Change runway tiles to be childsprites rather than buildings
As can be seen in the attached picture, when runway tiles are defined as buildings, they can cause an overlap bug when airplanes (or airships in this case) are extremely long. Changing them to childsprites rather than buildings (as is done in OGFX+ Airports itself) mitigates the issue.
The current building behavior is shown at the bottom of the attached image, whereas the patched behavior, with childsprites, is shown at top. The attached patch converts the appropriate spritelayouts to use childsprites rather than buildings, and is applied against the main .nml file found here at the repo.