What happened
On August 21, 2012, an Asiana Airlines Airbus A330-300, registration HL8258, was operating a scheduled flight from Honolulu to Incheon. While cruising at approximately 40,000 feet over Matsue City, Japan, the aircraft encountered intense atmospheric disturbances. The flight experienced rapid changes in wind direction and speed, accompanied by strong updrafts and significant vertical acceleration, reaching 1.88G.
During the period of instability, the aircraft's speed momentarily exceeded the maximum operating limit, triggering an overspeed warning. The pilot in command disengaged the autopilot to manually stabilize the aircraft, during which time the plane experienced significant pitch and roll oscillations. The turbulence was severe enough to cause physical harm in the cabin: one passenger walking in the rear aisle sustained serious injuries, and a second passenger, who had unbuckled their seatbelt to assist the first, was also seriously injured when a subsequent bout of shaking occurred.
The investigation
The investigation, conducted by the Japan Transport Safety Board, analyzed data from the Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR), alongside interviews with the flight crew and cabin attendants. Investigators examined the aircraft's flight path, weather radar status, and the crew's response to the turbulence. The investigation also involved external analysis of meteorological data to understand the nature of the atmospheric conditions encountered.
Findings
- The primary cause of the passenger injuries was the severe shaking of the aircraft while passengers were not properly restrained.
- The initial encounter with severe turbulence was likely caused by the aircraft passing through or near cumulonimbus clouds, characterized by intense wind shear and updrafts.
- The flight crew failed to notice that the weather radar was turned off, which prevented them from identifying the convective activity ahead.
- Insufficient monitoring of weather conditions and cockpit instruments by the pilot in command and the route captain contributed to the encounter with the unstable air.
- The pilot's manual control inputs following the disengagement of the autopilot may have influenced the secondary period of intense shaking.
Safety action
Following the incident, Asiana Airlines implemented several safety enhancements, including reinforced training for flight crews on turbulence briefings, improved monitoring of real-time weather via ATC and radar, and stricter adherence to seatbelt sign protocols. The airline also emphasized the importance of using standard ICAO terminology, such as "Severe Turbulence," when communicating with Air Traffic Control to ensure accurate information is disseminated to following aircraft.