Incident Overview
An aircraft experienced a total loss of engine power while descending from 17,500 feet mean sea level (MSL) to 10,000 feet MSL. The pilot's attempts to restart the engine were unsuccessful, and the aircraft was subsequently landed with the landing gear retracted in a rocky field.
Post-Accident Inspection
During the post-accident examination, investigators discovered a track of internal electrical arcing in the distributor section of both magnetos. The magnetos, manufactured by Slick and identified as model number 6220, had accumulated a total time since new of 401 hours.
Maintenance History
The aircraft's service instructions recommend that the magneto breaker compartment be inspected during the first 25-hour aircraft inspection and during each subsequent 100-hour inspection. The aircraft had undergone an annual inspection 36 hours prior to the accident. However, the manufacturer's seals on the breaker compartment screw heads were found intact, indicating that the magnetos had not been inspected during that annual inspection.
Conclusion
The investigation determined that the internal arcing in both magnetos led to the total loss of power. The absence of inspection, as evidenced by the unbroken seals, was noted in the maintenance records.