What happened
On July 5, 2012, a United Airlines Boeing 777-200, registered N224UA, was operating a scheduled flight from Incheon International Airport to Narita International Airport with 244 passengers and 12 crew members on board. While descending to 23,000 feet, the flight crew identified a small cumulonimbus cloud near the LIVET waypoint. Based on weather radar showing only weak green returns and a low cloud top, the pilots initiated a slight deviation to the left to avoid the cell.
During this maneuver, the aircraft entered the cloud and encountered sudden, moderate turbulence. The aircraft experienced two rapid, heavy jolts over a five-on-second period. In the rear galley, four flight attendants were performing cleaning and final checks. The sudden movement threw the crew members into the air and against the floor. This resulted in one serious injury and three minor injuries among the flight attendants.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, meteorological data, and the aircraft's configuration. Investigators noted that the flight's pre-flight briefing and real-time weather radar did not indicate significant weather or turbulence on the route. The investigation also reviewed the physical layout of the rear galley, noting that it lacked specialized handholds and that the distance between the crew and available fixed objects (such as cart handles) was relatively large.
Findings
- The pilots likely judged that the weather was non-hazardous because the radar showed only weak returns and the cloud tops appeared low.
- The cumulonimbus cloud likely developed rapidly just before the encounter, forcing the aircraft into a turbulent area despite the crew's attempt to deviate.
- Because the pilots did not anticipate significant turbulence, they did not provide specific instructions to the crew or warn the flight attendants of the impending deviation.
- The flight attendants in the rear galley were unable to secure themselves to fixed objects due to the suddenness of the shaking and the lack of specialized handholds in that section of the aircraft.