Together with subsidiary AirTran Airways, Inc., Southwest Airlines has reached a tentative agreement with Delta Air Lines, Inc. and Boeing Capital Corp. to sublease...

Together with subsidiary AirTran Airways, Inc., Southwest Airlines has reached a tentative agreement with Delta Air Lines, Inc. and Boeing Capital Corp. to sublease all 88 of AirTran’s Boeing 717 jets to Delta.

According to Southwest Airlines, a final agreement on the big sublease deal is subject to Delta and Southwest reaching certain agreements with all parties related to the aircraft leases.

The tentative agreement between Southwest and Delta Air Lines would see a three-year transition of the Boeing 717s from the AirTran Airways fleet to the Delta Air Lines fleet. The transition would start in the second half of 2013 and be completed in 2015.

Should a tentative deal among Southwest Airlines, AirTran Airways, Boeing Capital Corp. and Delta Air Lines come to fruition, Southwest would sublease all 88 of AirTran's Boeing 717s to Delta by 2015

“This is a very complex transaction that requires time and close coordination with multiple parties,” says  said Mike Van de Ven, Southwest Airlines’ executive vice president and chief operating officer. “While we do have a tentative agreement with Delta, final details must be completed with all parties before a binding agreement between Delta and Southwest can be completed.”

A transition of the Boeing 717s was an option that AirTran Airways acknowledged when it executed its fleet agreement with The Boeing Company.

The plan calls for the transition of approximately three Boeing 717 aircraft on average per month beginning in mid-2013. Southwest says it is not releasing any additional details about the tentative agreement at this time.

However, Southwest confirms it currently plans to keep its total fleet count relatively flat as the 717s transition to Delta. Southwest says it would replace AirTran’s 717 flying with 737s and would work with individual airports on facilities transition timelines. Southwest has affirmed its current plans to maintain service to all previously announced airports.

The decision to replace 717s with 737s means that eventually the merged Southwest-AirTran would become an all-Boeing 737 airline if the Boeing 717 sublease deal goes ahead as planned.

Dallas-based Southwest also confirms that its plans to integrate current AirTran employees into the Southwest operation over the next several years remain unchanged. All pilots would train and transition directly into the airline’s 737 fleet as the number of 717s in the fleet is reduced.

All Boeing 737-800s delivered to Southwest Airlines are to be fully equipped for in Extended-range Twin-engine Operational Performance Standards (ETOPS) operations, allowing Southwest to add long over-water sectors to destinations such as airports in Hawaii to its route network

AirTran flight attendants and maintenance personnel are currently trained on both aircraft types.

At present, according to Wikipedia, the merged Southwest-AirTran carriers operate 707 aircraft: 88 Boeing 717s and 619 Boeing 737s of various versions. These include the Boeing 737-300, 737-500, Boeing 737-700 and 737-800.

Southwest has another 405 Boeing 737s on order (150 of them Boeing 737 MAX jets, not due to begin deliveries until 2017). However, in addition to replacing the 88 Boeing 717s now operated by AirTran Airways, many of these new 737s would replace the 163 Boeing 737-300s, 25 Boeing 737-500s and possibly many of the older 737-700s now in the Southwest and AirTran fleets.

The tentatively agreed Boeing 717 sublease deal provides a distinct element of irony in that AirTran used its Boeing 717s, the first new aircraft in its fleet, to establish itself as a major low-cost competitor to Delta Air Lines at Hartsfield-Jackson Atlanta International Airport, Delta’s – and the world’s – biggest hub and previously a near-monopolistic fortress for Delta.

AirTran’s considerable presence at Atlanta has allowed Southwest to gain a strong foothold at Hartsfield-Jackson following its acquisition of AirTran. Until Southwest bought AirTran, Atlanta was the biggest U.S. destination and the only major city in the United States to which Southwest did not offer service.