Iowa travelers may want to call back their travel agent or get online to make changes in their holiday travel plans. United flies to 134 markets in the U-S, including the Des Moines International Airport. But if you planned on flying from there on a United flight, it may be time to have a standby plan. Stock in U-A-L, the airline’s parent corporation, plummeted this morning, and after it fell 60-percent on the New York Stock Exchange, trading in the stock was halted. Analysts are saying it’s virtually certain now the world’s second-largest carrier won’t be able to avoid declaring bankruptcy, after a federal panel turned down United’s bid for a one-point-eight (b) billion-dollar loan guarantee. It would be the largest bankruptcy in airline industry history.