Addit! Pro For Prepar3D Alternate Download Sites AVSIM Online Go to AVSIM's File Library and do a filename search on ap3dv852.zip. Flightsim.com Go to FlightSim's File Library and do a filename search on ap3dv852.zip. Simviation.com Go to Simviation and do a search on ap3dv852.zip. FSX Addons Download directly from FSX Addons. Flyawaysimulation The latest release of Addit! Pro is featured at Flyawaysimulation. FS-Freeware Download the latest version of Addit! Pro at fs-freeware.net.