What happened
During a cross-country flight, a private pilot experienced a sudden loss of engine performance approximately 20 minutes after departing from a recent refueling stop. The pilot reported that both engines began running roughly, prompting an immediate descent and a change in course toward the closest available airport.
As the flight progressed, the pilot determined that the aircraft would be unable to reach the intended landing site. Due to the presence of rugged terrain in the flight path, the pilot made the decision to ditch the aircraft into a large lake located beneath the flight path. The aircraft was not recovered from the water, and as a result, the NTSB has not been able to conduct a physical examination of the wreckage.
Findings
The pilot initially suspected that fuel contamination might have been the source of the engine malfunction, noting that the refueling process occurred during heavy rain. However, subsequent investigations by the FAA included testing fuel samples taken from both the aircraft's supply and the fueling equipment used during the stop. These tests confirmed that the fuel was clean and contained no contaminants. No mechanical issues were reported by the pilot prior to the onset of the engine roughness.