G5 altitude calibration

[Andy]

The G5 EFIS that I fitted to my FX-3 initially read 40 ft higher altitude than the GSU 25 altitude displayed on the GDU 465. After about 2 years the difference had increased to 60 ft and all the error seems to be in the G5.

I mentioned this to a friend who works on multiple aircraft and he commented that he had seen other G5 with poor altitude calibration.

If you have a G5 installed, what difference do you see between GDU and G5 when both have the same baro setting?

The 60 ft error bugs me but there is no way to enter a correction offset. Baro settings cannot be split when the G5 is fully integrated with G3X. The G5 must be calibrated at sea level, 10,000 ft, 20,000 ft, and (optionally) at 30,000 ft. That requires paying someone with an approved air data test set or designing and building my own test set. (That project is underway and I'll report if it works.)

[kshunz]

My G5 initially showed about 20' higher than on the G3X, and after about 18 months it's now about 30' higher.

[Andy]

My G5 initially showed about 20' higher than on the G3X, and after about 18 months it's now about 30' higher.

Thanks for the report which seems to agree with other comments on G5 altitude error that I found in a web search.

I'm making progress with my air data test set. I have the basic sensor interface working and displaying on an LCD. Next step is making a vaccum tight enclosure for the sensor so it reads instrument static rather than ambient pressure.

[ve6yeq]

In preparation for delivery of my CarbonCub, I have been flying a Super Decathlon that has both a Garmin G3x (front seat) and a uAvionics AV-30 (back seat). Even after multiple calibrations, it has not been possible to get both to match and the drift between them appears to vary slightly depending upon the day. I have not looked into the pressure transducer specifications to see how much variation is just inherent in the sensors, piping, etc.. By the sounds of this thread, I will be looking into this once I take delivery of my CarbonCub (G3x + G5)…