Hello:
To find the numeric [FSX install path]\Scenery sub-folder location, look up EGHD in the "Base File Information" section of the FSX Deluxe Environment SDK "Terrain and Scenery" document and you'll see that
EGHD is in the [FSX install path]\Scenery\0501\Scenery sub-folder.
After a default FSX SDK installation, you'll find the above document here:
"C:\Program Files\Microsoft Games\Microsoft Flight Simulator X SDK\SDK\Environment Kit\Terrain SDK\Terrain and Scenery.html"
An example airport location query is found in this thread:
http://www.fsdeveloper.com/forum/showthread.php?t=9223&highlight=base+file
It is easiest, of course to find the file in a utility such as ADE, AFX or FSX Planner, or in Winfried Orthmann's regional airports list:
http://library.avsim.net/esearch.php?CatID=fsxmisc&DLID=93343
AFX quickly showed me that
EGHD is in the FSX APX46140 airport file; related files will be in the "
*4614*.bgl " file name series.
As seen in the FSX Deluxe Environment SDK "Terrain and Scenery" document, VTP content is now created as a vector file in FSX using SHP files and a specific requested output type via a GUID parameter passed to SHP2VEC, and is respectively named with a cvx*.bgl file name structure, so you'd be looking for the "
cvx4614.bgl".
LWM content is also a type of polygon now created as a vector file in FSX using SHP files and a specific requested output type via a GUID parameter passed to SHP2VEC with various file name prefixes.
It is often best to see what airport structures might need to be considered first before changing the surrounding and/or underlying land class and associated textures or vector line content; many airport changes can simply be done by graphically adjusting aprons and runways etc. in an airport utility such as ADE, AFX or FSX Planner (very sophisticated FSX compatible successors to AFCAD).
Hope this points you in a good direction to get started!
GaryGB