G3x horizon malfunctioned

[TroyBranch]

On the last two flights I have had my Efis do this. I plan to recalibrate it so see if it solves it. It corrects itself in flight after a few minutes. Anyone else have this issue? Very concerning that it would even do this.


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[mikesutton]

Has this just shown up out of nowhere recently, and how many hours have you flown it? Are you getting any error messages - red X or messages down in the right hand corner where the message pop ups are shown? What does the unit show when the aircraft is sitting static on the ground, does it show wings level - within a degree or so, depending on how level the surface it is sitting on - and depending on the main tire diameter, anywhere from 8 to 12 or so degrees nose up pitch?

You could level the aircraft and compare to what you see, and then you could also go into the configuration mode and re calibrate the level of the GSU25 adahrs unit to the aircraft in the config mode. The G3X manuals are online via garmin, no special dealer access or anything to read or download them. Section 18 talks about how its mounted, Section 34 - specifically 34.4.5 talks about how the calibration is done.

Garmin just released sw version 5.40 for the GDU46X display, you may want to upload that prior to doing anything else. It may or may not make any difference but its the simplest and easiest thing one could start with.

Good luck

Mike Sutton
Cubcrafters Avionics

[TroyBranch]

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

[jmorrical]

I have removed the original GSU 25C ADAHRS (010-01071-50) and installed a new 011-02929-55 ADAHRS. To improve success I also added a support tube connecting the fuselage frame tube above to the remote transponder rack like Troy's installation. This likewise stiffens the avionics tray where the ADAHRS is mounted. Now the avionics tray has no play.

The pitch/roll offset test, magnetic interference test and the engine run-up vibration tests all passed. I expect my pitch attitude / horizon issues are resolved. The magnetometer had to be realigned also.

My support brace was made from 1/2" X .016 aluminum tubing available at my local Ace Hardware. It is connected to the fuselage tube with a non-cushion O'dell clamp. I couldn't close and line up a more difficult cushioned clamp because of the confined working space around wires. The LRU tray and the remote transponder rack has no movement now.

Attachment 13229

[TroyBranch]

There is no red X or any sign of an issue if you were IFR which is really scary. Can't fly the cub IFR but in the smokey weather with pour vis the horizon makes flying uncomfortable. I often fly at night and that would be equally uncomfortable.
This just started on the last two flights. The compass seams to adjust it self every now and again too. So I loose the wind indicator. No issues on the ground when static. Like I had said, it corrects itself after a few minutes while in flight. I can update the software but it should never do this. My RV10 has never done anything like this in 900hrs, it is a different brand.


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[mikesutton]

Just wondered if you were seeing any other signs of error. The compass issue is interesting, since the heading data comes from the magnetometer and all of the other airdata is from the GSU. No red x issues of heading, no magnetic anomaly error messages there either?

You might consider seeing if there are error in the error log, though I do not know the parameters for the system to log and track them...especially something intermittent. If there are errors in the log you could send them to Garmin for examination.

My first hunch was that the GSU has a fault, which is not unheard of but we have had very very few issues with them as far as getting bad units out of the box. The magnetometer is more critical in regards to environmental issues - too much ferrous metal nearby, wiring that is too close, that sort of thing. Those usually show up with error messages because you cant correct that with a compass swing.

Agreed that it shouldnt happen, the hardware behind most of these systems is far more similar than most people realize and most of these systems have very similar requirements for mounting the hardware, they have been pretty well shaken out by now and have proven themselves. Agreed also that software should not affect this, though Ive seen more than one case of random anomalies coming and going just as quickly as they came on.

Mike Sutton
Cubcrafters Avionics

[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?

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[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]

Just an update after the -55 ADAHRS replacement and my 'TroyBranch Modification'. I've flown my EX (1) almost 30 hours now and the ADHARS has performed flawlessly.