What happened
While cruising at 5,500 feet MSL, the pilot of the IO-520 powered aircraft reported that the engine began running rough and experiencing a gradual loss of power. In an attempt to reach an airport, the pilot continued the flight, but the engine eventually suffered a total loss of power. During the descent, the airplane contacted trees and cartwheeled into an open field.
The investigation
Mechanical inspections of the engine identified detonation and the disintegration of the number two piston. Additionally, metal fouling was found on seven spark plugs.
Bench testing was performed on the fuel and ignition systems. The investigation found no discrepancies with the fuel distributor, lines, or nozzles. Furthermore, there were no issues found regarding either magneto, magneto timing, or the ignition harness.
Maintenance records indicated that the engine had accumulated 1,560 hours since its last overhaul, which is below the 1,700-hour TBO recommended by manufacturer's service bulletin 91-8. The number two cylinder had been replaced 817 hours prior to the accident, and all six cylinders had undergone replacement at various times within the previous 998 hours.