AMR Corp. is again weighing a sale of its American Eagle regional unit, but some experts say the deal could be a hard sell. Republic Holdings, the parent company of Frontier and Midwest airlines, is seen as one potential buyer. But recent acquisitions mean "our plate is pretty full right now," according to a Republic spokesman, who refused to speculate further. Meanwhile, aviation consultant Michael Boyd doubts Republic would do a deal without negotiating very favorable terms. "It is getting hard to make money with 50-seat jets, and I'm not sure how many more of these small jets Republic would need," he says.