Arlington, Va. ? US Airways Group Inc., the nation’s seventh-largest airline, filed for bankruptcy protection Sunday for the second time in two years. The company’s president vowed to continue restructuring the airline into a low-cost carrier during the bankruptcy process.

“We have come too far and accomplished too much to simply stop the process and not succeed,” said Bruce Lakefield, US Airways’ president and chief executive. “A restructured US Airways with low costs and low fares will be a dynamic competitor.”

The Chapter 11 filing in U.S. Bankruptcy Court in Alexandria came after US Airways was unable to obtain $800 million in annual cost cuts from its workers’ unions that the airline said it needed to stay afloat.

Several weeks ago, US Airways Chairman David Bronner warned that the airline would most likely have to liquidate if it filed for bankruptcy. Lakefield subsequently backtracked from those comments, and on Sunday again sought to assure customers that the airline faced no immediate danger of shutting down.

“We have devoted the last six months to building and implementing a transformation plan that leverages our strengths and allows us to compete successfully,” Lakefield said. “We have made the difficult but necessary decision to complete this process with the help of the court.”

Bronner did not immediately return a call at home Sunday for comment.

A week ago, a deeply divided pilots union refused to allow its membership to vote on a company proposal that would have cut pay by 20 percent and retirement plan contributions by 50 percent.

As recently as Friday, US Airways made a last-ditch effort to reach a deal with the pilots, offering a proposal with minimum pay cuts that would have required more flight hours each month, putting more pilots at risk of furlough.

Some pilot representatives who opposed the new deal said the pilots and other US Airways workers had made enough concessions during the company’s first trip into bankruptcy in 2002. Then, the unions collectively agreed to contract concessions of more than $1 billion a year.

A US Airways jet takes off Saturday from Ronald Reagan Washington National Airport in Washington, D.C. US Airways on Sunday filed for Chapter 11 bankruptcy protection, but its president and CEO vowed to continue the airline's operations.

The bankruptcy filing probably will cost federal taxpayers. The government loaned the airline $900 million last year as part of a special program to assist airlines after the 9-11 attacks.

The airline still owes Uncle Sam $718 million, and it will be up to a bankruptcy court to determine the government’s place in line among the airline’s creditors.

US Airways said Sunday that it had an agreement in place with the government and with other lenders to use some of its cash reserves to continue operations while in bankruptcy. In its filing, the company listed $8.8 billion in assets — including $1.45 billion in cash — and $8.7 billion in liabilities.

A hearing was scheduled this morning in U.S. Bankruptcy Court.

US Airways said customers would notice no operational changes as a result of the bankruptcy and that it would seek permission to continue its frequent-flier program.