Southwest Airlines, once the most on-time airline in the industry, has lately been the least on-time, according to an analysis by the Chicago Tribune.
The Dallas-based airline, the dominant carrier at Chicago's Midway airport, placed at the bottom of monthly on-time statistics reported to the Department of Transportation for two consecutive months.
It's the first time since at least 1995, when the DOT's Bureau of Transportation Statistics started collecting data, that Southwest ranked last for any month, the Tribune reports.
At Midway, where Southwest has more departures than at any other airport, only two of three Southwest flights have been departing on time, according to the most recent data released this month.
In October, Southwest operated 37 of 41 flights that were late 70% of the time or more, according to the Tribune.
Midway had the worst on-time departure rate of any airport in the U.S. through the first 10 months of the year, with only 68.7% of flights leaving on time. That's down from 77% last year.
It's a surprising reversal for an airline that typically ranks high in terms of customer satisfaction thanks to a flexible flight change policy and the lack of fees for the first two checked bags.
Henry Harteveldt, a travel industry analyst at Hudson Crossing, told the Tribune that part of the reason for the deteriorating record is that Southwest tends to schedule flights close together to maximize efficiency. That ends up hurting the carrier when there are weather or other problems.
Most other airlines tend to pad their gate-to-gate times, according to a recent report by the Office of Inspector General of the Transportation Department.
"Southwest schedules its planes so tightly, to maximize efficiency and keep fares low, that even a slight delay early in the morning can snowball into a larger delay through the balance of the day," Harteveldt said.
Another reason: Southwest has expanded its network into congested airports in cities such as New York.
Southwest spokesman Brian Parrish blamed delays, especially in the months of August, September and October, on "a combination of unexpected summer weather and changes made to our schedule."
Southwest has recently changed its schedule to add more time for such in-between flight tasks as unloading passengers and preparing the plane for the next group of passengers.
Parrish said those changes will take some time to implement.
"But we do expect to see improvement by early next year," he told the Tribune.