[awiesenhofer]

From TFA: "Time 1:54, Tower: “Southwest 708, confirm on the roll?” Note that this comes 34 seconds after the previous transmission, and nearly a minute after the tower cleared Southwest for takeoff. In that minute, the FedEx plane has covered most of the distance to the airport. Presumably the visibility is so bad that the tower can’t even see the Southwest plane sitting on the runway. So the tower controller is asking: Hey, are you moving? Southwest immediately replies, “rolling now.” Investigators will also want to find out what the Southwest crew was doing through this time, in the minute after saying “we’re ready” and while knowing that another plane was about to land."