CNX and SYD are unique codes to identify airports used in the aviation industry. They are defined by IATA (International Air Transport Association) and are commonly called IATA codes. CNX to SYD refers to a flight route from Chiang Mai Airport to Sydney Kingsford Smith Airport. While you’re still figuring out your travel plans, it’s not a bad idea to learn the names and codes of other airports around these areas: Melbourne Airport (MEL), Brisbane Airport (BNE), Perth Airport (PER), Adelaide Airport (ADL), Coolangatta Gold Coast Airport (OOL).