More than a year and a half after Southwest Airlines closed its acquisition of AirTran Airways, the two carriers are finally beginning to link their flight schedules together.

The move will open up many more flight itineraries that connect AirTran and Southwest flights — a key way Southwest expects to reap the benefits of the merger.

A test of connections of Southwest flights with AirTran flights began Jan. 26 in Atlanta, Fort Myers, Louisville, Norfolk and Fort Lauderdale. Another 39 cities will be connected on Feb. 25 and the two airlines’ flight networks will be fully connected in April.

AirTran and Southwest combined fly nonstop to 50 cities from Atlanta. Southwest says linking the two carriers’ route networks enables customers to book flights to all 97 of their combined destinations, although connections are required for the additional cities.

Delta Air Lines, by far the largest carrier at Hartsfield-Jackson, flies nonstop to about 220 destinations from Atlanta. Southwest’s chief commercial officer Bob Jordan said in the markets Southwest and AirTran serve, “we’re going to be very competitive with Delta.”

While AirTran still charges baggage fees, for travelers with itineraries including an AirTran and a Southwest flight, Southwest will apply its policy allowing two free checked bags.

The link of route networks is an interim solution while AirTran planes are converted to Southwest service by 2015 — at which point the AirTran name will disappear.