What happened
On March 2, 2023, at approximately 10:41 JST, a Eurocopter EC 135 T2, registration JA37NH, operated by All Nippon Helicopter Co. Ltd., was performing a news coverage mission near Okayama Airport. After completing aerial filming of Okayama City, the crew began air-taxiing toward No.1 Spot at the airport for refueling.
As the helicopter approached the apron, the pilot encountered significant turbulence. Strong crosswinds and complex airflow patterns caused by nearby structures, including the control tower and a parking lot, led to erratic altitude changes and instability. To avoid the most dangerous conditions, the pilot attempted to land approximately 20 meters short of the intended spot. During the descent, the aircraft experienced multiple unstable pitch movements. The pilot reported a series of impacts, described as "boom, boom," where the aircraft's pitch attitude fluctuated sharply.
Following a third significant downward pitch, the helicopter lifted off momentarily and immediately began a rapid rotation to the right. The aircraft completed approximately 540 degrees of rotation before making a hard landing on the apron. The impact triggered the emergency locator transmitter (ELT) and caused substantial damage to the airframe, including a buckled left aft frame, broken fuselage sections, and damage to the tail bumper and vertical stabilizer. One passenger sustained a minor injury.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation with assistance from representatives of Germany and France. Investigators analyzed airport surveillance footage, which captured the sequence of the aircraft's pitch instability and the subsequent rightward rotation. The investigation also utilized Flight Full Simulator (FFS) verification and Advanced Helicopter Dynamics (AHD) simulations to model the aircraft's behavior.
Investigators focused on two primary phenomena: Collective Pitch Change (A-PC), also known as collective bounce, and Loss of Tail Rotor Effectiveness (LTE). The analysis examined how the pilot's physical response to the aircraft's pitching—specifically the movement of the upper body—might have inadvertently altered the collective pitch lever. Furthermore, the investigation explored whether the sudden rotation was caused by the aircraft encountering LTE due to specific wind conditions or if the pilot inadvertently applied the right pedal during the period of high lateral acceleration.
Findings
- The primary cause of the accident was the unstable pitch attitude during landing, which led to a hard landing and a rightward rotation.
- The aircraft lifted off unexpectedly because turbulence-induced instability caused the pilot's upper body to move, inadvertently inducing a collective pitch change (A-PC).
- The sudden right rotation was likely caused by the helicopter encountering Loss of Tail Rotor Effectiveness (LTE), though the possibility of inadvertent right pedal input during the high-G rotation could not be ruled out.
- The mechanic on board demonstrated effective crew resource management (CRM) by monitoring engine instruments and advising the pilot on engine shutdown procedures following the impact.