WASHINGTON — Alaska Airlines and its Horizon Air affiliate said Sunday they have resolved a computer outage that led to the cancellation of 150 flights a day earlier, disrupting travel plans for more than 12,000 passengers.

The company said in a statement that most of its flights are now operating on time, though about a dozen have been delayed due to crew scheduling issues. The company recommends passengers check their flight’s status online or by calling 1-800-ALASKAAIR.

Passengers are boarding the next available flights at no charge, and in some cases are flying with other airlines, the company said.

“On behalf of the 13,000 Alaska Airlines and Horizon Air employees, I offer my profound apology to customers inconvenienced by this disruption,” said Alaska Airlines President Brad Tilden in a statement.

Alaska Airlines spokeswoman Bobbie Egan said the outage occurred when a transformer blew and knocked out the company’s computer system for creating flight plans. Technicians had been trying to install a backup power supply for the system.

About 18 percent of Horizon and Alaska Airlines combined schedule for Saturday was affected by the problem, which grounded 152 flights.

Alaska Airlines uses versions of the Boeing 737 with roughly 124 to 172 seats, according to airline seating chart websites. Horizon uses smaller turboprop planes.

Seattle-based Alaska Airlines flies to cities in the U.S., focusing on the West Coast, and to Canada and Mexico. Alaska and Horizon are owned by Alaska Air Group Inc.