What happened
On February 1, 2020, an Agusta AW139, registration JA139F, was performing a critical mission to transport organs for transplantation. The flight, operated by the Fukushima Prefectural Police Aviation Unit, was traveling from Aizu Chuo Hospital toward Fukushima Airport. While flying over Mihota Town in Koriyama City, the aircraft encountered severe difficulties when the main rotor blades made contact with the tail drive shaft, severing it.
Following the mechanical failure, the crew attempted an emergency landing in a nearby paddy field. However, the loss of control led to a hard landing and a subsequent rollover. Of the seven people on board, including the flight crew and passengers, four sustained serious injuries and three suffered minor injuries. The aircraft was destroyed in the impact, though no fire broke out.
The investigation
The Japan Transport Safety Board (JTSB) conducted an extensive analysis of the flight data, including the Multi-Purpose Flight Recorder (MPFR), to reconstruct the sequence of events. Investigators examined the meteorological conditions, specifically looking for evidence of severe turbulence or sudden changes in wind velocity.
Technical inspections focused on the physical damage to the tail drive shaft and the contact marks left by the main rotor blades. The investigation also utilized Full Flight Simulators (FFS) to verify how the aircraft responded to rapid increases in airspeed and the effects of sudden downdrafts on flight stability and control.