Why are aircraft.cfg changes not taking effect in FSX?

FSX ignores aircraft.cfg edits when you changed the wrong copy, Windows saved the file elsewhere, FSX has not reloaded the aircraft, or the edited line is invalid, duplicated or overridden. Confirm the active aircraft folder, save a real aircraft.cfg file, restart FSX, then test one small change at a time.

This applies to both boxed Microsoft Flight Simulator X and FSX: Steam Edition. A mistake we see constantly is editing a valid-looking file in an inactive FSX installation while the simulator loads another copy.

How do I make FSX recognise aircraft.cfg changes?

The reliable method is to close FSX, verify the active file, save it as plain text and restart the simulator.

1. Exit FSX completely. Changing aircraft in the Free Flight menu can reload some data, but a full restart removes uncertainty about values retained by the loaded flight or aircraft.
2. Find the copy FSX actually loads. The usual location is <active FSX root>\SimObjects\Airplanes\<aircraft folder>\aircraft.cfg; helicopters may be under Rotorcraft. Add-ons can also use another SimObjects path configured in FSX. Our guide to finding and backing up the correct aircraft.cfg covers the standard locations.
3. Check the FSX edition. Boxed FSX and Steam Edition can coexist, leaving nearly identical aircraft folders. If both are installed, use the steps for identifying the active boxed or Steam Edition root before editing anything.
4. Confirm the real filename. With Windows file extensions visible, it must be aircraft.cfg, not aircraft.cfg.txt. Use a plain-text editor and preserve the section headings, brackets and line structure.
5. Verify that the save reached the original file. Reopen it and check both the changed value and modification time. If Windows reports access denied, silently redirects the edit or restores the old content, follow our aircraft.cfg permissions and VirtualStore fixes.
6. Check the edited entry. Put the parameter under its correct section, use a decimal point for numerical values, and remove duplicate versions of the same key. Keep comments on separate lines beginning with a semicolon rather than appending explanatory text to a value.
7. Restart FSX and load a fresh flight. For fuel, payload or switch-state tests, avoid an old saved flight because it can restore values that mask the new defaults.

How can I prove FSX is reading the edited file?

A temporary ui_variation edit separates a file or path problem from a parameter-specific problem.

Back up the file, find the relevant [fltsim.x] section and append a distinctive phrase such as CFG TEST to its ui_variation= value. Restart FSX and inspect that aircraft in the selection menu. Do not change title= for this test because saved flights and AI traffic can reference it.

There is no general aircraft.cfg cache that normally needs deleting. If a full restart does not reveal the temporary variation name, concentrate on the path, filename and save destination rather than deleting FSX.cfg or shader files.

Why are livery changes in aircraft.cfg not appearing?

A new livery normally fails because its [fltsim.x] section is invalid or does not match the installed texture folder.

• Number the sections consecutively from [fltsim.0], without reusing a number or leaving a gap.
• Give every aircraft variation a unique title= value.
• Match texture=BA to a folder named texture.BA; an empty value refers to the plain texture folder.
• Keep sim=, model= and panel= references valid for that aircraft.
• Check the aircraft-selection filters if the entry uses unexpected ui_manufacturer, ui_type or ui_variation values.

For this specific case, compare the entry against our worked FSX repaint and texture installation example.

Can an add-on override aircraft.cfg settings?

Yes. Aircraft.cfg supplies configuration data, but it does not control every part of an FSX aircraft.

• Flight dynamics: FSX uses both aircraft.cfg and the aircraft's .air file. Changing a parameter that belongs elsewhere will have no effect.
• Complex systems: Custom gauges or modules can control engines, electrical systems, doors, lights and other states after the aircraft loads.
• Visual geometry: The compiled model determines the aircraft's shape and animations; aircraft.cfg cannot add missing model parts.
• Panels and instruments: These are normally defined by panel.cfg and gauge files rather than aircraft.cfg.
• Saved-flight state: A saved flight can restore fuel, payload and cockpit conditions over the aircraft's defaults.

If the ui_variation test works but the intended setting does not, restore the test label and identify which file or custom system owns that setting. Testing the same type of change on a default FSX aircraft can also show whether the add-on is overriding it.