Accident Overview
On July 16, 2009, at approximately 0640 central daylight time, a Cessna A188B, registration N9747G, experienced a loss of engine power while maneuvering at low altitude during an aerial application flight. The pilot executed a forced landing to a wheat field near Suring, Wisconsin. During the landing, the left main landing gear collapsed, and the left wing and nose dug into soft soil, resulting in substantial damage to the aircraft. The pilot reported no injuries. Visual meteorological conditions prevailed, and no flight plan was filed.
Engine Inspection Findings
The engine, a 300-horsepower Continental IO-520-D (serial number 572952), was shipped to the manufacturer for a teardown inspection. The exterior crankcase showed minimal damage, but internal examination revealed extensive fretting on the number one through five main bearing supports. The number three main bearing support exhibited bearing shift. The crankcase backbone showed fretting between the number two and three main bearing supports, with red sealant applied to that area.
The number two crankshaft main bearings had extruded from their positions in both case halves, with mechanical damage consistent with bearing shift, rotation, and extrusion. Fragments of the bearing were found in the oil sump. The number three crankshaft main bearings also showed mechanical damage and bearing shift, with smeared babbit exposing the copper layer.
The number three connecting rod was fractured at the base of the I-beam and exhibited mechanical damage. Fragments of the connecting rod cap and bolts/nuts showed overload signatures. The crankshaft was fractured through at the number four short cheek at the number two main journal. A metallurgical examination revealed crack arrest marks indicative of a fatigue fracture originating from the surface.
Maintenance Records
The engine logbooks indicated a total time of approximately 1,778 hours, with about 500 hours since the last major overhaul performed on September 30, 1986. The most recent annual inspection was conducted on October 23, 2008. According to Teledyne Continental Aircraft Engine Service Information Letter SIL98-9A, issued November 17, 1998, the recommended overhaul interval for an IO-520-D engine is 1,700 hours or every 12 years, whichever occurs first. For aircraft used in aerial spraying, the recommendation is overhaul after 1,200 hours or 12 years, whichever occurs first.