Core OS?
It's a military combat aircraft it's not likely to be running Windows for its sensors or avionics. It'll either be some flavour of VXWorks or some massaged version of linux with a real time kernel and customised libraries and it'll be distributed across several procesors. Most likely that middle ware LM is talking about will be buildable for several different 'OS's and the 'core' software as you call it will be going via that middle ware thus reducing the amount of rework to the API that interfaces to the 'OS'.