WPR18LA021 · Metcalfe Robert B VANS RV 6 UNDESIGNAT

The pilot reported that about 25 minutes into the local personal flight in the experimental amateur-built airplane, with all systems appearing to operate normally, he noticed that the batteries (located near his right foot) were getting hot and that the system voltage indicated about 15.5V, which was above the normal value of about 13V. Almost immediately thereafter, the engine lost total power. The pilot activated the bus manager emergency power switch and independently selected each of the two engine control units but was unable to restore engine power. He chose a rural road for a forced landing but changed his path to clear a truck on the road; the airplane impacted a vineyard on the side of the road, nosed over, and came to rest inverted.

The pilot had recently decided to change the carburetor and conventional magneto ignition systems to electronic versions for "performance and efficiency improvements." He purchased a kit that included an electronic fuel injection system and replaced the magnetos himself with a fully electronic ignition system.

After completing the installations, the pilot began testing the systems and engine operation. Two days before the accident flight, he conducted two flights of the airplane with the new systems; both flights were brief and uneventful.

Postaccident examination revealed no anomalies with the airplane fuel system or the engine itself. Because the engine was completely reliant on electricity for operation and control of the ignition and fuel injection, the cause of the engine power loss was likely due to a problem with the electrical system or supply. The only nonimpact-related anomaly discovered during the engine and airframe examination was that the swage/crimp of the terminal to the conductor of the primary alternator ground cable was loose, and the conductor and terminal bore evidence (black residue) of electrical arcing. The appearance was consistent with that residue having been caused by the looseness of the swage/crimp and as having been loose for an extended period before the accident. This looseness and arcing indicated that there were transient power interruptions. Such interruptions also create the potential for spurious electrical power variations, which could potentially interfere with the operation of the airplane's electrical or electronic systems, including the alternator, batteries, bus manager, and both the fuel injection and ignition systems.

Verbatim NTSB analysis and probable cause from the NTSB dataset