Guess who’ll be picking up the pensions if they tank — you will.

Northwest Airlines and Delta Air Lines are both preparing to seek bankruptcy protection as soon as Wednesday, people close to both companies said today. Northwest and Delta are each finishing the details of their bankruptcy cases, including the financing that they will require to operate under bankruptcy protection, these people said. That could cause delays, but the fundamental work of preparing each bankruptcy case is complete, they said.

…If Northwest and Delta both file, that would mean four of the industry’s seven biggest airlines were operating under bankruptcy protection, reflecting the deep competitive issues that have battered the airlines since the year 2000.

United, which is the second-biggest airline behind American, has been operating under Chapter 11 protection since December 2002. Last week, it submitted a reorganization plan and said it hoped to emerge from court protection early next year. Meanwhile, US Airways, which sought bankruptcy protection last year for the second time in two years, expects to emerge from court protection this fall, when it plans to merge with America West. Those airlines will operate under the US Airways name.

That would leave American, the industry’s biggest carrier, Continental, the fourth largest, and Southwest, the sixth largest, as the major airlines operating outside bankruptcy protection.

Also see: “United Airlines can dump pension plans“

[UPDATE: Northwest Misses $42M in Debt Payments. Oops…”Conserving cash,” the story notes.]