Does anyone know if the Earth model in FSX is a WGS-84 ellipsoid or WGS-84 spheroid? I need to know this in order to compute accurate lat/lon from my simulation.

Ellipsoid according to http://www.fsinsider.com/Community/Develop...t+Simulator.htm

That's correct. Follow this reference for the details:12. NIMA Technical Report TR8350.2, Department of Defense World Geodetic System 1984, Its Definition and Relationships With Local Geodetic Systems, Third Edition, 4 July 1997. http://earth-info.nga.mil/GandG/publicatio...2/tr8350_2.html-Adam

I more than once had the impression that FSX is actually using a FLAT model for Earth in the "active" range which stems roughly from 1547.Take a plane, start, fly straight East or West and watch what happens after a couple minutes (and repeats to happen every now and then).