AXP340/322 ADS-B Transponder - IFD540 out for maintenance no mode C

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IFD540 out for maintenance no mode C

Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: https://avidynelive.com/forum_posts.asp?TID=2077
Printed Date: 26 Mar 2026 at 2:30pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com

Topic: IFD540 out for maintenance no mode C

Posted By: drapo
Subject: IFD540 out for maintenance no mode C
Date Posted: 26 Sep 2020 at 8:18am

I think I know the answer after reading a few posts here and asking around, but just want to make sure it's the right answer and wether there is a way around it.

So my IFD540 was sent to the factory with a com issue. Since I have a #2 radio, I decided to continue my VFR flying using it and bringing a portable Vertex radio just in case. What's is the link with the transponder you'll say, well here it is; our IFD540 being out of it's rack, the connection between the mode C and the transponder seems to be interrupted and ATC doesn't receive our altitude, although the AXP340 is in the Alt mode and there is no altitude on the transmitted altitude display.

Questions for @AviSteve or somebody at Avidyne:

1- Is there a way around that situation not using the controls on the IFD540?

2- When the IFD is back, is there a connection that can be made to make sure the AXP340 doesn't need the IFD for it's mode C information?

Replies:

Posted By: AviSteve
Date Posted: 28 Sep 2020 at 3:55am

The AXP340 can accept altitude inputs from other sources than the IFD. For instance, an Icarus encoder or an air data computer. Your installer probably already knows the options available to you given the equipment installed in your aircraft. Have him contact Avidyne tech support for assistance if necessary.

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Steve Lindsley
Avidyne Engineering

Posted By: drapo
Date Posted: 28 Sep 2020 at 10:25am

Thanks!