Before I had trees and buildings overlapping with standard Airport Scenery.
This is mine (taking ORBX, FS Global into account). All addon Airports are above the ORBX and FS Global
All my Addon Airports
...
Ftx Orbx LIbs
OpenLC Europe1
OpenLC Europe 2
OpenLC Europe3
OpenLC Europe4
OpenLC Europe5
OpenLC Europe6
OpenLC Europe7
OpenLC Europe8
OpenLc Europe9
OpenLC Europe10
OpenLc Namerica 1
ORBX OpenLC Base
Fs Global 2010 NAM
Fs Global 2010 OCE
Fs Global 2010 AFRICA
Fs Global 2010 Local Meshes
Fs Global 2010 EUR
Fs Global 2010 ANT
Fs Global 2010 ASIA
Fs Global 2010 CSA
Orbx Vector OBJ
Orbx Vector APT
Orbx Vector CVX
Orbx Vector EXX
Orbx FTX Vector AEC
...
Scenery Base
Scenery World
it works perfect...!!!
Good Luck !