Incident Overview
A flight attendant in the aft galley suffered serious injuries, and four other individuals aboard an air carrier flight received minor injuries after the aircraft encountered moderate to severe clear air turbulence while cruising at flight level 310 (FL310, 31,000 feet). The turbulence was associated with mountain wave activity, which had been forecast between FL310 and FL390 (39,000 feet).
Sequence of Events
Approximately 30 minutes before the turbulence was encountered, the company flight dispatcher communicated to the flight crew that the flight was approaching the forecast area of moderate to severe turbulence. The dispatcher recommended that the flight alter course and descend to FL280 (28,000 feet). Eighteen minutes later, the pilot requested a ride report at FL310 from air traffic control and was informed to expect occasional light chop, with nothing severe. Based on this information, the pilot remained at FL310 and continued on the existing routing. As the flight approached the forecast turbulence area, the pilot illuminated the seat belt sign and advised passengers of the potential for turbulence. He also instructed the flight attendants to stow galley equipment.
Turbulence Details
Approximately 3 to 4 minutes after the advisory, the flight encountered turbulence. The digital flight data recorder recorded three vertical acceleration excursions ranging from 1.449 g's to -0.379 g's over a 16-second period. The injured flight attendant was one of two working in the aft galley. The other flight attendant reported that when the turbulence began, they were jolted several times, during which her feet left the floor. After the initial jolts, the turbulence subsided momentarily. They scrambled toward their jumpseats but then encountered additional, more severe turbulence, making it impossible to maintain their grip. The flight attendant recalled being thrown about the galley, hitting the ceiling, counters, and doors before being slammed to the floor.
Injuries and Aftermath
Upon cessation of the turbulence, the flight descended to FL280 and continued to its intended destination without further incident. One flight attendant sustained serious injuries, and four others aboard the flight received minor injuries.