For some Subsystems split off from the existing FlightGear source, it's fairly easy to create an executable with its own property tree<ref>https://sourceforge.net/p/flightgear/mailman/message/34632142/</ref> and have shared C++ code to map FOM objects to property values. However, this is an implementation detail - the whole point of HLA and the FOM is that it makes no assumptions about what Federates do with the data.
==Current Status ==
Last updated: (
19/ 02/ 2016)
Currently, there is some very old HLA support in SimGear. This is very out of date and should be ignored.