CDI Key on GTN -> GI-275, GTN750,

Discussion in 'Avionics and Upgrades' started by CabanaBoy, Jan 14, 2022.

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  1. CabanaBoy

    CabanaBoy Filing Flight Plan

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    Is there any reason for the CDI Key NOT to be enabled on the GTN? I am talking about only using the GI-275 HSI and not an older NAV2 CDI.

    Question for any GI-275 drivers with a GTN 750, I am trying to figure out why My GTN 750xi does not have a CDI Key. (Oversight?) I can select the CDI on the GI-275 for VLOC navigation (turns Green).

    (Is there any reason for the CDI Key NOT to be enabled on the GTN? )
     

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    Last edited: Jan 14, 2022
  2. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    Yes, Per the GI-275 IM it is supposed to be disabled.


    69404CB2-E1FF-4EE3-8218-961C0D5DABC7.jpeg
     
  3. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Do you have any idea why? It's not that way with a GNS (you can't disable a hard button anyway) and a number of other GTN/PFD combinations,
     
  4. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    Actually, you can (and are required to) disable the CDI key on the GNS when installed with a GI-275. And it depends on the PFD/GTN combination and even software revisions. For the GI-275, you make the source selection on the unit itself. For The G500 TXi it depends on the software version of the GDU, later software supports localizer auto switch and the CDI key can be enabled, whereas earlier software the CDI key must be disabled.
     
  5. CabanaBoy

    CabanaBoy Filing Flight Plan

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    My GTN750xi supports localizer autoswitch but its not accessible with the CDI key not enabled. I do make the CDI selection on the GI275 and it works. My OBS key on GTN750xi does not seem to function either and never asks for course. thanks for your information and there is not much discussion on this matter hardly anywhere and hopefully others can find an understanding here. I am noting the above instructions say (Analog) whereas GI275 is an electronic HSI/EFIS.
     
    Last edited: Jan 15, 2022
  6. WDD

    WDD En-Route

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    So..... You can still control whether you use VLOC or GPS; it's just that you make the selection on the 275 and not the GTN?

    If so, I'm not sure why would it be configured that way? Why not just control the selection on the GTN like we do now with an analog CDI?
     
  7. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Yes you can still control it with the 275. Think of the older systems where we changed nav source with and external button. Same concept.

    The reason is above my pay scale. Someone it had something to do with the way the 275 switches among multiple nav sources. Dunno.

    Funny... a friend of mine has the equivalent setup - a GTN 650xi rather than a 750. Same. No CDI key in the GTN. The funny part is when I asked him he had to check because he never looked for one on the GTN. I might not have noticed it either.
     
  8. WDD

    WDD En-Route

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    All of the club planes but one have GTNs with steam CDI’s, so the only way I know to change source is on the GTN. I’ll make a mental note if I ever fly a plane with a 275.

    One of the planes does have a set of G5’s - I wonder which way that set up works?
     
  9. Ryan Klems

    Ryan Klems Pre-takeoff checklist

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    The G5 can only switch between navigators, so in order to switch between two sources in a single navigator you have to use the CDI key and it has to be enabled. This is also why you can’t do something like a GNS/GTN, a 2” GPS navigator (GPS175/GNC355/GNX375) and a GNC255 all connected to a G5 (no way to toggle between the GPS and VHF on the second source)
     
  10. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    I'm trying to remember. If I recall correctly, the G5 is (or was - they are always updating stuff) limited to a single nav unit for CDI information. It doesn't have its own CDI key. It uses the one from the nav unit, in this case the GTN.

    edit: just saw Ryan's post. Looks like my memory was correct for a change.

    OTOH, the GI275 has the CDI key right in the face of the instrument, My friend not noticing can be explained. When you have a CDI source selection key right on the HSI/OBS, I think we develop the tendency to use it. Look at the instrument. It's pink. Tap the instrument. Now it's green. In my own case, I fly some steam, some glass. My in-flight preference, especially when flying a procedure, is to have the flight plan page showing on the GTN rather than the 650 primary nav page/750 map page.The CDI key on the GTN is only on the primary NAV page. If you like a 650 showing the map, no CDI key there.
     
  11. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    @WDD, here's what the 275 HSI looks like
    upload_2022-1-16_23-1-22.jpeg
     
  12. NealRomeoGolf

    NealRomeoGolf En-Route

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    My G5 can do green needles off my GNS530W or my GNC255A. Only magenta needles off the 530. Are you just meaning magenta needles?
     
  13. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    That's why I said I wasn't sure. For some reason, I thought it was one source for CDI but multiple sources for bearing pointers.
     
  14. NealRomeoGolf

    NealRomeoGolf En-Route

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    They updated it about 2 years ago, I think. Originally they didn't do it but a software upgrade got it there. At least that's my understanding. It came in handy during my IR training but really haven't had to use the second nav real world yet.
     
  15. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    So... how do you switch the G5 CDI to NAV 2? IOW, how do you tell the G5, "I'm using NAV 2 for my CDI source now."? I pulled down the Pilot Guide for the most current software revision and while it says you control the CDI switch from either NAV 1 or NAV 2, I didn't see reference to a menu item changing the CDI connection from one to another in flight.

    (Bearing pointer, yes. That's pretty straightforward.)
     
    Last edited: Jan 17, 2022
  16. NealRomeoGolf

    NealRomeoGolf En-Route

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    On the G5, button push, scroll to source, button push, pick Nav2, button push.
     
  17. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    That's exactly what I would expect. Interesting the Pilot Guide makes no reference to than menu item - not even a picture - while going into detail on a number of other functions.

    Thanks.
     
  18. NealRomeoGolf

    NealRomeoGolf En-Route

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    I was hoping to go flying today (would be first time YTD....ugh) and could get you a video. The 1 foot snow drift in front of my hangar does not look promising and neither does the cloud deck.
     
  19. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    I don't doubt it. I was tentatively giving a lesson today but the 14-29 KT almost direct crosswind doesn't seem promising for an initial LSA transition lesson, even if the ice melts enough on our back roads.
     
  20. Martin Pauly

    Martin Pauly Line Up and Wait PoA Supporter

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    From the GI-275 manual:

    upload_2022-1-17_12-28-17.png
     
  21. WDD

    WDD En-Route

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    29kt crosswind? I guarantee your student would remember that lesson the rest of his life!
     
  22. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    Yes I know how it works on the 275. This was about the G5 which works differently.
     
  23. midlifeflyer

    midlifeflyer Touchdown! Greaser!

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    I might do that in an airplane the pilot was familiar with (there was a lesson going on, the only light aircraft activity), but not a first transition lesson.
     
  24. Martin Pauly

    Martin Pauly Line Up and Wait PoA Supporter

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    Sorry, my bad - I missed that.

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