Southwest Airlines formally announced that it began linking its network to subsidiary AirTran's.

"Customers are now able to purchase a growing number of itineraries between the Southwest and AirTran networks for travel on a single itinerary," according to the company, which described the codeshare development as "a major milestone" in the integration of the two carriers. The first "shared itineraries" were offered in five markets starting Jan. 26, with expansion to 39 markets set for Feb. 25. Southwest added that it is "on pace to fully connect the networks in April." Southwest closed the AirTran acquisition in May 2011. It expects full integration of fleets and ticketing systems "by the end of 2014."