A Day of Firsts, Including an ADS-B Anomaly

[Jay Honeck]

You would think after over 20 years of flying, and over 5 years of flying on the Texas coast, I wouldn't run into anything new anymore, but yesterday's flight was full of new experiences.

1. First time an entire sector's radar was down. Corpus Christi Approach could give us the barometric pressure -- and nothing else. Their radar was completely INOP.

2. First time hearing Spanish chatter on Unicom. 123.0 was non-stop Espanol. Dunno if it was someone local, or if we were picking up Mexico.

3. First time ADS-B reported another airplane's altitude incorrectly.

Here's what happened with #3: We were coming in to land at our home 'drome, KTFP, T.P. McCampbell Airport. Mary was PIC, and I was watching traffic on our tablet in the back seat, while she was watching it on our EFIS up front. On Unicom we heard a Navy T-34 Turbine Mentor coming in for a low approach to Rwy 31, and it was showing up on both of our screens as "+32" -- meaning it was 3200' above us.

I looked out the window, and there he was, at our altitude, or a bit below. WTH?

Here are the particulars. I was viewing ADS-B traffic on our Nexus 7, using Garmin Pilot and the GDL-39. This is a passive "ADS-B In" only system. Mary was viewing ADS-B traffic a completely independent system: Our GRT Avionics Horizon HXr EFIS, using Skyradar and two aircraft-mounted external antennas. This is an active "ADS-B In/Out" system.

Both systems showed exactly the same thing: The plane was moving on the map, exactly as the plane outside was moving, but it was showing up at 3200' above us.

(Yes, I looked through the bubble canopy to see if there was a trailer 3200' above the other guy. Nope.)

Anyone know how this could happen? Could it be a glitch with the Navy trainer's transponder? Or could it somehow be related to Corpus Approach being FUBAR?

 

[SixPapaCharlie]

2. First time hearing Spanish chatter on Unicom. 123.0 was non-stop Espanol. Dunno if it was someone local, or if we were picking up Mexico.

I had this over the summer.
I was flying between Austin and Dallas and a good 5 minutes of Spanish radio. I was on FF and had to tell them "I am hearing Mariachi's"

 

[Jim_R]

You say your systems both only show you the altitude delta, not the actual altitude of the bogey? That seems weird to me.

My first thought is that you were somehow misinterpreting the data you were looking at. You're 100% sure it wasn't telling you he was 32' above you?

My system displays actual altitudes, but uses colors to help highlight altitude deltas; like red within 500', yellow 501-1000', blue >1001'. Do your systems provide secondary cues like that? Did they agree with him being 3200' above you?

 

[jtheune]

I bet the t34 did not have adsb out so yiu were seeing the radar generated information given the other radar problems i would say that was the problem

 

[Bob Noel]

It is possible for an aircraft to appear to have an incorrect altitude when there are multiple radars interrogating the aircraft. If the radar receives a Mode A reply when it is expecting a Mode C, it can interpret the Mode A as an altitude.

 

[Rigged4Flight]

I know everyone is thinking it, so I'll go ahead and say it.

Aliens. And they have decided to learn only one human language, and for some reason they chose Spanish.

 

[Pedals2Paddles]

I agree. It's quite likely the T-34 does not have a 1090ES transponder, or a 978 UAT. In other words, the T34 probably doesn't have his own ADS-B out. His aircraft is a TIS-B target on your display, which is generated by ATC radar data being fed back into the ADS-B system. Given the radar system was completely hosed, that would completely explain the erroneous altitude.

 

[dell30rb]

His aircraft is a TIS-B target on your display, which is generated by ATC radar data being fed back into the ADS-B system. Given the radar system was completely hosed, that would completely explain the erroneous altitude.

X2

Additionally, could have been a malfunctioning mode C transponder on the other plane. But given ATC was having trouble with their radar anyway, that is the most likely culprit

 

[Arrow115]

Jay, I was in your neck of the woods yesterday. It was a great day to be flying along the coast. When I was coming in to KRAS, I noticed that I couldn't pick up the weather via xm, so I had to do it the old fashioned way. Maybe that was another effect of the outage. I was surprised there wasn't more traffic for such a nice day after weeks of bad weather.

 

[Pedals2Paddles]

When I was coming in to KRAS, I noticed that I couldn't pick up the weather via xm, so I had to do it the old fashioned way. Maybe that was another effect of the outage.

Actually this seems to lend more support to the theory of space aliens invading Mexico causing broadband spectrum interference.

 

[Rigged4Flight]

Actually this seems to lend more support to the theory of space aliens invading Mexico causing broadband spectrum interference.

That's what I'm sayin'. And just because I'm crazy doesn't mean it ain't so!

 

[Jay Honeck]

X2

Additionally, could have been a malfunctioning mode C transponder on the other plane. But given ATC was having trouble with their radar anyway, that is the most likely culprit

Interesting. Mary and I briefly discussed this possibility, but rejected it under the (probably false) assumption that SURELY the two systems (ground based radar and ADS-B wouldn't be inter-connected!


I thought ADS-B was supposed to ultimately supplant ground based radar? I thought it was supposed to be an added layer of redundancy in the national airspace system?

If one outage can cause the other to fail, I would say we have a potential problem, down the road.

 

[Jay Honeck]

Jay, I was in your neck of the woods yesterday. It was a great day to be flying along the coast. When I was coming in to KRAS, I noticed that I couldn't pick up the weather via xm, so I had to do it the old fashioned way. Maybe that was another effect of the outage. I was surprised there wasn't more traffic for such a nice day after weeks of bad weather.

Yeah, it was a spectacular afternoon to fly -- and we had the airspace pretty much to ourselves.

We are planning to fly to Hobby today, for their monthly Wheels and Wings fly-in at the 1940 Air Terminal Museum. Conditions couldn't be better, so we shall see if our pilot brothers and sisters take to the sky again.

(The flying weather has been so awful that we've had just one fly-in guest at the hotel since November! It's been the longest stretch of terrible weather since we moved to Texas.)

 

[Bob Noel]

I thought ADS-B was supposed to ultimately supplant ground based radar? I thought it was supposed to be an added layer of redundancy in the national airspace system?

Nope. ADS-B needs ground-based radar to validate ADS-B out messages.

Had ADS-B been properly designed (e.g., including a means to validate ADS-B out messages), then there wouldn't be a need for yet more ground infrastructure.

 

[jtheune]

Interesting. Mary and I briefly discussed this possibility, but rejected it under the (probably false) assumption that SURELY the two systems (ground based radar and ADS-B wouldn't be inter-connected!


I thought ADS-B was supposed to ultimately supplant ground based radar? I thought it was supposed to be an added layer of redundancy in the national airspace system?

If one outage can cause the other to fail, I would say we have a potential problem, down the road.

The ground based radar is how you see all the non ADSB traffic on your ADSB display. It interrogates the transponders and adds that data to the ADSB traffic stream

 

[texasag93]

With the radar down, lots of coke and weed were being imported.

 

[Jay Honeck]

We are planning to fly to Hobby today, for their monthly Wheels and Wings fly-in at the 1940 Air Terminal Museum. Conditions couldn't be better, so we shall see if our pilot brothers and sisters take to the sky again.

So we flew to HOU today for the (as always wonderful) Wings and Wheels event at the 1940 Air Terminal Museum.

Despite perfect weather and a wonderful venue, it was us, an RV-7A, and a Thorpe.

That's it -- three fly-in aircraft, at a major on-airport event in one of the largest metro areas in America?

There were lots of drive ins, thankfully, with lots of kids, and good food. We gave away over $500 worth of free hotel spiffs, and had a GREAT time -- but where in the hell were the fly-in airplanes???

*sigh* This is so frustrating. Every pilot I meet laments the lack of fly-in events (compared to the "old days"), and the diminished opportunities to fly -- and then, when someone puts out the effort to create a cool aviation destination, they can't be bothered...

If you want to know why there are fewer cool places to fly, if you want to know why all the on field restaurants are closing, and there are fewer fly-ins to attend, look in the mirror!

Get out and FLY, people!

 

[JGoodish]

Nope. ADS-B needs ground-based radar to validate ADS-B out messages.

Had ADS-B been properly designed (e.g., including a means to validate ADS-B out messages), then there wouldn't be a need for yet more ground infrastructure.

There isn't a need for ground-based infrastructure for an ADS-B In equipped aircraft to display traffic information from one or more ADS-B Out equipped aircraft. The GBT only transmits TIS-B and retransmits ADSR data based on an ADS-B Out client's capabilities.


JKG

 

[John Collins]

There are many ways the altitude can be off. Either the reference altitude in your own aircraft or the target may have an error. With grey codes, a single bit can throw the altitude off by over 30,000 feet.

 

[comanchepilot]

gotta wonder why the FAA did not just take the AWACs feed and run with it . . .

 

[Bob Noel]

There isn't a need for ground-based infrastructure for an ADS-B In equipped aircraft to display traffic information from one or more ADS-B Out equipped aircraft. The GBT only transmits TIS-B and retransmits ADSR data based on an ADS-B Out client's capabilities.


JKG

You need the ground infrastructure to validate the ADS-B messages (done via ground radar or multi-lateration).

 

[Pedals2Paddles]

No you don't. ADS-B IN receivers can and do receive direct air-2-air data from other ADS-B out equipped aircraft. There is no ground validation. In fact, the ground infrastructure (TIS-B ) will not rebroadcast the target for an ADS-B out equipped aircraft because it knows you will already be receiving it via Air-to-Air. It would be a waste of bandwidth to process and transmit that which can be received directly.

 

[Bob Noel]

No you don't. ADS-B IN receivers can and do receive direct air-2-air data from other ADS-B out equipped aircraft. There is no ground validation. In fact, the ground infrastructure (TIS-B ) will not rebroadcast the target for an ADS-B out equipped aircraft because it knows you will already be receiving it via Air-to-Air. It would be a waste of bandwidth to process and transmit that which can be received directly.

if you were responding to my post, actually you do. ADS-B out messages received directly from an aircraft have zero validation without the ground infrastructure.

 

[JGoodish]

if you were responding to my post, actually you do. ADS-B out messages received directly from an aircraft have zero validation without the ground infrastructure.

What "validation" do you think is required? The GBTs provide TIS-B and ADSR traffic service, but they do not transmit ADS-B Out targets to ADS-B client aircraft that report ADS-B In capability on the target's frequency. In other words, the air to air capability does not rely on ground stations.


JKG

 

[Pedals2Paddles]

if you were responding to my post, actually you do. ADS-B out messages received directly from an aircraft have zero validation without the ground infrastructure.

You're absolutely right. Direct air-to-air ADS-B is not validated. BECAUSE It isn't supposed to be. It doesn't have to be. And it isn't expected to be. There is nothing to validate and no reason to validate it. You're proclaiming a problem that doesn't exist. This is like proclaiming that the FAA isn't validating my selection of macaroni and cheese for dinner.

 

[jsnapp]

Interesting. Mary and I briefly discussed this possibility, but rejected it under the (probably false) assumption that SURELY the two systems (ground based radar and ADS-B wouldn't be inter-connected!


I thought ADS-B was supposed to ultimately supplant ground based radar? I thought it was supposed to be an added layer of redundancy in the national airspace system?

If one outage can cause the other to fail, I would say we have a potential problem, down the road.

There are three different types of signals that you can receive on your ADS-B in unit.

1) ADS-B (airplane-to-airplane). If another aircraft is equipped with ADS-B out it will send a message out about every second with its X/Y and altitude. The altitude should be both baro and GPS. This message could be sent out over its 1090ES transponder or its UAT transmitter depending on what is installed. A dual band received like the Garmin GDL39 will show both of those. If all planes had ADS-B out and we could receive on both bands, that is all we would be seeing. You also do not have to have ADS-B out or an ADS-B aircraft nearby to see this traffic

2) TIS-B (Ground to airplane). If you have ADS-B out or there is an aircraft near by that has ADS-B out (and they are requesting TIS-B uplinks), ATC will transmit to TIS-B traffic messages that show the position of other aircraft that are not ADS-B out equipped. The TIS-B traffic message is made from data from the secondary radar returns of ATC and will send the other aircraft's position and altitude if they are sending Mode C altitude data.

3) ADS-R (Ground to airplane) if you have an ADS-B out or there is an aircraft nearby that has ADS-B out (and is requesting ADS-R messages), ATC ground stations will send ADS-R retransmissions of 1090ES traffic on the 978 UAT band and will send 978 UAT traffic on the 1090ES band. If you have a dual band receiver like the GDL 39, this is not a lot of use since you will be seeing the original air to air signal.

If you were seeing the wrong altitude, if the aircraft was (1), there was a problem with their system. If the traffic was (2), it was an issue with their transponder, encoder or ATC. There are still a lot a bugs in the TIS-B data being sent by the ground stations. I have seen traffic that is on TIS-A (old Mode S traffic) that is not on TIS-B but I see it, traffic that is on TIS-B but not TIS-A that I have never visually seen and ATC does not see it (ghost traffic). Once they get all the other bugs figured out with ADS-B for ATC use, I hope they will start looking at the TIS-B issues.

Remember ADS-B in is a good second set of eyes but your eyes are still the primary way to spot traffic.

 

[coloradobluesky]

Does having ADS-B help in the pattern? Or close to the airport? Out in the boonies, yeah there are planes, but the most likely place is near an airport.

 

[Jay Honeck]

Does having ADS-B help in the pattern? Or close to the airport? Out in the boonies, yeah there are planes, but the most likely place is near an airport.

Yes!

When we are coming into TFP, it is not unusual to have a couple of Navy boys in the pattern, a few bug smashers, and the DHS and/or Coast Guard helicopters up. Combine this with more Navy guys enroute to wherever, and the Big Sky can look pretty crowded.

The ability to see precisely where everyone is often determines our pattern entry. If a full pattern is warranted, that's what we do. Conversely, if it is apparent that a straight in will blend best with traffic, we do that.

ADS-B isn't perfect, yet, but it's a great add-on to the ol' Mark V eyeballs...

 

[Bob Noel]

You're absolutely right. Direct air-to-air ADS-B is not validated. BECAUSE It isn't supposed to be. It doesn't have to be. And it isn't expected to be. There is nothing to validate and no reason to validate it. You're proclaiming a problem that doesn't exist. This is like proclaiming that the FAA isn't validating my selection of macaroni and cheese for dinner.

Without validatation there is nothing to detect malicious spoofing.

You are putting your head in the sand ignoring a flaw in the ADS-B architecture.

Perhaps you should tell the FAA not to waste mucho dinero on the ground radar validation processes or the multilateration equipment.

 

[Pedals2Paddles]

I'm not putting my head anywhere. You proclaimed that ADS-B requires ground based radar to validate it's own data. That is untrue. The data flows without validation now. There is no validation now. And there could never be any validation for air-to-air transmissions anyway.

You can have the opinion it should have validation and that it is a poor design without it. But that completely defeats the purpose to begin. The whole point (one of them) from the beginning was to not depend on ground radar. To proclaim it is a needed aspect in operation today is simply wrong.

 

[JGoodish]

Without validatation there is nothing to detect malicious spoofing.

You are putting your head in the sand ignoring a flaw in the ADS-B architecture.

Perhaps you should tell the FAA not to waste mucho dinero on the ground radar validation processes or the multilateration equipment.

I am interested in the source of your information, because it does not appear to accurately reflect the design nor operation of the ADS-B system.

ADS-B ground transmitters do not retransmit ADS-B traffic data to clients who report an ability to receive that data via air to air transmission. In cases where traffic is rebroadcast via ADSR, time is of the essence. The GBTs will transmit radar-derived targets to ADS-B clients via TIS-B. As far as I am aware, MLAT is a proposed long-term backup to the ADS-B system (as radar systems are decommissioned), but not a dependency of it.


JKG

 

[Pedals2Paddles]

The only system I'm aware of in the USA that actually uses MLAT for normal operations is ASDE-X ground traffic systems at maybe 30 something airports. And ASDE-X will continue to function without it if it goes down. It isn't used for air traffic. Raise your hand if you see that happening in the next decade or two?? lol. In any case, I don't know what you'd be validating even with MLAT. It doesn't require validation any more than ADS-B, which is zero.

Ironically though, FlightRadar24.com has managed to setup and elaborate MLAT air traffic surveillance network, for free, around the globe. It's quite amazing, yet quite simple.

 

[JGoodish]

The only system I'm aware of in the USA that actually uses MLAT for normal operations is ASDE-X ground traffic systems at maybe 30 something airports. And ASDE-X will continue to function without it if it goes down. It isn't used for air traffic. Raise your hand if you see that happening in the next decade or two?? lol. In any case, I don't know what you'd be validating even with MLAT. It doesn't require validation any more than ADS-B, which is zero.

You are correct that they are two distinct systems.

I didn't think that the FAA had committed to MLAT as a backup, only that it has been proposed as a potential backup should there be an issue with the GPS system. However, I haven't followed the nuances of FAA commitments very closely in the last couple of years.


JKG

 

[Pedals2Paddles]

My recollection is the same. And I did some searching on the matter to see if anything had changed. Nada. They were talking about it being a possible backup about 5 years ago. Not much has been said or done since. In fact most of the hits are actually vendors talking about how great their product that nobody uses is. Typical.

 

[N801BH]

Yes!

When we are coming into TFP, it is not unusual to have a couple of Navy boys in the pattern, a few bug smashers, and the DHS and/or Coast Guard helicopters up. Combine this with more Navy guys enroute to wherever, and the Big Sky can look pretty crowded.

The ability to see precisely where everyone is often determines our pattern entry. If a full pattern is warranted, that's what we do. Conversely, if it is apparent that a straight in will blend best with traffic, we do that.

ADS-B isn't perfect, yet, but it's a great add-on to the ol' Mark V eyeballs...

EAA had a great webinar just last week on the subject....

Pretty informative if you ask me....

http://www.eaavideo.org/video.aspx?v=3990999242001

 

[flyingron]

Interesting. Mary and I briefly discussed this possibility, but rejected it under the (probably false) assumption that SURELY the two systems (ground based radar and ADS-B wouldn't be inter-connected!

Of course they are interconnected.

I thought ADS-B was supposed to ultimately supplant ground based radar? I thought it was supposed to be an added layer of redundancy in the national airspace system?

That only works if everybody in your airspace is playing ADS-B OUT. If that's not the case (and you still have 6 more years until it's mandatory in SOME airspace and it will never be required in others) you'll need the TIS-B relay.