Learn how to safely edit aircraft.cfg in FS2004, make reliable backups, avoid broken variants, and fix changes the simulator ignores.
To safely edit aircraft.cfg in FS2004, close the simulator, locate the file inside the specific aircraft’s folder, make a backup, and use a plain-text editor. Change one value at a time without renaming sections or parameters, save it as aircraft.cfg, then restart FS2004 and test that aircraft.
Where is aircraft.cfg located in FS2004?
In FS2004 (FS9), aircraft.cfg sits inside each aircraft’s own folder under the simulator’s Aircraft directory. A typical installation might use C:\Program Files (x86)\Microsoft Games\Flight Simulator 9\Aircraft\AircraftFolder\aircraft.cfg, but the path depends on where FS2004 was installed.
If the installation location is uncertain, find fs9.exe; the Aircraft folder should be in that same main FS2004 directory. Do not confuse aircraft.cfg with the separate FS9.cfg file that controls simulator-wide settings. We have separate guidance for finding FS9.cfg on modern Windows.
One aircraft.cfg can control several liveries or variants through its [fltsim.x] sections. Our explanation of how FS2004 aircraft components fit together covers its relationship with the model, panel, sounds, textures and flight-dynamics files.
What is the safest way to edit aircraft.cfg?
The safest workflow preserves a known-good copy and limits each test to one identifiable change.
- Close FS2004. Editing while the simulator is running can leave you testing values that were already loaded into memory.
- Show file extensions in Windows. This helps prevent accidentally creating
aircraft.cfg.txt, which FS2004 will not recognise. - Back up the original. Copy the file as
aircraft.cfg.bak, preferably with another copy outside the aircraft folder. For extensive work, back up the complete aircraft folder. - Use a plain-text editor. Do not use Word or another rich-text program. Preserve the existing text encoding; avoid smart quotes and other formatted characters.
- Change one item at a time. Keep section names in square brackets, retain each equals sign and preserve the number and order of comma-separated values.
- Use decimal points. In numeric entries, a full stop is the decimal separator. Commas often separate several values and cannot safely replace decimal points.
- Save under the exact original name. Confirm that the result is still
aircraft.cfg, not a text document with a hidden extra extension. - Restart and test. Load the edited aircraft, check the affected system or view, and inspect both cockpit and external behaviour before making another change.
If Windows denies permission because FS2004 is under Program Files, copy the file to a working folder, edit it there, then copy it back and approve the replacement prompt. Confirm the modified time on the file in the actual aircraft folder. Older installations can also leave redirected files under %LOCALAPPDATA%\VirtualStore; check there if edits appear to save but FS2004 ignores them.
Which aircraft.cfg section should I change?
The correct section depends on the result you want; several apparent aircraft.cfg changes actually belong in another file.
| Change required | File or section to inspect |
|---|---|
| Livery name, registration or texture assignment | [fltsim.x] in aircraft.cfg |
| Empty weight, fuel capacity or loading stations | [weight_and_balance] and related sections; follow our dedicated FS2004 weight-and-balance method |
| Wheel position or ground stance | [contact_points] |
| Pilot viewpoint | The aircraft’s view or eyepoint entry; camera add-ons may also supply their own instructions |
| Panel gauges and panel windows | panel.cfg in the applicable panel folder |
| Sound assignments | sound.cfg in the applicable sound folder |
| Global display, weather or controller behaviour | FS9.cfg rather than aircraft.cfg |
| Visual model geometry | The compiled model files; aircraft.cfg can select a model variant but cannot reshape it |
| Flight dynamics | Aircraft.cfg and, for some behaviour, the associated .air file; the latter is not a normal text file |
How do the [fltsim.x] entries work?
Each [fltsim.x] block defines one selectable variation of the aircraft. Number the blocks from [fltsim.0] upwards and keep them consecutive; after deleting a variation, renumber later blocks to remove the gap.
title=must be unique across all installed aircraft. Duplicate titles can cause one variation to be omitted.sim=identifies the associated.airfile by filename without its extension. Changing it to a nonexistent name can produce an Aircraft Initialization Failure.model=doorpoints to a folder such asmodel.door. A blank value normally selects the basemodelfolder.texture=BApoints totexture.BA. The same suffix rule applies topanel=andsound=.ui_manufacturer=,ui_type=andui_variation=determine how the variation is labelled in the aircraft selection interface.
A mistake we see constantly is an extra nested folder, leaving the working aircraft.cfg one level deeper than FS2004 expects. Our FS2004 add-on folder and aircraft installation checks explain how to identify that layout problem.
Why are my aircraft.cfg changes ignored?
Ignored edits usually mean FS2004 is reading a different file, the edited file has the wrong extension, or the changed parameter points to something that does not exist.
- Wrong aircraft folder: The aircraft’s menu name does not have to match its Windows folder name. Check the active variation’s
title=and texture entry. - Hidden text extension: Rename
aircraft.cfg.txttoaircraft.cfgafter enabling visible extensions. - Wrong suffix: If
texture=blueis specified, the corresponding folder must be namedtexture.blue. - Duplicate or broken variation: Check for repeated
title=values, duplicate section numbers and gaps in the[fltsim.x]sequence. - Invalid numeric line: Restore the original number of comma-separated fields, including any zero values and minus signs.
- File permission or VirtualStore conflict: Verify that the file inside the real FS2004 aircraft directory contains the new value.
- Simulator not restarted: Close FS2004 fully and reopen it before judging the result.
How do I restore a broken aircraft.cfg?
Close FS2004, rename the damaged file to something such as aircraft.cfg.failed, then copy the backup into place under the exact name aircraft.cfg. Restart the simulator and confirm that the original aircraft or variation has returned.
If there is no backup, restore aircraft.cfg from the same original aircraft package. Avoid replacing the entire folder until you have copied out any added liveries, custom panels or sound changes that need to be retained.