(edit) I found the answer to the problem below at the A2A forums.  With a lot of people switching from the F1 GTN to the RXP, others may need this:

**Any time you switch the GPS in the panel of a A2A plane (or add a 3rd party GPS for the first time)  you MUST run the A2A "Aircraft Configurator" utility. This sets up a bunch of variables that prevent exactly the kinds of problems I describe below.  Now you (and I) know.**  This utility can be found in an A2A folder in the start menu of your PC..

(Note: as I read over what I wrote below, it's obvious that my problem is much more likely with A2A than RXP, and I'm off to post it on their forum, but I thought I'd leave it up here just on the off chance . . . )

I switched from the F1 GTN 750 to The RXP one a month or two ago. After a certain amount of fiddling, I now have it working beautifully on all my planes with one little exception:

Background: I'm running P3Dv4 on Win10 and I run the GTN  full size in a second monitor, so I'm not worried about displaying the GTN in the panel.

My problem is with A2A's Comanche and their V35 Bonanza. The default radio stack on both of these is modeled (realistically) with an older GPS-only instrument and separate Nav/Com radios. As a result, both have a toggle switch  on the panel to change the HSI source between GPS and VOR/LOC..  I never even noticed that switch when I was flying with the F1 GTN, because it just took over driving the HSI all the time, so that the HSI always displayed whatever source had been selected on the GTN.

For whatever reason, RXP used a different logic in their setup, so that you have to switch between GPS and VOR/LOC on both the GTN itself and with the toggle switch on the panel.  That, in itself, isn't the problem.  I'm OK with, for instance, having to flip two switches rather than one as you start down final on an ILS.  (It's kinda typical of the funky avionics setups you sometimes find in older real-world planes.)

My problem is that this only works as (apparently) intended on the Comanche. In the Bonanza, with the panel switch (and the switch on the GTN) on "GPS" the HSI displays GPS data, and with both switches on "NAV" it displays VOR/ILS data. However on the Bonanza, the HSI works only if both switches are set for GPS.  If either one is set for "NAV/LOC" the HSI goes dead with a red no-input flag.

I also have the A2A 182, but that has a more modern Garmin 430 in the default panel supplying both GPS and VOR/LOC output, so the GTN just replaces it seamlessly.

Anyone have any experience with this?

 

Edited October 26, 20214 yr by RXP
to add solution from A2A

Hi,

Thank you for reminding this, it might help a lot of A2A pilots!

As for the NAV/GPS switch, the issue could be due to many different things, but in general it boils down to a very simple difference in implementation:

The RXP GTN/GNS is can be configured to either:

a) Enforce its CDI mode onto the simulator NAV/GPS switch state
    GPS --> SIM in the GUI Settings Panel

b) bind its CDI mode from the simulator NAV/GPS switch state
    GPS <-- SIM in the GUI Settings Panel

c) synchronize its CDI mode and the simulator NAV/GPS switch state so that any one changing affects the other
    GPS <=> SIM in the GUI Settings Panel

In addition, the RXP GPS is only sending an event to the simulator, or changing its mode, if the CDI mode and the switch state disagree. This is a trigger based on differences only.

3rd party aircraft can be coded to either:

a) Enforce their NAV/GPS switch onto the simulator NAV/GPS switch state
    in this case you'd use GPS<=>SIM or GPS<--SIM

b) Send a switch state change command when activating the switch only, and displaying the switch position based on the NAV/GPS switch state.

Very often it is implemented as (a) and in this case there is no other way than configuring the RXP GPS to be a recipient, not a master.