N750WW

On February 22, 2024, at 1802 central standard time, an experimental, amateur-built Zenith CH750 STOL, N750WW, was substantially damaged when it was involved in an accident near Sextonville, Wisconsin. The pilot sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations part 91 personal flight.

The pilot reported that he had recently changed the carburetor on the airplane’s engine, and the accident flight was his third flight with the new carburetor. Although the previous flights had been uneventful, he thought that the fuel/air mixture was too rich. He stated that he intended to remain in the traffic pattern during the accident flight; however, he had no memory of the events of the flight.

A witness in the area reported seeing the airplane as it was departing Richland Airport (93C), Richland Center, Wisconsin. The witness reported that the airplane was flying about 60 ft agl and climbed to about 100 ft agl followed by a descending, shallow left turn. The witness did not hear any engine noise and thought that the propeller was not spinning. The witness noted that 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.

The airplane came to rest in a field on the edge of a tree line less than 1 mile north of 93C. The airplane came to rest upright with several tree branches lying near the wreckage. The left wing was impact separated.

Postaccident examination of the airplane 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 propeller hub and located near the wreckage. Both blades were mostly intact and did not exhibit rotational scoring, leading edge damage, or chordwise scratches. There were no preimpact anomalies found with the airframe or the flight controls.

The airplane was equipped with an automotive engine that had been modified for use in the airplane. There were two independent ignition systems that 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 airplane’s alternator and voltage regulator were examined and tested. Examination of the alternator revealed that the rotating magnet assembly slipped on the shaft when the drive coupling was rotated by hand. The torque nut was tightened, and the alternator functioned normally. The voltage regulator functioned normally when tested. No anomalies were found with the voltage regulator.