What happened
The pilot departed Erie, Colorado, at night on an IFR flight plan destined for Boise, Idaho. While in flight, the pilot received an IFR clearance and subsequently requested VFR-on-top clearance along with a radar vector toward Rock Springs, Wyoming. During these communications, the pilot noted difficulty with heading maintenance and indicated a transition to compass navigation, while also noting that conditions were essentially VFR below the aircraft.
Nine minutes after this communication, air traffic control lost radar contact with the aircraft. The airplane remained missing for approximately one month. It took seven months before the wreckage was recovered from a mountainside.
Radar data analyzed during the investigation showed that the aircraft descended from an encoded altitude of 15,100 feet to 13,900 feet over a period of 1 minute and 31 seconds, representing a descent rate of approximately 800 feet per minute. The pilot did not issue any distress call prior to the loss of contact.
The investigation
An examination of the wreckage was conducted to determine the cause of the descent and the subsequent crash. However, the examination of the aircraft failed to provide an explanation for why the airplane descended or identify any mechanical factors causal to the accident.