United Airlines filed for bankruptcy protection yesterday, the largest ever in the global airline industry, after high costs and low airfares left the world's number two carrier with too much debt and not enough cash. United Airlines, with one of the broadest networks in the world, will continue to fly worldwide as it attempts to re-organise under protection from the US bankruptcy court.

The entire US airline industry has been reeling from a slump in business travel and the September 11th attacks, posting losses last year of about $10 billion (€9.9 billion) and on track for at least $7 billion in losses this year.

United stressed in a statement it would be "business as usual" for customers. But for employees, suppliers and others, changes are in store, said the company's chief executive, Mr Glenn Tilton.

Mr Tilton added that he would consider selling some of the airline's assets in bankruptcy if they did not fit and someone else was willing to pay a "superior" price.

The airline would shrink, but he could not yet predict how much.

UAL shares swung wildly on the New York Stock Exchange yesterday, falling by 15 per cent in the morning but rising by as much as 24 per cent on speculative buying in the afternoon. UAL shares closed unchanged at $0.93 yesterday. The NYSE is still reviewing whether to delist the stock. United, with about 83,000 employees, had two of its Boeing jets commandeered in the September11th attacks. Since then it has posted nearly $4 billion in losses, with no end in sight to the red ink.

At a court hearing yesterday, attorney Mr James Sprayregen said United expected to burn through $20-$22 million a day in December and $10-$15 million a day in January, compared with its previous daily burn of $7-$8 million. The airline now has $800 million in unrestricted cash on hand and $600 million in restricted cash, Mr Sprayregen said.

The court filing had been expected and analysts generally predict a successful although lengthy court process.