Incident Overview
The pilot, an airline transport rated pilot with 2,919 flight hours, reported that while climbing through 5,500 feet mean sea level, he heard a "pop" and noticed an unusual odor, though no smoke was visible. He decided to proceed to the nearest airport for landing and discovered that the push-to-talk button was no longer functioning. The pilot set the transponder code to 7700 and began a descent.
Smoke and Fire
During the descent, the cockpit filled with thick, acrid black smoke, and the pilot observed flames through an opening in the instrument panel. He attempted to suppress the fire using a handheld fire extinguisher but was unsuccessful.
Emergency Landing
The pilot elected to execute an emergency landing in a field. During the landing, the airplane collided with a barbed wire fence and was subsequently consumed by fire.
Investigation Findings
Examination of the airplane's electrical system revealed that the main battery cable, running between the main power relay and the main power bus, was severed approximately two inches from the main bus. Both ends of the severed cable exhibited beading and localized melting. Under magnification, the damaged areas had an eroded appearance with some evidence of pitting. This type of damage is indicative of an electrical arcing event, which most likely ignited the insulation surrounding the main power wiring assembly and allowed the fire to spread to other combustible materials in the area. However, the initiating event for the arc could not be determined.