WAAS upgrade woes

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mhoran
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Re: WAAS upgrade woes

Post by mhoran »

Today's plan was to fly out for lunch and if I had no issues I would close out my work order with Lancaster Avionics. Well of course I had a traffic fail shortly after takeoff.

Thanks to Tosh I have a thread to pull on. GPS from the GTX was stable. Though the status page always shows 0 connected satellites. However, I noticed two things. First, before takeoff Garmin Pilot showed the AHRS as aligning for a long time. I thought nothing of it and took off. When I got the traffic fail I noticed that AHRS was degraded. It continued to jump from valid to degraded and eventually settled on valid and looked good.

I've noticed when reviewing track logs that the AHRS didn't look accurate for some time. Never thought anything of it. I can't tell from the maintenance manual whether an internal GTX AHRS fail would cause traffic to drop to the G1000 (seems unnecessary since the G1k has it's own AHRS). But next step is to see what Lancaster and Garmin have to say. Of course my GTX is nearly one year out of warranty at this point...
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Re: WAAS upgrade woes

Post by mhoran »

Well it seems the internal AHRS is likely bad but not the source of the issue, as the AHRS status was degraded for most of my return today as well. However, I noticed something else. When I got the traffic fail and for the entire leg to KVAY this afternoon, Garmin Pilot had lost airspeed and barometric altitude as well. Likely that latter one being most important for the traffic system. On the return leg Garmin Pilot properly displayed arispeed and barometric altitude.

I know that when I started up the plane on the first leg it did have barometric altitude -- and no traffic fail. Seeing as my ADS-B performance report for this morning came back showing no issues, I believe pressure is making it into the GTX-345 but dropping off somewhere inside the unit and therefore causes traffic fail. In the end it looks like I'll be getting an exchange GTX-345 but if there ends up being a cheaper solution I'll report back.
traffic-fail-degraded.jpg
Note the airspeed tape shows GS only, and the altitude tape shows GPS ALT.
return-leg.jpg
The airspeed tape shows IAS and altitude tape shows PRESS ALT.
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Re: WAAS upgrade woes

Post by mhoran »

Next step here is to replace the wiring harness and config module. Normally this would be a few hundred dollars in parts, but my shop is just going to charge me for labor (2-3 hours). If that doesn't work I'll be exchanging the GTX-345. Garmin would apparently rent me one for $400 but given an exchange is $1600 (and I'd still have to pay for an exchange if the rental turns out to solve the issue), seems an exchange wold be the way to go.
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Re: WAAS upgrade woes

Post by mhoran »

At the risk of prematurely declaring victory, I do believe we finally found the root cause here. It all goes back to the issue that brought me to Lancaster Avionics in the first place: mode C drop out (with corresponding traffic fail.)

Lancaster Avionics had found that the altitude source #1 for my GTX-345 had been changed from none (which actually means auto) to ARINC-429 port 2. While not technically incorrect, this does mean that if the ARINC-429 interface goes down for any reason, the transponder will lose altitude and therefore drop mode C.

I finally made the connection that the ARINC-429 interface is also integral to the traffic system, as it provides heading information to the traffic processor. This also brings us back to one of the original recommendations from Garmin that we had written off because we could not reproduce the issue on the ground at the shop, which would have involved wiring an additional heading input source into the transponder.

Pulling on this thread I then discovered in GIA #2 settings that the ARINC-429 port configs did not match those in the GTX-345 installation manual. The manual states that the data rate must be set to high. However, it was set to low. Now, the data link was working as both sides were set to low -- but I suspect that for some reason if the data rate is not set to high, the connection becomes unstable.
PXL_20220320_181045712.jpg
We set the ARINC-429 link from GIA #2 back to high. I suspect this was accidentally set to low during my WAAS upgrade. We also ran an additional heading input to the GTX-345 just to rule that out, and installed a new config module. The way this is wired up is that there are actually three things wired in parallel to a single ARINC-429 port on the GIA #2. This is because, and ultimately what I believe led to the confusion and misconfiguration, only a single ARINC-429 interface on the GIA-63W can be set to high speed. For some reason an unused port on my GIA #2 was already set to high -- meaning the ARINC-429 port wired to the GTX-345 could only be set to low. Sigh.
PXL_20220322_204251451.jpg
I truly hope this will be my last update to this thread.
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Re: WAAS upgrade woes

Post by Boatguy »

Cutting through the details. This is a configuration problem, not a hardware, software, or connectivity problem?
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Re: WAAS upgrade woes

Post by mhoran »

Boatguy wrote: Wed Mar 23, 2022 5:04 am Cutting through the details. This is a configuration problem, not a hardware, software, or connectivity problem?
Yes, that does seem to be the case. I need a week or so of flying to make sure this is truly resolved, but given the circumstances I'm fairly certain. We looked back through the original wiring diagrams from the GTX-345 install and the speed was indeed set to high at that time. This must have gotten changed during the WAAS upgade (complete software reload requires reconfiguration of the G1000.) There's nothing else at this point that would tie back to the WAAS upgrade or explain a sudden failure.

There were other issues with my WAAS upgrade as well -- RFI due to COM and ELT antenna resonance which should have been detected during required testing post install. Also, one of the used GIAs I had installed was bad and needed to be exchanged. However, these were ultimately unrelated to the original mode C / traffic failure that brought me to the shop. In the end I guess it's good that I had multiple issues since leaving the RFI issues unaddressed would have gotten me an NPE (Nonperforming Emitter) letter from the FAA. But it sure was expensive.
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Re: WAAS upgrade woes

Post by Charles K »

If the shop did not properly configure it (during GTX345R and/or WAAS upgrades) and that is the root cause - I'd be discussing with them the charges to you for the fixes.

Glad it is working now!
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Re: WAAS upgrade woes

Post by mhoran »

Charles K wrote: Thu Mar 31, 2022 4:45 pm If the shop did not properly configure it (during GTX345R and/or WAAS upgrades) and that is the root cause - I'd be discussing with them the charges to you for the fixes.
I wanted to get a few flights in to be certain, but at this point I haven't had a single transponder issue in over a week of flying, so it does seem the configuration was the root cause all along. Seeing as the configuration change and RFI issues trace back to the WAAS upgrade, I'll be bringing this up with SouthTec before I take my plane to them for my annual next month. They did say they'd make things right if I was still having issues by the time I brought my plane in, but it looks like they're off the hook there.
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Re: WAAS upgrade woes

Post by Charles K »

Why are they off the hook? If mis-configured by them....
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Re: WAAS upgrade woes

Post by mhoran »

Charles K wrote: Tue Apr 12, 2022 8:37 pm Why are they off the hook? If mis-configured by them....
Well, I just meant that there's nothing for them to fix at this point. But I will be bringing this up with them, since I spent more than the budget I had allocated for our upcoming annual and other maintenance items on addressing these issues...so there's no money left for them! 😂
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