On Friday, April 23, 2021 at 4:41:44 PM UTC-7, Matt Herron Jr. wrote:
Another thought on ADS-B. I did an annual a month ago, and the seat pan had to come out. The antenna lead runs under it. Crushed coax? Also, to replace the Fusion, I had to unplug the Trig box. I will check for good connection, bent pins etc.

Matt

OK great it's not a firmware version. It's unlikely to be any thing to to with the antenna or transponder/ADS-B Output RF side of things if it was you'd see other failures. And your report is very clean except for 100% failure on the GPS and pressure altitude data.

I forgot I'd helped on your setup before. It's hard to see what will cause GPS Altitude and Pressure Altitude to fail, esp. if nothing has changed. BTW the ADS-B settings are actually stored in the TC20 control head, so if that's ever replaced the settings are lost and need to be redone--but I'm at a loss because there is no config setting that I can think of that could cause both these altitudes to not report. Failing pressure altitude alone might be caused by things like having the pitot connected to the TC20 head static line. And other unrelated problems might explain a GPS Altitude problem.. But regardless of what that does and what the system might interpret is bad with pressure altitude it should still separately transmit the GPS Altitude, they are sent across different position reports, some with pressure alt, some with GPS alt. And it's hard to see how a data wiring problem could cause this but not other issues.

Maybe the easiest thing to is pull an PAPR report for a different recent flight and see if that is also failing. And when the FAA email that to you (or for this one here) just reply to the email and ask for a detailed kmz (Google Earth) and spreadsheet data reports. Eyeballing the data may give clues... although you don't actually see the real raw data, it's all unfortunately processed a bit).

Another simple thing to check is what FL is being shown in the transponder display during flight (or pull a slight vacuum on the static and see the FL climb to just confirm that the transponder encoder in the TC20 head is working at all.

Failing that I'm already looking with Andy at his JS3 which as you noted has some ADS-B Out weirdness also showing GPS Alt and Pressure Alt fails, but also has other issues, and if that turns up anything I'll be in touch.

No, GPS Jamming or anything else related to RF signal will not explain the lack of pressure altitude data. (And GPS jamming would need to be very sophisticated to just trash GPS Altitude, the average idiot with a cheap jammer purchased off EBay can't do anything like this even if hacked with high output power). I'd suspect a fault with say the FAA ground system or PAPR report if multiple aircraft experienced this at the same time... were other gliders with ADS-B Out or TABS flying at the same time... we can pull PAPR reports for them as well. If you reply to the FAA PAPR email and ask for those detailed reports you might mention the altitude failures and how that's difficult to explain and ask if other flights in the area were experiencing GPS Alt and Pressure Alt data problems... those emails seem to be read by humans.

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Oh the frustrations with ADS-B, nothing today really uses GPS altitude AFAIK -- and this came up recently in the NTSB report on the Ketchikan Alaska fatal mid air collision where pilots did not receive ADS-B traffic collision warning because the ADS-B Out in one aircraft was not getting pressure altitude data, but *was* getting and transmitting GPS altitude data... but the other ADS-B-In completely ignored the GPS Altitude and did not issue a traffic warning. A failure of design, and more a failure of maintenance and company processes, including the basic failure to obtain a PAPR report to validate ADS-B Out is working after maintenance... may not necessarily be required but damn common sense to do so. NTSB info he https://www.ntsb.gov/news/events/Pag...141AB-BMG.aspx. And to show the value of periodically checking with a PAPR report, in this case of Matt's glider if the altitude reporting problems are real we know that no other aircraft are getting ADS-B based traffic alerts from this glider, and ATC is not going to be seeing the glider via ADS-B (and maybe not transponder either) traffic (If this has happened for a while the glider will have been black-listed by the FAA as non-compliant and will be totally ignored).