Event Description
Approximately one minute after takeoff, while climbing through 400-500 feet msl and during the first power reduction, the right engine backfired. After several more violent backfires, the engine rpm dropped to zero. The pilot restarted the engine, but the same backfiring and subsequent loss of power recurred. Attempts to feather the right propeller were unsuccessful. To avoid an outcropping of lava, the pilot deliberately ditched the aircraft. The aircraft came to rest in approximately 25-30 feet of water. All 10 occupants were rescued.
Inspection Findings
Post-accident examination of the right engine revealed that the #2 cylinder exhaust rocker arm shaft, part number 45937, was missing. Continuity of the drive train was confirmed except for the #2 exhaust valve. It was also determined that the centrifugal stops prevent propeller feathering when engine speed drops below 500 rpm.
Probable Cause
The official investigation identified the probable cause as a loss of engine power (total) due to a mechanical failure/malfunction, specifically the separation of the exhaust system actuator (exhaust rocker arm shaft). The subsequent ditching was necessitated by the engine failure, and the inability to feather the propeller was a consequence of the low engine speed.