uAvionix skyBeacon: A false sense of security?

[Doug Reid]

Question for John Collins..on most of the issues with com interference that you reference in your post, were these ADS-B installs mostly associated with GPS antennas mounted on the fuselage or were they Skybeacon installs ?

I am aware of the notch filter requirement and have not needed to install one on about 2 dozen GDL82 installs so far. Almost all have either KX155 or KX175 coms.

 

[John Collins]

They were GPS navigator installations, but anytime a GPS is installed, it should be subject to the type of post installation checking described. If one doesn't check the frequencies for interference, then it is all dependent on the flight involved if one of the frequencies is used or not on the flight. The fact that the NIC or NAC is mostly good, suggest to me that sometime during the test flight, a frequency was used that clobbered the WAAS GPS reception. WAAS installations use antennas with greater gain requirements and lower mask angle than standard non WAAS GPS, so I would suspect that they would be more susceptible to interference. In my own aircraft, I had an issue with a KY197 that interfered, but not through the antenna even with a notch filter, but through RF leakage through the display. It was something that degraded over time. I could put Mu-metal or an antistatic bag over the front of the unit, and it would pass with flying colors. I replaced the KY197 and that solved the issue. Investigating the issue with the KY197 showed the RF energy was coming from an internal shielded cable to the modulator and it was probably caused by corrosion and internal grounding issues, so replacing the radio was the cheapest and most reliable means of resolving the issue.

 

[MRC01]

... I wonder why avionics shops want nothing to do with a device that installs in 1/2 hour and requires no other changes to the aircraft? Hmmm
I don't blame you for not liking them if you had a bad experience. I'd be the same. But avionics shops don't avoid them because they don't work. Quite the opposite.
...

A local Avionics shop (Spencer's at KPLU in Puyallup WA) installed dual AV30Cs in my airplane and removed the vac system. Did a great job, very experienced, good pricing, highly recommended. However, they won't touch SkyBeacon or TailBeacon. The reason is that while they are quick & easy 90% of the time, that other 10% where they don't work properly, they can be very difficult to troubleshoot and get working. Sadly, my experience is in that 10%. It works almost well enough, but not quite well enough, to pass.

In my case getting it to work well enough to pass a PAPR involves extensive troubleshooting, multiple test flights, assessing the detailed logs, and several other changes to the aircraft. To summarize:

1. Improve rudder to fin grounding across the hinge, to prevent intermittent power loss.
2. Replacing old panel switches, to prevent intermittent power loss.
3. Installing lowpass/notch filters on the com radios, to prevent radio interference from jamming the GPS.

Those may sound like simple changes, but they belie the many hours of test flights & troubleshooting to determine that these were the 3 things that needed to be done. And I'm not even sure this will be sufficient. Once these changes are done I'll have more test flights to see what's next...

 

[Randomskylane]

So, if everything works fine except when you transmit 121.5 on your king 155 or whatever, why do you fail the papr test? It’s probably a few minutes of disruption in a (say) 30 minute flight.

if you never transmit on that radio, do you pass papr? In other words, it passes on ground with everything on

tia

 

[MRC01]

On the ground, the RT-385 radio doesn't affect the Tailbeacon GPS no matter how much I xmit. The MX-385 does, but only on specific frequencies like 121.15 that I don't use in flight. Yet in the air, both radios will cause the Tailbeacon GPS to drop. Apparently, ground testing is not fully representative of in-flight behavior.

More accurately, the GPS isn't lost, but the NIC/NAC quality flags drop below acceptable levels. So the PAPR test fails. The PAPR test doesn't tell you where it failed, only that NIC/NAC were not high enough. So I contact the FAA to get the detailed track for the flight. You can't do this through the PAPR form, but you email them at 9-AWA-AFS-300-ADSB-AvionicsCheck@faa.gov. When they reply with your track log, load it in Google Earth and it shows the GPS NIC/NAC quality flags dropped exactly where I was transmitting on the radio. That can't be a coincidence.

For example, here's a recent flight:


The track is solid green even when departing KBFI talking on 118.3, until I got to the SW end of Bainbridge Island, turns red exactly where I transmitted to announce my position for KPWT on 123.05. Then green, then turned red again on each additional radio call. On the next flight departing KPWT (not shown), the Tailbeacon stayed green even while I was transmitting on 123.05 but dropped when I started transmitting on 118.3 for KBFI. So the GPS quality doesn't always drop when I transmit, but the only time it does drop is when I transmit.

 

[MRC01]

I was just reading that DME uses the frequency range 960 - 1200 Mhz, which is much closer to the 1500 Mhz of GPS. And unlike VORs which are receive-only at the aircraft, DMEs actually transmit. So it would seem that DME might also jam GPS reception. If so, fixing this wouldn't be as easy as a com radio xmit, because the frequencies are so much closer, a simple lowpass filter doesn't seem possible.

 

[Lindberg]

1. Turn radios off.
2. Fly test flight.
3. Pass PAPR test.
4. Profit!

 

[MRC01]

I can't do that. My home airport is a class D.

Today I made 2 flights with filters installed on both radios. The filters are TED 4-70 which are supposedly -52 dB at 1.5 GHz. The filters are working because during ground testing I can no longer get the Tailbeacon GPS to drop when transmitting on com radios. However, both flights still failed yet again due to NIC/NAC. Looks like some progress since my minimum NIC is now 6 instead of 0. But not good enough.

 

[Lindberg]

I can't do that. My home airport is a class D.

Today I made 2 flights with filters installed on both radios. The filters are TED 4-70 which are supposedly -52 dB at 1.5 GHz. The filters are working because during ground testing I can no longer get the Tailbeacon GPS to drop when transmitting on com radios. However, both flights still failed yet again due to NIC/NAC. Looks like some progress since my minimum NIC is now 6 instead of 0. But not good enough.

0. Fly to a different airport.
1. Turn radios off.
2. Fly test flight.
3. Pass PAPR test.
4. Profit!

 

[MRC01]

Yeah well I really want to fix this damn thing, not just pencil whip the certification.
And the FAA is monitoring my situation, so there's that too...

 

[John Collins]

I was just reading that DME uses the frequency range 960 - 1200 Mhz, which is much closer to the 1500 Mhz of GPS. And unlike VORs which are receive-only at the aircraft, DMEs actually transmit. So it would seem that DME might also jam GPS reception. If so, fixing this wouldn't be as easy as a com radio xmit, because the frequencies are so much closer, a simple lowpass filter doesn't seem possible.

It is not how close the frequency is to the GPS L1 frequency of 1575.42 MHz, it is a harmonic of the frequency. The 12th harmonic of 131.29 MHz and the 13th harmonic of 121.19 fall inside the GPS L1 frequency and can clobber it. Also frequencies near them will also impinge on GPS L1 band. A common cause of interference is the ELT, particularly an older 121.5 MHz unit. Even though an ELT does not transmit, the antenna system and ELT transmit circuit may be non linear and when it receives signals from your Com unit, it can re-radiate on frequencies near 121.5 whose 13th harmonics are close to the L1 frequency. Try a test flight with the ELT antenna coax disconnected at the ELT.

 

[MRC01]

Thanks for the tips. I was aware of this and the flights I made yesterday were with the ELT turned off and antenna disconnected. And as I mentioned, TED 4-70 filters on both com radios.

 

[John Collins]

I have occasionally seen RF energy radiating through the front face of a com unit. I was able to cover the front face with a coated anti-static bag used to ship avionics and it blocked RF energy from this source because of the gray metallic coating on the bag. This won't resolve your issue, but might identify the source if it is not coming from the antenna itself.

 

[MRC01]

Looking at the detailed track log from the FAA, it's no longer clear what is causing the Tailbeacon's GPS NIC and NAC values to drop. The spots where they drop are not obviously correlated with radio transmission or anything else. Installing the filters definitely solved one problem, because the drops used to happen when I was transmitting on the radio. Not any more. And when NIC drops, it now drops to 6 instead of to 0.

This has me wondering whether I solved the RF interference issue and now the problem is something else, maybe power? Or a faulty Tailbeacon?

 

[MajorTurbulence]

Sorry that your fun flying time is reduced to troubleshoot time. While I think you are an engineer, and this stuff may be up your alley, I have got to say that this stuff is illuminating. It just so happens that I have a KX170B installed with my Tailbeacon. My ELT was changed to a 406 unit years ago. But having passed the the PAPR, I’m intrigued enough to try to see if there is any evidence of GPS signal degradation when I transmit on that old NavCom on the harmonic frequencies. Without doing a new PAPR, I wonder if using my FLYQ EFB display on IPad(using the IPad gps)/ Stratux combination showing my tail number can be used to pick up changes in the the NIC and NAC? I would do it while flying since ground operations seem to mask any potential problems.

 

[MRC01]

As you probably know, ground monitoring the Tailbeacon is easy. Connect the uAvionix app to the Tailbeacon's WiFi. The app shows a real-time display of everything the Tailbeacon is sending: GPS position & quality flags, tail number, squawk code, altitude.

But monitoring it in flight is much harder. The ONLY field that is failing is NIC/NAC which are the GPS quality flags. All data, including the GPS position is correct. And I don't think the Stratux will show you NIC/NAC from ADS-B in.

 

[l_over_d]

I found this thread while attempting to troubleshoot what sounds like a similar situation in my recently installed Tailbeacon.

After installation, the first PAPR failed on NIC errors. Per my shop's guidance, lowered the transponder threshold from 38 to 36. Adjusting the threshold down seems to have cleared up the PAPR test...I flew again and got a clean PAPR. Hooray! So go, so far, right?

Well a few days later when I requested flight following, ATC noted (kindly) that they were seeing discrepancies in my mode-C and ADS-B altitudes (by around 300ft). Poking around on the uAvionix website, I found an faa email address where GA pilots can request the .kmz data for ads-b flights. Viewing the data they sent in Google Earth, it was apparent that my GPS signal was dropping out at all the same points where I'd been talking to ATC (actually looks pretty neat in a map, though definitely not something I'd prefer to be mapping!). I also pulled a PAPR test for that flight, and interestingly it passed even with the GPS gaps...weird!

From what I'm reading (and a response from uAvionix support), it sounds like I'll need a notch filter on at least my comm1 (430w) and maybe my comm2 (King) depending on what I see on the app when transmitting. I'm not sure ATC appreciates being asked "how many of me do you see now?", so hoping to get this figured out on the ground.

 

[MRC01]

... After installation, the first PAPR failed on NIC errors. Per my shop's guidance, lowered the transponder threshold from 38 to 36. Adjusting the threshold down seems to have cleared up the PAPR test...I flew again and got a clean PAPR. Hooray! So go, so far, right?

Strange, because the purpose of the transponder threshold setting is detecting your squawk code. It is unrelated to NIC, which is a GPS quality flag. Nowhere in uAvionix's GPS troubleshooting guide is the threshold setting mentioned.

... Well a few days later when I requested flight following, ATC noted (kindly) that they were seeing discrepancies in my mode-C and ADS-B altitudes (by around 300ft). Poking around on the uAvionix website, I found an faa email address where GA pilots can request the .kmz data for ads-b flights. Viewing the data they sent in Google Earth, it was apparent that my GPS signal was dropping out at all the same points where I'd been talking to ATC (actually looks pretty neat in a map, though definitely not something I'd prefer to be mapping!). I also pulled a PAPR test for that flight, and interestingly it passed even with the GPS gaps...weird!

From what I'm reading (and a response from uAvionix support), it sounds like I'll need a notch filter on at least my comm1 (430w) and maybe my comm2 (King) depending on what I see on the app when transmitting. ...

Yep. The filters I use and recommend are the Ted 4-70. Garmin also makes filters, but user comments say the Ted filters are more effective and fix some situations where the Garmin filters don't. They are pricey but you can find them much cheaper from reputable sellers on eBay. I bought 4 and only need 3, 1 for each radio and another for the ELT. So I have one spare I can send you if you PM me.

 

[l_over_d]

Interesting - yep confirmed NIC failure indicates GPS issues. My mistake! Adjusting the transponder threshold may have been a red herring for the comm interference issue.

Good to know about the ebay options...I might PM you about your spare after I run a few more ground tests. Looks like you're just a hop over the Cascades from my base in Wenatchee/KEAT.

 

[Jesse Saint]

I am amazed at how many planes come into my shop with these installed, either the TailBeacon or SkyBeacon. I have installed a few, but very few. Some installations work fine, others not so much. When UAvionix advertises such a low install time, how can I justify installing them when people expect to pay for 15 minutes of my time. I certainly won’t troubleshoot them. I take them off or disable them more often than not and install an ADS-B Transponder.

 

[MRC01]

I am amazed at how many planes come into my shop with these installed, either the TailBeacon or SkyBeacon. I have installed a few, but very few. Some installations work fine, others not so much. When UAvionix advertises such a low install time, how can I justify installing them when people expect to pay for 15 minutes of my time. I certainly won’t troubleshoot them. I take them off or disable them more often than not and install an ADS-B Transponder.

Your experience and policy toward {Sky,Tail}Beacon is similar to the local Avionix shop I mentioned in post #83 above. After troubleshooting this thing for the past 2 months, I understand.

Mine worked from the get-go back when it was first installed in late 2019. Fast forward 3 years, it started failing. Turned out to be corrosion on the circuit board. uAvionix replaced it and the new one can't maintain a high quality GPS fix even after adding filters on the radio and improving the wiring. Same airplane of course and nothing else changed, so it should have been an easy swap-in replacement. I think uAvionix is about to replace this replacement. We'll see.

If they can't get this thing working I'm going to have to rip it out and replace it with an entirely different ADS-B system.

 

[MRC01]

Here's the latest: I spoke with uAvionix at length on the phone. I will try 1 more thing and if it doesn't work they will send me another warranty replacement for this warranty replacement.

The 1 more thing is to connect a single continuous power wire from the nav panel switch to the Tailbeacon. This is just in case the OEM wiring currently in use (which is 43 years old), has connectors that add resistance. uAvionix says the power wire must have 2.6 mOhm or less. But this can't be true, since 16 gauge copper wire has 4 mOhm per foot, so a 20 foot length of wire would have 80 mOhm or 30 times more than that. Perhaps he meant to say 260 mOhm or 100 times more resistance. Either way, resistances less than 1 Ohm are too small to measure with most multimeters so we can't measure it, we can only rewire and see if that fixes things.

 

[Ed Haywood]

I would look closely at the grounding and bonding chain too. Lots of places to lose voltage on the trip back to the battery.

 

[mondtster]

The 1 more thing is to connect a single continuous power wire from the nav panel switch to the Tailbeacon. This is just in case the OEM wiring currently in use (which is 43 years old), has connectors that add resistance. uAvionix says the power wire must have 2.6 mOhm or less. But this can't be true, since 16 gauge copper wire has 4 mOhm per foot, so a 20 foot length of wire would have 80 mOhm or 30 times more than that. Perhaps he meant to say 260 mOhm or 100 times more resistance. Either way, resistances less than 1 Ohm are too small to measure with most multimeters so we can't measure it, we can only rewire and see if that fixes things.

You’re not the only person I’ve heard about that has been told and tried the same thing. I haven’t heard of it fixing a problem yet but maybe you’ll be the first.

 

[Gary Ward]

You’re not the only person I’ve heard about that has been told and tried the same thing. I haven’t heard of it fixing a problem yet but maybe you’ll be the first.

I have read that also, have never read that has fixed the problem.

I would cut your loses and go with something else before wasting anymore of your time trying another one.

There is a reason my shop won't install those. It's not because of the easy install.

 

[MRC01]

You’re not the only person I’ve heard about that has been told and tried the same thing. I haven’t heard of it fixing a problem yet but maybe you’ll be the first.

I have read that also, have never read that has fixed the problem.

I would cut your loses and go with something else before wasting anymore of your time trying another one.
...

A couple of the folks over at The Pilots Place have said this did fix their Tailbeacons. So now you've heard of it.
If this fixes it, or if it doesn't but the replacement unit works, then I'm happy and done.
If not, then what other ADS-B system should I get? If I had a crappy old xponder then I would have replaced it with an ADS-B out system. But my xponder is a GTX327 that I installed new about 6 years ago, it ain't broke and I'd like to avoid replacing it.

 

[Tom J]

GDL82 is one of the few that might make financial sense, and it's $1800. A GDL88 give in and out, but is over $4k. For that, may as well buy an ADS-B transponder. Not many certified options, once you exclude the uAvionix offerings.

 

[Gary Ward]

A couple of the folks over at The Pilots Place have said this did fix their Tailbeacons. So now you've heard of it.
If this fixes it, or if it doesn't but the replacement unit works, then I'm happy and done.
If not, then what other ADS-B system should I get? If I had a crappy old xponder then I would have replaced it with an ADS-B out system. But my xponder is a GTX327 that I installed new about 6 years ago, it ain't broke and I'd like to avoid replacing it.

Personally I would want ADS-B in. Either go GDL82 like Tom J suggested or sell your GTX327 and get something with in.
I am sympathetic to your troubles, but I think it's time to move on to something more reliable and more permanent. Those are not going last forever being outside in the weather.

 

[MRC01]

Personally I would want ADS-B in.

I built a Stratux with ADS-B in and a WAAS GPS dongle about 7 years ago. Not certified, of course. But this is a VFR only airplane. It provides in-flight near-real-time ADS-B traffic and weather with a fast-updating accurate GPS position. And it's been flawless over the years.

Either go GDL82 like Tom J suggested or sell your GTX327 and get something with in. I am sympathetic to your troubles, but I think it's time to move on to something more reliable and more permanent. Those are not going last forever being outside in the weather.

From what I read, replacing the Tailbeacon with a transponder ADS-B out solution will cost about $5k. Since this Tailbeacon is so close to working, I'll take 2 more troubleshooting steps before doing that.

 

[Gary Ward]

Good luck with it, I hope you get to the bottom of the problems so you can help others.

 

[Ed Haywood]

$2K for tailBeacon
- vs -
$3.8K for GTX 335 and sell the GTX 327 on eBay for $750

Hard to see where saving less than 1 AMU is worth the added aggravation.

I suppose you save money not having to pay a Garmin install shop. But OTOH the tailBeacon appears to have an added cost for voodoo shamans and witch doctors to troubleshoot.

 

[MRC01]

$2K for tailBeacon
- vs -
$3.8K for GTX 335 and sell the GTX 327 on eBay for $750

Thanks, that's the kind of recommendation I was looking for. Filed as "Plan B".

 

[mondtster]

If you have an external GPS source getting a gtx330es likely would have been the same or cheaper than the cost of the uAvionix sky/tail beacon. If a GPS source is needed the GDL 82 is basically the same price too.

Personal opinion, based on my observations and that of a friend's (who runs an avionics shop) I'd cut my losses with the sky/tail beacon. Some installations are trouble from the start and others seem to develop problems after a year or two of use. It's way too much time wasted for me.

 

[Lindberg]

$2K for tailBeacon
- vs -
$3.8K for GTX 335 and sell the GTX 327 on eBay for $750

Hard to see where saving less than 1 AMU is worth the added aggravation.

I suppose you save money not having to pay a Garmin install shop. But OTOH the tailBeacon appears to have an added cost for voodoo shamans and witch doctors to troubleshoot.

I, too, am bad at math.

 

[Ed Haywood]

Thanks, that's the kind of recommendation I was looking for. Filed as "Plan B".

FWIW I have had a GTX 335 for several years and it is bulletproof.

I also have a AV-30 and really like it. So, not harshing on uAvionics at all. I am a big fan of innovation. The tailBeacon just seems a bit Rube Goldberg-ish to me.

Good luck either way!

 

[Daleandee]

I also have a AV-30 and really like it. So, not harshing on uAvionics at all. I am a big fan of innovation. The tailBeacon just seems a bit Rube Goldberg-ish to me.

Agree. I don't quite understand it as I have the EchoUAT unit for my experimental (it goes inside the plane) and it has been excellent from the start. It gives ADSB in & out. Don't have a clue why uAvionics hasn't come up with a certified version of the Echo.

 

[MRC01]

If you have an external GPS source getting a gtx330es likely would have been the same or cheaper than the cost of the uAvionix sky/tail beacon. If a GPS source is needed the GDL 82 is basically the same price too.

Personal opinion, based on my observations and that of a friend's (who runs an avionics shop) I'd cut my losses with the sky/tail beacon. Some installations are trouble from the start and others seem to develop problems after a year or two of use. It's way too much time wasted for me.

FWIW, here's what led me to getting Tailbeacon back in late 2019:
I don't have an external GPS source.
I did have a great xponder, having recently installed a new GTX327.
So I did not want to replace my relatively new xponder.
Reading reviews across several sources (AOPA, EAA, and forums), Sky/Tail Beacon had 100% positive reviews.

Given the above, it was the best choice for my situation, knowing what I did at the time. And it did work without trouble for a couple of years, before it started failing.

 

[MRC01]

... I also have a AV-30 and really like it. So, not harshing on uAvionics at all. I am a big fan of innovation. The tailBeacon just seems a bit Rube Goldberg-ish to me.

Same here. Back in Oct 2022 my AI gyro needed to be rebuilt again, so I pulled the entire vac system and installed dual AV-30 units. They have been working fine, though my Tailbeacon also worked fine for the first couple of years...

I find that without an external magnetometer, the AV-30C in DG mode isn't any better or worse than a mechanical gyro in terms of drift. Mine drifts worse with the internal magnetometer enabled, most likely due to all the noisy EMR behind the panel. So I leave that feature disabled and run it unslaved. I don't mind setting it every 15 mins or so like I did with the mechanical gyro. At least I'll never have to rebuild another gyro or replace another vac pump, or have it fail in flight (again) when I need it. But I have been considering installing their new external magnetometer since it was just certified.

However, I am holding off on any further uAvionix purchases until I see how this Tailbeacon saga ends.

 

[Ed Haywood]

I pre-wired my AV-30 for the magnetometer and ran cable to the wing root. But I still have to update the firmware, which requires building a separate harness unless you wired tails for the 2 system update pins, which I did not. Have also heard that magnetometer installs can require troubleshooting to get the location right. So the magnetometer might turn out to be similar to the tailBeacon in terms of finicking.

 

[mondtster]

I pre-wired my AV-30 for the magnetometer and ran cable to the wing root. But I still have to update the firmware, which requires building a separate harness unless you wired tails for the 2 system update pins, which I did not. Have also heard that magnetometer installs can require troubleshooting to get the location right. So the magnetometer might turn out to be similar to the tailBeacon in terms of finicking.

I’ve installed one. It will.