"All sponsors of frozen plans knew that liabilities would increase even though benefit accruals were fixed. This would be due to simple aging of the participant population -- generally, very manageable. Combined with this historic investment performance over the past ten years, there was an expectation the funding deficits would return to pre-2008 levels. What was not anticipated was the corresponding increase in 'carrying costs' and an extremely low interest rate environment.... The single biggest cost increase of those listed has been PBGC premiums."