What happened
The pilot utilized updrafts to climb to an altitude of 7800 feet in an effort to clear a mountain ridge that was obscured by cap clouds. Upon reaching the lee side of the ridge, the aircraft encountered a significant downdraft. This atmospheric condition caused the aircraft to descend rapidly into fog. The pilot reported using the aircraft instruments to maintain a nose-up attitude in an attempt to arrest the descent. Despite these efforts, the aircraft continued to lose altitude and ultimately impacted the ground.
The investigation
The investigation focused on the meteorological conditions and the pilot's actions during the final phase of flight. Evidence indicated that the pilot was attempting to navigate over a mountain ridge covered with cap clouds by using updrafts to gain sufficient height. However, the lee side of the ridge presented a hazardous downdraft. The aircraft descended into fog, which likely reduced visibility. The pilot attempted to maintain control using instrument references, but the aircraft continued its descent until impact.
Findings
The primary factors contributing to this accident were the mountain wave downdraft and the subsequent loss of visual reference due to fog. The pilot's decision to fly over a ridge with cap clouds led to an encounter with severe sinking air. Despite the use of instruments to maintain attitude, the aircraft could not overcome the downward force of the downdraft.
Safety message
Pilots should be aware of the dangers of mountain wave activity and lee-side downdrafts. Flying over ridges with cap clouds can indicate strong vertical air movements that may exceed an aircraft's climb performance. Maintaining adequate altitude and avoiding areas of known or suspected downdrafts is critical for safety.