Dynon SV ADS-B traffic ghosting

[Dan Kent]

I was out flying a couple of weeks ago in an area that had full ADS-B coverage and all of a sudden I had an audio alert of traffic. When I checked the GPS screen it showed the traffic coming at me from the right 100 feet above me. I turned off the autopilot while doing a diving left turn. I never did see the traffic and I suspected it was a ghost of my airplane (I had the Zaon system before so I was familiar with the occasional ghosting).

 

Anyway I didn't know if ghosting was even possible with ADS-B, so I contacted Dynon support yesterday.

 

They came right back and said that they are investigating a ghosting problem as other had mentioned this.

 

Just wanted to give those of you that have a Dynon system with ADS-B of this potential issue.

[Jim Meade]

Thanks, Dan, I'm strongly considering getting that system and will pay attention to this aspect. Very timely.

[Dan Kent]

Jim,

As a side note, I love the ADS-B capability. I fly out of a towered airport and on the same flight I was monitoring the weather at my home airport as I was heading back and on the SV I saw the weather go from 900 feet few, to scattered to broken all in about 20 minutes.

 

I never needed to call the tower as the SV system showed the airport as IFR. What's interesting in this part of TX is that 30 miles to the north there were zero clouds, so I flew around up north for about 30 minutes (making sure the clouds weren't building there) and sure enough the SV system showed the weather had changed to 1700 scattered, so I flew back and landed with no issues.

 

I really got the system for traffic more than weather but this was a good example of how well the weather feature works also. Traffic is amazing almost too much info (especially early on).

[Jim Meade]

Here is from the Dynon site, in part:

"So two things are going on here:

 

On the TIS, side, I believe Garrett's right about that. TIS basically knows about your aircraft and says "here are all of the threats that you need to know about right now". It basically does all of the screening for you and only tells you about aircraft that are near you.

 

On the ADS-B side, the system doesn't screen traffic in exactly the same way, but it does include information that lets systems like SkyView filter out your own traffic target. From what we've seen, sometimes the ADS-B system doesn't correctly tag your aircraft in the way it should. We're keeping an eye on this (and we've seen it ourselves when flying).

 

The implementation challenge of trying to do anything too clever is that when there's an actual threat nearby, even when it seemingly pops out of nowhere, you want to know about it. Inventing the right screening mechanism that ignores phantom own-ships while including every actual threat is of course very possible, but it's easy to get it very wrong too."

 

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1372670994/1#1

[Ed Cesnalis]

Dan,

 

I read that TIS and ADS-B traffic are for situational awareness and to help you acquire the traffic visually. Its not for traffic avoidance yet your reaction was to dive from the probable 'ghost.'

 

I've done the same thing

[FlyingMonkey]

What good is more situational awareness if you are not going to react to the new situation? I'd be maneuvering too!

[FastEddieB]

What good is more situational awareness if you are not going to react to the new situation? I'd be maneuvering too!

 

From the Skywatch Supplement in the SR22:

 

"1. Traffic information shown on the GARMIN 430 displays is provided as an aid in visually acquiring traffic. Pilots must maneuver the aircraft based only upon ATC guidance or positive visual acquisition of conflicting traffic."

 

Bear in mind, the altitude of traffic is only known in 100' increments. So, in the example given to start this thread, a target showing 100' above could, in fact, actually be right at your altitude, or even slightly below, given normal margins of error in the equipment. Maneuvering blindly in response to traffic alerts could actually CAUSE a midair instead of avoiding one.

 

Anyway, the above is what the manufacturer recommends - one is certainly free to ignore it and do what one sees fit.

[FlyingMonkey]

From the Skywatch Supplement in the SR22:

 

"1. Traffic information shown on the GARMIN 430 displays is provided as an aid in visually acquiring traffic. Pilots must maneuver the aircraft based only upon ATC guidance or positive visual acquisition of conflicting traffic."

 

Bear in mind, the altitude of traffic is only known in 100' increments. So, in the example given to start this thread, a target showing 100' above could, in fact, actually be right at your altitude, or even slightly below, given normal margins of error in the equipment. Maneuvering blindly in response to traffic alerts could actually CAUSE a midair instead of avoiding one.

 

Anyway, the above is what the manufacturer recommends - one is certainly free to ignore it and do what one sees fit.

 

I get where you are coming from, but if you get an alert on a piece of hardware showing traffic at your altitude and on a course to cause a collision within 5 seconds, are you going to attempt to spot the traffic first or make a maneuver? I'd probably at *least* make a fairly aggressive altitude change while looking. I'd rather not get killed because I followed the Garmin manual slavishly...every event is unique especially when time is critical.

[FastEddieB]

Agreed.

 

But I think its fair to ask why a manufacturer would make such a recommendation. Is it because it understands the goals and limitations of its product? Is it because of fear of litigation? Each pilot must decide what they think and whether or not they wish to operate outside of the manufacturers recommendations.

 

I think one fear of the manufacturers is that their modest traffic alerting system may be mistaken for a full-fledged Traffic Avoidance System. With those, in a conflict the pilot of each plane is instructed which course of action to take to avoid the collision. Without that, with each pilot doing what he thinks is best independent of the other, any "fairly aggressive" action can actually make matters worse, kind of like the innocuous "stutter step" people sometimes do when walking towards each other on a collision course. Only not quite so innocuous at maybe two or three miles a minute.

 

Also consider that flight instructors may come at this from a slightly different perspective. Imagine I'm teaching a Cirrus pilot and I say, "The POH supplement says to never take evasive action solely on the basis of a Skywatch warning. Well, I say 'Forget that'. You'd better believe I'd probably at *least* make a fairly aggressive altitude change while looking." Then, two years down the road that pilot does exactly that and slices the tail off of a Cessna. Good news it that the Cirrus pilot has a chute and survives. Bad news is that all the occupants of the Cessna are killed. Further bad news is I'm named in a lawsuit where the Cirrus pilot testifies how I instructed him on what to do in reaction to a Skywatch warning. Oops.

 

But no one here is my student, so do what you feel best. I'm just pointing out recommendations to do with as you please.

[Ed Cesnalis]

I have taken evasive action to avoid traffic either because I was instructed to by ATC or because I had the traffic visually. I have also avoided traffic seen on my ZAON but never confirmed. The former case is a positive experience and the latter leaves me confused and unsure.

 

In most cases I really need a visual, sometimes the ZAON provides good awareness that leads to good separation.

[FastEddieB]

Just curious, what does ZAON have to say on the matter.

 

My experience is solely with the L3 Skywatch in the Cirrus.

[FastEddieB]

Never mind, Google comes through again:

 

Untilyouarefamiliarwiththeoperationsandlimitationsofthisunit,abruptchangesinthecontroloftheaircraft shouldbeavoidedunlesspositiveidentificationwiththetrafficismade,oryouhavebeenorderedtodosoby theAirTrafficController.TheFAA,theirrepresentatives,aswellaspublishedairspaceregulations,alwayssuper- sedeanyindicationgivenbythisunit.

 

Weird copy and paste - insert your own spaces.

 

The initial clause leaves it a little vague as to what they expect after familiarity!

[Dan Kent]

Here is from the Dynon site, in part:

"So two things are going on here:

 

On the TIS, side, I believe Garrett's right about that. TIS basically knows about your aircraft and says "here are all of the threats that you need to know about right now". It basically does all of the screening for you and only tells you about aircraft that are near you.

 

On the ADS-B side, the system doesn't screen traffic in exactly the same way, but it does include information that lets systems like SkyView filter out your own traffic target. From what we've seen, sometimes the ADS-B system doesn't correctly tag your aircraft in the way it should. We're keeping an eye on this (and we've seen it ourselves when flying).

 

The implementation challenge of trying to do anything too clever is that when there's an actual threat nearby, even when it seemingly pops out of nowhere, you want to know about it. Inventing the right screening mechanism that ignores phantom own-ships while including every actual threat is of course very possible, but it's easy to get it very wrong too."

 

http://dynonavionics...=1372670994/1#1

 

Thanks Jim. I had looked at their website but didn't see this. Helps me understand the system better.

[Dan Kent]

From the Skywatch Supplement in the SR22:

 

"1. Traffic information shown on the GARMIN 430 displays is provided as an aid in visually acquiring traffic. Pilots must maneuver the aircraft based only upon ATC guidance or positive visual acquisition of conflicting traffic."

 

Bear in mind, the altitude of traffic is only known in 100' increments. So, in the example given to start this thread, a target showing 100' above could, in fact, actually be right at your altitude, or even slightly below, given normal margins of error in the equipment. Maneuvering blindly in response to traffic alerts could actually CAUSE a midair instead of avoiding one.

 

Anyway, the above is what the manufacturer recommends - one is certainly free to ignore it and do what one sees fit.

 

My spur of the moment thinking was I want to be heading in the same direction to slow down the closing time and speed differential and then try to get to a different altitude. I didn't really think ghosting was possible with ADS-B but Jim's post above indicates it surely is.

[FlyingMonkey]

Agreed.

 

But I think its fair to ask why a manufacturer would make such a recommendation. Is it because it understands the goals and limitations of its product? Is it because of fear of litigation? Each pilot must decide what they think and whether or not they wish to operate outside of the manufacturers recommendations.

 

I think one fear of the manufacturers is that their modest traffic alerting system may be mistaken for a full-fledged Traffic Avoidance System. With those, in a conflict the pilot of each plane is instructed which course of action to take to avoid the collision. Without that, with each pilot doing what he thinks is best independent of the other, any "fairly aggressive" action can actually make matters worse, kind of like the innocuous "stutter step" people sometimes do when walking towards each other on a collision course. Only not quite so innocuous at maybe two or three miles a minute.

 

Also consider that flight instructors may come at this from a slightly different perspective. Imagine I'm teaching a Cirrus pilot and I say, "The POH supplement says to never take evasive action solely on the basis of a Skywatch warning. Well, I say 'Forget that'. You'd better believe I'd probably at *least* make a fairly aggressive altitude change while looking." Then, two years down the road that pilot does exactly that and slices the tail off of a Cessna. Good news it that the Cirrus pilot has a chute and survives. Bad news is that all the occupants of the Cessna are killed. Further bad news is I'm named in a lawsuit where the Cirrus pilot testifies how I instructed him on what to do in reaction to a Skywatch warning. Oops.

 

But no one here is my student, so do what you feel best. I'm just pointing out recommendations to do with as you please.

 

I agree that the recommendations are the way to go in 95% of cases, and we should always try to visually verify traffic. After all, if a contact suddenly "appears" at a quarter mile and same altitude, what are the chances it's a legitimate threat? I'd say very low, but I would not bet my life on that (after all, if a device can give a false contact, can't it also miss one until it gets real close?)...I just wonder if these recommendations are written by pilots, because they sound like they are written by lawyers to reduce liability.

 

I can bet what CT is saying is true, if you get an alert and move to avoid, but never spot the traffic, it would leave one very unsure. I don't have a Zaon, but I get similarly frustrated when near an airport and somebody calls out their position and I look in that location and never see them. Hard to know if the position called out was incorrect, or I'm just not seeing them.

[Dan Kent]

I agree that the recommendations are the way to go in 95% of cases, and we should always try to visually verify traffic. After all, if a contact suddenly "appears" at a quarter mile and same altitude, what are the chances it's a legitimate threat? I'd say very low, but I would not bet my life on that (after all, if a device can give a false contact, can't it also miss one until it gets real close?)...I just wonder if these recommendations are written by pilots, because they sound like they are written by lawyers to reduce liability.

 

I can bet what CT is saying is true, if you get an alert and move to avoid, but never spot the traffic, it would leave one very unsure. I don't have a Zaon, but I get similarly frustrated when near an airport and somebody calls out their position and I look in that location and never see them. Hard to know if the position called out was incorrect, or I'm just not seeing them.

 

I agree with you on this and the thought that the lawyers may have written the direction also. Actually what went though my mind was this an UAV and I just can't spot it?

 

And the key to me was that it just had popped up. If I had been tracking it my eyes are only good for about 3 miles in clear skies, so it often takes me some time to actually spot a small plane, but this recorded as much closer (Dynon audio alert is 20 to 30 seconds out). Now that I know ghosting is in the equation, I will react probably less quickly but would still probably make the maneouver just to be safe. I think I have pretty good situational awareness while flying so if I decide to make a turn I'm pretty confident that there hasn't been a plane secretly flying in formation with me.

[Jim Meade]

Deciding how to react to a traffic alert is a serious proposition. Dan did a diving turn to the left to avoid traffic from his high right. Why not turn into the traffic while changing altitude so as to have a better chance to see it? Was closure rate part of his concern? If the other aircraft were in or about to enter a dive, Dan may not have helped much with a flight path that delayed but didn't obviate the impact.

In this kind of situation, we don't know if the threat is real. We don't know what the target is doing in real time; that the threat trend as presented is what the threat will be in fact. We don't know how the target will react to a collision warning.

 

I didn't find anything really current, but here is a 2007 TCAS study that discusses the above issues and uses as one example the Ueberlingen collision, a tragedy of errors. (The Russian father of one of the victims stabbed the controller to death about a year after the accident.)

http://www.ll.mit.edu/publications/journal/pdf/vol16_no2/16_2_04Kuchar.pdf

 

Indeed, gliders, hot air balloons, crop dusters, planes taking off, planes that present a poor primary target and have not avoidance gear and other threats may not be announced until their present is physically obvious.

 

I'm not sure I'm ready to make automatic responses to unspecified threats.

 

There is no doubt this is a topic that we should start seeing more of in popular aviation press.

[FlyingMonkey]

Dan, I hadn't even thought about UAVs/drones...I guess that is becoming another traffic concern for us though. I really worry about some operator in a bunker flying those things who only has a 30° cone of forward vision, his situational awareness can't possibly be good enough to see and avoid most traffic. My cynical inner voice sometimes whispers that ADS-B was designed just for them to avoid hazards, not really to help us...

 

At my home airport we have a small detachment of National Guard Blackhawk helicopters who are often conducting training. They are really good at calling out their positions on the radio, but even when you know where to look, those charcoal gray helicopters hovering down by the trees are just about invisible. usually all you can see is their strobes, then you can work out the outlines of the actual chopper.

[Jim Meade]

The FAA has a paper out calling for UAS to have "see and avoid" capability by 2016. What that constitutes I have no clue. One can guess it will drive the UAS and maybe RC folks crazy, because it won't be cheap.

 

Right now, the crop dusters are busy putting on fungicides. You can bet they will be as concerned with UAS as they are with the cell and test towers that can pop up at less than 200' and don't need FAA approval or public notification.

[Dan Kent]

 

At my home airport we have a small detachment of National Guard Blackhawk helicopters who are often conducting training. They are really good at calling out their positions on the radio, but even when you know where to look, those charcoal gray helicopters hovering down by the trees are just about invisible. usually all you can see is their strobes, then you can work out the outlines of the actual chopper.

 

As a side note there is also a fairly large contingent of Blackhawk's at my airport also. I had pulled my plane out of the hanger and was just standing there watching one taxi by and it blew my hat off, and really jostled my plane. The next time I saw one coming I moved my plane as far back on the ramp as I could. Just taxiing they put out quite a down blast and I was probably 40 feet away the 1st time.

[FlyingMonkey]

The ADS-B is for traffic awareness and collision avoidance. The FAA is clear on it's intended use and implementation.

 

GPS was developed for military use only. For years it was not usable by civilians, and when it was the signal accuracy was intentionally degraded. Now it's a general use consumer product, but few realize it's all still completely controlled by the Air Force Aerospace command, who can shut the whole enchilada down whenever they choose.

 

If I were about to put ten thousand drones in the air with civilian and commercial traffic, I'd think long and hard about how to avoid the PR nightmare of drones crashing into airplanes. A solution I might consider would be an updated and integrated data and radar system to provide greater traffic and weather awareness to my drone drivers so they could get awareness approaching what a pilot might have looking around with his MK 1 eyeballs.

 

Of course, this system would only be of maximum use if all aircraft participate so my drone drivers can avoid them (or maybe even find, track, and surveil them if I so choose...). Perhaps I could mandate it for installation in all aircraft, say by 2020. In order to get pilots to comply, I'd offer the carrot of letting them see the traffic as well (though maybe I would mask certain special homeland security traffic from their view...). This would actually help me in that all these general aviation chumps would also be working to avoid crashing into my important drones. At least the ones I allow them to see.

 

Believe the FAA or any government agency is giving you the complete picture or has your interests at heart at your peril.

[Jim Meade]

C'mon, Andy, take a couple of deep breaths.

 

Globalnaya navigatsionnaya sputnikovaya sistema

 

More and more use it.

[Craig]

Of course, this system would only be of maximum use if all aircraft participate so my drone drivers can avoid them (or maybe even find, track, and surveil them if I so choose...). Perhaps I could mandate it for installation in all aircraft, say by 2020. In order to get pilots to comply, I'd offer the carrot of letting them see the traffic as well (though maybe I would mask certain special homeland security traffic from their view...). This would actually help me in that all these general aviation chumps would also be working to avoid crashing into my important drones. At least the ones I allow them to see.

 

http://digital.gcn.com/?iid=79907&startpage=19#folio=18

 

Exactly.

[FlyingMonkey]

http://digital.gcn.c...age=19#folio=18

 

Exactly.

 

See, just because I'm paranoid doesn't mean they are not out to get me!

[Mick]

They are out to get all of us.