Background
During a landing approach to runway 13, the pilot observed that the tachometer RPM was changing drastically while the airplane was on a 2 to 2.5 mile extended downwind leg. The pilot reported the anomaly to the tower and advised that he needed to land. The tower controller immediately cleared the pilot to execute a left turn and proceed for a straight-in approach to runway 17.
Engine Failure
Approximately 30 seconds after turning for runway 17, the engine started to make a loud popping and backfiring noise, followed by a total loss of power. The pilot notified the controller of his predicament and advised that he would not be able to reach the runway.
Landing Sequence
The pilot elected to land the airplane on a field to the right of his course, about 1.5 miles north of the threshold for runway 17. During the landing roll, the main gear hit a drainage ditch along the side of a road crossing the field, and the airplane nosed over.
Examination Findings
Examination and teardown of the engine revealed that the crankshaft had failed in a heavy cast area (web) between the #1 and #2 rod journals.