GTN 750, CDI Key, VLOC Navigation

[N231BN]

I just did a quick read-through of the GI-275 manual (google finally found one) and I didn't see any requirement to disable the CDI key on the GTN. There isn't any point to enable it either, the GI-275 communicates via ethernet(HSDB) so it is receiving both sources through that interface. If you had a GI-106a also connected to the GTN as a backup indicator then it would control that but has no effect on the GI-275.

[midlifeflyer]

This is what it looks like with a CDI key. The VLOC indicates the CDI selection. The LNAV indicates what the GPS, not the PFD CDI, is tracking. With no CDI key I wouldn't necesssarily expect to see the VLOC annunciation at all.

Edited January 11, 2022 by midlifeflyer

[Brent]

On 1/10/2022 at 8:21 PM, Ragsf15e said:

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

Safety net:

[Cabanaboy]

On 1/11/2022 at 4:10 PM, midlifeflyer said:

This is what it looks like with a CDI key. The VLOC indicates the CDI selection. The LNAV indicates what the GPS, not the PFD CDI, is tracking. With no CDI key I wouldn't necesssarily expect to see the VLOC annunciation at all.

 

Mine just does not have the CDI enabled and I am trying to figure out why and what utility i may be missing. I have not heard back from shop yet and will have to call in i guess. I was hoping someone that uses the CDI key would be able to enlighten us.

 

 

 

[midlifeflyer]

4 hours ago, Cabanaboy said:

 

Mine just does not have the CDI enabled and I am trying to figure out why and what utility i may be missing. I have not heard back from shop yet and will have to call in i guess. I was hoping someone that uses the CDI key would be able to enlighten us.

 

I'll be interested to hear what the shop says. My guess is that the only utility you use is the ability to change the source feeding the OBS or HSI course indicator from the 750, unless something is very wrong. That's really all the CDI key does.  But it's significant. On a missed approach from an ILS, you will probably have to unsuspend on the 750 and switch to pink needles on the PFD rather than pushing two buttons right next to each other.

 

Edited January 13, 2022 by midlifeflyer

[N231BN]

39 minutes ago, midlifeflyer said:

I'll be interested to hear what the shop says. My guess is that the only utility you use is the ability to change the source feeding the OBS or HSI course indicator from the 750, unless something is very wrong. That's really all the CDI key does.  But it's significant. On a missed approach from an ILS, you will probably have to unsuspend on the 750 and switch to pink needles on the PFD rather than pushing two buttons right next to each other.

 

When you activate the MAP it should auto-switch back to GPS.

[midlifeflyer]

3 minutes ago, N231BN said:

When you activate the MAP it should auto-switch back to GPS.

Should would could. Yes, in a perfect Garmin digital setup you  "should" not need  to touch anything. While in NAV mode, load the approach. Confirm the blue altitudes on the flight plan page. Once direct to a transition fix, hit VNV and APR on the autopilot and sit back as the airplane flies the transition, and  hits all the altitude step-downs. When the FAF becomes the active waypoint, the PDF switches itself to green needles and captures the ILS glideslope.  At DA, if you don't see anything, you power up and press TOGA. Since the autopilot didn't disconnect when you hit TOGA, the airplane begins the climb. The system prompts your to unsuspend and when you do, the green needles on the PFD change back to pink. Since you've already placed the top of the missed approach climb in the altitude selector, you select or confirm NAV and IAS/FLC mode on the autopilot and you are done. 

I think there are a few systems and system combos which do all that, smoothly. One of the things I've learned from flying and teaching with multiple setups is not to let my expectations of what should happen in a system I haven't seen  based on some other system get in the way. I've seen auto-switching that works great, auto-switching which you have to watch like a hawk, and no auto-switching at all when you think it "should." I think it's the The standard installation of the GFC 500 AP, unlike the 700 (and I think the 600),  doesn't let you arm both VNV and APR at the same time. There are so many variations on that theme I can't say which way this setup does it. That's why I used the word "probably." Guess I should have used "may."

In terms of your specific "should," how about this note from the 750 User Guide?

[N231BN]

42 minutes ago, midlifeflyer said:

Should would could. Yes, in a perfect Garmin digital setup you  "should" not need  to touch anything. While in NAV mode, load the approach. Confirm the blue altitudes on the flight plan page. Once direct to a transition fix, hit VNV and APR on the autopilot and sit back as the airplane flies the transition, and  hits all the altitude step-downs. When the FAF becomes the active waypoint, the PDF switches itself to green needles and captures the ILS glideslope.  At DA, if you don't see anything, you power up and press TOGA. Since the autopilot didn't disconnect when you hit TOGA, the airplane begins the climb. The system prompts your to unsuspend and when you do, the green needles on the PFD change back to pink. Since you've already placed the top of the missed approach climb in the altitude selector, you select or confirm NAV and IAS/FLC mode on the autopilot and you are done. 

I think there are a few systems and system combos which do all that, smoothly. One of the things I've learned from flying and teaching with multiple setups is not to let my expectations of what should happen in a system I haven't seen  based on some other system get in the way. I've seen auto-switching that works great, auto-switching which you have to watch like a hawk, and no auto-switching at all when you think it "should." I think it's the The standard installation of the GFC 500 AP, unlike the 700 (and I think the 600),  doesn't let you arm both VNV and APR at the same time. There are so many variations on that theme I can't say which way this setup does it. That's why I used the word "probably." Guess I should have used "may."

In terms of your specific "should," how about this note from the 750 User Guide?

Well there ya go, when in doubt RTFM.

I thought it would be interesting to see how the GI-275 specifically behaves in this situation since it communicates via Garmin HSDB vs dual ARINC interfaces like an Aspen or other non-Garmin EFIS. I came across this in the GI-275 Pilot's Guide(I assume properly configured means CDI button enabled?):

 

Edited January 13, 2022 by N231BN
edit

[midlifeflyer]

51 minutes ago, N231BN said:

I assume properly configured means CDI button enabled?

The GTN "properly configured" could simply mean auto-switching is turned on regardless whether the manual CDI button is on the GTN or GI.  Or it could just mean the GTN knows where it is and is providing location information to the GI. 

I'm probably wrong but here's my mental picture. We don't fly the GTN CDI - that's only for situational awareness. There has to be an external CDI of some sort (I think that's actually in the limitations). We fly the CDI on the PFD/HSI/OBS. The only thing a CDI button does whether on the panel the PFD or the GPS is manually change the navigation source being used as primary by the PFD/HSI/OBS. That goes back to the earliest days of IFR GPS navigation. 

So I think that when the GTN is sans CDI button, it only means manual CDI switching has been deferred to something else like the PFD. Everything else is the same. 

That said, I would have the same complaint as you. There's no reason for the GTN to be without the CDI button. I've seen a number of GTN/PFD combos and you can manually switch CDIs on either unit. I'm flying with a pilot with a GTN650 and GI 275 and I'm pretty sure it can be done on both.  I've seen GTN/GDU installations with switching available in both places as well.

Edited January 13, 2022 by midlifeflyer

[Cabanaboy]

38 minutes ago, midlifeflyer said:

The GTN "properly configured" could simply mean auto-switching is turned on regardless whether the manual CDI button is on the GTN or GI.  Or it could just mean the GTN knows where it is and is providing location information to the GI. 

I'm probably wrong but here's my mental picture. We don't fly the GTN CDI - that's only for situational awareness. There has to be an external CDI of some sort (I think that's actually in the limitations). We fly the CDI on the PFD/HSI/OBS. The only thing a CDI button does whether on the panel the PFD or the GPS is manually change the navigation source being used as primary by the PFD/HSI/OBS. That goes back to the earliest days of IFR GPS navigation. 

So I think that when the GTN is sans CDI button, it only means manual CDI switching has been deferred to something else like the PFD. Everything else is the same. 

That said, I would have the same complaint as you. There's no reason for the GTN to be without the CDI button. I've seen a number of GTN/PFD combos and you can manually switch CDIs on either unit. I'm flying with a pilot with a GTN650 and GI 275 and I'm pretty sure it can be done on both.  I've seen GTN/GDU installations with switching available in both places as well.

Here is the GTN and 275 display when the Missed Apprch option appeared yesterdays ILS approach 18 KMYR

[N231BN]

Here is the GTN and 275 display when the Missed Apprch option appeared yesterdays ILS approach 18 KMYR

The next time you fly that approach go ahead and activate the MAP after landing to see if the HSI switches back to GPS automatically.

[midlifeflyer]

5 hours ago, Cabanaboy said:

Here is the GTN and 275 display when the Missed Apprch option appeared yesterdays ILS approach 18 KMYR

 

As @N231BN said, the next step is to unsuspend and activate the missed. Did you do that? If so, ideally, the GI should have switched to pink needles for guidance on the missed. If not, you'll need to use the GI to manually switch. 

Although I personally don't use the 750 CDI in this type of situation, I think  you should be able to use either. Hopefully you'll find out why the 750 CDI switch is disabled. Necessary for some reason or just an installer preference.

BTW, are you based at MYR or nearby?

Edited January 14, 2022 by midlifeflyer

[Cabanaboy]

11 hours ago, midlifeflyer said:

As @N231BN said, the next step is to unsuspend and activate the missed. Did you do that? If so, ideally, the GI should have switched to pink needles for guidance on the missed. If not, you'll need to use the GI to manually switch. 

Although I personally don't use the 750 CDI in this type of situation, I think  you should be able to use either. Hopefully you'll find out why the 750 CDI switch is disabled. Necessary for some reason or just an installer preference.

BTW, are you based at MYR or nearby?

Hey, yes I am based at KMYR!

[midlifeflyer]

3 hours ago, Cabanaboy said:

Hey, yes I am based at KMYR!

I'm northwest of you in the Raleigh area (based at TTA) and have been there a few times. It's still a bit of a maybe but I'm planning a round robin down to OGB and have been thinking about coming back via the coast to add some time (it's an insurance thing).

[midlifeflyer]

I see you got an answer on POA that it's supposed to be that way.  A friend of mine is going to check his similar installation for me.

[PT20J]

This whole thread would be unnecessary if Garmin would just make the STC documentation available to owners (who pay the bills, BTW). Then the OP could have just looked it up. 

Does your autopilot have a GO AROUND (a.k.a. TOGA) button that closes momentarily to ground? If so, you can hook the GTN up to it and pressing GO AROUND will cycle the GPS onto the missed approach (assuming there is not some configuration detail hidden in GI installation that prohibits this). It works with my G3X / GFC 500 but it shouldn't matter to the GTN -- it doesn't know what kind of autopilot you have.

Skip

[Cabanaboy]

20 hours ago, midlifeflyer said:

I'm northwest of you in the Raleigh area (based at TTA) and have been there a few times. It's still a bit of a maybe but I'm planning a round robin down to OGB and have been thinking about coming back via the coast to add some time (it's an insurance thing).

Feel free to stop in here at MYR(my base) or CRE on your way back, i'll can meet you at airport and if time for lunch we can go for lunch,.  Or anytime you want to just fly down, looks like a pretty short hop.  - King M.

[Cabanaboy]

12 hours ago, PT20J said:

This whole thread would be unnecessary if Garmin would just make the STC documentation available to owners (who pay the bills, BTW). Then the OP could have just looked it up. 

Does your autopilot have a GO AROUND (a.k.a. TOGA) button that closes momentarily to ground? If so, you can hook the GTN up to it and pressing GO AROUND will cycle the GPS onto the missed approach (assuming there is not some configuration detail hidden in GI installation that prohibits this). It works with my G3X / GFC 500 but it shouldn't matter to the GTN -- it doesn't know what kind of autopilot you have.

Skip

My AP is a KAP150, does not have a Go around feature(as far as i know anyway)

[midlifeflyer]

2 minutes ago, Cabanaboy said:

Feel free to stop in here at MYR(my base) or CRE on your way back, i'll can meet you at airport and if time for lunch we can go for lunch,.  Or anytime you want to just fly down, looks like a pretty short hop.  - King M.

It's still a "maybe," but if it looks like a possibility, I'll PM you. 

BTW, the answer that the STC IM says so still doesn't explain why. 

[N231BN]

It's still a "maybe," but if it looks like a possibility, I'll PM you. 
BTW, the answer that the STC IM says so still doesn't explain why. 

What was the reply on POA? I've read both manuals and didn't see any specifics regarding that setting. My GTN manual is a few years old now.

[midlifeflyer]

10 minutes ago, N231BN said:

15 minutes ago, midlifeflyer said:

It's still a "maybe," but if it looks like a possibility, I'll PM you. 
BTW, the answer that the STC IM says so still doesn't explain why. 

What was the reply on POA? I've read both manuals and didn't see any specifics regarding that setting. My GTN manual is a few years old now.

It was supposedly this page out of the most current STC Installation Manual.  I'll report what my friend finds. He doesn't use his GTN CDI key so he doesn't even recall whether it's disabled or not. 

[N231BN]

It was supposedly this page out of the most current STC Installation Manual.  I'll report what my friend finds. He doesn't use his GTN CDI key so he doesn't even recall whether it's disabled or not. 

Ok, that makes sense. I bet you still get auto switching because they are communicating on the Garmin protocol.

The GI-275 can interface to multiple navigators so to avoid any confusion they want all switching done at the HSI.

[Cabanaboy]

23 minutes ago, midlifeflyer said:

It was supposedly this page out of the most current STC Installation Manual.  I'll report what my friend finds. He doesn't use his GTN CDI key so he doesn't even recall whether it's disabled or not. 

Anyone pick up on the Main indicator "ANALOG" = disabled?

[Cabanaboy]

 

Of course the were it says GTN750 is greyed out for port number notes([1] [2])

 

[N231BN]

Anyone pick up on the Main indicator "ANALOG" = disabled?

That's the page in the setup menus where the CDI disable is.

As I stated before, the main purpose of the CDI button is to switch the main analog outputs. The GI-275 doesn't use that interface.