What happened
During the flight, the aircraft experienced turbulence while operating in the vicinity of a thunderstorm. At the time of the incident, a flight attendant was actively serving beverages when the sudden movement occurred. As a result of the encounter, the attendant sustained a fractured lumbar vertebra.
Radar data indicated that the aircraft was positioned approximately 4 miles west, or downwind, from heavy weather. Just prior to the turbulence event, the flight crew reported observing significant cloud structures, describing them as "some pretty good overhangs." Reports confirm that the seat belt sign was illuminated at the time the turbulence was encountered.
The investigation
The investigation reviewed radar data to determine the aircraft's position relative to the weather system. It also examined reports from the flight crew regarding their visual observations of the storm structure immediately preceding the encounter.
Findings
The primary factor in this incident was the aircraft's proximity to severe weather. Although the seat belt sign was on, the turbulence was sufficient to cause injury to a crew member performing duties in the cabin. The investigation noted that FAA guidance advises avoiding thunderstorms by at least 20 miles, particularly under the anvil of large cumulonimbus clouds. The crew's report of flying under heavy overhangs suggests they were within the hazardous zone defined by these standards.