It's a change in assumptions. Under accounting principals, CFOs must make a lot of assumptions. For one, a company is (generally) worth more than its assets. An organized company uses assets to generate profit, so an organized company is (generally) worth more than the liquidation, or even purchased value, of its assets.
Think of Microsoft: you could sell all of their computers and desks and whatnot on the open market and it would be worth less than what Microsoft as a going, profitable concern is worth.
To oversimplify, if Warren Buffet were to purchase Micosoft from Billg, the accounting for the purchase would be the value of the assets (not much) plus a lot of premium. The premium is for the profit that Microsoft can make with the assets.
This premium is sometimes referred to as "goodwill".
In this case, United wrote down (changed the value on their accounting books) the "goodwill" that was carried. See, back in the day, United was worth more than the sum of its assets.
Today, United is worth about a third of the amount of unrestricted cash they have on hand. Yes, UAL is worth less as an operating company than the value of the cash in their checking account.
This must be reflected in the assumptions, so UAL took a "charge", or simply changed an accounting entry to reflect that the goodwill was now mostly worthless.
I was very surprised to see that both USAir and UAL to be worth much less than the unrestricted cash in the bank. That is a very, very, very strange situation. One has to ask, "Why not just shut down, distribute the cash and distribute the assets and call it a day?"
But that won't happen.
