Careful study of when and where cancellations are most likely, and adjusting spare aircraft availability to keep flights moving if there is a breakdown helped, as did a rebuilt baggage system at its Atlanta hub to reduce lost luggage.

WSJ: Believe It or Not, Flying Is Improving

In the summer, United had reduced spare-airplane availability and reworked its schedule, and it all backfired with increased delays and cancellations.

WSJ: Believe It or Not, Flying Is Improving

Since then, the airline has taken serious measures to improve its efficiency, including rebuilding its luggage system at its Atlanta hub to cut down on lost baggage, and analysing historical cancellation data to adjust the availability of spare aircraft in different hubs in order to keep flights moving.

BBC: 2012's best and worst US airlines