B738, en-route, east northeast of Miyazaki Japan, 2023
B738, en-route, east northeast of Miyazaki Japan, 2023
On 7 January 2023, a fully secured passenger on a Boeing 737-800 very close to active convective cloud it was about to enter was forced against the arm rest of their seat during a momentary encounter with strong turbulence. Although feeling pain on the side of their body involved, they did not consider it indicated a significant consequence but when the pain subsequently continued, they sought a medical assessment which found two broken lower ribs at the impact site and attributed this serious injury to a change in lateral acceleration due to translational movement and yawing of the aircraft.
Description
On 7 January 2023, a Boeing 737-800 (JA307J) being operated by Japan Airlines on a scheduled domestic passenger flight from Tokyo Haneda to Miyazaki as JL687 encountered turbulence as the aircraft “just skimmed the top of” convectively active cumulus cloud during its descent in day IMC. A passenger who had secured their seat belt was thrown against the side of their seat and, although unaware at the time, this passenger was subsequently found to have sustained a serious injury as a result of the arm rest impact.
Investigation
After delayed notification because of the delayed recognition of the injury, the Japan Transport Safety Board (JTSB) began an Accident Investigation on 23 January. Recorded data from the FDR were downloaded and included useful information. Relevant meteorological data were also available. It was noted that the 51 year-old Captain, who was acting as PF for the accident flight, had a total of 12,373 hours flying experience including 1,450 hours on type. The 44 year-old First Officer had a total of 7,125 hours flying experience including 738 hours on type.
What Happened
Prior to beginning descent, a check of the destination weather led to receipt of information that other aircraft also inbound to Miyazaki had encountered in-cloud turbulence during the descent, so the Captain decided he would turn on the seat-belt signs earlier than usual in the descent as a precaution.
A satellite picture of the en-route cloud where the turbulence occurred. [Reproduced from the Official Report]
Once the descent had begun, the Captain reported having recognised visually scattered but spreading cumulus clouds with a top height of about 10,000 feet with neither space to avoid them nor echo images confirming their likely level of intensity on the airborne weather radar. He decided it would be reasonable to descend though the “thin cloud area” and so had turned on the seat belt sign and asked the cabin crew to check compliance with belt wearing and that any reclined seats and released seat back tables had been returned to their original position. The SCCM subsequently reported to the Captain that all the passengers and cabin crew were secured in their seats before any turbulence was encountered.
The aircraft continued to descend and as it was “closely skimming” the active cumulus cloud tops at around 11,000 feet a sudden onset and brief encounter with “strong turbulence” occurred. This did not last but less significant turbulence continued intermittently until the aircraft emerged from the cloud. The brief and sudden initial encounter with strong turbulence resulted in a passenger seated in Seat 39H (see the first illustration below) feeling pain on their left side as it hit hard against the armrest of the seat but did not perceive a serious injury and therefore disembarked from the aircraft on arrival at Miyazaki without reporting their experience.
However, when the pain the continued, the passenger consulted a doctor and was diagnosed with fractures of the left side eighth and ninth ribs. The second dual illustration below shows the location of the injured passenger’s broken bones and left hand side of the seat in which they were sitting.
The aircraft seating arrangement showing the seat occupied by the injured passenger (39H). [Reproduced from the Official Report]
The location of the two broken ribs. [Reproduced from the Official Report]
Seat 39H showing the armrest impacted. [Reproduced from the Official Report]
Why It Happened
The turbulence which led to the injury was identified by reference to QAR data which is reproduced in graphical form below. This data shows that in one second from 09:50:55 to 09:50:56, the heading of the aircraft suddenly changed by 4° to the left and that for two seconds from 09:50:55 to 09:50:57, the lateral acceleration fluctuated between 0.27g to the right and 0.20g to the left. It was concluded that “when the heading changed momentarily by 4° to the left, in addition to a change in lateral acceleration due to translational movement oscillating from side to side, the tail of the aircraft would have rotated (about a notional vertical axis) 4° to the right around the centre of gravity”. This sudden yaw would have been felt most abruptly at the rear of the aircraft where Seat 39H was located causing the passenger who was injured to involuntarily react to the rightward lateral acceleration by the upper body swinging to the left against the arm rest.
QAR data with the highlighted column indicating the effect of the sudden turbulence on the aircraft. [Reproduced from the Official Report]
The Probable Cause of the Accident was formally recorded as “the left side of the passenger most likely hit hard against the armrest of the seat, resulting in injury as the upper body of the passenger was swung to the left because the lateral acceleration changed due to the translational movement and yawing of the aircraft when the aircraft skimmed the cumulus clouds after the seat belt signs were turned on”.
Safety Action taken by Japan Airlines as a result of the occurrence was noted as:
- Making an overview of the accident known to all employees and in order to allow them to refer to each safety action, the accident case was shared in safety meetings in each internal department.
- As part of a variety of safety activities that the company carries out, it again disseminated thoroughly each safety action to prevent injuries involving turbulence.
The Final Report was adopted by the JTSB on 10 November 2023 and then published simultaneously in both the definitive Japanese language version and in an English language translation on 30 November 2023. No Safety Recommendations were made.