Cessna 205 Experiences Crankshaft Separation During Cruise; Forced Landing Ends in Ditch (N8464K)

Shortly after takeoff, while cruising at 3,000 feet mean sea level over Samish Bay, the Cessna 205's Continental IO-470-S engine ceased developing power, and the propeller continued to windmill. The pilot, observing that only muddy fields were available, initiated a forced landing to a north/south paved road at the south end of the bay. Noting power lines along the west side of the road, the pilot landed along the east side. During the landing roll, the left wing impacted a sign. Subsequently, the pilot was unable to maintain directional control, and the aircraft departed the left side of the road into a deep ditch. Post-crash examination of the engine revealed that the crankshaft had separated at the number six cheek. Metallurgical examination of the crankshaft showed that a large area in the central portion of the number six cheek fracture surface displayed a smooth texture and contained multiple crack arrest features, characteristic of fatigue progression. The fatigue originated at the outboard flat surface of the crankcheek, approximately at the midpoint between the horizontal centerlines for the main and rod journals. No further determination could be made regarding the initiating condition of the fatigue due to post-separation heat and mechanical damage to the fracture features.