Bangkok is one of Asia's busiest air transport hubs. Two commercial airports serve the city, the older Don Mueang International Airport and the newer Suvarnabhumi Airport. Suvarnabhumi, which replaced Don Mueang as Bangkok's main airport after its opening in 2006, served 52,808,013 passengers in 2015, making it the world's 20th busiest airport by passenger volume. This volume exceeded its designed capacity of 45 million passengers. Don Mueang reopened for domestic flights in 2007, and resumed international service focusing on low-cost carriers in October 2012. Suvarnabhumi is undergoing expansion to increase its capacity to 60 million passengers by 2019 and 90 million by 2021.