versions of you. Your airplane broadcasts its GPS position on ADS-B Out, and a ground station hears it. But that same ground station also sees you on radar as a TIS-B target. For a moment, the fusion logic doesn’t realize the ADS-B airplane and the radar blip are the same aircraft - so it rebroadcasts you back to yourself as traffic.

The result is a phantom that matches your altitude and track perfectly. Of course it does. It’s you.

Good avionics filter this out; your box knows its own address and suppresses the echo. But at the edge of coverage, or during a handoff between ground stations, the filter can slip and you end up chasing your own tail across the moving map. Once you understand the architecture, the ghost stops being spooky - it’s a fingerprint proving your traffic picture is assembled on the ground and handed back up to you.

How does ADS-B traffic actually reach my screen?

Start with what most pilots already know. Automatic Dependent Surveillance–Broadcast (ADS-B) lets your airplane determine its position by GPS and broadcast that position roughly once per second to anyone listening. That’s the “Out” side - the part the mandate required you to install.

The “In” side is receiving other airplanes, and that’s where it gets complicated. If every aircraft simply broadcast and you simply listened, you’d hear all of them. But that’s not how it works in the United States.

The FAA runs the system on two different frequencies. Some airplanes broadcast on 1090 MHz, others on 978 MHz, and an airplane transmitting on one link physically cannot hear an airplane transmitting on the other. If surveillance were purely airplane-to-airplane, you’d see only your own frequency’s traffic and be blind to the rest.

What is the fix for the two-frequency problem?

The fix is the ground. Your traffic picture does not come directly from other airplanes - it comes from that network of 700-plus ground stations on towers, rooftops, and remote hilltops. They listen to both frequencies and every airplane, then broadcast a stitched-together picture back up to you. Two services ride on that uplink.

ADS-R (Automatic Dependent Surveillance–Rebroadcast) is the translator. When a ground station hears a target on 1090 MHz and knows there’s a nearby airplane listening only on 978 MHz, it rebroadcasts that target down on 978 - and vice versa. Its entire job is to bridge the two frequencies the system split apart.

TIS-B (Traffic Information Service–Broadcast) solves a different gap. ADS-B is only as complete as the airplanes that carry it, and plenty still don’t - the taildragger with no electrical system, or the airplane with only a Mode C transponder that answers radar but broadcasts no position. Those aircraft are invisible to a pure ADS-B receiver. But ATC’s secondary surveillance radar still sees them, so TIS-B converts that radar picture into datalink targets and delivers it to your cockpit.

Is my traffic display one picture or several?

It’s a composite. The clean layer of little diamonds in your panel is actually three fused sources:

1. Your direct ADS-B receptions
2. ADS-R rebroadcasts of the other frequency
3. TIS-B radar feeds of aircraft that aren’t equipped at all

They all arrive looking identical, so you’d never know the difference. When it works, it’s extraordinary - a small experimental homebuilt with a portable receiver on the glareshield effectively gets a slice of the national air traffic control surveillance picture, capability that once lived only in a radar room.

What are the trade-offs of a ground-based traffic picture?

TIS-B is client-based. The ground station doesn’t broadcast the entire national radar picture to everyone - that would flood the frequencies. It only sends traffic near airplanes it knows are listening, meaning airplanes that are transmitting ADS-B Out. You have to announce yourself before the network builds a personalized traffic bubble around you.

This creates a trap. If you fly with a receive-only device and have no ADS-B Out, the ground station doesn’t know you exist and won’t create a bubble for you. You’ll see aircraft that happen to fall inside someone else’s nearby bubble and miss the rest. The picture looks complete but isn’t - it shows what it happens to overhear, not the whole world.

Latency is the second trade-off. The fused picture has to travel: airplane to satellite to ground station, or radar to fusion computer to tower to you. A direct air-to-air ADS-B reception is nearly instant, but a TIS-B radar target can be a second or more old and updates only as fast as the radar sweeps - which in the middle of the country can be several seconds between hits. The diamond on your screen shows where an airplane was, not where it is. On converging traffic, a few seconds is real distance.

What should pilots do with this knowledge?

Equip with ADS-B Out if you rely on ADS-B In. Out is your ticket into the system - it’s what makes the ground network build you a complete bubble instead of letting you eavesdrop on scraps.

Respect the latency. The traffic display is spectacular situational awareness and a poor substitute for looking outside. The diamonds are a few seconds in the past; your eyes are in the present. Use the screen to know where to look, then look.

Understand your coverage. All of this depends on being in range of a ground station. Low down, behind terrain, or out in wide empty country, you can drop below the network. When that happens the rebroadcast and radar feed stop, and your composite picture quietly thins to only the aircraft you can directly receive. The system doesn’t flash a warning - it just gets quieter. Know where that happens on your routes.

Key Takeaways

• Your ADS-B traffic picture is assembled on the ground by a network of more than 700 FAA stations, not received directly airplane-to-airplane.
• ADS-R bridges the 1090 MHz and 978 MHz frequencies; TIS-B adds radar-only, non-equipped traffic to your screen.
• The ghost target of your own airplane appears when the network briefly fails to correlate your ADS-B signal with your radar return - most often at coverage edges or during station handoffs.
• TIS-B is client-based: without ADS-B Out, the ground network won’t build you a full traffic bubble, and a receive-only device may show a dangerously incomplete picture.
• Displayed targets carry latency of a second or more and update only as fast as radar sweeps - use them to direct your eyes outside, not to replace them.