ok got it
The blender file /gtlf is ok, althought the origin of your object is slighly above ground
You can, in the scenery editor:
toggle the snap to ground in the object properties window, once you have done that you can move your object up and down as you want
OR
lower it in blender,
in object mode, press A to select all object, than press G to move, press Z to move along Z axes, move your mouse to move the object, confirm with enter,
than, prior to export, make sure to press CTRL+A to make sure to apply all transformation
Anyway, your real problem in this case is the terrain/mesh, it is not flat
You can easily solve that by adding a polygon with terraforming option (falloff 1), or a terraforming rectangle, lot of choices here, screen attached is polygon+snap to ground off
2 question for you:
- i had hard time looking for that specific point in the aiport, that i realized you have photogrammetry off, I not a fan of that but hey, in this area it adds a lot to the airport and surrodings
- was that terminal demolished? no sign of it in bing/google sat imagery or google street maps either? Anyway, free to put everything you like in your scene!