Japan’s Transportation Safety Board (JTSB) has concluded that incorrect tail rotor maintenance caused the fatal November 2017 crash of an Airbus Helicopters AS332L Super Puma. All four aboard were killed when the aircraft, operated by Toho Air Service, crashed while attempting to make an emergency landing following detection of abnormal vibration.
During the landing sequence, the tail rotor and tail boom departed the aircraft. The JTSB found that the tail rotor separated because a spindle bolt of its flapping hinge broke, causing it to become unbalanced. The bolt broke because flapping hinge bearing damage was undetected. That damage likely occurred due to incorrect lubrication procedures.
The aircraft's flapping hinge must be greased every 10 flying hours, at every 50- and 250-hour inspection, and daily if it is parked in hot/humid conditions. However, the JTSB found that this was not done while the aircraft was parked in such conditions during the summer of 2017 and that subsequent damage to the outer bearing was not detected and an associated seal was not replaced per the maintenance manual during a 250-hour inspection in September 2017.
Subsequent to the accident, Airbus and EASA mandated inspection of the flapping hinges and replacement of related components on all Airbus AS 332 C, AS 332 C1, AS 332 L, AS 332 L1, and SA 330 J model helicopters.