PORTLAND — Southwest Airlines, known for its superior service, low fares and “bags fly free” policy, will begin service at the Portland International Jetport in April after it ends AirTran Airways service.

Portland is one of four cities that will convert to the Southwest brand. The other cities are Charlotte. N.C.; Flint, Mich., and Rochester, N.Y.

Southwest said it will begin service in those cities on April 14. AirTran service will end the previous day, at the end of the current flight schedule.

Details of what cities Southwest will serve from Portland will be released on Monday. AirTran currently flies from Portland to its hub in Baltimore and then on to other destinations. Southwest also has a hub in Baltimore.

Southwest completed its acquisition of AirTran in May 2011. AirTran first came to Portland in 2007.

Last year, the Jetport completed a $75 million,145,000-square-foot terminal expansion and has been trying to lure new airlines. Southwest had confirmed in January that it would serve Portland, but the timing of the switch from AirTran had not been previously known.

Having Southwest serve Portland is expected to be a draw for tourists coming to Maine, and eliminate the need to fly to other Southwest locations in the region such as Manchester, N.H., or Boston.