As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT 400 HR TSO FOUND CYLINDER NR 4 CRACKED AT THE HEAD 5 FINS BACK TOWARD THE BARREL FROM THE TOP SPARK PLUG. CRACK GOES FROM THE EXHAUST VALVE SEAT TO THE TOP SPARK PLUG HOLE ON THE INSIDE OF THE CYLINDER. AD 04-08-10 DID NOT APPLY BY CLY. SN 13516-4 AND CODE A STAMPED ON THE BOSS FLANGE. (K)