What was found
ALUMINUM CYLINDER HEAD FRACTURED CIRCUMFERENTIALLY ADJACENT TO UPPER EDGE OF STEEL CYLINDER BARREL ON 4/28/13 DESPITE A SATISFACTORY COMPRESSION CHECK (79/80) 4 DAYS PRIOR 4/25/13, WITH NO USE IN THE INTERIM. HEAD SEPARATION OCCURRED AT HIGH POWER SETTING, TAKEOFF, JUST AFTER ROTATION. COMPRESSION CHECKS WERE PERFORMED AT EACH OIL CHANGE/ 50 HOURS EVEN THOUGH AD 2009-26-12 DOES NOT APPLY IAW SN OF THE CYLINDER ASSY. PROBABLE CAUSE WOULD BE DEFECTIVE DESIGN OF THE CYLINDER HEAD, INADEQUATE MATERIAL QUALITY, AND/OR POOR QUALITY CONTROL DURING MFG OF THE CAST CYLINDER HEAD. UNLESS/UNTIL MFG MAKES OR HAS MADE A CHANGE TO ITS CYLINDER HEAD MATERIAL OR DESIGN, TO FURTHER EXPAND AD 2009-26-12, APPLICABILITY TO INCLUDE LATER CYLINDER ASSY SN.