What happened
On 3 July 2003, a Boeing 777-236, registration G-YMME, was operating a scheduled passenger flight from London to Harare. While navigating near the airway reporting point of Kindu in Central Africa at flight level 370, the aircraft encountered a sudden period of severe turbulence.
At the time of the incident, the commander was on a scheduled rest break in a crew bunk, leaving two first officers operating the flight deck. Although the crew had previously encountered light turbulence an hour earlier, the flight had been smooth, and the weather radar indicated no immediate convective activity. The cabin lights were dimmed for the night, and while most passengers were resting, some cabin crew in the rear galley were preparing breakfast trolleys.
Following a brief positive 'g' movement and a slight airframe shake, the aircraft underwent a sudden, severe downward movement characterized by negative 'g' forces. The flight crew immediately activated the passenger seatbelt signs. The disturbance ended as quickly as it had begun, though the aircraft continued to encounter smaller amounts of clear air turbulence over the following hour.
The investigation
The investigation examined the circumstances surrounding the turbulence and the subsequent injuries. The crew noted that the stars remained visible, suggesting the aircraft had not entered cloud cover. The investigation looked into potential causes, such as wake turbulence from other aircraft or wind shear. However, the Traffic Alert and Collision-Avoidance System (TCAS) showed no other aircraft in the vicinity, and there were no significant changes in temperature or wind speed to suggest wind shear.
Findings
- The investigation established that the most likely cause was turbulence associated with cloud development occurring at a lower altitude than the aircraft's flight path.
- The encounter was consistent with clear air turbulence, as the aircraft remained clear of visible cloud and encountered further minor turbulence later in the flight.
- The incident resulted in one passenger and two cabin crew members sustaining minor injuries. The passenger suffered a head laceration, while the crew members sustained bruising and abrasions after being jolted by the movement along with the catering trolleys.
- The company's policy of advising passengers to keep seatbelts fastened while seated was noted as a significant factor in preventing more serious injuries during the sudden descent.