What was found
DURING CRUISE FLIGHT, THE AIRCRAFT EXPERIENCED AN IMMEDIATE PARTIAL LOSS OF ENGINE POWER ACCOMPANIED BY SEVERE ENGINE ROUGHNESS. AN EMERGENCY WAS DECLARED, AND THE AIRCRAFT LANDED SAFELY WITHOUT FURTHER INCIDENT. POST-FLIGHT MAINTENANCE INSPECTION REVEALED THAT THE NR 4 CYLINDER BOTTOM AVIATION SPARK PLUG, A TEMPEST URHB32S (FINE WIRE, LOT CODE 11WA), SUFFERED A CATASTROPHIC STRUCTURAL FAILURE. THE SPARK PLUG COMPLETELY SEPARATED BETWEEN THE PLUG'S SEAT ASSEMBLY AND THE HEXAGONAL NUT IN FLIGHT. THE REMAINING PLUGS FROM THE SAME LOT CODE ARE BEING REMOVED FROM SERVICE. THE CYLINDER THREADS AND INTERIOR ARE UNDERGOING A BORESCOPE INSPECTION FOR SECONDARY MECHANICAL OR THERMAL DAMAGE.