Piper PA-24-260 N8546P accident near Holton, Kansas

Probable cause

The mechanic's failure to adequately torque the right magneto attachment nuts, allowing the right magneto to come loose, which allowed engine oil to escape, causing the engine to seize.

NTSB analysis

During a cross-country flight, the pilot and passengers smelled something burning; smoke began to fill the cockpit, and the oil pressure dropped. The propeller then oversped, and the engine seized. In the ensuing forced landing in the dark, the airplane struck trees and impacted a ditch. The engine was covered with oil, and the right magneto was found hanging by spark plug wires. The separation of the right magneto from the engine allowed the engine oil to escape, causing the engine to seize. The magneto had been installed in the airplane about 7 hours before the accident. The mechanic who had replaced the magneto could not recall if he had torqued the magneto attachment nuts. It is likely that the right magneto attachment nuts were not torqued properly and came loose.

Text from the NTSB. Open the NTSB docket for CEN12LA551 for the full record.