Southwest Airlines Co said on Tuesday it would upgrade its crew scheduling software and hire more staff in the winter, as the under-pressure airline attempts to address gaps that led to large-scale cancellations during the holiday season.

The Dallas-based carrier has come under severe criticism ever since it suffered an operational meltdown around the Christmas holidays last year that disrupted travel plans for two million customers. (Reporting by Aishwarya Nair in Bengaluru; Editing by Krishna Chandra Eluri)