SAO PAULO (Reuters) - U.S. hedge fund Elliott Management is opposing a new plan by Brazilian airline Azul SA to purchase some of the routes operated by financially troubled rival Avianca Brasil for $145 million, according to a legal document seen by Reuters. Elliott, known in Latin America for forcing Argentina into bigger repayments on defaulted bonds, is Avianca Brasil's largest creditor by a wide margin, with claims totaling almost $490 million. Avianca Brasil filed for bankruptcy protection in December, setting off a dispute for its routes among Brazil's top three airlines.