G'day,

I've encountered a bit of a conflict between the GPS OBS and the stock CDI switch in the Carenado Grand C208 HD I was hoping someone may be able to help with.

Out of the box everything looks good until you go to OBS a waypoint - you can't move the CDI in GPS or GPS/OBS mode. You can move the dial until you initialize the GTN unit, then it freezes in GPS mode (although VLOC still works fine and you can still toggle between).

It seems that the master/autopilot is really tied to the stock 430 unit somehow. From what I've seen, if you toggle the "GNS NAV 1 CDI" to "NAV" (which is the command for the GPS / NAV switch on the dash of the original carenado c208) and use the GTN 750 or 650 as a master the NAV mode doesn't work correctly. You can also end up with an annoying NAV flag on the HSI depending on whether or not you're in range of an active VOR (I haven't 100% verified this as the cause but it's not all the time and makes sense) . For all I can see you just head off on random courses with the AP NAV engaged. HDG works though.

If you turn "GNS NAV 1 CDI" to GPS, the thing will happily fly a hold or approach on autopilot, but you can't OBS a waypoint. I tried having it set to manually inputting the OBS on the GTN (which almost works) but it doesn't update the HSI until you enter the OBS menu for a second time. This actually wouldn't be a bad workaround if it updated off the bat but having wrong info displayed is a bit of an issue.

The issue seems to be tied to the "master" setting of the unit. If I turn master off, the NAV / AP mode doesn't work and the unit doesn't cross-fill to the default 430, but everything else seems to more or less work. I can even set two different waypoints (one on the GTN, one on the stock 430) and OBS them both off the same knob. If anyone has any suggestions I'd really appreciate it, I'm out of ideas.

Cheers, Mark.

Hi,

It is possible this aircraft was coded in such a way that the OBS function was never meant to be used in GPS mode, and therefore the aircraft is artificially limiting this. Another possibility is that the aircraft is using a different set of datarefs from the ones you'd expect for their gauges. Sometimes gauges are for example using NAV1 related datarefs for the HSI instead of using the HSI datarefs, or the reverse. All of this can cause different sort of issues.

Nevertheless, are you using any of the "Link HSI", "Link VOR", "Link CRS" settings for example? What about disabling them all or enabling them all and compare?

Hi, 

Thank you very much for the response. The aircraft works fine with OBS and the default 430 unit - it just seems to fight with the GTN. I've been through all the settings at least a dozen times flicking the link settings on and off but no joy. The gauges work fine when you turn master off, but then the 'nav' mode on the autopilot doesn't.

I think the issue lies somewhere in a comment you made elsewhere regarding the realityXP software disabling the default GPS unit - I'm pretty sure this isn't happening. Is there any way I can try do that manually or check the status of the default unit?

Many thanks again, 

Mark.