SAITAMA (Kyodo) Governmental transport safety investigators began working Monday on the fatal crash of a rescue helicopter on a mountain in Chichibu, Saitama Prefecture.

Three officials dispatched by the Japan Transport Safety Board, which operates under the Land, Infrastructure, Transport and Tourism Ministry, inspected Sunday's crash site from the air and interviewed two rescue workers who were on board the chopper but had been lowered to the ground to rescue a climber moments before the crash.

Saitama prefectural officials quoted the two as telling investigators they heard abnormal sounds from the helicopter's engine or rotor after being lowered to the ground, just before the chopper went down at around 11:10 a.m., killing the remaining five people on board.

When the rescue workers were being lowered, the helicopter was hovering roughly 30 meters up and wasn't in danger of making contact with any obstacles, including trees or high-tension lines, officials said.

The chopper, used for disaster prevention, belonged to the Saitama Prefectural Government and was dispatched to rescue a 55-year-old female climber who fell into a waterfall basin on the mountain, according to local officials. The woman was later confirmed dead.

Killed in the crash were the pilot, Akira Matsumoto, 54, copilot Shinichi Nishikawa, 32, prefectural aviation security officers Yoshimasa Nakagomi, 42, and Kenichi Tobari, 32, and local fire department rescue worker Atsushi Osawa, 33.

There was no noticeable rain or wind in the area around Chichibu when the accident took place, although an advisory for heavy rain and lightning had been issued, according to the Kumagaya Local Meteorological Observatory.