AD 1.4 GROUPING OF AERODROMES
The criteria applied by Singapore in grouping aerodromes for the provision of information in this AIP is as follows:
1 Primary/Major International Aerodrome
1.1 The aerodrome of entry and departure for international air traffic, where all formalities concerning customs, immigration, health, animal and plant quarantine and similar procedures are carried out and where air traffic services are available on a regular basis.
2 Secondary/Other International Aerodrome
2.1 Another aerodrome available for the entry or departure of international air traffic, where the formalities concerning customs, immigration, health and similar procedures and air traffic services are made available, on a restricted basis, to flights with prior approval only.
3 National Aerodrome
3.1 An aerodrome available only for domestic air traffic, including those military aerodromes where civil air traffic is allowed under certain conditions.