Outerra is NOT an addon for FSX.
It's a completely different program. It's mostly a graphic engine for world/planet rendering. At the moment, it's very, VERY limited, and although it can simulate a flight, it's not realistic at all and not so interesting.
Actually it uses jsbsim which is what flightgear uses so it's fairly realistic.
And some developers are are
attempting t4o see what they can do. it's coming out well. I'm keeping my fingers crossed

Most people think that flying a plane is dangerous, except pilots because they know how easy it is.
Arguing with a pilot is like wrestling with a pig in the mud, after a while you begin to think the pig likes it.