San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is an international airport 13 miles south of downtown San Francisco, California, United States. SFO is the largest airport in Northern California and the second-busiest in CA, after Los Angeles International Airport. In 2014, it was the seventh-busiest in USA and the twenty-first-busiest airport in the world by passenger count. It is the fifth-largest hub for United Airlines and functions as United Airlines' primary transpacific gateway. It also serves as Virgin America's principal base of operations. It is the sole maintenance hub of United Airlines, and houses the Louis A. Turpen Aviation Museum and Library.