Background
On January 7, 2023, a Boeing 737-800 operated by Japan Airlines Co., Ltd. (registration JA307J) was operating as scheduled Flight 687 from Tokyo International Airport to Miyazaki Airport. The aircraft experienced shaking during approach, resulting in an injury to one passenger.
Incident Details
According to the Japan Transport Safety Board (JTSB) investigation, the aircraft encountered cumulus clouds during descent. The pilot in command had earlier obtained information about turbulence encountered by other aircraft in clouds and turned on the seat belt sign as a precaution. Cabin crew conducted a safety check and reported all passengers were seated and belted.
At approximately 09:51 JST, while skimming the cloud top at about 11,000 ft, the aircraft was suddenly and strongly shaken. The shaking continued intermittently while flying through clouds and subsided after exiting. The aircraft landed at Miyazaki Airport at 10:04.
A passenger seated at 39H (the rearmost aisle seat) felt pain in the left side after being thrown against the armrest. The passenger did not report the pain immediately but later sought medical attention and was diagnosed with fractures of the left eighth and ninth ribs.
Analysis
The JTSB analysis determined that a significant yawing of the aircraft occurred when it skimmed the cumulus cloud top. The heading momentarily changed 4° to the left, and lateral acceleration fluctuated between 0.27G right and 0.20G left. The tail rotated 4° to the right around the center of gravity, generating lateral acceleration near seat 39H.
The seated passenger's upper body was likely swung to the left due to inertial forces from the translational movement and yawing, causing the left side to strike the armrest. The armrest, approximately 20 cm above the seat surface, is made of metal with a plastic cover.
Probable Cause
The JTSB concluded that the probable cause was that the left side of the passenger most likely hit hard against the armrest, resulting in injury as the upper body was swung to the left because lateral acceleration changed due to translational movement and yawing when the aircraft skimmed cumulus clouds after the seat belt sign was turned on.
Safety Actions
Following the accident, Japan Airlines disseminated the accident overview to all employees and shared the case in safety meetings. The company also reinforced safety actions to prevent injuries from shaking during flights.