VANS RV4 — Telluride, CO

What happened

The pilot and passenger were concluding a cross-country flight and were flying in the traffic pattern at their intended destination when the airplane pitched nose down and descended rapidly into mountainous terrain during the turn from the base leg to final approach.

There were multiple witnesses who reported seeing the airplane enter a steep left turn toward the airport followed by a nose-down descent toward terrain. One witness reported that the airplane completed 3 or 4 spins while it descended nose down in a vertical descent and that the sound of the engine was “quite loud.” Airport security camera footage showed the airplane in a left-wing down, nose down, descending turn into terrain east of the airport.

According to automatic dependent surveillance-broadcast (ADS-B) data, shortly after the airplane entered the left turn from the base leg to final approach, the airplane decelerated to 50 knots calibrated airspeed (KCAS) and the descent rate increased from 600 to 3,850 ft/min. According to the airplane kit manufacturer, the airplane’s wings-level aerodynamic stall speed at a maximum gross weight was 47 KCAS. The airplane maneuvering in the traffic pattern would require turns and, as such, there was a corresponding increase to aerodynamic stall speed during the turns. Additionally, the airplane’s left-wing-down roll was increasing when the airplane entered the rapid descent.

Postaccident examination revealed no evidence of a preexisting mechanical malfunction or failure that would have precluded normal operation of the airplane.

Based on the surveillance video footage, witness accounts, and the recorded ADS-B data, it is likely the pilot did not maintain adequate airspeed during the left turn from the base leg to final approach, which resulted in the airplane exceeding its critical angle of attack and inadvertently entering an aerodynamic stall/spin at a low altitude over mountainous terrain.

Toxicology testing detected morphine in the pilot’s urine but not in his blood. The detection of acetaminophen suggests that the pilot had taken codeine with acetaminophen for mild to moderate pain relief. Since no morphine was present in the blood, no impairing effects would be expected. Thus, the effect of the pilot’s use of morphine or opiate pain reliever was not a factor in this accident.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.