Japan's Defense Ministry sources have told NHK the two Maritime Self-Defense Force helicopters that crashed on Saturday may have collided before beginning submarine search training.
Two SH-60K patrol helicopters crashed off Torishima Island in the Izu Islands in the Pacific Ocean during nighttime training. One of the eight crewmembers is confirmed dead and the others are missing.
The ministry sources said patrol helicopters use sonar arrays suspended on cables to detect underwater sound waves to search for submarines. The ministry believes the two helicopters had not dropped the sonars into the sea at the time of the accident.
They said sonars are deployed while helicopters are hovering above the sea, but that radar indicated the two helicopters were not doing so.
The MSDF is analyzing the recovered flight recorders, and is searching for the missing seven crewmembers.