Accident Overview
On December 4, 2017, about 0720 Pacific standard time, a Beechcraft A36, registration N251E, was substantially damaged in an accident near Rio Oso, California. The pilot sustained minor injuries. The aircraft was being operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight Details
The pilot reported that the flight originated from McClellan Airfield (MCC) in Sacramento, California, with a destination of Yuba County Airport (MYV) in Marysville, California. The preflight inspection, engine start, taxi, and takeoff from MCC were normal. During cruise flight, the pilot noticed a flicker beneath his seat. Upon inspection, he observed a fire had started. He then identified a field suitable for an emergency landing.
Emergency Landing and Fire
The pilot executed a gear-up landing in a plowed field. The airplane came to rest upright, facing approximately 150° from its original direction of travel. After the pilot exited the aircraft, it burst into flames, resulting in thermal damage to the cockpit.
Examination Findings
Examination of the airframe near the left side revealed burnt electrical wires and a hole in a fuel line near the fuel valve inside the cockpit. The fuel selector valve trim panel, attached wires, a fuel flow valve with fuel lines, and a portion of electrical wiring were sent to the NTSB Materials Laboratory for further examination.
Laboratory analysis found that the trim panel for the fuel selector valve had melted and missing insulation, consistent with fire exposure. The attached wiring showed no evidence of electrical arcing. The fuel selector valve exhibited sooting on some fuel lines, and a rough spot and pinhole were observed near a 90° bend. The rough spot displayed cratering and re-solidified metal splatter adhering to the fuel line surface, with a hole through the wall. These features are consistent with electrical arc erosion of the fuel line.
The trim panel and fuel selector valve were positioned as installed in the accident airplane. The damaged portion of the fuel line aligned with the damage on the trim panel. Examination of a portion of electrical wiring revealed electrical arc corrosion at the terminal connector.