Incident Overview
At night, while level at flight level 220 (FL220), an airplane experienced vertical altitude fluctuations of up to 500 feet above its assigned altitude, as observed by Salt Lake Center radar controllers. Immediately after these fluctuations, the aircraft began a descent and its transponder signal was lost.
Trajectory and Wreckage Analysis
A trajectory study indicated that the aircraft descended in a tight right turn. Examination of the wreckage revealed that the right elevator had separated in negative overload, and both wings separated under negative loads. The distribution of wreckage established that the empennage and its associated control surfaces separated before the wings detached.
Fire and Damage
Witnesses observed a preimpact fire. The main fuselage was destroyed by an intense post-crash fire. The initiating event that led to the altitude divergence and subsequent descending turn could not be determined by investigators.
Probable Cause
According to the official findings, the probable cause of the accident was a loss of control for undetermined reasons.