What happened
At 1325 MDT, the pilot reported encountering icing conditions during cruise flight at FL190. Air traffic control cleared the pilot to deviate from the assigned course and provided a block altitude between FL190 and FL210 to allow for altitude changes. During a query, the pilot noted that approximately 1/4 inch of rime ice had accumulated on the aircraft.
At 1332 MDT, the pilot made an unintelligible remark regarding his gyro instruments and stated he was turning south toward St. George. Shortly after this transmission, the pilot reported that he had lost control and that the airplane was going down.
The aircraft broke up in flight, with wreckage distributed over an area of approximately 1.2 miles. The left aileron and the outer portions of both wings were located at the furthest distance from the main wreckage site.
The investigation
Investigators determined that the outer portion of both wings had separated in a positive and aft direction. An examination of the engines and the airframe revealed no mechanical problems.