Pensions 101 How private employers' plans took a hit, and the changes being proposed; is your money at risk?(full story) • Pension gap could soar to $71 billion • Is your pension in peril?

NEW YORK (CNN/Money) - The bankruptcy of Delta Air Lines and Northwest Airlines could add billions of dollars to the government's already overburdened back-up pension scheme. If your company goes bust, will the emergency fund still be there to pick up the tab?

The fund, known as the Pension Benefit Guaranty Corp. (PBGC), already faces a $23 billion gap in what it takes in through corporate premiums and what it has promised to pay retirees.

If Delta and Northwest default on their pension plans, as United Airlines did in May 2005 after it went bankrupt, that gap could widen by as much as $12 billion.

Currently there is legislation moving through Congress that would double the premiums companies pay into this fund. It receives no public tax money.

But the head of the Congressional Budget Office told Congress in June that the fund would need a fivefold increase if it is to meet its projected deficit of $71 billion over the next decade.

"There is a huge pension problem here and someone is going to have to pay for it," said Douglas Elliott, president of the nonpartisan Center on Federal Financial Institutions, a Washington think tank.

Most people no longer have defined-benefit pension plans like the ones PBGC covers -- ones where you receive a check every month depending on your age of retirement and how long you worked for the company.

The number of such plans has declined by 70 percent over the past 20 years as more companies have switched to offering 401(k) plans.

And of the 44 million Americans that still have the defined pensions, the ones most at risk are those in older, heavily unionized industries, especially employees with higher salaries.

If your company goes bankrupt and the PBGC takes over your pension the fund will pay a maximum of $45,614 a year in benefits if you retire at 65. If you were slated to receive more, someone like a pilot or manager making $70,000 or $80,000 a year who had been with the company for 30 years, you'd be out of luck.

If you retired earlier you'd be even more disappointed. The maximum payout for those retiring at age 50 (see correction) is less than $16,000 a year, even if you were forced into retirement because your company went bankrupt.

Those payouts assume, of course, that the fund is still solvent.

The projected $71 billion shortfall is based on numbers that show the 31,000 defined-benefit plans that exist nationwide are underfunded by some $450 billion.

Yet things may not be as bad as they appear.

Part of the reason these plans seem to be so underfunded is that stocks have performed poorly over the past few years and interest rates have been low. Assets in these plans should grow if interest rates and stocks go up.

But part of the problem is that current federal rules governing pensions are so lax that only about 20 percent of companies fully fund their defined-benefit plans. In addition, rules penalize companies with a tax if they overfund their defined-benefit plans, so many companies don't sock away funds during good times to cover for downturns.

Also, only defined-benefit plans that are fully funded can be converted into a 401(k). That means that as many companies converted fully funded plans to 401(k) plans, what was left in the PBGC's pool of contributors were partially, riskier plans.

The current reform proposals moving through Congress would require full funding of these plans eventually. Because of this, and because of a penalty premium imposed on companies that don't meet full funding, Elliott believes the PBGC will eventually return to solvency in maybe 15 years.

But In the meantime it will face a big shortfall.

"Somebody's got to come up with money and you've got three choices," he said. "Corporations, the taxpayers or Santa Claus."

Correction: An earlier version of this story misstated the age at which less than $16,000 is the maximum payout a retiree can expect from the PBGC. CNN/Money regrets the error. (Return to story)

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For more on the airline bankruptcy bloodbath, click here.