GTN 750, CDI Key, VLOC Navigation

[Cabanaboy]

My GTN 750xi does not have a CDI Key that toggles between Navigation Sources. I have two GI-275's and can click CDI key on the GI275 HSI but the GPS remains in GPS Mode. 

My paper install manual filled out by installer has check mark on CDI Key enabled.

Most videos I see seem to have them on and working changing annunicator to VLOC in green on GPS.

Wondering if anyone understands how that works?

Thanks

[PT20J]

I believe it's a setting on the Main Indicator (Analog) page in configuration mode.

[Cabanaboy]

1 minute ago, PT20J said:

I believe it's a setting on the Main Indicator (Analog) page in configuration mode.

thanks, Configuration Mode probably means installer/dealer can only set it I assume, can you think of any reason why they would not have enabled? Forgot? I have an email in to them.

[PT20J]

 

20 minutes ago, Cabanaboy said:

thanks, Configuration Mode probably means installer/dealer can only set it I assume, can you think of any reason why they would not have enabled? Forgot? I have an email in to them.

There are a zillion settings, some different for different combinations of equipment. It’s easy to overlook one. 

You can get the Maintenance Manual from the Garmin website that describes how to use configuration mode. 
https://static.garmin.com/pumac/190-01007-c1_02.pdf

Skip

[PeteMc]

Picture you're showing of the 275 does show LOC and is green, so it would appear that it is following the ILS/LOC.  But certainly worth checking out if you're supposed to be able to change that on the 750 or just on the 275.

[Cabanaboy]

2 hours ago, PeteMc said:

Picture you're showing of the 275 does show LOC and is green, so it would appear that it is following the ILS/LOC.  But certainly worth checking out if you're supposed to be able to change that on the 750 or just on the 275.

Yeah thats what i was thinking and not sure why the CDI key is not there, I flew approach yesterday and it captured the Glide Slope flew me down. But the GPS remained in GPS Mode.

[PT20J]

I don’t have the GI 275 STC installation manual, but in reading the description of the CDI key for the GTN it’s likely that your installation is correct. I would consult with the installer before changing it.

[PeteMc]

It would appear the way they set it up is that you change it on the 275, not the GTN.  So the button is hidden.

But it would be nice if the avionics shop confirmed that.

[Cabanaboy]

great info guys, i am hoping my installer can help me understand what we need to do. I do not see much conversations or discussions on ILS,  VOR approach procedures with these avionics. What a great resource we have here on web/mooneyspace. Still learning and working through this. Hopefully the info can help others as well in the future trying understand the issue. Any info i get i will post. thanks everyone. Garmin Pilot ops could not answer this question but they are not an "install" information resource.

 

 

[midlifeflyer]

5 hours ago, Cabanaboy said:

do not see much conversations or discussions on ILS,  VOR approach procedures with these avionics. 

Many simply prefer the simplicity of RNAV and  avoid even ILS approaches with the new boxes unless they have to. When I do a checkout, IPC or recurrent instrument training, I insist on performance of an ILS to missed - coupled assuming they have an autopilot - simply because of all the extra switching / button pushing / confirmations involved. The ILS was the definition of simplicity old school but the coupled ILS to missed with a new box has the ability to demonstrate just about every gotcha the system is capable of. (My personal favorite is the non-GPSS autopilot turning the wrong way on a course reversal in NAV mode.)

[Cabanaboy]

6 hours ago, midlifeflyer said:

Many simply prefer the simplicity of RNAV and  avoid even ILS approaches with the new boxes unless they have to. When I do a checkout, IPC or recurrent instrument training, I insist on performance of an ILS to missed - coupled assuming they have an autopilot - simply because of all the extra switching / button pushing / confirmations involved. The ILS was the definition of simplicity old school but the coupled ILS to missed with a new box has the ability to demonstrate just about every gotcha the system is capable of. (My personal favorite is the non-GPSS autopilot turning the wrong way on a course reversal in NAV mode.)

Mark can you help me/us understand what the GPS is doing when it is switched into VLOC mode when pressing the CDI key(my GTN750 does not display CDI Key). How is the Autopilot tracking the ILS glide slope (I did have GPS Tuned to ILS Freq in NAV1 on GTN)  My GI-275 was in LOC Mode in green and the Autopilot captured the Glideslope although the GPS was displaying GPS mode. What benefit does the CDI provide on the GPS?  Im sure what i am asking is clear as mud the way i am describing this.  Anyone?

[midlifeflyer]

10 hours ago, Cabanaboy said:

Mark can you help me/us understand what the GPS is doing when it is switched into VLOC mode when pressing the CDI key(my GTN750 does not display CDI Key). How is the Autopilot tracking the ILS glide slope (I did have GPS Tuned to ILS Freq in NAV1 on GTN)  My GI-275 was in LOC Mode in green and the Autopilot captured the Glideslope although the GPS was displaying GPS mode. What benefit does the CDI provide on the GPS?  Im sure what i am asking is clear as mud the way i am describing this.  Anyone?

I'm not completely sure what you are seeing. This is based on what I see with multiple systems, so I hope this answers your question.

if I understood what's already been said, your GTN has relinquished its control over CDI selection and handed it over to the one on your GI275 PFD. Once you've switched the CDI on your PFD and are using green needles for navigation, your autopilot should be tracking the Localizer  and the ILS glideslope in NAV or APR mode, not the GPS output.

If you loaded the ILS approach in the 750, the GPS will track it (there's a possible gotcha in there, but we'll let it go). It will look like it's giving nav information and will even annunciate LNAV. But at  this stage, the Localizer is giving primary nav Information and the 750 has two functions. One, it's acting as a situational awareness tool, not a primary navigation tool. Second, it's sequencing through the approach, keeping up with you so it's ready to resume the primary navigation role when you tap the CDI back to pink needles and unsuspend for the missed.

This is so much easier to demonstrate than explain, especially in a forum post.

[PT20J]

2 hours ago, midlifeflyer said:

I'm not completely sure what you are seeing. This is based on what I see with multiple systems, so I hope this answers your question.

if I understood what's already been said, your GTN has relinquished its control over CDI selection and handed it over to the one on your GI275 PFD. Once you've switched the CDI on your PFD and are using green needles for navigation, your autopilot should be tracking the Localizer  and the ILS glideslope in NAV or APR mode, not the GPS output.

If you loaded the ILS approach in the 750, the GPS will track it (there's a possible gotcha in there, but we'll let it go). It will look like it's giving nav information and will even annunciate LNAV. But at  this stage, the Localizer is giving primary nav Information and the 750 has two functions. One, it's acting as a situational awareness tool, not a primary navigation tool. Second, it's sequencing through the approach, keeping up with you so it's ready to resume the primary navigation role when you tap the CDI back to pink needles and unsuspend for the missed.

This is so much easier to demonstrate than explain, especially in a forum post.

Mark, I was under the impression that the GTN will change annunciation from GPS to VLOC when switched to VLOC either by Auto Switch (assuming it is enabled), pressing the CDI key, or external control if that is enabled. In my case, I have a G3X so the PFD does not control the switching and the CDI key is enabled. Pressing the CDI key causes the GTN to annunciate VLOC. Also, the GTN annunciates the change from GPS to VLOC when intercepting a localizer with Auto Switch enabled. I have not flown a GTN with GI 275s. Since in this case the CDI key is apparently supposed to be disabled, I'm not clear if Auto Switch is still available on the GTN. But it would seem odd if switching to VLOC on the GI 275 didn't cause the GTN to annunciate VLOC. Can you clarify?

Skip

[N231BN]

Most likely the GI-275 is using both the MAIN and VLOC ARINC outputs of the GTN(or perhaps HSDB). It is receiving both outputs at the same time and decides which one to display, and then forwards that information on to the autopilot. This way they can provide different color needles for the difference source as well as VLOC preview while on GPS.

[midlifeflyer]

17 hours ago, PT20J said:

Mark, I was under the impression that the GTN will change annunciation from GPS to VLOC when switched to VLOC either by Auto Switch (assuming it is enabled), pressing the CDI key, or external control if that is enabled. In my case, I have a G3X so the PFD does not control the switching and the CDI key is enabled. Pressing the CDI key causes the GTN to annunciate VLOC. Also, the GTN annunciates the change from GPS to VLOC when intercepting a localizer with Auto Switch enabled. I have not flown a GTN with GI 275s. Since in this case the CDI key is apparently supposed to be disabled, I'm not clear if Auto Switch is still available on the GTN. But it would seem odd if switching to VLOC on the GI 275 didn't cause the GTN to annunciate VLOC. Can you clarify?

Skip

Without seeing what the GTN looks like when the PFD changes to green needles, I don't know. But your CDI and AP should  be following the localizer feed and the PFD should be following the glideslope not the glidepath.whatever the GTN says.

[PT20J]

On 1/7/2022 at 9:58 AM, Cabanaboy said:

My GTN 750xi does not have a CDI Key that toggles between Navigation Sources. I have two GI-275's and can click CDI key on the GI275 HSI but the GPS remains in GPS Mode. 

My paper install manual filled out by installer has check mark on CDI Key enabled.

Most videos I see seem to have them on and working changing annunicator to VLOC in green on GPS.

Wondering if anyone understands how that works?

Thanks

So, back to the original post: Without the installation manuals (which Garmin only makes available to dealers) it's hard to tell. But perhaps the CDI key is supposed to be disabled for a dual GI 275 installation and perhaps the documentation showing that it was enabled is correct. Maybe this confuses the GTN software? I would go back to the installer and have them sort it out.

[Cabanaboy]

Few images from 750xi Manual

[carusoam]

Let’s see if @Fly_M20R is around…

He has documented a fair amount of GI275 experience….

Best regards,

-a-

[N231BN]

So, back to the original post: Without the installation manuals (which Garmin only makes available to dealers) it's hard to tell. But perhaps the CDI key is supposed to be disabled for a dual GI 275 installation and perhaps the documentation showing that it was enabled is correct. Maybe this confuses the GTN software? I would go back to the installer and have them sort it out.

As I tried to state last night, I believe it is supposed to be disabled on the GTN as the GI-275 is receiving VLOC data on a separate output.

The CDI key on the GTN only switches the main analog outputs which aren't used by the GI-275.

[PT20J]

10 minutes ago, N231BN said:

As I tried to state last night, I believe it is supposed to be disabled on the GTN as the GI-275 is receiving VLOC data on a separate output.

I understand that. Clearly the GI 275 is displaying the localizer and glideslope properly. The question no one has answered is why the GTN continues displaying GPS rather than VLOC after switching to VLOC on the GI 275. Maybe that's the way it is supposed to work, but it is not the way it works when the GTN auto switches or has a CDI key enabled.

[N231BN]

I understand that. Clearly the GI 275 is displaying the localizer and glideslope properly. The question no one has answered is why the GTN continues displaying GPS rather than VLOC after switching to VLOC on the GI 275. Maybe that's the way it is supposed to work, but it is not the way it works when the GTN auto switches or has a CDI key enabled.

That is because the main analog outputs are still displaying GPS data.

Section 5.5.5 of GTN manual:

CDI Key

To enable or disable the CDI key, touch the key to the right of CDI key to toggle between enabling and disabling the CDI key. Disabling the CDI key causes the CDI source to always display as GPS and removes the CDI key. This may be necessary for certain EFIS systems where navigation sensor selection must be accomplished on the EFIS or its control panel.

[PT20J]

1 hour ago, N231BN said:

That is because the main analog outputs are still displaying GPS data.

Section 5.5.5 of GTN manual:

CDI Key

To enable or disable the CDI key, touch the key to the right of CDI key to toggle between enabling and disabling the CDI key. Disabling the CDI key causes the CDI source to always display as GPS and removes the CDI key. This may be necessary for certain EFIS systems where navigation sensor selection must be accomplished on the EFIS or its control panel.

Well, that's embarrassing. I somehow missed the second sentence when I posted that excerpt way back early in this thread. I will now enroll in a reading comprehension course .  So, it appears that everything in @Cabanaboy's installation is working correctly.

Since the G500 allows CDI selection from the PFD, does it also require disabling the GTN CDI key?

 

[N231BN]

Well, that's embarrassing. I somehow missed the second sentence when I posted that excerpt way back early in this thread. I will now enroll in a reading comprehension course .  So, it appears that everything in [mention=8332]Cabanaboy[/mention]'s installation is working correctly.
Since the G500 allows CDI selection from the PFD, does it also require disabling the GTN CDI key?
 

I suppose it would depend on the EFIS install manual but I don't think it would have any effect if it were enabled. I flew a G500/GTN equipped aircraft this summer but I don't remember if the button was available.

Years ago I flew a G600/GNS equipped aircraft, I always used the CDI button on the display, I can't remember if the button on the 530 did anything.

[Ragsf15e]

You guys and your fancy toys are making me love my old 430w even more!  

[Cabanaboy]

Using the PC Garmin Trainer Software download (does not have a gi275) but shows CDI enabled and seems to function to effect a VLOC on the GPS and Digital EFIS when pushed. I do not remember my GTN ever switching to VLOC mode in the GPS but need to  check the Autoswitch setting and watch when flying into switching range. See screen print, loaded only ILS 18 approach to KMYR. Flight plan KHYW - KMYR