I don't want to replicate my later post but I think that this issue has not been solved. 

 

Over XPlane forum I ask for the same problem to ToLiss A319. Their reply is as follow:

 

Following this discussion, I did the following test, which you can do also:

I open the dataref tool, and go to the appropriate datarefs for VHF1 and VHF2:

VHF1:
sim/cockpit/radios/com1_freq_hz
sim/cockpit2/radios/actuators/com1_frequency_hz

VHF2:
sim/cockpit/radios/com2_freq_hz
sim/cockpit2/radios/actuators/com2_frequency_hz

All of these are WRITABLE. Meaning, if you enter a new value in dataref editor, this value will be accepted by the aircraft. Try it out. So, whatever problem P2A has, it is not on the ToLiss side. There is nothing in the ToLiss that prevents P2A to write to these datarefs and tune the appropriate frequency for either VHF1 or VHF2.

Note that the standby frequencies are NOT writable, as I have different standby frequencies for each of the 3 RMPs, which is not supported by Xplane. But having the standby frequencies different between P2A and the ToLiss is not a problem, as only the active frequencies are relevant for communication.

 

 

Then a proper answer is needed. 

 

Thank you ery mcuh

 

IPA

That explains why it doesn't work.

In the real world, a pilot cannot change the Active Frequency directly.  You enter the Standby Frequency and press the Swap Key.  That is how P2A operates.  That is also how most SIM aircraft operate. 

Dave