Incident Overview
A passenger flight encountered turbulence during cruise, resulting in an injury to a flight attendant. The captain reported that after takeoff, he waited until reaching FL370 and passing beyond a line of weather before turning off the seat belt light. The flight was smooth for 10 to 15 minutes, with intermittent cirrus clouds, and weather radar scans from 160 to 40 miles showed no weather.
Crew Accounts
The captain stated that about 10 to 15 minutes after level-off, the aircraft experienced moderate turbulence for 10 to 15 seconds. He immediately made an announcement for flight attendants and passengers to sit. Shortly thereafter, he was informed a flight attendant had been injured.
The first officer said that during climb, the aircraft easily transited between two cells into clear skies and smooth air. After the seat belt sign was turned off, the captain continued scanning with weather radar. The first officer noted intermittent high cirrus clouds but no weather that would pose problems. About 10 to 15 minutes after level-off, the aircraft encountered what he called severe turbulence, tossing both pilots in their seats. They were initially unable to grab the flight controls or turn on the seat belt sign. After the initial bump, the first officer grabbed the controls and followed through with thrust levers and yoke. The captain then turned on the seat belt sign and made an announcement for everyone to sit down. Soon after, a flight attendant asked for a doctor.
Flight Attendant Statements
All flight attendants provided consistent statements affirming that turbulence occurred and that the seat belt sign was not lit during the turbulence prior to the accident.
NTSB Investigation
The NTSB conducted studies of the aircraft's Digital Flight Data Recorder (DFDR) and weather around the time of the accident. Examination of the DFDR revealed information affirming that the autopilot was engaged and consistent with a turbulence encounter. The weather study examined multiple weather products and provided data consistent with convectively induced turbulence in the vicinity of strong to severe thunderstorms.