IFD540, Loss of integrity, What does the 440do?

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   This is a question specific to the IFD 540 and 440 dual installations.

On a practice LPV approach the other day the 540 lost gps integrity and downgraded to RNAV+V. At the same time the 440 retained integrity and said it was still LPV.

In that instance, I just stopped using the guidance on the PFD that the 540 is linked to and started using the guidance the 440 is linked to, a "steam" CDI.  Assuming it was a true back up.  But is it?

The manual says the course input for GPS is the same.  I think that means that it will only accept one course when inputting. But, Is the guidance on the CDI that is linked to the 440 coming from the 440 and was it really getting LPV from it when the 540 downgraded?

If it is on an ILS or VOR they are separate, but I'm not clear on how it interacts when on GPS.

I am also wondering how the 440 is actually giving redundancy in the install. If I shut off the 540 the 440 would happily operate the CDI, but not the PFD on my main display. The 440 isn't connect to the main PFD.  And neither is the 540 connect to the Steam CDI.  So, if the 540 is shut off, I think I can just tool along with the 440 and all is well...?

The issue is fixed, btw. It was a failing GPS antenna on the 540.  Thanks Avidyne for the support on that.

This is installed in Glasair Sportsman, so there is no manufacturer to ask these questions, really.
Any thoughts would be appreciated.  

James

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Flyxaos Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 18 Mar 2025 Location: Usa Status: Offline Points: 2	Post Options Post Reply Quote Flyxaos Report Post Thanks(0) Quote Reply Topic: IFD540, Loss of integrity, What does the 440do? Posted: 12 hours 45 minutes ago at 4:14pm
	This is a question specific to the IFD 540 and 440 dual installations. On a practice LPV approach the other day the 540 lost gps integrity and downgraded to RNAV+V. At the same time the 440 retained integrity and said it was still LPV. In that instance, I just stopped using the guidance on the PFD that the 540 is linked to and started using the guidance the 440 is linked to, a "steam" CDI. Assuming it was a true back up. But is it? The manual says the course input for GPS is the same. I think that means that it will only accept one course when inputting. But, Is the guidance on the CDI that is linked to the 440 coming from the 440 and was it really getting LPV from it when the 540 downgraded? If it is on an ILS or VOR they are separate, but I'm not clear on how it interacts when on GPS. I am also wondering how the 440 is actually giving redundancy in the install. If I shut off the 540 the 440 would happily operate the CDI, but not the PFD on my main display. The 440 isn't connect to the main PFD. And neither is the 540 connect to the Steam CDI. So, if the 540 is shut off, I think I can just tool along with the 440 and all is well...? The issue is fixed, btw. It was a failing GPS antenna on the 540. Thanks Avidyne for the support on that. This is installed in Glasair Sportsman, so there is no manufacturer to ask these questions, really. Any thoughts would be appreciated. James

rpostmo Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 20 Jul 2015 Location: North Dakota Status: Offline Points: 163	Post Options Post Reply Quote rpostmo Report Post Thanks(0) Quote Reply Posted: 9 hours 45 minutes ago at 7:14pm
	When I first had the combination 540/440 installed, I had them synced. To test the backup utility, I shut down the power on the 540 in flight. I felt the 440 then put out bad ?reverse? signal to my CDI. I subsequently took them out of sync mode and let them operate individually. I feel more reassured now that one failure won't affect the other one. For my flying, I don't think the advantage of programming both units at the same time is that beneficial as I often program to do different things. I'm still unclear as to what happens in sync mode with a single failure, as I never tracked it down further.