Accident Overview
On July 29, 2022, at approximately 0652 central daylight time, a Sonex Aircraft Sonex airplane, registration N1557S, was involved in an accident near River Falls, Wisconsin. The aircraft was operating as a Title 14 Code of Federal Regulations Part 91 test flight. The pilot reported serious injuries, and the airplane suffered substantial damage to the right wing and fuselage.
Flight Details
According to the pilot, the purpose of the flight was to check the position of the trim tabs because the right wing was "heavy" and required "a little left" rudder input for straight-and-level flight. A preflight inspection was completed without any issues. The airplane carried approximately 10.3 gallons of UL94 avgas for the local flight.
Departure was from South St. Paul Municipal Airport (SGS) in South St. Paul, Minnesota. After several miles en route, the pilot completed the trim tab checks. Between 30 and 45 minutes into the flight, the pilot decided to return to SGS. Shortly after turning back toward the airport, at about 2,700 ft msl, the engine experienced a total loss of power. The pilot reported no unusual noises or a drop in rpm. Three restart attempts were made; the engine would turn over but failed to start.
Forced Landing and Damage
The pilot executed a forced landing into a corn field. During the landing, the right wing struck a traffic sign, and the airplane came to rest upright in a grass ditch. Substantial damage was noted to the right wing and fuselage.
Postaccident Examination
On-site examination revealed the sole fuel tank, located forward of the instrument panel, was intact with the fuel cap properly installed. No fuel was found inside the tank; when the drain plug was removed, no fuel drained. There were no signs of a fuel leak on the airframe, engine, or ground (e.g., vegetation blighting), and no fuel odors were present.
Postaccident examination confirmed flight control continuity and airframe-to-engine control continuity. Rotational continuity was established throughout the engine and valvetrain. The fuel line to the carburetor showed no fuel, nor did the fuel supply line to the strainer. The drain from the fuel strainer was found separated, and the strainer bowl was empty. No preimpact mechanical malfunctions or failures were identified that would have precluded normal operation.
Fuel System Description
According to the Sonex Builders & Pilots Foundation, the stock fuel tank is a rotationally molded polyethylene cell located under the glareshield in the forward fuselage. Capacities vary by model: legacy Sonex models hold 16 gallons, B-Models hold 20 gallons, and the Onex holds 15 gallons. The system operates on gravity feed without a fuel pump. Fuel level monitoring is achieved via an electronic capacitance probe or a clear visual sight tube. A shutoff ball-valve is standard, located under the instrument panel at the tank outlet, and it is common practice to close this valve when the aircraft is not in use.