The Dallas-based carrier has blamed the hour-long outage on a vendor-supplied network firewall failure, causing a temporary loss of connection to key systems. A message from a Southwest plane's ACARS system - a direct data messaging system for pilots - said a lack of data on "aircraft position and location" caused the grounding, according to a copy of the message the source gave Reuters. Southwest has developed a plan with inputs from aviation consultancy Oliver Wyman, which was hired to investigate the holiday disruption, to bolster its operations and prevent last year's debacle from repeating