What happened
The pilot and his passengers were traveling from Minden, Nevada, to Casper, Wyoming, with a stop at Ogden, Utah, for refueling. Before departure, the pilot secured an updated weather briefing from Flight Service Station (FSS) and filed an Instrument Flight Rules (IFR) flight plan.
Following takeoff, air traffic control instructed the pilot to climb within a holding pattern to 13,000 feet. Shortly thereafter, the pilot was cleared to join VOR airway V-6 and resume his own navigation. The pilot responded that he was in a spiral. Witnesses on the ground observed the aircraft descending in a near-vertical attitude. They reported that a thunderstorm had just passed overhead accompanied by heavy rain. The aircraft impacted the ground in a flat attitude.
The investigation
Post-accident evaluation included interviews with aviation professionals familiar with the pilot's background. One of the pilot's former Certified Flight Instructors (CFI) and an FAA Designated Examiner stated that the pilot should never have been instrument rated. The examiner had previously restricted the pilot's multiengine rating to 'VFR only' due to concerns about his proficiency.
Findings
The restriction on the pilot's multiengine rating was removed shortly before the accident by an FAA Inspector, despite the earlier professional assessments of his competency. The combination of instrument flight in deteriorating weather and the pilot's questionable instrument proficiency contributed to the loss of control.