You can fall just about anything is all just s matter of using the mission editor. Poke around and find what you'd like.
The helicopter uses an ins assisted by GPS. Effectively, if everything is work is pure GPS, but because if terrain masking or other factors you may not have a signal, it will then switch to INS. I forget what the symbology is but it's explained in great detail in the manual.
The PVI 800 uses an internal INS that works like every other INS system, they aren't terribly complicated.
If you want a challenge, turn off your abris, and PVI and navigate via NBD and dead reconning. You'll have to fly a specific heading and airspeed or track an NBD all at the same time. It makes you really good in the helicopter. Then do it in the fog, in the rain, at night, from one airport to another. And land all with like 1000m of visibility.
-Shadow