UPDATE 2-Sprint outages ground Alaska Airlines flights

(Adds Sprint comment on service restoration)

Oct 8 (Reuters) - An outage that cut phone and data service to Sprint customers in parts of California, Oregon and Washington also grounded some Alaska Airlines passengers on Monday as it knocked the air carrier's reservations system off line.

Crystal Davis, a spokeswoman for Sprint Nextel Corp , said the outages were caused by two cuts in the company's fiber optic cable network. Da vis said that the company had restored service to affected customers by 4.30 PM ET and that Alaska Airlines service was restored by 3 PM ET on Monday.

One cable was accidentally cut early Monday morning while maintenance work was being conducted on a railroad track between Chicago and Milwaukee, she said.

The company is still investigating the cause of the second cut, which occurred between Tacoma, Washington and Portland, Oregon a few hours after the first one.

Davis said that fiber cuts are typically accidental, but could not immediately confirm that this was the case for the second incident.

Alaska Airlines said in a statement that it and sister carrier Horizon Air had canceled 70 flights affecting more than 6,000 people by midday Monday. Some of the flights that had departed were up to four hours late, it said.

The carrier added that more cancellations were planned for later flights as it works to get operations back to normal. Sprint Internet service had been restored about 4-1/2 hours after being disrupted, the carrier added.

Alaska and Horizon, which are owned by Alaska Air Group , said customers traveling Monday or Tuesday can request refunds or change their tickets without incurring extra fees.

(Reporting By Sinead Carew in New York, Jim Finkle in Boston and Karen Jacobs in Atlanta; Editing by Kenneth Barry, Richard Chang and Andrew Hay)

((jim.finkle@thomsonreuters.com)(+1 617-856-4344)(Reuters Messaging: jim.finkle.thomsonreuters.com@reuters.us))