Amateur-built RV6A N52VC accident near Cody, Wyoming

Probable cause

The pilot’s failure to maintain sufficient altitude to avoid rising terrain. Contributing to the accident was the pilot’s visual illusion and disorientation due to the flat light conditions.

NTSB analysis

The pilot reported that, when the airplane was at 13,500 feet mean sea level and flying over snow-covered mountainous terrain, he changed course and initiated a descent to avoid moisture-laden clouds. During the descent into a valley, the pilot noticed "slightly rising terrain," so he initiated a climb. The pilot reported that it appeared he had a visual illusion because he thought the airplane was at a higher altitude than the approaching terrain. The airplane subsequently impacted the snow-covered mountain and sustained substantial damage to the fuselage. The passenger stated that he and the pilot had become disoriented. It is likely that the snow-covered terrain and the overcast sky created a flat light condition, which inhibited the visual cues necessary for the pilot to orient himself to the terrain. The pilot reported no preimpact mechanical failures or malfunctions with the airplane that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR11LA233 for the full record.