What happened
During a night cargo operation conducted under IFR conditions, the pilot requested and received clearance to descend from an altitude of 16,000 feet to fly via VFR-on-top procedures. At 21:06, the pilot confirmed awareness of the terrain along the flight path. Shortly thereafter, the aircraft performed a left turn of approximately 36 of degrees while descending through 13,800 feet, at which point radar contact was lost at 21:21:51 mdt. Air traffic controllers attempted to re-establish radio communication but were unsuccessful.
The wreckage was subsequently located roughly two miles southwest of the final radar position. The debris field spanned an area exceeding one mile. The accident resulted in two fatalities, as both pilots were killed in the crash.
Findings
Post-accident analysis determined that the left wing and the right horizontal stabilizer had separated from the airframe due to structural overload. Investigators found no evidence of pre-existing fatigue or mechanical malfunctions prior to the event. Environmental conditions at the time included moderate turbulence and towering cumulus clouds, with snow showers reported in nearby Pocatello, Idaho. The investigation concluded that the structural design stress limits of the aircraft were exceeded during the descent.