Find and fix a bad BGL file in FSX by isolating scenery areas, testing files in halves, confirming the culprit and restoring it safely.
To find a bad BGL in FSX or FSX: Steam Edition, reproduce the crash, disable suspect scenery areas, then halve the enabled BGL files until one file consistently triggers it. Back up scenery.cfg first. Replace or reinstall that add-on; never delete a stock BGL merely because it loaded last.
How can I tell whether a BGL file is causing the crash?
A BGL fault normally follows a geographical area or appears while FSX is building or loading scenery. BGL files can contain airports, terrain, landclass, object placements and object libraries, so the faulting filename is rarely shown in the crash message.
| Symptom | Likely interpretation | Best first test |
|---|---|---|
| FSX crashes near the same airport or coordinates | A local airport, terrain or object-placement BGL is suspect | Disable scenery covering that region and repeat the flight |
| Loading stops at 80% while adjusting scenery objects | An active scenery area, BGL or scenery index may be involved | Follow our 80% scenery-loading isolation procedure |
Event Viewer names terrain.dll | Scenery is a strong possibility, but the DLL name does not identify the bad BGL | Use the terrain-related crash checks to separate malformed scenery from configuration or memory faults |
| Only one aircraft causes the crash | The aircraft, panel or gauge is more likely than scenery | Repeat the flight with a stock aircraft |
A default airport outside the add-on's coverage loading normally while one particular region crashes is especially strong evidence. Do not assume that the newest, largest or last-accessed BGL is responsible: FSX preloads many scenery files, so the last file touched before a crash may be harmless.
How do I isolate the exact bad BGL?
The reliable method is a controlled binary search: disable half of the suspects, reproduce the same flight, and keep narrowing the failing half.
- Back up the active configuration and scenery. Copy
scenery.cfgand the suspect add-on's complete folder somewhere outside FSX. Windows installations can contain both an active configuration and an installation-root template; use the copy updated when you change the Scenery Library. - Create a repeatable test. Use a stock aircraft and the same airport, runway, route and conditions each time. Also test a default airport well outside the suspect scenery's coverage as a control.
- Disable the whole scenery product first. Untick its area in the FSX Scenery Library, restart the simulator and repeat the test. If the installer created several associated areas, disable them as a group. Avoid changing default or required entries at this stage.
- Split multiple suspect areas in half. If several add-ons cover the region, enable half and test. A crash means the culprit remains in the enabled group; no crash points towards the disabled group. Continue until one scenery product or area remains.
- Split that area's BGL files. Inside its
Sceneryfolder, move half of the.bglfiles to a temporary folder outside every active scenery area. Leave texture files where they are. Restart FSX and allow it to rebuild its scenery data before repeating the exact test. - Narrow the failing group. Keep halving the group that reproduces the crash until one file, or the smallest dependent set of files, remains. Keep known paired components together if the add-on's documentation identifies them as a set.
- Confirm the result both ways. With the suspect BGL absent, the flight should load; restoring it should bring the crash back. Repeat this once before changing or deleting anything permanently.
If the suspected file crashes only when another BGL is present, neither file must be corrupt. You may have duplicate airport data, overlapping terrain or an interaction between scenery packages. Test each package separately, then together, to identify the combination.
What if FSX crashes before I can open the Scenery Library?
Disable only the suspected add-on in the active scenery.cfg by changing its area entry from Active=TRUE to Active=FALSE. Make a backup first, do not renumber areas, and do not edit the installation template by mistake.
If entries are missing, duplicated or pointing at the wrong folders, use our instructions for repairing and correctly re-adding Scenery Library areas rather than rebuilding the file blindly.
How should I fix the BGL after finding it?
A compiled BGL has no universal repair operation; the correct fix depends on whether it belongs to an add-on, conflicts with another file or is part of the stock simulator.
- Damaged or incomplete add-on: remove the installed package and extract or reinstall a clean copy of the complete scenery. Replacing only one BGL can leave mismatched textures, libraries or companion files.
- Wrong simulator format: install the FSX-compatible edition of the scenery. Sharing the
.bglextension does not guarantee that a file compiled for another simulator will work correctly in FSX. - Duplicate airport or terrain file: keep the intended version active and quarantine the conflicting one. Merely changing scenery priority may not stop both BGLs being read, so it is not a dependable crash fix.
- Optional component: leave the individual BGL disabled only when the scenery documentation says that component is optional and repeated testing shows no missing dependencies.
- Your own compiled scenery: correct the source project and compile it again with FSX-targeted tools. Do not attempt to repair compiled scenery with a text or hex editor.
- Stock FSX file: restore it using Steam's file-verification function or the boxed edition's repair process. Back up add-ons placed inside default folders first because verification or repair can replace modified files.
Do not download an isolated replacement BGL or delete a default file based solely on its name. A single BGL may cover a wide region or provide an object library used by several unrelated airports.
What if no single BGL reproduces the crash?
If every BGL works alone, the failure is probably an interaction, a scenery-library problem or something outside scenery rather than one corrupt file. Re-enable packages one group at a time, preserve shared libraries, and test for duplicate airport or terrain coverage.
If the crash remains after the entire suspect area is disabled and FSX has rebuilt its scenery data, abandon the BGL assumption. Our broader FSX crash-diagnosis workflow covers aircraft, gauges, configuration files, drivers and faulting-module evidence without confusing correlation with proof.