What happened
On January 22, 2006, All Nippon Airways Flight 589, a Boeing 767-300 registered as JA8669, was performing a scheduled service from Tokyo International Airport to Matsuyama Airport. During the descent phase, the aircraft encountered unexpected atmospheric disturbances.
As the flight progressed through its descent, the aircraft began experiencing light vibrations at approximately 8,000 feet. While the flight crew had received weather updates via ACARS suggesting calm conditions up to 20,000 feet, the aircraft continued to descend toward 2,600 feet. At approximately 13:54 JST, while the aircraft was executing a left turn near Nakajima Island at an altitude of roughly 800 meters, it encountered a sudden and significant bout of turbulence. The force of the movement was sufficient to cause two cabin attendants in the aft galley to lose their footing and fall, resulting in one serious injury and one slight injury. The aircraft subsequently landed safely at Matsuyama Airport at 14:00.
The investigation
The investigation focused on the meteorological conditions and the flight crew's response to the changing environment. Investigators analyzed digital flight data recorder (DFDR) data, which revealed that the aircraft experienced peak vertical and lateral accelerations during the turn. The investigation also reviewed the weather reports provided to the crew via the company's automated systems, which had indicated stable air at higher altitudes.
Findings
- The turbulence encountered was identified as clear air turbulence, as no clouds were present along the flight path.
- While upper-level winds were stable, an increase in the strength of the westerly wind in the lower atmosphere created localized instability.
- The flight crew had performed standard safety checks and initiated the seatbelt sign at 10,000 feet, as the initial vibrations were perceived as light and not a reason to suspend cabin services.
- The simultaneous occurrence of lateral and vertical accelerations during the aircraft's bank angle of approximately 27 degrees created the forces necessary to displace the crew members in the aft section of the cabin.