What happened
While climbing through 5,500 feet mean sea level, the pilot of the aircraft heard a popping sound and noticed an unusual odor, though no smoke was initially visible. The pilot decided to divert to the nearest airport for an emergency landing. During this period, the pilot discovered that the push-to-talk button had ceased to function. After setting the transponder to code 7700, the pilot began a descent.
As the aircraft descended, the cockpit filled with acrid black smoke, and flames became visible through an opening in the instrument panel. The pilot attempted to use a handheld fire extinguisher to suppress the fire, but the effort was unsuccessful. The pilot subsequently executed an emergency landing in a field, where the aircraft struck a barbed wire fence and was consumed by fire.
The investigation
An examination of the aircraft's electrical system identified that the main battery cable, which ran between the main power relay and the main power bus, had been severed approximately two inches from the main bus. Investigators found beading and localized melting on both ends of the cable. Under magnification, the damaged areas exhibited an eroded appearance and evidence of pitting.
Findings
This specific type of damage is indicative of an electrical arcing event. This arc most likely ignited the insulation surrounding the main power wiring assembly, which then spread to other combustible materials in the area. The specific initiating event that caused the arc could not be determined.