Delta froze and United terminated right?
As WT pointed out, DL terminated its pilot pension but froze all others; NW froze all pensions, leaving DL with a fairly large underfunded pension liability.
UA terminated all pensions, giving it an advantage over all other airlines except for US, which also terminated all pensions. UA then merged with CO, which froze all pensions, leaving UA with some underfunded liability (albeit a small one, since CO was a small airline and didn't have as large an underfunded pension problem).
The bottom line is that AA filed for Ch 11 but didn't get anywhere near the same cost benefits since it gave into Gotbaum's demands that it not terminate its pensions. The only workgroup that benefitted from a freeze compared to a termination is, of course, the pilots, as their pensions greatly exceed the PBGC maximum guarantee. FAs, mechanics, fleet service and agents don't have pensions that exceed the PBGC maximum so the freeze doesn't benefit them. AA ends up with higher costs than US, UA or DL, increasing the odds of another Ch 11 filing.