Accident Overview
On February 22, 2024, at 1802 central standard time, an experimental, amateur-built Zenith CH750 STOL, registration N750WW, was substantially damaged when it impacted terrain near Sextonville, Wisconsin. The pilot, who was the sole occupant, sustained serious injuries. The flight was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
The pilot reported that he had recently replaced the carburetor on the airplane's engine. The accident flight was his third flight with the new carburetor. Although the previous flights were uneventful, the pilot believed the fuel/air mixture was too rich. He stated that he intended to remain in the traffic pattern during the accident flight, but he had no memory of the events of the flight.
Witness Account
A witness in the area observed the airplane as it was departing Richland Airport (93C) in Richland Center, Wisconsin. The witness reported that the airplane was flying about 60 feet above ground level (agl) and climbed to about 100 feet agl, followed by a descending, shallow left turn. The witness did not hear any engine noise and thought the propeller was not spinning. According to the witness, the airplane was traveling very slow and then dropped straight down. At 1802, the witness made a 911 call and rendered aid to the pilot. An odor of fuel was present at the accident site.
Postaccident Examination
The airplane came to rest in a field on the edge of a tree line less than 1 mile north of Richland Airport. The airplane was upright, with several tree branches lying near the wreckage. The left wing was impact-separated. Examination revealed that both wings and the fuselage sustained substantial damage during the accident sequence. One of the two propeller blades remained attached to the propeller hub; the other blade was broken at the hub and located near the wreckage. Both blades were mostly intact and did not exhibit rotational scoring, leading edge damage, or chordwise scratches. No preimpact anomalies were found with the airframe or the flight controls.
Engine and Systems Examination
The airplane was equipped with an automotive engine that had been modified for use in the aircraft. Two independent ignition systems were present and functioned properly when external power was applied to the electrical system. Examination of the engine revealed no anomalies that would have precluded normal operation. The alternator and voltage regulator were examined and tested. The alternator's rotating magnet assembly slipped on the shaft when the drive coupling was rotated by hand; after the torque nut was tightened, the alternator functioned normally. The voltage regulator tested normally with no anomalies found.