A320, en-route, near Okayama Japan, 2022
A320, en-route, near Okayama Japan, 2022
Summary
On 16 January 2022, an Airbus A320 in cruise unexpectedly and very briefly encountered light clear air turbulence. Despite being secured in a seat, one passenger sustained a serious injury not assessed as such by the passenger or the cabin crew at the time, but which subsequently resulted in hospitalisation with a broken rib. The minor turbulence encountered had included a lateral movement which caused firm impact with the seat armrest. The operators’ response included amending the safety briefing and related procedures and introducing a new video on turbulence awareness to be shown immediately after the briefing.
Flight Details
Aircraft
Type of Flight
Public Transport (Passenger)
Flight Origin
Intended Destination
Take-off Commenced
Yes
Flight Airborne
Yes
Flight Completed
Yes
Phase of Flight
Cruise
Location
Approx.
near Okayama
General
Tag(s)
CVR overwritten
WX
Tag(s)
CAT encounter
CS
Tag(s)
Pax Turbulence Injury - Seat Belt Signs off
Outcome
Damage or injury
No
Non-aircraft damage
No
Non-occupant Casualties
No
Occupant Injuries
Few occupants
Off Airport Landing
No
Ditching
No
Safety Recommendation(s)
Group(s)
None Made
Investigation Type
Type
Independent
Description
On 16 January 2022, an Airbus A320 (JA24MC) operated by StarFlyer on a scheduled domestic passenger flight from Tokyo Haneda to Kitakyushu, Japan, as 7G87 was in cruise at FL280 in night VMC. The aircraft suddenly encountered a short period of light turbulence, which had a significant lateral component and caused a secured passenger to move sharply sideways against a seat armrest. Bruising was suspected, but the passenger was not concerned. No other passengers were affected, and crew members active in the passenger cabin at the time all subsequently reported having regarded the event as insignificant on the turbulence encounter scale.
Investigation
On becoming aware of the serious nature of the injury on 4 February, an Accident Investigation was commenced by the Japan Transport Safety Board (JTSB). Both CVR and FDR data had been overwritten, but relevant QAR data was available as were relevant ATC radar and communications and meteorological data.
It was noted that the 47-year-old captain, who was designated PM for the sector but had temporarily taken over as PF when the turbulence occurred as the first officer was taking a toilet break, had a total of 11,349 hours flying experience including 6,102 hours on type. The 31-year-old first officer had a total of 2,663 hours flying experience, all except 282 hours of which were on type.
What Happened
The same two pilots had earlier operated a scheduled passenger flight into Haneda from Kitakyushu, cruising higher than usual at FL390. They had discussed the risk of encountering Jet Stream-source CAT on both the outbound and return sectors with the Dispatcher, since this altitude would keep them clear of the jet axis located at around FL320. On this basis, their return flight plan had been filed with FL380 as the provisional cruise level with a review on reaching Tokyo. This was because although the headwind would probably be strong, the airflow would be stable. However, it was decided that the final return cruising altitude would be decided once the latest weather information was available.
On the gate at Tokyo, the pilots were provided with updated weather information and learned that an earlier departure on the same route had used FL300 for the cruise and experienced only brief exposure to "light-minus" turbulence, a term which in Japanese use means “a level of turbulence which allows in-flight service without difficulty." As they had also not encountered any turbulence when descending through their usual FL280 cruise level, they decided to use this normal cruise for their return flight. When providing a pre-flight briefing to the SCCM, the first officer “told them that the seat belt sign would be turned off 10 minutes after the takeoff, after that, for 30 minutes until reaching the sky above Osaka Prefecture, the airstreams would be good and for 42 minutes after that, some light-minus to light level of turbulence could be expected”. It was noted that the term "light turbulence" in Japanese use means “a level of turbulence that allows in-flight service but requires attention” and the term "light-plus turbulence" means that “extreme caution must be used in providing in-flight service which may need to be temporarily put on hold."
Once the passengers had boarded, the SCCM made a PA to the passengers saying “in the air, turbulence is expected in some areas, please make sure that your seat belt is securely fastened tight and low, thank you". It was noted that the word “low” was not included in the Company’s announcement handbook and had been added by the SCCM based on their experience. The cabin crew carried out their usual pre-takeoff visual check that all passengers had fastened their seat belts and, as per their company procedures, also checked that fastened seat belts “were not twisted or loose”.
Climb to FL280 after departure was uneventful. But as there was light turbulence at that level, a climb to FL300 as cruise level was requested and approved and on reaching this level, it was found that there was no turbulence and the seat belt signs were turned off. The SCCM made a standard announcement that “the seat belt sign has been turned off, however for your safety, please keep your seat belt fastened while seated, thank you." In-flight service was completed and a little later, when light-minus turbulence was encountered, a request to descent to and maintain FL280 was made and approved with no turbulence initially present on reaching that level. The first officer then left the flight deck to use the toilet, and just before doing so, “asked the captain to descend to FL260, which would be less susceptible to jet stream, if there was any turbulence”. One of the cabin crew then entered the flight deck and sat in the supernumerary crew seat to await his return in accordance with company procedures.
Whilst the first officer was absent, turbulence which the captain described as ‘light’ suddenly occurred. Although the turbulence did not worsen, he turned on the seat belt signs and requested and received approval to begin a precautionary descent to FL 260. Turning on the seat belt signs automatically triggered a pre-recorded announcement “ladies and gentlemen, the captain has turned on the seat belt sign. Please return your seats and keep your seat belts fastened while the sign is on, thank you”.
At the time this happened, the passenger who was subsequently found to have sustained the injury was seated in 23A with their seat belt fastened even though the signs had been switched off earlier. They stated that they had “hit their right side against the armrest” and considered that the turbulence had been “lateral rather than vertical” as well as “the greatest the passenger had ever experienced." One of the cabin crew who had been in the vicinity of row 23 at the time reported having also considered that the movement of the aircraft had been lateral rather than vertical. Whilst this short turbulence episode was occurring, another passenger who had been using the toilet returned to their seat in row 26 “with no particular difficulty in walking after the fasten seat belt sign had been turned on." At this time, the first officer was also able to return to the flight deck with ease and without needing to hold on to anything.
The window seat (23A) where the injured passenger was sitting. [Reproduced from the Official Report]
Once at FL260, the fasten seat belt signs were turned off and a routine check of the cabin had “found no particular abnormality." The flight crew advised the company by radio that the turbulence they had encountered at FL280 had been light, and there was no further turbulence. The flight landed at Kitakyushu a little over half an hour later and the cabin crew subsequently observed that they had “felt that there was nothing wrong with the passengers” at disembarkation.
Why it Happened
The context for the injury was evidently the turbulence encountered and the prevailing atmospheric conditions at the time. All relevant meteorological data were obtained and examined in conjunction with QAR data. The latter showed that at the time the light turbulence episode had been reported, vertical acceleration had changed from 0.75g to 1.36g within 26 seconds, as pitch attitude went from +0.4° to +1.8°. Within the same interval, the recorded horizontal acceleration had varied between 0.22g to the left and 0.15g to the right, as the roll angle varied between 7.7° to the left and 3.5° to the right at a roll rate of 4.5°/second.
The general weather situation at the time was slack pressure with a weak cold front paralleling the flight track. A significant weather analysis chart timed shortly after the turbulence encounter (see below) showed there was in area 2 in the chart, an area of potentially moderate CAT and moderate turbulence with vertical windshear between FL300 and FL350 attributed to merging jet stream axes. The Meteorological Office were aware of a PIREP received at the same time as the turbulence event, which reported moderate turbulence at FL 300 approximately 14nm of the accident site.
An extract from the significant weather analysis chart for shortly after the time of the accident. [Reproduced from the Official Report]
The passenger who was injured was 1.56 metres in height and weighted 42 kg. The seat involved was leather-covered with a seat height of 43 cm and an armrest height of 63 cm, and according to the manufacturer of these seats, there had been no report of similar occurrences involving them. The Investigation was not able to estimate the speed at which the passenger had hit their right side against the armrest on that side “because it was unclear how tightly the passenger had fastened their seat belt." It was observed that “in order to prevent horizontal movement of the hips as much as possible, it is important that passengers always fasten the seat belt at a low waist position with no slack while seated." It was considered that this accident had demonstrated that “it is desirable for seat makers to consider the design of seats that accommodate passengers of various body sizes by actively collecting data on similar cases”.
The Probable Cause was formally determined as “when the aircraft encountered clear air turbulence created due to the jet stream, there was a sudden lateral movement to the left, as a consequence of which a passenger hit their right side against the armrest on the right side of the seat, resulting in their serious injury."
Safety Action taken by the aircraft operator as a result of the accident was noted to have included the following:
- issued a Notice to Cabin Crew that they should make announcements including the following contents and revised the announcement handbook accordingly:
- be sure to put the sentence, “keep your seat belt fastened tight and low” when making announcements related to seat belts.
- make an announcement, saying, “for your safety, please keep your seat belt fastened tight and low, when you are seated” when the fasten seat belt sign is off.
- make announcements that are easy for passengers to understand.
- special video on preparing for turbulence was produced and has been shown after the safety video with effect from 1 July 1 2022.
The Final Report was adopted by the JTSB on 26 May 2023 and published on 29 June 2023. No Safety Recommendations were made.
