The troubles led to late and canceled flights, lost baggage and angry customers.

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For every 1, 000 passengers, 3.5 lost baggage, more than the national average of 3.2 and worse than every big carrier but American.

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Neither are delays, lost baggage and jet lag.

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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.

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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.

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Fewer passengers and hefty baggage fees reduced the volume of checked luggage, and so airlines lost fewer bags per passenger.

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