When a commuter flight to Detroit ends in a harrowing death spiral, it's up to investigators to determine the cause and provide information to help prevent it from ever happening again. Evidence rules out initial theories of an in-flight fire. A problem with the plane's propellers and a close analysis of the flight data lead investigators to the culprit behind the crash: icing. The final report raises questions around the FAA's failure to establish adequate standards for flight in icing conditions.