Amateur-built Vans N470LM accident near Marysville, California

Probable cause

A partial loss of engine power for reasons that could not be determined due to the fragmentation of the electrical system.

NTSB analysis

The pilot stated that while en route on the personal cross-country flight, the engine experienced a loss of thrust, and the airspeed slowed. The propeller was windmilling, but the throttle had no effect on the engine. The pilot noted that the propeller circuit breaker had popped out but did not note any other indications of an anomaly in the cockpit. In addition, with the engine operating at partial power, the pilot was unable to maintain level flight so he configured the airplane for the best glide speed. He attempted to regain engine power twice and switched fuel tanks, to no avail. The pilot made a forced landing in a soft field, which resulted in substantial damage to the airframe.

A postaccident examination noted no evidence of engine mechanical anomalies or thermal distress. There were several wires and a wiring harness disconnected in between the cockpit and the firewall; it is unknown if this happened after impact. During an attempted engine test, a fuel source was rigged to the left fuel tank; the starter solenoid was heard activating, but the engine would not start. An external power source was used in an attempt to start the engine; the engine cranked but would not start. Fuel continuity and pressure in the system was confirmed. The fragmentation of the wreckage, specifically the electrical system, precluded a definitive determination of the cause of the engine failure.

Text from the NTSB. Open the NTSB docket for WPR17LA067 for the full record.