NEW YORK (CNN/Money) -
Computer problems, labor issues and bad weather stranded holiday travelers over the weekend, with US Airways and Delta Air Lines' Comair unit left to pick up the pieces Monday.
U.S. regulators also launched a probe into the holiday air travel mess as Transportation Secretary Norman Mineta said his department would investigate the disruptions.
"It is important that the department and the traveling public understand what happened, why it happened and whether the carriers properly planned for the holiday traveling period and responded appropriately to consumer needs in the aftermath," said Mineta, according to Reuters.
Shares of US Airways (unchanged at $1.26, Research) closed flat on Monday after falling nearly 6 percent in earlier session, while Delta Air Lines (down $0.14 to $7.42, Research) stock fell nearly 2 percent.
Comair resumed flight operations Sunday and said it was operating about 60 percent of its regularly scheduled flights Monday.
The company hopes to operate a full schedule of 1,160 flights by Wednesday, company spokesman Nick Miller told CNN/Money.
"Comair employees in every area of the organization continue working nonstop to resume full flight operations as safely and quickly as possible," Don Bornhorst, Comair's senior vice president of customer service, said in a statement.
Comair canceled all flights Christmas day as a result of severe weather, which caused the computer system that handles crew flight assignments to fail.
Delta, which was not affected by the computer shutdown, said its flights are operating normally. Delta Air Lines or one of Delta's other partner carriers can accommodate customers scheduled to fly on Comair.
US Airways back on track
Business at US Airways also ground to a halt over the weekend as labor problems exacerbated flight cancellations caused by bad weather. But the No. 7 air carrier said it was nearly back on track.
"US Airways expects normal flight operations today with the exception of approximately 15 flights cancelled due to heavy snow in the Boston and Providence, R.I., region," the company said in a statement to customers.
More than 300 US Airways flights were canceled during the weekend. The carrier is trying to restructure and emerge from bankruptcy.
Earlier in the day, the airline was still digging itself out of a massive pile of backed-up luggage that was part of the disastrous situation its chief executive called an "operational meltdown."
"Our efforts to recover from the severe weather on Thursday were complicated when some of our employees chose to call in sick at record numbers over the weekend," US Airways said in a statement.
"The last remaining bags in Philadelphia due to disrupted operations over the weekend are in the process of being cleared. Luggage is being ferried to Charlotte and Pittsburgh by airplane and truck for sorting, and we will have these bags delivered to our customers as quickly as possible," the statement said.
The company said it had managers in Philadelphia handling baggage and working as flight attendants.
The disruption was so severe that it caught the attention of the Transportation Department.
"The secretary [Transportation Secretary Norman Mineta] is not happy about it and wants it taken care of," Mineta spokesman Robert Johnson told Reuters, adding that the agency would look very closely at why so many employees called in sick at the height of the holiday rush.
Many of the 20,000 union workers at the carrier are facing pay and benefit cuts to help the airline fly, with US Airways saying it will probably liquidate in mid-January if union workers don't agree to about $1 billion in reductions.
The company and unions said the sick calls were not part of an organized labor action, though workers are bitter about the proposed cuts.