Incident Overview
A passenger suffered a broken ankle during a flight that encountered moderate turbulence. The captain reported that the seat belt sign had been activated prior to entering a buildup of clouds. According to the captain's statement, the passenger had not yet taken her seat despite the sign being on. He noted that she had been in the lavatory when he turned on the seat belt sign and was returning to her seat at the moment of the turbulence encounter.
Weather Context
An airline weather study examined the conditions surrounding the incident. The study stated that although the main band of convective activity had already passed the location of the incident, the possibility of a towering cumulus cell re-building behind the first band was possible. The air mass was becoming gradually unstable again. The study concluded that the pilot's report of encountering a jolt of light turbulence followed by moderate turbulence was plausible given the atmospheric conditions.
Sequence of Events
The flight experienced a jolt of light turbulence, which then escalated to moderate turbulence. During this period, the passenger who had not yet reached her seat was injured, resulting in a broken ankle. No other injuries were reported. The aircraft continued to its destination without further incident.