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G5 altitude data to IFD |
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Rallylancer122 
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Joined: 04 Sep 2020 Location: Oconto, WI Status: Offline Points: 20 |
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 Topic: G5 altitude data to IFDPosted: 13 May 2021 at 2:34pm |
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I've read through a few of the Garmin G5/IFD threads but I'm still a bit confused as to what data gets transferred between the two. I have an apx322 transponder which gets its altitude data from my IFD540, which in turn gets altitude data from a standalone encoder. Can the G5 provide that altitude data instead?
In other words, can I use the G5 as an encoder?
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Gring
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Joined: 30 Dec 2011 Location: Kingston, NY Status: Offline Points: 741 |
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Posted: 13 May 2021 at 2:48pm |
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Yes it can via the GAD29B
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dmtidler
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Posted: 13 May 2021 at 5:06pm |
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I'm not sure that the G5 can be used as a substitute for an encoder. It is my understanding that an encoder supplies only pressure altitude to the IFD. As far as I can tell, the G5 only provides altitude corrected for the G5 altimeter setting (Baro Altitude) to the IFD through the GAD29B.
While not conclusive, my main reasoning for this is that my aircraft's IFD Air Data Calculator shows the G5 indicated ALT, CAS, HDG, and OAT automatically on the IFD; however, the G5 altimeter setting (BARO) is not passed to the IFD. In order to get an accurate TAS, Density ALT, and winds calculation from the IFD that closely matches the G5 calculated TAS, Density ALT, and winds, the Air Data Calculator BARO has to be manually set to the local altimeter setting. If pressure altitude were automatically supplied from the G5 (or the encoder) and used in the Air Data Calculator instead of G5 BARO Altitude, then it would not be necessary to manually change the BARO setting from 29.92 to get the most accurate calculation. Maybe Steve can expand on this.
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Gring
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Posted: 13 May 2021 at 6:49pm |
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There was a recent (nov 2020 I think) firmware release that updated the GAD29B data to include some additional fields missing from earlier versions. I know this because my TAS620 now has heading information and we removed the altitude encoder for my AXP340 transponder.
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Rallylancer122
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Posted: 14 May 2021 at 10:22am |
Excellent. Is there any guidance or manual coverage from Garmin or Avidyne on this? Or is it just something that happens to work? It dawned on me last night that the G5 is not TSO'd, so I'm thinking it might not be legal as an altitude source for mode C and ADS-B.
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Rallylancer122
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Posted: 08 Jul 2021 at 5:59pm |
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FWIW, I did some more research on this, including actually reading the axp322 manual (I know, who wastes time reading the manuals...). Turns out that the IFD will take the "highest quality" air data source and transmit that on to the transponder. It ranks an efis (which it considers the g5 to be) higher than an encoder. Since the IFD manual approves the g5 as an air data source, I would assume that approves it as an altitude source for transponder also. If I were to wire in an encoder, it would just ignore it anyway.
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skitheo
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Posted: 11 Jul 2021 at 8:36pm |
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Good job reading the manual! All sorts of nuggets there! ;-)
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chflyer
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Posted: 13 Jul 2021 at 4:59am |
So is an encoder then still needed at all in that config? If so, what would be its purpose? Purely regulatory?
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Vince
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Rallylancer122
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Posted: 21 Jul 2021 at 10:56pm |
In my opinion, no. The 540/g5 interface and the 540/322 interface are both approved in the same manual. That's sometimes a slippery slope, but it's at least defensible. If the next owner or the FAA disagrees, add an encoder (I'm leaving the wires in.)
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Gring wrote: