If you have spent any time navigating the depths of your FlightGear installation directory or its associated cache folders, you may have stumbled upon a peculiar file named fg-optional-mp-files.bin . At first glance, it looks like a binary ghost—neither an executable nor a standard scenery file. For many users, this file becomes a source of confusion, especially when it grows to several gigabytes or appears to cause crashes.
Now you know the truth behind one of FlightGear’s most mysterious files. Happy flying, and may your binary caches always be small and uncorrupted. Have a persistent problem with fg-optional-mp-files.bin even after deletion? Visit the FlightGear forums or the official bug tracker at code.google.com/p/flightgear/issues/ — include your fgfs.log file for better assistance. fg-optional-mp-files.bin
When in doubt, delete it safely. FlightGear will rebuild it automatically. Include this step in your regular simulator maintenance routine, and you will avoid 90% of multiplayer loading issues. If you have spent any time navigating the
This article provides a deep dive into what fg-optional-mp-files.bin is, why FlightGear creates it, whether you can delete it, and how to troubleshoot common issues related to it. fg-optional-mp-files.bin is a binary cache file used by FlightGear’s Multiplayer (MP) system . Specifically, it is part of the fgcom (FlightGear Communications) module or the multiplayer aircraft model downloading system. Now you know the truth behind one of
/models/737-800.xml livery_united.png fgcom_voice_effects.cache These fragments confirm that the file is indeed a compiled index of multiplayer assets.
Do not confuse fg-optional-mp-files.bin with any system-critical binary. It is purely a runtime performance aid. fg-optional-mp-files.bin is not malware. It is not a hidden log file spying on you. And it is not a broken relic of an old install. It is a well-intentioned cache that makes FlightGear’s multiplayer experience smooth—until it grows too large or corrupts.