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ADS-B Traffic System Report

JoeLofton

Well Known Member
I just completed a 2500nm round trip (spread over 2weeks) after installing an ADS-B system in my RV-3 (Garmin 796 GPS, Garmin GDL-39 ADS-B receiver, Trig TT-21 Mode S transponder). Observations on the traffic side of the system:

1) The system was accurate. The targets that I was able to see were where the system reported them.

2) There were lots more aircraft in relatively near proximity than I expected. I passed within a couple miles of several that I could not locate visually. Hardest to spot were those below that tended to get lost in the ground clutter. An aircraft a mile or two away is a small visual target. I'm sure my little airplane is even harder to spot.

3) The system added a layer of safety. Twice I jogged off track a couple of miles to give space to an aircraft that appeared to be converging at my altitude.

4) Of course the highest density of traffic was around airports. The system helped me keep track of other planes approaching airports where I was landing.

5) Still have to keep the eyeballs outside the cockpit most of the time - the system doesn't show birds, for instance. And, flying low because of headwinds, I came upon a couple of towers in the middle of nowhere in northern MS that reached almost 2500ft AGL - truly scary things.

I was pleased with the system - good to have more info in the cockpit. The weather side worked well also, once at enough altitude to see a ground station.

Joe Lofton
 
Nice report.

I have ADS-B in my Rocket and around MSP it is great. When flying to Oshkosh, though, I found the reported traffic to not be in the place the system said it was, mostly in position but at least once in altitude. This was in the Ripon area and also to the northwest of it. Very perplexing. This happened to me 2 years in a row. Perhaps the targets were far enough from the radar site that position was subject to a large error margin, though I'd think the altitude would always be close.

So while it's nice, don't count on the reported traffic to always be where it is displayed.
 
I found the reported traffic to not be in the place the system said it was, mostly in position but at least once in altitude. This was in the Ripon area and also to the northwest of it. Very perplexing. This happened to me 2 years in a row. Perhaps the targets were far enough from the radar site that position was subject to a large error margin, though I'd think the altitude would always be close.

So while it's nice, don't count on the reported traffic to always be where it is displayed.

This may be because when flying into Osh during the show, xponders are suppose to be set to standby in that area. Primary radar targets can move a great deal in relation to you between sweeps and the latency built into the uplink.

Altitude of Mode-C targets are only as accurate as the altimeter/encoder/static system install. Static position errors here can be significant and can go unnoticed during the typical xponder/alt/static checks.

We also know that non-certified position sources are being used by many at this time to feed position/velocity data to aircraft with ADS-B out. These sources may or may not be accurate.

As a whole, I have found the TIS-B uplink service and air to air ADS-B accuracy to be amazing. As always....Trust but verify with eyeballs on the target!
 
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Me and my ADS-B shadow

Just bought a skyradar d2 and was flying in Tuscon / Phoenix area when I saw a return right below me at nearly the same altitude. I turned and climbed and it followed me. I soon figured out that it was representing my aircraft. I don't have an ADS-B transmitter though so it's not getting my position data from me. My guess is that ATC is feeding position data but I didn't think it could do or is supposed to work that way.


From the image, my position is the blue aircraft at the bottom center. Underneath that symbol is my aircraft position shown by ADS-B.

Anybody else seen this?
 
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Primary radar targets can move a great deal in relation to you between sweeps and the latency built into the uplink.

TIS-B shouldn't be broadcasting tracks from primary-only targets.

My guess is that ATC is feeding position data but I didn't think it could do or is supposed to work that way.

In all likelihood an aircraft in your vicinity was broadcasting ADS-B Out, triggering the system to transmit TIS-B tracks. Since you probably had your Mode C transponder on, a secondary radar on the ground saw you and put your track into TIS-B - that's how you saw yourself on the iPad.

Dave S
 
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encoder alt

I too was freaked out by the traffic 100 feet directly underneath me which poped up itermittently. I figured out that it showed up when my foreflight altitude differed from my encoder alt. by more than a little. I dont have adsb-out, so I'm just getting shared data. Overall, I'd still rate the benefit as outweighing the imperfections of the system. It's amazing the traffic out there that would have gone unseen without it.
 
Have Skyview with ADSB in and out. The ADSB weather radar imagary is cool - but I don't fly into that stuff, just around. What turns out to be REALLY cool for marginal VFR days is so easily calling up the current weather at airports on and off your route. Helps figure the best path very easily on the Skyview. Had similar positive experiences with the traffic - really helped me spot planes lower than myself, seeing overtaking traffic (would NEVER spot that visually) and in a couple of cases making an adjustment based on intersecting tracks. HUGE safety improvement.

Bill H. N412BR "Sweetie" RV12 Skyview 80 hours flying.
 
TIS-B shouldn't be broadcasting tracks from primary-only targets.

Dave S

I have not seen anything officially saying they will or won't. I have seen targets that I was pretty sure were primary targets however. One day I saw a powered power chute.

I have also spotted a few aircraft visually that did not show up so who knows....
 
Just bought a skyradar d2 and was flying in Tuscon / Phoenix area when I saw a return right below me at nearly the same altitude. I turned and climbed and it followed me. I soon figured out that it was representing my aircraft. I don't have an ADS-B transmitter though so it's not getting my position data from me. My guess is that ATC is feeding position data but I didn't think it could do or is supposed to work that way.


From the image, my position is the blue aircraft at the bottom center. Underneath that symbol is my aircraft position shown by ADS-B.

Anybody else seen this?

My skyview has traffic alerted me several times at the bottom of a loop or Cuban. Gets your attention for sure. Adsb is a huge safety feature flying north/south along the Florida coast (human guided propeller cruise missiles;)). I also use my 8 to commute to Orlando international. It's an amazing enhancement to situational awareness.
 
TIS-B shouldn't be broadcasting tracks from primary-only targets.

I was under the impression that ADS-B TIS will broadcast the same traffic picture ATC controllers see on their scopes, which includes primary targets if they are within radar coverage.

I was flying near Brenham airport in Texas (11R) and picked up an aircraft landing there on my ADS-B. It was a Piper Cub that didn't have an electrical system of any kind with the pilot using a handheld for communications.

I wonder if something else was happening in this case?

:cool:
 
I was flying near Brenham airport in Texas (11R) and picked up an aircraft landing there on my ADS-B. It was a Piper Cub that didn't have an electrical system of any kind with the pilot using a handheld for communications.
Interesting...was there an altitude associated with the Cub's track symbol on your ADS-B display?

Dave
 
Interesting...was there an altitude associated with the Cub's track symbol on your ADS-B display?

Dave

The targets that I have assumed were primary targets displayed by TIS-B did not have any altitude data on them.
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IDUNNO
 
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Nope, no altitude was displayed, just the track.
Wow...looks like my info was bad on primary tracks, thanks for the updated info!

I was part of the team that started the ADS-B program back in 2005-2007, and in my day job I deal with ADS-B avionics equipage for the Air Force and DoD. There are a lot of details about the ground segment (radar, TIS-B, ADS-R) that have obviously changed since I worked with that aspect of the system.

Cheers,

Dave
 
many of the older radar sites may have an adsb transceiver but still be incapable of tracking a primary target. there are still a few ASR-8 stations out there that are not even digital radar yet.

i don't know whether or not primary targets would be displayed on TIS-B, but if they are, one still needs a digital radar to do so. so there would be parts of the country where this is not be possible. many FAA facilities operate on hand-me-down tech from the larger approach controls in the area, which is usually pushing 20, sometimes 30 years old
 
I don't know if this has been mentioned yet because I didn't read the entire thread, but there is an important thing to note on altitude. I have flown extensively now with the Stratus and ads-b in/out on Dynon and GRT with Navworx. The altitude in the Dynon and GRT are much more accurate than the Stratus because it is comparing the altitude reported to your GPS altitude through the portables, but comparing to your static altitude with Baro correction on the Dynon and GRT. I regularly see a difference of up to 500 ft, and sometimes more than that. Position seems to be fairly accurate between the two types of systems.
 
Jesse,

I also have NavWorx/GRT and Stratus/Foreflight. Often GRT displays more targets than Foreflight. GRT usually filters out my own Xponder returns. When turned it on inflight, Foreflight will show a yellow warning at my position for a few seconds than filter it out.

One day I turned Stratus on in my study I saw Embry-Riddle traffic (tail numbers end with ER) queued up for landing. They are all ADS-B out equipped. Photo motion created by Google+ based on a few photos.
IMG_20131025_081336_389-MOTION.gif


A few days a go I went pick up a friend who flew his TBM to Sarasota for some work. I heard him checking in with Tampa Approach. Looked down on my iPad I saw him 2,500' above me. Looked out side I saw his plane flew by. It was really neat being able to do that.
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GOPR0123.JPG
 
AIM Section 4.5.8

Wow...looks like my info was bad on primary tracks
I did some digging in the AIM. Section 4.5.8 has a pretty good description of how TIS-B works, including the following words -

"Only transponder-equipped targets (i.e., Mode A/C or Mode S transponders) are transmitted through the ATC ground system architecture. Current radar siting may result in limited radar surveillance coverage at lower altitudes near some airports, with subsequently limited TIS-B service volume coverage. If there is no radar coverage in a given area, then there will be no TIS-B coverage in that area."

I'm not sure why folks on this thread would be seeing TIS-B tracks from non-transponder aircraft. It *may* be possible that a controller can "hook" a primary radar target on his or her display, creating a track in the system that's sent over TIS-B, but that'll take some more research to figure out.

The bottom line is that based on these words in the AIM, you shouldn't count on seeing non-transponder aircraft on TIS-B and don't assume that if there's nothing on your display, that there's really no traffic there. TIS-B is intended as a situational awareness aid, helping but not replacing good visual "see and avoid" practices.

Fly safe,

Dave
 
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The bottom line is that based on these words in the AIM, you shouldn't count on seeing non-transponder aircraft on TIS-B and don't assume that if there's nothing on your display, that there's really no traffic there. TIS-B is intended as a situational awareness aid, helping but not replacing good visual "see and avoid" practices.

Fly safe,

Dave

I totally agree. This is true regardless.

No traffic solution replaces "Eyeballs Outside"!
 
Missed target

On my last flight around the PHX class B area I was under the final approach path for PHX looking at traffic depicted on Foreflight with stratus, when an airliner passed right over me(I was under bravo airspace), which was not depicted on Foreflight. Other airline traffic farther out in the patern was depicted. Reminder that the system has limitations. Earlier in the flight I was alerted to one of the million flight school Pipers around here which was same alt., directly head on with me, so I still like ADSB!
 
I did some digging in the AIM. Section 4.5.8 has a pretty good description of how TIS-B works, including the following words -

"Only transponder-equipped targets (i.e., Mode A/C or Mode S transponders) are transmitted through the ATC ground system architecture. Current radar siting may result in limited radar surveillance coverage at lower altitudes near some airports, with subsequently limited TIS-B service volume coverage. If there is no radar coverage in a given area, then there will be no TIS-B coverage in that area."

I'm not sure why folks on this thread would be seeing TIS-B tracks from non-transponder aircraft. It *may* be possible that a controller can "hook" a primary radar target on his or her display, creating a track in the system that's sent over TIS-B, but that'll take some more research to figure out.

I know that primary tracks get automatically "hooked" by the computer if they fall within a set of parameters and are then displayed on the scope. No expanding information (altitude/tail#/squawk) is available but the heading/speed does show up. At least it did back when I was a controller.

The bottom line is that based on these words in the AIM, you shouldn't count on seeing non-transponder aircraft on TIS-B and don't assume that if there's nothing on your display, that there's really no traffic there. TIS-B is intended as a situational awareness aid, helping but not replacing good visual "see and avoid" practices.

AMEN to that! Keep your eyes looking for traffic outside the cockpit not on your equipment. ADS-B is there to supplement, NOT REPLACE, your traffic scan.

:cool:
 
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