What happened
On October 2, 2008, China Airlines flight CI 641, a B747-400 with registration B-18202, was operating a scheduled passenger service from Taoyuan International Airport via Hong Kong to Bangkok International Airport. The flight was cruising at 40,000 feet under generally good weather conditions.
While approaching Bangkok, the aircraft was cleared by Thai Air Traffic Control to proceed directly to the CAROS waypoint. At the time, a large cumulonimbus (CB) cloud with a diameter of nearly 10 nautical miles was visible on the radar, with tops exceeding 40,000 feet. Although the flight crew initially believed their heading would allow them to bypass the cell, a subsequent ATC instruction required a left turn to a heading of 210 degrees. This change in course brought the aircraft closer to the convective activity.
To avoid the cell, the crew transitioned from autopilot to manual flight to execute a steeper turn toward heading 190. Shortly after returning to autopilot, the aircraft encountered unstable air. Flight data recorder analysis confirmed vertical accelerations reaching -0.866g and 1.663g during a period of turbulence lasting approximately seven seconds. The turbulence resulted in 29 passengers and 11 cabin crew members being injured, with some requiring hospital treatment upon landing in Bangkok.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the flight data, radar imagery, and interviews with the flight and cabin crews. The investigation focused on the aircraft's proximity to the cumulonimbus cloud, the effectiveness of the crew's avoidance maneuvers, and the safety protocols followed during the event. The investigation also reviewed the accuracy of injury reporting and the medical response provided by the cabin crew.
Findings
- The aircraft failed to maintain an adequate safety distance from the cumulonimbus cloud, leading to the encounter with severe turbulence.
- Several injuries to passengers and crew were likely caused by unfastened seatbelts during the turbulence.
- There were deficiencies in the airline's standard operating procedures, specifically regarding the methods for notifying cabin crew when turbulence has subsided and the protocols for managing mass casualty situations.
- The cabin crew's injury statistics were difficult to verify immediately due to inconsistent reporting methods and a lack of systematic coordination by the cabin supervisor.
- Some crew members demonstrated insufficient familiarity with the use of medical kits and the proper handling of biohazardous materials (such as blood-stained items).