AMR Corp.’s four traditional pension plans have $8.3 billion in assets to cover about $18.5 billion in liabilities, although the U.S. government’s Pension Benefit Guaranty Corp. (PBGC) expects to assume responsibility for the majority of these obligations should the airline operator close its pensions under its newly filed Chapter 11 reorganization.

This week, “American Airlines’ parent company filed for bankruptcy. When this happens, employees and retirees worry—and they should. In past bankruptcies, workers and retirees have lost their health care and seen their pensions cut. Based on our estimates, American Airlines employees could lose a billion dollars in pension benefits if American terminates their plans,” says PBGC Director Josh Gotbaum.

This exposure, though, will pressure the government agency, which is already suffering from a record $26 billion deficit as a result of failed plans it has assumed, warns Gotbaum. Some of these plans were shed by Delta Air Lines and United Airlines during their own Chapter 11 reorganizations.

The ability to shed pension obligations made competitors more profitable than AMR, the carrier has said for years, and while voluntary restructuring provided some concessions, the airline says it had no option but to seek the protection provided by Chapter 11 to overhaul its costs structure, particularly its labor expense.