Northwest Airlines says the value of its $213 million investment in Midwest Airlines has dropped to zero.
In a regulatory filing, Northwest cites Midwest's financial deterioration since the end of January, when Northwest and a partner acquired Midwest.
Milwaukee-based Midwest has scaled back its service and cut about 1,200 people, or 40 percent of its workers. The airline is reportedly considering bankruptcy. The airline industry is struggling in a period of soaring prices for fuel.