Background
A student pilot was conducting a flight when the engine began to sputter during cruise at 6,500 feet mean sea level. Approximately 30 seconds later, the engine ceased operating entirely. The pilot initiated a forced landing descent.
Accident Sequence
During the descent, the pilot attempted to restart the engine four times. While maneuvering to land on an airstrip, the pilot performed 360-degree turns to lose altitude. After completing the second turn, the aircraft was too low to reach the airstrip, so the pilot landed in an orchard. The aircraft collided with trees during the landing.
The aircraft had half a tank of fuel in the left wing and a full tank in the right wing. Recovery personnel at the accident site drained approximately 2 gallons of fuel from the aircraft before the fuel flow stopped. When the fuel caps were removed, the drain stream returned to full flow.
Post-Accident Findings
A post-accident test-run of the engine did not reveal any operational anomalies. The fuel vent line extending from the bottom of the left fuel tank and the cross-vent line between the right and left fuel tanks were tested with air flow; neither line was obstructed. The fuel caps were tested on a Cessna fuel tank with vacuum suction applied; neither cap vented. Examination of the fuel caps did not determine why they failed to vent. The fuel caps provide secondary venting, and if the fuel vent line is also plugged, no venting is possible.
The aircraft was recovered a few days after the accident and moved to a storage facility over unimproved dirt roads, where the engine test-run and vent system examination took place. Any obstruction in the vent system could have been dislodged during recovery and transport. According to the operator, the fuel caps and wing vents were checked during the last 100-hour inspection.