Spooky traffic from ADS-B

Bill Watson

Bill Watson

En-Route
Joined
Dec 5, 2007
Messages
2,703
Location
Durham NC
Display Name
MauleDriver
Home Airfield
Lake Ridge Aero Park
Yesterday on a leg from Pittsburgh's KAGC to White Plains KHPN, I had traffic appear on my display that was exactly at my altitude and at one point, exactly at my position. Does anyone else experience that with ADS-B traffic?

I've been using the Navworx transceiver hooked up to GRT's HX display (both experimental) for over 2 years.

Occasionally I will get a traffic shadow where it appears that another plane is at my altitude flying formation. It appears for a minute or two and then disappears. It's obvious that it is not another plane but rather some sort of shadow. No Problem.

What made this notable is that this looked like real traffic that appeared several miles in trail at my 7 o'clock. It slowly overtook me, crossed my path at my altitude and then proceeded to fly past me at 1 o'clock until 10+ miles away. Fortunately I was <500' above a solid undercast and could clearly see any conflicting traffic

You can imagine I was asking the controller about this but they assured me that no other traffic was in the vicinity. They said this happens occassionaly and mumbled something about a false return or something. This was a Wilkes Barre approach controller and the incident happened over Williamsport.
 
Just recently ,got a shadow aircraft at same alt and direction. Happens in high traffic area. Can be unnerving the first time it happens.
 
That is indeed an unusual "shadow" problem, assuming it was such. Shadowing appears to be common enough that it is discussed in the AIM, so it is worthwhile that anyone having ADS-B out read section 4-5-7, which can be found on this page:

https://www.faa.gov/air_traffic/publications/atpubs/aim/aim0405.html

2. While TIS-B is a useful aid to visual traffic avoidance, its inherent system limitations must be understood to ensure proper use.
(a) A pilot may receive an intermittent TIS-B target of themselves, typically when maneuvering (e.g., climbing turns) due to the radar not tracking the aircraft as quickly as ADS-B.
(b) The ADS-B-to-radar association process within the ground system may at times have difficulty correlating an ADS-B report with corresponding radar returns from the same aircraft. When this happens the pilot may see duplicate traffic symbols (i.e., “TIS-B shadows”) on the cockpit display.
(c) Updates of TIS-B traffic reports will occur less often than ADS-B traffic updates. TIS-B position updates will occur approximately once every 3-13 seconds depending on the type of radar system in use within the coverage area. In comparison, the update rate for ADS-B is nominally once per second.
(d) The TIS-B system only uplinks data pertaining to transponder-equipped aircraft. Aircraft without a transponder will not be displayed as TIS-B traffic.
(e) There is no indication provided when any aircraft is operating inside or outside the TIS-B service volume, therefore it is difficult to know if one is receiving uplinked TIS-B traffic information.
 
Actually it's pretty common for me - WingX Pro on Mini iPad from iLevil. Scared me ....less first time it happened. Now I just look and ignore.
Hilton commented on a ghost buster fix with next update.
 
I've seen this in my iFly software a few times, but there was a software update a while ago that was supposed to help with the issue and I don't believe I've seen it since. It definitely gets your attention though.
 
My Garmin Pilot does it as well. The app does show it can detect "own ship" but doesn't go into detail in the user guide how it works.

9cb4464e822e9f886c36d3d2492aae55.jpg
 
Own ship detected occurs when the App detects an ADS-B Out Broadcast coming from nearby, presumably your ADS-B Out equipped aircraft. I don't know the specific criteria used. ForeFlight with Stratus does the same.
 
It seems I see this occasionally and briefly when going in and out of the ATC radar coverage.. I see my own tail number show up right on top of me with Garmin Pilot yelping "traffic" Scared he bejesus out of me he first time it happened !!:hairraise: :yikes::eek::dunno:
 
John Collins said:
Own ship detected occurs when the App detects an ADS-B Out Broadcast coming from nearby, presumably your ADS-B Out equipped aircraft. I don't know the specific criteria used. ForeFlight with Stratus does the same.
Click to expand...


Thanks for the explanation John. I couldn't find any documentation in the help section that even mentioned it. I'm sure the certified solutions have a way to deal with this.
 
Marauder said:
Thanks for the explanation John. I couldn't find any documentation in the help section that even mentioned it. I'm sure the certified solutions have a way to deal with this.
Click to expand...

Assuming you have ADS-B Out, there is no ambiguity with respect to own ship as it uses a unique 24 bit address. However, ghosts will still occasionally occur. The GBT does not broadcast a TISB for a target that is an ADS-B Out client, so although the GBT receives your transponder reply as a separate target, it is supposed to filter it out and not generate the TISB ghost. There are many parameters that can be used for filtering, same transponder squawk, same pressure altitude, and if the transponder is mode S, same 24 bit aircraft ID. Unfortunately, even if the transponder is mode S, the enroute radar may not be mode S capable, in which case it doesn't have access to the transponder aircraft ID. At greater distances, even a 1 degree error in position of the radar target can be greater than the filtering distance the GBT uses and the radar target is not recognized as being the same as the ADS-B target. This is more likely to occur with a mode A/C transponder because it does not have an aircraft ID in its reply.
 
Bill Watson said:
Yesterday on a leg from Pittsburgh's KAGC to White Plains KHPN, I had traffic appear on my display that was exactly at my altitude and at one point, exactly at my position. Does anyone else experience that with ADS-B traffic?

I've been using the Navworx transceiver hooked up to GRT's HX display (both experimental) for over 2 years.

Occasionally I will get a traffic shadow where it appears that another plane is at my altitude flying formation. It appears for a minute or two and then disappears. It's obvious that it is not another plane but rather some sort of shadow. No Problem.

What made this notable is that this looked like real traffic that appeared several miles in trail at my 7 o'clock. It slowly overtook me, crossed my path at my altitude and then proceeded to fly past me at 1 o'clock until 10+ miles away. Fortunately I was <500' above a solid undercast and could clearly see any conflicting traffic

You can imagine I was asking the controller about this but they assured me that no other traffic was in the vicinity. They said this happens occassionaly and mumbled something about a false return or something. This was a Wilkes Barre approach controller and the incident happened over Williamsport.
Click to expand...

You were getting feedback from a plane in a parallel universe.;)

I've seen the immediate 'ghost of ourselves' pull a hit, there are enough complications in the system that they are inevitable. The other week I was flying with 2 other guys, 3 pilots, saw the traffic on the box, and none of us could spot the traffic even though we should have been able to without an issue as the target closed on us and flew past.:dunno:
 
You must log in or register to reply here.
Back
Top