Comair says it has returned to operating a normal flight schedule Wednesday.

Comair said a failure of its computer system forced the airline to cancel its entire national flight schedule on Christmas Day. Comair has gradually been restoring service, operating almost 75 percent of its flights Tuesday.

Comair operates about 1,100 daily flights that carry a total average of 30,000 passengers each day. The airline serves 119 cities, including Birmingham and Huntsville.

The U.S. Transportation Department says it will investigate Comair's computer failure and the flight cancellations. Comair, owned by Delta Air Lines, said it will cooperate with the government's investigation.