Korean Air and Delta Air Lines are seeking antitrust immunity from the U.S. government. The two companies filed a joint application with the Transportation Department Wednesday ... to deepen their alliance and edge closer to heavyweight rivals in the Asian Pacific market. Approval would allow the two airlines to effectively operate as one carrier on trans-Pacific routes by coordinating more closely on scheduling and pricing. Atlanta-based Delta, the No. 3 U.S. airline, and the South Korean flagship carrier are already partners in the SkyTeam alliance Delta and Korean Air have already signed a code-sharing agreement which will cover service between seven U.S. cites and flights to Seoul and other Asian cities. While that practice allows airlines to share passengers by placing the codes on each other's flights, with antitrust immunity carriers can further expand shared networks, fares and route schedules.