Appreciate the continued work on this project.   I noticed in the latest version (5.5.4) that transition levels are now based on pressure altitude as selected on the new Realism>Weather menus.  Certainly makes it more realistic in some countries.  Not in the US however, as QNE is always selected passing 18000 climbing and QNH is set passing FL180 on descent.  (Abnormal QNH pressure can affect the lowest assignable  FL but not for purposes of this game and rarely in real life.)

The fix for custom location files for US operations is to change the location text files labeling to reflect "transitionaltitude" as being 18000 instead of the present "transitionlevel" label used in older examples.  Simply change "transitionlevel" to "transitionaltitude" = 18000 and altitude selections up to 18000 will be in QNH pressure altitude and voice communications will be accurate once again.

Excellent simulation!

Thanks for your message!

Indeed, it's better to use "transitionaltitude" now. In earlier versions of the game, when variable pressure was not a thing, I choose the name "transitionlevel" (removed) or "transition" (now interpreted as transition altitude). Removing "transitionlevel" was a mistake, I'll add it back for better compatibility with older files.

As for the transition level (or lowest usable level), that's currently calculated the same way for all locations, even though in reality it differs per country. The level is set at least 1000 feet higher than the transition altitude, in steps of 500 feet. This avoids conflicts between altitude/FL.

Also, I recently noted that FAA documents say that already at 18000 feet standard pressure should be used. If I read this correctly, this means "transitionaltitude"=18000 should mean FL180 is the lowest level at high pressures. Perhaps I will adjust this for "usa"=True airports in the future, as well as increasing the step size from 500 to 1000 feet.