Incident Overview
According to the pilot report, the flight crew was navigating around two thunderstorm cells located approximately 20 to 25 miles east of their position. While descending through the base of a cirrus cloud layer, they observed a dissipating cumulus cloud along their flight path. This cloud had not been detected by the aircraft's weather radar, and the pilots determined that avoiding it would have required an abrupt, violent maneuver.
Sequence of Events
As the aircraft approached the cloud, the flight crew activated the seat belt sign just prior to penetration. The subsequent turbulence episode lasted approximately four seconds. During this brief period, a female passenger who was in the process of entering the lavatory caught her foot in the lavatory door, resulting in a broken ankle.
Weather Conditions
At the time of the incident, two thunderstorm cells were present to the east. The dissipating cumulus cloud encountered was not depicted on the weather radar, suggesting it may have been of low reflectivity or developing rapidly. The pilots reported no other significant weather along their planned route.
Passenger Injuries
The only reported injury was the female passenger's broken ankle, sustained when her foot became trapped in the lavatory door during the turbulence. No other injuries were reported among passengers or crew.
Aircraft and Crew Actions
The flight crew stated that the seat belt sign was activated immediately before entering the cloud, indicating their awareness of potential turbulence. The decision to proceed through the cloud rather than attempting an avoidance maneuver was based on the assessment that such a maneuver would have been abrupt and possibly hazardous.