What happened
On January 16, 2022, an Airbus A320-214, registration JA24MC, operated by Star Flyer Inc., was performing a scheduled flight from Tokyo International Airport to Kitakyushu Airport. While cruising at FL 280 over Kurashki City, Okayama Prefecture, the aircraft encountered sudden, unexpected turbulence.
Prior to the event, the flight crew had adjusted the cruising altitude to avoid the jet stream's influence, and the seat belt sign had been turned off after a period of smooth flight. During the encounter, the aircraft experienced significant lateral and vertical accelerations. A passenger seated in 23A, who remained buckled in, was shaken toward the right side of the cabin, striking their right side against the seat armrest. The impact resulted in a 9th rib fracture.
The investigation
The Japan Transport Safety Board (JTSB) examined flight data from the Quick Access Recorder (QAR) and analyzed meteorological conditions. The investigation focused on the nature of the turbulence, the movement of the aircraft, and the physical circumstances of the passenger's injury. Investigators reviewed the aircraft's flight path, the stability of the airstream, and the specific seat configuration, noting that the armrest height was approximately 20cm from the seat surface.
Findings
- The turbulence was identified as clear air turbulence likely generated by the jet stream, as no radar echoes or significant cloud formations were present in the area.
- QAR data confirmed that the aircraft experienced vertical acceleration changes between +0.75 G and +1.36 G, alongside lateral accelerations of up to 0.22 G.
- The passenger's injury was caused by the lateral shaking of the aircraft, which moved the passenger's body into the armrest.
- While the passenger was wearing a seat belt, the investigation noted that the effectiveness of the restraint in preventing lateral movement depends on the belt being fastened low and tight against the waist.