G3x horizon malfunctioned

[jmorrical]

I've flown almost 6 hours on my CarbonCub EX (1). During the last flight my G3X GDU 465 attitude banked 30* or so and froze there. It looked much like Troy's at the beginning of this thread. I flew about 40 minutes after the event. It did not self correct as was Troy's experience. There were no red Xs or warnings on the display. HSI heading continued to function normally.

After landing and shutdown I rebooted the G3X on IBBS. ADHRS aligned normally at a normal attitude.

I talked to Garmin. Immediately they said I needed to replace the GSU 25 ADAHRS. After some discussion I have decided to recalibrate the ADAHRS by re-running the pitch/roll offset, magnetic interference test, engine run-up vibration test and magnetometer calibrations. Some how I missed running a vibration test first time around. I'm anxious to see how it turns out after seeing Troy's added tray support.

Is there any other recent experience with this failure mode?

[TroyBranch]

I am still running trouble free after replacing the ADHRS. 500hrs and climbing.

[Andy]

Is there any other recent experience with this failure mode?

My misleading attitude events have all been abnormal high pitch angle indication and they have all recovered in flight. Garmin investigated this problem, published a safety alert, and later redesigned the GSU 25C.

If I needed to replace my GSU 25C I'd want part number 011-02929-55.

[jmorrical]

I have seen Garmin Service Alert 2144: Revision A & B. Interesting. My serial number is included in Revision A. Revision B applies to earlier wing mounted ADAHRS. My harness had extra wire for that, but my ADAHRS mounted on the equipment tray behind the instrument panel.

Today I recalibrated the Garmin GSU 25C ADAHRS by confirming the unit orientation, pitch/roll offset test, and engine run-up vibration test. The magnetometer had to be realigned after the pitch/roll offset test.

The pitch/roll offset was completed with the A/C in flying level attitude. The engine run-up vibration test Failed three times. The manual directed one or two minute cycle from idle to full power and back to idle. During the test the gyro deviation ranged from 0 to 35%. Yet, when the AHARS gyro test was completed it showed 136%, 108% and 111% in the three tests. I don't understand that exactly.

I'll check mounting security and electrical connection and go from there. Sounds like I'm headed to replacing the GSU 25C.

Andy why do I want part number 011-02929-55 with my installation?

IMG_7293.jpg

[Andy]

why do I want part number 011-02929-55 with my installation?

011-02929-55 is the latest design of GSU 25C which was developed after Garmin reproduced the misleading pitch attitude issue in the lab. They did not share any detail of the design change but I assume it is more tolerant of vibration and/or acoustic coupling that was blamed for the issues with the original part number.

Lots of installations use the original part number GSU 25C with no issues. I have no reason to think your roll attutude issue was caused by the same problem that resulted in the re-design.

[Andy]

I have seen Garmin Service Alert 2144: Revision A & B.

I only had the original version on file. 2 revisions later and they still say:

"

• Wing of a tube-and-fabric airframe when flown through precipitation
• Beneath the baggage floor of an aluminum airframe in a small, enclosed compartment"

This despite the fact that I provided data for the same anomaly seen during a static run-up on a dry sunny day. I still believe that flying in rain in an FX-3 with wing mounted GSU-25 increases the probability of seeing this error. However, I made several flights in rain in an attempt to get data for Garmin but could not induce the problem in multiple attempts.

I'm convinced that reproducing this problem requires a specific noise/vibration frequency and a specific phase relationship between the noise and the MEMS sampling frequency. Since the two frequencies are normally asynchronous there is some luck (good or bad) involved with reproducing the issue.

The last time I saw the problem was in rain and, after the pitch attitude went stupid, I felt a shudder in the airframe. That shudder persisted until I changed prop pitch and did not come back when I went back to the original rpm. I have no explanation for the shudder but suspect prop imbalance due to water contamination. I know that's a long shot and would be interested to hear any other explanation.

That most recent event produced some good data as it showed how attitude miscompare and source reversion was handled with G5 and GSU 25 both providing data. Very disppointing result as it took nearly 20 seconds for Garmin software to display G5 data on GDU instead of obviously wrong GSU 25 data.

If you have a G5 keep it in the scan and don't trust software to pick the right atitude source for you. Hopefully Garmin will use my data to improve miscompare and reversion logic.

[jmorrical]

Garmin is replacing my GSU 25C ADAHRS (010-01071-50) with the newer -55.

I sent the data log. They were also interested to see photos of the equipment tray where my ADAHRS is mounted. I learned from Kit Support that CC EX kits used the tray under the boot cowl while others like the FXs had the ADAHRS mounted in the left wing. That explains the difference in chatter I see here on this thread. Well, Garmin expressed some concern over seeing the tray install, but found sensor anomalies in the log that suggested ADAHRS replacement as the first course of action.

If vibration continues as a problem they suggest moving the ADAHRS to mount pad on the back of G3X if there is room. Before I did that I would try adding a support like Troy has shown in his first posts here. While investigating all this I was surprised how much movement I could impart on the tray just by putting finger pressure on the remote transponder mount that's attached below it. With the G3X powered up I found I could change the pitch attitude displayed by a couple degrees because the ADAHRS was being displaced by tray movement. How much tray vibration is added by that the remote transponder hanging there? Troy's brace has to help reduce it.

My propeller seems to run smooth but a balance may help too.

[Andy]

Jim,

Good to hear that Garmin is exchanging for a -55. I'll be very interested to hear how that works out for you.

Andy

[jmorrical]

An interesting side note to a warrantee replacement of an LRU component of CubCrafters Executive Panel: When I began having problems with my GSU 25C ADAHRS (010-01071-50) I immediately started asking questions about replacement. Garmin said it should be replaced. When it came to sending the replacement -55 model payment arrangements needed to be in place for the exchange. As they looked at my record I was out of warrantee! In the end they decided to replace the unit mostly free of charge. There may be postage or some other service charges related I don't know.

What I've learned is that for builders like me who are on a 'slow build' schedule of several years need to ask questions as to when the clock starts for warrantee protection especially of expensive avionics. Garmin says clearly that a component like the GSU 25C (non-TSO Products) has coverage for 1 year or 400 hours from date of purchase. Mine set in the shipping box or in the fuselage for over a year before I ever powered it up to fly it. Technically my warrantee was expired. They knew my date of purchase, my airworthiness certificate date and of course the date I registered my G3X and LRUs with Garmin on their website. They settled on using my airworthiness certification date as the beginning of the warrantee period. I think I was lucky.

[Ak Paul]

Warranties for us ‘slow’ builders has my attention also. While in Oshkosh I visited with several suppliers of our kits. Lycoming confirmed that my engine will be long out of warranty when I first fire it up. A surprise - Hartzell props said the constant speed prop warranty doesn’t start till I fire up the engine, however, the prop has a shelf life - it needs servicing within 2 years of use. I’ll need to take it to a prop shop for inspection and grease servicing. Certainly did save $ on prop purchase by getting it several years ago tho!