NTSB Factual Report

On August 11, 2018, about 1056 Pacific daylight time, an experimental, amateur built Zenith CH-750 airplane, N328SK, was substantially damaged during a forced landing near Napa County Airport (APC), Napa, California. The commercial pilot/owner and his pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions existed at APC about the time of the accident. The local flight had originated from APC, and was returning when the accident occurred.

According to the pilot, who was also the builder of the airplane, the airplane was for sale, and the accident flight was a demonstration/familiarization flight for a potential buyer. The pilot reported that the potential buyer had requested that the pilot conduct slow flight, stalls, and other "steep maneuvers" that required pitch attitudes in excess of those that the pilot experienced during his typical flights. After an unspecified amount of time conducting these maneuvers in the local area, the two decided to return to APC for landing and takeoff demonstrations. At some point during the approach, the engine lost all oil pressure, and stopped producing power shortly thereafter. The pilot initially attempted to glide to the airport, but then realized that the airplane was unable to reach APC. The pilot then decided to land on a nearby levee. The airplane touched down on the levee, and the initial rollout was satisfactory. However, due to wind and the levee width, the airplane veered off the levee, and damaged the wing and fuselage. The airplane came to rest on the slope of the levee, about 0.6 miles west of the APC runway 6 threshold.

The airplane was equipped with a Belgian ULPower brand piston engine. The pilot reported that he believed that the unusual (for him) pitch attitudes during the demo flight had caused the oil to be vented overboard via the oil breather assembly. He also reported that he had had other problems previously with the engine, and that he had sent the engine back to the manufacturer for replacement of several components, including all four cylinder heads, one cylinder, and all piston rings.

Examination of the airplane and engine by a Federal Aviation Administration (FAA) inspector revealed that the engine was void of lubricating oil. Significant oil residue was observed in the region of the starter ring gear and its drive penetration of the engine case. The engine did not exhibit any other evidence of non-impact related damage or failures. Separately, communications with the US-based engine manufacturer's representative indicated that there were no records of the engine being returned to the manufacturer.

FAA records indicated that the pilot held a commercial pilot certificate with airplane single-engine land, rotorcraft-helicopter, and instrument airplane ratings. He also held a repairman experimental aircraft builder certificate valid for the accident airplane. His most recent FAA third-class medical certificate was issued in December 2014.

FAA records indicated that the airplane was manufactured in 2014. The pilot-provided flight and maintenance records were all essentially devoid of entries.

APC was situated at an elevation of 36 ft above mean sea level, and was equipped with three paved runways, designated 06/24 and 18/36 L and R. APC was equipped with an air traffic control tower, which was staffed and operating at the time of the accident.