The Pension Benefit Guaranty Corp.'s takeover and termination of three underfunded pension plans sponsored by failed law firm Dewey & LeBoeuf L.L.P. of New York was one of the agency's most costly losses of fiscal 2012, according to updated agency estimates.

The PBGC says the plans, which have 1,765 participants, are 53% funded, with $147.6 million in assets to cover $279.2 million in benefits. The agency, which took over the plans in May, expects to cover $93.7 million of the $131.6 million funding shortfall.

Among other things, the PBGC doesn't guarantee benefits above a certain level, which in 2012 was just under $56,000 a year for a 65-year-old retiree. Many of the law firm's veteran attorneys earned pension benefits far greater than the maximum guaranteed by the PBGC.

Dewey once employed more than 1,000 lawyers in 26 offices worldwide and was renowned for its insurance industry practice. In May, though, it became the largest U.S. law firm to file for bankruptcy. Its demise has been largely attributed to compensation guarantees provided to certain partners.

The PBGC's biggest loss in fiscal 2012, which ended Sept. 30, was its takeover in January of a pension plan sponsored by Friendly Ice Cream Corp. of Wilbraham, Mass., which filed for Chapter 11 bankruptcy last year but has since exited. The plan had $115 million in unfunded benefits of which the PBGC has guaranteed $114 million.

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But for several months this year, the PBGC faced the possibility of being hit with its biggest-ever loss. In January, American Airlines Inc., whose parent company, AMR Corp. of Fort Worth, Texas, filed for bankruptcy a year ago, said it intended to terminate its four pension plans, shifting to the PBGC the liability to pay about $8.7 billion in promised but unfunded benefits. One plan alone — the plan offered to the airline's pilots — had $2.3 billion in unfunded PBGC guaranteed benefit, the agency said last week in a court filing.

If the plans had been terminated, that $8.7 billion loss would have eclipsed the PBGC's previous biggest loss: $7.4 billion from its 2005 takeover of five United Airlines' pension plans.

But in March, American, which faced strong pressure from the PBGC to keep the plans, reversed course and agreed to freeze the plans, which it did on Nov. 1.