As U.S. Airways (LCC) tries to buy larger rival American Airlines, it's been in talks with private equity giant TGP Capital about teaming up for a joint bid, sources close to the companies said. A merger of U.S. Airways, the No. 5 airline in revenue, with bankrupt AMR, the third largest, has been inching closer. Tempe, Ariz.-based U.S. Airways recently got buy-in from key creditors, including the airline industry's largest labor unions. TPG,