What is the MDL file format?
.mdl files store 3D models of aircraft and scenery objects used in Microsoft Flight Simulator games.
.mdl files store different data depending on which version of Flight Simulator produced them. Older .mdl files - originating with Flight Simulator 95 and Flight Simulator 98 - store models as a proprietary binary stream of drawing commands and vertex geometry, loosely derived from the .BGL scenery format's opcode system. They were saved in binary format, but did not contain executable code. The models were only accessible after .mdl files were loaded by Microsoft Flight Simulator.
Since Flight Simulator 2002, each new iteration uses .mdl files that store data based on the RIFF format (data is organized in well-defined named chunks). The following MDL implementations exist:
MDL8MDL9MDLX
Each implementation is used by FS2002, FS9, and FSX, respectively. FS9 supported both MDL9 (environment models) and MDL8 (aircraft models). MDLX was a completely new implementation of the MDL format, introduced with Flight Simulator X to support improved geometry detail and animated parts such as landing gear and control surfaces.
Third-party developers frequently converted .mdl models to .DXF or .OBJ for editing in standard 3D applications using tools such as MDL2DXF and ModelConverterX. Modern Microsoft Flight Simulator (2020 and later) moved away from the .mdl format, adopting glTF-based 3D assets instead.
Security & safety
RISK: LOWAn FS .mdl is passive 3D model data, not executable, so the file itself is low-risk. The practical cautions are about TOOLING and IDENTITY: the converters are old, niche utilities best obtained from reputable Flight Simulator communities (fsdeveloper.com) rather than random 'free MDL converter' sites that bundle adware; and make sure your .mdl is actually a Flight Simulator model - if it came from a game or chemistry app it's a different format entirely and these tools won't help.
Format details
in a nutshell- Half-Life / GoldSrc & Source model (Valve) - Binary 3D model+animation for Half-Life/Counter-Strike; magic 'IDST'/'IDSQ' at offset 0 - opened/decompiled with Crowbar.
- MDL Molfile (chemistry) - A TEXT file describing a molecule's atoms and bonds (MDL/Symyx Molfile); opened in chemistry tools like Avogadro or ChemDraw.
- Rhino / MicroStation / other CAD-3D model - Several 3D/CAD applications reuse .mdl for their own model files; identify by the originating program.
Programs that open MDL files
Windows3 apps
MDL2DXF
Free Convert the FS .mdl to AutoCAD DXF, then open the DXF in Blender or a CAD/3D viewer. The classic (legacy) route to get the geometry out; sourced from Flight Simulator add-on archives.
Blender (via DXF/OBJ)
Open-source Open the DXF/OBJ produced by a converter to view and re-export the model. Blender cannot read the proprietary .mdl directly.
FS model design tools (FSDS / ModelConverterX)
Free Flight Simulator developer tools (e.g. ModelConverterX on fsdeveloper.com) import/convert FS model formats across sim generations. The active community hub for FS modeling. Technical details
deep spec| Encoding | Binary, little-endian |
| Older container (FS95/98) | Proprietary BGL-derived opcode/draw-command stream; no stable public magic bytes or header signature |
| Newer container (FS2002-FSX) | RIFF-based named chunk structure with MDL8, MDL9, and MDLX variants |
| Geometry data | Vertex positions, face indices, and drawing-command opcodes defining aircraft and scenery shapes |
| Texture references | Stores external texture filenames (BMP or DDS); textures are not embedded in the MDL file itself |
| Animation support | Present in MDLX (FSX) for moving parts such as landing gear, flaps, and propellers; absent or very limited in MDL8/MDL9 |
| Executable code | None - purely a data model file containing geometry and draw commands only |
| Compression | None; model data is stored uncompressed |
| Typical file size | Tens of KB to a few MB per model, depending on polygon count and detail level |
| Operating system | Windows (required by Microsoft Flight Simulator) |
| Format variants | MDL8 (FS2002 aircraft), MDL9 (FS2004 aircraft and scenery), MDLX (FSX) - variants are not cross-compatible across simulator generations |
| Companion files | .air (flight dynamics), .bgl (scenery placement), .bmp and .dds texture files |
| Extension overloading | .mdl is also used by Half-Life/Source Engine models, MDL chemistry molfiles, and Rhino 3D - these are completely unrelated formats |
| Superseded by | Microsoft Flight Simulator 2020 and later use glTF-based 3D assets, replacing the legacy .mdl format |
| Add-on obfuscation | Third-party payware aircraft models were sometimes locked or obfuscated by external tools to prevent unauthorized extraction |
| Released | mid-1990s (Microsoft Flight Simulator 95 / 98 scenery and aircraft models) |
| Latest version | FS2002/FS2004 MDL era; later sims (FSX/MSFS) moved to .mdl variants and then ModelDef/glTF |
MDL conversions
Community Q&A
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