The outside pane of the triple-pane window broke about 20 minutes after the 7:35 p.m. takeoff from Dallas-Fort Worth International Airport.
The MD-80's two engines are mounted at the tail rather than on the wings, and Smith said the broken window "was unfortunately near the engine." Smith said the glass shards sucked into the engine would have created "a disconcerting noise" for passengers.
He said the plane could fly safely on the remaining engine, but the plane returned to DFW rather than continue on to Florida.
Asked about the cause of the break, he said, "We don't really know. Just repeated pressurization can put stress on the window without breaking. That is fairly unusual."
The passengers departed on another flight about an hour after landing, he said. The pilot lowered the oxygen masks, but only as a precaution, and he did not instruct the passengers to put them on, Smith said.