Accident Overview
On January 10, 2005, a Japan Coast Guard Sikorsky S-76C (registration JA6903) was conducting rescue hoist training with the Japan Coast Guard ship "Yahiko" approximately 9 km southeast of Konosehana, Sado Island, Niigata Prefecture. The aircraft had two pilots, two mechanics, a radio operator, and a diver on board. During the training, the No.1 engine failed, and the helicopter ditched into the sea, subsequently capsizing and sinking.
Flight History
The aircraft departed Niigata Airport at 11:59 local time under visual flight rules, with an estimated endurance of 3 hours 30 minutes. After reaching the training area near the ship, an out-of-ground-effect hover check confirmed good engine condition. Rescue hoist training commenced, with the aircraft hovering at 75–85 feet above the sea surface, heading approximately 270° against a wind of 250° at 15 knots.
Engine Failure and Ditching
About 10 minutes into the training, the captain heard a warning tone and observed a warning light on the instrument panel. The No.1 engine parameter indication dropped to nearly zero, while the No.2 engine parameter showed near maximum. The captain judged the No.1 engine had failed and began a fly-away maneuver from the ship. The hoist cable was severed by a mechanic after a brief delay. The captain determined that the altitude was insufficient to gain airspeed for a conventional flyaway and opted for a level attitude landing. The landing gear was not extended, and the emergency floats were not deployed; the captain noted that the operations manual assigned float deployment to the captain, but he could not reach the switch in time.
Evacuation and Capsizing
Upon ditching, the aircraft banked to the right, and water entered the cabin. The helicopter then capsized, coming to rest inverted. The captain evacuated through the right cockpit door after unbuckling his harness. The copilot struggled to open the left door initially but succeeded as water rose. The mechanics and radio operator escaped via emergency exits; one mechanic used the Spare Air oxygen bottle. The diver reported noticing a loss of engine power before water rushed in. All six crew members evacuated, with one sustaining serious injuries and another minor injuries.
Investigation
The Aircraft and Railway Accidents Investigation Commission (ARAIC) conducted the investigation. An accredited representative from the United States participated. The investigation included interviews with the crew and witnesses, examination of recovered debris, and inspection of the identical aircraft type and the ship. The aircraft was not recovered from the seafloor. The cause of the No.1 engine failure was not determined from the available evidence.