Hello,
It is not possible to set the transistion altitude / level in the Citation Longitude.
Did I miss something or ost this a bug?
Boris
Personal Comments, this is not a Technical Support Response
Sim wide, the transition altitude is fixed to FL180.
But you do know what TA/TL is, don’t you? QNH? Standard altimeter setting?
And what would it have to do with the platform - it’s a function of the avionics. I thought the G3000 is just as realistic. At least that’s what they’re saying. The CJ4 can do it, so why not the Longitude?
The option shows in the GTC under VNAV, it’s just greyed out.
I was thinking about this so looked at the in sim files
It is quite literally not implemented. You can change what is shown within the game files, but there is no functionality to click it. I would like to implement a way to change it, but tbh I have no clue how to.
Line 32093 in Packages/Official/Steam/workingtitle-instruments-g3000/html_ui/Pages/VCockpit/Instruments/NavSystems/WTG3000/GTC/GTC.js
Lol. Thanks. Seems like somebody lost his to do list 
This function was not implemented. It doesn’t really have an effect on the avionics even when set, so it was not a priority for us to model.