What happened
On 1 August 2017, a Singapore Airlines Boeing 777-200, registration 9V-SQN, was en route from Singapore to Bangkok when it encountered moderate to severe turbulence. While the flight crew was attempting to navigate around developing weather, the aircraft passed through the edges of scattered clouds.
At the time of the encounter, a male passenger was walking toward his seat after visiting the lavatory, and several cabin crew members were performing meal services. The sudden turbulence caused the passenger to fall, resulting in a serious injury involving a fractured right foot. Additionally, two cabin crew members sustained serious injuries consisting of hairline heel fractures, while three other cabin crew members suffered minor injuries.
The investigation
The investigation focused on the timing of the fasten seatbelt sign activation and the flight crew's weather avoidance maneuvers. Flight data from the Quick Access Recorder (QAR) confirmed that the pilot flying switched the fasten seatbelt sign to the 'on' position approximately 28 seconds before the turbulence hit. This was supported by the accounts of the injured passenger and the flight crew.
However, the cabin crew members involved did not recall the sign being illuminated or hearing the chime. Investigators noted that the crew may have been too preoccupied with service duties to notice the change, or the suddenness of the impact may have affected their memory. The investigation also examined the flight path, noting that while the crew requested a significant heading change to avoid heavy cumulonimbus clouds, Air Traffic Control could only provide a limited heading change due to heavy traffic in the area.
Findings
- The aircraft encountered turbulence while flying through the edges of scattered clouds.
- The flight crew was unable to achieve a sufficient lateral deviation from the weather because Air Traffic Control could only grant an incremental heading change.
- The fasten seatbelt sign was activated 28 seconds prior to the turbulence, though the cabin crew did not perceive its activation.
- The passenger was injured while walking in the cabin, and the crew members were injured while performing service duties.