Japan's Defense Ministry said Tuesday crew failing to keep a lookout was among the causes for two Maritime Self-Defense Force helicopters colliding in April over the Pacific in an incident that claimed the lives of all eight personnel aboard.
The two SH-60K choppers may have mistaken the distance between them and taken no maneuvers to avoid contact until they collided during a night drill to detect submarines, according to the investigation results released by the ministry.
Each of the helicopters was under the control of a ship-based officer giving instructions, and poor communication between the two officers in charge was also a factor in the collision, it said, noting they failed to take preventive steps such as ordering the choppers to fly at different altitudes.
As measures to prevent such incidents occurring in the future, the ministry will consider installing proximity warning devices, ensuring crew maintain a proper lookout, and requiring officers in charge to communicate adequately and keep the choppers at separate altitudes when necessary, it said.
"Taking the investigation results seriously, we will make every possible effort to take countermeasures, with a determination not to cause any single casualty," Defense Minister Minoru Kihara told a press conference.
Drills involving multiple SH-60Ks are allowed from Tuesday. Since early May, operations had been restricted to flights by single helicopters.
The two choppers, each carrying four MSDF members, collided on April 20 when conducting the exercise above waters around 270 kilometers east of Torishima Island, about 600 km south of Tokyo, in the Izu island chain, with the water's depth at about 5,500 meters.
The two aircraft were moving to the same target spot to drop sonar devices into the water to detect a submarine.
One of the eight crew members was confirmed dead the following day. Last month, the SDF declared the seven missing crewmen dead, while continuing its search efforts for their bodies and the fuselages of the crashed helicopters.
Flight recorder data indicated no abnormalities in either of the choppers, according to the ministry.
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