American Airlines is selling investment-grade debt even as it spends a 15th month in bankruptcy while bond buyers look ahead to the merger with US Airways Group Inc. that will create the world's largest carrier.

The AMR Corp. unit issued $663 million of so-called enhanced equipment trust certificates Tuesday that included a portion paying 4 percent, matching the record low coupon for similar airline debt, which was first awarded to United Continental Holdings Inc. in September, according to data compiled by Bloomberg. American is also seeking to refinance about $1.3 billion of bonds backed by aircraft after receiving court approval to do so in January.

Debt investors are wagering a heftier American will benefit from consolidation that will help the carrier restore profitability as it fills more seats and boosts fares. Airlines are also adding more efficient planes such as those securing the new American debt, helping to support the value of EETCs.