Atlanta-based Delta began flights with the first twin-engine Boeing 717s purchased from AirTran on Friday.
The Atlanta Journal-Constitution reports the planes have 110 seats and a single aisle for passengers.
The planes were supposed to begin flying in September, but Delta delayed the launch because of certification issues with the configuration of the aircraft.
Delta struck a deal for 88 of the 717 planes last year with AirTran parent Southwest Airlines. Delta will use them to replace less-efficient, 50-seat regional jets.
The Dallas-based Southwest sold the old AirTran aircraft to maintain an all-Boeing 737 fleet. The transfer is taking place over two years.
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