What happened
The pilot reported that the engine lost power during a swath run, resulting in the aircraft being damaged during a forced landing in a field of mature sunflowers.
The investigation
An examination of the aircraft revealed that both fuel tanks and the gascolater contained fuel. Subsequently, the engine was started at the accident site and it ran normally to 1000 RPM, but was not operated at a higher RPM due to a bent propeller. The owner-operator reported that on previous occasions, fuel fed from the left fuel tank faster than from the right, when the fuel selector was in the ON position. Also, he reported that on previous occasions, the bladder liners of the fuel tanks were found to be unsnapped and appeared to have collapsed; but reportedly, no action was taken other than to reattach the bladders.
Findings
The investigation suggests that fuel exhaustion or inadequate fuel flow due to a malfunctioning fuel system contributed to the accident. The owner-operator's reports of uneven fuel feeding and collapsed bladder liners indicate potential issues with the fuel tank bladder liners and fuel selector valve.