What is the BGL file format?
A .bgl file (BAO Graphical Language) is a proprietary binary scenery data file used by Microsoft Flight Simulator and its add-on ecosystem. The name reflects its origin: BAO stands for Bruce Artwick Organisation, the developer behind the original Flight Simulator engine.
The format dates to FS5 (1993) and has been revised with each major simulator release - FS98, FS2000, FS2002/2004, FSX (2006), and MSFS 2020/2024. FSX-era BGL is the most documented variant and remains the target for a large library of community add-ons. MSFS 2020/2024 introduced an updated BGL pipeline through the MSFS SDK that is not fully backward-compatible with FSX BGL.
A .bgl file begins with a 0x38-byte header containing version information, a section count, and bounding geographic coordinates, followed by a section pointer table. Each section carries different internal structures for its type:
- Airport layouts (runways, taxiways, ILS, gates)
- Terrain elevation tiles and CVX coastline vectors
- AI traffic schedules
- Autogenerated building data
- Navigation database records
.bgl files reference companion .mdl files for 3D object models and .xml project files in SDK-based workflows. For MSFS 2020/2024 development, raw BGL editing has been largely replaced by the MSFS SDK project editor, which compiles .xml source into BGL output.
Security & safety
RISK: LOWBGL files are read by the flight simulator engine only; they do not execute arbitrary code. Malicious BGL crafted to exploit parser vulnerabilities is theoretically possible but essentially unheard of in practice. Download add-on scenery only from reputable sources (MSFS Marketplace, FlightSim.to, AVSIM, Orbx).
Format details
in a nutshell- Babylon Glossary File - Babylon translation software uses .bgl for compiled glossary/dictionary data - unrelated to flight simulation.
Programs that open BGL files
Windows4 apps
Microsoft Flight Simulator 2020 / 2024
Paid Place BGL in Community/ folder (add-on) or Scenery/ subfolder; simulator loads it automatically on startup.
Airport Design Editor (ADE)
Free File → Open BGL - reads FSX/P3D airport BGLs for viewing and editing.
Microsoft Flight Simulator X (FSX)
Paid Place BGL in Addon Scenery/ folder; FSX loads it on startup. Technical details
deep spec| Origin of name | BAO Graphical Language - BAO = Bruce Artwick Organisation, original Flight Simulator engine developer |
| Byte order | Little-endian |
| File header | 0x38-byte header: version, section count, bounding geographic coordinates |
| Structure | Header + section pointer table + typed subsection blocks |
| Section types | Terrain, airport, AI traffic, autogen objects, navdata, CVX coastline/terrain vectors |
| Format generations | FS5 (1993), FS98, FS2000, FS2002/2004, FSX (2006), MSFS 2020/2024 |
| FSX compatibility note | FSX BGL is the most documented; MSFS 2020/2024 BGL is not fully backward-compatible with FSX |
| Companion formats | .mdl (3D models), .xml (SDK project source), .bmp (textures) |
| Typical file size | 10 KB - 50 MB; airport BGLs ~1-5 MB; CVX terrain tiles ~50-500 KB |
| Compression | None in the BGL container; some sub-records may use proprietary packing |
| Associated OS | Windows only |
| MSFS 2020/2024 workflow | XML source compiled to BGL by MSFS SDK project editor; direct hand-editing not recommended |
| Released | 1993 (FS5 era); extensively revised for FS2000, FSX (2006), MSFS 2020/2024 |
| Latest version | MSFS 2020/2024 BGL (extended header; backward-incompatible with FSX BGL) |
| Specification | docs.flightsimulator.com |
BGL conversions
Community Q&A
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