The deal, announced in May, hinged upon Delta's securing a contract deal with its pilots, which it reached late last month.
Delta will use the 717s to replace 50-seat regional jets, which are increasingly unprofitable at higher fuel prices. They'll also replace the DC-9s that Delta got when it bought Northwest in 2007. Those planes are similar in size to the Boeing 717, which seat 117 passengers, but they are getting close to retirement age.
Business travelers also favor the roomier 717s, a key for Delta as it tries to capture more of those lucrative fliers.
Southwest inherited the 717s when it bought AirTran last year. Southwest wants to get back to flying all 737s, like it did before that combination. Flying only one type of plane allows it to save on maintenance and streamlines pilot training.
The aircraft will be transferred starting next year, with 16 scheduled to arrive next year. Another 36 will come in 2014 and the rest will be delivered in 2015.
Southwest has orders for more 737s, and it said its overall fleet count will stay about the same as the 717s leave. AirTran 717 pilots will retrain to fly the 737s.
Delta shares added 9 cents to $11.09 in morning trading. Southwest shares added 5 cents to $9.32.
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