The National Transportation Safety Board has determined carburetor icing as the cause of engine power loss during a May 2016 interisland flight in which the pilot of a Beachcraft Sundowner was forced to ditch his plane into the ocean off Makaha.

The final report, recently released by the NTSB, also said the pilot’s delay to apply carburetor heat during the flight to Oahu from Kauai “while operating in an area conducive to carburetor icing” was a contributing factor.

On May 23, Eric Kawamoto and his wife, Leslie, were heading back to Oahu after attending a friend’s wedding on Kauai when the engine began to run rough during the climb-to-cruise portion of the flight.

Kawamoto applied carburetor heat, which resolved the roughness, and he continued with the flight, climbing to 5,500 feet.

As the plane approached Oahu, the NTSB report said, the engine began to run rough again, and there was a significant loss of engine revolutions per minute. “The pilot applied carburetor heat and adjusted the mixture, but the engine power was not restored.”

Kawamoto, a Navy electrical engineer who has about 10 years of experience flying single-engine planes, initiated a forced landing into the ocean, approximately 50 to 75 feet off Makaha.

The couple got out of the plane and started swimming while wearing life vests. Lifeguards spotted the plane’s tail protruding from the water’s surface and rescued the Kawamotos, who sustained minor injuries in the forced landing.

The NTSB report said weather conditions 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,” adding, “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.”

NTSB report on 2016 Makaha plane crash by Honolulu Star-Advertiser on Scribd