The asset group must be Spb
The source dir must be
PackageSources/AirportServices/ICAO/Services.xml
And the output must be
Packages/packageName-ICAO/AirportServices/ICAO/Services.spb
So the services file Is gonna be called Services.spb, (not ICAO.spb)
Only in this way you avoid your Custom services to affect the whole world