Comair resumed a normal flight schedule Wednesday, following a computer failure the airline said forced it to cancel all of its flights nationwide on Christmas.
Comair, owned by Delta Air Lines and based at the Cincinnati-Northern Kentucky International Airport, has gradually been restoring service since the weekend, operating 10 percent of its flight schedule on Sunday and nearly 75 percent of its flights on Tuesday.
The airline operates about 1,100 daily flights, serves 119 cities and carries an average of 30,000 passengers each day.
U.S. Transportation Secretary Norman Mineta on Monday asked the Transportation Department's inspector general to investigate the problems that caused Comair and US Airways to cancel thousands of holiday flights.
The inspector general, Kenneth Mead, said he would also review whether all major airlines are meeting their 1999 commitments to improve service for customers.