Why can’t I save aircraft.cfg in FSX on Windows 10 or 11?

In FSX and FSX: Steam Edition, aircraft.cfg usually will not save because Windows protects installations under Program Files. Close FSX, back up the file, edit a copy in Documents, then copy it back and approve the administrator prompt. If it saves but nothing changes, you probably edited the wrong copy or created aircraft.cfg.txt.

These instructions apply to Microsoft Flight Simulator X, including the boxed and Steam editions. Some people write MFSX as shorthand for Microsoft Flight Simulator X; they do not apply to Microsoft Flight Simulator 2020 or 2024, which use a different package system.

Why does Windows block aircraft.cfg changes?

Windows blocks a direct save when aircraft.cfg is under Program Files and the text editor has not been elevated. Signing in with an administrator account does not automatically give every programme permission to overwrite protected files.

The active configuration file is inside the installed aircraft’s folder:

For a helicopter, the file may be under SimObjects\Rotorcraft. Custom Steam libraries and extra SimObjectPaths can also place aircraft elsewhere, so a File Explorer search result is not proof that you found the copy FSX loads. Our guide to finding and safely editing the active aircraft.cfg covers those location checks.

How do I save aircraft.cfg changes safely?

The safest approach is to edit a working copy outside the protected FSX installation, then replace the original with Windows approval.

1. Close FSX and its add-on utilities. A manager left running may lock or regenerate the file, while FSX may continue using configuration data already loaded into memory.
2. Find the active aircraft folder. Confirm that it belongs to the boxed or Steam edition you actually launch. The folder name need not match the name displayed in the aircraft-selection menu.
3. Make an untouched backup. Copy the original aircraft.cfg to a folder under Documents and retain one unchanged copy. Edit a second copy.
4. Use a plain-text editor. Do not use a word processor. Preserve the existing section headings, brackets, line structure and text encoding.
5. Save the exact filename. It must remain aircraft.cfg, not aircraft.cfg.txt. Turn on file-name extensions in File Explorer and, if the editor asks for a file type, choose the option that allows all files.
6. Copy the edited file back. Place it in the original aircraft folder, select the option to replace the destination file, and approve the User Account Control prompt or enter administrator credentials.
7. Verify the destination. Reopen aircraft.cfg from the installed aircraft folder and confirm that your edited line is present. Do not rely only on the copy in Documents.
8. Restart FSX. A complete restart is the reliable way to make the simulator read the revised configuration.

For repeated work, another option is to start a trusted plain-text editor with Run as administrator and open the installed file from inside that editor. We favour copy, edit and replace for occasional changes because it limits the time an elevated editor remains open. Running FSX itself as administrator does not grant permission to a separate editor.

What if aircraft.cfg still says Access denied?

If Windows refuses the replacement even after a UAC prompt, the problem is usually the file attribute, inherited permissions, security software or another utility controlling the file. Follow our FSX file permission and Access denied fixes before changing ownership or access rules.

• Read-only file: open the individual file’s Properties and clear Read-only if selected. A shaded or filled Read-only box on the aircraft folder is not, by itself, evidence that every file is locked.
• Damaged permissions: files copied from another computer, drive or old Windows installation can retain unsuitable ownership and access entries. Repair only the affected FSX folder; do not grant Everyone full control over the entire Program Files directory.
• Security software: check the protection history for a specific block against the editor or copy operation. Allow the trusted application where appropriate rather than disabling protection permanently.
• Add-on manager: some aircraft utilities rebuild aircraft.cfg. Make the change through that utility when possible, or close it before replacing the file.
• Standard Windows account: replacing a protected file requires valid administrator credentials, even if the account can otherwise run FSX.

I already did it and it did not work — “ya lo hice y no funciono”

If the installed file reopens with your edit intact but “non cambia nulla” — nothing changes — the save worked; FSX is reading another copy, has not reloaded the file or rejected the edited entry.

1. Reopen the destination file. If the edit is missing, it never reached the installed copy. Repeat the replacement procedure and resolve any permission warning.
2. Check which FSX installation is running. Boxed FSX and Steam Edition can coexist. Also look for duplicate aircraft folders in custom libraries or other paths referenced by SimObjectPaths.
3. Expose file-name extensions. Delete or rename an accidental aircraft.cfg.txt; FSX only reads the correctly named aircraft.cfg.
4. Check VirtualStore. An older non-elevated editor may redirect its save to %LOCALAPPDATA%\VirtualStore\, mirroring part of the Program Files path. Preserve any useful edits found there, then update the real installed file using the approved replacement method.
5. Restart the simulator fully. Returning to the aircraft-selection screen may not reload every configuration value.
6. Restore the backup if the syntax is damaged. A missing bracket, altered section name or unsuitable value can cause FSX to ignore an entry even though the file saved successfully.

Our checklist for aircraft.cfg edits that FSX ignores covers redirected files, competing copies and syntax faults in more detail.

Why does a new livery still not appear — “tot nu apare”?

A newly added livery usually remains absent because its [fltsim.x] block is missing, duplicated, misnumbered or points to the wrong texture folder. Use consecutive, unique section numbers beginning with [fltsim.0], give each variation a unique title=, and ensure texture= matches the suffix of its texture.<suffix> folder.

Saving permission alone cannot repair an invalid variation entry. Our explanation of FSX fltsim entries and livery fields shows what each line controls and which errors keep a variation out of the aircraft menu.

Is aircraft.cfg the same file as FSX.cfg?

No. aircraft.cfg belongs to one installed aircraft and sits inside that aircraft’s SimObjects folder. FSX.cfg belongs to the Windows user profile and stores simulator-wide settings such as display, sound and SimObject paths. Editing one cannot substitute for editing the other.