Accident Description
The airplane was in flight when the engine ceased producing full power. The pilot executed a forced landing in a pasture. During the landing roll, the airplane collided with a fence.
Pilot Account
The pilot inspected the fuel system after the landing and found fuel present in both tanks. However, the right fuel tank had collapsed. The pilot attributed the collapse to a blocked fuel tank vent. The vent was plugged with residue left by mud daubers. The left fuel tank, which contained more fuel than the right, had not collapsed.
Manufacturer's Information
The manufacturer of the airplane stated that the fuel system features individual fuel tank vents that are not interconnected. This design means that each tank has its own vent and the tanks do not share venting capacity.
Conclusion
The investigation determined that the right fuel tank collapsed due to its vent being obstructed by mud dauber residue. This collapse likely led to fuel starvation from that tank, resulting in the engine's loss of full power.