IAG was formed by the merger of British Airways and Iberia in January 2011. It is one of the largest airline groups with over four hundred aircraft flying 55 million passengers to 200 destinations. They are also major conveyors of air-cargo. BA is principally located in the UK and are sole tenants of Terminal 5 at Heathrow, the world's busiest hub and biggest premium travel market. Iberia, principally based at Madrid's Terminal 4, operates a major network between Europe and Latin America.