Western Air Lines Flight 34 departed from Salt Lake City (SLC) at 08:50. The Convair proceeded IFR to Rapid City Regional Airport, SD (RAP). The flight reported as being over the Wright intersection at 10:25, at 17,000 feet, estimating Rapid City at 10:50. Weather conditions in the area probably included moderate to heavy icing and moderate to severe turbulence. The Convair suddenly entered a rapid descent and struck the ground at high speed. PROBABLE CAUSE: “A sudden emergency of undetermined origin under adverse weather conditions resulting in rapid descent and impact with the ground at high speed.”