What was found
DURING POWER REDUCTION AT 20" LEFT ENGINE STARTED TO SHUTTER AND VIBRATE MAP INDICATION FLUCTUATED BETWEEN 20 AND 24" INCHES. ENGINE WAS NEVER SHUT DOWN AIRCRAFT WAS ON SHORT FINAL AND LANDED WITHOUT ISSUE. POSTFLIGHT INSPECTION REVEALED THE HEAD PORTION OF THE NR 4 CYLINDER OF THE LT ENGINE HAD SEPARATED COMPLETELY FROM THE BARREL SECTION. THE EXHAUST VALVE WAS FOUND TO BE BROKEN AT THE STEM AND HAD CAUSED SIGNIFICANT MECHANICAL DAMAGE TO THE PISTON AND HEAD PORTION OF CYLINDER. THE ENGINE MANUFACTURE HAS BEEN NOTIFIED AND WILL PARTICIPATE IN A COMPLETE TEAR DOWN INSPECTION TO IDENTIFY ROOT CAUSE OF FAILURE IF ABLE. THE CYLINDER HAD ACCUMULATED 916.7 SNEW.