Circumstances of the Flight
According to FAA records, the pilot contacted the Reno Automated Flight Service Station (AFSS) at 0941 to file an IFR flight plan and requested winds aloft data, which was provided. He did not seek any additional weather briefing from official sources. Several AIRMET advisories had been issued hours earlier, warning of occasional moderate turbulence below 18,000 feet in strong westerly winds near mountainous terrain, and clear air turbulence between 18,000 and 40,000 feet due to jet stream wind shear and mountain wave activity.
The pilot departed under visual flight rules (VFR) and later obtained an IFR clearance en route, climbing to 14,000 feet. Subsequently, he requested to maintain 12,500 feet, but the controller advised that the minimum IFR altitude on that segment was 14,000 feet. The pilot then canceled his IFR flight plan. The controller lost radar contact and instructed the pilot to squawk VFR, which he acknowledged. The final radar target was approximately half a mile east of Eagle Peak, elevation 9,920 feet, in the Warner Mountains.
Wreckage and Investigation
Rescuers discovered the wreckage near the crest of Eagle Peak on November 23. Investigators found no anomalies with the airframe, engines, or propellers that would have precluded normal operation.
Weather Conditions
The National Weather Service had issued a full series of AIRMETs for the route, including mountain obscuration, turbulence, and icing. Analysis of weather conditions revealed a layer between 9,500 and 11,000 feet over the accident site with a high likelihood of severe or greater turbulence. A pilot on the same route reported at 1127 being in instrument conditions at 11,000 feet, experiencing light turbulence and light clear icing, with updrafts of 2,000 feet per minute, indicative of mountain wave activity.
A company pilot flying a second, turbocharged Aero Commander trailing the accident airplane reported encountering a severe downdraft at 1147 near the accident site. Despite applying full climb power, the airplane continued to lose altitude as it passed over the accident position. He was able to regain altitude and return to 14,000 feet at 1159. The accident airplane was not turbocharged.
Terrain and Flight Path
The accident site was at an elevation of 9,240 feet on the eastern slope of Eagle Peak. The flight track was normal along the airway until immediately downwind of the higher terrain. As the flight approached the lee side of the mountain, it entered a mountain wave, first encountering an updraft then a downdraft that increased in amplitude as it progressed toward Eagle Peak. Eagle Peak, the tallest point in the Warner Mountains, has steep slopes known to enhance vertical downdrafts and updrafts associated with intense mountain wave turbulence.