Learn what Prepar3D.cfg controls, where P3D stores it, and how to back up, edit, test, restore or rebuild it without losing settings.
Prepar3D.cfg is Prepar3D’s per-user, version-specific configuration file, generated by the simulator to store many display, graphics, traffic and other preferences. To edit it safely, close Prepar3D, back up the correct file, use a plain-text editor, change one verified value, preserve its syntax, then restart and test before making another change.
What does Prepar3D.cfg control?
Prepar3D.cfg stores many of the simulator’s global user settings in an INI-style plain-text format. Its contents are divided into bracketed sections, with individual settings generally written as Setting=value.
The file can contain preferences related to:
- Display and rendering behaviour
- Graphics and scenery options
- Traffic, weather and simulation settings
- Sound and interface preferences
- Certain paths or entries added by compatible add-ons
It does not contain every Prepar3D setting. Files such as Scenery.cfg, aircraft.cfg, add-on definition files and controller profiles serve different purposes. Backing up Prepar3D.cfg alone is therefore not a complete simulator backup; before a major upgrade, use a broader Prepar3D update and add-on backup procedure.
Where is the Prepar3D.cfg file?
Prepar3D.cfg is normally stored in the signed-in Windows user’s roaming AppData folder, not inside the main Prepar3D installation directory. Most versioned installations follow this pattern:
%APPDATA%\Lockheed Martin\Prepar3D vX\Prepar3D.cfg
Replace Prepar3D vX with the folder belonging to the installed major version. Entering %APPDATA%\Lockheed Martin in File Explorer is safer than manually browsing hidden folders. Older releases may use slightly different folder names; our version-specific Prepar3D.cfg location and reset instructions cover the normal paths.
Each major Prepar3D release has its own file. Do not assume that the file with the newest modification date belongs to the version being launched, and do not copy an entire configuration from one major release to another.
How do you edit Prepar3D.cfg safely?
The safest method is to use Prepar3D’s own settings menus whenever the required option is available and edit the file manually only when a trusted add-on instruction or documented adjustment requires it.
- Close Prepar3D completely. Wait until the simulator process has ended. Editing while it is running can cause Prepar3D to overwrite the change when it closes.
- Open the correct version folder. Use
%APPDATA%\Lockheed Martin, then verify that the folder name matches the Prepar3D version being edited. - Make an external backup. Copy
Prepar3D.cfgto a clearly labelled backup folder, preferably with the simulator version and date in the folder name. Keeping the backup outside the live configuration directory prevents accidental editing. - Use a plain-text editor. Windows Notepad is sufficient. Do not use Word or another editor that can insert formatting, smart punctuation or document metadata.
- Find the exact section and key. Preserve section brackets, the equals sign and the existing spelling. Avoid creating a second copy of a key in another part of the file unless the instructions explicitly require it.
- Change one value at a time. This makes a visual defect, crash or performance loss traceable to one edit. For performance problems, follow a structured Prepar3D performance-tuning process instead of pasting a collection of old configuration tweaks.
- Save under the original name. Confirm that the result is still
Prepar3D.cfg, notPrepar3D.cfg.txt. Enabling file-name extensions in File Explorer makes this easier to verify. - Launch and test the same scenario. Check the setting under repeatable conditions, then close Prepar3D normally. The simulator may reorder, normalise or remove unsupported entries when it writes the file; that behaviour is not necessarily corruption.
Do not mark the file read-only as a routine way to preserve a tweak. That can stop Prepar3D from saving legitimate settings and makes later troubleshooting unnecessarily confusing.
When should you edit the file manually?
Manual editing is appropriate only when the required setting is absent from the interface or documented instructions specify an exact Prepar3D.cfg entry.
| Situation | Best choice |
|---|---|
| A normal graphics, traffic or display option | Change it through Prepar3D’s settings interface. |
| A documented add-on parameter or advanced setting | Back up the file and edit the specified key only. |
| An old FSX or earlier-P3D optimisation copied from a forum post | Do not add it unless its relevance to the installed Prepar3D version is confirmed. |
| Several unexplained crashes or display faults | Rename the file and let Prepar3D generate a clean one before reapplying settings gradually. |
A common mistake we see is copying a complete Prepar3D.cfg from another computer or simulator release. The file may contain hardware-dependent display data, obsolete keys and add-on entries that do not belong on the destination system.
Why does a Prepar3D.cfg edit not work?
Most failed edits are caused by changing the wrong version’s file, saving it with the wrong extension or using a setting that the installed Prepar3D release does not recognise.
| Symptom | Likely cause and fix |
|---|---|
| The edit disappears after closing Prepar3D | The simulator was running during the edit, or its interface rewrote that setting. Close it first and change the value through the interface if possible. |
| The edit has no effect | Check the major-version folder, section name and key spelling. An obsolete or unsupported key may simply be ignored. |
| Notepad created a second file | Show file-name extensions and remove an accidental .txt suffix. |
| Prepar3D no longer saves settings | Remove read-only status and confirm that the Windows account can write to its own AppData folder. |
| Prepar3D crashes or displays incorrectly | Restore the backup or regenerate the file rather than stacking further edits on top of the failed change. |
How do you restore or rebuild Prepar3D.cfg?
Restore a known-good backup when one specific edit caused the problem; rebuild the file when its history is uncertain or several settings may be damaged.
- Close Prepar3D completely.
- Rename the active file to something recognisable, such as
Prepar3D.cfg.old. - Launch Prepar3D so it creates a fresh configuration with default values.
- Reapply essential settings through the interface in small groups, testing between changes.
- Copy back only individual, understood entries if they are still required; do not paste the entire old file over the new one.
Rebuilding Prepar3D.cfg does not uninstall aircraft or scenery, but it can remove simulator preferences and custom entries that an add-on placed in that file. If a regenerated configuration does not stop the fault, continue with a controlled Prepar3D crash diagnosis rather than repeatedly deleting configuration files.