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g3xpert help with 650xi and G3X

Flyyak

Well Known Member
Friend
I have recently upgraded my RV7 from a GNS 430W to a GTN 650xi. I have spoken to several of the guys in the Garmin experimental area (Ken, Caleb and Mike) and one member of the Garmin pilot support side over the last week to resolve several issues, mainly configuration issues. I have a G3X system (370 and 375) with a GSU73, GSU25, GMU44, GTX23ES, roll and pitch GSA28, GMC305 and a GMA240. With the great help from these guys, I have all the wiring and configuration bugs resolved with the exception of one issue. My G3X configuration shows all green with all connections and interfaces and I do not have any errors displayed on the GTN650xi. The issue that remains is - the G3X will not capture the Glide Path on an approach and will not provide vertical guidance to the autopilot. With the help of your team, we have verified the configuration and interface between the G3X and the GTN on a couple of occasions but still no luck.

First let me verify that before I removed the 430W, I flew several approaches and the G3X, GNS and autopilot worked flawlessly. Here is what happens now with the GTN - I have test flown the RV using the autopilot for gps navigation with a flight plan and it captures and flies the plan (lateral navigation) without any issues. I have flown a flight plan from KEKY to OKW with the RNAV rwy 5 LPV approach and all is well with lateral navigation but the G3X will show GP in white when on the final approach course but it will not capture the GP for vertical navigation. I have tried this approach loading the approach and activating the approach when reaching OKW and the autopilot will fly the approach from OKW to KHANN to MEATA to WONOR to Rwy 5 but it will not provide or capture vertical navigation and the plane will be at 2400 or 2500 at the end of the rwy. I have tried the approach by activating the leg OKW to KHANN , then when established on the leg, activating the approach and it captures lateral navigation but same result with vertical navigation. I have flown the approach by using vectors to final to KHANN , activating the approach and again it will fly lateral navigation but will not capture vertical navigation. On each flight the G3X (PFD) will annunciate GP in white but it will never show vertical bars or will cature (turn green). On each of the flights the GTN will switch (annuciate at the bottom) from gps (magenta) to LPV (green) as it should on the final approach course. The screen will display a visual approach icon. On each flight, I have activated the approach on the GTN and I have activated the approach on the GMC305. The 305 will couple for lateral navigation but will not capture the GP. Each time the GP is white on the PFD on the G3X but it never captures for vertical guidance and turns green. I do not get an error message on the GTN or G3X. I have photos of the G3X and the GTN configuration pages if needed.

Has anyone who has completed this upgrade had this issue and been able to resolve it. I am told that it is not a wiring issue and it appears not to be a configuration issue between the G3X and GTN since no error messages. Obviously the unit is receiving a valid gps signal and I understand that the lateral and vertical navigation is split internally in the unit. Any help will be appreciated.
 
Hi Flyyak,

You mention several times that the system does not capture the LPV glidepath, but not sure if you have told us whether or not it displays the glidepath vertical deviation field next to the altitude tape.

Each time you cross the FAF-1 waypoint (KHANN) and the FAF waypoint (MEATA) becomes active, the vertical deviation field (shown circled here) should appear on the PFD, and the magenta diamond will drop in this field until it reaches the center where the system will capture the glidepath and follow it down. Are you seeing the vertical deviation field appear between KHANN and MEATA?

BeforeGPCapture.png

The presence of the vertical deviation field prior to the FAF is an indication that the G3X system is receiving vertical guidance from the navigator over A429. Without this guidance, it can never capture the glidepath when the vertical deviation approaches zero at the glidepath.

You can activate the LPV approach with either the AKGOS or OKW transition 40 nm out if you wish. The system is not at all picky about when the approach is activated.

Steve
 
I think I know what we will see, but it would also be good to see a section of your datalog like the one below from one of my recent LPV approaches.

You can see how the blue highlighted vertical deviation data is ticking down towards zero reflecting the movement of the vertical deviation diamond before the glidepath is captured at 11:54:36. It would also be good to verify that your selected NavSrc is GPS1 as shown in this example.

LPV Appr Datalog.png

Keep in mind that you can navigate an LPV approach laterally with just the RS-232 MapMX guidance, but without A429, there is no vertical approach guidance. It seems that you have a problem with the A429 output (wiring) from the GTN to the GAD 29.

Steve
 
Last edited:
Settings...

On 650xi power on holding the "Home" button, select GTN Setup, then select ARINC 429

Verify ARINC settings are as follows:

ARINC 429 In 1 - Speed: LOW Data: EFIS/AIRDATA
ARINC 429 Out 1 - Speed: LOW Data: GAMA FORMAT 1
SDI to LNAV 1

-
G3X

ARINC 429 TX 1 format to "EFIS/AIRDATA FORMAT 1" and "NAV 1"
ARINC 429 RX 1 format to "GARMIN GPS" and "NAV 1"
 
Here is a ground test. When you power on the GTN, there is an instrument test page that drives both the lateral and vertical deviation indications. The vertical deviation is driven only by A429.

GNXInstrumentTestPage.png

When you do this test with the GPS1 navigator selected on your HSI, do you see the "half up" vertical deviation indication on the PFD that is being driven by the A429 out of the GTN?

VDI PowerOnTest.png

Steve
 
Here is a ground test. When you power on the GTN, there is an instrument test page that drives both the lateral and vertical deviation indications.

Is that on the configuration page? (I'm not in the airplane at the moment.)

Thanks!

PS. Mine seems to be working, hope this doesn't jinx it.
 
I was out of town today but will verify the info you have suggested tomorrow. Thanks for the input.
 
I do not have a gad 29 but a GSU73 and a GSU 25. I have sent a pin placement between the GTN and GSU 73 to the g3xperts for their review. I am hoping it is a configuration issue rather than wiring.
 
I do not have a gad 29 but a GSU73 and a GSU 25. I have sent a pin placement between the GTN and GSU 73 to the g3xperts for their review. I am hoping it is a configuration issue rather than wiring.

Flyyak,

Sounds good.

The GSU 73 will work fine with the GTN. You do not need a GAD 29. I am still using a GSU 73 for ADAHRS/EIS/A429 in my plane that was installed over 10 years ago.

Steve
 
GSU 73 Capabilities

I think that's the issue. You need the GAD 29 to create the vertical deviation "link" between the 650 and the G3X.

For a bit of background on this, the GSU 73 is an original design of the non-touch G3X system and combines the abilities of the GSU 25, GAD 29, and GEA 24, to act as an ADAHRS/EIS/429 Hub. We later changed the design of the system to separate these individual components out into their own line replaceable units for ease of maintenance. So in this case this aircraft has no need for a GAD 29. It sounds like the G3X is receiving RS232 MAPMX data from the Navigator, but not ARINC 429 GPS data, so there is likely a configuration or wiring issue in the ARINC 429 GPS datapath somewhere.

Thanks,

Justin
 
650xi and G3X

You guys were correct. Both bjdecker and longez. I had misinterpreted the 429 setup. I selected ARINC 429 and failed to scroll the screen down to select Garmin 429. The g3xperts helped me reconfigure and indicated the Gama format or the Garmin 429 would work. After reconfiguring, the self test of the 650 indicated like longez stated.

I will try to load a few photos. I also learned that the G3X HSI indicated VFR even while on the approach. This was because the 650 wasn’t communicating with the G3X.
 

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Hidden APPR ?

Great diagnostics and help!!! Interesting read as I have the 73, 370 and 650 too and found the data to be invaluable in understanding what was happening after the fact. The OP has the 305, but I don't.

When practicing and using VNAV to descend to the IAF, the APPR activation is hidden under the VNAV soft key indicator. So, don't let that trip anyone up. It took several flights to see what was happening. When arriving at the IAF, tap ALT, then cycle VNAV off, the APPR will appear and can be engaged for the vertical couple. Otherwise HSI will show vertical indication, but maintain the last set VNAV altitude. Lateral remains coupled. In real IMC/IFR, I don't usually find it helpful to use VNAV, or haven't learned how to, but in practices I was just exercising VNAV to see how it might be incorporated in the process.
 
Nothing to add...but posts and threads like this are always helpful for us watching to think about troubleshooting steps.
 
WX down here in south is really not very good especially for a test flight in IMC but I hope to test it in the next couple of days and will let you know.
 
Test flew today after proper configuration and 650 with G3X flew a perfect LPV approach, captured GP and noted proper notations on PFD.

Next question - I note that the 650xi pilot manual sets out “database sync” in the system status menu. I purchased the full spread of databases for the G3X and only the navigation database for the 650xi at the recommendation of Garmin product support. It saved about $100 from purchase of the full subscription for the 650xi and the Garmin rep indicated that the G3X would have all the info stored in it and I only need the navigation in the 650.

I tried the database sync on the 650xi and it does not recognize any other databases available- does not recognize the G3X databases. Is there a setup that will enable the two units to share the database info. I have non touch 370/375 G3X units.
 

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Test flew today after proper configuration and 650 with G3X flew a perfect LPV approach, captured GP and noted proper notations on PFD.

Next question - I note that the 650xi pilot manual sets out “database sync” in the system status menu. I purchased the full spread of databases for the G3X and only the navigation database for the 650xi at the recommendation of Garmin product support. It saved about $100 from purchase of the full subscription for the 650xi and the Garmin rep indicated that the G3X would have all the info stored in it and I only need the navigation in the 650.

I tried the database sync on the 650xi and it does not recognize any other databases available- does not recognize the G3X databases. Is there a setup that will enable the two units to share the database info. I have non touch 370/375 G3X units.

The GTN650xi has the WAAS GPS which allows you to fly IFR GPS precision approaches. So, you must be using the "external" GPS when flying approaches. Logic would dictate that the GTN650xi should contain the IFR database, as the G3X GPS is VFR only. When you manage the approach on the GTN650xi, everything is displayed on the G3X. Just my 2 cents.
 
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