What happened
A pilot and a passenger were conducting a cross-country flight when the pilot noticed a burning smell during the initial climbout. The pilot elected to return to the airport for landing. During the descent, white smoke entered the cockpit, which was followed by black smoke and a small flame appearing under the instrument panel.
As the aircraft was on short final approach, the engine lost power. The smoke within the cabin became so dense that the pilot was unable to see outside the airplane. The aircraft touched down, and both occupants escaped not injured. However, the fire continued after landing, and the airplane was destroyed.
The investigation
An examination of the wreckage determined that a worn clamp in the exhaust system had become loose. This caused the exhaust pipe to disconnect, which directed hot gases onto the voltage regulator. The heat from these gases caused the electrical wiring on the regulator to burn and short out, leading to both an electrical fire and a cabin fire.
The pilot, who was also an A&P mechanic, had purchased the aircraft three months prior following an annual inspection. Because the maintenance log books were not recovered, investigators could not verify previous inspections or confirm compliance with an FAA airworthiness directive that requires an exhaust system inspection every 50 hours.