American Airlines announced today that it will take over troubled Trans World Airlines and some U-S airways assets in a deal valued at about five (B)billion dollars. If the complicated transaction survives review by the justice department and other authorities, American will own a quarter of the U-S market, about equal to the size of its rival, United airlines. Barbara Beyer is President of AVMARK, an aviation consulting firm. She says the deal makes Northwest an attractive candidate for an aquisition or merger: