Mayors from Charlotte, Chicago, Dallas, Fort Worth, Philadelphia, Phoenix and Miami-Dade County wrote to Attorney General Eric Holder on Wednesday, urging him to allow American Airlines Inc. and U.S. Airways Group Inc. to merge.  The mayors encouraged the Justice Department to “reconsider [the] ill-conceived lawsuit,” and asserted that the deal would benefit both consumers and their respective communities where the largest hubs for the two airlines are located.  “Without this merger,” the letter continued, “American and U.S. Airways will be at a permanent competitive disadvantage to Delta and United, each of which has been allowed to build superior route networks through mergers that were cleared by the Justice Department.”  The letter comes one week after 68 House Democrats, led by legislators from Texas and Arizona – home to American and U.S. Airways headquarters, respectively – wrote a similar letter of support to President Barack Obama, pressing him to call off the lawsuit.  The Justice Department and seven state Attorneys General sued to block the $11 billion merger back in August, but the Texas Attorney General dropped out of the lawsuit earlier this month.