United experienced an approximate two-hour Unimatic computer outage Wednesday morning that affected our mainline systems for critical operating functions such as load planning, maintenance release, flight planning, pilot communication and crew scheduling.

* The outage resulted in a systemwide ground stop for mainline flying. United Express flights were not affected as they are not dependent on Unimatic for these operating functions.

* The preliminary root cause was determined to be an operational error at 8:05 CDT during routine system testing, causing Unimatic to fail. During the Unimatic recovery, employees encountered unrelated hardware problems that delayed the restoration of services. Unimatic was brought back online at 10:15 CDT.

* The 42 flights enroute during the outage landed uneventfully. As of Wednesday afternoon, there were 24 computer-related cancellations and 268 computer-related delays, which averaged about 100 minutes. Based on further research with the stations, it appears that there were no Flights of Note (North American flights that exceed four hours on taxi-out, 90 minutes on taxi-in, or have on-ground diversion delays over four hours) for taxi-in or taxi-out holds.

* We advised customers to check united.com for the status of their flight before going to the airport, and apologized for any inconvenience caused by the outage.

* ISD is taking steps to ensure that proper controls are in place to avoid this occurrence in the future.