NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The private pilot reported that, during the climb-to-cruise portion of the cross-country interisland flight over open ocean water, the engine began to run roughly. The pilot applied carburetor heat, which resolved the engine roughness. The pilot decided to continue his flight. As the flight approached his destination, the engine began running roughly again, accompanied by a significant loss of engine rpm. The pilot applied carburetor heat and adjusted the mixture, but the engine power was not restored. He then ditched the airplane into the water just offshore of the island.The airplane wreckage was recovered from the water 3 days after the accident, and it had sustained significant damage from tidal forces. Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.Weather conditions in the area at the time of the accident were conducive to the formation of carburetor icing at glide and cruise power and serious carburetor icing at glide power. If the pilot had either kept the carburetor heat on or applied it earlier, the loss of engine power and subsequent ditching could have been avoided.