What was found
(CAN) ACFT WAS CLIMBING OUT ON A TRAINING FLIGHT. SHORTLY AFTER HEARD A LOUD BANG AND RPM DROPPED TO APPROX 1200. TURNED BACK AND LANDED SAFELY FOUND THE NR1 CYL HEAD SEPARATED FROM THE BARREL WITH APPROX 1 INCH OF BARREL EXPOSED PAST THE CYLINDER FINS. NR1 INTAKE LIFTER WAS DAMAGED AS WELL AS THE ENG CRANKCASE, ENG REMOVED FOR OVERHAUL. ENG WAS OPERATING ON AN ON-CONDITION PROGRAM. (@2567 HOURS, TBO IS 2000) FIRST FAILURE OF THIS TYPE. CYL WAS NOT AFFECTED BY AD 2006-12-07 AND WAS IN FACT NOTED AS AN ACCEPTABLE REPLACEMENT CYLINDER FOR THE PN MENTIONED IN THE AD. ENGINE WAS INSTALLED IN THIS AIRFRAME. REPLACED ORIGINAL ENGINE.