What happened
Approximately one minute after takeoff, while the aircraft was climbing between 400 and 500 feet above mean sea level, the crew initiated the first power reduction. During this phase, the right engine backfired. This was followed by increasingly violent backfires that caused the engine RPM to drop to zero. The pilot attempted to restart the right engine, but the same failure pattern recurred immediately.
With the engine unresponsive, the pilot tried to feather the right propeller to reduce drag, but this action was unsuccessful. Faced with a complete loss of power on one side and an inability to secure the propeller, the pilot made the decision to deliberately ditch the aircraft. The maneuver was executed to avoid colliding with an outcropping of lava visible in the vicinity. The aircraft settled into approximately 25 to 30 feet of water and came to rest.
The investigation
Post-accident inspection of the engine revealed a critical mechanical failure. The shaft for the exhaust rocker arm on cylinder #2, part number 45937, was found to be missing from its assembly. A continuity check of the drive train confirmed that all other components remained intact, with the sole exception of the #2 exhaust valve.
The investigation also noted a design limitation regarding the propeller system. Centrifugal stops are built into the mechanism to prevent feathering when the engine speed falls below 500 RPM. This feature likely contributed to the pilot's inability to feather the propeller after the RPM dropped to zero, as the engine had already stalled below that threshold.
Findings
The primary mechanical cause was the loss of the exhaust rocker arm shaft on cylinder #2. The subsequent failure of the drive train continuity at the exhaust valve prevented normal operation. The inability to feather the propeller was a direct result of the engine speed dropping below the operational limit for the centrifugal stops, leaving the aircraft with significant drag and no power on the right side.