Where is FSX.cfg, and how do I edit it safely?

In FSX and FSX: Steam Edition, the active fsx.cfg is normally in your Windows roaming AppData profile, not the simulator's installation folder. Open %APPDATA%\Microsoft\, identify the active FSX or FSX-SE folder, close the simulator, copy the file as a backup, then edit it with a plain-text editor.

Where is the FSX.cfg file?

Windows stores FSX's configuration separately for each user account. Press Windows key + R, enter %APPDATA%\Microsoft\ and press Enter.

Steam Edition's folder and filename can depend on the computer's FSX installation history, so do not assume that FSX-SE must be correct. Our edition-specific AppData folder guidance covers the location differences and hidden-folder issue in more detail.

If no configuration file exists, run that edition of FSX at least once and exit normally. FSX creates the file in the Windows account used to run the simulator.

Which FSX.cfg is active in Steam Edition?

The active file is the one FSX: Steam Edition reads and updates when it closes, which matters when both FSX and FSX-SE folders exist.

1. Start the required FSX edition. Temporarily change a display option.
2. Exit FSX normally. Do not leave the simulator running while inspecting or editing the file.
3. Check the modified time. Compare the configuration files in the FSX and FSX-SE folders. The file updated when FSX closed is the active one.
4. Restore the temporary setting after confirming the correct file.

If installation history has left several plausible files, our utility for locating and opening the active FSX configuration helps avoid editing an unused copy.

How do I edit FSX.cfg without breaking it?

The safest method is to close FSX, preserve the original file and make one logical change at a time.

1. Close FSX completely. Editing while it is running is a common mistake because FSX may overwrite your changes when it exits.
2. Back up the file. Copy it to another folder or create a clearly named copy such as fsx.cfg.before-edit. For larger changes, follow our guidance for backing up the wider FSX profile and add-on setup.
3. Open it in a plain-text editor. Windows Notepad is sufficient. Do not use Word or another rich-text editor.
4. Find the correct section. Section names appear in square brackets. Edit the required key under that section rather than adding another copy elsewhere in the file.
5. Change only what you understand. Record the original value, preserve punctuation and avoid pasting an entire configuration made for somebody else's hardware.
6. Use the normal Save command. This reduces the risk of changing the filename, extension or text format.
7. Launch FSX and test. Check the affected aircraft, location or graphics condition before making another change.

Leave the configuration file writable. Marking it read-only may prevent FSX from saving display, sound and other menu changes, and it can interfere with add-on configuration tools.

Why are my FSX.cfg changes not working?

Changes usually fail because the wrong file was edited, FSX overwrote it on exit or Windows saved it with the wrong extension.

• Wrong configuration: verify the file's modified time after closing the exact FSX edition you use.
• Hidden extension: enable file-name extensions in File Explorer and confirm the name ends in .cfg, not .cfg.txt.
• Duplicate entry: search the entire file for the setting and retain one intended entry in the correct section.
• Incorrect section: a valid setting placed beneath the wrong bracketed heading may be ignored.
• FSX was open: close it, edit again and save before restarting.
• Add-on rewrites: some configuration utilities replace their own entries when run, so test before and after opening the relevant utility.

What should I do if FSX will not start after editing?

Rename the damaged configuration rather than deleting it, then let FSX generate a clean replacement.

1. Close FSX.
2. Rename the active file to something such as fsx.cfg.bad, using the equivalent name if Steam Edition created fsx_se.cfg.
3. Start FSX. A fresh default configuration should be generated.
4. Test the clean file before copying back only the entries you genuinely need.

This resets settings held in the configuration but does not uninstall aircraft or scenery. Add-ons referenced through custom SimObjectPaths may remain unavailable until those lines are restored. If FSX still crashes, use our step-by-step configuration reset and crash checks rather than restoring the whole suspect file.