As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ENGINE ROUGHNESS ON APPROACH AND LOSS OF RIGHT ENGINE NR 3 CYLINDER EGT INDICATION. AIRCRAFT LANDED WITH OUT INCIDENT. INSPECTION REVEALED NR 3 CYLINDER LOWER SPARK PLUG HAD SEPERATED INTO TWO PIECES BETWEEN THE GASKET SURFACE AND THE WRENCH HEX ALOWING THE CENTER ELECTRODE TO BE EJECTED FROM THE SPARK PLUG. THE COWLING SUFFERED MINOR FLAME DAMAGE.