Overview
The flight experienced an engine failure caused by the separation of the number six connecting rod from the crankshaft. The rod separated after the connecting rod bearing failed. During the subsequent forced landing attempt in darkness, the aircraft struck trees and crashed to the ground.
Mechanical Sequence
The failure began with the number six connecting rod bearing. The bearing had a tin overlay that peeled away from the aluminum bearing material. The reason for this peeling was not determined. After the overlay separated, the aluminum bearing became damaged and eventually separated from the connecting rod. With the bearing missing, the connecting rod overheated. The rod bolts then failed, resulting in the rod detaching from the crankshaft. This sequence caused a complete loss of engine power.
Forced Landing and Collision
In the dark conditions, the pilot attempted a forced landing. The aircraft descended but collided with trees and subsequently crashed to the ground.
Examination Results
Post-accident examination of the engine revealed that the tin overlay of the number six connecting rod bearing had detached from the aluminum bearing. The examination was unable to determine why the overlay peeled. The aluminum bearing was found damaged and had separated from the rod. Additionally, the connecting rod showed signs of overheating, and the rod bolts had failed, consistent with the rod separation from the crankshaft.