Description

On 28 May 2021, a Boeing 767-300 (HL7528) being operated by Asiana Airlines on a scheduled domestic passenger flight from Seoul Gimpo to Jeju as OZ8913 encountered turbulence during the climb and a member of the cabin crew, who had released their safety harness to deal with a passenger in the adjacent toilet who had not responded to an instruction to return to their seat when the seat belt signs were on, was seriously injured when severe turbulence occurred.

Investigation

A Serious Incident Investigation was carried out by the Korean Aviation and Railway Accident Investigation Board (ARAIB) based on relevant data from the FDR but relevant data on the CVR was overwritten when it was not isolated after the occurrence. Recorded communications between the flight crew and the airline’s OCC (Operations Control Centre) and relevant actual and forecast meteorological data were available.

The 47 year-old Captain had a total of 7,810 hours flying experience including 3,535 hours on type of which 1,034 hours were in command. He had been employed by the airline for over 10 years and had been command-qualified on type for just over two years. The 30 year-old First Officer had a total of 1,707 hours flying experience of which 1,406 hours were on type and had been employed by the airline for four years.

The seriously injured cabin crew had been employed as such at the airline for over 20 years.

What Happened

The significant weather forecast chart available prior to departure showed that most if not all of the flight above 10,000 feet would be with an area covering much of the country in which isolated embedded CB cloud was forecast and through which an easterly Jet Stream was expected to be present at FL 240. The Captain therefore briefed all crew members about the likelihood of en route turbulence. On departure, the flight was cleared to climb to FL160 and the Captain concluded that the risk of turbulence would continue above 10,000 feet and advised the Purser by interphone that he intended to keep the seatbelt signs on.

On reaching FL160, conditions had briefly improved but on seeing significant radar returns both ahead and on either side of the current track, the Captain decided to maintain the track and request further climb which resulted in a clearance to climb to FL 280. Because he was expecting further significant turbulence as cloud was again entered during the resumed climb, the Captain then cycled the seatbelt signs twice (a standard company procedure) to alert the cabin crew to the possibility of severe as well as moderate turbulence and to remind passengers to keep their seat belts on. He followed this action immediately with a corresponding cabin announcement before beginning the climb.  

Earlier, whilst the aircraft had been climbing through about 10,000 feet, a male passenger had asked one of the cabin crew if he could use the toilet and this had been permitted with a caution that turbulence may occur. However, when this passenger had still not come out of the toilet after about five minutes, one of the cabin crew who was fully secured in her crew seat close to the occupied toilet asked the passenger to return to his seat whilst remaining seated. When she got no response, she was concerned about the passenger’s safety and released her harness to stand up just as the Captain cycled the seat belt sign and began his announcement. She subsequently lost her balance in the turbulence which followed almost immediately and tried to kneel down in accordance with the airline’s turbulence procedure but sprained her left ankle before being thrown up by one more severe turbulence jolt after which her ankle bore the weight as she fell back onto the floor. The injury was so painful that she was unable to move and complained of severe pain when the Purser came to check her condition.

The Captain was immediately notified and contacted the company office at Jeju to arrange for emergency medical service and a replacement crew member. The turbulence continued until landing about half an hour later and the injured cabin crew later stated that this had aggravated the pain from the injury.

FDR data showed that the significant turbulence which led to the injury had begun three minutes after the Captain had proactively warned of the likelihood of significant turbulence before beginning the climb from FL160. As the aircraft passed a recorded 16,736 feet (and according to the Captain had been about to re-enter cloud), turbulence began during which vertical acceleration varied between +1.86g and +0.50 g with the peak positive ‘g’ occurring after an instantaneous increase in climb rate from around 3,000 fpm to a maximum 5,100 fpm. The AP had remained engaged and FDR data showed “no notable change in OAT [Outside Air Temperature], wind velocity or angle of attack”. Once the aircraft had climbed through the severe turbulence zone and was clear of cloud, the fight path soon stabilised. The FDR trace highlighting the time of the injury event is shown below.

The FDR data for five minutes either side of the injury event. [Reproduced from the Official Report]

When the flight arrived at Jeju, the injured cabin crew member was taken to hospital where “multiple fractures of the ankle” requiring surgery were confirmed. As she wanted to have a treatment from nearer her home in Seoul, she was stabilised and then flew back to Seoul on a later company flight. She subsequently had surgery requiring eight weeks of medical treatment.  

Why It Happened

It was found that the Captain had complied with the airline’s ‘Flight Crew Turbulence Response Procedure’ in respect of communication with cabin crew and passengers. However, at a time when other aircraft in the same area were requesting lateral track changes to reduce turbulence risk, the accident aircraft turbulence avoidance action did not include such action and it was considered that the Captain “possibly demonstrated a lack of effort to avoid turbulence except by requesting to climb to a higher altitude”.

The appropriate procedures for turbulence appeared to have been followed by the cabin crew team on board including the injured person, although it was not possible to ascertain exactly how long she had been out of her seat in the period just before and just after the Captain cycled the seat belt signs and made his cabin announcement about the risk of severe turbulence.

The Cause of the Serious Incident was formally documented as “the aircraft encountered turbulence during its climb on the planned route”.

Two Contributory Factors were also identified as:

1. The pilot’s lack of effort to avoid turbulence. 
2. The injured cabin crew member’s lack of self protection when turbulence was encountered.

Two Safety Recommendations were made as a result of the Findings of the Investigation as follows:

• that Asiana Airlines provides refresher training for all flight crew members to avoid turbulence for occupants’ safety and implement enhanced actions to appropriately respond to turbulence. [AAR2102-1]
• that Asiana Airlines establishes safety measures to prevent similar occurrences including cabin crew injuries when encountering in-flight turbulence. [AIR2102-2]

The Final Report was completed on 28 November 2022 and subsequently released in an English language translation on 1 May 2023.

Related Articles

• Turbulence
• Weather Radar
• Weather Radar: Storm Avoidance
• Cumulonimbus (Cb)
• Weather Forecast
• Serious Injury
• In-flight Seat Belt Requirements