What happened
On December 31, 2013, a Robinson R44II helicopter, registration JA106Y, operated by ILAS Air Service Co., Ltd., was conducting local sightseeing flights near Kouri Island in Okinawa Prefecture. After completing several morning flights, the aircraft departed for a counter-clockwise tour of the island.
During the flight, the pilot decided to deviate from the original plan to provide a special service for the passengers, intending to fly low near the Kouri Bridge. As the aircraft approached the bridge, it was descending at approximately 120 knots. To observe the bridge girders closely, the pilot descended toward the sea surface. While the pilot increased the collective pitch to initiate a climb, they did not pull back the cyclic pitch lever due to a fear of the tail rotor striking the water. The helicopter subsequently struck the sea surface near the bridge, causing the aircraft to break apart. The captain and two passengers all sustained serious injuries. The occupants were eventually rescued by a local fisherman using a boat.
The investigation
The investigation examined the aircraft's condition, the environmental factors, and the operational procedures of the company. Investigators found that the engine was still operating at the time of impact, as evidenced by the main rotor blades striking the water and wrapping around the mast.
Analysis of the sea conditions revealed that the water was calm and highly transparent, making it extremely difficult to distinguish the sea surface from the seabed. Furthermore, the investigation found that the aircraft was not equipped with a lifeboat, which is required for single-engine helicopters operating over water beyond the reach of an emergency landing site. The investigation also noted that the company lacked Standard Operating Procedures (SOPs) for specific flight tasks, leaving much of the flight execution to the pilot's discretion.
Findings
- The primary cause of the accident was that the helicopter descended at an excessive speed and descent rate while approaching the sea surface.
- The pilot misjudged the aircraft's altitude due to the difficulty of depth perception over the calm, transparent water.
- The pilot delayed the necessary transition from a descent to a climb.
- The pilot's actions lacked sufficient safety considerations, specifically regarding the maintenance of minimum safety altitudes and the risks of low-altitude maneuvers.
- The lack of established SOPs allowed for unsafe flight maneuvers to occur without oversight.