G3XTouch reversion to G5 source

[Cactus Charlie]

Most who have a G3X Touch system using GSU 25 ADAHRS and a G5 will never see a source reversion. This is what an attitude reversion looks like after G3X Touch detects a problem with GSU 25 attitude data:

Indicated pitch attitude is about 17 degrees nose up but velocity vector and VS show aircraft is not climbing. An impossible condition at IAS 90 mph. G3X Touch alerts to ATT MISCOMP (attitude miscompare) indicating that GSU 25 and G5 pitch attitude do not agree. It has not yet decided which pitch source is correct -

7:56:02 local time

The GSU 25 recovered for a while and ATT MISCOMP was removed:

7:57:07 local:

Later GSU 25 pitch attitude goes bad again and for long enough that G3X Touch reverts to G5 as source for PFD attitude. GSU 25 remains as source for PFD air data. GSU 25 goes into align mode in an attempt to recover to normal operation -

7:59:32 local:

Then all back to normal (no image captured)

These images were captured in an FX-3 with a wing mounted GSU 25C. The rubber isolator option was not installed and the GSU 25C was a -50 part number not the newer -55 version.

If you have this configuration be aware that, if GSU 25C outputs misleading pitch attitude, it may take several seconds for there to be any alerting. If AP is engaged it will follow the spurious pitch attitude. If AP is disconnected the FD will still follow the spurious pitch attitude.

 

[lrobichaux]

When was your plane built?

 

[Cactus Charlie]

When was your plane built?

2020.

Do you ask because it does not have the GSU 25 isolators?

 

[lrobichaux]

Asking because my EX-3 was just completed a few months ago, and I'm wondering if I need to check out mine (CCK-2000-021) to see if it has the isolators.

 

[Cactus Charlie]

I would expect it to have the isolators but I have not seen any data that shows they prevent the problem. It's a long story that, for me, started with an autopilot nose down hard-over during phase 1 flight test back in June 2020.

GSU 25C -55 was developed by Garmin after they had succeeded in reproducing the misleading pitch problem in the lab. I do not know when, or if, CC started using the -55 GSU 25C.

The point of my post was to alert owners to the potential for the problem and to show what the PFD looks like. There are lots of FX-3 with no G5 and these will have no miscompare alerting.

 

[lrobichaux]

Excellent info. I will confirm what my EX-3 has.