Why does my aircraft sink into the runway in FSX?

In FSX and FSX: Steam Edition, an aircraft sinks into a runway for one of two main reasons: its wheel contact points do not match the model, or the airport’s visible runway sits at a different elevation from its physical surface. Cross-test a default aircraft and a stock airport before editing anything.

Is the aircraft or airport causing the sinking?

A two-way cross-test identifies whether the fault follows the aircraft or remains at one airport.

1. Start a fresh Free Flight with a default aircraft on the affected runway. Do not load the saved flight that showed the problem.
2. Move the problem aircraft to a stock airport outside the coverage of the suspect scenery package.
3. Test another surface at the affected airport. If the runway fails but a taxiway or parking stand does not, the runway surface itself may be incorrectly hardened or positioned.
4. Follow the result. Edit the aircraft only if the fault follows that aircraft. Investigate scenery if several aircraft fail at the same location.

If you need to build the comparison from scratch, follow the normal process to change the aircraft and departure location in Free Flight.

How do I fix incorrect FSX landing-gear contact points?

Edit aircraft.cfg only when the sinking follows one aircraft to otherwise normal airports.

1. Close FSX and make a backup. Copy the aircraft’s complete folder or at least its aircraft.cfg file before changing anything.
2. Find the active configuration. Aircraft are normally stored below SimObjects\Airplanes, although an add-on can use another registered SimObjects folder. If boxed FSX and Steam Edition are both installed, confirm that you are editing the copy used by the simulator you launched.
3. Open the contact-point section. Find [contact_points]. A wheel entry normally begins in the form point.n = 1, longitudinal, lateral, vertical, ...; the initial type value 1 identifies a wheel.
4. Inspect the vertical coordinate. This is the third positional value after the type and is measured in feet relative to the aircraft reference datum. Making it more negative lowers the physical contact point, causing that part of the visible aircraft to sit higher above the runway.
5. Change one area at a time. If all wheels are buried equally, adjust the wheel points consistently. If only the main gear is wrong, leave the nose or tail wheel alone. Use small changes and preserve every comma in the entry.
6. Check suspension behaviour. If the aircraft spawns correctly and then settles too far, inspect the static-compression, maximum-compression and damping values later in each wheel entry rather than repeatedly moving the wheel position.
7. Restart and retest. Fully exit FSX, reopen it and start a new flight. This avoids mistaking an unchanged or cached aircraft for a failed edit.

A mistake we see regularly is copying contact points from an aircraft that merely has a similar shape. The values are tied to that model’s reference datum and geometry; borrowed figures can cause bouncing, tipping, ineffective brakes or an aircraft floating above the runway.

The static_cg_height and static_pitch values affect initial ground placement and attitude, but they are not substitutes for correct wheel points. If only the visible tyres clip into the runway while the fuselage height and attitude are right, raising the whole aircraft will create a second fault. That usually needs corrected wheel geometry, animation or configuration from the aircraft package.

How do I fix an airport where every aircraft sinks?

If several aircraft sink at one airport, the airport scenery and the physical ground surface are using incompatible elevations or surfaces.

1. Disable the add-on airport temporarily. Turn off its Scenery Library entry, restart FSX and test the default airport with a default aircraft. If the problem disappears, the aircraft is not at fault.
2. Check scenery priority. A dedicated airport should normally sit above broad regional scenery covering the same area. Reordering cannot fix every conflict, but it can stop an older airport definition or ground polygon from appearing over the intended one.
3. Look for duplicate airport definitions. Two active BGL files for the same airport can provide different runway altitudes, flattens or ground polygons. Do not delete default FSX files or remove BGLs merely because their names look related.
4. Inspect separate elevation corrections. Some installers place an altitude-correction BGL in Scenery\World\Scenery. That file can remain active after the main airport is disabled or uninstalled. Move only a file you can positively associate with the add-on, and keep a backup.
5. Consider the hardened surface. A visually modelled runway, bridge or raised platform needs a matching collision surface. If the aircraft falls completely through that object but behaves normally on nearby terrain, its hard surface is absent or at the wrong height.
6. Repair or reinstall the airport package. The airport reference altitude, terrain flatten, runway model and hardened surface must agree. Reinstalling is safer than making several speculative BGL changes at once.

Our airport elevation, terrain-mesh and scenery-priority checks cover the wider causes of raised and sunken runways. When reordering scenery does not help, use the more detailed method for tracing duplicate BGL files and stale elevation corrections.

Can terrain mesh make an aircraft sink into a runway?

Terrain mesh can expose or exaggerate an airport elevation mismatch, but it cannot make one faulty aircraft sink at every airport.

Temporarily disable the mesh and repeat the same fresh-flight test. If the airport works without it, the lasting fix is compatible airport elevation and flatten data, not permanently reducing terrain detail. If the problem follows one aircraft with or without the mesh, return to its contact points.

Why does the aircraft sink only in a saved flight?

An old saved flight can retain a position and altitude that no longer match the airport after scenery has been installed, removed or corrected.

Select the airport and runway again in Free Flight instead of loading the old save. If the aircraft then starts at the correct height, replace the saved flight; editing the aircraft or airport would address the wrong problem.

What if the aircraft sinks only on touchdown?

Touchdown-only sinking usually indicates landing-gear compression or damage rather than a permanent runway-elevation fault.

Repeat the landing gently at a stock airport. If a hard arrival makes the gear disappear, changes the aircraft’s attitude or causes a wing, engine or propeller strike, check the causes of landing-gear collapse and touchdown damage. If gentle landings at several airports still make the aircraft settle below the surface, inspect its contact-point and suspension values.

If every aircraft falls through the same custom runway at the moment of touchdown, the runway probably lacks a correctly positioned hardened surface. That remains a scenery fault even though it first appears during landing.

Will Slew mode fix a sunken aircraft?

Slew mode can lift an aircraft back above the surface temporarily, but it does not repair contact points, airport elevation or runway collision geometry.

Use it only to recover an aircraft for the session. A fresh flight is still required for diagnosis because an aircraft placed slightly above the ground may appear normal until FSX settles it onto the faulty gear or surface.

Still not working? Check that FSX loaded the change

If the first fix leaves you thinking “nah bro, it’s still not working”, stop changing values and verify that FSX loaded the file or scenery entry you edited.

• Confirm the installation. Boxed FSX and Steam Edition can coexist, leaving more than one aircraft or scenery folder on the computer.
• Reopen the edited file. Check that the new value was saved and that Windows did not create aircraft.cfg.txt because file extensions were hidden.
• Check write permissions. An editor may appear to save a file under a protected installation folder without replacing the active copy. Verify the file’s modified time and reopen it before testing.
• Restart FSX completely. Merely returning to the menu may leave the previous aircraft or scenery data loaded.
• Use a fresh flight. Saved positions can conceal a successful scenery correction or recreate the original bad altitude.
• Restore the backup if symptoms multiply. Return to the known configuration, then make one controlled change. Altering contact points, suspension and airport scenery together makes the result impossible to interpret.