Fix FSX runway elevation and ground-level conflicts by tracing duplicate BGLs, stale altitude files, library order and terrain mesh mismatches.
Fix runway elevation and ground-level conflicts in FSX and FSX: Steam Edition by finding which BGL controls the airport, disabling duplicate airport definitions or stale altitude corrections, and checking the airport flatten against the terrain mesh. Correct library priority helps, but genuine mismatches require compatible airport-altitude, terrain-flatten or mesh data.
What causes FSX runway elevation conflicts?
FSX builds an airport from several independent scenery components, and a disagreement between any two can produce raised runways, trenches, cliffs or floating objects.
- Airport facility BGL: Defines the airport altitude, runways, taxiways, parking and related data. These files are commonly called AFCADs, even when created with newer airport-design tools.
- Airport background or flatten: Shapes the terrain beneath and around the airport.
- Terrain mesh: Supplies the surrounding ground elevation. Higher-resolution mesh can be selected even when its scenery area has lower library priority.
- Elevation-adjustment BGL: Allows an add-on to replace the altitude FSX would otherwise obtain from the stock airport. It may be installed in
Scenery\World\Scenery. - Object-placement BGL: Positions terminals, jetways and other models independently of the runway surface.
| Symptom | Likely cause |
|---|---|
| Runway sits on a plateau or in a trench | Airport altitude or flatten disagrees with the terrain mesh. See our focused diagnosis of runway plateaus and trenches. |
| Two runway, taxiway or apron layouts appear | Duplicate airport facility BGLs are active. |
| The whole add-on airport floats or sinks | Its airport, flatten and elevation-adjustment files are missing, mismatched or from different releases. |
| Runways are correct but buildings float | The object-placement scenery is incompatible or has the wrong altitude mode. Our add-on airport object and terrain checks cover this distinction. |
| A cliff or sharp seam surrounds an otherwise level airport | The flatten boundary meets terrain mesh at a substantially different elevation. |
How do I identify the conflicting FSX scenery?
Isolate the scenery one layer at a time rather than deleting BGL files at random.
- Record the affected airport: Note its ICAO code and whether the runway, surrounding terrain, buildings or every component is displaced.
- Make a backup: Copy
scenery.cfgand any suspect add-on folders before changing them. Scenery may be installed outside the main FSX directory, especially in FSX: Steam Edition. - Disable the airport add-on: Untick its scenery area in the FSX Scenery Library, restart FSX and inspect the stock airport. If the stock airport is correct, the add-on or one of its companion files is responsible.
- Test regional scenery: Disable nearby city, vector and mesh packages one at a time. Restart between tests and use the same saved flight so each result is comparable.
- Look for duplicate airport definitions: Old airport versions, AI traffic packages and regional scenery can all contain facility BGLs. File names often include the ICAO code, but this is not guaranteed. Follow our method for finding overlapping scenery BGLs rather than removing every matching file.
- Check for an orphaned elevation adjustment: Inspect
Scenery\World\Sceneryfor files installed by the affected add-on. A correction can remain active after the main airport has been uninstalled. Confirm ownership from the package documentation or backup before moving it out of the active scenery folder. - Restore the intended package: Enable its components in the developer-specified order, keeping the chosen airport above competing airport or regional scenery.
Never remove stock APX, CVX or terrain files from FSX's numbered default scenery folders. If an individual add-on BGL must be tested, move it to a backup folder outside every active scenery area instead of deleting it.
Which elevation fix should I use?
Use the repair that matches the failed component; adding another generic flatten often hides one symptom while creating a new edge or plateau.
- Duplicate airport BGL: Keep one airport definition active. If two versions contain features you need, merge them into one airport project rather than loading both.
- Stale altitude correction: Remove the orphaned add-on correction or reinstall the correction belonging to the airport version in use. Do not substitute a correction from another release.
- Missing package component: Reinstall the airport's matching facility, terrain and elevation files together. Mixing an updated airport BGL with an older flatten is a common cause of mismatched ground.
- Mesh disagreement: Use the airport developer's mesh option or corrected airport background. Disabling the mesh is a useful test, but sacrificing regional mesh is not normally the best permanent repair.
- Incorrect custom airport altitude: Edit the airport with an FSX-compatible airport design tool. When changing a stock airport's altitude, the project may need an early-loading elevation adjustment as well as the main airport BGL and a matching flatten. Changing only the runway altitude does not reshape the terrain.
- Perimeter cliff: Replace or revise the flatten so its altitude and boundary blend with the surrounding mesh. Object exclusions alone do not change terrain elevation.
Why does changing Scenery Library priority not fix it?
Library priority cannot override every type of FSX terrain conflict.
It helps when two airport, vector or object BGLs compete, so the intended local airport should sit above older airport and regional packages. Our FSX scenery priority guide explains the practical ordering rules.
An elevation-adjustment file inside Scenery\World\Scenery loads outside the airport's normal scenery area, however. Terrain mesh selection also considers resolution, so merely moving high-resolution mesh lower may not stop it being used. Disable the suspect mesh or adjustment file to test it directly.
Should I delete an ALT or elevation BGL?
Remove an elevation BGL only after confirming that it belongs to an obsolete or uninstalled add-on.
Back it up outside active scenery, restart FSX and retest. If the airport becomes correct, the file was stale; if the airport changes to a different wrong altitude, that correction was required and the real problem lies in another package component. Never delete an unknown file from a default FSX scenery folder.
How do I confirm the runway repair?
A correct repair aligns the runway, airport background, objects and surrounding terrain after a complete FSX restart.
Check both runway ends, taxiways, aprons and the flatten perimeter rather than testing only the initial parking position. If every aircraft follows the same incorrect surface, the scenery remains at fault. If the ground is visually correct and only one aircraft sinks or floats, inspect that aircraft's contact points instead of changing the airport elevation.