What happened
The pilot reported that during a cross-country flight, the engine began shaking and emitting smoke. He made an emergency landing in a cultivated field, but the aircraft nosed down in soft muddy terrain and was damaged.
The investigation
The pilot reported that before he took off, he serviced the aircraft with fuel. He also stated that he added one quart of oil, checked the oil level and replaced the oil cap. However, an investigation revealed the oil cap was absent and the engine was damaged by lack of lubrication.
Findings
The pilot's actions prior to flight did not prevent the loss of the oil cap, leading to engine failure due to lack of lubrication. The aircraft sustained damage during the subsequent forced landing in a field.