Bought the GTN 750 for my Bonanza: KFC 200 struggle

[KarelPatch]

Flying RNAV approaches has been a bit of a struggling. I’ve read the KFC 200 manual a dozen times.
Here is an example sequence I tried:

- Reach IAF at requested altitude.
- Turn on APPR mode. I also tried NAV mode.
- Switch from GPS to VLOC when I am on the vector to final.

What I get 99% of the time is that the autopilot will disconnect APPR or NAV mode at the moment I reach the FAF. When this happens, I can’t even use NAV mode to follow the missed approach track (NAV and APPR are blinking when I select them.)
The 2 or 3 first times I tried, I was able to go into GS mode. So I know it’s not a limitation.

What could be the issue? Also the last time I tried, I noticed the O letter lighting up on the annunciator panel just before the APPR disconnected. What is it? (And what are the 3 letters A O M on the panel? I couldn’t find it in the manual.)

Oh and also, I tried a vectored RNAV approach and the autopilot would not catch the track. I would fly in HDG mode towards the line with NAV ARM or APPR ARM and the plane would just fly past the line! Any tips?

Thanks a lot!

[Nick - A2A]

Hi KarelPatch,

- Switch from GPS to VLOC when I am on the vector to final.

If you're flying an RNAV (GPS) approach, you shouldn't be switch the GPS from GPS to VLOC mode at all. VLOC (VOR/Localizer) mode is for using ground-based navaids and would be used for a traditional ILS approach.

If you can give us an example of a specific approach from the GTN which you've tried, it'll be easier to offer advice.

What could be the issue? Also the last time I tried, I noticed the O letter lighting up on the annunciator panel just before the APPR disconnected. What is it? (And what are the 3 letters A O M on the panel? I couldn’t find it in the manual.)

These are indicator lights for marker beacons: A = Airway (used for the inner marker); O = Outer; and I = Inner marker.

Thanks,
Nick

[KarelPatch]

Hi KarelPatch,

- Switch from GPS to VLOC when I am on the vector to final.

If you're flying an RNAV (GPS) approach, you shouldn't be switch the GPS from GPS to VLOC mode at all. VLOC (VOR/Localizer) mode is for using ground-based navaids and would be used for a traditional ILS approach.

If you can give us an example of a specific approach from the GTN which you've tried, it'll be easier to offer advice.

My bad about the VLOC switch. I’ve been trying so many options that I’ve been all mixed up! On my last test approaches I was unable to select NAV nor APPR unless I was on VLOC so this may have put VLOC in my head.

But when I do a GPS approach with NAV and/or APPR I get back to only FD ALT as soon as I reach the FAF, the minute the outer marker beacon lighten up.

My last tests were at LDDU (Orbx scenery). RNAV approach to RW 12, it’s the only RNAV procedure available on the Reality XP GTN 750.

[Nick - A2A]

Hi KarelPatch,

Apologies for the delayed response, but I've now had a chance to do some test flights of my own with the RealityXP GTN 750 installed in the Bonanza and I have been able to reproduce exactly the problem you describe. Upon the RNAV approach becoming 'live', the autopilot NAV mode will disconnect and subsequent attempts to rearm NAV or APP mode result in just a few rapid flashes of the relevant mode indicators on the KA 285 annunciator panel.

I did some further tests with the Cessna 182 and the KAP 140 autopilot also appears to suffer from a similar disconnect issue on intercepting GPS approaches from the RealityXP GNS products. As far as I can tell at this time, something has changed in recent months, either with the RealityXP gauges, the Garmin trainer or Prepar3D itself.

Anyway, we'll investigate this issue and hopefully it'll be possible to restore this functionality at some point.

Thanks,
Nick

[KarelPatch]

Thank you Nick, I really appreciate you looking for this issue. I feel better knowing that this isn’t coming from my way of following procedures.

[kielsf4]

I had the same issue. Go to the RXP GTN settings (hold left shift and right click the top bezel of the unit), scroll down to "Aircraft Flight Manual Supplement (AFMS)" and enable "GPS Selected".
That solved it for me. (https://www.avsim.com/forums/topic/5491 ... ching-dtk/)

[Nick - A2A]

I had the same issue. Go to the RXP GTN settings (hold left shift and right click the top bezel of the unit), scroll down to "Aircraft Flight Manual Supplement (AFMS)" and enable "GPS Selected".
That solved it for me. (https://www.avsim.com/foru

Hi kielsf4,

Thanks very much for this tip. I've now had a chance to try it with my own RXP products and can confirm this does seem to resolve the issue described by KarelPatch. Evidently this setting has been added by RXP in recent months.

So, to confirm, users should enable "GPS selected" in the "Aircraft Flight Manual Supplement (AFMS)" section of the RXP settings to prevent the AP disconnection issue when using the autopilot to follow an RNAV approach. We'll also add this change to the RealityXP .ini files with the next update.

Thanks again,
Nick

[kielsf4]

RXP has released v2.5.12 yesterday so this should be fixed now. https://www.avsim.com/forums/topic/5348 ... -released/
Jan