Winter Storm Elliott hit every US airline just before Christmas 2022. Southwest's chief operating officer told the US Senate: "What began as a weather event on December 21st turned into a Crew Scheduling event by December 24th."
Southwest's pilots and flight attendants work three-day trips that start and end at one of eleven crew bases. The storm forced it to cancel almost its whole schedule at Denver and Chicago Midway, two bases that together hold 25 percent of its flight crews. Those crews couldn't start their trips, leaving later flights without a crew.
Flights were now cancelled close to departure, not in planned batches. "Our Crew Scheduling software didn't stop working," the COO testified. But crew schedulers couldn't keep up with the overwhelming volume of changes, so crew assignments weren't updated in time, and without up-to-date schedules the software couldn't reassign crews to uncovered flights. The teams fell back on time-consuming manual processes that couldn't keep pace.
The call centre was so overwhelmed, the US Department of Transportation (DOT) found, that callers sometimes got a busy signal.
On 26 December, Southwest cut its flying by two-thirds for 27 to 29 December, to about 1,500 daily departures from a holiday peak of about 4,000, to get crews and planes back into position. It returned to a normal schedule on 30 December.
The DOT counted 16,900 flights cancelled and over two million passengers stranded, and fined Southwest $140 million. Southwest's fixes included a crew software upgrade to work through a backlog of broken crew schedules, and staff trained to surge in and help crew scheduling.
- 16,900 flights cancelled and over two million passengers stranded
- 25 percent of flight crews were based at the two worst-hit airports
- About 4,000 daily departures at the holiday peak, cut to about 1,500 to reset
- $140 million penalty, 30 times larger than any earlier DOT consumer protection penalty
Why it matters: A system can be up and still useless when the data it relies on falls behind. If changes outpace processing, the backlog feeds itself; the way out may be to shed load on purpose.