Southwest cancelled 16,900 flights because crew schedules couldn't keep up with the changes

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16 thousand 900 flights. Cancelled. Over Christmas. And the software never crashed.

21 December. Winter Storm Elliott hits every US airline. By the 24th, Southwest's COO said, it's a crew scheduling event. Flights keep getting cancelled. Day after day.

Almost every flight at Denver and Chicago Midway, cancelled. Bases for 25 percent of crews. Those crews can't start their trips. Later flights have nobody. Cancellations land close to departure. The changes pile up. Schedulers can't keep up. So the schedules go stale. Without current schedules, the software can't reassign crews.

Here's the twist. The COO testified the crew software didn't stop working. It was planning with data that had fallen behind. Teams went manual.

Meanwhile, passengers call customer service. The call centre is so overwhelmed, some just get a busy signal.

26 December. Southwest makes the call. From about 4 thousand flights a day at the holiday peak... To about 1,500. Cut on purpose, to get crews back in place. 30 December. A normal schedule again.

Over two million passengers stranded. A 140 million dollar penalty. 30 times any earlier DOT consumer penalty.

A system can be up, and still useless. Its data just fell behind. When changes outpace you, the backlog feeds itself. Shed load. Reset.

Full story in the article.