What happened
The aircraft was involved in an incident during a precautionary landing on a roadway. The pilot had been operating the flight for two and a half hours when he observed the oil pressure gauge drop to zero. In response to this mechanical indication, the pilot elected to land on a nearby highway.
During the landing roll, the right wing of the aircraft struck a signpost. This impact caused the aircraft to swerve off the paved surface and enter a ditch. The collision with the post resulted in damage to the airframe.
The investigation
Post-accident examination of the aircraft revealed that it contained between three and four quarts of oil. Prior to takeoff, the pilot reported adding one quart of oil, which raised the total oil level to nine quarts. Investigators found no evidence of an external oil leak.
The engine was partially disassembled to determine the cause of the rapid oil loss. Despite this inspection, mechanics could not identify a specific reason for the consumption of five or six quarts of oil in less than three hours of flight time.
Findings
The primary factor leading to the accident was the loss of oil pressure during flight. This mechanical failure necessitated an emergency landing on a public road. The subsequent impact with a signpost during the rollout caused the aircraft to depart the roadway.