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PostPosted: Wed Jan 09, 2019 3:56 pm 
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Airman

Joined: Wed Nov 07, 2018 3:25 am
Posts: 16
Hello,

... can somebody please point me to the proper settings and understanding of an ILS approach with the RXP GNS530 in the A2A C172?

The RXP website tells me: " ... Like its real world counterpart, the GNS 530W XP comes with built-in WAAS navigation capabilities, and is capable to fly LPV “glideslope” approaches without reference to ground-based navaids of any kind. ...".

I am in P3DV4.3. I am through with my learnings of the KAP140. I can also handle the GPS menues and settings quite properly. I had happy landings with the autopilot along the glideslope, when it was set to approach mode.

But there always used to be this "handover" from GPS mode to the VLOC mode with setting the autopilot to approach then. So the autopilot is following ground based navigation aids and the GPS is out of the game at that point in time at the end of the transition.

I might be wrong but I thought guidance for vertical approach can also be completely based on the GPS unit telling the autopilot how to descent. But it is not happening with me here. All the options menue of the GPS config concerning links to the HSI etc. are activated. The ILS frequency is also right. Glideslope from below is also good. Does the autopilot need to be in a special mode (VS or Alt)?

So far I did fail with all my efforts to have the GPS controlling the vertical descent. There is the message to switch from GPS to VLOCmode and then nothing happens. No vertical control.


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PostPosted: Sat Jan 12, 2019 12:45 pm 
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A2A Captain
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Joined: Fri Jun 06, 2014 1:06 pm
Posts: 8339
Location: United Kingdom
Hello Magnus,

If you're flying a GPS approach which provides vertical guidance (such as an LPV or LNAV+V approach), you'll need to keep the GNS 530 in 'GPS' mode all the way to the ground, rather than switch to 'NAV' mode as you'd do if tuning a traditional, ground-based ILS.

That's because in this case, the information that's fed to the VOR1 gauge (and hence used by the autopilot) doesn't come from the NAV radio, and in fact it doesn't matter if the ILS frequency (assuming there is a ILS too) is tuned into the NAV radio in order to fly a GPS approach; as you say the GPS approach is entirely based on satellite guidance, so it's independent of any ground-based stuff.

One thing to bear in mind is that the "connect GPS to VOR indicator" option should be ticked in the RealityXP options. This option is enabled by default in the A2A 172.

If you can give us a specific example of an approach you've tried, ideally with a screenshot or two showing the cockpit setup (including the GNS), we can hopefully provide a bit more targeted advice and maybe spot where the problem is.

Thanks,
Nick


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PostPosted: Sun Jan 13, 2019 12:08 pm 
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Airman

Joined: Wed Nov 07, 2018 3:25 am
Posts: 16
Nick - A2A wrote:
Hello Magnus,

If you're flying a GPS approach which provides vertical guidance (such as an LPV or LNAV+V approach), you'll need to keep the GNS 530 in 'GPS' mode all the way to the ground, rather than switch to 'NAV' mode as you'd do if tuning a traditional, ground-based ILS.

That's because in this case, the information that's fed to the VOR1 gauge (and hence used by the autopilot) doesn't come from the NAV radio, and in fact it doesn't matter if the ILS frequency (assuming there is a ILS too) is tuned into the NAV radio in order to fly a GPS approach; as you say the GPS approach is entirely based on satellite guidance, so it's independent of any ground-based stuff.

One thing to bear in mind is that the "connect GPS to VOR indicator" option should be ticked in the RealityXP options. This option is enabled by default in the A2A 172.

If you can give us a specific example of an approach you've tried, ideally with a screenshot or two showing the cockpit setup (including the GNS), we can hopefully provide a bit more targeted advice and maybe spot where the problem is.

Thanks,
Nick


Hi Nick,

thanks for this replay and clearification. "... GPS approach which provides vertical guidance" ... does this mean that only some dedicated approaches of special airports allow a GPS guided vertical descent? And if so how can I distinguish them? Around the final approach fix the GPS requests me to do the switch. Is this supposed to happen all the time no matter if a pure GPS guided descent is possible? Or will it disinguish the LPV and NAV situations on its own and not ask me to switch?

I will touch this again the next days and post the information.

Rgds,

Stefan


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PostPosted: Sun Jan 13, 2019 6:35 pm 
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Chief Master Sergeant
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Joined: Mon Sep 02, 2013 7:30 pm
Posts: 3533
Location: Typically hanging around N07, 12N, KLDJ, KCDW
Not all approaches offer vertical guidance.

Localizer or Localizer type, VOR and GPS approaches without vertical guidance will no offer glidepath information.

LPV and ILS offer a glidepath and glideslope.

LNAV/VNAV also offers a glidepath.

LNAV or LP do not, but some GPS installations offer an advisory only glidepath usually denoted by adding +V to the approach type.

_________________
Flight Simmer since 1983. Private Pilot
Paramus Flying Club http://www.flyingclub.org


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PostPosted: Fri Jan 18, 2019 3:44 pm 
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Airman

Joined: Wed Nov 07, 2018 3:25 am
Posts: 16
Success! I just had a nice landing in LPV mode. Just special airports have it. I tried with KAPF. When adding the procedure to the flightplan in the GNS530 they are marked with "GPS" even. Now it is clear. Thanks!


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