Mesa Airlines is an American regional airline based in Phoenix, Arizona, United States. It is a FAA Part 121 certificated air carrier operating under air carrier certificate number MASA036A issued on June 29 1979. It is a subsidiary of Mesa Air Group. It was known briefly as Mountain West Airlines from 1995 to 1996. It operates flights as United Express, US Airways Express, Delta Connection (via Freedom Airlines), and under the brand go! for flights within the Hawaiian Islands. The brand Mesa Airlines is also used to market flights from Albuquerque and Dallas/Fort Worth that are operated by Air Midwest. It serves more than 180 markets in the Western Hemisphere.