What happened
On 15 June 2023, a Boeing 777-336ER, registration G-STBL, was operating a passenger flight from Singapore to London. While traversing the Bay of Bengal, the crew encountered severe turbulence. Although the pilots had proactively switched on the seatbelt signs and requested a track deviation to avoid visible thunderstorms, the aircraft experienced a violent 12-second episode. During this event, the aircraft's normal acceleration spiked to 2.3g, and the stall warning was briefly activated. The sudden motion threw unsecured cabin crew members around the cabin, resulting in two serious injuries and three minor injuries. Due to the medical needs of the crew, the aircraft returned to Singapore.
In a separate incident on 28 June 2023, a Boeing 777-236, registration G-YMML, was arriving at Beijing Daxing International Airport. While the crew attempted to manoeuvre around convective weather identified on radar, the aircraft encountered moderate turbulence. The cabin crew, who were in the process of securing the cabin for landing following a standard landing announcement, were unable to remain standing. One crew member fell and sustained an ankle injury that later required surgery.
The investigation
The investigation examined the flight data and meteorological conditions for both events. For G-STBL, investigators found that while the flight briefing had warned of thunderstorms and the crew had noted lightning, the weather radar did not show significant returns immediately prior to the severe event. Satellite imagery later revealed significant updraughts and overshooting cloud tops in the area.
For G-YMML, the investigation noted that the seatbelt signs had been illuminated 25 minutes before landing, which the cabin crew interpreted as a standard procedure for landing preparation rather than a specific warning of imminent turbulence. This led to the crew continuing their duties instead of immediately securing themselves.
Findings
- In both instances, the pilots took active measures to avoid known or suspected convective weather.
- The turbulence encountered by G-STBL was of sufficient severity to cause significant vertical acceleration, reaching 2.3g.
- The primary cause of the injuries was the encounter with turbulence of sufficient severity to displace unsecured cabin crew.
- In the case of G-YMML, the timing of the seatbelt sign illumination contributed to the crew not being fully secured before the onset of the turbulence.