As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOLLOWING DISCOVERY OF A CRACKED SPARK PLUG ON ANOTHER AIRCRAFT, A PRECAUTIONARY INSPECTION WAS CONDUCTED OF THE SPARK PLUG ON THIS AIRCRAFT AS IT WAS THE SAME LOT # AS A PREVIOUS SPARK PLUG FAILURE. VISUAL INSPECTION FOUND CRACKING AT A POINT BETWEEN THE SPARK PLUG GASKET BOSS AND THE HEXAGONAL NUT PORTION (WHAT TEMPEST REFERS TO AS THE HOT LOCK ASSEMBLY). THE AIRCRAFT HAD NOT FLOWN SINCE THIS SPARK PLUG WAS INSTALLED AT ITS SCHEDULED INSPECTION.