Incident
The aircraft experienced an engine failure while in flight. The pilot reported that the engine began making unusual sounds, describing them as indicative of a poorly running engine. Subsequently, the engine lost compression and seized, leaving the aircraft without power. The pilot executed a forced landing onto a highway. The landing resulted in damage to the aircraft's hull.
Investigation
Following the incident, an examination of the aircraft was conducted. The investigation revealed a problem with the engine's oil system. Specifically, the main oil breather had frozen. This freezing prevented the venting of oil vapor pressure. As a result, the engine seals failed, leading to a depletion of the oil supply. The loss of oil caused the engine to seize, which necessitated the forced landing.
Probable Cause
The probable cause of the engine failure was a frozen main oil breather, which prevented oil vapor pressure from venting, caused the engine seals to fail, and thereby depleted the oil supply.