Avoid shady “FS2004 addon mega packs” on torrent sites. They often contain corrupted files, viruses, or broken registry entries.
Microsoft Flight Simulator 2004 (FS2004, a.k.a. FS9) remains popular among enthusiast simmer communities for its moddability, lightweight requirements, and huge legacy library of add‑ons. Add‑ons for FS2004 broadly fall into these categories: aircraft, sceneries/world enhancements, airports, utilities/tools, weather engines, and sound packs.
Since FS2004 is an older sim (released in 2003), most official add-on stores have moved on, but you can still find a wealth of content from community archives and specialized websites.