What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

GTN 625 with GNC255 - or GTN650

JDA_BTR

Well Known Member
I originally planned for a 625/255 combo and based on some flawed logic decided to get the 650. I didn't understand how the G3X works with the 650 and figured I could look at a VOR or the GPS pretty interchangeably. But that isn't the case.

The HSI only looks at one thing at a time, so you can't really check on a VOR with the Nav radio while following a GPS track. You have to select at the 650 to change the output from GPS to NAV radio and back to check on a VOR. Same for an ILS or other NAV source.

Also I figured that a failure in one part of the 650 wouldn't affect the NAV much because it has a separate power supply and board. But if the display isn't working then both GPS and NAV go away. No redundancy in what I have right now.

So now I wish I had the 625/255 combo. Or I wish the 650 would put out both the GPS and the NAV data to the G3X. And that the G3X could show the NAV data separate from the GPS, with maybe a popup HSI and an OBS.

Can't figure out how to do a VOR check or get a fix with GPS on autopilot; don't think it can be done.

I know a lot of you don't care about VOR/ILS in the GPS world. But is there something I'm missing in the functionality that will give me more what I want?
 
Unless you have multiple displays, I'm not sure the GTN 625 and GNC255 combo would give you what you want because the G3X will still only display one input at a time. It would be a nice feature for the G3X to display a serial input of a NAV radio in a popup window while navigating on GPS, or vice versa . Maybe that's something that should be posted in the feature wish list thread.
 
Doesn't the G3X have a bearing pointer display? If so, you should be able to wire it so that you can select various NAV sources for the bearing pointer(s).
The G5 allows that.

George
 
I originally planned for a 625/255 combo and based on some flawed logic decided to get the 650. I didn't understand how the G3X works with the 650 and figured I could look at a VOR or the GPS pretty interchangeably. But that isn't the case.

The HSI only looks at one thing at a time, so you can't really check on a VOR with the Nav radio while following a GPS track. You have to select at the 650 to change the output from GPS to NAV radio and back to check on a VOR. Same for an ILS or other NAV source.

Also I figured that a failure in one part of the 650 wouldn't affect the NAV much because it has a separate power supply and board. But if the display isn't working then both GPS and NAV go away. No redundancy in what I have right now.

So now I wish I had the 625/255 combo. Or I wish the 650 would put out both the GPS and the NAV data to the G3X. And that the G3X could show the NAV data separate from the GPS, with maybe a popup HSI and an OBS.

Can't figure out how to do a VOR check or get a fix with GPS on autopilot; don't think it can be done.

I know a lot of you don't care about VOR/ILS in the GPS world. But is there something I'm missing in the functionality that will give me more what I want?

Hello JDA_BTR,

It would be good to spend some time reviewing the pilot guide.

You can certainly tune and track a VOR with your GTN 650 and G3X Touch system. Just toggle the CDI source select between GPS (magenta needles) and VLOC (green needles) depending on which navigation source you wish to use.

You also have 2 bearing pointers that can be shown on the HSI, so while you are navigating with GPS, you can also display a VLOC bearing pointer to point to the tuned VOR and even a 2nd bearing pointer that is always pointing to the nearest airport in case of an inflight emergency.

We think that once you get to know your system, you will find that you have everything you need and more.

Thanks,
Steve
 
Are you sure?

The reason I titled this ‘Are you sure?’ is that I thought everyone had pretty much copied everyone else’s features by now. I have the older version of your nav equipment (or I should say, your desired equipment. For the same redundancy reasons mentioned by the OP): a 420W/SL30 combo. I have a GRT Hx for displaying nav data. The electronic HSI needle displays CDI data from the primary nav selected. But it also displays, in the form of RMI pointers, nav data from others sources. So, for example, the ILS at KSCK, which has a VOR cross fix: SL30 selected as primary nav; ILS in active nav window, cross fix vor in SL30’s standby window, SL 30 in monitor mode (SL30 can output nav data from both primary and standby channels), gps on the missed approach holding fix. Inbound I track the HSI CDI; double check at GS intercept that the cross fix RMI bearing is correct; if I miss, fly heading via the gps RMI needle. If the G3X won’t do this, this is what you should lobby Garmin for. I know the 430 will output both gps and nav data at the same time, so I’d be surprised if the 650 doesn’t. As to the 30 day vor check: Remember you can use a visual landmark (with a 6 deg tolerance!). There is a prominent local hill that I try to fly over on departure. I have measured the bearing to the closest vor, using a sectional. I display the bearing on the SL30, note that it is what it is suppose to be. The real challenge is remembering to record it in the plane’s logbook.

Edit: I see that while I was typing, Garmin answered, and as I guessed, it will already do what I tried to describe.
 
Last edited:
You also have 2 bearing pointers that can be shown on the HSI, so while you are navigating with GPS, you can also display a VLOC bearing pointer to point to the tuned VOR and even a 2nd bearing pointer that is always pointing to the nearest airport in case of an inflight emergency
Thanks,
Steve

Steve, can a 420W do this? e.g. track to KABC, while simultaeously outputing the heading to the nearest airport? Can you point me to the page in the manual describing how to do this? Or were you referring to using a second gps for this?
 
I can setup the GTN 625 for a VOR approach and the G3X autopilot will fly it beautifully complete with the recommended entry into a holding pattern for course reversal. The accuracy and situational awareness is much greater than I can hand fly the plane tracking the VOR with the NAV. However, the FAA says unless I have a way to monitor the underlying NAV signal, I cannot let the autopilot fly this approach legally in IMC.

The bearing pointer is nice, but being able to monitor the green needles in window would make that approach legal and add the safety of allowing the autopilot to fly it perfectly. Is a bearing pointer enough information to say you are monitoring the underlying navigational signal?
 
Steve, can a 420W do this? e.g. track to KABC, while simultaeously outputing the heading to the nearest airport? Can you point me to the page in the manual describing how to do this? Or were you referring to using a second gps for this?

Bob,

A G3X or G3X Touch system with/without a 420W can provide both the Best Airport bearing pointer (within glide range) and the Nearest Airport bearing pointer, both of which are described on page 136 of the Rev. K G3X Touch Pilot Guide.

In both cases the bearing pointer window automatically shows the airport identifier and shows distance to the airport. This bearing pointer feature is being provided by the G3X/G3X Touch system, not the IFR navigator, so this feature is available in all G3X/G3X Touch systems, even without an IFR navigator.

In a system like the O.P. has, there are actually 3 navigators at work. The GTN 650 WAAS GPS and VOR/ILS navigators, and the WAAS GPS navigator built-into the G3X Touch primary flight display.

Thanks,
Steve
 
I can setup the GTN 625 for a VOR approach and the G3X autopilot will fly it beautifully complete with the recommended entry into a holding pattern for course reversal. The accuracy and situational awareness is much greater than I can hand fly the plane tracking the VOR with the NAV. However, the FAA says unless I have a way to monitor the underlying NAV signal, I cannot let the autopilot fly this approach legally in IMC.

The bearing pointer is nice, but being able to monitor the green needles in window would make that approach legal and add the safety of allowing the autopilot to fly it perfectly. Is a bearing pointer enough information to say you are monitoring the underlying navigational signal?

Hello Mark,

We can't tell from your post if you have a NAV radio or not, but if you do, you can monitor the VOR signal from the NAV radio with a bearing pointer on the HSI and use the GTN 625 to fly the VOR approach.

Sort of surprised you have much reason to fly a VOR approach these days.

Thanks,
Steve
 
How can I see the VOR bearing on a bearing pointer when the gtn650 can only send one or the other? It’s my understanding I have to pick which one is sent at the 650?

The pilot guide has been reviewed. It is very GPS focused.
 
How can I see the VOR bearing on a bearing pointer when the gtn650 can only send one or the other? It’s my understanding I have to pick which one is sent at the 650?

The pilot guide has been reviewed. It is very GPS focused.

Hello JDA_BTR,

You are able to select and show a VLOC bearing pointer on the G3X/G3X Touch HSI even when navigating with GPS since the GTN 650 is providing everything needed to do that.

Are you flying your plane yet?

Thanks,
Steve
 
Last edited:
I?m very close and not wanting to learn airborne. If the 650 is sending gps and vloc to the g3x at all times why is there a nav source select in the 650?
 
I?m very close and not wanting to learn airborne. If the 650 is sending gps and vloc to the g3x at all times why is there a nav source select in the 650?

On the back of your 650 there are pins designed to be connected directly to a CDI (needle left, right, up, flag,....). This data is switched VLOC-GPS by the switch on the 650. But there are also pins on the back that are dedicated to VLOC data, and more that are dedicated to GPS data. (These are ARINC format). These pins are not switched by tbe 650 button. They need to be wired to the EFIS to get the functionality bring discussed.
 
I?m very close and not wanting to learn airborne. If the 650 is sending gps and vloc to the g3x at all times why is there a nav source select in the 650?

Hello JDA_BTR,

That is exciting to be close to flying. We appreciate the desire to get the basics down before trying to use them in the air.

The CDI source select button is how you switch navigation sources which drive the course pointer and lateral/vertical deviation indicators on your primary flight display.

You are only navigating with one of these at a time, so you only have a single course pointer on the HSI.

The dual bearing pointer capability on the HSI is something quite different. Regardless of which navigation source you have selected to drive the HSI course pointer, you can still set a bearing pointer to VLOC to monitor the bearing to any tuned VOR or to GPS to monitor the active waypoint (in addition to the bearing pointer choices for nearest/best airport).

The CDI source select also determines what navigation source your autopilot is coupling to. Again, the course pointer and information shown on the HSI (e.g. GPS or VLOC) tell you which navigation source will be coupled when you press the NAV or APR button on your GMC 307/507.

You may always contact us directly at [email protected].

Thanks,
Steve
 
One of the reasons I like the 650 is the auto transition from GPS to an ILS approach when an ILS approach is loaded and activated. Can't do that with seperate units.
 
One of the reasons I like the 650 is the auto transition from GPS to an ILS approach when an ILS approach is loaded and activated. Can't do that with seperate units.

Well, my set up will. I think most EFISs will.
420W, SL30, GRT Hx.
Set up gps nav to intercept localizer
Set up ILS
Hx will auto switch as the localizer is intercepted.
 
Well, my set up will. I think most EFISs will.
420W, SL30, GRT Hx.
Set up gps nav to intercept localizer
Set up ILS
Hx will auto switch as the localizer is intercepted.

Thanks for the info, I didn't know the Hx would do that.
Perhaps the G3X will do the same thing with a 620/255 or 420/SL30? (never had an opportunity to fly these combo's)
 
Last edited:
So I got a VOR/ILS tester in the hangar and found out some things.

My setup didn't work at first. On the G3X ARINC page I had the GPS as Nav1 -> GPS and the Nav as Nav1->VOR/ILS. I had to change the VOR/ILS to Nav2, and then it seemed to work right. With both on Nav1 the VOR/ILS was totally ignored and the CDI could not be selected to anything but GPS.

So now my inputs to the G3X show as GPS1 and VOR/ILS2. I wish it was just GPS or VOR/ILS. The 1 and 2 aren't needed. The G3X config has room for more on the ARINC with 4 channels, but you can only have Nav1 or Nav2. Not sure what you would do to have Nav3/4.

It is my observation that the heading indicator, when enabled for VOR/ILS, shows the frequency of the Nav radio, not the heading the VOR is found on. Not sure what to look at otherwise.

I also checked with the test set the ILS LOC/GS. The LOC is on the HSI, and the GS is along the altitude strip. Is it possible somewhere to see the GS/LOC together like an analog instrument?

Lastly, when looking at a VOR, the indicator for the error shows both as the line on the HSI, and as the bar across the top of the HSI.... not sure why the information is displayed in two places. I must be missing something there.

Thank goodness for the test set VOR though. I was able to figure out a lot about the system today. I highly recommend you find someone with one when learning this for the first time. It also proves my antenna works, with a good response down to -60dB on the test set. It also tracked the nearby runway ILS in my hangar.
 
So I got a VOR/ILS tester in the hangar and found out some things.

My setup didn't work at first. On the G3X ARINC page I had the GPS as Nav1 -> GPS and the Nav as Nav1->VOR/ILS. I had to change the VOR/ILS to Nav2, and then it seemed to work right. With both on Nav1 the VOR/ILS was totally ignored and the CDI could not be selected to anything but GPS.

So now my inputs to the G3X show as GPS1 and VOR/ILS2. I wish it was just GPS or VOR/ILS. The 1 and 2 aren't needed.

Hello JDA_BTR,

Just taking a guess here, but it sounds like you were not using the CDI Source Select button on the GTN 650 to switch between GPS and VOR/ILS nav sources shown on the PFD HSI. That is why you could not change the HSI nav source from GPS to VOR/ILS and why your system did not respond to the VOR/ILS test setup.

What you did was configure your system to have two separate navigators (one GPS and one NAV), which caused a navigator select feature to become available on the PFD.

You should put your configuration back the way it is supposed to be as defined on page 27-30 of the Rev. AG G3X Installation manual which explains how to properly configure a single GTN 650 navigator. This will restore your single GTN 650 system to having a GPS1/NAV1 instead of a GPS1/NAV2.

We encourage you to consider contacting us via [email protected] so we can assist you more directly.

Thanks,
Steve
 
But I did use the GPS CDI select button to go back and forth to no avail. It was only when I changed the Nav1 to Nav2 that it worked.

Perhaps being able to select at the G3X and not at the GTN is a feature and not a flaw; is there a reason to NOT set it up that way? I was pretty easily able to pick what I wanted to do with the G3X in that config without doing anything at the GTN.

I'll call later today.
 
Thanks - we look forward to hearing from you.

Hopefully you are using current G3X Touch software instead of something old. We hear from quite a few customers who pull things out of the boxes, turn them on, and never load new software that gets everything operating at the same level.

Thanks,
Steve
 
... However, the FAA says unless I have a way to monitor the underlying NAV signal, I cannot let the autopilot fly this approach legally in IMC.

The bearing pointer is nice, but being able to monitor the green needles in window would make that approach legal and add the safety of allowing the autopilot to fly it perfectly. Is a bearing pointer enough information to say you are monitoring the underlying navigational signal?
I would argue yes, a bearing pointer alone adequately monitors the underlying signal. If the IAP only requires lateral guidance, that's what the bearing pointer is providing. Just like flying an NDB approach, only easier.

George
 
Back
Top