For finding the correct LVAR to use with SPAD.neXt for controlling an addon aircraft, the first stop is always the creator or the aircraft. Ask them for a LVAR List. (If you got it, it would be nice if you send it to support@fsgs.com so I can add it to the list).

If the manufacturer does not have a list, it's a bit more complicated:

1. Load the aircraft into the sim, make sure SPAD.neXt is connected to it, and the SPAD.neXt Bridge is running. (It's running if you have an option “SPAD.neXt” in the addons menu of the sim)
2. Open the SPAD.neXt Eventmonitor. (Addons → Eventmonitor)
3. Either browse the LVARs ( “Add Data” ) and look for one that is named like the stuff you are looking for, or press the “Add LVAR” button to monitor all LVAR provided by the aircraft. (However this can be many!)
4. Do whatever you need to do in the aircraft, and check which LVAR changed in the Eventmonitor.
5. Now you know which LVAR you need to program, and just need to find out the correct values.