Singapore Airlines Limited is the flag carrier of Singapore with its hub at Singapore Changi Airport. The airline uses the Singapore Girl as its central figure in its corporate branding. The Singapore Airlines group includes many airline-related subsidiaries. SIA Engineering Company handles maintenance, repair and overhaul (MRO) business across nine countries, with a portfolio of 27 joint ventures, including with Boeing and Rolls-Royce. Singapore Airlines Cargo operates SIA's freighter fleet and manages the cargo-hold capacity in SIA's passenger aircraft. It has two subsidiaries: SilkAir operates regional flights to secondary cities, while Scoot operate as low-cost carriers. Singapore Airlines was the launch customer for the Airbus A380, the world's largest passenger aircraft. It ranks amongst the top 15 carriers worldwide in terms of revenue passenger kilometers, and is ranked 10th in the world for international passengers carried. On 15 December 2010, Singapore Airlines was named by the International Air Transport Association as the second largest airline in the world by market capitalisation, worth US$14 billion.