ADS-B in saved my bacon

[Kiddo's Driver]

Edit:
This is a good example of something called TIS-B shadow. There was no aircraft behind and below me. It has happened to me several times since then. Now I just ignore it. Hopefully it will always be a shadow and not a real aircraft coming up from behind... I have left my comments unchanged so that the thread maintains its continuity.


Yesterday I was doing a short flight from Nashville to Fayetteville, TN. In the attached photos you see an aircraft directly behind me and a few hundred feet lower go from about 10 miles back to less than a mile in less than 8 minutes. His icon would disappear periodically and when it last reappeared he was right on me at less than a nm. At that point I did a full power climbing turn away from him while I looked over/down to try and spot him. I never saw him. He must have spotted me when I put the plane sideways and made it much more visible. His icon did a hard turn away from me and then disappeared off of my screen. I assume he had an "Oh ****" moment and turned off his transponder & ADS-B out equipment.

9 miles of closure in 8 minutes means he was going 67+ knots faster than me, so it was something relatively fast. I go 102-104 knots so he was probably going 170 knots. It reminds me of the Lancair that ate the back of a 172 a few years back.

It is safe to assume that if he had ADS-B out he probably had ADS-B in, and that if I had ADS-B out he would have seen and avoided me.

Does this warrant a report of some kind? Is this a NASA form?

Oh, and notice that he does not have an identifier shown under his icon...

 

[txflyer]

Glad you're o.k.

As far as making a report, my old bones would look at it like what did you do before ADS-B? Probably nothing. The guy would have run up on you and hopefully he would see you before any metal touched and you may have never known he was there.

Before ADS-B or PCAS or any of those what just happened to you would fall under the category 'see and avoid' in my opinion. I don't think I'd bother the FAA with it.

 

[MAKG1]

Why would you turn toward a target?

The right answer is to CLIMB. Slow to Vy really quickly and you'll get a few hundred feet almost instantly in an 172.

When you turn, you dramatically increase the closure rate. By over 200 knots given the heading you showed.

And use flight following. This sort of thing is exactly what it is for. ADSB should have seen you with only a transponder. It wouldn't be able to identify you, but it would know you were there (through a relay with a ground station). Flight following has another set of eyes with some different equipment, including radar.

Quite a number of ADSB displays (e.g., the common GTN650) have poorly thought out user interfaces. I get false traffic alerts all the time, most obviously on the ground. That trains people to ignore them.

 

[petrolero]

I had almost the exact same thing happen to me on a recent mountain flight as we were departing the Denver Class B veil to the SW toward Wilkerson Pass. I had been looking out the window but glanced down at the iPad to show my brother the traffic feature and I saw it right as he said it... "is that guy really that close?" It showed traffic 5 oclock, less than 1 mile, same direction, 100 ft below, climbing. I whipped my head around, saw nothing, then did a climbing turn away from the 'traffic'. The traffic was faster than me and eventually diverged but I never saw it and I still wonder if it was real (I have no reason to say it wasn't, but still). It was squawking a tail number so I don't think it was some kind of ownship echo or whatever. Plus it was going faster than me. I never saw it, but I avoided it. So

 

[TommyG]

I know of a couple of times using Stratus 2 that I have had a phantom airplane right up my butt, completely disappear, go to my side showing same altitude, disappear, and the again right on my butt same altitude.

I was looking like crazy to find him and see him, but it was never there.

 

[Kiddo's Driver]

Why would you turn toward a target?

The right answer is to CLIMB. Slow to Vy really quickly and you'll get a few hundred feet almost instantly in an 172.

When you turn, you dramatically increase the closure rate. By over 200 knots given the heading you showed.

Initial turn was 90 degrees to get separation. Once he hard turned to the right away from me I continued my turn to try to spot the guy. The scary part is that I HAD climbed! I added 500 feet in my turn. He was climbing at that point also. Also, part of the reason I was so far turned back towards him was that it took both hands to do the screen shot on the iPad. I think I bumped the yoke while doing it.

And use flight following. This sort of thing is exactly what it is for. ADSB should have seen you with only a transponder. It wouldn't be able to identify you, but it would know you were there (through a relay with a ground station). Flight following has another set of eyes with some different equipment, including radar.

I was on flight following for the entire flight from BNA to FYM. I was on with Memphis Center when this happened.

Quite a number of ADSB displays (e.g., the common GTN650) have poorly thought out user interfaces. I get false traffic alerts all the time, most obviously on the ground. That trains people to ignore them.

I don't think this was false. It was flying straight the whole time until I turned sideways to show more aircraft, then he banked hard away from me.

 

[petrolero]

I was on flight following for the entire flight from BNA to FYM. I was on with Memphis Center when this happened.

This is what makes me think it was false. Did you ask ATC about it?

 

[Kiddo's Driver]

This is what makes me think it was false. Did you ask ATC about it?

I did not.

If it was false then the entire system is just about useless. Bad information is worse than no information! It makes you question the good information because you cannot tell the difference.

 

[Brad Z]

Initial turn was 90 degrees to get separation. Once he hard turned to the right away from me I continued my turn to try to spot the guy. The scary part is that I HAD climbed! I added 500 feet in my turn. He was climbing at that point also. Also, part of the reason I was so far turned back towards him was that it took both hands to do the screen shot on the iPad. I think I bumped the yoke while doing it.

I was on flight following for the entire flight from BNA to FYM. I was on with Memphis Center when this happened.

I don't think this was false. It was flying straight the whole time until I turned sideways to show more aircraft, then he banked hard away from me.

You flew straight, he flew straight. You turned, he turned. You climbed, he climbed. You never saw the other aircraft?

Sounds like you were trying to avoid your shadow. Which makes sense...it was probably a radar based target, coming from two different radar sources. It's not uncommon to see false traffic coming from ground based traffic systems. I've seen it in Mode S TIS, and I also see it in TIS-B traffic from ADS-B in (I have In & Out). The traffic will jump around, from behind to in front, to over top...usually within a couple hundred feet of your altitude. This is when ATC is helpful, as they generally don't see this type of traffic shadowing.

...so either that or it's the guy who was refueling his plane with the prop spinning earlier now messing with you.

 

[Stewartb]

Do you have and use a tail strobe?

 

[Kiddo's Driver]

You flew straight, he flew straight. You turned, he turned. You climbed, he climbed. You never saw the other aircraft?

Sounds like you were trying to avoid your shadow. Which makes sense...it was probably a radar based target, coming from two different radar sources. It's not uncommon to see false traffic coming from ground based traffic systems. I've seen it in Mode S TIS, and I also see it in TIS-B traffic from ADS-B in (I have In & Out). The traffic will jump around, from behind to in front, to over top...usually within a couple hundred feet of your altitude. This is when ATC is helpful, as they generally don't see this type of traffic shadowing.

...so either that or it's the guy who was refueling his plane with the prop spinning earlier now messing with you.

He turned the opposite direction from me, but who knows how a false target could act...

Do you have and use a tail strobe?

Wing tip strobes that are visible from the front, rear, and sides.

 

[Stewartb]

Wing tip strobes that are visible from the front, rear, and sides.

Maybe, maybe not. If this event happened as you believe the guy didn't see you. A tail strobe would certainly help with that.

I almost ran into a Cub once while talking to ATC and about to enter downwind. I was about 40-50mph faster than him, more because he was flying slow than me flying fast) and by the time ATC asked if I saw him I was scary close to running smack into his tail. I never saw him until the last second. I'v had other similar experiences but not as close. My cub got lights to protect me from behind and I encourage other owners to do the same. Light me up like Las Vegas. I wanna be seen.

 

[Xcfire]

That Happen to me, I used Flight Following and I have a stratus 2s twice a phantom aircraft came up right behind me and was my shadow. I know I was in a very remote area and new it was a glitch or something was causing it to read itself.

 

[Kiddo's Driver]

That Happen to me, I used Flight Following and I have a stratus 2s twice a phantom aircraft came up right behind me and was my shadow. I know I was in a very remote area and new it was a glitch or something was causing it to read itself.

A shadow of what? I don't have ADS-B out.

 

[Xcfire]

I don't know but I know I was the only plane in the area and it showed a yellow closing down on me or following me then it just vanished.

 

[Stewartb]

Aren't transponders translated to ADS-B screens?

 

[petrolero]

In my case I suspected it could be some kind of shadow or ownship phenomenon except that my ADS-B in showed a different tail number. That's what made me believe it was real - plus the fact that it eventually diverged. I was heading into the mountains and not on FF or I'd have asked.

 

[Brad Z]

A shadow of what? I don't have ADS-B out.

A shadow of you!

Like I mentioned in my last post, your ADS-B in device picks up not just other ADS-B out equipped aircraft, but traffic information from the ADS-B ground station. The ground station transmits all known traffic information (TIS-B), regardless of the source.

So most of the traffic coming from TIS-B originated from ATC radar equipment.

In some cases, from multiple radars. It sounds like your ship was picked up by two radar facilities, and transmitted by TIS-B as two separate targets.

There's inherent error from radar position data due to time, distance, etc., so two radar facilities, many miles apart, sweeping at different rates, may paint you in two different locations at the same time. And if the prevailing altimeter setting is different, the two targets will have two different altitudes.

Your software that depicts traffic uses its own algorithms to figure out if a target sent out by TIS-B is your own ship. If it is, it doesn't display it. If two targets are transmitted, it picks the nearest one as yours, and shows the other target as nearby traffic.

 

[Kiddo's Driver]

If ADS-B out would stop that from happening that would another good reason for me to add it.

 

[Direct C51]

Oh, and notice that he does not have an identifier shown under his icon...

Here is a pretty good clue for you. As Brad is trying to tell you, it was probably TIS data of your own aircraft. So ADS-B In probably did not "save your bacon." I would wager instead that it had you doing some aggressive maneuvering while taking screenshots with 2 hands.

 

[petrolero]

I did not.

If it was false then the entire system is just about useless. Bad information is worse than no information! It makes you question the good information because you cannot tell the difference.

But to be fair, was it really 'bad information' or good information that was misinterpreted? I wouldn't be ready to write off the whole ADS-B concept just because I saw and misinterpreted my own radar return.

In my situation I actually thought about whether I was picking up my ownship. In the end I discounted that possibility because the target carried a tail number that wasn't mine. Given that I wasn't on FF as I usually am, I 'avoided' what I could not see and could not immediately confirm from ATC.

The thing that is perhaps instructive is how much your ownship target (if that's what it was) lagged your actual position. That would stand to reason, and is why I initially questioned my target as being possibly an ownship effect. But what if it were a real target and or I 'avoided' its former position by turning right into its actual one? That's a bit frightening, but...

I do agree that if adding ADS-B out can give more confidence in the ADS-B in data, and hopefully reduce the lag in the location of other non-ownship targets, then that is a good thing.

 

[txflyer]

A shadow of you!

Like I mentioned in my last post, your ADS-B in device picks up not just other ADS-B out equipped aircraft, but traffic information from the ADS-B ground station. The ground station transmits all known traffic information (TIS-B), regardless of the source.

So most of the traffic coming from TIS-B originated from ATC radar equipment.

In some cases, from multiple radars. It sounds like your ship was picked up by two radar facilities, and transmitted by TIS-B as two separate targets.

There's inherent error from radar position data due to time, distance, etc., so two radar facilities, many miles apart, sweeping at different rates, may paint you in two different locations at the same time. And if the prevailing altimeter setting is different, the two targets will have two different altitudes.

Your software that depicts traffic uses its own algorithms to figure out if a target sent out by TIS-B is your own ship. If it is, it doesn't display it. If two targets are transmitted, it picks the nearest one as yours, and shows the other target as nearby traffic.

I'm taking this explanation and running with it.

I have seen a yellow/red paint on my GP ADS-B through the GDL-39 that looks like a plane magically appeared +100 feet and right up my keester. Then it's gone.

It'll get your attention the first few times until you convince yourself it's bogus. It does make the whole ADS-B thing seem less bullet proof, but the targets out away from the aircraft have been spot on I can report.

 

[yetti]

Were you using a transponder? Then it was probably your shadow. based on the one flight where I had the Stratux raspberry PI running, there is a latency in updating the signals and your shadow catches up with you. The radar is at my home airport but most of the ADSB antennas are in Houston and Austin area and I was flying between them

 

[petrolero]

Here is a pretty good clue for you. As Brad is trying to tell you, it was probably TIS data of your own aircraft. So ADS-B In probably did not "save your bacon." I would wager instead that it had you doing some aggressive maneuvering while taking screenshots with 2 hands.

I would wager that he wasn't maneuvering while taking the screenshots.

Anyway taking a screen shot on an iPad is probably the least coordinated thing a pilot does.

 

[yetti]

If you did not get a selfie while maneuvering and screen capturing, you are not doing it right

 

[Let'sgoflying!]

multiple events of phantom planes with my ipad/stratus.

 

[geneseib]

Yesterday I was doing a short flight from Nashville to Fayetteville, TN. In the attached photos you see an aircraft directly behind me and a few hundred feet lower

How'd it save you bacon if he was a few hundred feet below?

 

[PA28Flyer]

The important question is: did you get a visual on him? You were flying VFR which means "see and avoid", not "see your iPad and avoid".


In any case, you were probably experiencing what is called the "TIS-B Shadow".

 

[cowman]

i had to look very closely at your screenshot as I was flying in the same area around that time. Wasn't me, I was there an hour later NW bound and wishing I could do 170kts.

Lots of traffic though. Sadly I didn't have the stratus up. The charge port on mine broke

 

[Kiddo's Driver]

The important question is: did you get a visual on him? You were flying VFR which means "see and avoid", not "see your iPad and avoid".


In any case, you were probably experiencing what is called the "TIS-B Shadow".

Never saw him. The view looking out the back of my plane at something 400 feet below me is awful. Too much metal in the way. It's awfully hard to see and avoid something in your six that is catching up with you. The iPad gave me an indication that I would not have otherwise had. Too bad it looks like it was a false indication. Someone tell me again how this ADS-B stuff is supposed to make us safer?

The only thing you can do is turn. I also never saw him when I turned.

Well, it looks like it is time for me to go read up on "TIS-B Shadow".

 

[petrolero]

Someone tell me again how this ADS-B stuff is supposed to make us safer?

Mostly... it shows you weather. The traffic will be less useful until post-2020.

 

[Kiddo's Driver]

Mostly... it shows you weather. The traffic will be less useful until post-2020.

I still have a problem with a system that shows false positives. It will lull you into going "oh, that's not real" and ignoring the information.

 

[denverpilot]

Mostly... it shows you weather. The traffic will be less useful until post-2020.

And still questionable after that.

 

[petrolero]

I still have a problem with a system that shows false positives. It will lull you into going "oh, that's not real" and ignoring the information.

That wasn't a false positive, it was just you! If you'd had ADS-B "out" it would have shown your tail number. But you (and I) only have half the stuff (OK, not half by price )

I think your expectations are too high or you haven't been paying attention to the numerous caveats from the FAA or both.

Pilots and the FAA have been talking about the limitations of ADS-B "in" traffic and weather since even before it was introduced.

Maybe you should just give up on ADS-B because, guess what, the weather isn't perfect either. The radar isn't current and the METARs and TAFs often turn out to be wrong.

 

[MAKG1]

There is a HUGE difference between a false alarm and unreliable information you're not supposed to use as primary anyway.

Training operators to ignore alarms is a nice way to make really bad things happen. I'm sure you've seen the dozen or so gear up videos where the pilot ignores the gear warning all the way down. At least gear ups aren't usually fatal.

TIS-B (and ADSB-in) give ridiculous rates of false traffic alarms. This makes them effectively useless.

Yes, one should understand limitations, but false alarms are in a class by themselves, and they are less than excusable.

 

[PA28Flyer]

Maybe you should just give up on ADS-B because, guess what, the weather isn't perfect either. The radar isn't current and the METARs and TAFs often turn out to be wrong.

Do you have a source for this? First time I've seen that METARs/TAFs being transmitted via FIS-B were wrong.

 

[denverpilot]

Pilots and the FAA have been talking about the limitations of ADS-B "in" traffic and weather since even before it was introduced.

Citation? I don't believe you'll find a document with a publication date on it *prior* to introduction.

(Because they were too busy pushing the marketing spin to the public and indirectly Congress, prior to deployment as far as I remember.)

Let's see that doc with an FAA logo on it. I'm more than willing to be wrong on this one but I damned sure know there weren't any FAA folks speaking at safety seminars about how broken the "in" side of the system was going to be, and still haven't seen one.

Have seen one, exactly one, FAASTeam topic go by in the announcement list about real world ADS-B usage and caveats, and that's a volunteer speaker, of course.

Saw exactly zero topics about it at OSH in the schedule for the FAA Pavilion.

So color me skeptical of your claim. The community has figured out the caveats and problems, they were not mentioned *prior* to deployment by any FAA person on the ADS-B team in anything other than perhaps design docs and specification meetings.

Definitely not as an educational "push" to prepare pilots for the built in design flaws.

 

[RotorDude]

Do you have a source for this? First time I've seen that METARs/TAFs being transmitted via FIS-B were wrong.

Not "wrong", but sometimes delayed by as much as a few hours, so you have to read the timestamp on each METAR/TAF very carefully. Ditto for radar reflectivity maps, which have a lag even beyond the shown timestamp. Thankfully in my own experience that's not been a big issue.

 

[denverpilot]

Not "wrong", but sometimes delayed by as much as a few hours, so you have to read the timestamp on each METAR/TAF very carefully. Ditto for radar reflectivity maps, which have a lag even beyond the shown timestamp. Thankfully in my own experience that's not been a big issue.

Seems like a simple fix for that one is available in the display device. Refuse to show old data.

Old weather data is as useless as a one-armed trapeze artist with an itchy ass.

 

[boom3]

This is from the AIM. No avoidance maneuvers without visual contact.

e. ADS−B Limitations
1. The ADS−B cockpit display of traffic is NOT
intended to be used as a collision avoidance system
and does not relieve the pilot’s responsibility to “see
and avoid” other aircraft. (See paragraph 5−5−8, See
and Avoid). ADS−B must not be used for avoidance
maneuvers during IMC or other times when there is
no visual contact with the intruder aircraft. ADS−B is
intended only to assist in visual acquisition of other
aircraft. No avoidance maneuvers are provided nor
authorized, as a direct result of an ADS−B target
being displayed in the cockpit.