Iberia incorporated four more DC-4s to its fleet during the first half of 1950, enabling both the strengthening of current services and the launch of new ones. With the Pact of Madrid in 1953, visa requirements were eliminated for US visitors to Spain. This stimulated the start of transatlantic flights between Spain and United States the following year. The airline phased in the first of three Super Constellations in June 1954. The aircraft was named "Santa María" to commemorate Columbus' first voyage and was deployed in the inauguration of the new Madrid–New York service two months later, on , the same day that Columbus left the port of Palos de la Frontera. The amendments to Article 6 of the Convention on International Civil Aviation of 14 June 1954 made in Paris on 30 June 1956 about non-scheduled air services enabled mass tourism using chartered aircraft since allowing European member states to carry out this type of operation with international flights between their territories. This favored the airline given that it had in its territory several highly sought after destinations, mainly those on the eastern and southern Mediterranean coast and in the Balearic and Canary Islands, highly demanded by seaside tourism which began with this type of operation.