GI 275 upgrade - Will I retain CDI?

[CT583]

Hello,

I can’t seem to get a clear answer on this topic. I am upgrading to dual GI-275 in my 182.
Currently I have dual Garmin GI-106a CDI driven by Nav1 GNS430 and Nav2 SL30

Will I be able to retain these CDI or are they eliminated upon install of the 275?

I read something about lightning protection could possibly eliminate these items.

I appreciate the insight in advance.

 

[GLDP]

If it’s anything like a G5 install I am fairly certain that you are not supposed to have both hooked up at the same time as per the STC.

 

[AA5Bman]

Eeerm, I’m not sure I understand the question, but I can give an example. My setup is a GI275 in DG (HSI) mode and then a GNC255 (essentially like your SL30) and a KI-209, equivalent to your GI-106A. The GI275 displays all of the NAV indications coming out of the the GPS, ie both the GPS magenta line as well as the #1 VOR. The GNC 255 displays the #2 VOR on the KI-209.

I don’t see why you couldn’t do the exact same thing, swapping the SL30 and GI106A where I have the GNC255 and KI209. If you’re asking if you can run your #1 VOR to indicate on both the GI275 AND a GI106A, I have no idea but can’t see any reason why you would want to.

 

[bbarrett]

I’m pretty sure that you’ll have to pull the CDI for the 430. The manual requires the GNS CDI switch to be disabled, so a CDI wouldn’t make sense at that point.

The manual explicitly says you can have the SL30 drive both a CDI and be an input to the GI275. The course selector in the GI275 needs to be disabled for the SL30 input, so that the GI106 is the only course selector input. Or you could remove both CDIs, of course

My install is similar; I have a GTN650 and SL30. The shop removed the GTN CDI and configured the SL30 to drive both the CDI and the GI275: the GTN input is to the ADI and the SL30 is wired to the SL30, so that if one unit dies, I still have a nav input. Honestly, I think I’d remove both CDIs if I had it to do over. I haven’t really used the backup CDI and those 106s still sell well on eBay.

 

[Mtns2Skies]

The GI275 can split the signal. If you *want* to retain your CDI you may, if you don't want to, then you can ditch it.

 

[Bruce Wallen]

The GI275 can split the signal. If you *want* to retain your CDI you may, if you don't want to, then you can ditch it.

Hi, I just came across this an am having dual GI 275s installed. My primary navigator is a Garmin GNS 480 and my shop tells me that it is not possible to retain my original CDI and have the GI 275 also configured as a CDI. They claim that this was confirmed by Garmin. Are you aware of any approval basis or configuration specifics that I could provide the shop to support this.

 

[Mtns2Skies]

Hi, I just came across this an am having dual GI 275s installed. My primary navigator is a Garmin GNS 480 and my shop tells me that it is not possible to retain my original CDI and have the GI 275 also configured as a CDI. They claim that this was confirmed by Garmin. Are you aware of any approval basis or configuration specifics that I could provide the shop to support this.

Welcome to PoA. No, that's just what my avionics tech told me. Maybe he was wrong.

 

[CT583]

Hi, I just came across this an am having dual GI 275s installed. My primary navigator is a Garmin GNS 480 and my shop tells me that it is not possible to retain my original CDI and have the GI 275 also configured as a CDI. They claim that this was confirmed by Garmin. Are you aware of any approval basis or configuration specifics that I could provide the shop to support this.

I actually switched to dual G5, but yes, the data from the gps unit will go direct to the 275(or G5 in my case).

I was able to retain a cdi and have it connected to the SL30 as a separate navigation system.

if you have a good CDI, try to get some trade-in value or sell it individually. They are not cheap.
Best of luck with the 275, they are awesome

 

[Jon Wilder]

As of current, I've yet to see anything in the STC Installation Manual that explicitly states that an existing nav indicator must be removed.

That said, the GI 275 uses the VOR/ILS ARINC 429 out interface on the GNS 430, while using an RS-232 interface between the SL-30 and the GI 275. The main analog outs from either unit are not used by the 275. As the main analog outputs are always active, the GI 106A can remain interfaced to the main analog outs.

Where you do run into an issue is in the event of a failure mode on the GI 106A units (or in the wiring between them and the navigators) that causes them to give indications which conflict with what's being indicated on the GI 275s. Now you have an issue of nav displays which are out of agreement.

 

[asicer]

Where you do run into an issue is in the event of a failure mode on the GI 106A units (or in the wiring between them and the navigators) that causes them to give indications which conflict with what's being indicated on the GI 275s. Now you have an issue of nav displays which are out of agreement.

Digital signals carry checksums, so there's a certain degree of self-checking. Analog signals are open-loop, so I'd be more inclined to believe the digital indication. But yeah, disagreeing NAV displays are never good.

 

[Jon Wilder]

Digital signals carry checksums, so there's a certain degree of self-checking. Analog signals are open-loop, so I'd be more inclined to believe the digital indication. But yeah, disagreeing NAV displays are never good.

Digital "signals" are the simple discrete signals used by discrete ins/outs, and are active high or active low over a long time period. They're in only one of two possible states at any given time - 1 or 0, high or low.

What you are referring to are "serial data packets". While these are digital and only swing between 1 or 0, it's a string of 1's and 0's following one right after the other over a short time period, as opposed to a discrete signal that remains high or low over a much longer time period.

It's very important to distinguish the difference between the two.

That said, not all serial data packets carry checksums. ARINC 429 uses parity checking and ignores any label packet with incorrect parity. RS-232 may or may not use checksum, parity, or any method of error checking at all depending on the protocol and format. To state that "all" packets carry checksums (or any form of error checking for that matter) without knowing the protocol specification and frame format is a mere assumption at best.

 

[asicer]

That said, not all serial data packets carry checksums. ARINC 429 uses parity checking and ignores any label packet with incorrect parity. RS-232 may or may not use checksum, parity, or any method of error checking at all depending on the protocol and format.

You mentioned the RS232 interface/protocol from SL30 to GI275 (NMEA 0183 based). That does carry a checksum. I'm not aware of any other RS232 interface/protocol from NAV radio to CDI. That said, an 8bit checksum isn't much.

 

[Jon Wilder]

You mentioned the RS232 interface/protocol from SL30 to GI275 (NMEA 0183 based). That does carry a checksum. I'm not aware of any other RS232 interface/protocol from NAV radio to CDI. That said, an 8bit checksum isn't much.

But certainly better than parity checking.

 

[s12dxer]

I’m having a G5 hsi installed replacing the dg, it will interface with a 530W, the existing GI-106A will be moved to interface with a 430W as a #2 NAV. The other cdi I have will be removed.