CHC stands for Christchurch Airport, while IST stands for Istanbul Airport. These codes are often called IATA codes, a set of identifiers established by IATA (International Air Transport Association) that is widely used by airlines and the aviation industry. Istanbul Sabiha Gokcen Airport (SAW), Bursa Yenişehir Airport (YEI), İzmit Cengiz Topel Airport (KCO), Tekirdag Corlu Airport (TEQ) are some additional IATA codes for airports related to your trip.