What happened
The aircraft was operating under visual flight rules during a cruise phase when the engine ceased producing power. The pilot reported that the right fuel tank had been completely depleted of fuel. In an effort to restore engine operation, the pilot switched the fuel selector to the left tank. However, the engine failed to restart despite the presence of fuel in the selected tank.
The pilot initiated a forced landing procedure due to the inability to maintain power. The aircraft was landed on rough, sloping terrain under conditions of low light visibility. Upon impact with the uneven ground, the landing gear structure collapsed under the stress of the touchdown. The force of the collision caused the aircraft to flip over onto its upper surfaces.
The investigation
Post-accident examination of the aircraft revealed that the fuel system was functional but improperly vented. Inspection of the left tank filler cap showed that the vent passage was obstructed by debris or ice, preventing air from entering the tank as fuel was consumed. This blockage created a vacuum within the tank, stopping fuel flow to the engine even though fuel remained in the tank.
Findings
The primary factor leading to the accident was the pilot's failure to ensure adequate ventilation of the fuel tanks. The obstruction in the vent cap prevented proper fuel flow from the left tank after the switch from the right tank. Contributing factors included the rough terrain and low light conditions which complicated the forced landing maneuver.
Safety message
Pilots should regularly inspect fuel filler caps for obstructions in the vent passages. Ensuring that fuel tanks are properly vented is critical to maintaining uninterrupted fuel flow, especially during emergency fuel management situations.