NTSB Identification: CHI03LA095.
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Accident occurred Monday, March 31, 2003 in Knox, IN
Probable Cause Approval Date: 07/29/2004
Aircraft: Air Tractor AT-401, registration: N45297
Injuries: 1 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The aircraft was substantially damaged during a forced landing following an engine failure. The pilot reported that a newly overhauled engine had recently been installed on the aircraft. Several ground test runs had been completed with no problems noted. Immediately prior to the accident flight, the pilot stated that the engine was warmed up and the oil temperature was within takeoff limits. He reported that he departed uneventfully and climbed to 400 feet above ground level. He noted that the oil temperature rose to 180 - 200 degrees before dropping back to 135 degrees, indicating the oil was being circulated through the oil cooler. About five miles south of the departure airport the pilot noted a drop in oil pressure and decided to divert to an intermediate airport. The oil pressure continued to drop and the engine started losing power. The aircraft was not able to maintain altitude at this point. The pilot estimated that he was not going to be able to clear a line of trees adjacent to the intermediate airport. He selected and made a forced landing in a field short of the airport. He stated that he touched down in the field "all right," but to avoid hitting trees at the end of the field, he applied the brakes causing the aircraft to flip over. The aircraft came to rest inverted at the edge of a harvested soybean field. An on-scene inspection revealed that three cylinder heads had failed. The lower fuselage was covered in oil emanating in a fan-shaped pattern from the engine oil breather tube and extending to the tail of the aircraft. An engine teardown was performed. The master rod bearing was deformed and had extruded from the rod. It appeared to have a bluish tint consistent with overheating of the material. The oil pump would not rotate under hand pressure. The drive gear, housing and attachments appeared undamaged. The oil check valve was free to move. Upon disassembly, the oil pump gears appeared undamaged. Scrape marks were observed on the interior of the pump housing. At the oil pump inlet a small piece of rubber hose was recovered. The engine fittings were not capped when the NTSB arrived for the teardown.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A loss of engine power due to oil starvation as a result of the failure of the master rod bearing. Contributing factors were the tree line at the edge of the field, and the unsuitable terrain.

Full narrative available

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