N1557SHulse Steven T SONEX · 2020

On July 29, 2022, about 0652 central daylight time, a Sonex Aircraft Sonex airplane, N1557S, sustained substantial damage when it was involved in an accident near River Falls, Wisconsin. The pilot sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.

The pilot reported the purpose of the flight was to check the position of the trim tabs, as the right wing was “heavy,” and he would have to hold “a little left” rudder to maintain the airplane in straight-and-level flight. The pilot completed the preflight inspection with no issues noted and the airplane had about 10.3 gallons of UL94 avgas onboard for the local flight.

The airplane departed from the South St. Paul Municipal Airport (SGS), South St. Paul, Minnesota. While enroute for several miles, the pilot completed the trim tab position checks and after between 30 and 45 minutes decided to return to SGS. Shortly after turning back toward the airport, at about 2,700 ft msl, the engine sustained a total loss of power. The pilot reported that the engine did not emit any noises, nor did he notice a drop in the engine’s rpm. The pilot tried restarting the engine three times. Although the engine would “turn over,” it would not start. The pilot elected to perform a forced landing to a corn field. During the landing, the right wing impacted a traffic sign and the airplane came to rest upright in a grass ditch. The airplane sustained substantial damage to the right wing and the fuselage.

On-site examination of the airplane found that the sole fuel tank, located forward of the instrument panel, was intact with the fuel cap installed properly. No fuel was observed inside of the fuel tank. The fuel tank drain plug was removed, and no fuel came out. There were no signs of a fuel leak on the airframe or from the engine, nor were there any signs of a fuel leak or spillage on the ground such as with vegetation blighting at the accident site. There were no odors of fuel at the accident site.

Postaccident examination of the airplane confirmed flight control continuity. Airframe to engine control continuity was established. Rotational continuity was established throughout the engine and valvetrain when the crankshaft was rotated. The fuel line to the carburetor was removed and no fuel was observed. No fuel was observed from the fuel supply line to the strainer. The drain from the fuel strainer was found separated. The bowl from the strainer was removed and no fuel was found. There were no preimpact mechanical malfunctions or failures with the airframe or the engine that would have precluded normal operation.

Fuel System

The Sonex Builders & Pilots Foundation has published the Sonex Aircraft New Pilot Training Guidelines and Transition Training Syllabus. This document discusses the fuel system and states:

The stock fuel tank in the Sonex is a rotationally molded, polyethylene fuel cell located under the glareshield in the forward fuselage. Fuel tank capacities vary depending on model, with the legacy Sonex models holding 16 gallons, the B-Models holding 20 gallons, and the Onex holding 15 gallons. The system is designed to operate on a gravity feed setup, and as such a fuel pump is generally not installed or needed. Fuel level monitoring can be accomplished by an electronic, capacitance style fuel probe threaded into the bottom of the fuel tank, or by incorporating a clear visual sight tube into an upper and lower port into the fuel tank. A shutoff ball-valve is standard, located under the instrument panel at the outlet of the fuel tank. It is common practice to close this valve when the aircraft is not in use.