G3X Attitude Error

[ronrapp]

On a flight today, my G3X Touch began displaying incorrect attitude and heading for some reason. I'll attach a photo. The G5 is showing the proper attitude, about a 1 degree right bank. The GDU460 (or whatever it is) is displaying about 11 degrees right bank.

After a while flying like this, I got three amber messages on the screen. AHRS REVERT, ADS REVERT, and another one I can't recall. Basically the GDU460 was using the G5 for attitude information. But the PFD display still remained very inaccurate.

I looked into the "Diagnostic" menu and it said that the PFD was not receiving any GPS data at all.

After landing, I shut everything down, then powered it up again, and all was normal.

Any thoughts?

--Ron

 

[Avanza]

GPS data is used for ADAHRS performance monitoring, at least one source of GPS data is required.
The G3X system is capable of displaying basic position data from an external IFR GPS navigator, but this data is not used for ADAHRS monitoring.
I would look at the integrity of the RG400 cable, BNC-connectors and the GPS antenna for the PFD (GDU). I assume you have no MDF with it´s own GPS antenna as a back up.

Good luck

 

[jliltd]

I thought the GDU GPS connection with it's own antenna was optional when paired with a WAAS TSO'd navigator via GAD 29B. In fact, doesn't Garmin merely "recommend" the GDU have it's own GPS antenna as a backup in case the external navigator goes down? I will presume the GSU 25 is getting GPS data for it's attitude solution over the CAN Bus whether the source be the GDU or external WAAS navigator.

EDIT: To the OP, I saw you had planned on a GTN during design but then see that later in the end you didn't go with a TSO'd WAAS Navigator so the GSU 25 does depend on the GDU's internal GPS for attitude. The G5 will not share it's GPS position with any external device like the GSU, even over CAN. It can, however, take over the GSU's job when there is a problem, exactly like this. The reversion message is letting you know that the ADHARS data source has switched to the G5 because the system saw problems with the GSU. The GPS data to the GSU is one of many things that could go wrong but is one of the most likely and the easiest to troubleshoot.

 

[Avanza]

2.1.1.8 GPS
Each GDU display includes an internal VFR GPS receiver, and a connection for an external antenna. GPS position data is shared between GDU displays using the CAN bus. For a list of GPS antennas supported by the GDU display, refer to Appendix E, or Section 6.
The GPS 20A is a TSO-compliant WAAS GPS position source that is compatible with the G3X system.
The GPS 20A provides GPS data to the G3X system using the CAN bus, and can send ADS-B position data to a transponder using RS-232. For GPS 20A installation information and a list of supported GPS antennas, refer to Section 15.
GPS data is used for ADAHRS performance monitoring, so at least one source of GPS data is required.
This requirement can be met by installing a GPS 20A, or by connecting a GPS antenna to at least one GDU GPS receiver. In a system with multiple GDU displays, additional GPS antennas may be connected to the other displays for redundancy, if desired.
The G3X system is capable of displaying basic position data from an external IFR GPS navigator, but this data is not used for ADAHRS monitoring and thus does not satisfy the above requirement.

Good luck

 

[Dan 57]

This kind of stuff always makes me cringe... following a couple of "events" on my steed, I installed another mini ADI from another manufacturer, running a different software.

One never knows...

 

[Auburntsts]

This kind of stuff always makes me cringe... following a couple of "events" on my steed, I installed another mini ADI from another manufacturer, running a different software.

One never knows...

I feel sort of the same way. However, while the G5 is a Garmin product, it's architecture and software aren't common to the G3X so it fills the square in my book.

 

[lr172]

On a flight today, my G3X Touch began displaying incorrect attitude and heading for some reason. I'll attach a photo. The G5 is showing the proper attitude, about a 1 degree right bank. The GDU460 (or whatever it is) is displaying about 11 degrees right bank.

After a while flying like this, I got three amber messages on the screen. AHRS REVERT, ADS REVERT, and another one I can't recall. Basically the GDU460 was using the G5 for attitude information. But the PFD display still remained very inaccurate.

I looked into the "Diagnostic" menu and it said that the PFD was not receiving any GPS data at all.

After landing, I shut everything down, then powered it up again, and all was normal.

Any thoughts?

--Ron

I think the revert message only translates to reality if there is a second G3X ADHRS installed that it can revert to; Otherwise it is essentially an error message.. Unless something changed, the G3X will NOT use the G5 data, unless you power down the G3X ADHRS. This was proven in your case, as the attitude did not change, which means it didn't revert to anything. Good news is that the s/w was smart enough to catch the error. Next time, kill the power to the AHRS and see if it properly reverts.

 

[mburch]

I think the revert message only translates to reality if there is a second G3X ADHRS installed that it can revert to; Otherwise it is essentially an error message.. Unless something changed, the G3X will NOT use the G5 data, unless you power down the G3X ADHRS.

I am traveling so cannot quote from the G3X documentation, but the above statements are incorrect.

To the OP: typically this is an installation-related issue. An email to [email protected] with a data log file will be more helpful than posting on this forum.

 

[lr172]

I am traveling so cannot quote from the G3X documentation, but the above statements are incorrect.

To the OP: typically this is an installation-related issue. An email to [email protected] with a data log file will be more helpful than posting on this forum.

Like I mentioned, it may have changed. However, 2 or 3 years ago a garmin representative posted here in a reply to my query that the only way to have the G3X revert to G5 AHRS data when that data is corrupt is to power down the G3X AHRS. OP got a reversion message, but clearly it didn't revert to the G5 data, as it remained in conflict. That seems to confirm that things haven't changed.

Originally Posted by lr172 View Post
Sorry for the thread drift here. When I asked this question a few years ago (non-touch system), you indicated that the 25 must be powered down in order for the system to use the G5 ADHRS data. Have you updated the s/w to now support automatic cross fill without powering down the 25? Does this apply to the 370 based systems also?

Larry


Larry,

No it is the same behavior, I could have been more clear. If the GSU 25C were to fail (equivalent to pulling the power on the GSU 25C), the ADAHRS information from the G5 will be crossfilled to the G3X Touch display automatically.

Thanks,

Justin
__________________
Garmin G3X Support

From this reply one can assume that a complete failure of the AHRS (i.e. stops communicating on CANBUS) will cause a revert. However, if it is just spitting out inaccurate data, but still communicating, the AHRS must be shut down to revert to G5 AHRS data.

 

[KatanaPilot]

Just to add to the mix - I've seen four GSU 25 failures in the past year on different airplanes. The last one presented somewhat similar to yours. Replacement of the ADAHRS unit fixed the problem in all cases.

Aircraft was wings level -

 

[Walt]

IFR redundancy, dual GSU25, GI275, 3 puck GPS antennas (1 for each screen plus GI275)+ GTN:

 

[Draker]

Assuming it's a GSU 25, where is that mounted? I struggled with a very similar problem for a while, going through about three different GSU units. Finally determined it was likely vibration-related. Fixed it by mounting the GSU to a sturdier, heavier piece of metal and cross-bracing it against the aircraft structure.

 

[ronrapp]

Thanks for all the feedback, guys. I think the best suggestion was to email the G3Xpert with the log file, which I have done.

Speaking of log files, I took a look at the AHRS Dev % and it normally sits around 40% or so. But there are times when it spikes very briefly as high as 250%. Those are rare, but they happen consistently during climb on a wide variety of flights I've looked at over the past 100+ hours.

So it makes me wonder: are these momentary spikes normal? How much is permissible? And if these spikes never manifested themselves in any attitude issues before, why now? The lost of the PFD GPS position is the only thing I can think of.

I didn't build the plane, so I'm not sure where the GSU25 is located, but by virtue of having a high compression engine, this powerplant has always had a bit more vibration than other RVs I've flown. I did have the prop dynamically balanced a few months ago, but that didn't change much.

Re: pulling the AHRS breaker, I did do that since I was in VMC. That seemed to correct the attitude, which I assume is because it was getting AHRS information from the G5 at that point.

Interestingly, once I was safely on the ground at home base, I shut everything down and then rebooted it, and the PFD got its GPS position back.

--Ron

 

[KatanaPilot]

Thanks for all the feedback, guys. I think the best suggestion was to email the G3Xpert with the log file, which I have done.

Speaking of log files, I took a look at the AHRS Dev % and it normally sits around 40% or so. But there are times when it spikes very briefly as high as 250%. Those are rare, but they happen consistently during climb on a wide variety of flights I've looked at over the past 100+ hours.

So it makes me wonder: are these momentary spikes normal? How much is permissible? And if these spikes never manifested themselves in any attitude issues before, why now? The lost of the PFD GPS position is the only thing I can think of.

I didn't build the plane, so I'm not sure where the GSU25 is located, but by virtue of having a high compression engine, this powerplant has always had a bit more vibration than other RVs I've flown. I did have the prop dynamically balanced a few months ago, but that didn't change much.

Re: pulling the AHRS breaker, I did do that since I was in VMC. That seemed to correct the attitude, which I assume is because it was getting AHRS information from the G5 at that point.

Interestingly, once I was safely on the ground at home base, I shut everything down and then rebooted it, and the PFD got its GPS position back.

--Ron

I just talked with my son who flew one of the affected RV-14's for many hours during the troubleshooting time at the avionics vendor. He said the AHRS Deviation % was usually 40-60% before the problem GSU 25 was replaced and less than 10% afterwards. This was a single GSU 25 installation with the unit mounted on the back of the GDU 460. IO-390, M-T 3 bladed prop that had not been dynamically balanced.

Hope this helps.

 

[Draker]

g3xpert@ can explain the significance of the AHRS Dev%. It's very nuanced. The high values did often, but not always, correlate with my AHRS failures. Mine spiked up to around 700% !! during full power takeoffs. They'll probably ask you how it's mounted to the airframe, or if it's mounted to the back of the display. Good luck. This was a pretty frustrating problem to fix.

 

[mburch]

Don't pay too much attention to the meaning of those numbers, as they are only meaningful in certain regimes of flight. They are just one of several items Garmin will look at when examining your installation.

 

[rcarsey]

Looks similar to a problem I had during the first few flights of my RV-12.

https://youtube.com/shorts/0kbcRh1brfY

Garmin apparently changed some internals in the GSU 25C ADAHARS unit and they subsequently issued a bulletin (recall): https://support.garmin.com/en-US/?faq=WMWhNSdwO83csyCLAkL029

Serial numbers 5Q2000000 through 5Q2099999 were the ones affected.

You can consider using the same workaround method that Van's came up with in the RV-12 if it is indeed a vibration issue (https://www.vansaircraft.com/service-information-and-revisions/sb-00028/), or, if you're in the affected range, get an exchange from Garmin.