Garmin G3X 12.10 software bug - VNAV Unavailable

November 2020 - G3X (non-touch), GSU73, GTN650Xi.

After updating my G3X to software load 12.10, I begain receiving the following message on my GTN650Xi: "VNAV Unavaialble:Barometric altitude lost." After several back and forths with Garmin, the pinouts were check, and all configurations were checked. Don't be tempted to just set the GTN to VCALC so the message goes away. In VCALC you lose VNAV and transition to approach. This is a very valuable tool for approach workload and safety. We then dove into the GTN diagnostics.

GTN Diagnostics page - Main Data Inputs: Barometric altitude was blank. It should show barometric altitude.

GTN Diagnotics page - ARINC Inputs: I was directed to select ARINC 429 port 1 input. If working correctly, you will see a live data stream. I paused the stream, and was directed to look for label 204. This label is the barometric altitude data. If I looked deep enough, I would find a sporatic label 204. Sometimes I could not find it at all. This began to point towards the GTN not seeing the GSU73 barometic data.

As of right now, the G3X engineers have found a bug in the 12.10 software, with the label 204 data on the G3X side. Hopefully, a new software release will be coming soon.

Garmin sent me the previous G3X software load, 12.00. Installed it and everything works perfectly, with no messages. This further points to an issue with the G3X 12.10 software.

I also posted elsewhere that 12.1 has a bug. It will not load the GSU25 in my system. I also reverted back to 12.0 and now back to normal.

Any update

Any update from Garmin on a fix for the VNAV issue w/ v12.10?

They sent me and I loaded the 12.00 software which resolve the problem. They said that the next software release would address the VNAV issue. So, we will have to wait until that happens.

VNAV and APPR on same G3X soft key.

VNAV, Non-touch. While talking to guys who use this . . .


I had a little issue transitioning from the descent to an RNAV transition point. I had the procedure loaded and activated in the 650, also the flight plan had the via point with the VNAV altitude - -so I said, lets use VNAV for the crossing.

I found that lateral guidance will continue but VNAV remained illuminated on the G3X and covered the APPR button. I touched ALT, then VNAV to toggle off VNAV, then the APPR function showed up in the soft key bar and it could be selected and illuminated. This little hiccup bit me 4 times before I figured out what I was doing.

Hope this will help, but you guys have probably learned this a long time ago.

OK- back to the SW glitch, I will be waiting for the correction.

I don't want to be accused of "piling on" but... My G3X non-touch won't channelize my SL-30 after v12.1. Worked fine before.

rvsxer said:

I don't want to be accused of "piling on" but... My G3X non-touch won't channelize my SL-30 after v12.1. Worked fine before.

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I would suggest you contact Garmin. They may have a fix. If not, they will simulate your setup, and if they find an issue, they will address it in the next update. Otherwise, they may not know about it.