The Department of Transportation says it plans to look into what it refers to as Southwest Airlines' "unacceptable" number of flight cancellations the day after Christmas. Southwest canceled nearly 29-hundred flights on Monday, or about 71-percent of its scheduled flights, and about ten-times as many as any other major U.S. airline. The Dallas-based carrier apologized to its customers and employees, but said it may take several days to rebook passengers on new flights. At a news conference Monday night at Hobby Airport in Houston, a Southwest official said the situation resulted from the weekend's winter storm.