What happened
While operating in cruise flight, the pilot reported a drop in engine manifold pressure followed by a loss of oil pressure. In response to the engine issues, the pilot decided to divert to a nearby airport. During the descent, the engine began to fail, leading the pilot to execute a forced landing on a road.
As the pilot was setting up for the landing, the engine seized. During the subsequent landing roll, the aircraft's right wing struck a road sign. The impact resulted in substantial damage to the aircraft.
The investigation
An initial examination of the aircraft revealed oil adhering along the entire length of the bottom fuselage, which originated from the engine's right-side exhaust pipe. An inspection of the engine showed that the right-hand turbocharger impeller blades were worn at the tips, with some blades being fractured. Additionally, excessive play was noted in the compressor assembly.
Further examination of the turbocharger was conducted at the NTSB Materials Laboratory. This analysis determined that the aluminum bearings of the impeller were heavily worn and distorted, though no signs of overheating were found in the bearings. While attempts were made to perform a Rockwell hardness test, accurate readings could not be obtained due to the softness of the metal. The investigation also identified damage to the oil seal at the impeller shaft.