What happened
The pilot had a mechanic perform a pre-purchase inspection of the aircraft prior to acquisition. The mechanic found no malfunctions within the fuel system and reported that the aircraft was overall in good condition. Later that same day, the pilot completed the purchase and took off after verifying that the main fuel tanks were virtually full. According to the pilot's calculations, with the main tanks full, the aircraft should have had an endurance of 2.8 hours.
During the flight, the pilot monitored the main tank fuel gauges, which indicated fuel levels at one-half and one-quarter capacity. Ten minutes after these observations, both engines lost all power. The pilot executed a forced landing in an underlying soft field.
The investigation
An examination of the fuel tanks' bladders revealed that some of the snap fasteners designed to secure the tops of the bladders were excessively weather checked and had shrunk. This degradation likely compromised the integrity of the fuel system, leading to the loss of power despite the gauges indicating remaining fuel.
Findings
The primary causal factor was fuel exhaustion resulting from the failure of the fuel tank bladder fasteners. The pre-purchase inspection failed to detect this specific mechanical defect, as the snap fasteners were not identified as malfunctioning during the initial assessment. The discrepancy between the gauge readings and actual fuel availability highlights the importance of verifying physical fuel levels when gauges are unreliable or when mechanical integrity is in question.