False ForeFlight Traffic Alerts

Gilbert Buettner

Gilbert Buettner

Line Up and Wait
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Wausau, Wisconsin
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Four times today on a short round-robin training flight, I had ForeFlight alert me to nearby traffic. Each time the screen on my iPad alerted me to traffic less than one quarter mile away, same altitude. When it disappeared from the screen, there was no traffic displayed near us on the moving map. One of these alerts was inside Class D airspace where we would have been aware of someone else talking to the tower.

I had never seen this before and found it a bit alarming at first. Traffic that close suddenly appearing would probably be fairly easy to see, especially at the same altitude. It certainly got our attention.
 
Gilbert Buettner said:
Four times today on a short round-robin training flight, I had ForeFlight alert me to nearby traffic. Each time the screen on my iPad alerted me to traffic less than one quarter mile away, same altitude. When it disappeared from the screen, there was no traffic displayed near us on the moving map. One of these alerts was inside Class D airspace where we would have been aware of someone else talking to the tower.

I had never seen this before and found it a bit alarming at first. Traffic that close suddenly appearing would probably be fairly easy to see, especially at the same altitude. It certainly got our attention.
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Happened to me last Monday and to a friend here in Colorado also!! Scared the heck out of both of us!! Don't you just LOVE ADS-B !!
 
What are you using for your ADSB?
I have a stratus transponder and I get this on most flights especially if I do a steep turn or some mildly aggressive maneuver.

It's always a quarter mile and same altitude.
 
The downside is it can kind of train you to ignore that sort of stuff. Two years ago I was leaving Oshkosh and I got one of those and I shrugged it off and a dude flew right out from under me.

The other thing I'm not a fan of is it will show traffic two or three miles away and suddenly that traffic just disappears for a half a minute. Definitely not the greatest system but contrary to what a lot of people my age think it's way better than my aging eyeballs.
 
Happened to me also turning base to landing in a delta. I called tower to ask if they saw anything. I think foreflight sometimes mistakes your ownship as another traffic.
 
I have ADSB-In traffic on four devices: iPhone (FF) two Avidyne 440s and the big Entegra MFD. You'd think, since they all receive the same data in, that they would all show the same traffic but they don't. One will sometimes show a phantom aircraft that's very close and same altitude. I've learned to check the other displays for confirmation. My avionics shop says it has to do with a double image of my own aircraft that sometimes doesn't get filtered out by the device. I saw phantoms a lot last year, no so many this year. No idea why its better now. And, yes, it's scary the first few times you see it.
 
Sounds like what you're seeing is your own aircraft. With ADS-B In, there are two sources for traffic: 1) direct reception of another aircraft's ADS-B out, and TIS-B, which is a rebroadcast from ADSB ground stations of traffic that is obtained through ATC radar. The latter includes both ADS-B Out aircraft and non ADS-B aircraft.

Your software should be able to distinguish duplications of aircraft. For example: your ADS-B in should be able to quickly filter out your own ADS-B out signal. However, if due to terrain issues, multiple radar sites, etc., ATC radar transmits your position on TIS-B in a location that you're not at at the present, your software might interpret your TIS-B return as another aircraft.
 
This is what I understand it to be. I have had it happen once or twice. Close by traffic, I turn away and it follows. Then disappears.

I always honor the traffic until I determine it is false.
 
my mode-S traffic sometimes doesn't show on the iPad......this is inside the Bravo airspace. Very frustrating.
 
I used to get mode S TIS alerts for same-altitude traffic reliably at a given point between CJR and OKV. I assume it was some anomaly in the radar mosaic that caused me to show up twice.
 
You fix this by having 4 different ads-b devices on 4 different ipads and crosschecking..

I'm here all day if you need more advice
 
I’ve had a ‘partner’ shadowing me as well. Not just Foreflight, I have Garmin Pilot app. It’s the mix of TIS and ADSB locations not matching and the software thinking there are two of us.
 
On this particular flight I was using a different iPad and now I wonder if that has anything to do with it. The student pilot was using ForeFlight on his iPhone and did not get the false traffic alerts.
 
I don't believe that's a foreflight issue. Foreflight just reports what it is told.
 
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