American Airlines parent AMR Corp., which is planning to merge with US Airways Group, has asked a judge for another extension of its exclusive period to file a plan to exit bankruptcy, Reuters reported yesterday. The carrier and its unsecured creditors' committee asked the U.S. Bankruptcy Court yesterday to extend the time during which creditors cannot pursue their own restructuring plans for the airline to May 29. Currently, American has until April 15 to file its reorganization plan. American and US Airways announced their plan to combine last month in an $11 billion deal that would form the world's biggest airline.