Accident Sequence
The pilot departed and climbed to a cruising altitude of 14,500 feet mean sea level. After leveling off, the pilot leaned the fuel mixture and set a cruise power of 24 inches of manifold pressure and 2,400 rpm. Shortly thereafter, manifold pressure dropped to 22 inches. The pilot increased power, which briefly restored manifold pressure before it dropped again. The pilot then located an open field for an emergency landing. During the approach, the left wing impacted a tree prior to touchdown. The aircraft nosed over upon contact with the ground.
Post-Accident Examination
Following the accident, maintenance personnel performed a teardown inspection of the turbocharger. The examination revealed evidence of rotational scoring on the turbine components. Displacement of the anti-rotation pins below the surface of the center housing allowed rotation of the thrust bearing. Rotational score marks on the back side of the turbine wheel provided evidence that the turbine wheel had contacted the turbine shroud.
Maintenance History
According to the aircraft maintenance records, the last major overhaul of the turbocharger was performed in 1987.