Overview
A night instrument cross-country flight encountered mountain wave conditions with severe turbulence at 9,000 feet mean sea level (msl). The aircraft subsequently entered an uncontrolled descent and impacted mountainous terrain at an elevation of 2,300 feet msl.
Flight Path and Communications
The flight was level at 9,000 feet while crossing a mountainous area. The pilot reported to air traffic control (ATC) that he was experiencing light rime icing conditions. Shortly thereafter, the controller observed the aircraft descending, and the pilot requested a lower altitude. The controller informed the pilot that the flight was already at the minimum assignable altitude. The pilot then stated that he was in extreme turbulence. Immediately following this transmission, the aircraft dropped off radar, and no further radio communications were received.
Weather Conditions
The Area Forecast valid for the flight predicted multiple layers of broken to overcast ceilings from 6,000 to 12,000 feet, with a freezing level at 10,000 feet. AIRMETS were in effect for mountain obscuration, moderate turbulence, and moderate rime or mixed icing conditions, though these conditions were forecast at elevations above the pilot's planned en route altitude. No SIGMETS were in effect for turbulence.
An analysis of the weather conditions found increasing wind velocities from the surface to 7,000 feet over the mountains crossing the airplane's flight path. Several layers of strong vertical wind shear increased the likelihood of very strong turbulence. The conditions were favorable for localized mountain wave activity and supported the potential for moderate to severe turbulence, rotors, and downdrafts up to 1,500 feet per minute. An automated weather observation station in the mountains near the accident site reported wind gusts of 45 knots ten minutes prior to the accident.
Weather Briefing
No record was found that the pilot obtained a preflight or in-flight weather briefing from any official aviation weather source.
Other Pilot Reports
The pilot of a Gulfstream G-IV descending near the accident location reported encountering strong turbulence with both vertical and lateral components.