What was found
DURING FLIGHT, A SLIGHT VIBRATION WAS NOTICED. A PRECAUTIONARY LANDING WAS MADE WITHOUT FURTHER INCIDENT. DURING AN INSPECTION TO DETERMINE CAUSE, NOTED THE PROPELLER COULD BE ROCKED FROM SIDE TO SIDE. SUBSEQUENT ENGINE TEAR-DOWN REVEALED A HORIZONTAL CRACK EXTENDING AROUND THE ENTIRE DIAMETER OF THE CRANKSHAFT FORWARD OF THE NR 1 MAIN BEARING SURFACE. THE CRACK CAUSED THE PROPELLER HUB TO LOOSEN CAUSING EXTENSIVE DAMAGE TO THE TAPERED CRANKSHAFT.