By Toshi Aoki
The Japanese AH-64 attack helicopter that crashed into a home north of Nagasaki in February was brought down by a damaged main rotor-head bolt.
Both pilots aboard the aircraft died Feb. 5 when the Boeing AH-64D crashed into a private home in a residential area of Kanzaki, Saga Prefecture. An 11-year-old girl who lived in the house escaped with injuries, according to Japan's Asahi Shinbun. The newspaper originally reported the results of a report by the Japanese defense ministry published May 28.
A bolt in the main rotor head was damaged several seconds before the crash, according to the Japanese defense ministry’s report. One of the four main rotor blades then separated from the rotor head, resulting in a catastrophic loss of lift, according to the report.
A second rotor broke from the main hub and smashed into the cockpit before the aircraft spiraled to the earth. The report diagnoses a failure to the “cylindrical precipitation hardening stainless steel bolt,” which is about two and a half inches long and a third of an inch thick, according to the report. Investigators found a 6-mm crack in the middle of the bolt.
The Japanese government keeps the same rotor head as a spare part for its Apache fleet and has decided to keep all 12 of its AH-64Ds grounded until it has completed preventive maintenance to avoid similar future mishaps.
Flight recorder data shows no abnormality in the operation of the aircraft, nor does the voice recording taken for about five seconds before the data ended, according to the report.
Neither pilot error nor lax maintenance caused the crash, according to the report.