Ghost target

[bernardsv]

Flying at 3,500 ft, I was accompanied by a target for a two hour period indicated as being 4,300 ft below me. I've seen targets reported as being at my altitude close by (presumably my own aircraft) but never an aircraft below ground level. Any explanation of how the system can report such erroneous data would be helpful.

 

[Dynon]

If it normally works, then I'm guessing that may have been a glitch in the ADS-B system it its reporting of your position. If it happens again, and you have the ability to cycle the transponder via a breaker, you might try resetting it to see if that makes a difference. Is the transponder's position source SkyView's GPS, or do you have another device (usually a 430w or GTN) hooked up for that? Also, if this happens all the time, you should check that your hex code is set correctly.

 

[dynonsupport]

I notice that your transponder is "ON" not "ALT". This means you are not transmitting your altitude, and you are only a Mode-A transponder. This is also why your ADS-B is "Partial" not "Full." Without altitude data, the ADS-B system has a hard time figuring out what altitude you are at, so you're going to get weird ghosts...

You need to go into the transponder menu and press "ALT". Even better, go into setup, turn on auto air/gnd mode, put the system in AUTO, and forget about messing with it every takeoff and landing.

 

[bernardsv]

Is the transponder's position source SkyView's GPS, or do you have another device (usually a 430w or GTN) hooked up for that? .

My Transponder uses the Skyview GPS. Would there be a difference if I switched it to a GNS430?

I notice that your transponder is "ON" not "ALT". This means you are not transmitting your altitude, and you are only a Mode-A transponder. This is also why your ADS-B is "Partial" not "Full." Without altitude data, the ADS-B system has a hard time figuring out what altitude you are at, so you're going to get weird ghosts...
.

I'd set my Transponder to ON as requested for departure from KOSH Airventure. I do see ghost targets when set to ALT. I'd like to know if there is any way of reducing their occurrence. It can be a major distraction in the high traffic areas I fly in.

 

[dynonsupport]

There should not be a difference in this situation with a certified GPS.

As an FYI, the OSH NOTAM requires your transponder to be in Standby within 30nm, not just ON but without ALT. The only time you ever really want to use ON is if ATC specifically asks you to stop transmitting your Mode-C because your altitude encoder is busted.

It's hard for us to track down other ghost reports when the only one we have an image of is with a transponder in the wrong mode. If you could get some screenshots or data logs of ghost targets with the transponder in ALT and the ADS-B STATUS of "FULL" then we can help a lot easier. Also knowing where you were in the world when you saw this is helpful, and if it's always in the same area. We fly in Seattle where we can see hundreds of targets an hour and we don't get ghosts, but we've seen radars improperly installed in some places leading to ghosts in those regions, and we've worked with the FAA to get that fixed.

If you never see "ADS-B FULL" then that's also an indication of something misconfigured.

Also, what software version are you running?

 

[bernardsv]

I'll take a screenshot with ADS-B Full Status next time I see a ghost target.
I'm running 10.1 software.

 

[swatson999]

I'd set my Transponder to ON as requested for departure from KOSH Airventure.

Whatever else is going on, you were supposed to turn it OFF, not ON.