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Glideslope Failure on RNAV/LPV

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D-EACY View Drop Down
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    Posted: 20 Oct 2020 at 5:21am
Did a practice RNAV/LPV approach on Sunday and had a glideslope failure in the middle of the glidepath, at around 1000 ft AGL. 

Details:

- Entegra with 2xIFD440 and DFC90
- Flew standard RNAV GPS procedure to EDMS (Germany)
- Had a green LPV indication on both navigators (crossfill is activated)
- Flew by hand with FD ON
- Was exactly on virtual glidepath when Glideslope indicator on PFD diseappeared
- Two seconds later there was a yellow "glideslope not available" warning on the PFD for about 3 seconds
- Localizer indication stayed up and PFD said FD NAV APPR
- Green LPV indication stayed on on both IFDs, no warning on the IFDs
- 1 minute later the GS indicator came back and stayed on until landing

This video was started ten seconds after the GS indication failed. It comes up at 1:42 again.

https://youtu.be/tsv4ncGGYG4

Any idea what happened?
2006 SR22-G2 DFC90 IFD440
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 2020 at 10:22am
We would need to see the Event, Flight, and System logs to know for sure.  You can either go through tech support or send them directly to me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote D-EACY Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 2020 at 5:19pm
Do you mean the IFD logs? I can send those to you, although i got 2 exchange units from Bryan Kahl 3 weeks ago after the original ones took a long time to lock on to GPS. 

I will first test the system again tomorrow. 

Is it normal that the LPV label stayed on even after i lost the GS indication?

PS: Can somebody please watch the video I posted above and tell me what they think about the indications on the PFD and the IFD? Why does "LPV" stay on after the GS failed? And shouldn't there be a "GS" in the PFD status line when the GS is on (after 1:42)

Here it is what it looked like with the 430W. 

https://youtu.be/ArL9fLRsnIc


Edited by D-EACY - 21 Oct 2020 at 3:22am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote D-EACY Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 2020 at 10:45am
... looks like the system is ok after all! Did 2 more practice approaches, one coupled, one with the FD - all worked flawlessly! 

Is it possible that it was only a momentary WAAS outage? But why wasn‘t the approach downgraded on the IFD?


Edited by D-EACY - 21 Oct 2020 at 1:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 2020 at 11:27am
Yes, I'm sure is was a momentary, localized event.  My guess is that the VPL from the GPS exceeded the VAL.  That could be confirmed by looking through the logs.  I would have expected the VDI on the MFD to be flagged instead of going away, though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote D-EACY Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 2020 at 1:34pm
Thanks for now! I guess it's ok. 
But shouldn't the IFD show "LNAV" instead of "LPV" is the GS fails? That's the one thing that confused me.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 2020 at 2:15pm
No, it will continue to display LPV, but the vertical deviation should be flagged.  It's like an ILS when the GS is out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote D-EACY Quote  Post ReplyReply Direct Link To This Post Posted: 22 Oct 2020 at 3:18am
How is it possible that these labels didn't come up on the PFD? Is it a sw version thing? Setup?

Aas I said I had a yellow "glideslope not available" message in the status line of the PFD ... but that is not documented anywhere.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 22 Oct 2020 at 9:45am
I looked through the EXP5000 Pilots Guide and you are correct that there was no mention of the "glideslope not available" message.  I did find that the description of the VDI said it is displayed when "GPS vertical deviation data has been received".  That's consistent with the behavior you documented.  Though admittedly undocumented, the yellow message provides further notification that vertical guidance is unavailable.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote D-EACY Quote  Post ReplyReply Direct Link To This Post Posted: 23 Oct 2020 at 4:25am
Thank you for clarifying! As I said, two more practice approaches showed that the system works perfectly, so it could have been a WAAS outage after all.

I do find it interesting that the IFD will not downgrade the approach to LNAV if the GS fails, I was sure it would. 
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