What happened
On February 13, 2013, a Korean Air A330-300, registration HL7710, was operating a scheduled international passenger flight from Incheon International Airport to Tianjin Binhai International Airport. While cruising at 23,600 feet, approximately 187 miles east of Tianjin, the aircraft encountered two instances of clear-air turbulence.
Upon the first encounter of light turbulence, the captain activated the fasten seatbelt sign. Shortly thereafter, the aircraft hit moderate turbulence, prompting the captain to chime the seatbelt sign twice and reduce engine thrust to manage increasing airspeed. The flight crew requested a descent from Dalian Air Traffic Control and successfully lowered the aircraft to 21,65 and feet, where the atmosphere stabilized. While the passengers remained uninjured, the sudden movement caused two flight attendants working in the aft galley to fall, resulting in two serious injuries.
The investigation
The ARAIB examined flight recorder data, including QAR data, and analyzed meteorological reports from the Korea Meteorological Administration, the Korea Aviation Meteorological Agency, and the China Meteorological Center. The investigation reviewed the flight crew's actions, the aircraft's maintenance and weight/balance status, and the cabin crew's activities at the time of the event. The investigation also confirmed that the pilots had conducted a pre-flight briefing regarding potential turbulence due to the jet stream.
Findings
- The aircraft encountered clear-air turbulence that was not detectable via weather radar due to the lack of clouds.
- At the time of the turbulence, the fasten seatbelt sign was turned off, and flight attendants were actively collecting meal trays and preparing duty-free carts.
- The turbulence was caused by fluid vortices occurring in the vicinity of a strong jet stream.
- The flight crew followed established Pilot Operation Manual procedures by reducing airspeed and initiating a descent to find stable air.
- The injuries occurred specifically in the 'C' zone galley when the sudden motion threw the crew members to the floor.