In its latest SEC filing, Midwest disclosed that Northwest is investing $213.3 million in TPG Capital’s buyout of Midwest Air Group, putting its level of investment at 47 percent although the major carrier reiterated it was a passive investor in the low-cost carrier with no say in controlling Midwest. The two airlines also formalized their code-sharing relationship. The program will be phased in by market, with the initial destinations to include Midwest flights between Milwaukee, Kansas City and Omaha to major West Coast cities, where passengers can connect to Northwest flights to several points in Hawaii.