Southwest Airlines is creeping up on Delta Air Lines in on-time rankings. For the second month in a row, the carrier finished in second place among the four big airlines in the United States, according to airlines data company OAG. Delta, however, is still on top. “The carrier finished September with 85.9% of flights arriving on time,” according to the Chicago Business Journal. To be on time, a flight must reach the gate within 14 minutes of its scheduled arrival time.