Here you may download the whole airport buildings in one shot ...
The file: LIDA_Airport.zip contains all the files of the building modelled for the LIDA airport.
The 3138042.stg file is included.
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1) Unzip the .zip file somewhere.
2) Copy the unzipped files into the directory:
C:/Programs/FlightGear/data/Scenery/Objects/e010n40/e011n45
Or, if you prefer, you may download the individual buildungs below ...