Walsenburg, CO, USA
N456MC
VANS RV-4
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.
HISTORY OF FLIGHTOn December 8, 2021, about 1013 mountain standard time, a Vans RV-4 airplane, N456MC, sustained substantial damage when it was involved in an accident near Walsenburg, Colorado. The pilot sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to two other pilots involved in the flight, the accident flight was a three-airplane formation flight to practice position changes and low-level maneuvering. The three airplanes departed Meadow Lake Airport (FLY), Colorado Springs, Colorado, and headed south with the accident airplane as the lead airplane. About 30 minutes after takeoff, the airplanes flew south past Pueblo, Colorado, and began a descent toward the Cucharas Reservoir, northeast of Walsenburg. The airplanes were in a right-echelon route formation and were prepared to go to a trail formation for low-level maneuvering within the river canyon. About 1 mile north of the reservoir, the accident pilot directed the two other pilots to “go trail,” and he made a left turn and a 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 a high speed. The airplane fragmented and came to a stop in the canyon. After the accident, the pilots circled the area, contacted air traffic control to report the accident location, and then returned to FLY. A review of the automatic dependent surveillance-broadcast (ADS-B) data revealed the flight tracks for the three airplanes were consistent with the witness reports. The accident airplane’s data ended about 1 mile west of the accident site. AIRCRAFT INFORMATIONThe airplane logbooks and records were not located during the investigation. METEOROLOGICAL INFORMATIONThere were several pilot reports (PIREPs) of light-to-moderate turbulence over the area prior to the accident, with at least four urgent reports of moderate-to-severe turbulence after the accident. The National Weather Service Graphic Turbulence Guidance provided eddy dissipation rates between 20 and 45 over southern Colorado in the vicinity of the accident site consistent with moderate-to-severe turbulence. Huerfano County Sheriff’s personnel, who responded to the accident site shortly after receiving the report of a missing airplane, reported the winds above the canyon rim were different in intensity and direction than the winds encountered within the canyon. The winds within the canyon were strong and variable depending on the terrain features. AIRPORT INFORMATIONThe airplane logbooks and records were not located during the investigation. WRECKAGE AND IMPACT INFORMATIONPostaccident examination of the accident site revealed the left wing and wing tip were at the initial impact area. The airplane’s forward fuselage impacted rocky terrain, and the airplane fragmented into multiple sections. The engine, fractured composite propeller blades, and the main landing gear were separated and came to rest between the initial impact and the main wreckage. The main wreckage consisted of the cockpit/cabin, empennage, and inboard sections of the left and right wings (see figure). Figure. Accident Site and Main Wreckage Flight control continuity was established from the cockpit to all flight control surface connections. The engine/propeller control assembly was separated inside the cockpit. The throttle and mixture control levers were found in the full forward positions. The composite propeller blades were sheared off at the propeller hub. Postaccident examination of the airplane revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operations. A fragmented Dynon SV-D1000 Skyview Display unit was sent to the National Transportation Safety Board recorders laboratory for data extraction. The unit sustained impact damage, and the display was missing from the device. The unit stored data in the nonvolatile memory (NVM); however, further examination of the device revealed that the NVM was damaged in the accident. The extent of damage precluded normal recovery procedures and additional attempts were unsuccessful in recovering usable data. MEDICAL AND PATHOLOGICAL INFORMATIONThe El Paso County Coroner’s Office, Colorado Springs, Colorado, performed an autopsy on the pilot’s remains. The autopsy report listed the cause of death as “multiple blunt force injuries,” and the manner of death was an accident. In addition, severe coronary artery disease was identified; the left anterior descending and right coronary arteries exhibited focal eccentric stenosis of about 75%. The right coronary artery exhibited evidence of recanalization (meaning previously having greater occlusion and reopening to some degree). No other mention was made of other cardiac findings and no other significant disease was identified. Toxicology testing performed at the Federal Aviation Administration Forensic Sciences Laboratory found salicylic acid in the pilot’s blood and liver. Salicylic acid is a metabolite of aspirin, an over-the-counter analgesic that may be used to prevent heart attacks. No ethanol was detected.
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.
Source: NTSB Aviation Accident Database
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