NTSB Identification: LAX97LA076.
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Accident occurred Tuesday, December 24, 1996 in DAVIS, CA
Probable Cause Approval Date: 03/31/1998
Aircraft: Trickle TR-4, registration: N91RT
Injuries: 2 Minor.

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 in cruise at 3,500 feet when a slight engine vibration became apparent to the pilot. The engine oil pressure and temperature were normal; however, as a precaution he turned toward a nearby airport. One minute later, a severe vibration began shaking the aircraft. The pilot could not make the airport and landed in a marshy field. The engine ran the entire time from vibration onset until just before ground contact. The engine was factory new 2.5 years and 358 hours prior to the accident. During recovery of the aircraft, no oil film was observed on the aircraft or in the engine compartment. Significant quantities of clean oil were found in the oil filter canister, and the undamaged oil pump. No metal contamination or scoring was observed to the oil pump housing or impeller rotors. Complete engine disassembly revealed that the number 3 connecting rod was separated from the crankshaft journal, with severe peening noted to both the rod end and crankshaft journal. No significant heat distress or scoring signatures were noted on any bearing or journal. The battered number 3 rod end cap and the two associated bolts were found in the oil sump. One bolt was found fractured just below the head. The second bolt was bent about 20 degrees, with severe battering noted to the bolt threads and a portion of the nut. The direction of bend in the distorted bolt was observed to be 180 degrees from the center of the rod cap. Metallurgical examination of the fractured bolt revealed a fatigue crack with multiple plane origins in the radius between the head shoulder and the decreased diameter portion of the bolt. Hardness tests disclosed values in the acceptable range according to Lycoming specifications.

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

The fatigue fracture and separation of one rod end cap bolt. A factor in the accident was the nature of the terrain for the forced landing.

Full narrative available

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