Amateur-built RV-4 N456MC accident near Walsenburg, Colorado

Probable cause

The pilot’s failure to maintain clearance from terrain while intentionally maneuvering in a canyon at low altitude. Contributing to the accident was the pilot’s decision to enter a canyon environment at a low altitude, and the sudden change in wind conditions within the canyon.

NTSB analysis

The accident occurred during a three-airplane formation flight to practice position changes and low-level maneuvering. About 30 minutes after takeoff, the pilots began a descent toward a reservoir, with the accident airplane as the lead. The airplanes were in a right-echelon route formation and were prepared to go to a trail formation for low-level maneuvering in the river canyon.

About 1 mile north of the reservoir, the accident pilot directed the two other pilots to “go trail,” and he executed a left turn and descent toward a river canyon that extended north of the reservoir. The pilots reported they entered a descent and encountered strong surface winds and turbulence above the canyon rim. The accident pilot’s airplane descended below the canyon rim and continued the descent to near the bottom of the canyon. One pilot reported there was a strong south-southwest wind (210° at 35 mph) a couple thousand feet above the surface, so he remained above the canyon rim to assess potential turbulence. During the third turn and less than a minute inside the canyon, the pilots observed the accident airplane’s left wing contact the edge of the canyon at high speed. The airplane fragmented and came to a stop in the canyon.

Postaccident examination of the airplane revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operations. Local authorities who responded to the accident location reported intense and variable winds within the canyon that were different than the winds they encountered above the canyon rim. Available weather information indicated that conditions in the vicinity of the accident site were favorable for the presence of moderate-to-severe turbulence. The circumstances of the accident are consistent with the pilot’s loss of control due to high-speed, variable wind conditions while maneuvering at low altitude in a canyon.

The autopsy revealed the pilot’s severe coronary artery disease put him at risk for an acute coronary event, which could acutely cause chest pain, shortness of breath, palpitations, or fainting. However, there is nothing about the operational information in this investigation to suggest such an event contributed to the circumstances of the accident. Therefore, it is unlikely his coronary artery disease contributed to this accident.

Text from the NTSB. Open the NTSB docket for CEN22FA064 for the full record.