Nav Source knob

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   If I select a LPV approach that has LNAV/VNAV and LNAV and circling minima, will turning the Nav Source knob scroll through any of these options?  i.e  disable the glide slope for instance or change the missed approach point.
Never tried it and thought someone might be able to shed light on it.

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cavu Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 17 Apr 2015 Location: KRME Status: Offline Points: 152	Post Options Post Reply Quote cavu Report Post Thanks(0) Quote Reply Topic: Nav Source knob Posted: 15 Dec 2023 at 8:42pm
	If I select a LPV approach that has LNAV/VNAV and LNAV and circling minima, will turning the Nav Source knob scroll through any of these options? i.e disable the glide slope for instance or change the missed approach point. Never tried it and thought someone might be able to shed light on it.

vas4avidyne Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 21 Jun 2022 Location: SF Bay Area Status: Offline Points: 50	Post Options Post Reply Quote vas4avidyne Report Post Thanks(0) Quote Reply Posted: 18 Dec 2023 at 1:17am
	My experience is that you pick a particular RNAV approach (e.g. RNAZ Z Rwy 31 KRHV) and the IFD picks the lowest minimums that it can support for that approach. If LPV minimums are available and the IFD is getting the appropriate GPS signal, you will get a glide slope with the ability to fly down to LPV minimums. I have had some situations where it started with the LPV minimums but somewhere along the approach, I received a message about the loss of GPS integrity and it "downgraded" to LNAV minimums. In some other cases, it gave me only the LNAV minimums even though there were LPV minimums published for the approach. In my specific case, it seemed to be related to my antenna - once I cleaned it, those issues seem to have gone away. I guess the other way of looking at it is that you can decide what minimum you want to use for the approach (LPV or LNAV or circling). If LPV minimums are available, you will get a glide slope but you can choose to terminate your approach at the MDA dictated by the LNAV or circling minimum. As far as I know, the missed approach procedure on an RNAV approach with different published minimums is the same regardless of whether you did the approach to LPV, LNAV or circling minimums. Vas

cavu Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 17 Apr 2015 Location: KRME Status: Offline Points: 152	Post Options Post Reply Quote cavu Report Post Thanks(0) Quote Reply Posted: 20 Dec 2023 at 3:50pm
	Thanks, that's a very good rely. I did not get a message on the IFD that the GPS integrity was lost while on the LPV (and the GS dropped out). I did get the message when I selected the LPV into another airport. It only showed the L/VNAV selection. I did a little more investigation and there was a solar flare episode shortly before I began the LPV approach. The antennas look clean. How dirty was yours (or how dirty is dirty) to cause this? Thanks again.

vas4avidyne Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 21 Jun 2022 Location: SF Bay Area Status: Offline Points: 50	Post Options Post Reply Quote vas4avidyne Report Post Thanks(0) Quote Reply Posted: 20 Dec 2023 at 5:08pm
	You're very welcome! There was nothing obvious on the antenna connections when I opened it up. I just used an electronics cleaning agent and cleaned all the surfaces before putting it back. As best as I can tell, things have improved since then. There was one approach (RNAV 32 at KSTS) that initially had this problem (in low IMC for good measure) and the LNAV minimum was higher than the reported ceiling so I landed up doing a missed approach and coming back to do the ILS. I haven't had a chance to try it again there. I've heard that local conditions could also cause the "downgrade" from LPV to LNAV minimums (like your solar flare example). Vas