As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CYLINDER NR 4 HAD LARGE CRACK ACROSS CYLINDER, BELOW TOP SPARK PLUG HOLE. A CYLINDER DIFFERENTIAL CHECK CONFIRMED CYLINDERS 2, 6, AND 3 TO HAVE CRACKS IN THE SAME GENERAL LOCATION. ALL 6 CYLINDER ASSEMBLIES WHERE REMOVED. 6 NEW CYLINDER ASSEMBLIES P/N 655471A4. NOTE: THIS MAKES 16 I0-520 AND I0-550 CYLINDER ASSEMBLIES REPLACED DUE TO THE SAME PROBLEM SINCE MAY 2005 ON A FLEET OF 6 AC OPERATED BY 2 INDEPENDENT COMPANYS.