Installation:

1: Extract the two .dds files

2: Install this mod:
https://www.gta5-mods.com/vehicles/airport-service-pack-add-on-liveries

3: Add the "feroci_sign_10.dds" file to the "airportferoci.ytd" and "airportferoci_hi.ytd" file and the "perennial_sign_10.dds" to the "airportperennial.ytd" and "airportperennial_hi.ytd" files. You'll find them in this directory. "E:\SteamLibrary\steamapps\common\Grand Theft Auto V\mods\update\x64\dlcpacks\airportservice\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\" OpenIV is needed to access this, and Edit Mode must be enabled.