BRIEF-United Continental Holdings files prospectus supplement related to offering of $400 million of its senior notes (UAL) | Markets Insider

I would be willing to wager this has to do with the acquisition of a number of used A319's or 20's on the horizon. With rumors floating around of a deal to sign for around 30 more from either a Chinese source or European LCC, the timing and amount of money to be drummed up seems appropriate. I am definitely no business guru, though.