Federal investigators said Tuesday they had "overwhelming evidence" that a Northwest Airlines jet crashed last August, killing 156 people, because the plane's flaps had been improperly set before takeoff.

The investigators told the National Transportation Safety Board that their conclusion was based in part on the plane's performance as it left the runway at Detroit and on a cockpit tape.The probers also noted questions over cockpit discipline and questioned why a warning device that might have prevented the crash, the nation's second worst, did not work.