WAAS upgrade woes

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mhoran
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Re: WAAS upgrade woes

Post by mhoran »

Charles K wrote: Wed Mar 09, 2022 6:13 pm Here is a photo of data label and of the rack (you can see 345R to left of GIA63W I - that is best photo I could find). You can see it is a -20 which is a newer version which has slightly better radio specs. 345R is still in same place and not on the outside (outboard) of the rack as far as I can tell.
Thanks for helping me rule that out. I figured it was a long shot but just wanted to check. The G1000 STC maintenance manual states for the GTX 33 mode S transponder:
Aircraft with GIA 63W P/N 011-01105-20, the unit is mounted on the outboard side of the
remote avionics enclosure below the baggage compartment.
Somewhere it also talks about relocating the transponder when a 011-01105-20 GIA is installed, but I can't find that at the moment. Regardless, it seems we have identical hardware yet you've encountered no issues, so something else must be to blame.
Charles K wrote: Wed Mar 09, 2022 6:17 pm Did they replace the lightning protection resistor array - they are at least supposed to do that was my understanding. The only way to do that is to splice the new one into the old wiring or replace the wiring. Since we were given a new wiring bundle with lightning protection resistor array - we decided why not replace the 17 year old wiring.
I don't see the resistor array as depicted in the STC drawings. Certainly concerning, but likely not to blame for this issue. Something to bring up with SouthTec at my next annual.
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Re: WAAS upgrade woes

Post by Rich »

Matt, There have been known problems with some GA35 antennas intermittently causing interference with other WAAS GPS antennas, including other GA35's. I haven't scanned the topic to see if this possibility has been eliminated.
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Re: WAAS upgrade woes

Post by mhoran »

Rich wrote: Wed Mar 09, 2022 6:58 pm Matt, There have been known problems with some GA35 antennas intermittently causing interference with other WAAS GPS antennas, including other GA35's. I haven't scanned the topic to see if this possibility has been eliminated.
Doesn't seem to be. One antenna is brand new, the other is a few years old. However, I'm not seeing the telltale signs of that failure mode.
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Re: WAAS upgrade woes

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While I had originally written off the GA-35 as the cause of this issue, I'm now starting to suspect that it could be to blame. I don't see regular complete loss of GPS on my G1000; however, the ADS-B fail alert does seem to indicate that the transponder is losing its GPS fix. The SB improving GPS signal acquisition seems to have helped -- these losses are now incredibly short, and I haven't gotten a single traffic fail in nearly a week flying every other day. However, today I was out at the airport poking around in the back with all systems on and heard the G1000 chime -- ADS-B fail. Cleared immediately. I went up for a flight and my performance report came back with some exceptions indicating GPS integrity issues. Given the extensive work already done to resolve RFI issues, I'm starting to suspect that what we thought were _continued_ RFI issues may actually be the older antenna I have acting up. I've asked Lancaster Avionics if we can try to swap the antenna and see if it helps. Much cheaper than replacing the transponder.
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Re: WAAS upgrade woes

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Edit: Garmin says this is expected behavior.

Does anyone on this thread have TAWS-B and WAAS? I think I finally found some proof for the antenna theory. I noticed that when I flip on my avionics master switch after starting my engine, TAWS-B goes N/A for a moment and then clears. I am now wondering if this is because of a momentary loss of GPS for GIA #1 that isn't otherwise detected by the G1000. But it would make sense that when GIA #2 starts up (with avionics master power) that if its antenna were bad it would cause TAWS-B to drop. Or maybe this is just how TAWS-B works...
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Re: WAAS upgrade woes

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I had my co-owner run some tests today when he was out flying. It doesn't seem that the older antenna is to blame for our issues. In fact, he found that GIA #2 is connected to the older antenna, while GIA #1 is cnnected to the new one.

I had thought GPS signal acquisition took longer for GPS #2, but he found it to be the same for both GPS #1 and GPS #2 (about 1:30 for each.) No noticeable drop for GPS #1 when bringing GIA #2 online.

Performance reports for both of his flights today came back nearly perfect. Some drops, but nothing that would trigger a call from the feds. After talking with Lancaster Avionics they agree that it'd be a waste of time and money to chase these issues further at this point. Since the persistent traffic fail seems to be resolved with the latest GTX-345 software update and the ADS-B failures are only momentary, there's not much point in continuing to troubleshoot.

So I guess I'll put this issue to bed for now and hope it doesn't get any worse. If it gets worse hopefully it'll become easier to troubleshoot. Thanks to all for your help.
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Re: WAAS upgrade woes

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When I had intermittent issues with a failing GA35 antenna (when the antenna failed it would create interference that jammed the other GPS antenna) I did not see any problems w my ADS-B. However, the antenna for my GTX345R is mounted way back inside the tail cone so it is a long way from the GPS antenna.

Where is your GTX345 antenna installed relative to the GA35?
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Re: WAAS upgrade woes

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MarkA wrote: Fri Mar 11, 2022 11:44 pm When I had intermittent issues with a failing GA35 antenna (when the antenna failed it would create interference that jammed the other GPS antenna) I did not see any problems w my ADS-B. However, the antenna for my GTX345R is mounted way back inside the tail cone so it is a long way from the GPS antenna.

Where is your GTX345 antenna installed relative to the GA35?
Same as you -- I have the combo XM/WAAS antenna in the tail cone. It's frustrating since I can't see the status of the transponder GPS without the dealer only software. FAA performance reports suggest that transponder GPS may be dropping intermittently, but I haven't been able to reproduce the issue reliably. It does seem that Garmin's latest GTX-345 software update did add some stability here, so I'm hopeful the worst of this may be over.
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Re: WAAS upgrade woes

Post by arksat »

Matt, have you tried the Garmin Pilot app? It shows the GTX-345R status on my iPad. It's not as detailed as the special laptop software, but at least you can tell if the transponder is getting a GPS signal or not.

You don't need a subscription to access this feature on the Garmin Pilot app.
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Re: WAAS upgrade woes

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arksat wrote: Sat Mar 12, 2022 4:37 am Matt, have you tried the Garmin Pilot app? It shows the GTX-345R status on my iPad. It's not as detailed as the special laptop software, but at least you can tell if the transponder is getting a GPS signal or not.
I do, thanks for the reminder! Hadn't thought to check this. Will keep an eye on it next time.
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