Delta Air Lines

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reported success in one part of a debt exchange, a development crucial to the airline's efforts to shore up liquidity and slash costs.

Delta said late Tuesday that creditors have tendered $252 million of Series 2000-1C and 2001-1C pass-through certificates, satisfying the minimum tender amount. The airline is looking to exchange a total of $330.0 million of the certificates for 9.5% senior secured notes due 2008.

By meeting the threshold for the certificates, Delta has satisfied a key condition of recent deals with lenders. They include

General Electric's

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$500 million financing commitment, announced Monday, and

American Express's

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agreement to prepay $500 million worth of Delta frequent-flier points its cardholders rack up.

The successful exchange of the certificates is also a condition for the package of concessions that airline management and pilot union negotiators agreed upon last Wednesday. On Monday, Delta's members of the Air Line Pilots Association began voting on the package, which the airline estimates will save it $1 billion a year. Voting ends Nov. 11.

Aside from the pass-through certificates, Delta's exchange offer is not going so well. The airline hopes to exchange another $2.27 billion of unsecured intermediate and long-term debt for new senior secured notes, and the amount tendered so far is "substantially" below minimum tender conditions, Delta said in a news release. The exchange offer, which Delta extended last month, ends Nov. 18.

Delta is trying to improve its liquidity to weather the winter, when airlines typically burn cash. This year, the situation is dire, as high fuel costs have driven up airline expenses just as the industry overcapacity and harsh price competition has made it difficult for carriers to raise fares. Delta has warned repeatedly that it could file for Chapter 11 bankruptcy protection if it can't lower costs and restructure some of its $20.6 billion in debt.

Shares gained 19 cents, or 3.3%, to $5.87.