What happened
On April 27, 2011, an All Nippon Airways Boeing 767-300, registered JA8569, was performing a scheduled flight from Miyazaki Airport to Tokyo International Airport. While cruising at approximately 25,000 feet, roughly 27 nautical miles east-southeast of Kushimoto, the aircraft encountered sudden and intense atmospheric disturbances.
The turbulence was characterized by a rapid change in wind velocity and a significant vertical acceleration of -0.34 G. The impact was so violent that one cabin attendant, located near the left aft lavatory, was thrown into the air and fell to the floor, sustaining serious injuries. Additionally, four other individuals, including both passengers and cabin crew, suffered slight injuries as they were tossed by the movement of the aircraft.
The investigation
The Japan Transport Safety Board (JTSB) examined flight data from the Digital Flight Data Recorder (DFDR) and Cock/Cockpit Voice Recorder (CVR), alongside air traffic control communications and crew statements. The investigation focused on the flight's altitude changes, which included a climb to 29,000 feet and a subsequent descent to 25,000 feet, as well as the meteorological conditions present at the time of the encounter.
Investigators analyzed the aircraft's radar performance, noting that the airborne weather radar did not detect any significant cloud echoes at the time of the event. The investigation also reviewed the flight crew's decision-making regarding cruising altitudes and the company's existing safety protocols for turbulence.
Findings
- The primary cause of the injuries was a sudden and severe atmospheric disturbance that physically displaced the cabin attendant and passengers.
- The turbulence was likely a localized instance of Clear Air Turbulence (CAT), potentially generated by wind shear near a frontal zone beneath a jet stream.
- While the crew had implemented precautions by requesting passengers keep seat belts fastened, the suddenness of the event prevented effective bracing for those not in their seats.
- The investigation noted that while some aircraft in the fleet had handrails installed near lavatories, the effectiveness of such measures in preventing injuries during unexpected, high-intensity turbulence remains a point for further evaluation.