Great question - CRK to SYD just means Angeles City Clark Intl Airport to Sydney Kingsford Smith Airport. Now you’ll know what these unique codes when you look for flights! Melbourne Airport (MEL), Auckland Intl Airport (AKL), Brisbane Airport (BNE), Perth Airport (PER), Tamuning Guam Intl Airport (GUM) are other airports near this flight route and their unique identifiers/IATA codes.