ZENITH STOL CH701 — Randsburg, CA

What happened

The pilot and pilot-rated passenger planned to fly the experimental, amateur-built short take-off and landing (STOL) airplane to a series of desert airports and backcountry airstrips. The accident airstrip was the first stop on their itinerary. They had flown together at least once before in the accident airplane, but this was the first time the pilot, who was the owner of the airplane, had landed at a remote, backcountry airstrip.

The accident airstrip was located within a bowl-like feature in the foothills of a mountain range. Published information about the airstrip recommended a traffic pattern altitude of about 825 ft above ground level (agl); however, flight track data indicated that the airplane’s altitude on the downwind leg was about 50 ft above the ridge that ran roughly parallel to the airstrip, and about 125 ft above the runway surface, with very little lateral separation from the runway. Witnesses observed the airplane fly low over the ridgeline while on the downwind leg, during which it appeared to encounter turbulence. The airplane then began a left turn onto the base leg of the traffic pattern and overshot the runway centerline toward rising terrain as it continued in a left turn onto final approach.

The airplane’s bank angle increased to between 60° and 90° as it turned from base to final, and the airplane then rapidly descended, consistent with an aerodynamic stall. The airplane impacted the ground about 700 ft short of the runway threshold and about 300 ft right of the runway centerline.

Examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation, and damage to the propeller blades indicated that the engine was producing power at impact.

Witness accounts regarding the direction and velocity of the wind at the time of the accident varied; however, information from a GPS unit onboard the airplane recorded an increased groundspeed on the base leg of the traffic pattern, suggesting crosswind conditions that would have resulted in a tailwind while on the base leg. This likely contributed to the pilot overshooting the runway extended centerline, which placed the airplane closer to rising terrain on the other side of the runway. The runway overshoot, combined with the proximity to rising terrain, likely resulted in the pilot’s steep turn in the direction of the runway as reported by witnesses before the airplane’s descent into terrain. It is likely that, during that turn, the pilot exceeded the airplane’s critical angle of attack, resulting in an accelerated aerodynamic stall.

Although the airport windsock was inoperative at the time of the accident, there were flags present at a campsite within the airport valley that would have indicated the direction of the wind. Additionally, the pilot was likely aware of the wind during the downwind leg because the airplane maintained a relatively straight track, which would have required control inputs to compensate for the crosswind conditions. Even without the crosswind, the airplane’s reduced lateral separation from the runway during the downwind leg would have required an aggressive turn onto final to avoid overshooting the runway.

The investigation could not rule out the possibility that the pilot-rated passenger was flying the airplane at the time of the accident; however, the airplane’s owner was seated in the left seat, which was the only seat equipped with wheel brake controls. Given that the accident occurred during the approach to land, it is likely the owner was flying the airplane. The terrain surrounding the accident airstrip would have provided an unusual sight picture during the landing approach, likely compounded by the pilot’s decision to fly the traffic pattern at a very low altitude. It is likely that the pilot’s limited experience flying into remote, backcountry airstrips such as the accident airstrip contributed to his failure to establish a stabilized approach to the runway in the presence of unfamiliar topography.

The airplane was originally equipped with leading edge slats to enhance short field takeoff and landing performance, but they had been removed. The airplane could be flown without them, and a safe landing at this airstrip could still have been accomplished if a stabilized approach was performed.

Although autopsy of the pilot revealed cardiovascular disease, operational evidence indicates that it is unlikely that he experienced a sudden medical event.

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